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Applied Catalysis A, General (v.303, #1)
Synthesis and characterization of titania photocatalysts: The influence of pretreatment on the activity by Tünde Alapi; Pál Sipos; István Ilisz; Gyula Wittmann; Zoltán Ambrus; Imre Kiricsi; Károly Mogyorósi; András Dombi (pp. 1-8).
The preparation of mesoporous titanium dioxide by using the sol–gel method is described. For the syntheses a triblock copolymer (P-123) surfactant as structure directing agent and titanium isopropoxide as Ti source was employed. In earlier studies the critical synthesis step was found to be the removal of the organic template from the catalyst, which often destroyed the mesostructure and resulted in significant decrease in the specific surface area of the product. Therefore, novel low-temperature surfactant elimination procedures such as ozone treatment at 150°C or solvent extraction combined with ozone treatment have been systematically tested and compared to find how the textural properties of the product can be preserved ensuring the total removal of the block copolymer. The products were characterized by transmission electron microscopic (TEM), Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), thermogravimetry/derivative thermogravimetry/differential thermoanalysis (TG/DTG/DTA) and BET methods. Specific surface areas of over 500m2/g were achieved in the template free materials, and both the pore size and the anatase content were found to depend on the method of template removal and thermal treatment. The subsequent calcination applied to get higher crystallinity and higher photocatalytic activity resulted in structure collapse and surface area reduction. The catalytic performance of the samples was characterized by determining the apparent rate constant of the heterogeneous photocatalytic degradation of phenol and was found to depend not only on the anatase content, but also on the conditions of the synthesis. The characteristics of the samples prepared by us were compared with those of the commercially available Hombikat TiO2 photocatalyst.
Keywords: Heterogen photocatalyst; Mesoporous TiO; 2; Sol–gel method; P-123; Ozone; Phenol decomposition; Hombikat
Depolymerization of HDPE to wax in the presence of a catalyst formed by homonuclear macrocyclic zirconium complex chemically bonded to alumina support by Sunder Lal; K.S. Anisia; A. Kumar (pp. 9-17).
A homonuclear macrocyclic Zr–Zr complex was prepared starting with 2,6-diformyl-phenol and 1,2-phenylene diamine and is chemically bonded with carbamate-modified alumina. The TPD of the catalyst having adsorbed NH3 shows the presence of acid sites on the surface of the catalyst and the catalyst is stable under the reaction temperature studied. The catalytic depolymerization of commercially available high-density polyethylene (molecular weight 4.79×105) was carried out in the presence of nitrogen as well as oxygen at about pressure of 300 of kg/cm2 and temperature of 370°C. Catalytic depolymerization in the presence N2 occurs with the time delay of 2h (as opposed to 4h for thermal depolymerization occurring above 400°C) and stops with the formation of wax (as opposed to C5–C16 liquidous alkanes in thermal depolymerization). The wax thus formed was characterized and shown to be the Arge wax (available commercially) having a melting point of 80°C and molecular weight of 392. We have proposed a kinetic model in which the catalyst forms a complex with polyethylene radical formed at high temperature, which gives depolymerization to form wax molecules.
Keywords: Heterogeneous catalyst; Depolymerization; HDPE; Wax; Zr–Zr catalyst
Direct gas-phase epoxidation of hexafluoropropylene with molecular oxygen using Ag catalyst by Zhongxi Huang; Yongming Zhang; Chengxue Zhao; Jianzhao Qin; Hong Li; Minzhao Xue; Yangang Liu (pp. 18-22).
A new potential Ag catalytic system for direct gas-phase epoxidation of hexafluoropropylene with molecular oxygen is reported. The practicability of epoxidation of hexafluoropropylene with molecular oxygen using Ag/γ-Al2O3 catalyst at low temperature and under ambient pressure is investigated. Modified the Ag catalyst by Cs, both the conversion of hexafluoropropylene and the selectivity to hexafluoropropylene oxide could be improved significantly. The catalysts were characterized by XRD, TEM and EDS.
Keywords: Epoxidation; Hexafluoropropylene; Molecular oxygen; Silver catalyst
Reduction of heterocyclic carboxaldehydes via Meerwein–Ponndorf–Verley reaction by César Jiménez-Sanchidrián; Julia MarÃa Hidalgo; José Rafael Ruiz (pp. 23-28).
