Applied Catalysis A, General (v.360, #1)
Editorial Board (CO2).
Catalytic combustion of methane at high temperatures: Cerium effect on PdO/Al2O3 catalysts by Lílian M.T. Simplício; Soraia T. Brandão; Daniela Domingos; François Bozon-Verduraz; Emerson A. Sales (2-7).
The catalysts applied in the combustion of methane at high temperatures (above 600 °C) were prepared in order to investigate the role of palladium precursors on the catalytic properties of these systems and on the thermal stability of PdO (active phase). PdO/Al2O3 and PdO/CeO2/Al2O3 catalysts were obtained from different palladium precursors with the objective of evaluating CeO2 effect on the thermal stability of PdO and catalytic activity. The best results were obtained with the catalyst prepared with palladium acetylacetonate.PdO/Al2O3 and PdO/CeO2/Al2O3 catalysts were prepared in order to investigate the role of palladium precursors and cerium addition on the catalytic properties of these systems and on the thermal stability of PdO (active phase) in the catalytic combustion of methane at high temperatures (above 600 °C). The catalysts were obtained from different palladium precursors and presented distinct interactions with CeO2/Al2O3, thermal stability of PdO and catalytic activity. The use of cerium improved PdO thermal stability and the cerium effect was more pronounced on the catalyst prepared from acetylacetonate indicating that a PdO–CeO2 interaction is more favorable in this system.
Keywords: Methane combustion; Palladium catalysts; Cerium effect;
Promoted metal utilization capacity of alkali-treated zeolite: Preparation of Zn/ZSM-5 and its application in 1-hexene aromatization by Yuning Li; Shenglin Liu; Sujuan Xie; Longya Xu (8-16).
The metal utilization capacity of ZSM-5 zeolite was promoted via the intracrystalline mesopores created by alkali treatment. Parts of the metal species were located in the mesopores and consequently the synergy effect between metal species and Brønsted acid sites was enhanced. The 1-hexene aromatization was used as a model reaction to demonstrate the predominance of the alkali-treated metal-zeolite bifunctional catalysts.Promoted metal utilization capacity of ZSM-5 zeolite has been achieved via the intracrystalline mesopores created by alkali treatment. The untreated and alkali-treated Zn/ZSM-5 catalysts were prepared by the conventional liquid ion exchange and impregnation methods. These catalysts were investigated by several techniques: N2 adsorption–desorption, transmission electron microscopy, X-ray photoelectron spectroscopy, ammonia temperature-programmed desorption, and Fourier transform infrared spectroscopy. Compared with the untreated catalysts, the alkali-treated catalysts exhibited higher Zn-loading in liquid ion exchange, better metal distribution and more Lewis acid sites in impregnation, owing to the location of Zn species in the created intracrystalline mesopores. The alkali-treated Zn/ZSM-5 catalysts displayed dramatically improved catalytic stability in 1-hexene aromatization. These findings show new potential for developing some advanced bifunctional metal-zeolite catalysts by a facile and low-cost method.
Keywords: ZSM-5 zeolite; Alkali treatment; Zn; 1-Hexene; Aromatization;
Ethanol steam reforming for production of hydrogen on magnesium aluminate-supported cobalt catalysts promoted by noble metals by Luciene P.R. Profeti; Edson A. Ticianelli; Elisabete M. Assaf (17-25).
The addition of the noble metals to the Co catalyst caused a marked modification in the Co K-edge XANES spectra from 250 °C (b), whereas the Co/MgAl2O4 catalyst (a) was reduced at higher temperatures. The decrease of the reduction temperature of the cobalt species, seen in the spectra of the promoted catalysts, may result from a hydrogen spillover phenomenon that occurs in noble metals. This enhancement of reducibility may be closely related to the improved catalytic performances of the promoted catalysts.The performance of noble metal (Pt, Ru, Ir)-promoted Co/MgAl2O4 catalysts for the steam reforming of ethanol was investigated. The catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, temperature-programmed reduction, temperature-programmed oxidation and X-ray absorption near edge structure (XANES). The results showed that the formation of inactive cobalt aluminate was suppressed by the presence of a MgAl2O4 spinel phase. The effects of the noble metals included a marked lowering of the reduction temperatures of the cobalt surface species interacting with the support. It was seen that the addition of noble metal stabilized the Co sites in the reduced state throughout the reaction. Catalytic performance was enhanced in the promoted catalysts, particularly CoRu/MgAl2O4, which showed the highest selectivity for H2 production.
