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Applied Catalysis B, Environmental (v.58, #1-2)
Preparation of beta-coated cordierite honeycomb monoliths by in situ synthesis by A. Bueno-López; D. Lozano-Castelló; I. Such-Basáñez; J.M. García-Cortés; M.J. Illán-Gómez; C. Salinas-Martínez de Lecea (pp. 1-7).
In this paper, a method for the preparation of beta-coated cordierite honeycomb monoliths suitable as Pt supports for deNO x application is described. The main advantage of this in situ process is the elimination of the need for a binder. The presence of beta zeolite on the supports was confirmed by XRD and SEM. SEM characterisation clearly showed that zeolite grows both into the cordierite macroporous structure and on the surface of the monolith channels. The formation of a compact zeolite network may be the reason of the strong anchorage of zeolite to the cordierite support. Maximum thickness of the zeolite-coating layer is 10μm and coating is stable up to 600°C in air. Single- and two-step syntheses have been performed in order to increase zeolite loading. Single-step syntheses yielded monolith samples with average size of beta crystallites ca. 0.5μm and BET surface areas that present a linear relationship with zeolite loading. Samples prepared in a two-step synthetic procedure had an average crystal size of 1μm and present diffusion limitations in N2 adsorption measurements.NO x conversion of 70% with 0.5wt.% Pt-beta-coated monolith has been reached at 210°C under a simulated diesel exhaust (5600h−1) containing 1000ppm NO x, 1500ppm C3H6 and 5% O2 in He. This value is similar to the previously observed for Pt-beta powder catalysts.
Keywords: Beta zeolite; Cordierite monolith; Coating; Structured catalyst; Thermal stability; deNO; x
Interaction of adsorption and catalytic reactions in water decontamination processes by Anett Georgi; Frank-Dieter Kopinke (pp. 9-18).
This series of papers addresses the role of sorption in heterogeneous catalysis aimed at the removal of organic contaminants (OCs) from water. This first part is focused on the oxidative treatment of OCs by H2O2 catalyzed by activated carbon (AC). The relative reaction rates of compounds with different hydrophobicities and therefore different sorption tendencies on AC (methyl tert-butyl ether, trichloroethene, 2,4,5-trichlorophenol) in the AC/H2O2 system differed drastically from those observed in a classical homogeneous Fenton system. Quantitative considerations that take into account the ratio of the reaction rate constants of MTBE and TCE in the AC/H2O2 system and the homogeneous Fenton system as well as the ratio of their freely dissolved fractions lead to the conclusion that the predominant pathway for the degradation reaction in the AC/H2O2 system is the attack of OH radicals on the OC fraction that is freely dissolved in the pore volume of the AC. In contrast, the sorbed fraction is nearly unreactive, i.e. protected against radical attack. Quenching experiments with methanol, a strong competitor for reactions with OH radicals in the solution phase, further confirmed this hypothesis. Consequently, sorption on AC has an adverse effect on the oxidation of OCs via OH radicals, even though the radicals are formed directly on the AC surface, i.e. in close proximity to the sorbed OCs.
Keywords: Hydrogen peroxide; Activated carbon; Heterogeneous catalysis; Oxidation; Adsorption; Water treatment
Low temperature selective catalytic reduction of NO x by ammonia over H-ZSM-5: an IR study by Vicente Sanchez-Escribano; Tania Montanari; Guido Busca (pp. 19-23).
The IR study of the interaction of NO2 with ammonia-covered H-ZSM-5 zeolite shows a very fast reaction at room temperature between NO2 and adsorbed ammonium ions. An adsorbed NO2 species is also formed. In the presence of NO+NO2 mixture ammonium ions are completely rapidly decomposed at 300–373K. These data suggest some speculations on the mechanism of the reduction of NO x by ammonia on H-ZSM-5 catalysts.
Keywords: Catalytic reduction of NO; x; IR study; H-ZSM-5 zeolite; Low temperature ammonia SCR; SCR; Nitrogen oxides
Electrochemical DeNO x in solid electrolyte cells—an overview by K. Kammer (pp. 33-39).