A series of Mg/Al and Mg/Al/Zr layered double hydroxides (LDHs) was prepared for use as catalysts in the Meerwein–Ponndorf–Verley (MPV) reaction of heterocyclic carboxaldehydes. Analysis of the solids revealed that zirconium is in fact incorporated into the LDH structure; as a result, their calcination produces Mg/Al/Zr oxides that are effective catalysts for the MPV reduction of heterocyclic compounds. In fact, the catalysts thus obtained exhibited higher activity than a catalyst obtained from an LDH containing Mg and Al only. The reaction was conducted under very mild conditions (viz. atmospheric pressure and a temperature of 82°C) and provided conversions close to 90 and 100% selectivity in all instances.
Keywords: Hydrotalcite; LDH; Meerwein–Ponndorf–Verley reaction; Hydrogen transfer; Heterocyclic carboxaldehydes
Substituent effects in enantioselective hydrogenations catalyzed by immobilized Rh complexes by �gnes Zsigmond; Sushen Undrala; Ferenc Notheisz; �ron Szöllősy; József Bakos (pp. 29-34).
Differently substituted [Rh( S,S)BDPP]PF6 complexes were immobilized on Al2O3 support, via a modified Augustine method. The heterogenized catalysts were successfully applied in the hydrogenation of ( Z)-α-acetamidocinnamic acid and its methyl ester. The ligand basicity was varied with the different substituents and the electronic tuning could improve the activity and the selectivity of the studied reaction. Additionally the immobilized catalysts can be reused in several subsequent experiments without any significant loss of catalytic properties.
Keywords: Anchored homogeneous catalysts; [Rh(; S,S; )BDPP]PF; 6; complexes; Enantioselective hydrogenations; (; Z; )-α-acetamidocinnamic acid; Methyl (; Z; )-α-acetamidocinnamate; Catalyst recycling
Low temperature water–gas shift: Characterization and testing of binary mixed oxides of ceria and zirconia promoted with Pt by Sandrine Ricote; Gary Jacobs; Mark Milling; Yaying Ji; Patricia M. Patterson; Burtron H. Davis (pp. 35-47).
A series of Pt promoted ceria–zirconia mixed oxides was prepared, characterized, and tested for the low temperature water–gas shift reaction. An enhancement in the water–gas shift rate was observed by doping zirconium atoms into ceria to form a binary oxide for Pt promoted catalysts. By characterization using TPR and XANES, doping zirconia to ceria decreased the temperature for the surface reduction step. However, the total number of bridging OH group defect sites decreased, as Zr remained to a great extent in the Zr4+ oxidation state. This was confirmed by CO adsorption, whereby the density of total surface formates was found to decline with increased Zr concentrations. However, the formate forward turnover rate in steam was increased by zirconia addition, and was found to be higher than either Pt/ceria or Pt/zirconia alone. Both the overall rate of the formate decomposition and the water–gas shift rate, as measured by the CO conversion, passed through a maximum with increasing Zr content.Two types of formates were observed, those associated with a ceria-rich surface phase, and those associated with a zirconia-rich surface phase. The relative amounts of the two formates correlated with the Zr/Ce atomic ratios obtained by XPS. EXAFS results provided direct evidence that a solid solution was present in the mixed oxide, as a distinct peak in the Fourier transform magnitude corresponding to the Zr–Ce interaction was observed, increasing with increasing Ce/Zr ratio. The sensitivity to added carbon dioxide in the feed of the undoped and a Zr doped catalyst was also explored.
Keywords: Binary oxides; Solid solutions; CeO; 2; (ceria); ZrO; 2; (zirconia); Pt (platinum); Water–gas shift; EXAFS; XANES; DRIFTS; XPS; TPR; Bridging OH; Formates
Difference in the reaction behavior between Pt–Re/TiO2 (Rutile) and Pt–Re/ZrO2 catalysts for low-temperature water gas shift reactions by Hajime Iida; Akira Igarashi (pp. 48-55).