Keywords: Cobalt; Noble metal; Ethanol steam reforming; Magnesium aluminate;
Effect of CO pretreatment on the performance of CuO/CeO2/γ-Al2O3 catalysts in CO + O2 reactions by Haiqin Wan; Dan Li; Yue Dai; Yuhai Hu; Yanhua Zhang; Lianjun Liu; Bin Zhao; Bin Liu; Keqin Sun; Lin Dong; Yi Chen (26-32).
The influence of CO pretreatment on the properties of CuO/CeO2/γ-Al2O3 catalysts was investigated by XRD, H2-TPR and IR, and the activities of the catalysts in low-temperature CO oxidation reactions were tested. The results indicate that CO treatment leads to the decrease of the activity of CuO/CeO2/γ-Al2O3 catalysts while such treatment causes an increase of the activity of the CuO/γ-Al2O3 catalysts in low-temperature CO oxidation (≤200 °C).The influence of CO pretreatment on the properties of CuO/CeO2/γ-Al2O3 catalysts was investigated using X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The activities of the treated catalysts were measured in low-temperature CO oxidation reactions (≤200 °C). For this reaction, the activities of CuO/CeO2/γ-Al2O3 catalysts are intimately related to operation temperature, copper oxide loading amount and CO pretreatment. The influence of the first two factors, i.e., operation temperature and copper oxide loading amount, is similar to the previous results of CuO/γ-Al2O3 catalysts [H.Q. Wan, Z. Wang, J. Zhu, X.W. Li, B. Liu, F. Gao, L. Dong, Y. Chen, Appl. Catal. B: Environ. 79 (2008) 254–261]. CO conversions are clearly promoted with increasing operation temperatures and the maximum CO conversions are always reached over the catalysts with a copper oxide loading amount of 0.6 mmol Cu2+/100 m2 γ-Al2O3, at the set operation temperatures. For the third factor, CO conversions over the CO-treated CuO/CeO2/γ-Al2O3 catalysts are slightly lower than those over the fresh catalysts with the same amount of copper oxide. In contrast, the activity was enhanced over the CO-treated CuO/γ-Al2O3 catalysts in the previous report. XRD, TPR and XPS results show that CO pretreatment at 250 °C mainly results in the reduction of crystalline CuO to Cu0 and of partially dispersed Cu2+ to Cu+ and Cu0 in CuO/CeO2/γ-Al2O3 catalysts. IR results indicate that besides the CO–Cu+ adsorption band at ∼2110 cm−1 on the fresh and CO-pretreated catalysts exposed to CO stream when temperatures are above 50 °C, a new adsorption band at 2170 cm−1 is detectable corresponding to CO–Cu2+ or CO–Cu0 over the CO-treated CuO/CeO2/γ-Al2O3 catalysts with copper oxide loading amounts of 0.3 and 1.2 mmol/100 m2γ-Al2O3 at the adsorption temperatures beyond 150 °C. The influences of the ceria modification on the generation of copper species in fresh and CO-treated CuO/CeO2/γ-Al2O3 catalysts and their activities in CO oxidation were discussed.
Keywords: CuO/γ-Al2O3; Ceria modification; CO pretreatment; CO oxidation; In situ IR;
Preparation of benzoyl fluoride from benzotrifluoride catalyzed by niobium oxide by Joseph Zakzeski; Irene S. Fan; Alexis T. Bell (33-37).