The investigations in the field of electrochemical reduction of nitric oxide are reviewed. Using a cell based on an oxide ionic conductor it is shown that the selectivity and activity of the cathodes is strongly dependent on the temperature and of the composition of the cathode material. In general the selectivity is highest at the lowest temperatures. Cathode materials with a high redox capacity are shown to have the highest performance towards the reduction of nitric oxide. Different approaches using a protonic conductor are also reviewed. In the end a few examples of the electrochemical promotion of the reduction of nitric oxide with a reducing agent are given. Literature reveals that electrochemical promotion of the reduction of nitric oxide with a reducing agent is possible also under lean conditions. The electrochemical promotion is accompanied by an increase in the selectivity towards the formation of nitrogen.
Keywords: NO; NO; 2; O; 2; Electrochemical DeNO; x
Direct epoxidation of propylene by molecular oxygen over Pd(OAc)2–[(C6H13)4N]3{PO4[W(O)(O2)2]4}–CH3OH catalytic system by Yanyong Liu; Kazuhisa Murata; Megumu Inaba; Naoki Mimura (pp. 51-59).
The catalytic system containing Pd(OAc)2 and peroxo-heteropoly compound [(C6H13)4N]3{PO4[W(O)(O2)2]4} (denoted by THA-PW4) in methanol showed 81.6% selectivity for propylene oxide at a propylene conversion of 42.7% using molecular oxygen as an oxidant in an autoclave reactor at 373K for 6h, whereas, Pd(OAc)2 or THA-PW4 alone showed low conversions. The catalytic system containing Pd(OAc)2 and THA-PW4 in methanol is reusable for propylene oxidation by means of vacuum distillation after reaction. XRD patterns and Pd K-edge EXAFS indicate that Pd0 species formed by the reduction of Pd(OAc)2 with methanol acts as an active species in propylene epoxidation with molecular oxygen. FT-IR spectra of Pd–THA-PW4 before and after reaction proved that the peroxy oxygen bonds of THA-PW4 could be regenerated in methanol medium by molecular oxygen in the presence of Pd, but could not be regenerated in acetonitrile medium. It is likely that methanol molecule reacts with oxygen molecule over Pd0 species to form a peroxy intermediate HOCH2OOH, which regenerates the peroxy oxygen bonds of THA-PW4 and achieves catalytic turnover for propylene epoxidation. Because the peroxy intermediate HOCH2OOH is not stable and finally decompose to CO x and H2O, a part of methanol is co-oxidized. Moreover, hydrogen peroxide also probably formed in situ in the catalytic system during the reaction and plays an important role to regenerate the peroxy oxygen bonds of THA-PW4.
Keywords: Propylene; Epoxidation; Peroxo-heteropoly compound; Palladium; Molecular oxygen
Poisoning mechanism of perovskite LaCoO3 catalyst by organophosphorous gas by Ruiqin Tan; Yongfa Zhu (pp. 61-68).
The reaction and poisoning mechanism of organophosphorous gas with LaCoO3 model catalyst have been studied. Organophosphorous gas diffused into LaCoO3 model catalyst and reacted to form some new species such as LaPO4, La4(P2O7)3 and CoO, which resulted in the distortion and destruction of perovskite structure. The residual concentration of phosphorus in the catalyst layer reached a maximum after the catalyst was poisoned at 600°C for 2h. The diffusion depth of phosphorus in LaCoO3 layer increased with poisoning temperature and time. After the model catalyst was poisoned at a high temperature above 700°C or for a longer period, the distribution of phosphorus in the LaCoO3 layer became homogeneous and the distribution peak of P concentration shifted into the layer. The catalytic performance test for oxidation of CO indicated that the formation of phosphate and the destruction of the perovskite structure in LaCoO3 catalyst layer resulted in the deactivation of the perovskite catalyst.
Keywords: LaCoO; 3; Phosphorous poisoning; Perovskite structure
Cu/MCM-41 for selective catalytic NO reduction with NH3—comparison of different Cu-loading methods by Chi-Cheng Liu; Hsisheng Teng (pp. 69-77).
