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Applied Catalysis B, Environmental (v.113-114, #)
Methanation of CO2: Further insight into the mechanism over Rh/γ-Al2O3 catalyst by Antoine Beuls; Colas Swalus; Marc Jacquemin; George Heyen; Alejandro Karelovic; Patricio Ruiz (pp. 2-10).
.Display Omitted► CH4 is formed at low temperature by hydrogenation of CO2 on Rh/γ-Al2O3 catalyst. ► O2 in gas feed improves the CH4 production as long as O2 concentration is small. ► CO2 and O2 oxidize Rh particles whereas CO reduces them. ► Nature and reactivity of the dissociated species depend on the Rh oxidation state.The methanation of CO2 was performed on Rh/γ-Al2O3 catalyst at temperatures between 50 and 150°C at 2bar of pressure in a pulse reactor. Experiments confirm the formation of methane at low temperature and pressure. The formation of formiate species during the adsorption of CO2 can be excluded. After reaction with CO2, the catalyst is oxidized. Oxidation is not observed in the presence of CO. The CO2 is adsorbed dissociatively, forming CO (ads) and O (ads). Gem-dicarbonyl Rh(CO)2 species are more reactive than the Rh–CO linear species. The type of adsorbed species depends on the Rh oxidation state. The formation of methane by hydrogenation of CO2 and CO is carried out with 100% selectivity. The activation energy for the hydrogenation of CO2 and CO is lower than values presented in the literature which have been obtained at higher temperature. In the presence of CO2 and CO, the reaction of methanation of CO2 seems to be inhibited by CO. When oxygen is added in low amount in the reactant gas feed, a positive effect on methanation is observed. When the amount of oxygen is too high, oxygen has a negative effect. These results are in agreement with thermodynamics equilibrium calculations, except when O2 is present, confirming the importance of kinetic effects in the reaction. These results open new perspectives of application of catalysis, in order to recycle CO2 in the presence of H2.
Keywords: Carbon dioxide; Mechanism methanation; Hydrogenation; Influence carbon monoxide oxygen
Effect of sulphur on the performance of Rh–LaCoO3 based catalyst for tar conversion to syngas by P. Ammendola; E. Cammisa; R. Chirone; L. Lisi; G. Ruoppolo (pp. 11-18).
The high sulphur tolerance of a Rh–LaCoO3/Al2O3 catalyst has been shown in tar conversion to syngas at 700°C. The protective effect of the perovskite layer under reaction conditions preserving the reforming properties of rhodium has been demonstrated.Display Omitted► Rh–LaCoO3/Al2O3 performance in tar conversion is poorly affected by S. ► At high S levels reforming is inhibited, cracking and oxidation are less influenced. ► The perovskite layer preserves rhodium from S poisoning. ► Alumina protects rhodium but at lower extent with respect to the perovskite. ► S causes a partial loss of LaCoO3 structure and a limited formation of Rh(SO4) x.The effect of sulphur addition on the catalytic activity of 1%Rh/Al2O3, LaCoO3/Al2O3 and 1%Rh–LaCoO3/Al2O3 catalysts in reforming of tar produced by biomass pyrolysis has been investigated by adding 20 or 200ppm H2S in a fixed bed reactor at 700°C using a S-free biomass slowly pyrolyzed. The catalysts have been characterized by ICP-MS and BET analyses. The poisoning effect of sulphur has been also studied by in situ DRIFT and TPR analyses. A very high sulphur exposure of the catalysts leads to the partial inhibition of the reforming properties related to the poisoning of dispersed rhodium sites. The LaCoO3 layer effectively preserves rhodium from sulphur poisoning in the 1%Rh–LaCoO3/Al2O3, the catalyst containing both phases showing mostly unchanged catalytic properties also upon 200ppm S-treatment under reaction conditions. The LaCoO3/Al2O3 catalyst shows reduced reforming properties coupled to an increase of cracking and total oxidation reactions associated to the partial destruction of the perovskite structure.
Keywords: Rh catalysts; Perovskite; Sulphur-poisoning; Biomass; Tar
Stable low-temperature dry reforming of methane over mesoporous La2O3-ZrO2 supported Ni catalyst by Sergey Sokolov; Evgenii V. Kondratenko; Marga-Martina Pohl; Axel Barkschat; Uwe Rodemerck (pp. 19-30).
Display Omitted► Supported Ni catalysts for dry reforming of methane at 400°C have been developed. ► Ni supported on mesoporous ZrO2-La2O3 is active and stable for 180h. ► Ni supported on non-structured and macroporous ZrO2-La2O3 deactivates. ► Major deactivation mechanism is covering Ni particles by graphene and surface oxidation of Ni. ► Ni sintering does not appear to play a significant role in deactivation.A series of supported Ni catalysts was prepared using various supports and tested in low-temperature (400°C) dry reforming of methane. Ni/La2O3-ZrO2 showed near-to equilibrium yields of CO and H2 and the highest stability. This catalyst was studied in greater detail in order to determine the influence of the support morphology on the catalyst activity and stability. To this end, nonstructured, mesoporous, and macroporous La2O3-ZrO2 were prepared and characterized before and after loading with Ni. Among them, only Ni on the mesoporous support showed practically no change in activity over 180h on-stream, whereas the others deactivated. Formation of graphene-like coke layers on the catalysts and of NiO shell over Ni particles appears to be responsible for catalyst deactivation, while sintering of Ni did not play a major role. The enhanced stability of Ni on the mesoporous La2O3-ZrO2 is attributed to stronger interaction of the Ni particles with the support stemming from a pore confinement effect.
Keywords: Carbon dioxide; Methane; Synthesis gas; Dry reforming; Coke formation; Mesoporous; Macroporous
Synergetic effect of plasma/catalysis hybrid system for CH4 removal by A. Baylet; P. Marécot; D. Duprez; X. Jeandel; K. Lombaert; J.M. Tatibouët (pp. 31-36).
Methane abatement from rich gas mixture was performed in a plasma-catalyst reactor. The inlet concentration of CH4 varied from 0.15 to 1vol.% of the total flow rate. Influences of different parameters such as temperature, gas composition and catalyst were investigated. The catalyst was an alumina wash-coated monolith made of cordierite containing 0.15wt% of palladium and 15wt% of Al2O3. The plasma was generated by means of a high voltage monopolar excitation. The higher the energy density, the higher the methane conversion. For plasma experiments carried out without catalyst, the CH4 conversion reached a maximum of 33% for 1vol.% CH4 and 49% for 0.3vol.% CH4 in a N2/O2/CO2/H2O gas mixture (75/18.7/4/2vol.%) at 200°C and 1823JL−1. Carbon monoxide (CO) was observed to be the main product. The CO yield reached 29% and 49% for 1 and 0.3vol.% CH4, respectively. Moreover, experiments performed with a hybrid plasma-catalytic reactor showed two different behaviours depending on the catalyst location. In POST-plasma position, the presence of the catalyst did not modify the methane conversion but oxidized CO into CO2. In IN-plasma position, the catalyst inhibited the methane conversion by decreasing the plasma volume between electrodes but oxidized CO into CO2.
Keywords: Methane; Carbon monoxide; Non-thermal plasma discharge; Monolith; Palladium
Natural gas removal of hydrogen sulphide and mercaptans by A. de Angelis (pp. 37-42).
Display Omitted► Processes for removal of H2S from natural gas can be divided according to the quantities of H2S (large, medium, small). ► Large quantities of H2S are removed through Claus and related processes (Superclaus, SCOT). ► Intermediate quantities are removed through liquid phase (Locat, Sulferox, Sulfint, Bio-redox, Chemical redox etc.) or non aqueous phase processes (Sulfatreat DO, Crystasulf etc.). ► Small quantities are removed by scavengers. ► Large quantities of mercaptans are removed through extraction processes (Merox extraction, Merichem extraction) while small quantities are removed by scavengers.Methane is the main component of natural gas but not the only one. In fact in natural gas are usually present also higher alkanes (ethane, propane, butane, and pentanes), water, nitrogen carbon dioxide and sulphur containing molecules.Within sulphur containing molecules the most abundant is hydrogen sulphide, but mercaptans, elemental sulphur and, less frequently, carbonyl sulphide may also be present.The treatment of natural gas in order to remove sulphur containing compounds is dependent not only on the quantity of these compounds but also on the volume of natural gas to be treated.In this review, will be illustrated the main industrial processes to remove H2S, in large (more than 20tonsulphur/day), intermediate (20kgsulphur/day
Keywords: Natural gas; Hydrogen; Sulphide; Mercaptans
Study of N-bridged diiron phthalocyanine relevant to methane oxidation: Insight into oxidation and spin states from high resolution 1s core hole X-ray spectroscopy by Evgeny V. Kudrik; Olga Safonova; Pieter Glatzel; Janine C. Swarbrick; Leonardo X. Alvarez; Alexander B. Sorokin; Pavel Afanasiev (pp. 43-51).
