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Applied Catalysis B, Environmental (v.71, #1-2)
Catalytic NO–H2–O2 reaction over Pt/Mg–Al–O prepared from PtCl62−- and Pt(NO2)42−-exchanged hydrotalcites by S. Hamada; K. Ikeue; M. Machida (pp. 1-6).
The catalytic NO–H2–O2 reaction at low temperatures (50–130°C) has been investigated over Pt-supported Mg–Al binary oxides, which were prepared from PtCl62− and Pt(NO2)42−–exchanged hydrotalcite(HT)-like compounds by heating at 600°C in H2. Although the NO x conversion of both catalysts was similarly high (>80%) at around 70°C, the Pt(NO2)42−–HT catalyst exhibited the higher selectivity to N2 (53% N2 and 47% N2O), compared to 12% N2 and 88% N2O for the PtCl62−–HT catalyst. The XANES/EXAFS spectroscopy showed that Pt prepared from PtCl62−–HT is partly oxidized due to the coordination of residual chlorides, whereas Pt(NO2)42−–HT yielded highly dispersed metallic Pt. Because of the presence of chloride strongly bound to Pt, the oxidative NO adsorption as NO2/NO3 was inhibited for PtCl62−–HT. The improved N2 selectivity with an increase of oxidative NO adsorption is in accord with the catalytic property of Na–Pt/ZSM-5 in our previous work [M. Machida, T. Watanabe, Appl. Catal. B: Environ. 52 (2004) 281.], suggesting that the N2 would be formed via NO2/NO3 intermediates.
Keywords: NO–H; 2; –O; 2; reaction; Platinum; Ion exchange; Hydrotalcite
Nanocrystalline Cu-Ce-Zr mixed oxide catalysts for water-gas shift: Carbon nanofibers as dispersing agent for the mixed oxide particles by Florian Huber; Zhixin Yu; John C. Walmsley; De Chen; Hilde J. Venvik; Anders Holmen (pp. 7-15).
Nanocomposite catalysts containing carbon nanofiber (CNF) and Cu-Ce-Zr mixed metal oxide (MMO) have been prepared by homogeneous co-precipitation with urea. The water-gas shift (WGS) reaction has been used as test reaction. The CNF-containing nanocomposite catalysts exhibit similar overall catalytic activity and stability as the corresponding CNF-free catalyst. Thirteen weight percent of the MMO could be replaced by CNF without decreasing the overall activity and stability of the catalyst. The specific activity of the nanocomposites based on the total metal oxide content is similar or higher than the activity of the CNF-free material, depending on the CNF content. Similar activation energies are, however, obtained for the CNF-free and CNF-containing materials. We cannot exclude that the CNF material acts as reaction promoter under certain conditions, but suggest that the impact of CNF addition on the precipitation of the mixed oxide particles, and hence the catalytic activity relative to the CNF-free MMO, should also be considered. CNF may be regarded as inert dispersing agent material improving the precipitation of the MMO under conditions where the co-precipitation of the MMO precursors does not result in materials with high surface area.
Keywords: Carbon nanofibers; Dispersing agent; Cu; Ce; Zr; Mixed metal oxides; Nanocomposites; Homogeneous co-precipitation; Water-gas shift
Hydrothermal stability of Fe-ZSM-5 and Fe-BEA prepared by wet ion-exchange for N2O decomposition by Johannis A.Z. Pieterse; Gerhard D. Pirngruber; Jeroen A. van Bokhoven; Saskia Booneveld (pp. 16-22).
