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Applied Catalysis A, General (v.411-412, #)
Low content cerium oxide nanoparticles on carbon for hydrogen peroxide electrosynthesis by M.H.M.T. Assumpção; A. Moraes; R.F.B. De Souza; I. Gaubeur; R.T.S. Oliveira; V.S. Antonin; G.R.P. Malpass; R.S. Rocha; M.L. Calegaro; M.R.V. Lanza; M.C. Santos (pp. 1-6).
Display Omitted► 4% CeO2/C was the best choice for H2O2 electrogeneration among all materials used. ► 4% CeO2/C transferred 3.1 electrons and had a H2O2 percentage efficiency of 44%. ► Gas diffusion electrodes containing 4% CeO2/C produced 871mgL−1 of H2O2. ► X-ray diffraction analysis identified two phases for 4% CeO2/C (CeO2 and CeO2− x).A comparative study using different proportions of CeO2/C (4%, 9% and 13% CeO2) was performed to produce H2O2, a reagent used in the oxidation of organic pollutants and in electro-Fenton reactions for the production of the hydroxyl radical (OH), a strong oxidant agent used in the electrochemical treatment of aqueous wastewater. The CeO2/C materials were prepared by a modified polymeric precursor method (PPM). X-ray diffraction analysis of the CeO2/C prepared by the PPM identified two phases, CeO2 and CeO2− x. The average size of the crystallites in these materials was close to 7nm. The kinetics of the oxygen reduction reaction (ORR) were evaluated by the rotating ring-disk electrode technique. The results showed that the 4% CeO2/C prepared by the PPM was the best composite for the production of H2O2 in a 1molL−1 NaOH electrolyte solution. For this material, the number of electrons transferred and the H2O2 percentage efficiency were 3.1 and 44%, respectively. The ring-current of the 4% CeO2/C was higher than that of Vulcan carbon, the reference material for H2O2 production, which produced 41% H2O2 and transferred 3.1 electrons per molecule of oxygen. The overpotential for this reaction on the ceria-based catalyst was substantially lower (approximately 200mV), demonstrating the higher catalytic performance of this material. Gas diffusion electrodes (GDE) containing the catalyst were used to evaluate the real amount of H2O2 produced during exhaustive electrolysis. The 4% CeO2/C GDE produced 871mgL−1 of H2O2, whereas the Vulcan carbon GDE produced a maximum amount of only 407mgL−1. Thus, the 4% CeO2/C electrocatalyst prepared by the PPM is a promising material for H2O2 electrogeneration in alkaline media.
Keywords: Oxygen reduction reaction; Electrogeneration of hydrogen peroxide; Cerium oxides; Low content
Light-induced self-cleaning properties of ZnO nanowires grown at low temperatures by G. Kenanakis; D. Vernardou; N. Katsarakis (pp. 7-14).
Display Omitted► Highly c-axis oriented ZnO nanowires were grown on glass using aqueous solutions. ► The growth temperature does not exceed 95°C in any step of the synthesis. ► The photocatalytic and wetting properties were studied upon UV irradiation. ► ZnO nanowires show superior photocatalytic activity. ► We report a reversible photo-induced transition from hydrophobic to super-hydrophilic.Highly c-axis oriented ZnO nanowires’ arrays were grown on glass substrates using an aqueous solution approach, in which the growth temperature does not exceed 95°C in any step of the synthesis. Both their photocatalytic and wetting properties were studied upon ultraviolet (UV) light irradiation. It is revealed that ZnO nanowires’ arrays show advanced photocatalytic activity, along with a remarkable reversible photo-induced transition from hydrophobic to super-hydrophilic under UV light exposure, reaching a nearly zero contact angle in short time. The capability to control the morphological characteristics of ZnO nanowires via the deposition of an amorphous seed layer is discussed, which can be significant for self-cleaning applications.
Keywords: Aqueous solution growth; Seed layer; ZnO; Nanowires; Photocatalysis; Stearic acid; Wettability
Fischer–Tropsch catalysts deposited with size-controlled Co3O4 nanocrystals: Effect of Co particle size on catalytic activity and stability by Jo-Yong Park; Yun-Jo Lee; Prashant R. Karandikar; Ki-Won Jun; Kyoung-Su Ha; Hae-Gu Park (pp. 15-23).
Display Omitted► Co3O4 nanocrystals embedded catalysts x-CoAl prepared with different crystal sizes. ► x-CoAl catalysts show superior activity for Fischer–Tropsch reaction. ► Uniform distribution of defined size cobalt particles enhances the efficiency. ► Rapid growth in the activity with increase in the cobalt crystal size up to 9.3nm. ► With the increase in the crystals size deactivation rate turns negligible.The influences of cobalt particle size on the Fischer–Tropsch reaction have been studied by using pre-synthesized cobalt oxide nanoparticles. Cobalt oxide nanoparticles in the range of 3–16nm were synthesized by reacting colloidal solution of Co3O4 at the different reaction temperatures from 150 to 250°C and stabilized by capping agent. The nanoparticles were impregnated on γ-Al2O3 to prepare 5wt% Co/Al2O3 catalysts and compared with the catalysts prepared by conventional methods. The reduction degree by TPR and O2-uptake increased with the increase in the cobalt crystal size from 4.8 to 17.5nm, however H2-uptake decreased. The rapid growth in the catalytic activity was observed when the cobalt crystal size increased from 4.8 to 9.3nm and then the activity decreased with further increase in crystal size showing volcano shape in catalytic activity. The catalyst with the cobalt particle size of 9.3nm showed higher CO conversion, better C5+ selectivity and lower methane conversion. These size-defined cobalt catalysts showed considerably higher FTS activity and better TOF (S−1) than conventional catalysts and with the increase in the cobalt particle size, their deactivation rates also decreased as well even after 54h on stream.
