Applied Catalysis A, General (v.255, #2)
Application of a WO3/SiO2 catalyst in an industrial environment: part I by C.van Schalkwyk; A. Spamer; D.J. Moodley; T. Dube; J. Reynhardt; J.M. Botha (121-131).
An 8% WO3/SiO2 catalyst was used in the metathesis reaction of 1-octene and an industrial cut, 1-heptene. The industrial 1-heptene feed stream consists of 75% 1-heptene, 10% n-alkane and the balance are branched hydrocarbons. The reaction conditions for the metathesis reaction were optimized using a reactor, equipped with a recycle loop. Temperature, liquid hour space velocity (LHSV) and recycle ratio were used to optimize the reaction conditions. It was found that 460 °C, LHSV=16 h−1 and feed to recycle ratio of 1:5.6 gives a conversion of about 88%, C10–C13 selectivity of 60%, C12 selectivity of 41% and an online lifetime of about 700 h when using the 1-heptene feed stream. The lifetime of the catalyst increased to 1200 h after regeneration in a flow of air at 550 °C. The conversion drops slightly, but the selectivity to the primary metathesis product increases to 46%. Both the spent catalyst and the regenerated catalyst have about 46% coke formation after deactivation.
Keywords: Tungsten oxide; Heterogeneous; Metathesis; Optimization; Coke formation;
Application of a WO3/SiO2 catalyst in an industrial environment: part II by A. Spamer; T.I. Dube; D.J. Moodley; C. van Schalkwyk; J.M. Botha (133-142).
During investigations into the activity of the 8% WO3/SiO2 catalyst it was observed that the selectivity and online lifetime of the catalyst improved, while the overall feed conversion decreased slightly after the first regeneration. It was further observed that the online lifetime of the catalyst was different after the first regeneration of the catalyst. Analysis of the fresh, coked and regenerated catalyst did not show any sintering of the catalyst taking place. It was concluded that coking of the catalyst is mostly occurring in the pores of the support. Analysis also indicated a possible change in the morphology of the catalyst after the first regeneration. The purpose of this investigation is to highlight the significant effect that regeneration has on the lifetime and selectivity of a WO3/SiO2 metathesis catalyst.
Keywords: Tungsten oxide; Heterogeneous; Metathesis; Reduction; Coke formation;
Factors that could influence the activity of a WO3/SiO2 catalyst: Part III by C. van Schalkwyk; A. Spamer; D.J. Moodley; T. Dube; J. Reynhardt; J.M. Botha; H.C.M. Vosloo (143-152).
An 8% WO3/SiO2 catalyst was used for a metathesis reaction of 1-octene in the presence of different additives. These additives represents the possible components in an industrial 1-heptene feed stream that might have an influence on the performance of a WO3/SiO2 metathesis catalyst. The reaction conditions for the metathesis reaction in a once-through mode reactor were 460 °C and a Liquid Hour Space Velocity (LHSV) of 5 h−1. The operating conditions for the recycle reactor were 460 °C, LHSV=16 h−1 and a feed to recycle ratio of 1:5.6. The oxygenates used for the poison testing were 2-pentanone, hexanal, acetic acid, butanol and water. Both Brønsted acids and Lewis bases used, slows the reaction rate down if the amount of oxygenates are more than 500 ppm. The reaction was unstable with more than 500 ppm of oxygenates present in the feed, but this resulted in a product with a clearer colour (more colourless). Changing the feed back to pure feed resulted in reactivation of the catalyst. The catalyst was thereafter more selective and active towards the primary metathesis products, indication a permanent change in morphology of the catalyst.
Keywords: Tungsten oxide; Heterogeneous; Metathesis; Deactivation;
The reduction of isomerisation activity on a WO3/SiO2 metathesis catalyst by A Spamer; T.I Dube; D.J Moodley; C van Schalkwyk; J.M Botha (153-167).