Copper supported on MCM-41, through the template- and the conventional hydroxyl group-ion exchange and incipient-wetness impregnation, were employed for selective catalytic NO reduction with NH3 within a temperature range of 200–450°C. Cu/MCM-41 catalysts with a low Cu content (ca. 0.7wt.%) from the template- and hydroxyl group-ion exchange methods, i.e., TMCu and HMCu, respectively, showed high activities in the NO reduction. Further increase of the Cu content did not obviously improve the activity of the catalysts. HMCu has a higher activity than TMCu, especially at temperatures lower than 350°C. The Cu species on HMCu exhibited stronger tendencies towards reduction and oxidation, indicating that both reduction and oxidation of the active species controlled the NO reduction rate. The Mars–van Krevelen kinetic model gave a satisfactory simulation of the experimental data, which supported the argument that the NO reduction was governed by a cyclic redox of the Cu species. The reaction orders with respect to NO and NH3 were of a fraction (between 0.5 and unity) and of ca. 0, respectively. The activation energies were similar for reactions over these two catalysts, whereas the reactions over HMCu were seen to have larger values of the frequency factor, a parameter closely related to the intrinsic chemical structure. XANES spectra reflected that the catalysts were mainly composed of CuO. The coordination number of CuO analyzed by EXAFS reflected that HMCu had a slightly larger content of CuI, which has been suggested to facilitate NO attack on active sites.
Keywords: Selective catalytic reduction; Nitric oxide; Ammonia; MCM-41; Copper loading
Degradation of phenol and benzoic acid in the presence of a TiO2-based heterogeneous photocatalyst by Davide Vione; Claudio Minero; Valter Maurino; M. Eugenia Carlotti; Tatiana Picatonotto; Ezio Pelizzetti (pp. 79-88).
This paper reports the results of a study on the titanium dioxide Wackherr's “Oxyde de titane standard�, which shows very interesting photocatalytic activity. Produced for cosmetic purposes as a white pigment, its features make it very interesting in the field of heterogeneous photocatalysis. The results obtained with this photocatalyst are compared with the behaviour of the well-studied and widely used TiO2 Degussa P25 under the same conditions. In particular, the TiO2 Wackherr induces relevantly faster phenol degradation than P25 when high photocatalyst loading is used (up to 2.00gl−1), as phenol degradation rate in the presence of TiO2 Wackherr continues to increase with increasing photocatalyst loading. This is most likely due to the lower radiation scattering in the UV region of TiO2 Wackherr when compared with Degussa P25, which is linked with the higher particle size of TiO2 Wackherr. The initial phenol degradation rate by TiO2 Wackherr as a function of phenol concentration has a maximum for [phenol]≈3×10−4M, and decreases for higher concentration values. The addition of fluoride ions to TiO2 Wackherr at pH 3.7 increases phenol degradation rate, as already found for Degussa P25. The increase is more relevant for higher phenol concentration values and makes the maximum as a function of phenol concentration to disappear. Comparable results are also obtained when benzoic acid is used as a substrate, with some differences from phenol that can be accounted for by benzoic acid more strongly interacting with the surface. The use of TiO2 Wackherr in heterogeneous photocatalysis can be desirable when high photocatalyst loading is required.
Keywords: Pollutant photodegradation; Photocatalysis; Laser light scattering; Kubelka-Munk equation; Diffuse reflectance; Surface recombination processes
Performance of CoMoS/Al2O3 prepared by sonochemical and chemical vapor deposition methods in the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene by Jung Joon Lee; Heeyeon Kim; Jae Hyun Koh; Ara Jo; Sang Heup Moon (pp. 89-95).
Highly dispersed CoMoS/Al2O3 was prepared by dispersing MoS2 crystallites on Al2O3 by a sonochemical method, followed by the selective deposition of Co on the resulting MoS2 crystallites. The newly prepared catalyst contained larger amounts of CoMoS phase, a known active site for hydrodesulfurization (HDS), than a catalyst prepared by sequential impregnation and, as a result, exhibited a two to three times higher activity than that of the impregnated one for the HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The former catalyst promoted hydrogenation (HYD) route to a greater extent than direct desulfurization (DDS) route. Therefore, the extent of activity increase for the new catalyst was larger for 4,6-DMDBT HDS, which proceeds largely via the HYD route, than for DBT HDS, which proceeds largely by DDS.
Keywords: Hydrodesulfurization; Sonochemistry; Chemical vapor deposition; Dibenzothiophene; 4,6-Dimethyldibenzothiophene
Vanadia on sulphated-ZrO2, a promising catalyst for NO abatement with ammonia in alkali containing flue gases by A.L. Kustov; M.Yu. Kustova; R. Fehrmann; P. Simonsen (pp. 97-104).
