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Applied Catalysis A, General (v.297, #2)
Preparation of a hybrid organic–inorganic material containing macrocyclic triolefinic 15-membered palladium(0) complex by Belén Blanco; Marina Brissart; Marcial Moreno-Mañas; Roser Pleixats; Ahmad Mehdi; Catherine Reyé; Sandrine Bouquillon; Françoise Hénin; Jacques Muzart (pp. 117-124).
The synthesis of a bis-silylated 15-membered azatriolefinic macrocycle is described as well as its co-gelification with tetraethyl orthosilicate. The resulting material was treated with Pd(dba)2 affording an hybrid organic–inorganic material containing macrocyclic palladium(0) complex covalently bonded to the silica matrix. The activity of this material as catalyst or precatalyst in Suzuki cross-coupling and telomerization of butadiene with methanol and phenol is presented.
Keywords: Cross-coupling; Macrocycles; Palladium supported catalyst; Sol–gel processes; Telomerization
Soot combustion with K/MgO as catalyst by Romel Jiménez; Ximena García; C. Cellier; Patricio Ruiz; Alfredo L. Gordon (pp. 125-134).
The catalytic combustion of carbon black (CB), a model compound for soot, was studied in the presence of MgO and of KOH/MgO, the latter prepared by impregnation of MgO with an aqueous solution of KOH. The catalysts were characterized by atomic absorption spectroscopy, thermal programmed desorption, carbothermic reduction, X-ray photoelectron spectroscopy, diffuse reflectance FT-infrared spectroscopy and X-ray diffraction. The addition of potassium to MgO shows significant catalytic activity for CB combustion. The role of potassium can be attributed to: (i) an important increase of oxygen concentration on the surface of the catalyst, (ii) an interaction between K and MgO which leads to a weakening of the MgO bonds, thus facilitating the formation and migration of oxygen species on the surface; this migration might be a rate-limiting step in the combustion and (iii) an easier decomposition of carbonates which takes place at lower temperature than on MgO.Furthermore, the KOH/MgO catalyst showed a high stability, as its activity was kept constant during isothermic cycles of CB combustion in air.
Keywords: Soot; Catalytic combustion; Potassium; Mechanisms
The state of (K)(Ni)Mo/γ-Al2O3 catalysts after water–gas shift reaction in the presence of sulfur in the feed: XPS and EPR study by D. Nikolova; R. Edreva-Kardjieva; G. Gouliev; T. Grozeva; P. Tzvetkov (pp. 135-144).
The one-, bi- and tri-component (K)(Ni)(Mo)/γ-Al2O3 systems are studied after water–gas shift reaction tests in the presence of sulfur in the feed. The samples are characterized after the calcination procedure (oxidic state) and after the catalytic activity test (tested state) by SSA, XRD, XPS and EPR measurements. The Mo4+, Mo5+ and Mo6+ oxidation states are registered on the surface of the tested samples. The different sulfur species such as: sulfide sulfur, oxysulfides, polysulfides, paramagnetic sulfur and sulfate sulfur are present on the sample surface in the reaction redox environment (CO, H2O, H2S, H2 and CO2 agents). The XPS and EPR characterization of the tested state points to the idea that both the molybdenum reducibility (i.e. the Mo4+/(Mo5++Mo6+) and Mo4+/Mo5+ ratios) and the sulfur lability (sulfide/sulfate ratio) represent informative indices in regard to the catalytic properties of the Mo-containing systems in the WGS reaction in case of sulfur presence in the feed mixture.
Keywords: Water–gas shift reaction; (K)(Ni)(Mo)/γ-Al; 2; O; 3; systems; Sulphur-tolerant catalysts; Molybdenum reducibility; Sulfur lability
Silication of γ-alumina catalyst during the dehydration of linear primary alcohols by N.P. Makgoba; T.M. Sakuneka; J.G. Koortzen; C. van Schalkwyk; J.M. Botha; C.P. Nicolaides (pp. 145-150).