Nb2O5 was found to catalyze the conversion of benzotrifluoride to benzoyl fluoride in the presence of carboxylic acids, together with the corresponding anhydride, and molecular oxygen. The composition of the acid and anhydride were found to play two roles – as a proton source to activate the C–F bond and as an oxygen transfer agent to form benzoyl fluoride.Several metals were found to catalyze the conversion of benzotrifluoride to benzoyl fluoride in the presence of carboxylic acids and sulfonic acids, together with the corresponding anhydride, and molecular oxygen. Nb2O5 exhibited the highest activity, and a conversion of ∼99.8% and a selectivity of ∼90% were obtained in 10 min under mild conditions. The composition of the acid and anhydride was found to play two roles – as a proton source to activate the C–F bond and as an oxygen transfer agent to form benzoyl fluoride. Oxygen facilitated fluorine transfer but did not enter into the reaction products. A possible mechanism for the conversion of benzotrifluoride to benzoyl fluoride was proposed.
Keywords: Benzoyl fluoride; Niobium oxide; Benzotrifluoride; Heterogeneous catalysis;
Three-stage deactivation of Pd/SiO2 and Pd-Ag/SiO2 catalysts during the selective hydrogenation of acetylene by In Young Ahn; Ji Hoon Lee; Seok Ki Kim; Sang Heup Moon (38-42).
Pd/SiO2 was deactivated in three stages during acetylene hydrogenation: the initial slow deactivation with the accumulation of large amounts of green oil, the transfer of green oil from Pd to SiO2, and the final rapid deactivation with the deposition of small amounts of green oil. The deactivation was retarded for Pd-Ag/SiO2, without showing the final stage of rapid deactivation.The deactivation of Pd/SiO2 and Ag-promoted Pd/SiO2 catalysts was monitored during their use in the selective hydrogenation of acetylene. Based on the analysis of green oil accumulated on the deactivated Pd/SiO2 catalysts, it was proposed that the catalyst deactivation proceeded in three stages. In the initial stage (Stage I), a large amount of relatively light green oil was deposited on, or in the vicinity of, the Pd surface, but the catalytic activity decreased only slightly. As the deactivation proceeded (Stage II), the 1,3-butadiene that had accumulated on the Pd surface was polymerized to relatively heavy green oil, a part of which moved from the Pd surface to the support. In the later stage of deactivation (Stage III), catalytic activity was drastically decreased because catalyst pores were blocked and hydrogen diffusion was limited in the thick film of the relatively heavy green oil.Although the initial activity of Ag-promoted Pd/SiO2 was slightly lower than that of the unpromoted one, the amount of green oil deposited on the former catalyst was much smaller than that deposited on the latter. Consequently, the final stage of deactivation (Stage III) was not observed with Pd-Ag/SiO2 during the reaction period of this study. Pd-Ag/SiO2 showed Stage II, characterized by the transfer of green oil from the Pd to the support, at a period earlier than in the case of Pd/SiO2, which additionally contributed to the slow deactivation of the former catalyst. The green oil that formed on the Pd-Ag/SiO2 was more volatile and mobile than that formed on Pd/SiO2, because the added Ag geometrically blocked multi-coordinated large ensembles of the Pd surface and also modified the Pd electronically such that the adsorption of 1,3-butadiene on the Pd became weaker than in the absence of promotion.
Keywords: Acetylene hydrogenation; Pd catalyst; Ag addition; Deactivation; Green oil; Formation mechanism;
Sulphur inhibition on the catalytic partial oxidation of methane over Rh-based monolith catalysts by S. Cimino; R. Torbati; L. Lisi; G. Russo (43-49).