Vanadia supported on TiO2, ZrO2, and sulphated-ZrO2 have been prepared. These catalysts were characterized by elemental analysis, N2-BET, XRD, FTIR, and NH3-TPD methods. The stability of surface sulphated groups, studied by FTIR-spectroscopy, was found to depend dramatically on the temperature of the calcination of the samples. No considerable decomposition of surface sulphates was observed below 350°C. The influence of potassium oxide additives on the acidity and activity in NO SCR with ammonia was studied. It was found that the introduction of small amounts of potassium (K/V molar ratio<0.5) led to almost complete depression of the samples acidity and considerable weakening of the remaining acid sites for TiO2 and ZrO2 based systems. For the sulphated system, surface sulphur groups, due to their strong acidity, represent attractive sites for the localization of potassium oxide and the decrease in the total acidity is less pronounced in this case. The results of NO SCR with ammonia reveal a noticeable shift of the maximum catalytic activity towards higher temperatures in going from the conventional catalyst to vanadia supported on sulphated zirconia. The loading of the catalysts with potassium leads to considerable decrease of their catalytic activity, and to a shift of the maximum catalytic activity towards lower temperatures. Among all the catalysts, V2O5/sulphated-ZrO2 reveals the highest resistance towards alkali poisoning. The presence of SO2 in the reaction mixture was found to enhance stability and activity of the V2O5/sulphated-ZrO2 probably due to regeneration of surface sulphated groups at the reaction conditions. The potassium-doped V2O5/sulphated-ZrO2 catalyst reveal high activity and stability at 300°C, comparable with unpoisoned catalysts. At 400°C the presence of potassium compounds seems to enhance the deactivation of the catalyst under reaction conditions during 30h, possibly due to formation of potassium sulphate–pyrosulphate species reacting with vanadium oxide.
Keywords: NO SCR with ammonia; Potassium poisoning; Deactivation; V; 2; O; 5; -based catalysts; Sulphated-ZrO; 2; NH; 3; -TPD
Catalytic wet air oxidation of substituted phenols using activated carbon as catalyst by M. Eugenia Suarez-Ojeda; Frank Stüber; Agustí Fortuny; Azael Fabregat; Julián Carrera; Josep Font (pp. 105-114).
Continuous catalytic wet air oxidation (CWAO) was investigated as a suitable precursor for the biological treatment of industrial wastewater that contained phenols (phenol, o-cresol, 2-chlorophenol and p-nitrophenol), aniline, sulfolane, nitrobenzene or sodium dodecylbenzene sulfonate (DBS). Seventy-two-hour tests were carried out in a fixed bed reactor in trickle flow regime, using a commercial activated carbon (AC) as catalyst. The temperature and total pressure were 140°C and 13.1bar, respectively. The influence of hydroxyl-, methyl-, chloride-, nitro-, sulfo- and sulfonic-substituents on the oxidation mechanism of aromatic compounds, the occurrence of oxidative coupling reactions over the AC, and the catalytic activity (in terms of substrate elimination) were established. The results show that the AC without any supported active metal behaves bifunctionally as adsorbent and catalyst, and is active enough to oxidate phenol, o-cresol, 2-chlorophenol and DBS, giving conversions between 30 and 55% at the conditions tested. The selectivity to the production of carbon dioxide was considerable with total organic carbon (TOC) abatement between 15 and 50%. The chemical oxygen demand (COD) reduction was between 12 and 45%. In turn, aniline, sulfolane, p-nitrophenol and nitrobenzene conversions were below 5% and there was almost no TOC abatement or COD reduction, which shows the refractory nature of these compounds.
Keywords: Activated carbon; Substituted phenols; Dodecylbenzene sulfonate; Oxidation; Trickle bed
Synthesis and characterization of Y2O3/Fe2O3/TiO2 nanoparticles by sol–gel method by Adel Ali Ismail (pp. 115-121).
Binary and ternary mixed oxide of Y/Fe/Ti with homogeneous distribution of yttrium and iron oxides into TiO2 has been prepared by sol–gel method using metal alkoxide precursors in presence of acid–base catalysts. The structural features of Y2O3/Fe2O3/TiO2 mixed oxide fired at 550°C have been investigated by XRD, FT-IR, SEM, AFM, XPS and surface area measurements. A preliminary investigation of photocatalytic activity of mixed oxide on EDTA photo-oxidation showed that Y/Fe/Ti is more photoactive than pure TiO2.