By increasing the WO3 loading on WO3/SiO2 metathesis catalysts it was observed that metathesis activity is closely related to the tungsten surface compound and not to the crystalline WO3. It was observed that metathesis activity reached a maximum while WO3 crystalline material continued to increase with increasing WO3 loading. At high WO3 loadings the formation of crystalline material also protected the active tungsten surface compound from deactivation by being the preferred species for over-reduction. The occurrence of branched metathesis products was attributed to an increase in Brønsted acidity indicating an alkoxide (carbenium ion) mechanism responsible for skeletal isomerisation. Reduction of branched metathesis products were achieved with the addition of small amounts of an alkali-metal ion. Large amounts of the alkali-metal ion resulted in a sharp decline in conversion indicating destruction of the Lewis acidity necessary for metathesis activity. Preparation of WO3/SiO2 catalysts at a pH above the iso-electric point of silica also had a significant effect on catalyst selectivity.
Keywords: Tungsten oxide; Heterogeneous; Metathesis; Isomerisation; Mechanism; Alkali-metal;
Catalyst development for the gasification of biomass in the dual-bed gasifier by Mohammad Asadullah; Tomohisa Miyazawa; Shin-ichi Ito; Kimio Kunimori; Muneyoshi Yamada; Keiichi Tomishige (169-180).
A dual-bed gasifier system combined with catalysts was evaluated in the catalytic gasification of cedar wood at low temperatures (823–973 K). The dual-bed gasifier consisted of a primary-bed section for pyrolysis of biomass and separation of pyrolyzed gas and tar from solid products and a secondary-catalytic tar reformer. Catalyst development was carried out on the basis of Rh/CeO2/SiO2, which has been developed for the higher conversion of carbon to gas and higher yield of CO+H2+CH4. We have also carried out the optimization of reaction conditions. Especially, the tar derived from maximum of 250 mg biomass/min can be totally converted to the gas product by 3 g catalyst in this system using ER=0.25 of total carbon present in the biomass. This performance was much higher than that over commercial steam reforming catalyst. In addition, the amount of coke deposited on Rh/CeO2/SiO2 was much smaller. In the dual-bed system combined with excellent catalysts, almost all the tar can be converted to syngas at lower temperature than that needed by the conventional method with high energy efficiency.
Keywords: Biomass; Catalytic gasification; Synthesis gas; Fluidized bed; Dual-bed; Rhodium; Cerium oxide;
Infrared study of the adsorption of formic acid on clean and Ca-promoted Pd/SiO2 catalysts by Griselda C Cabilla; Adrian L Bonivardi; Miguel A Baltanás (181-195).
The adsorption and decomposition of formic acid on a highly dispersed supported Pd/SiO2 catalyst (2 wt.% Pd) prepared via ion exchange (IE) of [Pd(NH3)4]2+ in alkaline solution, together with two Ca-promoted preparations (Ca/Pd=2 at./at.) where calcium was added either to the prereduced Pd crystallites or to the diammine palladium complex, were studied by FTIR at 298–653 K.On the support, HCOOH is mostly adsorbed molecularly at room temperature, with partial dimerization, condensation and extensive hydrogen bonding, but readily decomposes, on the Pd crystallites of Pd/SiO2, via decarbonylation, to give CO multicoordinated to the metal surface, and water. With heating, formic acid decomposition is accompanied by some water gas shift as well, while CO reacts to give methyl (methane) and methoxy.Calcium promotion to both the prereduced Pd and its diammine complex precursor, enhanced HCOOH decomposition onto the catalyst surface, even at 298 K. Together with sorbed HCOOH and chemisorbed CO, mono- and bidentate formates were observed on these materials, owing to the incorporation of well-dispersed CaO x H y . These formates were readily decomposed by atomic hydrogen produced by decarbonylation/WGS of formic acid on Pd. At increasing temperatures, some carbonates (polydentate and simple) were formed, but hardly any methane was detected. On Ca–Pd/SiO2 with calcium added to prereduced Pd metal particles the extension and/or onset of all these processes was more straightforward than on the promoted Ca–Pd/SiO2 where calcium was added to diammine palladium instead, most likely owing to the combined impact of a higher dispersion of the Pd crystallites on the former preparation, and calcium oxyhydroxide decoration (CaO x H y ) of the metal particles on the latter, which hamper H-spillover from them.