Display Omitted► (FePc)2N – efficient catalyst for mild oxidation of methane. ► XES and RIXS study of model complexes in different oxidation states. ► Different Fe spin states of putative intermediates involved in the catalytic cycle. ► Mechanism of formation of active species.μ-Nitrido diiron phthalocyanine [PcFe+3.5NFe+3.5Pc]0 is a highly efficient catalyst, able to oxidize methane under near-ambient conditions. In this work, high resolution X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) were applied to study iron species in the series of μ-nitrido diiron phthalocyanines including initial [PcFe+3.5NFe+3.5Pc]0 and oxidized complexes [PcFeIVNFeIVPc]+PF6 and [PcFeIVNFeIV(Pc+)]2+Br2 as model compounds for the intermediates in the catalytic cycle. These systems contain 3d4 configuration of iron in high oxidation state Fe(IV). XES spectra of Kβ line are sensible to the local iron spin density and show unexpected difference in the spin state between the initial [PcFe+3.5NFe+3.5Pc]0 (LS), one-electron oxidized [PcFeIVNFeIVPc]+PF6 (HS) and two electron oxidized cation radical species [PcFeIVNFeIV(Pc+)]2+Br2 (LS). Fe K-edge XANES spectra were recorded at the fluorescence energy of the main Kβ1,3 line or Kβ′ line in the Kβ emission spectrum. The conclusions of RIXS study corroborated XES data. Our study suggests that the main catalytic pathway of oxidation includes two-electron transformation from the LS initial complex to the LS two–electron oxidized [PcFeIVNFeIV(Pc+)(O)]0 to generate powerful oxidant able to oxidize methane via two-electron process.
Keywords: Iron phthalocyanine; μ-Nitrido dimer; Methane oxidation; X-ray spectroscopy; XES; RIXS
The NO/NO x ratio effect on the NH3-SCR efficiency of a commercial automotive Fe-zeolite catalyst studied by operando IR-MS by Irene Malpartida; Olivier Marie; Philippe Bazin; Marco Daturi; Xavier Jeandel (pp. 52-60).
Display Omitted► The SCR efficiency was greatly enhanced when using pure NO2. ► NO2 favours the CO oxidation into CO2 producing NO. ► NO formed would participate in the fast SCR path (like a ‘masked’ fast SCR process). ► NH4NO3 deposit at low temperature when using NO2 is evidenced by operando methodology. ► After single thermal regeneration of the catalyst, the SCR efficiency was fully recovered.A commercial zeolite-based catalyst for NO x removal via ammonia SCR was studied with either pure NO or pure NO2 (as NO x compounds). The SCR efficiency was greatly enhanced when using pure NO2. The CO conversion levels enabled to illustrate that NO2 favours the CO oxidation into CO2, while NO formed would participate in the fast SCR path (like a ‘masked’ fast SCR process). The formation of NH4NO3 at low temperature, when using pure NO2, and its deposit onto the catalyst was evidenced by mean of the IR operando methodology. Its accumulation leads to a loss of activity for the NO x reduction, which must certainly be associated to an obstruction of the microporous system. Nevertheless, after a single thermal regeneration of the catalyst (which would arise during the catalyst ‘real life’ upon any increase of the engine regime), the SCR efficiency was fully recovered.
Keywords: Automotive depollution; NO; x; removal; NH; 3; -SCR; Fe-zeolite; Operando; Ammonium nitrate; NO/NO; x; ratio
The effect of infrared light on visible light photocatalytic activity: An intensive contrast between Pt-doped TiO2 and N-doped TiO2 by Caixia Feng; Yan Wang; Jingwei Zhang; Laigui Yu; Deliang Li; Jianjun Yang; Zhijun Zhang (pp. 61-71).
Visible light photocatalytic activity toward oxidation of propylene of (a) Pt-doped TiO2 and (b) N-doped TiO2 before/after infrared light irradiation. Curves A and C in the absence of infrared light participation, B and D in the presence of infrared light participation. An intensive contrast between the effects of infrared light on the visible light photocatalytic activity was observed.Display Omitted► Pt or N-doped TiO2 were prepared using nanotubular titanic acid as precursor. ► Infrared light can improve the visible light photoactivity of Pt-doped TiO2. ► Infrared light cannot improve the visible light photoactivity of N-doped TiO2. ► The Pt/TiO2 heterojunctions function as the thermal catalytic sites.Pt-doped TiO2 and N-doped TiO2 were prepared, using nanotubular titanic acid as precursor, by wet impregnation and NH3-heating method, respectively. Both Pt-doped and N-doped TiO2 show an apparent photocatalytic oxidation of propylene under visible light irradiation. The origin of visible light sensitization was ascribed to the intra-band contributed by the formation of single-electron-trapped oxygen vacancies, while dopants platinum or nitrogen play a role not only in suppressing the recombination of photoinduced electrons and holes but also in increasing the ability of visible light absorption of TiO2. The visible light photocatalytic activity of Pt-doped TiO2 can be greatly improved by additional infrared light irradiation, while visible-light-active N-doped TiO2 has no such phenomenon. Infrared light per se is unable to excite Pt-doped TiO2 catalyst to initiate photocatalytic reaction, but the strong interaction between platinum and oxygen vacancies resulted in absorption peaks at 800–900nm, resulting in a giant enhancement in visible light photocatalytic activity of Pt-doped TiO2 in the presence of infrared light irradiation because the formed heterojunctions between dopants Pt and TiO2 may function as thermal catalytic sites. The influences of reaction temperatures on visible light photoactivity of both Pt-doped and N-doped TiO2 were studied. It was found that both C3H6 removal and CO2 selectivity over Pt-doped TiO2 were increased with increasing the reaction temperature, while it was inert for N-doped TiO2.
Keywords: Titanium dioxide; Platinum-doped; Nitrogen-doped; Oxygen vacancy; Infrared light
Superior performance of multi-wall carbon nanotubes as support of Pt-based catalysts for the preferential CO oxidation: Effect of ceria addition by E.O. Jardim; M. Gonçalves; S. Rico-Francés; A. Sepúlveda-Escribano; J. Silvestre-Albero (pp. 72-78).
Display Omitted► Pt/CNT and Pt/AC catalysts have been compared in the preferential oxidation of CO. ► Large Pt nanoparticles improve both catalytic activity and selectivity towards CO2. ► Incorporation of oxygen functionalities to the carbon support becomes detrimental. ► Pt/CeO2/CNT catalysts overpass the catalytic behaviour reported for Pt/CeO2 catalysts.Preferential oxidation of CO in excess hydrogen (PROX) was studied over Pt catalysts supported on multi-wall carbon nanotubes in the temperature range between room temperature and the temperature of the water–gas shift unit (∼473K). Experimental results show that the Pt/CNT catalyst exhibit a superior performance in terms of catalytic activity and selectivity towards CO2 formation compared to a Pt/AC catalyst prepared under similar conditions. Apparently, preferential CO oxidation in excess hydrogen over Pt nanoparticles supported on carbon materials is a particle size dependent reaction, i.e. larger particles exhibit higher activity and selectivity. In any case, the incorporation of oxygen functionalities to the carbon support becomes detrimental for the CO oxidation reaction independently of the carbon support used. Finally, CeO2 addition to the Pt/CNT catalyst further improves both catalytic activity and selectivity at low temperatures (CO conversion rate of 46% at 313K), the catalytic performance being superior to that exhibited by a traditional PROX catalyst such as Pt/CeO2.
Keywords: CO oxidation; PROX; CNT; CeO; 2; Platinum
Synthesis and photocatalytic activity of Mn-doped TiO2 nanostructured powders under UV and visible light by V.D. Binas; K. Sambani; T. Maggos; A. Katsanaki; G. Kiriakidis (pp. 79-86).