Keywords: Synthesis; Characterization; Y; 2; O; 3; /Fe; 2; O; 3; /TiO; 2; Nanoparticles; Sol–gel
Treatment of cooking oil fume by low temperature catalysis by Ji Yang; Jinping Jia; Yaling Wang; Weisong You (pp. 123-131).
Similar to cigarette smoke, fumes from cooking oil contain lots of carcinogens such as aromatic amines, polycyclic aromatic hydrocarbons (PAHs), nitro-polycyclic aromatic hydrocarbons, etc. and are notoriously difficult to remove by traditional static method. In this paper, low temperature catalytic oxidation was employed to treat cooking oil fume. A novel catalyst, based on MnO2/CuO, was developed successfully and its characteristics were studied. Catalytic activity was studied under different oil temperatures, catalyst temperatures and contact times results show that the method employed in this work can give impressive treatment effect on cooking oil fume. Lifetime experiments, poisoning experiments by water steam, and thermal stability study of catalyst were also performed to check the catalyst robustness.
Keywords: Cooking oil fumes; Catalysis; Polycyclic aromatic hydrocarbons (PAHs); Organic gas; Volatile organic carbon (VOC); Oxidization
Catalytic combustion of methane over Pd containing perovskite type oxides by SrÄ‘an Petrović; Ljiljana Karanović; Plamen K. Stefanov; Miodrag Zdujić; Ana Terlecki-BariÄ?ević (pp. 133-141).
The mixed perovskite type oxides with nominal formula LaTi0.5Mg0.5− xPd xO3, (0≤ x≤0.10) were prepared by anneling the ethanol solution of precursor in nitrogen flow at 1200°C. X-ray powder diffraction (XRPD) analysis shows that the orthorhombic perovskite structure was found in all investigated samples. However, at least a part of palladium is not incorporated into perovskite structure and remains as separate phase, which is reduced to Pd0 at 1200°C. X-ray photoelectron spectroscopy (XPS) reveled the presence of Pd2+, which indicate a reoxidation of Pd0 in the surface layers during cooling. The Pd content in the samples has a small influence on the methane oxidation activity below the temperature of 500°C. At temperatures higher than 500°C, the methane oxidation activity of the sample with x=0.05 exceeds the activity of the sample with x=0.10. The sharp increase of methane oxidation activity over the sample with lower content of palladium at about 500°C was ascribed to the higher dispersion of PdO and Pd0 phases. Thus, the higher contribution of lattice oxygen and possible local change in oxidation state of palladium can be a reason for the enhanced activity. Contrary to the supported Pd/Al2O3 catalyst, the incorporation of palladium into perovskite matrix and interaction of PdO–Pd0 benefits the activity of smaller particles at higher reaction temperatures.
Keywords: XPS; Perovskite; Catalytic combustion
Catalytic methane combustion on Pd-Pt-La catalysts and their surface models by Natthakorn Kraikul; Sirirat Jitkarnka; Apanee Luengnaruemitchai (pp. 143-152).
Catalytic combustion of methane has been studied over a library of Pd, Pt, and La in mono-, bi-, and tri-element system supported on γ-Al2O3 washcoated ceramic monolith using an eight-tubular flow reactor. Simulated operating conditions of a small-size gas turbine were employed to investigate the combustion activity. Lead formulations from an initial high throughput screening were classified into two categories: Pd-Pt bi-element catalysts, and Pd-Pt-La tri-element catalysts with relatively constant 20% Pd (equivalent to 1% Pd of 5% total elemental loading). The substitution of Pd by Pt, while maintaining 5% total loading, was observed to improve the combustion activity as expected due to the co-existence of PdO and Pd–Pt alloy on the catalytic surface. However, its combustion activity was only slightly decreased when Pt was further substituted by La with relatively fixed 20% Pd loading due to the metal dilution by La. Nevertheless, the catalyst with Pd and Pt in equivalent amount with three times of La dilution (Pd:Pt:La=1:1:3) was suggested to be the best formula not only due to its high combustion activity at even low temperatures, but also the reduction of noble metal usage.
Keywords: Catalytic combustion; High-throughput; Multi-flow reactor; Pd-Pt-La catalyst
Erratum to “Effect of charge trapping species of cupric ions on the photocatalytic oxidation of resorcinol� [Appl. Catal. B: Environ. 55 (2005) 123–132]
by S.W. Lam; K. Chiang; T.M. Lim; R. Amal; G.K.-C. Low (pp. 153-153).