Keywords: Syn-gas conversion; CO2 hydrogenation; FTIR spectroscopy; Supported palladium; Calcium promotion; Formic acid adsorption;
Synthesis of diphenylamine catalyzed by zeolites by Milan Hronec; Zuzana Cvengrošová; Jiřı́ Čejka (197-202).
Catalytic activity of various molecular sieves, activated bentonite and BF3 .etherate was investigated in the condensation of aniline to diphenylamine. Among the tested catalysts, the zeolite Beta with a Si/Al atomic ratio of 12.5 exhibited the highest activity (ca. 34% aniline conversion) and selectivity (above 98%) for diphenylamine formation. Zeolites Beta with higher Si/Al atomic ratio were less active but the selectivity to diphenylamine remained almost the same. It is assumed that the differences in the catalytic activities of molecular sieves are not caused only by the differences in the pore geometry but depends also on the concentration of acid sites. The type of acid sites, Bronsted or Lewis sites, does not significantly influence the catalytic performance. Strong acid sites prepared by activation of bentonite with hydrochloric acid are probably responsible for the formation of by-products and the resulting catalyst is, thus, less selective to diphenylamine formation.
Keywords: Zeolites beta; Bentonite; Bronsted site;
Novel boron trifluoride cocatalyst for norbornene polymerization by G. Myagmarsuren; O-Yong Jeong; Son-Ki Ihm (203-209).
A simple Lewis acid, boron trifluoride etherate, was applied as novel activator towards a new nickel precursor Ni(PPh3)4 for the polymerization of norbornene. The system Ni(PPh3)4/BF3OEt2 is highly active in the polymerization of norbornene. The product obtained showed exclusively 2,3-connectivity of polymer backbone. Catalyst activities up to 4200 kg/(mol Ni h) and intrinsic viscosities up to 1.30 dl/g were observed at appropriate conditions. The catalytic activity of the system is comparable to that of the most active nickel systems with traditional MAO activators. Catalyst activity and polymer molecular weight can be controlled by variation of the reaction parameters over a wide range. Polymer characterization was carried out by IR, 1 H and 13 C NMR, TGA, DSC, and viscosimetry. Nickel hydrides are likely to be catalytically active species.
Keywords: Boron trifluoride; Cocatalyst; Nickel; Norbornene; Polymerization;
Role of vanadium in Ni:Al2O3 catalysts for carbon dioxide reforming of methane by Antoninho Valentini; Neftalı́ Lenin Villarreal Carreño; Luiz Fernando Dias Probst; Paulo N Lisboa-Filho; Wido H Schreiner; Edson Roberto Leite; Elson Longo (211-220).
The CO2 reforming of CH4 was performed over V-promoted Ni/Al2O3 catalysts similarly prepared by the polymeric precursor method. The H2 chemisorption, X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) analyses show that a low V wt.% addition suppresses the NiAl2O4 formation. Moreover, the CHN results point out to a low carbon deposition and the surface area (BET) abruptly increases upon the addition of 0.8 wt.% V. On the other hand, the sample with high V wt.% presented the highest carbon deposition, what was attributed to the CH4 decomposition increase promoted by the V.
Keywords: Methane; CO2 reforming; V-promoted Ni/Al2O3; Coke deposition;
Photoelectrocatalytic degradation of reactive brilliant orange K-R in a new continuous flow photoelectrocatalytic reactor by Wenbing Zhang; Taicheng An; Xianming Xiao; Jiamo Fu; Guoying Sheng; Mingchao Cui; Guiying Li (221-229).