The dehydration of alcohols to alkenes over heterogeneous catalysts such as γ-alumina occurs at temperatures of around 300°C, and it could be accompanied by undesirable reactions such as double-bond shift and, in severe cases, skeletal isomerization of the alkene products. In the dehydration of 1-hexanol and of 1-octanol (separately) over γ-alumina, we found that the selectivity to 1-alkenes decreased substantially with time-on-stream (TOS), while the alcohol conversion remained virtually constant. The loss in 1-alkene selectivity is a result of an increase in the extent of double-bond isomerization with increasing TOS. Upon analysis of the catalysts (fresh and used) and of the alcohol feeds (all by ICP spectroscopy), it was found that the feeds contained on average 1ppm silicon and that the silicon content in the used catalysts was as high as 15 times that in the fresh one (3000ppm as compared to 200ppm, in one of our examples). The results show, therefore, that there is accumulation of silicon on the catalyst during the reaction and that this leads to the formation of additional and stronger acid sites, such as those found in silicated aluminas, which account for the increasing isomerization activity of the γ-alumina catalyst.
Keywords: Silicon; Alumina; Alcohol dehydration; 1-Hexene; 1-Octene; 1-Hexanol; 1-Octanol
Effect of preparation method on the hydrogen production from methanol steam reforming over binary Cu/ZrO2 catalysts by Cheng-Zhang Yao; Lu-Cun Wang; Yong-Mei Liu; Gui-Sheng Wu; Yong Cao; Wei-Lin Dai; He-Yong He; Kang-Nian Fan (pp. 151-158).
Several methods (impregnation, oxalate gel–coprecipitation and conventional aqueous coprecipitation) have been comparatively examined for the preparation of binary Cu/ZrO2 catalysts for the catalytic production of hydrogen by steam reforming of methanol (SRM). A variety of techniques including N2 adsorption, XRD, N2O chemisorption, XRD, H2-TPR, and XPS were used to characterize the physical and chemical properties of the as-obtained catalysts. The results show that the preparation method significantly affects the component dispersion, microstructural properties and the resulting catalytic performance with respect to methanol conversion, H2 production and CO concentration. The catalyst with higher specific copper surface area and component dispersion shows higher activity for methanol conversion at lower temperature. The best Cu/ZrO2 catalyst has been prepared by an oxalate gel–coprecipitation method, which shows much higher catalytic activity and enhanced long-term stability in the SRM reaction as compared to the catalysts prepared by conventional aqueous–coprecipitation and impregnation methods.
Keywords: Hydrogen production; Steam reforming of methanol; Binary Cu/ZrO; 2; catalysts; Oxalate gel–coprecipitation
Highly active, selective and stable Mo/Ru-HZSM-5 catalysts for oxygen-free methane aromatization by Azfar Hassan; Abdelhamid Sayari (pp. 159-164).
Highly active, selective and stable catalysts for oxygen-free methane aromatization were prepared by using ion-exchange and vapor deposition techniques rather than the conventional metal impregnation methods. Ruthenium (0.15wt%) was incorporated first to ZSM-5 as a promoter by ion-exchange at room temperature. Then 1–3wt% of Mo was loaded using Mo(CO)6 as a Mo precursor. High benzene yields of 4.0–4.2% using a 1.5–2wt% Mo catalyst were achieved at 600°C with methane flow rate of 270cm3/gh and 1atm pressure. Effect of changes in the pretreatment conditions (carburization time) was also investigated. Slower heating rates decreased the induction time and improved benzene yield. Mo loading beyond 2.5wt% led to lower methane conversions. Temperature-programmed oxidation technique was used to characterize the nature of coke formed on spent catalysts. The amount of coke formed was negligible, resulting in high catalyst performance.
Keywords: Methane aromatization; ZSM-5 zeolite; Mo/Ru-HZSM-5; Molybdenum hexacarbonyl; TPO characterization
Alumina-catalysed degradation of ethyl pyruvate during enantioselective hydrogenation over Pt/alumina and its inhibition by acetic acid by D. Ferri; S. Diezi; M. Maciejewski; A. Baiker (pp. 165-173).