The hydrothermal stability of WIE-based Fe-ZSM-5 and Fe-BEA for N2O decomposition in the presence of NO, H2O and O2 was studied at 723K. Catalysts were characterized with UV–vis, IR and Al-XANES. The N2O conversion remains at a constant level with Fe–H-BEA even in the presence of large amounts of H2O. Deactivation was, however, observed with Fe–H-ZSM-5 already in the presence of 0.5vol.% water. The analysis of deactivated samples indicated that steam-dealumination and clustering of iron occurred during the reaction with Fe-ZSM-5. Replacement of protons for sodium in Fe-ZSM-5 slowed down the rate of catalyst deactivation significantly. Steam-dealumination is likely to precede the clustering of iron in Fe–H-ZSM-5. The excellent hydrothermal stability of WIE-based Fe–H-BEA relates to the high initial degree of dealumination in the as-received BEA.
Keywords: Hydrothermal stability; Dealumination; Fe-ZSM-5; Fe-BEA; N; 2; O decomposition
High rates of NO and N2O reduction by CO, CO and hydrocarbon oxidation by O2 over nano crystalline Ce0.98Pd0.02O2− δ: Catalytic and kinetic studies by Sounak Roy; A. Marimuthu; M.S. Hegde; Giridhar Madras (pp. 23-31).
The catalyst Ce0.98Pd0.02O2− δ was synthesized by combustion synthesis method and characterized by XRD and XPS. The three way catalytic activity of this catalyst was investigated by performing NO+CO reaction and CO and hydrocarbon oxidation. The rates and the apparent activation energies of the reaction for NO reduction by CO and CO and hydrocarbon oxidation were determined and the rates were higher than the reported values. The N2 selectivity in NO+CO reaction was around 80% all over the temperature region and showed complete selectivity at high temperatures. A reaction mechanism of NO+CO reaction was proposed and the experimental findings were verified with the predicted model. The high rates of the NO+CO reactions even in the presence of oxygen and the complete selectivity to the products are rationalized by the high dissociative chemisorption of adsorbed NO over the catalyst, which is for the vacant sites in CeO2 lattice due to presence of Pd2+ in Ce4+ position. The catalyst also showed high rates and lower activation energies for the oxidation of CO and hydrocarbons.
Keywords: Three way catalyst; Hydrocarbon oxidation; CO; +; NO reaction; Kinetic models
Single step catalytic production of diisopropyl ether (DIPE) from acetone feedstock over nickel based catalysts by V. Chidambaram; B. Viswanathan (pp. 32-43).
Single step production of DIPE as oxygenates from acetone feed stock was evaluated by employing Ni–Cu and Ni–Cu–Cr supported on H-zeolite-β catalysts. The influence of experimental parameters like effect of amount of catalyst loading, hydrogen pressure, reduction temperature of the precursor, volume of acetone and temperature on DIPE production is studied. Ni–Cu (25wt.%) metal supported on H-zeolite-β catalyst shows higher activity. The dependence of the yield of DIPE on the other loadings has also been studied. The reduction temperature of the catalyst precursor is found to be less significant above 573K. A moderate reaction temperature in the range of 433–453K and hydrogen pressure (30–80bar) favor the higher yield of DIPE. Ni–Cu–Cr/H-zeolite-β is also found to be active for the production of DIPE from acetone.
Keywords: Diisopropyl ether; Isopropanol; H-zeolite-β; Bimetallic catalysts; Acetone feedstock
Fenton-like oxidation of Orange II solutions using heterogeneous catalysts based on saponite clay by J. Herney Ramirez; Carlos A. Costa; Luis M. Madeira; G. Mata; Miguel A. Vicente; M.L. Rojas-Cervantes; A.J. López-Peinado; R.M. Martín-Aranda (pp. 44-56).