A new continuous flow three-dimensional electrode-packed bed photocatalytic reactor was developed to investigate the feasibility of an electrochemically assisted photocatalytic process in the degradation of reactive brilliant orange K-R dye in 0.5 mmol l−1 NaCl solution. It was found that the dye could be degraded more efficiently by this photoelectrochemical process than the degradation obtained by photocatalytic oxidation or by electrochemical oxidation alone, in terms of both decolorization and TOC removal. Various parameters, such as applied cell voltage, initial concentration of chloride ion and the dye, pH value and airflow were the major factors affecting the oxidation rate of the dye. It is interesting to find that an obvious enhancement effect rather than a scavenging effect on the photoelectrocatalytic degradation of the dye in a salt solution was obtained in the new-designed photoelectrocatalytic reactor.
Keywords: Photoelectrocatalytic; Photocatalytic; Reactor; Dye; Wastewater;
Solubility measurements of isobutane/alkenes in sulfuric acid: applications to alkylation by Wen-Shing Chen (231-237).
An easy experimental method to measure the solubility of isobutane/alkenes in sulfuric acid is established. By addition of minor amounts of anionic, cationic or ampholytic surfactants, the solubility value of isobutane/alkenes changes; that also influences the yield pattern of sulfuric-acid catalyzed alkylation reaction. According to solubility parameters, some additives are evaluated to enhance the solubility ratios of isobutane/alkenes. This gives rise to an improvement of the higher selectivity to trimethylpentanes; the research octane number is between 100 and 110 and the material is an excellent component of gasoline. These additives are applied to isopentane/alkenes alkylation reaction simultaneously. It was found that the quality of alkylate gets better, due to the obvious decrease of the yield of heavy end materials (C10+). These facts reveal the industrially practical of solubility parameter and additives. Meanwhile, the yield of trimethylpentane is related linearly with the solubility ratio of isobutane/alkenes.
Keywords: Alkylation; Sulfuric acid; Isobutane/alkenes solubility ratio;
The effect of Mo2C synthesis and pretreatment on catalytic stability in oxidative reforming environments by David C LaMont; Andrew J Gilligan; Anna R.S Darujati; Anand S Chellappa; William J Thomson (239-253).
The role of catalyst pretreatment on the stability of Mo2C catalysts in oxidative reforming environments has been studied. Catalysts were produced by both the temperature programmed reaction (TPR) and a solution-derived (SD) synthesis method, and compared to a low surface area commercial catalyst. Using a variety of techniques, including in situ dynamic X-ray diffraction (DXRD), the effects of various hydrogen pretreatment protocols were evaluated, including catalyst thermal stability, oxidation resistance and susceptibility to coking. The high surface areas produced by the SD synthesis is attributed to the presence of excess synthesis carbon and, whereas the presence of excess synthesis carbon enhances thermal stability, it also appears to accelerate coking. It is pointed out that the lowered oxidation resistance of the high surface area catalysts is due to a combination of smaller crystallite sizes and competitive oxidation of the excess synthesis carbon, which alters the oxidation mechanism. In addition, it was also found that incomplete carburization during TPR synthesis, forms an oxycarbide and its acidity also promotes coking. Hydrogen pretreatment at 700 °C not only removes all excess synthesis carbon, but it also reduces the oxycarbide to Mo, which is easily carburized under reforming conditions. Pretreatment at 600 °C, was largely ineffective and it is concluded that high temperature pretreatment is necessary to form the stoichiometric carbide, which is required for stability during reforming. Both the TPR and SD catalysts pretreated at 700 °C, were found to be stable over a 72 h period, whereas the commercial carbide had almost identical activity but slowly deactivated over the same period, probably because of its low surface area. Finally, labeled isotope experiments revealed that carbon exchange occurs readily with bulk Mo2C at temperatures above 550 °C, lending credence to a reforming redox mechanism.
Keywords: Molybdenum carbide; Dry methane reforming; Excess carbon; Pretreatment; Oxidation; Stability; TPR; Solution synthesis; Dynamic X-ray diffraction;
Effect of the compensating cation on the adsorption of t-butylchloride on zeolite Y by Rodrigo J. Correa; Claudio J.A. Mota (255-264).