Pt–Re/TiO2 (R: Rutile) and Pt–Re/ZrO2 catalysts were characterized by in situ FT-IR and CO-TPD measurements. Results indicated that the strength of the CO bonding was weakened upon addition of Re, meaning that the CO species adsorbed on the catalysts was activated for steam. Further, a linear relationship was identified between the strength of the adsorbed CO and the turn over frequency (TOF) for LT-WGS, except in the case of Pt–Re/ZrO2. Pt–Re/ZrO2 exhibited a higher TOF than that predicted from the strength of the adsorbed CO. This may be due to Re redox reaction. Additionally, in situ FT-IR measurements of CO–H2O and CO–D2O reaction over Pt–Re catalysts were carried out in order to elucidate the details of the reaction mechanism. Results of these investigations indicated that the bidentate formates observed on Pt–Re/TiO2(R) were similar to those on Pt/TiO2(R); the type of formates did not change upon Re addition. On the other hand, the bidentate formates were only observed on Pt–Re/ZrO2, whereas bidentate and bridging-type formates were observed on Pt/ZrO2. These results suggest that the reaction changed upon addition of Re to Pt/ZrO2.
Keywords: Water gas shift reaction; Pt–Re/TiO; 2; (R: Rutile); Pt–Re/ZrO; 2; Pt dispersion; Re redox reaction
Adsorption and catalytic reactions of acetonitrile and acetonitrile–oxygen mixture on TiO2-supported rhodium catalysts by J. Raskó; J. Kiss (pp. 56-61).
The adsorption and surface reactions of acetonitrile and acetonitrile–oxygen gas mixture were studied on TiO2-supported Rh catalysts at 300–673K. FTIR spectra show different kinds of molecularly adsorbed CH3CN; acetonitrile can be bonded to weak Lewis acid sites (2295cm−1), to strong Lewis acid sites (2319cm−1), to very strong Lewis acid centres (2347cm−1) of titania; it can be coordinated linearly through the lone electron pair of the N atom on Rh sites (2193cm−1) and η2 (C,N) CH3CN species can be formed on Rh particles (1691–1708cm−1). CH3CN dissociates on Rh sites, the resulting CN(a) can be oxidized into NCO surface species. CN(a) can be dissociated only on Rh particles into N(a) and C(a). The hydrogenation of N(a) resulted in the appearance of NH3 among the gaseous products from Rh/TiO2 catalysts. The formation of other products (CH3NH2, H2, CO2, CH4, C2H4 and CO) was demonstrated and discussed.
Keywords: Acetonitrile adsorption; Effect of gaseous oxygen; Surface species; Gas phase products; FTIR; MS
Water-gas shift reaction over Cu/ZnO and Cu/ZnO/Al2O3 catalysts prepared by homogeneous precipitation by Tetsuya Shishido; Manabu Yamamoto; Dalin Li; Yan Tian; Hiroyuki Morioka; Masahide Honda; Tsuneji Sano; Katsuomi Takehira (pp. 62-71).
Both binary Cu/ZnO and ternary Cu/ZnO/Al2O3 catalysts were prepared by homogeneous precipitation (hp) using urea hydrolysis. The structure and the activity for the water-gas shift reaction of these catalysts were studied compared with those prepared by coprecipitation (cp). The binary precursors contained hydroxycarbonates such as malachite and aurichalcite phases, whereas the ternary precursors were composed of hydrotalcite, malachite and aurichalcite phases depending on the metal composition. After thermal decomposition, both catalysts contained apparently CuO and ZnO as crystalline phase. No phase derived from Al was observed, since the amount of Al was small as 10at.% in the ternary catalysts. After reduction pretreatment with hydrogen, the catalysts were tested for the shift reaction between 150 and 300°C. The activity of hp-catalysts was higher than that of cp-catalysts; binary hp-Cu/ZnO showed higher activity than ternary hp-Cu/ZnO/Al2O3 catalysts none the less the surface area was larger for the latter than for the former. The activity apparently depended on the surface area of Cu metal formed on the surface of hp-catalysts and a good correlation was observed between the Cu metal particle size and the activation energy of the shift reaction. However, more precise evaluation of the activity based on turn-over frequency strongly suggested the formation of Cu+ species as the active sites at the boundary between Cu metal particles and ZnO particles. Even after the pre-reduction at the high temperature, 250°C, hp-Cu/ZnO catalyst showed no significant deactivation as well as no detectable sintering of the Cu metal particles during 50h of the reaction, indicating that the hp-preparation method afforded the Cu catalysts with high sustainability in the shift reaction.