Display Omitted► Mn doped TiO2 as photocatalytic material. ► This photo catalytic material lies on the degradation of indoor pollutants such as NO using visible light (vis). ► The synthesis procedure is simple, quick and inexpensive and allows for large scale material composition. ► Amount of dopant influences the efficiency of NO degradation. Activity of 0.1% Mn:TiO2 maintained when embedded in building matrix.A straight forward, simple and inexpensive process has been developed by sol–gel method for the synthesis of manganese (Mn) doped and undoped TiO2 photocatalysts. X-ray powder diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the presence of structural nanoparticles with an average nanocrystalline size of about 20nm. FT-IR/vis adsorption has shown enhanced sub-band-gap absorption as a function of Mn concentration. The photocatalytic activity of these materials was evaluated by the degradation of a basic Methylene Blue (MB) as organic contaminant. Mn-doped TiO2 powder with molar ratio 0.1:100 was mixed with calcareous filler (5% and 10% respectively) and the photocatalytic activity was evaluated by the degradation of inorganic pollutants such as NO x under UV and visible light.
Keywords: Mn-doped TiO; 2; nanoparticles; Photocatalysis under UV/visible light; Degradation of NO; x; Heterogeneous photocatalytic oxidation; In-door depollution
Simultaneous hydrodesulfurization and hydrodenitrogenation on MoP/SiO2 catalysts: Effect of catalyst preparation method by A. Infantes-Molina; C. Moreno-León; B. Pawelec; J.L.G. Fierro; E. Rodríguez-Castellón; A. Jiménez-López (pp. 87-99).
. A new synthetic approach was carried out to prepare silica-supported MoP catalysts using ammonium molybdate ((NH4)2MoO4) and phosphorous acid (H2PO3H) as precursors and subsequent H2-TPR. The lower reduction temperature required to form the MoP species is responsible for the enhancement in catalytic performance since highly dispersed MoP particles are formed.Display Omitted► Dispersed MoP particles are formed at lower temperature with the new synthetic route. ► Key factors are a high surface area, acidity and good dispersion of MoP phase. ► S-removal does not appear to be inhibited by the presence of quinoline. ► N-removal is enhanced in the presence of a small amount of DBT.Silica-supported MoP catalysts were prepared by temperature-programmed reduction (H2-TPR) at 550, 600 and 700°C of the corresponding dried or calcined substrates. Two catalysts were prepared by using two different synthetic approaches. A MoP catalyst was prepared using the method described in the literature that uses ammonium phosphate (NH4H2PO4) and ammonium heptamolybdate ((NH4)6Mo7O24·4H2O) precursors, calcination and subsequent H2-TPR at high temperature. A new synthetic approach was carried out to prepare another MoP catalyst using ammonium molybdate ((NH4)2MoO4) and phosphorous acid (H2PO3H) as precursors and subsequent H2-TPR. The catalytic activity was evaluated in the individual and simultaneous hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions performed in a flow reactor under a hydrogen pressure of 3.0MPa. The fresh reduced and spent catalysts were characterized by ICP, N2 adsorption–desorption isotherms at −196°C, XRD, HRTEM, NH3-TPD, XPS and elemental chemical CNHS analysis. The silica-supported MoP catalysts prepared by the new synthetic method were more active in the HDS of DBT than the catalyst prepared by reduction of calcined substrate. The catalyst characterization results showed that the lower reduction temperature required to form the MoP species is responsible for the enhancement in catalytic performance. The key factors influencing on the catalytic activity are: a large specific surface area, high acidity and good dispersion of MoP phase on the support substrate. Activity measurements in simultaneous HDN–HDS showed that quinoline conversion is enhanced in the presence of a small amount of DBT whereas the HDS of DBT reaction does not appear to be inhibited by a small amount of quinoline added to the feed.
Keywords: Silica; Molybdenum phosphide; Dibenzothiophene; HDS; Quinoline; HDN
Enhancement of the advanced Fenton process (Fe0/H2O2) by ultrasound for the mineralization of phenol by Y. Segura; F. Martínez; J.A. Melero; R. Molina; R. Chand; D.H. Bremner (pp. 100-106).
Display Omitted► Activation of ZVI particles by a short input of ultrasound. ► Degradation values of up to 90% of phenol mineralization. ► No expensive catalyst, solvent, pH maintenance nor long-time external sources of energy are required.In this study, a successful mineralization of phenol was achieved by means of coupling zero-valent iron (ZVI) particles, hydrogen peroxide and a short input of ultrasonic irradiation. This short sono-advanced Fenton process (AFP) provided a better performance of ZVI in a subsequent silent degradation stage, which involves neither extra cost of energy nor additional oxidant. The short input of ultrasound (US) irradiation enhanced the activity of the Fe0/H2O2 system in terms of the total organic carbon (TOC) removal. Then, the TOC mineralization continued during the silent stage, even after the total consumption of hydrogen peroxide, reaching values of ca. 90% TOC conversions over 24h. This remarkable activity is attributed to the capacity of the ZVI/iron oxide composite formed during the degradation for the generation of oxidizing radical species and to the formation of another reactive oxidant species, such as the ferryl ion. The modification of the initial conditions of the sono-AFP system such as the ultrasonic irradiation time and the hydrogen peroxide dosage, showed significant variations in terms of TOC mineralization for the ongoing silent degradation stage. An appropriate selection of operation conditions will lead to an economical and highly efficient technology with eventual large-scale commercial applications for the degradation organic pollutants in aqueous effluents.
Keywords: Ultrasound; Heterogeneous Fenton; Zero-valent iron; Hydrogen peroxide
Thermal effect of carboxylic acids in the degradation by photo-Fenton of high concentrations of ethylene glycol by J. Araña; J.A. Ortega Méndez; J.A. Herrera Melián; J.M. Doña Rodríguez; O. González Díaz; J. Pérez Peña (pp. 107-115).
. Photo-Fenton degradation of 11,600ppm of ethylene glycol (as TOC ■). Evolution of: intermediates (as carbon concentration) (▪ formic, ▪ oxalic and ▪ acetic acid) and temperature (♢). [H2O2]=120g/L, [Fe2+]=200ppm.Display Omitted► Highly concentrated ethylene glycol was mineralized in minutes. ► Some reaction intermediates produced highly exothermic reactions. ► Fe–oxalate complexes slow down the process. ► The temperature rise is responsible for the mineralization achieved.The degradation by Fenton and photo-Fenton of high concentrations of ethylene glycol (1000–25,000mg/L), similar to those found in wastewater has been studied. Strongly exothermic reactions led to temperature increments up to 70–94°C. In most experiments, temperature increments favored radical formation that provided almost complete mineralization. Oxalic, formic and acetic acids were identified as degradation intermediates. The obtained results indicate that the radicals formed in the degradation of formic and acetic acids with H2O2 were responsible for the exothermic reactions. Nonetheless, Fe–oxalic complexes inhibited the previous reactions by slowing down the process in such a way that complete mineralization did not occur until those complexes were degraded.FTIR studies allowed the identification of some of the complexes and species formed in the process.
Keywords: Fenton; Photo-Fenton; Temperature; Complexes; Carboxylic acid; Ethylene glycol
Synthesis of a catalytic support from natural cellulose fibers, and its performance in a CO2 reforming of CH4 by Heeyeon Kim; Nam Jo Jeong; Seong Ok Han (pp. 116-125).
Display Omitted► Porous carbon for use as a catalytic support was synthesized by using natural cellulose fibers. ► Ni/cellulose showed superior activity and long-term durability in the CO2 reforming of CH4. ► Alkaline earth metals improved the dispersion and retarded the agglomeration and sintering of Ni. ► These study results open a new avenue for the application of various biomass resources.Porous carbon was synthesized from natural cellulose fibers and its performance as a catalytic support was investigated for a CO2 reforming of CH4. Ni particles supported on cellulose fibers showed little agglomeration, even after a 168-h reforming reaction, but superior catalytic activity and long-term durability compared to a Ni/Al2O3 model catalyst. One of the reasons for these results was the lower extent of coking originating from the carbonaceous support. Another reason for these results was the high dispersion of Ni particles on the cellulose support, which was caused by the presence of alkaline earth metals such as Ca and Mg in the original structure of the support. Alkaline earth metals in the shape of nanosized particles significantly improved Ni dispersion and the interaction between the Ni particles and the support; they also retarded the agglomeration and sintering of the Ni particles. The cellulose fibers treated with different conditions were characterized by Raman and were observed by scanning and transmission electron microscopy. X-ray diffraction was performed to estimate Ni particle size before and after the catalytic usage. The interaction between the Ni particles and the support was measured by X-ray photoelectron spectroscopy.
