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Applied Catalysis B, Environmental (v.75, #3-4)
Industrial H2-SCR of NO on a novel Pt/MgO–CeO2 catalyst by Costas N. Costa; Petros G. Savva; José Luis G. Fierro; Angelos M. Efstathiou (pp. 147-156).
We describe here the performance of a novel MgO–CeO2-supported Pt (0.1wt%) catalyst towards the selective conversion of NO into N2 ( SN2>80%) by using H2 (H2-SCR) under process conditions similar to those encountered in the NH3-SCR in the low-temperature range of 150–200°C. At 200°C, 100% conversion of NO and 85% N2-selectivity were obtained with a feed stream containing 1000ppm NO, 5% O2, 5% H2O, 10% CO2, 0–0.5% CO, and using 1.5% H2 in the feed as reducing agent (GHSV=40,000h−1). Thus, a N2-yield of 85% similar to that obtained in most NH3-SCR applications could make H2-SCR as the most environmentally friendly NO x control catalytic technology with great potential to replace the existing NH3-SCR technology. The latter is currently used industrially mainly in power and nitric acid plants, gas turbines, furnaces, boilers, and waste incinerators for the elimination of NO x. However, this technology faces several problems such as catalyst deterioration, emissions of non-reacted toxic NH3 (ammonia slip), ash odor, air-heaters fouling, and a high running cost.
Keywords: H; 2; -SCR; NO reduction; Lean de-NO; x; Supported-Pt catalyst
Studies of the activation process over Pd perovskite-type oxides used for catalytic oxidation of toluene by J.-M. Giraudon; A. Elhachimi; F. Wyrwalski; S. Siffert; A. Aboukaïs; J.-F. Lamonier; G. Leclercq (pp. 157-166).
Calcined and reduced catalysts Pd/LaBO3 (B=Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T50 values (temperature at which 50% of toluene is converted): Pd/LaFeO3>Pd/LaMnO3+ δ>Pd/LaCoO3>Pd/LaNiO3. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H2-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO3 (B=Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200°C for Pd/LaFeO3 and either 200 or 250°C for LaCoO3. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200°C for 2h (2L/h, 1°C/min). As LaFeO3 was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B3+ (B=Mn) or B2+ even to B0 (B=Co, Ni). In the reactive stream (0.1% toluene in air), Pd0 reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd2+/Pd4+ and Pd0/Pd2+/Pd4+ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co3+ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO3 for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity.
Keywords: Palladium; Perovskite; XPS; Catalytic oxidation
Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst by Li Xue; Changbin Zhang; Hong He; Yasutake Teraoka (pp. 167-174).
A series of CeO2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N2O). Addition of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCe0.05 catalyst below 400°C even in the presence of O2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H2-TPR and O2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO2 could increase the surface area of Co3O4, and then improve the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO2, are responsible for the enhancement of catalytic activity of Co3O4.
Keywords: N; 2; O decomposition; Co; 3; O; 4; CeO; 2; Mixed metal oxide; TPR; TPD
Cooperative effect induced by the mixing of Na-ZSM-5 and Pd/H3PW12O40/SiO2 in the selective catalytic reduction of NO with aromatic hydrocarbons by Ryosuke Yoshimoto; Takashi Ninomiya; Kazu Okumura; Miki Niwa (pp. 175-181).
Pd was loaded on the dispersed H3PW12O40 (HPW) over the SiO2 surface, and the catalyst was applied to the selective reduction of NO with aromatic hydrocarbons. The catalyst exhibited high activity in the NO reduction when branched aromatic hydrocarbons, such as toluene and xylene, were used as reductants. The catalytic activity of Pd/HPW/SiO2 was improved remarkably by physically mixing it with Na-ZSM-5. From the temperature programmed desorption (TPD) of toluene and the analysis of the products, it was inferred that the activity was enhanced when Pd/HPW/SiO2 and Na-ZSM-5 were mixed. In other words, aromatic hydrocarbons were partially oxidized to yield oxygenated hydrocarbons, e.g., benzaldehyde and phthalic anhydride, over Pd/Na-ZSM-5; in this reaction, a part of Pd migrated from Pd/HPW/SiO2 to Na-ZSM-5 during the course of the physical mixing procedure. Subsequently, the oxygenated hydrocarbons reacted with NO entrapped with HPW over Pd to yield N2.