Keywords: Hydrogen; Water-gas shift reaction; Cu/ZnO catalyst; Homogeneous precipitation; Cu; +; species
Evaluation of catalyst library optimization algorithms: Comparison of the Holographic Research Strategy and the Genetic Algorithm in virtual catalytic experiments by András Tompos; József L. Margitfalvi; Ernő Tfirst; Lajos Végvári (pp. 72-80).
In this study two catalyst library optimization methods, the Holographic Research Strategy (HRS) and the Genetic Algorithm (GA) were compared based on their ability to find the optimum compositions in a given multi-dimensional experimental space. Results obtained in three different case studies were used to investigate both the rate and the certainty of the optimum search. In these case studies the activity–composition relationships were established using Artificial Neural Networks (ANNs) trained with catalytic data published earlier. The above relationships were used in “virtual optimization experiments� using both HRS and GA for catalyst library optimization. Upon using the stochastic GA its exceedingly divers mode of sampling often resulted in poor catalytic materials in the next catalyst generation. This fact resulted in a decreased rate of convergence to the optimum. In contrast, in HRS, which is a deterministic optimization algorithm, a moderate level of diversity in the catalyst library can easily be achieved. In this way an acceptable rate in optimum search can be accomplished. The visualization ability of HRS allows the illustration of all virtually tested compositions in a two-dimensional form regardless the optimization algorithm used. Upon using HRS a structured arrangement of experimental points in the virtual holograms was observed. However, when GA was applied for virtual optimization “starry sky�-like arrangement of compositions in the virtual holograms was obtained. Therefore based on virtual holograms, upon using HRS the relationship between the composition of catalytic materials and their performance can be qualitatively revealed, while no similar correlation can be obtained using GA.
Keywords: Catalyst library design; Combinatorial catalysis; Holographic Research Strategy; Genetic Algorithm; Visualization
An investigation into the Ti-grafting structure on MCM-41 and epoxidation catalysis by Qingchun Yuan; Anke Hagen; Frank Roessner (pp. 81-87).
The structure of titanium species grafted on a purely siliceous MCM-41 and their catalysis in the epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) were investigated. FT-IR, XANES and UV–vis were used for the examination of the Ti-grafted MCM-41. The results indicated that the titanium atoms are grafted on the wall surface of the MCM-41 by four-fold coordination. The four-fold coordinated titanium species are mainly grafted by two or one –O–Si–O– bridges on the MCM-41, resulting in so-called bipodal or monopodal titanium centres in partially polymerised states. The ratio of monopodal to bipodal titanium increases with the increase in Ti-content. These partially polymerised titanium species considered as catalytic active centres have high activity and selectivity in the epoxidation reaction. The used Ti-grafted MCM-41 samples were regenerated by heating in nitrogen or air atmosphere. The regeneration in nitrogen atmosphere gives samples with significantly higher catalytic activity than in air.
Keywords: Ti-grafted MCM-41 structure; Ti-content; UV–vis; Epoxidation; Regeneration
Modification of catalytic properties over carbon supported Ru–Cu and Ni–Cu bimetallics by E. Asedegbega-Nieto; B. Bachiller-Baeza; A. Guerrero-RuÃz; I. RodrÃguez-Ramos (pp. 88-95).