Keywords: Porous carbon; Natural cellulose fiber; CO; 2; reforming of CH; 4; Alkaline earth metal
Use of carbon monoxide and cyanide to probe the active sites on nitrogen-doped carbon catalysts for oxygen reduction by Dieter von Deak; Deepika Singh; Jesaiah C. King; Umit S. Ozkan (pp. 126-133).
Display Omitted► The interaction of CO on nitrogen-doped graphite (CN x) was investigated. ► Pt supported on Vulcan carbon was used in similar experiments for comparison. ► In an acidic half-cell saturated with CO and O2, CO poisoned Pt, but did not affect CN x. ► CO was found to chemisorb and react on Pt, but did not interact with CN x. ► CN x catalysts did not show any poisoning by cyanide.Interaction of carbon monoxide with CN x catalysts was investigated using pulse chemisorption, DRIFTS, and cyclic voltammetry techniques. Pulsed chemisorption experiments showed no CO uptake over the CN x catalysts. Cyclic voltammetry and potential hold studies showed carbon monoxide not to have any electrocatalytic interaction with nitrogen-doped graphite surfaces and not to have any poisoning effect for the oxygen reduction reaction. This is in contrast to the preferential adsorption of CO in the presence of oxygen on ORR sites of Pt catalysts, inhibiting the oxygen reduction activity drastically. Cyanide poisoning experiments performed using KCN showed no activity loss for CN x, while Pt/VC catalysts showed significant deactivation. These studies suggest that it is unlikely for coordinated metal sites to have significant contribution to the oxygen reduction reaction in CN x catalysts.
Keywords: CN; x; Nitrogen-doped graphite; Carbon monoxide; Cyanide; Poisoning; Platinum; Oxygen reduction; ORR
High photocatalytic performance of zinc hydroxystannate toward benzene and methyl orange by Yibin Chen; Danzhen Li; Miao He; Yin Hu; Hong Ruan; Yangming Lin; Junhua Hu; Yi Zheng; Yu Shao (pp. 134-140).
A photocatalyst ZnSn(OH)6 with remarkable photocatalytic activity has been synthesized by means of two facile and green routes which were homogeneous precipitation (ZnSn(OH)6-HP) and hydrothermal method (ZnSn(OH)6-HT), without any templates, catalysts, surfactants or organic solvents. The results demonstrated that, compared with commercial P25-TiO2, the photoactivity of ZnSn(OH)6 was remarkably improved. Especially on the ZnSn(OH)6-HP, the conversion ratio and mineralization ratio in the photocatalytic degradation of benzene were up to 75% and 68%, which is about 20 times and 2 times higher than that of P25, respectively. Furthermore, the catalyst also presented notably high photocatalytic activities toward cyclohexane, acetone and methyl orange under UV light irradiation. Hence, this improve the photocatalyst ZnSn(OH)6 was very important to the environmental remedy application in practice.Display Omitted► Two facile solution method can synthesize the ZnSn(OH)6 nanoparticles. ► Attention to its remarkable photocatalytic activity for benzene and methyl orange. ► The catalyst also performs high activity on other volatile organic compounds. ► This new photocatalyst would be widely applied to environmental remedy in the future.Two facile and green methods without any templates, catalysts, surfactants or organic solvents were applied to synthesize ZnSn(OH)6 nanoparticles, i.e. homogeneous precipitation (HP) and hydrothermal (HT). The photocatalytic activities were evaluated on the degradation of organic pollutants under ultraviolet light illumination. Compared to commercial P25, the photoactivity of ZnSn(OH)6 was remarkably improved. The conversion and mineralization ratio of the photocatalytic degradation of benzene by the ZnSn(OH)6-HP were up to 75% and 68%, which is about 20 and 2 times higher than that of P25. The ZnSn(OH)6 has also exhibited high performance toward other persistent organic compounds as well as methyl orange in suspended solution. The order of photodegradation efficiencies of different catalysts was ZnSn(OH)6-HP>P25>ZnSn(OH)6-HT. Based on the characterization results and the detection of active species, the possible mechanism of the high photocatalytic activity of ZnSn(OH)6-HP was discussed. The simplified synthesis of zinc hydroxystannate with outstanding activity could be promisingly used in the future photocatalytic application.
Keywords: ZnSn(OH); 6; Photocatalysis; Homogeneous precipitation; Hydrothermal method
Fullerene modification CdS/TiO2 to enhancement surface area and modification of photocatalytic activity under visible light by Ze-Da Meng; Mei-Mei Peng; Lei Zhu; Won-Chun Oh; Feng-Jun Zhang (pp. 141-149).
Display Omitted► C60 have good effect in photo-degradation process. ► C60 has larger pore sizes, volumes, conjugated structures, electron-accepting ability. ► Enhanced adsorption capacity can increase the degradation effect. ► Increase the photo-absorption effect by C60 and cooperative effect of CdS.C60-TiO2, CdS-TiO2 and CdS-C60/TiO2 composites were prepared using a sol–gel method, and their photocatalytic activity was evaluated by measuring the degradation of methylene blue (MB) solutions under visible light. The surface area, surface structure, crystal phase and elemental identification of these composites were characterized by nitrogen adsorption isotherms, scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and UV–vis absorption spectra (UV–vis). XRD showed that the CdS-C60/TiO2 composite contained a typical single and clear anatase phase. SEM of the CdS-C60/TiO2 composites revealed a homogenous composition in the particles. EDX revealed the presence of C and Ti with strong Cd and S peaks in the CdS-C60/TiO2 composite. The degradation of dye was determined by UV–vis spectrophotometry. An increase in photocatalytic activity was observed and attributed to an increase in the photo-absorption effect by fullerene and the cooperative effect of the CdS. The advisable advance BET surface area can enhance the photo-degradation effect. The repeatability of photocatalytic activity was also tested in order to investigate the stability of C60 and CdS-C60/TiO2 composites.
Keywords: CdS-C; 60; /TiO; 2; FTIR; Visible light; UV–vis; TEM
Oxidation of perchloroethylene—Activity and selectivity of Pt, Pd, Rh, and V2O5 catalysts supported on Al2O3, Al2O3-TiO2 and Al2O3-CeO2 by Satu Pitkäaho; Lenka Matejova; Satu Ojala; Jana Gaalova; Riitta L. Keiski (pp. 150-159).
Display Omitted► H2O as a hydrogen source increasing the HCl yield was optimized to 1.5wt-%. ► All supports were active, but also selectivity towards CO2, CO and HCl was seen. ► The introduction of TiO2 or CeO2 into Al2O3 made these catalysts superior. ► Redox properties and activated oxygen amount plays a big role in PCE oxidation. ► Pt/Al2O3-CeO2 showed highest activity and Pd/Al2O3-CeO2 was most HCl selective.The total oxidation of perchloroethylene (PCE) over Pt, Pd, Rh and V2O5 metallic monolith catalysts supported on Al2O3 as well as CeO2 and TiO2-doped Al2O3 was examined. To ensure high HCl yields, the amount of water as a hydrogen source was optimized to be 1.5wt-% by testing the effect of water content on PCE oxidation. Water not only enhanced the selectivity towards HCl formation but also improved the PCE oxidation to some extent.Both, the activity and selectivity of the catalysts were found to be related to the properties of the catalyst support; addition of TiO2 or CeO2 into Al2O3 enhanced catalysts’ efficiency regardless of the active phase. Pt, Pd and Rh catalysts showed high catalytic activity, PCE conversions ranging from 72% to 99%, and HCl yields from 59% up to 93% were observed. Both activity and selectivity of the Pt/Al2O3-CeO2 and Pd/Al2O3-CeO2 catalysts were superior to the other tested catalysts. The results show that over the oxidation of PCE, the redox properties of the catalyst and the amount of activated oxygen may play bigger role than the acidity. To confirm the suspected positive effect on the PCE oxidation coming from the bidispersed mesopores seen over ceria-doped catalysts needs further testing.