Keywords: Cobalt oxide nanocrystals; Co/Al; 2; O; 3; catalysts; Crystal size effect; FT synthesis
Kinetics and mechanism of organic pollutants degradation with cobalt–bicarbonate–hydrogen peroxide system: Investigation of the role of substrates by Xiaoxia Li; Zhongduo Xiong; Xinchao Ruan; Dongsheng Xia; Qingfu Zeng; Aihua Xu (pp. 24-30).
Display Omitted► Co2+–HCO3−–H2O2 system efficiently catalyzes degradation of highly stable organic dyes. ► The rate ofOH radicals production increases after Co2+–methylene blue complexes formation. ► The tested other pollutants play an important role inOH radicals production in the system.The kinetics and mechanism of a simple system, Co2+–HCO3−–H2O2 for degrading highly stable organic pollutants have been reported. Fast and versatile decolorization of organic dyes was observed in an aqueous solution containing 10mM NaHCO3, 10μM Co2+ ions and 10mM H2O2, while the degradation rate of p-nitrophenol and 2,4-dinitrophenol was very slow. From cyclic voltammetry and UV–vis spectra, it was found that different complexes between Co2+ ions and methylene blue (MB) were formed in HCO3− solution, and being confirmed by photoluminescence probing and electron spin resonance spin-trapping technologies, the 1:1 complex [CoII(HCO3−)(MB)]+ was more efficient in catalyzing decomposition of H2O2 intoOH radicals. The other tested pollutants also played an important role in the rate ofOH radicals production in the system. Based on the kinetic observations of MB decolorization, a possible mechanism was proposed.
Keywords: Cobalt; Bicarbonate; Hydrogen peroxide; Oxidative degradation; Organic pollutants
Preferential CO oxidation in hydrogen (PROX) on unsupported PtSn catalyst by D. Teschner; A. Wootsch; Z. Paál (pp. 31-34).
Display Omitted► Unsupported PtSn was more active catalyst in PROX than Pt black. ► Pretreatment by H2 and by O2–H2 increased activity. ► PROX activity had a sharp maximum at about 400K. ► In situ XPS: Pt 4f showed Pt0, Sn 3d contained Sn0 and Sn oxides. ► Whenever surface OH, H2O are present, PROX reaction is more rapid.PROX reaction was studied over an unsupported PtSn catalyst. CO2 and H2O were produced from a H2 flow containing 1% CO, and 0.4–2% O2. PtSn pretreated with O2 and H2 contained more Pt in the near-surface region and was more active towards CO oxidation than a sample pretreated in H2 only. In situ XPS was also carried out during PROX reaction. Sn 3d indicated the presence of Sn-oxides, near to the surface region, along with Pt3Sn. Pt 4f peak showed metallic Pt under all conditions. Water and OH enrichment was observed in the O 1s spectrum, taken during PROX reaction.
Keywords: PROX reaction; PtSn catalyst; In situ XPS
Study of the role of the catalyst and operating conditions on the sediments formation during deep hydroconversion of vacuum residue by Charles Marchal; Denis Uzio; Isabelle Merdrignac; Loïc Barré; Christophe Geantet (pp. 35-43).
Display Omitted► Hydroconversion of vacuum residue. ► Fluorine effect on NiMo sulfide catalyst. ► Effect of catalyst and operating temperature on sediment formation. ► Asphaltenes and resins molecular structures.The aim of this work is to investigate the influence of the catalyst and the operating temperature on the sediments formation occurring during vacuum residue hydroconversion. At high conversion, instability phenomena occurring due to carbonaceous sediments formation is a tricky issue to address and has detrimental effects on the operability of industrial units. The impact of the catalyst properties on this phenomenon has been scarcely studied. Therefore, a doped F doped NiMo/Al2O3 catalyst has been prepared and catalytic tests performed at two temperature levels (430 and 390°C) in order to study the effect of catalytic hydrocracking or thermal conversion on the sediment formation. For both temperature regimes, it has been observed that the amount of sediments is strongly reduced with the F-NiMo catalyst compared to the undoped one and attributed to the improvement of the conversion of the sediment precursors (asphaltenes). This improvement is mostly due to the promotion of the acidic and hydrogenation functions by F addition. At 390°C, coke deposition on F-NiMo catalyst is reduced which limits the plugging of the porous volume and preserve the intragranular diffusion of large molecules in the porosity. It has been shown that deep asphaltenes conversion can be achieved using an improved hydrogenation catalyst by reducing their polarity through the removal of heteroatoms and the saturation of some aromatic rings by hydrogen addition. The residual molecules exhibit lower interactions and self association ability resulting in a lower sediment formation.The temperature has also a great impact on the sediment formation in the effluents since the decrease of the temperature favors hydrogenation and catalytic hydrocracking route which is more appropriated to produce stable effluents compared to radical chemistry predominant at high temperature.