The effect of sulphur addition during the CPO of methane was investigated on Rh-based honeycombs tested under self-sustained high T condition. It was found that sulphur reversibly adsorbed on Rh selectively inhibits the steam reforming path and increases catalyst temperature. The extent of SR inhibition is greater when operating in air and diminishes at lower CH4/O2 feed ratios, whereas it is independent on the type of sulphur bearing compound.The effect of sulphur addition (2–58 ppm) during the catalytic partial oxidation (CPO) of methane was investigated on Rh-based honeycomb catalysts tested under self-sustained high temperature condition. Both steady state and transient operation of the CPO reactor were investigated particularly with regard to poisoning/regeneration cycles and low temperature light-off phase. The analysis of products distribution in the effluent and a heat balance demonstrates that sulphur reversibly adsorbed on Rh selectively inhibits the steam reforming (SR) reaction path to syngas production. The extent of SR inhibition is greater when operating in air and diminishes at lower CH4/O2 feed ratios. The poisoning effect has been shown to be independent from the type of sulphur bearing compound and only indirectly affected by the type of catalyst support (La2O3 or SiO2 stabilized alumina) through the value of Rh dispersion.
Keywords: Sulphur poisoning; Partial oxidation; Steam reforming; Rh; Stabilized alumina; Honeycomb; Methane;
Cs-doped H4SiW12O40 catalysts for biodiesel applications by L. Pesaresi; D.R. Brown; A.F. Lee; J.M. Montero; H. Williams; K. Wilson (50-58).
Cs doped H4SiW12O40 is an effective heterogenous catalyst for the transesterification of C4 and C8 triglycerides (TAG) and the esterification of free fatty acids (FFA). Reactivity correlates with the accessible mesopore acid site density, with optimal performance obtained for Cs1.9–3.4 per Keggin.Cs exchanged silicotungstic acid catalysts of general formula Cs x H4−x SiW12O40 (x = 0.8–4) have been synthesised and characterised by a range of techniques including elemental analysis, N2 gas adsorption, XRD, XPS and NH3 flow calorimetry. Cs substitution promotes recrystallisation of the parent H4SiW12O40 polyoxometallate to the Cs4 salt, via a stable intermediate phase formed at compositions between Cs0.8–2.8. This recrystallisation is accompanied by a pronounced rise and subsequent fall in porosity, with a maximum mesopore volume obtained for materials containing 2.8 Cs atoms per Keggin unit. Calorimetry reveals all Cs x H4−x SiW12O40 are strong acids, with ΔH θ ads(NH3) ranging from −142 to 116 kJ mol−1 with increasing Cs content, consistently weaker than their phosphotungstic analogues. Cs x H4−x SiW12O40 materials are active catalysts for both C4 and C8 triglyceride transesterification, and palmitic acid esterification with methanol. For loadings ≤0.8 Cs per Keggin, (trans)esterification activity arises from homogeneous contributions. However, higher degrees of substitution result in entirely heterogeneous catalysis, with rates proportional to the density of accessible acid sites present within mesopores.
Keywords: Solid acid; Biodiesel; Heterogeneous catalysis; Green Chemsitry; Heteropolyacid;
Synthesis and characterization of aluminium incorporated mesoporous KIT-6: Efficient catalyst for acylation of phenol by Azhagapillai Prabhu; Loganathan Kumaresan; Muthaiahpillai Palanichamy; Velayutham Murugesan (59-65).
Aluminium incorporated mesoporous KIT-6 materials with different Si/Al ratios were synthesized by a hydrothermal method. The materials upon characterization exhibited ordered mesoporous pores with cubic Ia3d structure. The acylation of phenol with acetic acid over Al-KIT-6 materials in the vapor phase resulted in selective O-acylation.Mesoporous Al-KIT-6 materials with Si/Al ratios of 20, 30, 40, 50, 100 and 150 were synthesized hydrothermally and were characterized by X-ray diffraction (XRD), nitrogen sorption isotherm, Fourier transform infrared spectroscopy (FT-IR), pyridine-adsorbed DRIFT-IR, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The surface area of the catalysts decreased with the increase of aluminum content in Al-KIT-6. The high quality of cubic Ia3d silica product was judged by HR-TEM. The nature and the strength of the acid sites of the catalysts were probed by pyridine-adsorbed DRIFT spectra. The vapor phase acylation of phenol with acetic acid was carried out over all the materials to evaluate their catalytic activity. All the catalysts were found to be active in the formation of phenyl acetate with high selectivity. The formation of coke was not significant at any temperature. The time-on-stream study revealed steady conversion of phenol (80%) and steady selectivity to phenyl acetate (90%) during the entire period. The activity of the catalysts followed the order: Al-KIT-6 (20) > Al-KIT-6 (30) > Al-KIT-6 (40) > Al-KIT-6 (50) > Al-KIT-6 (100) > Al-KIT-6 (150). The selectivity of phenyl acetate was almost the same over all the catalysts, but the selectivity of o-HAP over Al-KIT-6 (40) was slightly lower than others. The effect of reaction parameters was examined exclusively over Al-KIT-6 (40).