Adsorption of t-butylchloride on a series of metal-exchanged Y zeolite (Na+, Ag+, Cu2+, Fe3+) was studied by infrared spectroscopy, at different temperatures. At 148 K, the adsorption of t-butylchloride on NaY and AgY zeolites forms isobutene as main product, characterized by a band a 1639 cm−1. Upon increasing of temperature the isobutene forms an alkoxide and oligomerizes on the zeolite surface. On CuY and FeY zeolites no significant olefinic band was observed at 148 K upon adsorption of the t-butylchloride, although bands relative to CH stretching and bending vibrations could be easily observed. Upon increasing the temperature to 298 K, both zeolites give rise to olefinic bands. The results suggest that on NaY and AgY zeolite, proton elimination is the main pathway, while on CuY and FeY, formation of an adsorbed t-butoxy group is preferential at low temperature. In all zeolites, at room temperature, oligomerization occurs. This was confirmed by co-adsorption of t-butylchloride with 2-methyl-1-butene, showing that olefin was consumed.
Keywords: Zeolite Y; t-Butylchloride; Adsorption; Alkoxide; Elimination;
Isoamyl acetate production catalyzed by H3PW12O40 on their partially substituted Cs or K salts by Luis R Pizzio; Mirta N Blanco (265-277).
The Cs2.9H0.1PW12O40, Cs2.6H0.4PW12O40, K2.9H0.1PW12O40 and K2.5H0.5PW12O40 salts were synthesized and impregnated by means of the incipient wetness method with a H3PW12O40 solution in ethanol–water. The solids were characterized by N2 adsorption–desorption isotherms, FT-IR, XRD, 31 P MAS–NMR, thermogravimetric and differential thermal analysis, and the acidic behavior was studied by potentiometric titration with n-butylamine and isopropanol dehydration. The proton content evaluated from the thermogravimetric weight loss in the temperature zone ascribed to the deprotonation step showed a good agreement with the values drawn from the synthesis stoichiometry. The physical–chemical characterization led to establish the presence of the Keggin salt structure and well dispersed acid impregnated on the partially substituted salts. The mainly microporous salts as well as the impregnated salts possessed higher acidity than the bulk acid. Their catalytic activity in the esterification of acetic acid and isoamyl alcohol to obtain isoamyl acetate showed a straight correlation with the acidic characteristics of the studied solids. Both the high conversion and selectivity obtained are important results for the use of these type of heteropolycompounds mainly in the flavor and fragrances industries.
Keywords: Esterification; Partially substituted Keggin salts; Cesium Keggin salts; Potassium Keggin salts; Catalysts; Isoamyl acetate;
Experimental investigation of the activity and thermal stability of hexaaluminate catalysts for lean methane–air combustion by Roderick W Sidwell; Huayang Zhu; Brian A Kibler; Robert J Kee; David T Wickham (279-288).
This paper reports a quantitative comparison between two metal-substituted hexaaluminate catalysts and supported Pd catalyst (3 wt.% Pd/γ-Al2O3). Measured species profiles in stagnation-flow boundary layers are used to infer reaction rates by heterogeneous catalysis. The Pd-substituted material (Sr0.5Pd0.5Al11O18−α ) is suitable for low-temperature operation and the La x Sr y Mn0.4Al11O18−α (x/y=0.8, 0.9, and 1.1) material is a good high-temperature catalyst. A wide range of operating temperatures and methane-air equivalence ratios are considered. The La x Sr y Mn0.4Al11O18−α catalysts show good catalytic activity at temperatures up to 1100 °C and are insensitive to La/Sr ratio and coating thickness. The supported-Pd catalyst and the Sr0.5Pd0.5Al11O18−α exhibit similar hysteresis characteristics when exposed to temperatures around 900 °C. The supported Pd deactivates upon exposure to temperatures above 900 °C, but the Pd-substituted hexaaluminate maintains good catalytic activity after high-temperature exposure. The supported Pd is generally more active than either hexaaluminate, but can suffer permanent deactivation upon high temperature exposure.