Keywords: Hydroconversion; Vacuum residue; Sulfide catalyst; Fluorine; Effluent stability; Sediment formation; Asphaltenes; Resins
Effect of the kinds of alcohols on the structure and stability of calcium oxide catalyst in triolein transesterification reaction by Kohei Urasaki; Shunsuke Takagi; Takashi Mukoyama; Jayaraj Christopher; Kaori Urasaki; Shigeru Kato; Akihiro Yamasaki; Toshinori Kojima; Shigeo Satokawa (pp. 44-50).
Display Omitted► Transesterification of triolein with C1–C4 aliphatic alcohols over CaO catalyst. ► Ca(C3H7O3)2 formation and Ca leaching occurred in case of methanol. ► The structure of CaO was maintained and Ca did not leach in case of higher alcohols. ► Ca(C3H7O3)2 formation started by continuing reflux after reaction finished. ► Triolein inhibited the contact of glycerol with CaO to form Ca(C3H7O3)2.Transesterification of triolein with various alcohols like methanol, ethanol, 1-propanol, 2-propanol and 1-butanol over CaO catalyst was performed at atmospheric pressure and the temperature near to the boiling point of each alcohol with various catalyst dosages. High transesterification reaction rate was obtained by the reaction with methanol over CaO catalyst. However some amounts of the catalyst dissolved into the products during the transesterification reaction and the crystalline phase of catalyst changed to Ca(C3H7O3)2 at the early stage of reaction. On the other hand, the moderate transesterification reaction rates were obtained by the reaction with higher alcohols like ethanol, 1-propanol and 1-butanol over CaO catalyst. Calcium was hardly dissolved into the product and the structure of catalyst was not changed until the triolein conversion reached to 100%. After all of the raw triolein converted to products, both calcium leaching and the formation of Ca(C3H7O3)2 started. Some experiments and characterization implied that triolein suppressed the formation of Ca(C3H7O3)2 by inhibiting the contact of glycerol with CaO in the absence of methanol and methanol seems to eliminate such inhibitory effect of triolein.
Keywords: Biodiesel; Calcium oxide; Calcium glyceroxide; Transesterification
The nature of the sulfur tolerance of amorphous silica-alumina supported NiMo(W) sulfide and Pt hydrogenation catalysts by Alessandro E. Coumans; Dilip G. Poduval; J.A. Rob van Veen; Emiel J.M. Hensen (pp. 51-59).
Display Omitted► Sulfur tolerance of NiMo(W)S and Pt in aromatics hydrogenation evaluated. ► Sulfur tolerance does not depend on support Brønsted acidity. ► Sulfur tolerance correlates with support electronegativity. ► Lewis acid Al sites essential to introduce the support electronegativity effect on the active phase.Amorphous silica-aluminas (ASA) based NiMo and NiW sulfide and Pt hydrogenation catalysts were prepared and compared in toluene hydrogenation in the presence of H2S to alumina- and silica-supported reference catalysts with the aim to elucidate the influence of (strong) Brønsted acidity of the support on the sulfur tolerance. Despite precautions to prepare NiMo sulfide catalysts with equal morphology, the stacking degree of the MoS2 phase was found to decrease with alumina content of the ASA. Similar but more pronounced differences of the stacking degree were observed among the NiW sulfide catalysts. This variation in the stacking degree had a substantial effect on the catalytic activity of dibenzothiophene hydrodesulfurization. ASA-based catalysts show higher activity and improved sulfur tolerance in toluene hydrogenation compared to their alumina- and silica-based counterparts. However, the sulfur tolerance does not correlate with the number of strong Brønsted acid sites, nor, indeed, with total Brønsted acidity. Instead, it decreases with increasing Al content of the ASA support. The sulfur tolerance of the active metal sulfide phase is related to the electronegativity of the support. That silica itself does not follow this trend is surmised to be due to its lack of Lewis acid sites, necessary for introducing the active phase-support effect.
Keywords: Sulfur tolerance; Hydrogenation; Amorphous silica-alumina; Support effect
Ultrasound assisted preparation of stable water-based nanocrystalline TiO2 suspensions for photocatalytic applications of inkjet-printed films by I. Fasaki; K. Siamos; M. Arin; P. Lommens; I. Van Driessche; S.C. Hopkins; B.A. Glowacki; I. Arabatzis (pp. 60-69).
Display Omitted► Investigation of ultrasound assisted deaggregation mechanism of TiO2 suspensions. ► Environmentally friendly method of industrial preparation of titania suspensions. ► Deposition of TiO2 suspensions by inkjet printing on glass and tile. ► Photocatalytic coatings for self-cleaning and self-sterilizing surfaces.The use of titania photocatalytic materials in industrial applications is strongly dependent on the stability, nanoparticle size distribution, ease of deposition and cost of the relevant titania precursor solutions or suspensions. The present contribution presents the preparation of inkjet-printed titania films, derived from stable water-based suspensions. The suspensions were synthesized by applying a “top-down” synthetic strategy, namely the ultrasonication of commercially available titania powder (Evonik Aeroxide P25). Crucial parameters, such as suspension stability, energy input requirements, particle size distribution, surface characteristics, compatibility with industrially proven inkjet systems and photocatalytic performance were investigated. The developed synthetic procedure proves environmentally friendly, low cost and most suitable for large scale production of titania thin films, by inkjet printing commercially available ceramic tiles.