Keywords: Selective catalytic reduction of NO; SCR; Heteropoly acid; Palladium; Toluene
Combined CO/CH4 oxidation tests over Pd/Co3O4 monolithic catalyst: Effects of high reaction temperature and SO2 exposure on the deactivation process by L.F. Liotta; G. Di Carlo; G. Pantaleo; A.M. Venezia; G. Deganello; E. Merlone Borla; M. Pidria (pp. 182-188).
CO and CH4 combined oxidation tests were performed over a Pd (70g/ft3)/Co3O4 monolithic catalyst in conditions of GHSV=100,000h−1 and feed composition close to that of emission from bi-fuel vehicles. The effect of SO2 (5ppm) on CO and CH4 oxidation activity under lean condition ( λ=2) was investigated. The presence of sulphur strongly deactivated the catalyst towards methane oxidation, while the poisoning effect was less drastic in the oxidation of CO. Saturation of the Pd/Co3O4 catalytic sites via chemisorbed SO3 and/or sulphates occurred upon exposure to SO2. A treatment of regeneration to remove sulphate species was attempted by performing a heating/cooling cycle up to 900°C in oxidizing atmosphere. Decomposition of PdO and Co3O4 phases at high temperature, above 750°C, was observed. Moreover, sintering of Pd0 and PdO particles along with of CoO crystallites takes place.
Keywords: Pd/Co; 3; O; 4; monolith; CO and CH; 4; oxidation; PdO and Co; 3; O; 4; thermal stability; SO; 2; poisoning
Potential rare earth modified CeO2 catalysts for soot oxidation by K. Krishna; A. Bueno-López; M. Makkee; J.A. Moulijn (pp. 189-200).
Ceria (CeO2) and rare-earth modified ceria (CeReO x with Re=La, Pr, Sm, Y) catalysts are prepared by nitrate precursor calcination and are characterised by BET surface area, XRD, H2-TPR, and Raman spectroscopy. Potential of the catalysts in the soot oxidation is evaluated in TGA with a feed gas containing O2. Seven hundred degree Celsius calcination leads to a decrease in the surface area of the rare-earth modified CeO2 compared with CeO2. However, an increase in the meso/macro pore volume, an important parameter for the soot oxidation with O2, is observed. Rare-earth ion doping led to the stabilisation of the CeO2 surface area when calcined at 1000°C. XRD, H2-TPR, and Raman characterisation show a solid solution formation in most of the mixed oxide catalysts. Surface segregation of dopant and even separate phases, in CeSmO x and CeYO x catalysts, are, however, observed. CePrO x and CeLaO x catalysts show superior soot oxidation activity (100% soot oxidation below 550°C) compared with CeSmO x, CeYO x, and CeO2. The improved soot oxidation activity of rare-earth doped CeO2 catalysts with O2 can be correlated with the increased meso/micro pore volume and stabilisation of external surface area. The segregation of the phases and the enrichment of the catalyst surface with unreducible dopant decrease the intrinsic soot oxidation activity of the potential CeO2 catalytic sites. Doping CeO2 with a reducible ion such as Pr4+/3+ shows an increase in the soot oxidation. However, the ease of catalyst reduction and the bulk oxygen-storage capacity is not a critical parameter in the determination of the soot oxidation activity. During the soot oxidation with O2, the function of the catalyst is to increase the ‘active oxygen’ transfer to the soot surface, but it does not change the rate-determining step, as evident from the unchanged apparent activation energy (around 150kJmol−1), for the catalysed and un-catalysed soot oxidation. Spill over of oxygen on the soot surface and its subsequent adsorption at the active carbon sites is an important intermediate step in the soot oxidation mechanism.
Keywords: Diesel soot; Oxidation; Rare earth oxide; Mixed oxides
Potential rare-earth modified CeO2 catalysts for soot oxidation part II: Characterisation and catalytic activity with NO+O2 by K. Krishna; A. Bueno-López; M. Makkee; J.A. Moulijn (pp. 201-209).