This study extends and amplifies earlier work carried out over two series of bimetallic catalysts, Ru–Cu and Ni–Cu, supported on a high surface area graphite. The n-hexane hydroconversion, and the selective hydrogenation of paracetamol to cis and trans-4-acetamidocyclohexanol were studied on both catalyst series. The activity in the hydroconversion of n-hexane was reduced for the bimetallic catalysts in comparison with the monometallic counterpart (Ni or Ru), and it decreased as the Cu content increased. On the other hand, while the selectivity to the hydrogenolysis products followed the trend Ni>4Ni1Cu>4Ni2Cu>4Ni3Cu in the Ni–Cu series, the catalyst 2Ru0.3Cu points up among its series, leading to lower selectivities to the fragmentation products than the Ru monometallic catalyst and the rest of the Ru–Cu bimetallic catalysts. On the other hand, no clear variation of the activity was observed for the Ni–Cu series in the hydrogenation of paracetamol. Also, the selectivity patterns were similar for all the catalysts among the series, i.e. the selectivity to the cis and trans-4-acetamidocyclohexanol higher than 90% and stereoselectivities to the trans isomer of ca. 60%. However, a reduction of the catalytic activity was again observed for the Ru–Cu catalysts, particularly for the two catalysts with highest Cu content. Furthermore, modifications on the product distribution were detected. While the 4-acetamidocyclohexanols were the main products formed on 2Ru and 2Ru0.3Cu catalysts with selectivities higher than 97%, higher amounts of secondary products were detected for 2Ru0.6Cu and 2Ru0.9Cu, where selectivities to the 4-acetamidocyclohexanols of only 22 and 14% were reached. The correlation of the data obtained in these two reactions with those reported previously provide information concerning the influence of the addition of different amounts of Cu on the structure and reactivity of the final bimetallic catalyst depending on the base metal, Ru or Ni.
Keywords: Bimetallic Catalysts; Ruthenium catalysts; Nickel catalysts; Paracetamol hydrogenation; n; -Hexane hydroconversion
Kinetic considerations of H2 assisted hydrocarbon selective catalytic reduction of NO over Ag/Al2O3 by Kalle Arve; Henrik Backman; Fredrik Klingstedt; Kari Eränen; Dmitry Yu. Murzin (pp. 96-102).
Hydrogen assisted n-octane-SCR under lean conditions over a 1.91wt.% Ag/alumina catalyst was studied. The kinetic behaviour of the catalytic reaction at 200°C at steady state conditions was examined in the concentration range:PH2=0.25, 0.5 and 1vol.%, PNO=375, 500 and 1000ppm, Poctane=187.5, 375 and 500ppm andPO2=1.5, 3 and 6vol.%. The results showed that all the rates increased along the increasing H2 concentration with the reaction order equal to 0.4 in NO and 1.4 in octane at 0.5vol.% hydrogen concentration. Moreover it was observed that the effect of hydrogen was more predominant on the NO to N2 reduction than varying reactant (NO, C8H18) concentration. The main mechanistic effect of hydrogen in significantly improving the low temperature performance of silver/alumina catalysts in HC-SCR cannot only be attributed to the reduction of surface nitrates with hydrogen suggesting its involvement in the catalytic cycle of NO reduction.
Keywords: Hydrocarbon selective catalytic reduction; Hydrogen; Lean conditions; Kinetic behaviour
Naphthenic acid removal from crude oil through catalytic decarboxylation on magnesium oxide by Aihua Zhang; Qisheng Ma; Kangshi Wang; Xicai Liu; Patrick Shuler; Yongchun Tang (pp. 103-109).
Naphthenic acid (NA) has been recognized as one of the major sources of corrosion in oil production and refining. In this study, catalytic decarboxylation of carboxylic acid model compounds and naphthenic acid removal from crude oil were investigated. A metal oxide catalyst, MgO has been developed and its effectiveness in catalyzing decarboxylation reactions involving carboxylic acid compounds such as naphthoic acid has been determined based on the formation of CO2 and the conversion of acid. The major reaction takes place in the temperature range of 150–300°C. The role of MgO in the system is considered to be multiple. It has the ability to adsorb acidic compounds via acid–base neutralization and it can also promote reactions such as decarboxylation and hydrocarbon cracking at the increased temperature. Direct application of MgO to crude oil results in significant naphthenic acid removal and lower total acidity of the oil as evidenced by a decrease in RCOOH concentration as determined by FT-IR and a lower total acid number (TAN).
Keywords: Catalytic decarboxylation; Naphthenic acid removal; Magnesium oxide; Naphthoic acid; Crude oil upgrading
On the interpretation of temperature programmed reduction patterns of transition metals sulphides by P. Afanasiev (pp. 110-115).