Keywords: Stability of water based suspensions; TiO; 2; nanoparticles; Ultrasonication; Self-cleaning surfaces; Inkjet printing
An efficient method for the transformation of naturally occurring monoterpenes into amines through rhodium-catalyzed hydroaminomethylation by Daniela S. Melo; Schubert S. Pereira-Júnior; Eduardo N. dos Santos (pp. 70-76).
Display Omitted► Naturally occurring monoterpenes were transformed into homologous amines. ► The transformation was made in one-pot (hydroaminomethylation). ► Rhodium complexes promote both hydroformylation and enamine hydrogenation. ► The concurrent double-bond isomerization was minimized by the use of phosphines. ► This study allowed insights about the nature of the catalytically active species.The hydroaminomethylation (hydroformylation/reductive amination) of the naturally occurring monoterpenes, i.e., limonene, camphene, and β-pinene, was studied having as condensation counterparts the amines di-n-butylamine, morpholine or n-butylamine. Moderate to good yields (75–94%) were obtained employing [Rh(cod)(μ-OMe)]2 as pre-catalyst in the presence or not of triphenylphosphine or tribenzylphosphine as ancillaries in toluene, at 100°C and 60bar of an equimolar mixture of carbon monoxide and hydrogen. Some of the hydroaminomethylation products derived from limonene have biological activity and the products derived from camphene and β-pinene are new.
Keywords: Hydroaminomethylation; Hydroformylation; Amination; Monoterpene; Tandem catalysis
Acid catalyzed organic transformations by heteropoly tungstophosphoric acid supported on MCM-41 by Abd El Rahman S. Khder; Hassan M.A. Hassan; M. Samy El-Shall (pp. 77-86).
Display Omitted► MCM-41-suppported 12-tungstophosphoric acid was used as catalyst. Catalysts show high acidity and surface saturation conerage up to 60HPWwt%. ► The catalysts exhibit high activity towards many organic reactions. The catalysts can be recycled several times without significant loss in activity.In this work, solid acid catalysts of the Keggin-type 12-tungstophosphoric acid (H3PW12O40, HPW) incorporated within the mesochannels of MCM-41 are prepared through a simple and effective impregnation method. The catalysts are characterized by various techniques such as XRD, FTIR, TEM, N2 adsorption and thermal analysis. The surface acidities are measured by non-aqueous titration of n-butyl amine in acetonitrile and FTIR spectra of chemisorbed pyridine. The acidity and the textural parameters of the nanocomposites can be controlled simply by changing the loading of HPW on the MCM-41. The results indicate that the surface saturation coverage of MCM-41 is reached with 60wt% HPW. The high saturation coverage is indicative of the well-dispersion of HPW within the mesochannels of MCM-41. The catalytic activities of the HPW/MCM-41 catalysts for the Pechmann, esterification reaction and Friedel–Crafts acylation reactions are studied in detail. Both the surface acidity and the catalytic activity sharply increase with the modification of MCM-41 by HPW. The sample with 60wt% HPW shows the highest acidity and catalytic activity. The reusability tests of the catalysts show that the catalysts can be used several times without significant loss in activity. The HPW/MCM-41 catalysts have great potential for applications as commercial catalysts in promoting acid-catalyzed organic transformations under environmental friendly conditions and processes.
Keywords: Solid acid catalyst; MCM-41; Heteropoly acid; Pechmann; Esterification; Friedel–Crafts acylation reactions
Autothermal partial oxidation of butanol isomers by Jacob S. Kruger; Reetam Chakrabarti; Richard J. Hermann; Lanny D. Schmidt (pp. 87-94).
Display Omitted► Autothermal butanol gasification over Pt, PtCe, Rh, and RhCe catalysts. ► High yields to syngas and olefins from the four butanol isomers. ► Tunable product spectrum by varying fuel/O2 ratio. ► Qualitative mechanisms for butanol partial oxidation proposed.The four isomers of butanol offer an interesting platform from which to study the reaction pathways of alcohols in an autothermal partial oxidation system, as they comprise one tertiary, one secondary, and two primary alcohols with the same number of carbon atoms. We demonstrate high yields of syngas or unsaturated molecules at contact times on the order of 10 ms, and investigate the reaction pathways of each isomer over Rh, RhCe, Pt, and PtCe catalysts for a range of carbon-to-oxygen (C/O) ratios.For each isomer, conversion to equilibrium syngas products is essentially complete at C/O=0.8. As C/O ratio increases, the major product from the primary and secondary butanols switches to the corresponding carbonyl, producing butyraldehyde, isobutyraldehyde, and butanone from 1-butanol, isobutanol and 2-butanol, respectively. Selectivity to the carbonyls approached 30–50% as C/O approached 2.0. Dehydration to the corresponding butenes is relatively minor in comparison, representing less than 20% selectivity at C/O=2.0. tert-butanol reacted differently, selecting mainly for the dehydration product isobutene. Acetone was the main carbonyl product from tert-Butanol, but selectivity to acetone was always ≤10%. Global mechanisms in an autothermal reactor, based on pyrolysis, combustion and surface science literature, are proposed for each alcohol. Surface chemistry likely accounts for much of the syngas formation and heat generation, while the carbonyls and alkenes may be formed primarily through homogeneous routes.
Keywords: Butanol; Catalytic partial oxidation; Rhodium; Platinum; Cerium
Aqueous-phase hydrodeoxygenation of propanoic acid over the Ru/ZrO2 and Ru–Mo/ZrO2 catalysts by Lungang Chen; Yulei Zhu; Hongyan Zheng; Chenghua Zhang; Yongwang Li (pp. 95-104).