Ceria (CeO2) and rare-earth modified ceria (CeReO x with Re=La3+, Pr3+/4+, Sm3+, Y3+) supports and Pt impregnated supports are studied for the soot oxidation under a loose contact with the catalyst with the feed gas, containing NO+O2. The catalysts are characterised by XRD, H2-TPR, DRIFT and Raman spectroscopy. Among the single component oxides, CeO2 is significantly more active compared with the other lanthanide oxides used in this study. Doping CeO2 with Pr3+/4+ and La3+ improved, however, the soot oxidation activity of the resulting solid solutions. This improvement is correlated with the surface area in the case of CeLaO x and to the surface area and redox properties of CePrO x catalyst. The NO conversion to NO2 over these catalysts is responsible for the soot oxidation activity. If the activity per unit surface area is compared CePrO x is the most active one. This indicates that though La3+ can stabilise the surface area of the catalyst in fact it decreases the soot oxidation activity of Ce4+. The lattice oxygen participates in NO conversion to NO2 and the rate of this lattice oxygen transfer is much faster on CePrO x. In general, the improvement of the soot oxidation is observed over the Pt impregnated CeO2 and CeReO x catalysts, and can be correlated to the presence of Pt°. The surface reduction of the supports in the presence of Pt occurred below 100°C. The surface redox properties of the support in the Pt catalysts do not have a significant role in the NO to NO2 conversion. In spite of the lower surface area, the Pt/CeYO x and Pt/CeO2 catalysts are found to be more active due to larger Pt crystal sizes. The presence of Pt also improved the CO conversion to CO2 over these catalysts. The activation energy for the soot oxidation with NO+O2 is found to be around 50kJ/mol.
Keywords: Catalytic diesel soot; Oxidation; Mixed oxides; Rare-earth oxide; O; 2; NO; NO; 2
Potential rare-earth modified CeO2 catalysts for soot oxidation by K. Krishna; A. Bueno-López; M. Makkee; J.A. Moulijn (pp. 210-220).
CeO2 and CeReO x_ y catalysts are prepared by the calcination at different temperatures ( y=500–1000°C) and having a different composition (Re=La3+ or Pr3+/4+, 0–90wt.%). The catalysts are characterised by XRD, H2-TPR, Raman, and BET surface area. The soot oxidation is studied with O2 and NO+O2 in the tight and loose contact conditions, respectively. CeO2 sinters between 800–900°C due to a grain growth, leading to an increased crystallite size and a decreased BET surface area. La3+ or Pr3+/4+ hinders the grain growth of CeO2 and, thereby, improving the surface catalytic properties. Using O2 as an oxidant, an improved soot oxidation is observed over CeLaO x_ y and CePrO x_ y in the whole dopant weight loading and calcination temperature range studied, compared with CeO2. Using NO+O2, the soot conversion decreased over CeLaO x_ y catalysts calcined below 800°C compared with the soot oxidation over CeO2_ y. CePrO x_ y, on the other hand, showed a superior soot oxidation activity in the whole composition and calcination temperature range using NO+O2. The improvement in the soot oxidation activity over the various catalysts with O2 can be explained based on an improvement in the external surface area. The superior soot oxidation activity of CePrO x_ y with NO+O2 is explained by the changes in the redox properties of the catalyst as well as surface area. CePrO x_ y, having 50wt.% of dopant, is found to be the best catalyst due to synergism between cerium and praseodymium compared to pure components. NO into NO2 oxidation activity, that determines soot oxidation activity, is improved over all CePrO x catalysts.
Keywords: Catalytic diesel soot oxidation; Rare earth oxide; Mixed oxides; O; 2; NO; 2
The catalytic activity and methanol tolerance of transition metal modified-ruthenium–selenium catalysts by H. Cheng; W. Yuan; K. Scott; D.J. Browning; J.B. Lakeman (pp. 221-228).
The activity of ruthenium-based catalysts towards oxygen reduction was enhanced by addition of tungsten, molybdenum and rhodium. The catalysts were produced by decarbonylation of the ruthenium and transition metal carbonyls in the presence of selenium (sulphur) and carbon powders. The produced materials were characterised by scanning electron microscopy and energy dispersive spectroscopy as well as by electrochemical evaluations in both half cells and direct methanol fuel cells. All transition metal-modified catalysts exhibited better performance than those of ruthenium–selenium (sulphur) alone, but the tungsten modification seemed the best approach. The RuSe0.20W0.29 catalyst delivered the maximum power density of up to 40mWcm−2. The improvement is a consequence of the enhanced activity towards oxygen reduction with a minor loss in methanol tolerance as well as a stabilising effect of tungsten on catalysts. The new catalysts were compared to Pt and to sulphur-containing catalysts.