Keywords: Hexaaluminate catalysts; Stagnation-point flow; Catalytic combustion; Thermal stability;
Influence of the reaction conditions on the activity properties of vanadium–aluminium oxynitride propane ammoxidation catalyst by Mihaela Florea; Ricardo Prada Silvy; Paul Grange (289-300).
The influence of different reaction conditions on the catalytic activity of vanadium–aluminium oxynitride “VAlON” in propane ammoxidation is investigated. This new catalytic material exhibits amorphous character, high specific surface area, basic-redox properties and remarkable acrylonitrile production per hour and amount of catalyst. Optimal performance is achieved when the reaction temperature is 500 °C and the molar ratio of propane, oxygen, and ammonia in the gas feed is 1.25:3:1. Under these optimal reaction conditions, the catalyst showed a propane conversion level of 60%, an acrylonitrile selectivity of 56%, and an acrylonitrile productivity of 812 l/kg h. The formation of a propylene intermediate compound as well as hydrogen cyanide was detected only for those reaction conditions where the NH3:C3H8 ratio was lower than 1. This suggests differences in the reaction mechanism with respect to conventional V–Me-oxide propane ammoxidation catalysts. In propane ammoxidation over VAlON catalysts, ammonia seems to play a double role: (i) as a reagent necessary for the thermal nitridation and generation of nitrogen species, (ii) participating in N-insertion step for the acrylonitrile formation from propane. The catalytic performances depend on the generation of nitrogen species as a function of the reaction conditions, which determine the level of propane conversion and selectivity to the reaction products.
Keywords: Oxynitride catalysts; Nitrogen species; Contact time; Propane ammoxidation;
Catalytic hydrogen transfer from 2-propanol to cyclohexanone over basic Mg–Al oxides by Marı́a A Aramendı́a; Victoriano Borau; César Jiménez; José M Marinas; José R Ruiz; Francisco J Urbano (301-308).
Magnesium–aluminium mixed oxides in mole ratios from 2 to 4 were obtained by thermal decomposition of layered double hydroxides (LDHs) as precursors. The effect of the Mg/Al ratio on the structure and surface properties of the resulting oxides was studied by using various instrumental techniques including X-ray diffraction (XRD), thermogravimetric analyses (TGA), MAS NMR, X-ray photoelectron spectroscopy (XPS) and gas adsorption–desorption, and so was their influence on the catalytic activity of the solids in the hydrogen transfer from 2-propanol to cyclohexanone. The results were compared with those for a pure MgO oxide and the Mg–Al mixed oxide obtained from the LDH with an Mg/Al ratio of 2 was found to provide the best catalytic activity. The influence on catalytic activity of other experimental variables including the pH of the medium used to synthesize the precursor LDHs, the temperature employed to prepare the Mg–Al oxides and the amount of catalyst used was also examined. Catalyst recycling tests were also conducted. Based on the results, a mechanism is proposed for the overall catalytic hydrogen transfer.
Keywords: Layered double hydroxides; Calcination; Decomposition;
Effects of alcohol content and calcination temperature on the textural properties of bimodally mesoporous titania by Jiaguo Yu; Jimmy C. Yu; Wingkei Ho; Mitch K.-P. Leung; Bei Cheng; Gaoke Zhang; Xiujian Zhao (309-320).
Bimodally mesoporous titania was prepared by hydrolysis of titanium tetraisopropoxide in pure water or the EtOH–H2O mixed solution under ultrasonic irradiation. Effects of alcohol content and calcination temperature on the phase composition and porosity of bimodally mesoporous titania was investigated by thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface areas. The results showed that for all TiO2 powders calcined from 400 to 600 °C, the pore size distribution is bimodal with fine intra-particle pore diameter at maximum pore diameters of ca. 2–4 nm and larger inter-particle pore diameter at maximum pore diameters of ca. 18–50 nm. The EtOH/H2O molar ratios obviously influenced the crystallization, crystallite size, BET surface areas, porosity and morphology of the prepared TiO2 powders.