Keywords: Catalytic oxidation; Chlorinated volatile organic compounds; CVOC; Perchloroethylene; Tetrachloroethylene; Tetrachloroethene; Emission abatement
Mono- and bimetallic Rh and Pt NSR-catalysts prepared by controlled deposition of noble metals on support or storage component by Robert Büchel; Sotiris E. Pratsinis; Alfons Baiker (pp. 160-171).
. Mono- and bimetallic Rh and Pt based NO x storage-reduction (NSR) catalysts with spatially controlled noble metal deposition were prepared using a twin flame spray pyrolysis setup. All catalysts performed well in the absence of SO2, while in the presence of SO2 Rh was essential.Display Omitted► Mono- and bimetallic Rh and Pt based NSR catalysts were prepared by flame spray pyrolysis. ► Noble metals were selectively deposited on support (Al2O3) and storage component (BaCO3). ► The location of nobe metal deposition had a significant influence on the NSR performance. ► Rh containing catalysts showed superior NSR efficiency in the presence of SO2. ► Combinations of Rh and Pt enhanced the NSR performance of the catalysts.Mono- and bimetallic Rh and Pt based NO x storage-reduction (NSR) catalysts, where the noble metals were deposited on the Al2O3 support or BaCO3 storage component, have been prepared using a twin flame spray pyrolysis setup. The catalysts were characterized by nitrogen adsorption, CO chemisorption combined with diffuse reflectance infrared Fourier transform spectroscopy, X-ray diffraction, and scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy. The NSR performance of the catalysts was investigated by fuel lean/rich cycling in the absence and presence of SO2 (25ppm) as well as after H2 desulfation at 750°C. The performance increased when Rh was located on BaCO3 enabling good catalyst regeneration during the fuel rich phase. Best performance was observed for bimetallic catalysts where the noble metals were separated, with Pt on Al2O3 and Rh on BaCO3. The Rh-containing catalysts generally showed much higher tolerance to SO2 during fuel rich conditions and lost only little activity during thermal aging at 750°C.
Keywords: Flame spray pyrolysis; NO; x; storage-reduction (NSR); Mono- and bimetallic catalyst; Platinum; Rhodium; Alumina; Barium carbonate; Selective deposition; Fast NO; x; storage; Lean NO; x; trap; Sulfur poisoning
Infrared studies of CO oxidation by oxygen and by water over Pt/Al2O3 and Pd/Al2O3 catalysts by Guido Busca; Elisabetta Finocchio; Vicente Sanchez Escribano (pp. 172-179).
Display Omitted► Pd/Al2O3 and Pt/Al2O3 catalysts have been studied by IR spectroscopy of CO adsorption. ► CO oxidation and water gas shift experiments have been performed. ► Dispersed Pt n+ and Pd n+ cations and PdO x species are revealed. ► After reduction by hydrogen, they are reformed by O2 and also by water at moderate temperature. ► They are not detectable in reaction conditions but can be active sites for CO oxidation and LTWGS.CO adsorption has been studied over Pd/Al2O3 and Pt/Al2O3 catalysts using IR spectroscopy in different conditions and after different pretreatments. The oxidation of CO by oxygen and water (water gas shift) has also been studied at 130–673K. The spectra show that the most active species as oxidant for CO are dispersed Pt n+ and Pd n+ cations and PdO x species mainly “decorating” the defects of alumina crystals where they modify completely the behaviour of surface OH's and Lewis acid sites. Some of these species oxidize CO to CO2 already below ∼200K. These highly oxidized species escape detection by IR during reaction at 500–673K, when only reduced sites are apparent due to their very strong interaction with CO. The data suggest that redox mechanisms could occur for both WGS and CO oxidation occurring on highly dispersed cationic species non detectable under reaction conditions.
Keywords: CO oxidation; Water gas shift; Noble metal catalysts; Platinum on alumina; Palladium on alumina; IR spectroscopy
Photocatalytic degradation of rhodamine B using Mo heterogeneous catalysts under aerobic conditions by Nuno U. Silva; Teresa G. Nunes; Marta S. Saraiva; Mohammad S. Shalamzari; Pedro D. Vaz; Olinda C. Monteiro; Carla D. Nunes (pp. 180-191).
Display Omitted► MCM-41 is a high-capacity mass-transfer agent for rhodamine B. ► Mo catalysts are very effective under aerobic conditions. ► Rhodamine B photodegradation by Mo arises from a secondary photochemistry process. ► Mo catalysts quench rhodamine B excited state leading to extended photodegradation. ► Results are sustained by UV–vis and ESI-MS measurements along with TD-DFT data.MCM-41 based materials were prepared with immobilized MoII and MoVI active sites based on [MoI2(CO)3] and [MoO2Cl2] cores, respectively, using a 2-aminopyridine glycidyloxypropyl derivative as anchoring ligand. Suitable characterization by powder X-ray diffraction, FTIR and,13C and29Si solid state NMR spectroscopy was accomplished. All new materials were successfully used in photodegradation experiments of rhodamine B under aerobic conditions. Control experiments using neat MCM-41 and direct photolysis of rhodamine B were also carried out. All experiments were run without any external source of oxygen other than air. Photocatalytic results show that the presence of Mo and its oxidation state is not innocent in this process. In addition, Mo catalysts act most probably by quenching rhodamine B excited state leading to extended degradation of the dye, through secondary photochemistry, beyond a simple de-ethylation process. Density functional theory (DFT) results corroborate with this showing that when rhodamine B is in excited state the xanthene moiety bond orders change.
Keywords: DFT; Dye; MCM-41; Molybdenum; Catalysis
Simultaneous production of H2 and C2 hydrocarbons by gas phase electrocatalysis by A. Caravaca; A. de Lucas-Consuegra; J. González-Cobos; J.L. Valverde; F. Dorado (pp. 192-200).
Display Omitted► A new single chamber solid electrolyte cell (Pt/YSZ/Ag) has been developed. ► It allows to produce H2 and C2 hydrocarbons from a humidified methane atmosphere. ► On the Pt electrode, steam is electrolyzed leading to the production of H2 and O2− ions. ► On the Ag electrode CH4 reacts with the O2− ions producing C2s hydrocarbons. ► This novel system may have multiple advantages for its further practical application.This study reports, for the first time in literature, the possibility of simultaneously producing H2 and C2s hydrocarbons by using an anionic single chamber solid electrolyte cell of Pt/YSZ/Ag (working/solid electrolyte/counter) tested under a humidified CH4 atmosphere (no direct O2 feeding gas to the reactor). Hydrogen was mainly produced in the Pt working electrode under application of negative polarizations by a steam electrolysis process (H2O+2e−→H2+O2−). Simultaneously, the produced O2− ions were electrochemically pumped to the Ag counter electrode, leading to the production of C2s hydrocarbons (ethane and ethylene), via oxidative coupling of CH4 (CH4+O2−→C2H4+C2H6+2e−). The influence of the applied current, reaction temperature and feeding composition on the electrocatalytic performance of the cell was evaluated for both processes. It was found that the possibility of controlling the rate of O2− supply allows to control and optimize the production rate of the desired compounds (H2 and C2s) at varying the reaction conditions. In addition, the stability of the cell for long polarization times has been demonstrated under the optimal conditions for the production of both compounds.
Keywords: H; 2; production; Oxidative coupling of methane; C; 2; hydrocarbons; Gas phase electrocatalysis; Steam electrolysis
Aqueous-phase furfural-acetone aldol condensation over basic mixed oxides by Laura Faba; Eva Díaz; Salvador Ordóñez (pp. 201-211).