In this work, the degradation and mineralization of Orange II solutions (0.1mM) using catalysts based on pillared saponite impregnated with several iron salts is reported. Oxidation is carried out in a batch reactor, in presence of various hydrogen peroxide concentrations, and in a wide range of temperature and pH values. Twelve samples are prepared, with three iron loads (7.5, 13.0 and 17.0wt.%) and four iron salts as precursors, namely Fe(II) acetate, Fe(II) oxalate, Fe(II) acetylacetonate and Fe(III) acetylacetonate. The samples are characterized using X-ray diffraction, thermal analysis, infrared spectroscopy, energy dispersive spectroscopy and adsorption of nitrogen at 77K. The catalytic results show that these solids present good properties for the degradation and mineralization of Orange II solutions, allowing to reach, in the best conditions and after 4h of oxidation, 99% of dye degradation with 91% of total organic carbon (TOC) reduction (at 70°C), using only ca. 90mg of clay catalyst per litre of solution. Nevertheless, 96% of dye removal with 82% of mineralization are also reached at 30°C. Besides, the amount of iron released into the final solution is lower than 1ppm, in the worst of the cases, and 0.09ppm in the best case.
Keywords: Orange II; Fenton's reagent; Oxidation; Clay-Fe catalysts; Heterogeneous catalysis
Characteristics in oxygen storage capacity of ceria–zirconia mixed oxides prepared by continuous hydrothermal synthesis in supercritical water by Jeong-Rang Kim; Wan-Jae Myeong; Son-Ki Ihm (pp. 57-63).
Continuous hydrothermal synthesis in supercritical water (supercritical synthesis) is a method to prepare metal oxide nanoparticles rapidly and continuously using supercritical water. Highly crystallized nanoparticles of homogeneous complex metal oxides as well as single metal oxides could be produced easily by the supercritical synthesis. Ceria–zirconia mixed oxide is widely used as oxygen storage material, for example, in the three-way catalysts for the clean up of automotive gases. Ceria–zirconia mixed oxides were prepared by the new supercritical synthesis method and also by the conventional co-precipitation method. The characteristics in oxygen storage capacity (OSC) of ceria–zirconia mixed oxide prepared by the supercritical synthesis were compared with those by the co-precipitation method. It was confirmed through physical characterizations with N2 adsorption, SEM, TPR and O2-uptake that the supercritical synthesis could lead to ceria–zirconia mixed oxides with higher thermal stability and better OSC due to its morphology.
Keywords: Ceria–zirconia mixed oxide; Co-precipitation; Hydrothermal synthesis; Supercritical water; Oxygen storage capacity (OSC); Thermal stability
Deactivation and reactivation of Pd/C catalyst used in repeated batch hydrodechlorination of PCE by Neil C. Concibido; Tetsuji Okuda; Wataru Nishijima; Mitsumasa Okada (pp. 64-69).
The deactivation of the palladium catalyst supported on activated carbon (Pd/C) was investigated in the repeated runs of the catalytic hydrodechlorination (HDC) of tetrachloroethylene (PCE) in pure MeOH and in 50/50 water–MeOH mixture with catalyst and solvent reuse at 20°C and atmospheric pressure. Faster PCE dechlorination rates and slightly slower catalyst deactivation were observed in the runs in the mixture than in those in pure MeOH. Washing by stirring in either water or MeOH could completely recover the initial activity of the catalyst repeatedly used in the mixture, but could only partially recover that of the catalyst repeatedly used in pure MeOH. These results clearly show the superiority of using a 50/50 water–MeOH mixture over pure MeOH as a solvent for the HDC of PCE.
Keywords: Pd/C; Catalyst reuse; 50/50 water–MeOH mixture; Catalytic activity; Deactivation; Reactivation
Support effect on methane combustion over palladium catalysts by Hisao Yoshida; Tomoyuki Nakajima; Yoshiteru Yazawa; Tadashi Hattori (pp. 70-79).