Keywords: Bimodally mesoporous titania; Titanium tetraisopropoxide; Hydrolysis; Calcination temperature; Water content; Porosity; Phase composition;
Effect of the preparation of Ir-Mo/Al2O3 sulfide catalyst on activity and HDN/HDS selectivity by Josef Cinibulk; Daniela Gulková; Yuji Yoshimura; Zdeněk Vı́t (321-329).
Two series of the mixed Ir-Mo/Al2O3 catalysts of different Ir loading (0.1–0.7 wt.%) were prepared by deposition of Ir4(CO)12 on an oxidic and sulfidic Mo/Al2O3 catalyst. The catalysts were tested in the hydrodesulfurization (HDS) of thiophene (TH) and hydrodenitrogenation (HDN) of pyridine (PY) and characterized by transmission electron microscopy (TEM), temperature-programmed reduction (TPR) and X-ray diffraction (XRD). It was found that Ir addition to a Mo/Al2O3 catalyst had positive effect on the activities in both reactions. A much larger effect was observed when Ir was deposited on the presulfided instead of oxidic Mo/Al2O3 catalyst. In the former case, the mixed catalysts displayed a synergism between Ir and Mo of about 3. We ascribe the higher activities of the catalysts prepared from the presulfided Mo sample to higher dispersion of the Ir sulfide phase. In addition, sulfidation of the Mo/Al2O3 probably protected the Mo phase against interaction with Ir4(CO)12, which could lead to partial formation of MoO2. It is assumed that both factors improved the reducibility of the sulfur surface species of the MoS2 phase and contributed in this way to higher catalytic activity.
Keywords: Hydrodesulfurization; Hydrodenitrogenation; Mo sulfide; Iridium; Ir-Mo/Al2O3 catalyst;
Comparative study of CuO/Ce0.7Sn0.3O2, CuO/CeO2 and CuO/SnO2 catalysts for low-temperature CO oxidation by Rui Lin; Meng-Fei Luo; Yi-Jun Zhong; Zong-Lan Yan; Guang-Yu Liu; Wei-Ping Liu (331-336).
CuO/Ce0.7Sn0.3O2, CuO/CeO2 and CuO/SnO2 catalysts were prepared using impregnation methods. The catalysts were characterized by means of H2-TPR, X-ray diffraction (XRD) and CO-TPD studies. CuO/Ce0.7Sn0.3O2 catalysts have three reduction peaks, α, β, and γ. The α peak is attributed to the reduction of CuO and Sn4+ species on the surface of Ce0.7Sn0.3O2, β peak to the reduction of bulk SnO2 and surface Ce4+, γ peak to the reduction of bulk CeO2. Only a small amount of CuO (6%) is needed to form the active site for CO oxidation, and the excess CuO forms bulk CuO particles which contribute little to the activity. Combining the results of CO-TPD, XRD and catalytic activity measurements, we propose that the well-dispersed CuO, which can adsorb CO, is responsible for low-temperature CO oxidation. The bulk CuO that cannot adsorb CO contributes little to the oxidation activity. Among the supported CuO catalysts, a synergistic interaction between CuO and Ce0.7Sn0.3O2 makes the reduced CuO/Ce0.7Sn0.3O2 catalyst easily oxidized, thus it can easily supply active species. This is responsible for the highest CO oxidation activity at low-temperature.
Keywords: CuO/Ce0.7Sn0.3O2 catalysts; CO-TPD; H2-TPR; TPO; CO oxidation;
Alkylation of 1,3,5-trimethylbenzene with γ-butyrolactone over heteropolyacid catalysts by Jianxin Mao; Yuichi Kamiya; Toshio Okuhara (337-344).