Display Omitted► Studied reaction strongly depends on the concentration of medium-strength basic sites. ► Selectivity towards C13 depends on the molar ratio of reactants, being 1:1 the optimum ratio. ► Rates and selectivities are consistent with consecutive reversible reactions yielding C8 and subsequently C13. ► Catalyst stability in aqueous phase is a key issue in the process development.Catalytic aqueous-phase aldol-condensation of acetone and furfural has been studied in this work. Three different mixed-oxides catalysts (Mg–Zr, Mg–Al and Ca–Zr, with different basic sites distribution) were studied, their activity and selectivity being correlated with their physico-chemical properties. Catalysts with the highest concentration of basic sites (especially medium-strength basic sites) are the most active and selective for the C13 fraction, whereas molar ratios of 1:1 yield the highest selectivities for C13 fraction (more than 60% atomic yield for the Mg–Zr mixed oxide). Concerning to reaction mechanism, cis isomers are the first ones formed, whereas trans isomers are the most abundant at higher reaction times. The main causes of catalysts deactivation are the modification of the physico-chemical properties of catalysts – because of the interaction with water – and in minor extent, the leaching effect; although homogeneous catalytic effects are discarded at studied conditions.The products formed, and the kinetic dependence on reactant concentration, are consistent with a catalytic mechanism in which the rate-determining step is the formation of the enolate species. The model considers consecutive reversible reactions yielding C8, in the first step, and C13, in the second step; with a first-order dependence on the species with α-hydrogen (acetone and C8), and zero-th order on those species without it (furfural and C13).
Keywords: Aldol reaction; Basic catalysis; Biomass upgrading; C–C coupling
Synthesis of glycerol carbonates by transesterification of glycerol in a continuous system using supported hydrotalcites as catalysts by Mayra G. Álvarez; Martina Plíšková; Anna M. Segarra; Françesc Medina; François Figueras (pp. 212-220).
Display Omitted► Hydrotalcites supported by alumina beads as catalyst in continuous reactor. ► Active and stable catalysts in the synthesis of glycerol carbonate. ► Glycerol valorization.MgAl hydrotalcites have been grown onto α- and γ-Al2O3 and characterized by XR diffraction, N2 and CO2 adsorption. XRD patterns show the crystallization of hydrotalcites as nanometric crystals. On the calcined supported materials, the thermal desorption of CO2 evidences the presence of relatively strong basic sites which are absent on the pure supports. The samples supported by α-Al2O3 exhibit a higher basic strength than those supported on γ-Al2O3. After rehydration, the total number of sites changes only little, but the original sites, presumed to be of Lewis type are converted to stronger Brønsted sites. The synthesis of glycerol carbonate and dicarbonate has been performed by transesterification of glycerol by diethyl carbonate in a green, efficient and selective process catalyzed by these hydrotalcites supported on α- and γ-Al2O3. The control of grain size of the support allows to operate in a flow reactor, then to evaluate the extent of deactivation as a function of time on stream at full conversion of glycerol. Stable catalysts are obtained when α-Al2O3 is the support.
Keywords: Supported hydrotalcite; Glycerol; Glycerol carbonate; Transesterification; Continuous flow reactor; Basicity; Deactivation
Degradation of diphenhydramine pharmaceutical in aqueous solutions by using two highly active TiO2 photocatalysts: Operating parameters and photocatalytic mechanism by Luisa M. Pastrana-Martínez; Joaquim L. Faria; José M. Doña-Rodríguez; Cristina Fernández-Rodríguez; Adrián M.T. Silva (pp. 221-227).
Display Omitted► Diphenhydramine pharmaceutical is photorecalcitrant in the absence of a catalyst. ► Heterogeneous photocatalysis leads to its complete conversion in 60min. ► ECT is an excellent TiO2 photocatalyst for degradation of diphenhydramine. ► Photogenerated holes are the main responsible species in the catalytic process. ► ECT is more efficient than P25 to generate highly reactive oxidant radicals.In the present work the efficiency of a new TiO2 catalyst (ECT), synthesized by means of an optimized sol–gel method, is studied for degradation of an important pharmaceutical water pollutant, diphenhydramine (DP). Its activity is compared to P25, the benchmark catalyst, produced by Evonik Degussa Corporation, under different catalyst loadings (up to 2.00gL−1) and initial solution pH (3.0–11.0). The results show that DP is very stable under non-catalytic conditions but complete degradation and considerable mineralization (ca. 60–70%) under near UV to visible irradiation (∼50mWcm−2) can be achieved in 60min by selecting the appropriate TiO2 loading. ECT is significantly more active than the benchmark catalyst for loadings higher than 1.00gL−1 while the pseudo-first order rate constant increased with the initial solution pH from 3.0 to 11.0. The highest rate constant was obtained with ECT at pH 11 (173×10−3min−1 against 116×10−3min−1 for P25). Scavenger agents were used as a diagnostic tool for the analysis of the photocatalytic mechanism and it was possible to prove that holes were crucial active species participating in the photocatalytic mechanism as well as that ECT has a higher availability than P25 to generate reactive radicals, such as hydroxyl (HO•) and hydroperoxyl (HOO•) radicals.
Keywords: Diphenhydramine (DP); Heterogeneous photocatalysis; Titanium dioxide; Kinetics; Scavengers for holes and radicals
Study of the “Fast SCR”-like mechanism of H2-assisted SCR of NO x with ammonia over Ag/Al2O3 by Dmitry E. Doronkin; Sebastian Fogel; Stefanie Tamm; Louise Olsson; Tuhin Suvra Khan; Thomas Bligaard; Pär Gabrielsson; Søren Dahl (pp. 228-236).
Display Omitted► Presence of both Ag and Al2O3 is vital for high activity of Ag/Al2O3 in NO x SCR. ► The primary role of Ag is the H2-assisted oxidative activation of NO. ► The second role of hydrogen is the removal of nitrates blocking the Al2O3 surface. ► NO, NO2 and NH3 can react over pure alumina according to “Fast SCR” mechanism. ► The results are obtained using transient experiments, FTIR and DFT calculations.It is shown that Ag/Al2O3 is a unique catalytic system for H2-assisted selective catalytic reduction of NO x by NH3 (NH3-SCR) with both Ag and alumina being necessary components of the catalyst. The ability of Ag/Al2O3 and pure Al2O3 to catalyse SCR of mixtures of NO and NO2 by ammonia is demonstrated, the surface species occurring discussed, and a “Fast SCR”-like mechanism of the process is proposed. The possibility of catalyst surface blocking by adsorbed NO x and the influence of hydrogen on desorption of NO x were evaluated by FTIR and DFT calculations.
Keywords: Ag/Al; 2; O; 3; Alumina; NO; x; SCR; Fast SCR; FTIR
CO2 hydrogenation at low temperature over Rh/γ-Al2O3 catalysts: Effect of the metal particle size on catalytic performances and reaction mechanism by Alejandro Karelovic; Patricio Ruiz (pp. 237-249).
Display Omitted► Rh/γ-Al2O3 catalysts were studied in CO2 methanation at low temperature. ► Turnover frequencies and activation energies depend on Rh particle size. ► CO(ads) dissociation is a critical step in the reaction pathway.Low temperature CO2 methanation was studied on Rh/γ-Al2O3 catalysts. Catalysts were prepared with varying amounts of Rh to obtain different mean particle sizes, ranging between 3.6 and 15.4nm. In the conditions studied, selectivity to methane was 100%. The intrinsic activity of Rh/γ-Al2O3 catalysts in CO2 hydrogenation to methane was found to do not depend on particle size at temperatures between 185 and 200°C, whereas at lower temperatures larger particles favored higher activity. Apparent activation energies were found to be in the range 14.5–22.7kcal/mol. Lower activation energies were obtained for catalysts with larger particles. Operando-DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) experiments showed that CO2 is readily dissociated on these catalysts at 50°C giving rise to different Rh carbonyl and formates species. Rh–CO species are proposed to be associated with H forming Rh carbonyl hydrides. According to transient experiments performed in different gas atmospheres, it is proposed that adsorbed CO is an important intermediate and that formates are spectators in the reaction path. Activation energy for CO dissociation is found to be similar to that of the overall reaction which suggests the importance of CO bond dissociation in the reaction path.
Keywords: CO; 2; Methanation; Rhodium; γ-Al; 2; O; 3; Operando-DRIFTS; Transient MS; Particle size
Electrochemical promotion of CO combustion over Pt/YSZ under high vacuum conditions by Chun Xia; Cyril Falgairette; Yongdan Li; György Foti; Christos Comninellis; Wolfgang Harbich (pp. 250-254).