Keywords: Mesoporous; Al-KIT-6; Hydrothermal; Phenol acylation; Acetic acid;
Dehydration of glycerol on H-MFI zeolite investigated by FT-IR by Eisuke Yoda; Ayako Ootawa (66-70).
Adsorbed glycerol on H-MFI zeolite was investigated by FT-IR. Dehydration of glycerol was confirmed to have occurred at 353 K. A comparison of the IR spectra of dehydrated glycerol with the adsorbed acrolein on H-MFI suggests that the product on H-MFI upon dehydration of glycerol was acrolein. Although two reaction pathways were suggested in the acid-catalyzed dehydration of glycerol, acrolein was found to be formed selectively on H-MFI.Dehydration of adsorbed glycerol on H-MFI zeolite was investigated by FT-IR. Dehydration of glycerol was confirmed to occur at 353 K. A comparison of the adsorption of acrolein on amorphous silica and on H-MFI suggests that the product on H-MFI upon dehydration of glycerol was acrolein. Although two reaction pathways in which the OH groups on C1 and C2 of glycerol dehydrate were suggested in the acid-catalyzed dehydration of glycerol, the pathway in which the OH groups on C2 dehydrate was found to proceed selectively on H-MFI.
Keywords: MFI zeolite; Glycerol; Dehydration; Acrolein; FT-IR;
A kinetic and mechanistic study of the double bond and skeletal isomerization of 1-tetradecene on SAPO-11 by Jeffrey C. Gee; Daniel S. Prampin (71-80).
We studied the double bond and skeletal isomerization of 1-tetradecene on SAPO-11 at 142 and 180 °C. A kinetic analysis determined relative rate constants and Arrhenius parameters for six different reactions in the system. We also report new observations on the mechanism of skeletal isomerization in linear olefins.We present kinetic data for the double bond and skeletal isomerization of 1-tetradecene on SAPO-11 at 142 and 180 °C. The kinetic model permitted calculation of five different rate constants for double bond movements, methyl branch formation, and dimerization, as well as the corresponding Arrhenius parameters. We also discuss observations on the mechanism of the skeletal isomerization, concluding that methyl groups can form at significant distances from the carbon–carbon double bonds, apparently via rapidly interconverting carbenium ions on the catalyst's surface.
Keywords: Olefin isomerization mechanism; SAPO-11 catalyst; Kinetics;
Catalytic oxidation of diesel soot: New characterization and kinetic evidence related to the reaction mechanism on K/CeO2 catalyst by Martín S. Gross; Maria A. Ulla; Carlos A. Querini (81-88).
Temperature-programmed oxidation analysis carried out up to intermediate temperatures (320–350 °C) made it possible to observe an unexpected result regarding the reaction rate for the catalytic soot oxidation. A maximum was observed in the rate of oxidation at constant temperature, which is explained taking into account the formation of different intermediates involving CeO2 and K unstable compounds.The oxidation of diesel soot using K/CeO2 catalysts is studied in this paper. The reaction system involved in the catalytic oxidation of soot is quite complex; therefore, the study of reaction mechanisms is particularly difficult to address and, consequently, there are few publications related to this topic. In this work, kinetic tests providing new information on this mechanism are shown. Using temperature-programmed oxidation experiments designed in order to get the combustion of only a fraction of the soot, it was possible to observe transient phenomena that demonstrate that the soot oxidation reaction involves many steps and intermediate species. Fourier transform infrared spectroscopy (FTIR), SEM and energy-dispersive X-ray analysis (EDX) characterization results obtained before and after partial burning experiments of soot, also provided information on catalysts morphological changes during the reaction. It was found that peroxide and superoxides associated to CeO2 are present on the catalyst during soot oxidation. On the other hand, carbonates are formed on the catalyst surface reaching a pseudo-steady-state. The formation of peroxides and superoxides and its surface diffusion explained the transient behavior observed during temperature-programmed experiments designed to burn a fraction of soot under isothermal condition.