Keywords: Direct methanol fuel cells; Oxygen reduction; Methanol tolerant cathode catalysts; Ruthenium–selenium–tungsten; Ruthenium–selenium–molybdenum; Ruthenium–selenium–rhodium
Degradation of neonicotinoid insecticides by different advanced oxidation processes and studying the effect of ozone on TiO2 photocatalysis by Urh Černigoj; Urška Lavrenčič Štangar; Polonca Trebše (pp. 229-238).
Although some studies concerning the effect of pH and ozone dosage on TiO2 photocatalysis (O2/TiO2/UV) have already been published, no complete investigation and explanation of the effects of both parameters on photocatalytic ozonation (O3/TiO2/UV) have been carried out. Aqueous solutions of neonicotinoid insecticides (thiacloprid and imidacloprid) were chosen as a degradation medium, since they exhibit a high threat for aquatic systems and it is of great importance to find an effective method for their elimination from the environment. In preliminary stability tests, thiacloprid showed higher photo- and chemical stability compared to imidacloprid, therefore its degradation was studied in detail. To assess the suitability of various treatments for degradation and mineralization of thiacloprid in water at different pH values and ozone dosages, we applied ozonation (O3) and three different photochemical advanced oxidation processes, namely ozonation, coupled with UV radiation (O3/UV), O3/TiO2/UV and O2/TiO2/UV. Light source emitting mainly in UVA range was applied in all three processes. The photocatalytic ozonation (O3/TiO2/UV) was found to be the most efficient process irrespective of pH. The synergistic effect of ozone and TiO2 photocatalysis was noticed at acidic and neutral pH, but the synergism was lost at basic pH, probably due to faster self-decompositon of ozone under alkaline conditions. At acidic pH, also the oxidation of chloride anions to chlorate(V) was noticed in O3/TiO2/UV and in O3/UV processes. By plotting the disappearance rate constants of thiacloprid degradation in O3/TiO2/UV and O3/UV systems as a function of the flow rate of ozone, the synergistic effect of ozone was undoubtedly proven. The slope of the linear fit in case of O3/TiO2/UV process was considerably steeper than in case of O3/UV, which would not happen in absence of synergistic effect. The linearity in O3/TiO2/UV system was lost only at very high flow rates of ozone.
Keywords: Abbreviations; AOP; advanced oxidation process; k; reaction rate constant; IC; ionic chromatography; O; 2; /UV; UV irradiation of oxygenated solutions in the absence of catalyst; O; 3; ozonation; O; 3; /UV; ozonation, coupled with UV radiation; O; 2; /TiO; 2; /UV; photocatalysis; O; 3; /TiO; 2; /UV; photocatalytic ozonation; t; 1/2; half-life of the organic molecule; TN; total nitrogen; TOC; total organic carbonDegradation; Ozonation; TiO; 2; photocatalysis; Neonicotinoid insecticides; Chlorate(V)
Effect of Co content on the catalytic activity of CoSiBEA zeolite in the selective catalytic reduction of NO with ethanol: Nature of the cobalt species by Janusz Janas; Tadeusz Machej; Jacek Gurgul; Robert P. Socha; Michel Che; Stanislaw Dzwigaj (pp. 239-248).
The effect of Co content on the catalytic activity of CoSiBEA zeolites in the selective catalytic reduction (SCR) of NO with ethanol is investigated. The Co xSiBEA zeolites ( x=0.3, 0.7, 3.6 and 6.75Cowt.%) are prepared by a two-step postsynthesis method which allows to control the introduction of cobalt into zeolite and thus to obtain catalysts with specific Co sites. The nature of the active sites is characterized by XRD, diffuse reflectance UV–vis, H2-TPR and XPS.The catalytic activity of Co xSiBEA strongly depends on the nature and environment of Co species. Zeolites with isolated lattice tetrahedral Co(II) (Co0.3SiBEA and Co0.7SiBEA samples) are active in SCR of NO with ethanol with selectivity toward N2 exceeding 85% for NO conversion from 20 to 70%. When additional isolated extra-lattice octahedral Co(II) species appear (Co3.6SiBEA sample), the full oxidation of ethanol by dioxygen becomes a very important reaction pathway. In presence of additional cobalt oxides (Co6.75SiBEA sample), the activity and selectivity toward N2 substantially change and full oxidation of ethanol to CO2 is the main reaction pathway and full NO oxidation also takes place in the temperature range 550–775K. The lack of correlation between the activity in SCR of NO with ethanol and NO oxidation to NO2 suggests that the two reactions are more competitive than sequential.