Oxygen evolution and catalytic rate measurements under high vacuum conditions show that electrochemical promotion is related to PtO x, which is stable at 300°C but thermodynamically unstable at 400°C. During anodic polarization, PtO x is first formed at the Pt/YSZ interface. With prolonged polarization time, the formed PtO x either migrates over the Pt/gas interface inducing electrochemical promotion or diffuses into the Pt bulk leading to the oxygen storage. After polarization, the stored O species is released and acts as sacrificial promoter causing the persistent electrochemical promotion effect.Display Omitted► EPOC of CO oxidation is investigated under high vacuum conditions. ► O2 evolution and catalytic reveal that EPOC is related to stable PtO x. ► Polarization time and O2 pressure strongly influence the oxygen storage. ► O2 is released after polarization and acts as sacrificial promoter.Electrochemical promotion of CO combustion over Pt/YSZ was investigated under high vacuum conditions. A galvanostatic step was coupled to mass spectrometric gas analysis using an electrochemical mass spectrometric monitoring device. Non-Faradaic electrochemical promotion of catalysis took place at 300°C while only electrochemical oxidation was observed at 400°C. Oxygen evolution measurements revealed that electrochemical promotion is related to the thermodynamically stable PtO x species over the Pt/gas interface. The polarization time and O2 pressure show strong influence on the relaxation transient upon current interruption. We propose that during anodic polarization, PtO x is first formed at the Pt/YSZ interface. With prolonged polarization time, the formed PtO x either migrates over the Pt/gas interface inducing electrochemical promotion or diffuses into the Pt bulk leading to the oxygen storage. After polarization, the stored O species is released and acts as sacrificial promoter causing the persistent electrochemical promotion effect.
Keywords: Electrochemical promotion; Pt/YSZ; Oxygen storage; High vacuum; Persistent electrochemical promotion
NO reduction with NH3 under oxidizing atmosphere on copper loaded hydroxyapatite by Jihène Jemal; Hassib Tounsi; Kamel Chaari; Carolina Petitto; Gérard Delahay; Samir Djemel; Abdelhamid Ghorbel (pp. 255-260).
Display Omitted► Cu-Hap catalysts prepared by ion exchange in solution. ► Copper ion exchange capacity of Ca-Hap host structure is highly dependent on the initial copper concentration. ► The increase in copper content exchanged has no effect on the profile of conversion of NO by NH3. ► Highly dispersed CuO clusters on Ca-Hap surfaces were responsible for the activity at temperatures below 250°C.Copper loaded hydroxyapatite catalysts were prepared by ion exchange in aqueous phase. The copper ion exchange capacity of hydroxyapatite host structure is highly dependent on the initial copper concentration of the solution. For the lowest concentration, a pH variation of the exchange solution is observed. This change in pH may allow the deposition of a small amount of copper hydroxide at the expense of cationic substitution of copper. The increase in copper content exchanged has no effect on the profile of conversion of NO by NH3. From this, it is assumed that the copper cations substituted for calcium are not active in the reaction. The profiles of NO conversion obtained, are in agreement with the presence of a small amount of copper oxide clusters deposited on the surfaces of the apatite.
Keywords: Selective catalytic reduction; Nitric oxide; Ammonia; Copper; Hydroxyapatite
Ethanol electro-oxidation activity of Nb-doped-TiO2 supported PdAg catalysts in alkaline media by Son Truong Nguyen; Yanhui Yang; Xin Wang (pp. 261-270).
Display Omitted► Mesoporous Nb-doped titania materials, Nb xTi1− xO2, were synthesized. ► The effect of Nb ratio and synthesis temperature on the conductivity of Nb-doped TiO2 was examined. ► Much improved durability in alkaline media was observed for Nb xTi1− xO2. ► PdAg/Nb xTi1− xO2 shows improved activity and stability towards ethanol oxidation compared with carbon black and titania.Various mesoporous Nb-doped titania materials were synthesized by a hydrothermal method and examined as catalyst support for PdAg alloy particles for alkaline direct ethanol fuel cell (ADEFC). X-ray diffraction, nitrogen adsorption/desorption, transmission electron microscopy (TEM), cyclic voltammetry (CV) and chronoamperometry (CA) were used to investigate the properties of the supports and catalysts. 700°C was found as the optimal activation temperature for Nb-doped TiO2 due to the high electronic conductivity achievement and mesoporosity conservation. X-ray diffraction (XRD) revealed that Nb xTi1− xO2 had a structure of mixed anatase and rutile phases. PdAg/Nb xTi1− xO2 exhibited excellent performance for the electrooxidation of ethanol and higher durability in alkaline solution compared with PdAg/C and PdAg/commercial TiO2. The results open a new way to develop durable and effective electrocatalysts for ADEFC.
Keywords: Ethanol oxidation; Palladium-silver; Direct ethanol fuel cell; Nb-doped TiO; 2
Insights on the role of Ru substitution in the properties of LaCoO3-based oxides as catalysts precursors for the oxidative reforming of diesel fuel by N. Mota; M.C. Alvarez-Galván; R.M. Navarro; S.M. Al-Zahrani; A. Goguet; H. Daly; W. Zhang; A. Trunschke; R. Schlögl; J.L.G. Fierro (pp. 271-280).
Catalysts derived from Ru-substituted perovskites (LaCo1− xRu xO3, x=0.05 and 0.2) show better catalytic performance associated to the higher development of active metallic phases achieved on the surface. Additionally, Ru promotes the catalytic activity and stability for this reaction increasing the reduction degree of cobalt and decreasing coke formation and sulfur poisoning through the formation of smaller cobalt crystallites.Display Omitted► Co and Ru-Co lanthanum perovskites as catalysts precursors. ► Catalysts for hydrogen production by oxidative reforming of diesel. ► We found Ru as a promoter. ► Ru incorporation decreases coke formation and sulfur poisoning.The partial substitution of Co by Ru in lanthanum cobaltite perovskites (LaCo1− xRu xO3, x=0.05 and 0.2) and its influence on the reducibility and structural modifications in the perovskite lattice have been evaluated by N2 adsorption isotherms, in situ X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). Characterization of LaCo1− xRu xO3 perovskite precursors reveals that Ru is incorporated into the perovskite lattice, producing a distortion of the original rhombohedral structure, a decrease in mean crystallite size and some increase in the surface area. The structural evolution of the LaCo1− xRu xO3 precursors under a reductive treatment indicates that Ru promotes the reducibility of the perovskite leading to a greater reduction degree of cobalt species. Moreover, the smaller perovskite crystallites obtained with the partial substitution of cobalt by ruthenium evolve to smaller crystal domains of both Co0 and La2O3 after reduction. The catalysts formed after the reduction of perovskite precursors present very high catalytic efficiency to extract hydrogen from diesel molecules by oxidative reforming. However, those catalysts derived from Ru-substituted perovskites show better catalytic performance associated with the higher development of active metallic phases achieved on the surface of these catalysts. Additionally, Ru promotes the catalytic activity and stability for this reaction increasing the reduction degree of cobalt and decreasing coke formation and sulfur poisoning through the formation of smaller cobalt crystallites.
Keywords: Hydrogen; Diesel; Oxidative reforming; Lanthanum cobaltite; Ruthenium
Steam reforming of phenol–ethanol mixture over 5% Ni/Al2O3 by Gabriella Garbarino; Vicente Sanchez Escribano; Elisabetta Finocchio; Guido Busca (pp. 281-289).
Display Omitted► Steam reforming of ethanol–phenol mixture is studied as model of biomass tar SR. ► Ethanol–phenol mixture is completely steam reformed over Ni–alumina at 800–900K. ► Phenol SR occurs at higher T than ethanol SR but is very selective to CO x+H2. ► Over low loading Ni–alumina phenol alkylation by ethanol occurs at T<800K. ► Ethoxide and phenate species appear to act as active intermediates.The steam reforming of 1:2 phenol–ethanol mixture (ca. 80gph+eth/Nm3 in He) as a model of biomass gasification tar, has been investigated over Ni/Al2O3, Ni/MgO-Al2O3 and Ni/ZnO-Al2O3 catalysts. In this paper interest is focused over a 5% Ni-Al2O3 catalyst, that has been characterized in the unreduced and reduced states by IR of CO adsorbed at low temperature. The steam reforming reaction of ethanol and phenol has also been studied, separately, by IR spectroscopy. In spite of its low Ni content and the absence of alkali and alkali earth ions, this catalyst is actually active in the steam reforming of both ethanol and phenol. The reaction is, however, shifted to higher temperature than with catalysts containing higher Ni-loadings and also Mg and/or Zn ions. Ethanol steam reforming occurs at lower temperature than phenol steam reforming and does not seem to be much hindered by the presence of phenol. Phenol steam reforming in the presence of ethanol starts after, but is highly selective to CO x and H2. At low temperature, however, alkylation of phenol mainly occurs over the 5% Ni-Al2O3 catalyst to give mostly o-ethylphenol. Active ethoxide, acetate and phenate species are observed on the surface.