Display Omitted► The APHDO of propanoic acid over the Ru/ZrO2 and Ru–Mo/ZrO2 catalysts was studied. ► The incorporation of Mo improves the selectivity of CO hydrogenation products. ► The incorporation of Mo suppresses the C–C bond cleavage reaction greatly. ► The inhibition of CC bond cleavage is ascribed to formation of Ru–MoO x interface.The conversion of propanoic acid under high hydrogen pressure has been studied over zirconia-supported monometallic Ru and bimetallic Ru–Mo catalysts. The cleavage of C–C bond of propanoic acid to methane and ethane is improved and the formation of CO hydrogenation products (propanol and propane) is decreased with increasing the temperature. Upon addition of Mo, both the overall activity and the C–C bond cleavage selectivity decrease while the selectivity of CO hydrogenation increases. With increase of Mo contents, the C–C bond cleavage reaction is significantly inhibited, especially at high temperature. This is also confirmed by the DRIFTS of propanoic acid, showing that the propanoyl intermediate species on Ru–Mo bimetal catalysts is more difficult to dissociate to CO compared with Ru monometal catalyst. Based on H2-TPR, CO-FTIR and DRIFTS of propanoic acid characterizations, the reaction mechanisms and the resulting selectivity towards the possible reaction paths (C–C bond cleavage/CO hydrogenation) are discussed in terms of the formation of Ru–MoO x and the stability and variety of propanoyl intermediate species occurring on the Ru–Mo bimetal catalysts. It is suggested that the interaction of Ru and MoO x species and the formation of Ru–MoO x interface are the important factors for the decrease in the TOF of propanoic acid and the C–C bond cleavage selectivity.
Keywords: Hydrodeoxygenation; Propanoic acid; Ru catalyst; Ru–Mo catalyst; Effect of Mo
Nanostructured supported palladium catalysts—Non-oxidative methane coupling by Silvia F. Moya; Ruth L. Martins; Antje Ota; Edward L. Kunkes; Malte Behrens; Martin Schmal (pp. 105-113).
Display Omitted► Pd on α-Al2O3 catalysts were prepared by sonochemical and colloidal methods. ► The PdSON with smaller and homogeneous particles than PdCOL is highly dispersed. ► Chemisorption of CH4 in the temperature range 473–773K, followed by hydrogenation. ► Activity evidenced different adspecies during methane coupling and chemisorption. ► Carbon adspecies evidenced different C phases, which are reactive.The Pd on α-Al2O3 catalysts with Pd particles in the low nanometer range have been prepared by a sonochemical reduction and a colloidal method, respectively. The two catalysts differ in their particle size, the widths of their particle size distributions and the amount of carbon incorporation in the Pd lattice.The adsorptive properties of the Pd/Al2O3 samples are different as a result of the different preparation methods. The methane adsorption capacity of that sample with smaller particles is lower than that of the catalyst with larger particles and the energy of activation is nearly doubled. DRIFTS and TPD results of CO adsorption supported by transmission electron microscopy data indicate that the PdSON catalyst with smaller and more homogeneous particles than PdCOL is highly dispersed which influences the coupling-hydrogenolysis process.The catalytic activity evidenced the formation of different adspecies during methane coupling and chemisorption on both catalysts. During the hydrogenation the carbon adspecies formed mainly methane at low adsorption temperatures. The significant amount of adsorbed methane at 773K is governed by the highly active coordination unsaturated sites at the surface.
Keywords: Palladium; Nanostructure; Sonochemistry; Colloidal method; Methane activation; Non-oxidative process
Parametric study of methane steam reforming to syngas in a catalytic microchannel reactor by Mustafa Karakaya; Seda Keskin; Ahmet K. Avci (pp. 114-122).
Display Omitted► Microchannel reactor is more productive and CO selective than packed bed. ► Near equilibrium CO selectivity is obtained for Rh at ∼50ms residence time. ► Rh-coated catalyst has superior chemical activity and mechanical stability. ► Microchannel reactor enables selectivity control by allowing short contact times.The aim of this work is the parametric investigation of methane steam reforming (MSR) to synthesis gas (syngas, CO+H2) in a wall-coated catalytic microchannel reactor. Methane conversion and CO selectivity on coated Rh, Ru, Pt and Ni catalysts, all supported on Al2O3, are compared in the parameter ranges of 12.86–77.14ms residence time, 600–800°C temperature and 0.5–3.0M steam-to-carbon ratio at the reactor inlet. Among the active metals, Rh is the best one in terms of both methane conversion and productivity (rate of methane consumption per weight of catalyst). Productivity decreases in the order of Rh > Ru > Pt ≈ Ni. For all catalysts, conversion increases with residence time, temperature and steam-to-carbon ratio. CO selectivity is highest in all cases on Rh, and increases with increasing temperature and decreasing steam-to-carbon ratio. However, in the range of residence times considered, a maximum CO selectivity for each catalyst is encountered where the water–gas shift equilibrium becomes significant, and converts more of the CO produced by MSR to CO2. Time-on-stream runs conducted on Rh and Ni show that the former has excellent chemical and mechanical stability for 72h even at extreme conditions such as steam-to-carbon ratio of 0.5 and residence time of 12.86ms. Activity of Ni starts to decrease after 20h even though it is operated at a steam-to-carbon ratio of 3.0. Comparative tests conducted between microchannel and packed-bed reactors show that the former outperforms the packed bed in terms of productivity and CO selectivity.