Keywords: SiBEA; Cobalt; SCR of NO; Ethanol; DR UV–vis; TPR; XPS
Volatile organic compounds (VOCs) removal over dual functional adsorbent/catalyst system by M. Guillemot; J. Mijoin; S. Mignard; P. Magnoux (pp. 249-255).
This study is focused on the elimination of tetrachloroethylene (PCE) and methylethylketone (MEK) by adsorption/catalytic oxidation in humid conditions using zeolites as adsorbent and catalyst. Adsorption experiments have led to the conclusion that HFAU(17) zeolite was a very efficient adsorbent for the removal of PCE and MEK. Furthermore, complete transformation of PCE into CO2 and HCl was achieved at 500°C over 1.2%Pt/HFAU(5). MEK was completely converted into CO2 at 220°C over 1%Pt/NaX, without formation of CO. Formation of coke occurs during MEK oxidation reaction, especially over acid catalyst, and at low reaction temperature. Furthermore, it was pointed out that water has a negative effect on MEK conversion. Lastly, adsorption/catalytic oxidation of PCE and MEK was performed over a dual functional HFAU(17)-Pt/FAU adsorbent/catalyst system. The adsorption step was performed at 30°C with an HFAU(17) adsorbent, and the oxidation step was carried out at 450°C for PCE with 1.2%PtHFAU(5), and at 250°C for MEK transformation with 1%PtNaX. It appeared that the adsorbent-catalyst couple remains efficient for MEK transformation during successive adsorption/oxidation cycles.
Keywords: VOC; Zeolite; Adsorption; Catalytic oxidation; MEK; PCE
Fe3+/Fe2+ cycling promoted by Ta3N5 under visible irradiation in Fenton degradation of organic pollutants by Yifeng Wang; Wanhong Ma; Chuncheng Chen; Xuefeng Hu; Jincai Zhao; Jimmy C. Yu (pp. 256-263).
Ta3N5 was synthesized by nitridation of Ta2O5 under NH3 flow at 700°C. The catalyst was pure Ta3N5 according to X-ray diffraction (XRD), and was about 5nm in size with a BET specific surface area 52.8m2/g. When Ta3N5 was added to Fe3+/H2O2 solution (known as Fenton-like system), most Fe3+ were adsorbed on the Ta3N5 surface and could not react with H2O2 in the dark, which is different from the general Fenton reaction. Under visible light irradiation, adsorbed Fe3+ ions were reduced to Fe2+ rapidly and Fe2+ were reoxidized by H2O2 on the Ta3N5 surface, thus a fast Fe3+/Fe2+ cycling was established. Kinetics and ESR measurements supported this mechanism. The Ta3N5/Fe3+/H2O2 system could efficiently decompose H2O2 to generate hydroxyl radicals driven by visible light, which could accelerate significantly the degradation of organic molecules such as N, N-dimethylaniline (DMA), and 2,4-dichlorophenol (DCP). A mechanism was proposed for iron cycling on the basis of experimental results.
Keywords: Tantalum nitride; Iron cycling; Photocatalyst; Degradation; Photo-Fenton reaction
Reactor design limitations for the steam reforming of methanol by Hyung Chul Yoon; Jonathan Otero; Paul A. Erickson (pp. 264-271).
In this paper the limiting mechanisms in the methanol-steam reformation process are analyzed theoretically and compared experimentally as to determine each contribution and limitation to the overall process. Experimental data from steam reformers are presented and analyzed. Models of each mechanism are provided to quantify theoretical times necessary for each process to occur. While the models in this paper are not precise representations of all steam reforming processes, the models do provide enough evidence to conclude that heat transfer is the dominant limiting mechanism in methanol-steam reformation. Further studies quantifying the experimental effects of heat transfer should be pursued with the ultimate goal of properly sizing steam reformers.