The support effect on the low temperature catalytic combustion of methane over palladium catalysts was studied by using a series of metal oxides as the support. The catalytic activity varied with the support, and support oxides with moderate acid strength gave maximum methane conversion. The oxidation state of palladium after the catalytic run, characterized by XRD and XAFS, also varied with the support, and it was higher on more basic supports. The relation between the catalytic activity and the oxidation state derived from these results did not agree with that obtained by changing oxygen partial pressure. The catalytic activity increased with oxygen partial pressure even up to that corresponding to 30 times as high as the stoichiometric ratio, indicating that the activity was higher at higher oxidation state. This agreed with lower activity of palladium supported on acidic support, but not with that on basic support. The lower activity of palladium supported on basic support in spite of higher oxidation state was attributed to excess stabilization of palladium oxide cluster anion such as (PdO) nδ− by electrophobic cation in a similar way to the formation of binary oxide from PdO and basic support at the boundary of them. Lower reactivity of oxidized form of palladium was confirmed by TPR by methane and TPD of oxygen, and the formation of binary oxide containing palladium and magnesium in Pd/MgO catalyst was confirmed by Pd K-edge XAFS study.
Keywords: Palladium catalyst; Methane combustion; Support effect
Effects of hydrogen and oxygenated hydrocarbons on the activity and SO2-tolerance of Ag/Al2O3 for selective reduction of NO by Ken-Ichi Shimizu; Masao Tsuzuki; Atsushi Satsuma (pp. 80-84).
De-NOx performance and SO2-tolerance of Ag/Al2O3 catalyst for selective catalytic reduction of NO by hydrocarbon (HC-SCR) and HC-SCR in the presence of H2 (H2-HC-SCR) were investigated using 10 types of reductant (Et2O, ETBE, EtOH, 1-propanol, 2-propanol, t-butanol, 1-propanal, ethyl acetate, acetone, C3H8). Among various reductant tested, Et2O was most effective for achieving high de-NOx activity for HC-SCR and H2-HC-SCR. For all the reductants, de-NOx activity at low temperature region was increased by H2 co-feeding. Degree of activity enhancement was higher for C3H8 than for oxygenates, which is consistent with our previous proposal that H2 enhances de-NOx activity by promoting the oxidative activation of alkane into partially oxidized hydrocarbon intermediates. Effects of reductants and H2 co-feeding on the SO2-tolerance were examined using Et2O, ETBE, and EtOH. The result showed that use of oxygenates as well as H2 co-feeding resulted in the higher SO2-tolerance.
Keywords: Nitrogen oxides; Silver alumina; Oxygenates; Sulfur oxide
Selective destruction of nitrogen-containing organic volatile compounds over Sb–V–O catalysts by M.O. Guerrero-Pérez; J. Janas; T. Machej; J. Haber; A.E. Lewandowska; J.L.G. Fierro; M.A. Bañares (pp. 85-93).
Mixed Sb–V oxide catalysts are evaluated in the total selective removal of nitrogen-containing organic volatile compounds. Two different synthesis methods and two different supports (alumina and niobia) are studied. The combination of characterization before and after reaction and activity data is used to provide information about the structure–activity/selectivity relationship in vanadium antimonate catalysts. Best results are obtained with alumina-supported catalysts since niobia support tends to interact with antimony forming inert structures. When the catalysts are prepared with antimony tartrate soluble complex, the formation of VSbO4 is favoured; at the same time, the formation of segregated antimony oxides is inhibited. V5+ active sites on the surface of catalysts reduce during the catalytic cycle to V3+ and are stabilized in the VSbO4 structure.
Keywords: Catalytic total oxidation; Nitrogen-containing organic compounds; Sb–V–O catalysts; Sb–V–Nb–O; In situ; Raman; XPS
The support effect in oxidizing atmosphere on propane combustion over platinum supported on TiO2, TiO2–SiO2 and TiO2–SiO2–WO3 by Motonobu Kobayashi; Atsushi Morita; Mitsuaki Ikeda (pp. 94-100).