Keywords: Methane; Microchannel reactor; Steam reforming; Syngas; Wall-coated catalyst
Friedel–Crafts propionylation of veratrole to 3,4-dimethoxypropiophenone over superacidic UDCaT-5 catalyst by Ganapati D. Yadav; Santosh R. More (pp. 123-130).
Display Omitted► Green propionylation of veratrole to 3,4-dimethoxypropiophenone. ► Different sulfate modified zirconia based catalysts. ► UDCaT-5 as the most active mesoporous solid acid catalyst ► 100% selective and reusable catalyst. ► Eley–Rideal mechanism.3,4-Dimethoxypropiophenone (3,4-DMPP) is of considerable commercial importance due to its use in fine chemical and drug industries. 3,4-DMPP is traditionally produced by the Friedel–Crafts propionylation of veratrole using homogeneous catalysts which are highly polluting. Zeolites have also been used but they are known to deactivate rapidly. A variety of novel solid acid catalysts such as UDCaT-4 (persulfated alumina zirconia on hexagonal mesoporous silica, HMS), UDCaT-5 (superacidic modified sulfated zirconia) and UDCaT-6 (modified sulfated zirconia nanoparticles on HMS) were synthesized in our laboratory and characterized. Amongst them UDCaT-5 was the most active and selective. The current work deals with development of clean and benign route for 3,4-DMPP synthesis using UDCaT-5 as catalyst in the absence of any solvent. Effects of various parameters were studied in order to optimize the conversion of veratrole and selectivity to 3,4-DMPP. Based on the experimental data a suitable mathematical model was developed to represent the reaction kinetics.
Keywords: Solid superacids; Veratrole; Friedel–Crafts acylation; Kinetics; Selectivity
Selective catalytic oxidation of ammonia to nitrogen over ceria–zirconia mixed oxides by Zhong Wang; Zhenping Qu; Xie Quan; Hui Wang (pp. 131-138).
Display Omitted► It was the first time to report the Ce1− xZr xO2 catalysts for SCO of ammonia to N2. ► The Ce1− xZr xO2 ( x=0.2–0.6) catalysts showed high activity for ammonia oxidation. ► The phase transformation and formed moderate acid sites favored the SCO of ammonia. ► The Zr-rich (tetragonal) phase ( x>0.4) improved the N2 selectivity of the catalyst.The selective catalytic oxidation of ammonia to nitrogen (NH3-SCO) has been studied over ceria–zirconia mixed oxides (Ce1− xZr xO2). The addition of Zr into ceria leaded to the phase transition from the cubic fluorite structure to the tetragonal structure and the generation of oxygen vacancies. The Ce1− xZr xO2 (0.2⩽ x⩽0.8) mixed oxide catalysts exhibited certain amount of moderate acid sites. Particularly, the Ce0.4Zr0.6O2 catalyst achieved the largest amount of moderate acid sites and highest proportion of Ce3+ (oxygen vacancies). Meanwhile, it showed the best NH3 oxidation activity, and the complete conversion temperature was about 360°C. In addition, numerical results also indicated that the higher zirconium content in Ce1− xZr xO2 catalysts improved the N2 selectivity which was about 100% with x>0.4. The formation of N2O was the main reason for low N2 selectivity over these catalysts ( x⩽0.4) proved by TPSR experiments. Meanwhile, the reaction mechanism of NH3 with lattice oxygen was observed to be different from the gaseous oxygen, and the gaseous oxygen species was much more active than lattice oxygen for NH3 oxidation.
Keywords: Selective catalytic oxidation of ammonia; Ce; 1−; x; Zr; x; O; 2; catalysts; Phase transition; Acid sites
Synthesis, characterization and evaluation of efficiency of new hybrid Pc/Fe-TiO2 nanocomposite as photocatalyst for decolorization of methyl orange using visible light irradiation by Zohreh Mesgari; Mehrnaz Gharagozlou; Alireza Khosravi; Kamaladin Gharanjig (pp. 139-145).
Display Omitted► Synthesis of novel nanocomposite of Fe-doped TiO2 and phthalocyanine. ► We report the photocatalytic efficiency of nanocomposite for the first time. ► Nanocomposite showed more photocatalytic activity than TiO2 under visible light. ► Nanocomposite as a visible light photocatalyst expands applicability of TiO2. ► Pc and Fe3+ ions caused a significant shift of absorption edge into visible area.Novel hybrid nanocomposite based on the Fe-doped TiO2 and phthalocyanine, (Pc/Fe-TiO2), has been synthesized and characterized. Also, the efficiency of the nanocomposite as a photocatalyst for the decolorization of methyl orange using visible light irradiation has been evaluated. For the preparation of the nanocomposite, at first Fe-doped TiO2 nanoparticles have been prepared by a sol–gel method. Then the nanocomposite was synthesized by anchoring the Pc complex on the Fe-TiO2 nanoparticles calcined at 400°C. Prepared nanoparticles and the nanocomposite have been characterized by XRD, FT-IR, EDX, BET, DRS, STA (TG–DTA) and TEM techniques. Results revealed that the nanocomposite possesses the anatase structure with the specific surface area of 7.16m2/g. The TEM micrograph demonstrated that the average particle size of the nanocomposite was about 15–20nm. Phthalocyanine and Fe3+ ions in the TiO2 structure caused significant shift of absorption edge into the visible region. The band gap energy of the nanocomposite was calculated as 2.48eV. Results of decolorization revealed that the nanocomposite has shown much more photocatalytic activity than the pure TiO2 under the visible light. It was found that about 87% of the methyl orange solution was decolored over the nanocomposite after 450min under visible light irradiation. Therefore, the synthesized nanocomposite is a suitable photocatalyst to use under the visible light which makes the applicability of TiO2 photocatalysts even more versatile.