Keywords: Steam reformer; Hydrogen; Limiting mechanisms
The adsorption and catalytic transformations of chromium on Mn substituted goethite by Wen-Ching Wu; Shan-Li Wang; Yu-Min Tzou; Jen-Hshuan Chen; Ming-Kuang Wang (pp. 272-280).
Goethite widely occurs in the environment and its role in photoreduction of toxic Cr(VI) to less toxic Cr(III) has been previously reported in the literature. However, natural goethite is rarely stoichiometric and usually contains certain substitutional cations, such as Mn(III) or Mn(IV), which, on the other hand, is an oxidant for Cr(III). In order to provide more insight into the fate of Cr(VI) in the environment, the influence of Mn-substitution in goethite on its Cr(VI) photoreduction capability needs to be clarified. The objectives of this study were to evaluate the adsorption and photo-transformations of Cr on Mn-substituted goethite with Mn/(Mn+Fe) molar ratios ranging from 0 to 0.1. The results showed that Cr adsorption and photo-catalytic transformation on goethite were strongly influenced by the Mn content of goethite. When the system was under illumination, Cr(VI) reduction was decreased with increasing Mn-substitution in goethite. The re-oxidation of photo-reduced product, i.e., Cr(III), at the Mn sites on the surface of goethite is responsible for the lower Cr(VI) photo-reduction capacity of Mn-substituted goethite. The role of goethite in the reduction of Cr(VI) may be overestimated unless its Mn-substituted counterparts are considered. The effectiveness of Mn sites in goethite to increase toxic Cr(VI) has important implications in determining the fate and threat of Cr(VI) contamination.
Keywords: Chromium; Mn-substituted goethite; Oxidation reaction; Photo-reduction reaction
Oxidative degradation properties of Co-based catalysts in the presence of ozone by M. Gruttadauria; L.F. Liotta; G. Di Carlo; G. Pantaleo; G. Deganello; P. Lo Meo; C. Aprile; R. Noto (pp. 281-289).
Four series of cobalt-based catalysts, such as bare Co3O4 and CoO, CoO x–CeO2 mixed oxides, CoO x supported over alumina and alumina–baria and CoMgAl and CoNiAl hydrotalcites have been synthesized and investigated for the oxidative degradation of phenol in the presence of ozone. Characterizations were obtained by several techniques in order to investigate the nature of cobalt species and their morphological properties, depending on the system. Analyses by XRD, BET, TPR, UV–visible diffuse reflectance spectroscopy and TG/DT were performed.The CoNiAl hydrotalcite exhibits, after 4h of reaction, the highest phenol ozonation activity followed by Co(3wt%)/Al2O3–BaO and CoMgAl. The samples Co(1wt%)/Al2O3–BaO and Co(1 and 3wt%)/Al2O3 show a comparable medium activity, while the oxidation properties of bare oxides Co3O4, CoO and CoO x–CeO2 are really low. Leaching of cobalt ions in the water solution was detected during the reaction, the amount varied depending on the nature of catalysts. A massive release was observed for the CoMgAl and CoNiAl hydrotalcites, while cobalt catalysts over alumina and alumina–baria look much more stable. The recycle of CoO x/Al2O3 and CoO x/Al2O3–BaO was studied by performing three consecutive cycles in the phenol oxidation. Because of the potential interest of the cobalt-supported catalysts in the ozonation process, the oxidative degradation of naphtol blue black was also investigated.On the basis of TPR and UV–visible results it appears that highly dispersed Co2+ ions especially present over Co(3wt%)/Al2O3–BaO are the main active sites for phenol and naphtol blue black oxidative degradation by ozone.
Keywords: Oxidative degradation by ozone; Phenol; Naphtol blue black; CoO; x; /Al; 2; O; 3; –BaO; Hydrotalcites
Full phenol peroxide oxidation over Fe-MMM-2 catalysts with enhanced hydrothermal stability by Maria N. Timofeeva; Maxim S. Mel’gunov; Oxana A. Kholdeeva; Mikhail E. Malyshev; Aleksander N. Shmakov; Vladimir B. Fenelonov (pp. 290-297).