A Friedel–Crafts-type reaction of 1,3,5-trimethylbenzene with γ-butyrolactone was conducted over various solid acid catalysts such as zeolites, polymer resins, and heteropolyacids. The alkylation to 4-(2,4,6-trimethylphenyl) butyric acid proceeded exclusively with these catalysts; no acylation to the ketone occurred. The heteropolyacids, such as H3PW12O40 and H4SiW12O40, were superior in activity to the other catalysts; they also accelerated the reaction of the product acid with γ-butyrolactone to the corresponding carboxylic acid. When the heteropolyacids were supported on silica, alkylation proceeded efficiently with high mass balance, suppressing further reaction. The reusability of the supported heteropolyacids also was confirmed.
Keywords: Friedel–Crafts reaction; Alkylation; 1,3,5-Trimethylbenzene; γ-Butyrolactone; Heteropolyacids; Zeolite; Nafion-H;
Exploratory study on upgrading 1-butene using spent FCC catalyst/additive under simulated conditions of FCCU’s stripper by Yong Lu; Ming-Yuan He; Xing-Tian Shu; Bao-Ning Zong (345-347).
A novel method for upgrading n-butene into more useful propylene, iso-butene, iso-butane even gasoline using spent fluid catalytic cracking (FCC) catalysts/additives in the stripper part of fluid catalytic cracking unit (FCCU) has been proposed. The simulative tests were carried out on a widely used MAT equipment, using 1-butene as feed. High temperature and low space velocity favor the formation of propylene, iso-butene and iso-butane. The presence of MFI additives promotes propylene and iso-butene but suppresses iso-butane formation.
Keywords: FCC catalyst/additive; Stripper; Butene; Propylene; iso-Butane;
Oligomerization as an important step and side reaction for skeletal isomerization of linear butenes on H-ZSM-5 by Olaf Klepel; Andrei Loubentsov; Winfried Böhlmann; Helmut Papp (349-354).
The skeletal isomerization of n-butenes on a H-ZSM-5 zeolite with high Si/Al ratio was investigated by using a gradientless recirculation batch reactor. It was concluded that at the very beginning of the reaction, the formation of C8 surface species should be the first step. These species decompose into propene and pentenes, one part of the just formed and still adsorbed C3 species immediately dimerizes to hexenes. In the further course of reaction, an oligomerization to C12 surface species (trimerization) occurs followed by decomposition as shown by the products pentenes, hexenes, and heptenes. The tendency to oligomerization decreased with increasing temperature. For the reaction of lower olefins like propene and ethene, the reaction course was the same as it was observed for n-butene: a gradual increase of the degree of oligomerization with reaction time followed by immediate decomposition.
Keywords: Butene; Isomerization; Gradientless recirculation batch reactor;
Ethylene trimerisation catalyst based on substituted cyclopentadienes by Hamdani Mahomed; Annette Bollmann; John T Dixon; Vikash Gokul; Louisa Griesel; Cronje Grove; Fiona Hess; Hulisani Maumela; Lana Pepler (355-359).
A four-component homogeneous catalyst system comprising a substituted cyclopentadiene ligand, a chromium compound, an alkyl aluminium and a halogen source is effective for the trimerisation of ethylene to 1-hexene in good selectivity and activity. In a typical example a catalyst system containing chromium(III) tris (2-ethylhexanoate), 1,2,3,4,5-pentaphenylcyclopenta-1,3-diene, hexachloroethane and triethylaluminium produced 1-hexene in up to 76 mass%, at an activity of 40 700 g of product/(g Cr h). Approximately 15 mass per cent of internal hexenes are also produced as well as smaller quantities of C-10’s and polyethylene. The effect of changes in temperature, pressure and reagent ratios has been investigated as well as the use of other substituted cyclopentadienes.
Keywords: Trimerisation; 1-Hexene; Chromium cyclopentadiene-based catalyst; Alkyl aluminium; Cyclopentadiene; Oligomerisation;
Erratum to “Kinetics of liquid-phase hydrogenation reactions over supported metal catalyst—a review” [Appl. Catal. A: Gen. 213 (2001) 1–24] by Utpal K. Singh; M.Albert Vannice (361).
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