Keywords: Hybrid nanocomposite; Fe-doped TiO; 2; Phthalocyanine; Photocatalyst; Methyl orange; Visible light
Supported sulfonic acids: Metal-free catalysts for the oxidation of hydroquinones to benzoquinones with hydrogen peroxide by Raimondo Maggi; Calogero G. Piscopo; Giovanni Sartori; Loretta Storaro; Elisa Moretti (pp. 146-152).
Display Omitted► Sulfonic acid supported on both amorphous and mesoporous siliceous materials. ► Physico-chemical characterization of the supported catalysts. ► Test of these catalysts in the oxidation of hydroquinones to benzoquinones. ► Good yields and excellent selectivities with SiO2–(CH2)3–SO3H.Some silica- and polystyrene-supported sulfonic acids, prepared by tethering or sol–gel techniques, were employed as metal-free heterogeneous catalysts in the oxidation of hydroquinones to the corresponding 1,4-benzoquinones, carried out with 30% aqueous hydrogen peroxide. The activity of these catalysts was tested in the model oxidation of methylhydroquinone under batch conditions: high yield and selectivity at room temperature and under environmentally friendly conditions can be achieved in the presence of SiO2–(CH2)3–SO3H. The heterogeneous catalyst, that can be easily recovered by simply filtration, can be used for at least three cycles affording the same good results (∼80% yield, ∼91% selectivity).
Keywords: Oxidation; Hydrogen peroxide; Hydroquinones; Benzoquinones; Supported sulfonic acids
Effect of hydrothermal treatment on structural and photocatalytic properties of TiO2 synthesized by sol–gel method by E. Pulido Melián; O. González Díaz; J.M. Doña Rodríguez; G. Colón; J.A. Navío; J. Pérez Peña (pp. 153-159).
Display Omitted► TiO2 has been prepared by sol–gel precipitation and further hydrothermal treatment. ► The hydrothermal treatment previous to calcination affects the structure evolution of the starting materials. ► The hydrothermal treatment leads to obtain better photocatalysts. ► TiO2ht600 exhibits high photocatalytic activity for different pollutants tested. ► TiO2ht600 is removed from solution by gravity sedimentation in only 2h.TiO2 nanoparticles have been prepared by sol–gel precipitation and further hydrothermal treatment. In this way, the effect of the hydrothermal treatment on the structural properties and photocatalytic activity of sol–gel synthesized catalysts has been investigated. These catalysts have been produced by hydrolysis of a mixture of isopropanol–titanium tetraisopropoxide (iPrOH–TiiP). The prepared photocatalysts were characterized by means of X-ray diffraction (XRD), surface area analysis (BET), transmission microscopy (TEM), thermogravimetric analysis (TG), scanning electron microscopy (SEM) analysis, diffuse reflectance, sedimentability analysis and aggregate size study. Besides, the structural evolution with the temperature of the photocatalysts treated or not hydrothermally was studied. It was observed that the calcination produces approaching between the characteristics of both sets of photocatalysts.The photocatalytic activity of the obtained photocatalysts was investigated, using phenol as a model pollutant. The calcination temperature is the most remarkable factor that can affect the ultimate photocatalytic activity of the prepared photocatalysts. However, the hydrothermal treatment previous to calcination led to obtain photocatalysts which exhibit larger photocatalytic activity than their homologous photocatalysts without hydrothermal treatment. The obtained photocatalyst TiO2ht600 exhibits the same photocatalytic activity per surface area than the commercial TiO2 Degussa P25 but with much faster sedimentability.
Keywords: TiO; 2; Photocatalysis; Hydrothermal; Sol–gel
Effect of steam content on nickel nano-particle sintering and methane reforming activity of Ni–CZO anode cermets for internal reforming SOFCs by D. Hari Prasad; S.Y. Park; H. Ji; H.-R. Kim; J.-W. Son; B.-K. Kim; H.-W. Lee; J.-H. Lee (pp. 160-169).
Display Omitted► ISRM over Ni–CZO anode cermets of SOFCs has been investigated. ► Steam rich conditions showed high reforming activity which decreased and stabilized with time. ► Steam lean conditions showed a moderate and constant reforming activity. ► Excess steam content is the primary cause for nickel nano-particle sintering and resulted in decrease of reforming activity. ► TEM/EDS analysis manifested the nickel nano-particle sintering.In this work, the reforming activity of Ni–Ce0.75Zr0.25O2 (Ni–CZO) solid oxide fuel cell (SOFC) cermet anodes for steam reforming of methane has been investigated in the absence of electrochemical effects and the results were compared with Ni–Ce0.9Gd0.1O2 (Ni–CGO) cermet anodes. From X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy/energy dispersive X-ray spectroscopy (TEM/EDS) and CHN analysis on the spent Ni–CZO anode cermets, it was found that a decrease in reforming activity at higher steam-to-carbon ratios (S/C) was due to sintering of nickel nano-particles rather than re-oxidation or sintering of bulk nickel and carbon formation. Time-on-stream analysis demonstrated a higher reforming activity for Ni–CZO cermet anodes compared to Ni–CGO cermet anodes. While the initial sizes of nickel nano-particles were similar (5–10nm) for both cermet anodes, after the operation under steam-rich conditions (S/C=1.5) the nickel nano-particles on Ni–CGO were found to be significantly larger (20–40nm) than those on Ni–CZO (15–25nm). Under steam-lean conditions (S/C=0.5), the size of nickel nano-particles remained below 10nm for both cermet anodes during the operations, indicating that the effect of sintering of Ni nano-particles on the performance was negligible. The reforming activity is still higher for Ni–CZO cermet anodes than Ni–CGO cermet anodes, which could be attributed to higher concentration of ex-solved nickel nano-particles as well as lower Ce4+/Ce3+ reduction energy of CZO than CGO support.