The platinum catalyst supported on TiO2–SiO2–WO3, TiO2–SiO2 and TiO2 was studied with respect to the support effect in the oxidizing atmosphere on propane combustion. The catalysts and supports were characterized by using BET, XPS, IR, acidity measurement by the titration method and pulsed CO chemisorption. Although for the reduction-pretreated catalyst, the propane combustion activity is slightly changed with the support materials, for the oxidation-pretreated catalyst it significantly varies with the support materials and increases in the order of Pt/TiO22–SiO22–SiO2–WO3, indicating that the Pt/TiO2–SiO2–WO3 catalyst exhibits the most superior catalytic performance. In agreement with this order, the acidity at fairly strong acid strengths, particularly Brønsted acidity of the corresponding support is enhanced, thereby preventing platinum from the oxidation, as evidenced by the XPS result that the platinum on TiO2–SiO2–WO3, TiO2–SiO2 and TiO2 exists in metallic state, partially oxidized state and platinum oxide, respectively. These results suggest that the excellent propane combustion activity and good durability of the Pt/TiO2–SiO2–WO3 catalyst are attributed to the superior oxidation-resistance of platinum which is due to that the support has higher acidities at fairly strong acid strengths of −5.6≤ H0≤−3.0 containing Brønsted acidities rather than very strong acid strengths of H0≤−5.6.
Keywords: Acidity; TiO; 2; TiO; 2; –SiO; 2; TiO; 2; –SiO; 2; –WO; 3; Platinum catalyst; Propane combustion; Support effect; Oxidation-resistance
Heterogeneous photocatalysis of Cr(VI) in the presence of citric acid over TiO2 particles: Relevance of Cr(V)–citrate complexes by Jorge M. Meichtry; Marta Brusa; Gilles Mailhot; María A. Grela; Marta I. Litter (pp. 101-107).
TiO2-photocatalytic reduction experiments of Cr(VI) (0.8mM) under near UV (366nm) irradiation in the presence of citric acid (0≤[citric acid] (mM)≤40) were performed at pH 2 under air bubbling. Addition of citric acid facilitates Cr(VI) reduction, hindering the electron-shuttle mechanism taking place in pure water. TOC monotonously decreases until all Cr(VI) was reduced. The maximum rate of Cr(VI) reduction was attained for an initial citric acid/Cr(VI) molar ratio, R, equal to 1.25, a further increment in R being detrimental; however, Cr(VI) decay in the presence of citric acid was always faster than in its absence. Cr(VI) reduction takes place through Cr(V) species, readily complexed by citrate and detected by EPR spectroscopy. Quantitative EPR determinations indicate that an important fraction (nearly 15%) of the reduced Cr(VI) is transformed to Cr(V)–Cit, which also undergoes a photocatalytic transformation. The detrimental effect taking place at high conversions for R>1.25 can be ascribed to secondary steps, i.e., the competition between Cr(VI) and Cr(V) complexes for conduction band electrons or to the competition of Cr(V)–Cit and Cit for holes.
Keywords: Heterogeneous photocatalysis; TiO; 2; Cr(VI); Cr(V); Citric acid
Removal of dibenzothiophene from simulated petroleum by integrated γ-irradiation and Zr/alumina catalyst by Zan Qu; Naiqiang Yan; Jinping Jia; Dan Wu (pp. 108-115).
Catalysts that can enhance the radiolytic decomposition of dibenzothiophene (DBT) in the simulated petroleum were identified. Among the tested catalysts, zirconium oxide impregnated on alumina (Zr/Al2O3) showed the highest catalytic activity in the presence of γ-rays irradiation. The preparation condition of the catalyst was optimized. The main factors that affected the conversion efficiency of DBT were studied. The results showed that in the presence of Zr/Al2O3 catalyst when the applied radiation dose was 179kGy, the removal efficiency of DBT was 98.9%, an increase of over 80% compared to that without catalyst. The removal efficiency was higher with the lower dose rate at the same irradiation dose. The effect of γ-rays irradiation upon the structure of the catalyst was investigated by XRD, XPS and SEM techniques. The catalyst appeared to be stable under the γ-rays irradiation except the surface coverage by the oxidized organic compound. In addition, the possible mechanism for the synergistic effect of γ-rays irradiation and catalyst was proposed.
Keywords: Dibenzothiophene; Petroleum; γ-Irradiation; Zr/Al; 2; O; 3; catalyst