Keywords: Biomass tar; Steam reforming; Nickel/alumina; Infrared spectroscopy; Phenol; Ethanol; Hydrogen
Kinetics and mechanism of pyruvic acid degradation by ozone in the presence of PdO/CeO2 by Weiwei Li; Zhimin Qiang; Tao Zhang; Fenglin Cao (pp. 290-295).
Display Omitted► PdO/CeO2 effectively catalyzed the ozonation of PA at pH 4.7–6.0. ► Interfacial reactions predominated the catalytic ozonation of PA with PdO/CeO2. ► The catalytic ozonation of PA did not involve the radicals ofOH and O2−.This work investigated the catalytic ozonation of pyruvic acid (PA) in the presence of PdO/CeO2 (i.e., Pd deposited on CeO2) with focus on the kinetics of PA degradation at different catalyst dosages, reaction pHs and temperatures, as well as the possible catalytic mechanism. By analyzing the kinetic contributions of heterogeneous and homogeneous reactions to PA degradation, it was found that the presence of PdO/CeO2 significantly enhanced the degradation of PA compared to ozonation alone especially at acidic pHs (3.0–6.0). The catalytic degradation of PA took place on the catalyst surface, which was irrelevant to hydroxyl radicals in the bulk solution. Temperature exhibited an insignificant effect on PA degradation in the range of 12–32°C. Synergic effect was observed between PdO and CeO2 on aqueous ozone decomposition, catalytic ozonation, and adsorption of PA with PdO/CeO2. Ozone and PA were first adsorbed and then activated by the active sites on catalyst surface, and thus becoming more reactive to each other. The influence of phosphate on catalytic ozonation of PA corroborated that the adsorption of PA onto PdO/CeO2 was a critical step for the overall reaction. ATR-FTIR analysis showed that PdO/CeO2 possessed more Lewis acid sites than CeO2, and Pd tended to be the main active sites. NeitherOH nor O2− was involved in the catalytic ozonation of PA as respectively substantiated by the experiments with t-BuOH (asOH scavenger) and nitro blue tetrazolium (as O2− indicator).
Keywords: Pyruvic acid; Catalytic ozonation; PdO/CeO; 2; Kinetics; Interfacial reaction
Ni-based sol–gel catalysts as promising systems for crude bio-oil upgrading: Guaiacol hydrodeoxygenation study by M.V. Bykova; D.Yu. Ermakov; V.V. Kaichev; O.A. Bulavchenko; A.A. Saraev; M.Yu. Lebedev; V.А. Yakovlev (pp. 296-307).
Display Omitted► A series of Ni-based catalysts has been tested in the hydrodeoxygenation of guaiacol. ► Catalysts prepared by sol–gel method possessed the highest HDO activity. ► The activity correlates with Ni loading and specific surface area of catalysts. ► Proposed guaiacol conversion scheme includes the stage with keto-enol tautomerism. ► The effect of temperature on the product distribution was also investigated.Catalytic hydrotreatment or hydrodeoxygenation (HDO) has been researched extensively with the crude bio-oil and its model compounds over conventional sulfided Ni(Mo), Co(Mo) catalysts and supported noble metal catalysts. These types of catalysts showed themselves unsuitable for the target HDO process, which resulted in an urgent need to search for a new catalytic system meeting such requirements as low cost, stability against coke formation and leaching of active components due to adverse effect of the acidic medium (bio-oil). In the present work a series of Ni-based catalysts with different stabilizing components has been tested in the hydrodeoxygenation (HDO) of guaiacol (2-methoxyphenol), bio-oil model compound. The process has been carried out in an autoclave at 320°C and 17MPa H2. The main products were cyclohexane, 1-methylcyclohexane-1,2-diol, and cyclohexanone. The reaction scheme of guaiacol conversion explaining the formation of main products has been suggested. The catalyst activity was found to rise with an increase in the active component loading and depend on the catalyst preparation method. The most active catalysts in HDO of guaiacol were Ni-based catalysts prepared by a sol–gel method and stabilized with SiO2 and ZrO2. According to TPR, XRD, XPS, and HRTEM, the high activity of these catalysts correlates with the high nickel loading and the high specific area of active component provided by the formation of nickel oxide–silicate species. The effect of temperature on the product distribution and catalyst activity in the target process (HDO) has been investigated as well. The catalysts were shown to be very promising systems for the production of hydrocarbon fuels by the catalytic upgrading of bio-oil.
Keywords: Guaiacol; Hydrodeoxygenation; Hydrogenation; Ni-based catalysts; Bio-oil; Biofuel
Highly dispersed ceria on activated carbon for the catalyzed ozonation of organic pollutants by Alexandra Gonçalves; Joaquín Silvestre-Albero; Enrique V. Ramos-Fernández; Juan Carlos. Serrano-Ruiz; José J.M. Órfão; Antonio Sepúlveda-Escribano; Manuel Fernando R. Pereira (pp. 308-317).
Display Omitted► Several catalysts of ceria highly dispersed on activated carbon (AC) were prepared. ► Oxalic acid removal is favored by catalysts prepared from a “Ce(IV)” precursor.► “Ce(III)” precursor favors the mineralization of aniline.► Surface reactions are predominant over liquid bulk reactions involving HO radicals. ► Highly dispersed CeO2 on AC catalysts present better performance than a CeO2–AC composite.Several catalysts of cerium oxide highly dispersed on activated carbon were prepared varying the cerium precursor, the solvent and the chemical surface properties of the support, and characterized by several techniques. Afterwards, these materials were investigated as ozonation catalysts for the mineralization of two organic compounds (oxalic acid and aniline). The ozonation results were compared with those obtained in the absence of catalyst and in the presence of the parent activated carbons used for the preparation of these materials. The prepared catalysts have better performances than the parent activated carbons, denoting a clear synergic effect between activated carbon and cerium oxide. The efficiency of the catalysts is mainly affected by the amount of Ce3+ species on the surface. However, in the ozonation of oxalic acid, the specific surface area and metal oxide particle diameter also played an important role. The use of activated carbon as support favors the removal of both organic compounds studied. Highly dispersed cerium oxide on activated carbon shows better catalytic performance than a composite with the same composition.
Keywords: Catalytic ozonation; Cerium oxide; Activated carbon; Oxalic acid; Aniline
Photoelectrocatalytic performance of TiO2 nanoparticles incorporated TiO2 nanotube arrays by Le Yu; Zhuyi Wang; Liyi Shi; Shuai Yuan; Yin Zhao; Jianhui Fang; Wei Deng (pp. 318-325).
Display Omitted► TiO2 nanotube arrays decorated by TiO2 nanoparticles were prepared. ► Decoration decreases absorption in UV region. ► Decoration increases the width of space charge layer. ► Decoration improves the photoelectrocatalytic performance of nanotube arrays.Highly ordered TiO2 nanotube arrays decorated by TiO2 nanoparticles were prepared via electrochemical anodization method, followed by evaporation induced self-assembly (EISA) strategy. Their photocatalytic (PC) and photoelectrocatalytic (PEC) degradation performance on different dyes were investigated. The dyes used were methylene blue (MB), methyl orange (MeO), rhodamine B (RhB) and reactive brilliant red (K-2G). The structure and compositions of photocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The optical properties of the samples were evaluated by UV–vis spectra. Effects of the incorporation of TiO2 nanoparticles on the charge transfer rate and charge carrier concentration of the TiO2 nanotube arrays during the photocatalytic and photoelectrocatalytic reactions were investigated with electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. In spite of the negative effects such as the decreased absorption in UV region and increased charge transfer resistance, incorporation of TiO2 nanoparticles into TiO2 nanotube arrays was found to not only increase the surface area of TiO2 nanotube arrays, but also enhance the width of space charge layer which promotes the separation of the photo-generated hole/electron pairs efficiently under external bias. Moreover, anodic bias can improve the degradation rates of anionic dyes more than cationic dyes.
Keywords: TiO; 2; nanotube arrays; TiO; 2; nanoparticles; Photocatalysis; Photoelectrocatalysis