In situ ATR-IR spectroscopy combined with catalytic hydrogenation, ex situ DRIFT spectroscopy and pulse thermal analysis have been applied to investigate the fate of ethyl pyruvate during enantioselective hydrogenation on Pt/Al2O3. ATR-IR investigations indicate that besides platinum-catalysed decomposition/polymerisation ethyl pyruvate can also undergo alumina-catalysed degradation reactions such as aldol type condensation leading to polymeric surface species. Related DRIFT and thermoanalytical measurements of the catalyst after use in enantioselective hydrogenation at different conditions corroborated that side reactions occur irrespective of pressure, solvent and presence or absence of chiral modifier (cinchonidine). The presence of (CO) and (CC)containing species and of carboxylates were observed during ATR-IR measurements and on catalysts recovered after use in hydrogenation. The carbon content of these species amounted to ca. 3wt.% of the used catalyst, as determined from the CO2 evolution upon combustion. Interestingly, acetic acid, the most suitable solvent for the enantioselective hydrogenation of ethyl pyruvate, was found to suppress the degradation reactions, adding a new facet to the beneficial role of this solvent. The implications of the occurrence of degradation reactions of ethyl pyruvate on Pt/Al2O3 on the behaviour of this catalytic system in enantioselective hydrogenation are discussed.
Keywords: In situ ATR-IR; DRIFT; Pulse thermal analysis; Ethyl pyruvate degradation; Enantioselective hydrogenation; Pt/Al; 2; O; 3; Aldol condensation; Acetic acid adsorption
Oxidation and oligomerization of ethyl linoleate under the influence of the combination of ascorbic acid 6-palmitate/iron-2-ethylhexanoate by Fabrizio Miccichè; Jacco van Haveren; Eef Oostveen; Weihua Ming; Rob van der Linde (pp. 174-181).
In this paper we report the oxidation and oligomerization of ethyl linoleate (EL), a model compound for alkyd resins, under the influence of iron-2-ethylhexanoate (Fe-eh) in combination with ascorbic acid 6-palmitate (AsA6p) at different AsA6p/Fe-eh molar ratios (0/1–4/1). Reactions were studied in time by FT-IR, NMR, size exclusion chromatography (SEC) and peroxide amount determination. The oxidation and oligomerization of EL were accelerated by the combination of AsA6p and Fe-eh, and the catalytic properties of the catalysts were strongly dependent on the molar ratio AsA6p/Fe-eh. The molar ratio of 2/1 appeared to be optimal, at which both the oxidation and oligomerization of EL were the fastest. At molar ratio smaller than 2/1, or only in the presence of Fe-eh, the EL oxidation showed a time lag of up to 100h; above the ratio 2/1 the rates of both EL oxidation and oligomerization decreased. Results are explained in terms of the multi-facet role played by AsA6p: its pro-oxidant or anti-oxidant properties, depending on the ratio of AsA6p/Fe-eh, and its effect on the Fe-eh complex.
Keywords: Ethyl linoleate; Iron; Ascorbic acid 6-palmitate; Oxidation
Comparison of commercial solid acid catalysts for the esterification of acetic acid with butanol by Thijs A. Peters; Nieck E. Benes; Anders Holmen; Jos T.F. Keurentjes (pp. 182-188).
Esterification of acetic acid with butanol has been studied in a heterogeneous reaction system, using a variety of solid acid catalysts. Comparative esterification experiments have been carried out using the homogeneous catalysts sulphuric acid, p-toluenesulphuric acid and a heteropolyacid. The catalysts have been characterised using gas adsorption analysis (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM) and temperature-programmed decomposition (TPD) techniques. The weight-based activity of the heterogeneous catalysts decreases in the following order: Smopex-101>Amberlyst 15>sulphated ZrO2>H-USY-20>H-BETA-12.5>H-MOR-45>Nb2O5>H-ZSM-5-12.5. The low activity of ZSM-5 is a result of internal diffusion limitations in the medium sized pores of this zeolite type material. For H-MOR the low activity can be explained by pore blocking in the one-dimensional H-MOR channels. For the H-USY-type zeolites, the influence of the Si/Al ratio on catalytic activity has been examined. Although the amount of acid sites decreases with an increase in the Si/Al ratio, an optimum Si/Al ratio of 20 has been found. The activity of sulphated zirconia shows an optimum calcination temperature, even though both the amount and acidity of the acid sites increase monotonically with calcination temperature. Most likely, at higher calcination temperatures Lewis acid sites are formed and Brønsted acid sites are removed. As Brønsted acid sites are essential for catalysis of esterification reactions this explains the decrease in activity.