Keywords: SOFC; Catalyst deactivation; Ni–CZO cermet anodes; Nickel nano-particle sintering; Methane steam reforming activity
Direct synthesis of DME from syngas on hybrid CuZnAl/ZSM-5 catalysts: New insights into the role of zeolite acidity by Andrés García-Trenco; Agustín Martínez (pp. 170-179).
Display Omitted► MeOH dehydration on ZSM-5 is mostly driven by the density of strong Brønsted acid sites. ► EFAL-related strong Lewis acid sites also contribute to the zeolite dehydration activity. ► STD performance of hybrid CZA/ZSM-5 catalysts is influenced by the method of preparation. ► Mixing the pre-pelletized solids lead to the most efficient STD catalysts.A commercial HZSM-5 zeolite (Si/Al=16) was submitted to mild acid treatment and partial exchange of H+ by Na+ and Co2+ cations in order to produce samples with different amounts and strengths of Brønsted and Lewis acid sites. The acid properties of the zeolites were determined by both FTIR of adsorbed pyridine and NH3-TPD. Then, hybrid catalysts comprising a CuO/ZnO/Al2O3 (CZA) methanol synthesis catalyst and the original and treated zeolites were prepared in order to analyze the impact of the zeolite acidity in the efficiency of the hybrids for the direct syngas-to-DME process. Independent methanol dehydration experiments on the bare zeolites and syngas-to-DME runs under methanol dehydration-controlled conditions were performed using hybrids with low zeolite concentration (CZA:zeolite mass ratio of 10:1) prepared by mixing the pre-pelletized CZA and zeolite components. The results revealed that both strong Brønsted and EFAL-related strong Lewis acid sites are the likely zeolite active sites for methanol dehydration at the typical syngas-to-DME temperature of 260°C. Interestingly, we have found that different conclusions regarding the effect of zeolite acidity may be reached depending on the specific method used for preparing the hybrid catalysts when the overall syngas-to-DME process becomes controlled by the methanol synthesis rate on the Cu-based catalyst (i.e. using hybrids with a CZA:zeolite mass ratio of 2:1, that is, with an “excess” of acid sites). Thus, for hybrids prepared by mixing the pre-pelletized components, the same CO conversion and product selectivity (with values approaching those predicted by the thermodynamic equilibrium at the studied conditions) with no signs of deactivation during at least 50h on stream was attained irrespective of the zeolite acidity. By contrast, significant differences in catalyst stability were found for hybrids prepared by grinding the component powders prior to pelletizing. This fact points towards the occurrence of detrimental interactions between the CZA and zeolite components during the grinding preparation stage. The kind and extent of such detrimental interactions are tightly related to the properties (i.e. acidity, chemical composition) of the ZSM-5 zeolite.
Keywords: Synthesis gas; Direct DME synthesis; CuZnAl catalyst; ZSM-5; Zeolite acidity
Copper catalyzed oxidation of benzylic alcohols in water with H2O2 by Jahir Uddin Ahmad; Minna T. Räisänen; Markku Leskelä; Timo Repo (pp. 180-187).
.Display Omitted► Efficient Cu-catalyzed methods for alcohol oxidation with H2O2 were introduced. ► CuSO4 alone oxidizes selectively secondary alcohols in sole water. ► With a ligand modified catalyst, the oxidation is selective toward primary alcohols.A straightforward, efficient and sustainable copper catalyzed method was developed for oxidation of benzylic alcohols with 30% H2O2 in water. The reaction proceeded with CuSO4 catalyst (1mol%) at 100°C without additional base or ligand. Primary benzylic alcohols were converted almost quantitatively to aldehydes with 70–90% selectivity, corresponding acids being the major side products. Also secondary benzylic alcohols afforded the corresponding ketones in high conversion with selectivities greater than 90%. It was demonstrated that the CuSO4 catalyst can be recycled and reused at least for three runs, even though with some loss of catalytic activity. Selectivity of the CuSO4 based catalyst system could be further increased by using 2- N-( p-fluorophenyl)-pyrrolecarbaldimine (1) as a ligand in combination with TEMPO in K2CO3 solution. The catalyst system was individually optimized (1mol% CuSO4, 2mol%1, 0.1M K2CO3 and 5mol% TEMPO) for a wide range of benzylic and allylic alcohols, which were quantitatively and selectively converted into the corresponding aldehydes with 3eq. of H2O2 in 1h.
Keywords: Oxidation; Alcohols; Copper; Hydrogen peroxide; Water