Transition metal sulphides show the temperature programmed reduction (TPR) patterns consisting of multiple reduction domains: those at lower temperatures are attributed to the “weakly bonded� sulphur, whereas the “bulk reduction� peaks are usually placed at high temperatures. The present paper is focusing attention on the last type TPR maxima. Due to the positive free energy of reduction of catalytically important sulphides, their TPR at high temperatures is controlled by thermodynamics. For several bulk and supported sulphides, the ascending branch of the “bulk reduction� event might be transformed to a linear (ln[H2S]–1/ T) plot from which standard enthalpy of reduction can be reliably extracted with good precision. Thermodynamics of sulphur abstraction from mixed sulphides (Mo–W sulphides, chromium thiospinels), or from highly dispersed bulk and supported systems can be estimated and compared using this approach.
Keywords: Sulphides; Temperature programmed reduction; Thermodynamics
Sulfur reduction in FCC gasoline using catalyst additives by M.A. Bari Siddiqui; Shakeel Ahmed; A.M. Aitani; C.F. Dean (pp. 116-120).
Among the various options available for the reduction of gasoline sulfur in fluid catalytic cracking (FCC), a viable option would be the use of FCC catalyst additives. Alumina supported zinc, titanium and gallium additives were prepared, mixed with Y-zeolite based FCC catalyst and the catalyst-additive mixture was evaluated for their sulfur reduction ability in micro-activity test unit (MAT). A 30% reduction in gasoline sulfur was achieved with Ga/alumina additive. The sulfur reduction ability of the Ga/alumina additive was higher than zinc/alumina and titanium/alumina additives. The additives slightly reduced catalyst's cracking activity with no change in coke yield.
Keywords: FCC additive; Gasoline sulfur; MAT testing
Modification of acid–base properties of alkali metals containing catalysts by the application of various supports by Vanesa Calvino-Casilda; Rosa Martin-Aranda; Izabela Sobczak; Maria Ziolek (pp. 121-130).
Four different supports, SiO2, Al2O3 and Nb2O5 (hydrated and dehydrated) were impregnated with alkali metal acetates to obtain alkali-modified materials. The textural parameters of the samples were estimated on the basis of XRD and IR measurements and nitrogen adsorption/desorption method. The acid–base properties of the obtained materials were tested in the cyclisation of acetonylacetone and decomposition of 2-propanol. Moreover, the prepared catalysts were used in the sulphurisation of methanol towards methanethiol and dimethyl sulphide production, which appeared a well-tested reaction and exhibits the commercial aspect—environmentally friendly production of thiol. The modification of both niobia supports with alkali metal species creates acid–base catalysts highly selective in the methanethiol production, whereas the impregnation of silica and alumina with these species leads to the generation of basicity.
Keywords: Silica; Alumina; Niobia; Alkali metal modification; 2-Propanol decomposition; Acetonylacetone cyclisation; Methanol sulphurisation
Sorbent enhanced steam reforming (SESR) of methane using dolomite as internal carbon dioxide absorbent: Limitations due to Ca(OH)2 formation by Nicolas Hildenbrand; Jennifer Readman; Ivar M. Dahl; Richard Blom (pp. 131-137).
High hydrogen yields can be obtained by sorbent enhanced steam reforming (SESR) of methane at temperatures below 600°C by using calcined dolomite as internal sorbent together with a Ni/NiAl2O4 catalyst in a fluidized bed reactor. Effluent gas compositions containing >90mole.% H2 are obtained, indicating that the sorbent acts efficiently after an induction period with low methane conversion. XRD examination of the catalyst/sorbent powder after different times-on-stream shows that during the induction period, CaO of the calcined dolomite reacts with water vapor to form Ca(OH)2. The induction period is directly proportional to the time the catalyst/sorbent mixture is in contact with steam at temperatures below 600°C where Ca(OH)2 is thermodynamically stable. The catalyst/sorbent mixture can be regenerated at temperatures above 800°C in H2/N2/H2O atmosphere.
Keywords: Hydrogen production; Natural gas; Sorbent enhanced steam reforming; Dolomite; Nickel catalyst; Fluidized bed reactor