Keywords: Esterification; Heterogeneous catalysis; Kinetics; Solid acid catalyst
Reduction of H xMoO3 with different amounts of hydrogen to high surface area molybdenum oxides by Hirotoshi Sakagami; Yoko Asano; Tomoya Ohno; Nobuo Takahashi; Hidenobu Itoh; Takeshi Matsuda (pp. 189-197).
The effect of the amounts of hydrogen in molybdenum bronze on the surface area of its reduction product was studied. H2 reduction of molybdenum bronze induced an increase in the surface area. Molybdenum bronze with the larger amount of hydrogen exhibited the higher surface area after H2 reduction. The reduction process varied with the amount of hydrogen in molybdenum bronze. The formation of MoO2 was suppressed and that of molybdenum oxyhydride, MoO xH y, was promoted by an increase in the amount of hydrogen. Molybdenum bronze decomposed to Mo4O11 and MoO2 on thermal treatment at 400°C in a flow of N2. The surface area of the thermally treated bronze changed very little with H2 reduction. We conclude from these results that the reduction of molybdenum bronze to MoO xH y, of which the formation was dominated by the amount of hydrogen in molybdenum bronze, involved an enlargement in the surface area.
Keywords: Hydrogen molybdenum bronze; H; 2; reduction; Surface area; Molybdenum oxides
Optimal conditions in fluid catalytic cracking: A mechanistic approach by X. Dupain; M. Makkee; J.A. Moulijn (pp. 198-219).
The effects of the catalyst-to-oil ratio (CTO), temperature, residence time, and feed composition on the product selectivities and product distribution in fluid catalytic cracking (FCC) will be discussed. Under simulated realistic conditions two distinctive time frames can be identified. In the ‘initial time-frame’, during the first 50ms of catalyst-oil contact, radical reactions play an important role, leading to the large extent of unselective conversion of the feed to coke, H2, and C1–C4. The presence of catalyst external surface area enhances radical reactions. Coke deposits mainly on the outer surface of the catalyst particle, thereby reducing its accessibility and apparent catalytic cracking activity. After 50ms, during the ‘steady-state time-frame’, radical reactions play a negligible role and no coke, H2, and C1–C2 are formed. In this stage, β-scission is dominant. A lumped kinetic scheme is proposed to describe the observed phenomena and how gasoline yield penalties could be avoided in commercial risers. Calculations on feed reactivities and mass-transfer have been made in order to describe the processes taking place on a molecular scale.
Keywords: Fluid catalytic cracking (FCC); Coke formation; Catalytic cracking; Thermal cracking; Process optimisation
Liquid phase oxidation of alkanes using Cu/Co-perchlorophthalocyanine immobilized MCM-41 under mild reaction conditions by P. Karandikar; A.J. Chandwadkar; M. Agashe; N.S. Ramgir; S. Sivasanker (pp. 220-230).