Iron-containing mesoporous mesophase materials Fe-MMM-2 have been synthesized by a sol–mesophase route under mild acidic conditions and characterized by DRS-UV–vis, XRD, and N2 adsorption measurements. It was found that pH of the synthesis solution and iron content in the samples affect both the textural characteristics and the state of iron atoms. Isolated iron species predominate in silica framework under Fe<2wt% and pH∼1.0 or Fe∼1wt% and pH<2.0. These species are stable to leaching and highly active in full H2O2-based phenol oxidation. The increase in iron loading and pH of the synthesis solution lead to the agglomeration and formation of oligomeric iron species, which, in turn, results in the reduction of the catalytic activity of Fe-MMM-2 and the increase of iron leaching.
Keywords: Iron-containing mesoporous mesophase materials; Full phenol oxidation; Hydrogen peroxide
Evidence for the formation, isomerization and decomposition of organo-nitrite and -nitro species during the NO x reduction by C3H6 on Ag/Al2O3 by Yunbo Yu; Xiuli Zhang; Hong He (pp. 298-302).
The formation of organo-nitrite and -nitro species (R-ONO and R-NO2) as intermediates during the selective catalytic reduction (SCR) of NO x by C3H6 over Ag/Al2O3 was investigated by temperature-programmed desorption (TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The addition of KBr to Ag/Al2O3 catalyses the isomerization of R-NO2 to R-ONO on KBr-Ag/Al2O3, which confirms the presence of R-NO2 on Ag/Al2O3.
Keywords: R-NO; 2; R-ONO; TPD; DRIFTS; KBr dilution
An IR study of thermally stable V2O5-WO3 -TiO2 SCR catalysts modified with silica and rare-earths (Ce, Tb, Er) by Maria Angeles Larrubia Vargas; Marzia Casanova; Alessandro Trovarelli; Guido Busca (pp. 303-311).
The catalytic activity of silica-free and silica-modified rare earth (Ce, Tb, Er) containing V2O5-WO3 -TiO2 catalysts in the selective catalytic reduction of NO by ammonia has been investigated as a function of ageing temperatures. The adsorption of ammonia on the catalysts and the behavior of their surface hydroxy groups and of bulk vibrations has also been studied by IR spectroscopy. Rare earths slightly decrease the catalytic activity of catalysts in a fresh state, and this has been attributed to the perturbation, observed by IR, of the vanadyl groups with a likely lowering of their Lewis acidity. However, rare earths (in particular Tb and Er) increase strongly the catalytic activity of catalysts after ageing. Silica only does not seem to have a positive effect on thermal stability and activity when vanadium is present. It has been concluded that rare earths strongly increase the thermal resistance of the catalysts and inhibit rutilization and surface area loss because they do not penetrate the anatase bulk while tend to cover the external surface. In addition the negative action of free vanadium on phase stability is decreased due to formation of rare earth vanadates.
Keywords: SCR; NO reduction; Ammonia SCR; Ammonia adsorption; Infrared spectroscopy; Vanadiatungsta-titania catalysts; Rare earths
Azo-dye Orange II degradation by heterogeneous Fenton-like reaction using carbon-Fe catalysts by J.H. Ramirez; F.J. Maldonado-Hódar; A.F. Pérez-Cadenas; C. Moreno-Castilla; C.A. Costa; L.M. Madeira (pp. 312-323).
In this work, the degradation and mineralization of the non-biodegradable azo dye Orange II (OII) was studied, making use of a heterogeneous Fenton-like oxidation process. For that, hydrogen peroxide activation was achieved by means of two different carbon-based catalysts, which have been impregnated with 7wt% of iron. The carbon supports employed are quite different, one of them being an activated carbon prepared from agricultural by-products (olive stone), while the other one is a carbon aerogel, prepared by carbonization of an organic resorcinol–formaldehyde polymer. The solids have been characterized using several techniques, namely N2 and CO2 adsorption at −196 and 0°C, respectively, mercury porosimetry, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Then, the catalyst's performance in the Fenton-like oxidation of OII was compared, and the effects of the most relevant operating conditions (pH, catalyst concentration, H2O2 concentration and temperature) analyzed for the most promising one (the carbon aerogel based catalyst). In this catalyst, characterization data point for a very good iron dispersion on the carbon surface. This sample showed very good catalytic performances, with mineralization degrees as high as 90%. However, iron leaching from the support is also considerable leading to a progressive deactivation in consecutive reaction cycles.
Keywords: Fenton-like; Oxidation; H; 2; O; 2; Orange II; Carbon-Fe catalysts