Keywords: Diesel soot; Kinetics; Mechanism; Cerium oxide catalysts;
Characterization of sulfated zirconia prepared using reference catalysts and application to several model reactions by Hiromi Matsuhashi; Hideo Nakamura; Tatsumi Ishihara; Shinji Iwamoto; Yuichi Kamiya; Junya Kobayashi; Yoshihiro Kubota; Takashi Yamada; Takeshi Matsuda; Koichi Matsushita; Kazuyuki Nakai; Hiroyasu Nishiguchi; Masaru Ogura; Noriyasu Okazaki; Satoshi Sato; Ken-ichi Shimizu; Tetsuya Shishido; Seiji Yamazoe; Tatsuya Takeguchi; Keiichi Tomishige; Hiromi Yamashita; Miki Niwa; Naonobu Katada (89-97).
The sulfated zirconia project was carried out to obtain a broad understanding of the preparation, characterization, and application of sulfated zirconia. The catalysts were prepared by the equilibrium adsorption method and the ammonium sulfate kneading method using the reference catalysts JRC-ZRO-2, -3, -4, and -5, supplied by the Reference Catalyst Division of the Catalysis Society of Japan.The sulfated zirconia project was carried out in order to obtain a broad understanding of the preparation, characterization, and application of the solid superacids of sulfated zirconia. The sulfated zirconia catalysts were prepared by the equilibrium adsorption method and the ammonium sulfate kneading method using the reference catalysts JRC-ZRO-2, -3, -4, and -5, supplied by the Reference Catalyst Division of the Catalysis Society of Japan. The catalysts were characterized by elemental analysis, NH3-TPD, XRD, TG-DTA, CO2-TPD, Raman spectroscopy, and measurements of the surface area, pore size distribution, coverage (by the BAT method), and heat of Ar adsorption. In order to compare the catalytic activities, we used the prepared catalysts in the isomerizations of butane and n-heptane, hydroisomerization of heptane, aldol condensation, acylation, esterification, and cracking of cumene. The sulfated zirconia prepared using JRC-ZRO-2 by the equilibrium adsorption method showed the highest activity and larger surface area. On the other hand, the kneading method provided catalysts with high reproducibility.
Keywords: Sulfated zirconia; Preparation; Characterization; Model reaction; Reproducibility;
A novel method for preparing high surface area copper zirconia catalysts by Gonzalo Águila; Javier Jiménez; Sichem Guerrero; Francisco Gracia; Boris Chornik; Sergio Quinteros; Paulo Araya (98-105).
A new and straightforward method to prepare high surface area Cu-ZrO2 catalysts is presented. This method considers a reflux treatment of commercial hydrous zirconia along with the inclusion of highly dispersed copper. The method allows the stabilization of high surface area ZrO2 supports with highly dispersed CuO throughout the support surface.A new and straightforward method to prepare high surface area Cu-ZrO2 catalysts is presented. This method considers a reflux treatment of commercial hydrous zirconia in the presence of a copper-containing NH4OH solution. The method allows the stabilization of high surface area ZrO2 supports with highly dispersed CuO throughout the support surface. It was observed that the addition of copper by this reflux treatment decreases the crystalline character of the ZrO2 support and increases the surface area. The potential catalytic application of these materials is exemplified with the CO oxidation and methanol reforming reactions.
Keywords: Reflux treatment; Copper; Zirconia; CO oxidation; Methanol reforming;