Amino-functionalized MCM-41 (NH2-MCM-41) was used to immobilize Cu/Co-Cl16Pc complex, i.e. Cu/Co-AM(PS) for liquid phase oxidation of alkanes under mild reaction conditions. Higher rates of reaction and better catalytic activity values were obtained for Cu/Co-AM(PS) as compared to Cu/Co-Cl16Pc grafted on (i) amino-functionalized SiO2 [Cu/Co-ASiO2] and (ii) non-functionalized MCM-41 [Cu/Co-M(I)] catalysts along with neat metal complex under identical conditions. The catalysts were evaluated by comparing two different oxidants: (i) TBHP and (ii) O2/aldehyde. The rate of conversion and percent selectivity differ for the above two oxidants due to differences in stability of radical species and in their homolytic/heterolytic pathways. The homolytic dissociation of oxygen favors a higher rate of conversion in the case of TBHP, whereas the heterolytic mechanism favors a higher selectivity for cyclohexanone in the case of O2/aldehyde. The catalysts were characterized by XRD, MAS NMR, N2-adsorption, microanalysis, UV–vis, FTIR and cyclic voltammetry. The UV–vis spectra reveal a blue shift for the metal phthalocyanine-immobilized samples, indicating unimolecular dispersion of metal complex within the channels of MCM-41. Cyclic voltammetry results suggest some coordinative interaction of the amino group of NH2-MCM-41 with the metal on grafting with the complex.
Keywords: MCM-41; Immobilization; Dispersion; Cu/Co-AM(PS); Alkane oxidation; Axo-metal species
Liquid phase isomerization of isoprenol into prenol in hydrogen environment by S.B. Kogan; M. Kaliya; N. Froumin (pp. 231-236).
Supported Pd, Pt, Ru and Ir catalysts doped with Cd, Sn, P, Sb, Bi, Se, Ca and Ce have been studied in a liquid phase isomerization of 3-methyl-3-buten-1-ol (isoprenol) into 3-methyl-2-buten-1-ol (prenol) in a continuous reactor in the temperature range of 60–100°C. Silica and different aluminas were used as supports. The catalyst containing 0.5% Pd–0.05% Se–0.3% Ce/SiO2 exhibited the best performance. A 45% conversion of isoprenol at selectivity of 93–94% to prenol was recorded in 100h run in hydrogen flow. The catalysts were characterized by SEM, XRD and XPS methods.The role of selenium consists in the stabilization of Pd in a partially oxidized state Pd n+, depressing completely hydrogenation activity, and thus selenium promotes a shift of double bond. Addition of Ce oxide improves dispersion of palladium species affecting catalyst activity significantly.
Keywords: Palladium; Promoter; Isoprenol; Prenol; Isomerization
Novelties of a superacidic mesoporous catalyst UDCaT-5 in alkylation of phenol with tert-amyl alcohol by Ganapati D. Yadav; Ganesh S. Pathre (pp. 237-246).
Alkylation of phenol is industrially important and several catalytic processes are developed. In the current work, the efficacies of several novel solid superacids designated as UDCaT-4, -5 and -6, and of sulphated zirconia were studied in liquid phase alkylation of phenol with tert-amyl alcohol. UDCaT-4, -5 and -6 are mesoporic superacids. The activity was found to be in order UDCaT-5>UDCaT-6>UDCaT-4>sulphated zirconia. The high sulphur content present in UDCaT-5 was found to be responsible for the greater activity at 120°C. The formation of products is correlated with the acidity of the catalyst. The conversion of tert-amyl alcohol and the selectivity for C-alkylated product were 96 and 85%, respectively, under optimum reaction conditions. The reaction was carried out without solvent in order to make the process cleaner and greener. The effects of various parameters on rates and product distribution are used to deduce the kinetics of the reaction. A second-order rate equation fits the data well under the assumption that both phenol and the alkylating agents are weakly adsorbed. The apparent activation energy was determined to be 8.57kcal/mol. An independent dehydration study of tert-amyl alcohol was done.
Keywords: Alkylation; tert; -Amyl alcohol; Green chemistry; Sulphated zirconia; Mesoporous materials; Solid super acids; UDCaT-4; UDCaT-5; UDCaT-6
Corrigendum to “The effect of calcination temperature on the adsorption of nitric oxide on Au–TiO2: Drifts studies� [Appl. Catal. A: Gen. 291 (2005) 98–115]
by M.A. Debeila; N.J. Coville; M.S. Scurrell; G.R. Hearne (pp. 247-247).