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Applied Catalysis A, General (v.278, #2)
On the hydrodesulfurization of FCC gasoline: a review by Sylvette Brunet; Damien Mey; Guy Pérot; Christophe Bouchy; Fabrice Diehl (pp. 143-172).
The possible origins of sulfur impurities in FCC gasoline are reviewed and discussed. Their mechanism of formation during the FCC process as well as their mechanism of transformation on hydrotreating catalysts are also examined.The article focuses on the desulfurization of FCC gasoline by means of catalytic processes considering the fact that deep desulfurization must be achieved (in accordance with new regulations) while preserving octane rating of the fraction. The various parameters (presence of a promoter, nature and modification of the support, additives and poisons) which may influence the selectivity in hydrodesulfurization (HDS) versus olefin hydrogenation are also discussed. Existing and potential processes for the HDS of FCC gasoline with octane preservation are described.
Keywords: FCC gasoline; Selective hydrodesulfurization; Sulfur impurities
Pt0.02Sn0.003Mg0.06 on γ-alumina: a stable catalyst for oxidative dehydrogenation of ethane by E.A. de Graaf; G. Rothenberg; P.J. Kooyman; A. Andreini; A. Bliek (pp. 187-194).
The advantages of two-step oxidative dehydrogenation as an alternative method for manufacturing small alkenes are outlined. In a nutshell, the process is based on separating the gaseous oxygen and hydrocarbon feeds in time. In the first step, alkanes are dehydrogenated in the presence of a solid oxygen carrier (without gaseous oxygen). Subsequently, the carrier is reoxidised using a gaseous feed. This process requires a dehydrogenation catalyst that is selective and stable under severe redox cycling. In search for such a catalyst, we prepare and study various platinum/tin catalysts supported on alumina. The catalysts are doped with either magnesia or potassium oxide. The activity, selectivity, and stability of these catalysts in the dehydrogenation of ethane to ethylene are then investigated under severe redox cycling conditions (600°C and 10% (v/v) oxygen in the regeneration step). Pt0.02Sn0.003Mg0.06 is found to be the most stable combination. The catalysts’ dispersion and the metal–support interactions are studied using transmission electron microscopy (TEM) and temperature-programmed hydrogen desorption (TPD). The effects of the (earth)alkali promoter and the interaction between the metal catalyst and support are discussed.
Keywords: Solid oxygen carriers; Catalyst synthesis; Sintering; Redox cycling; Bimetallic; Magnesium; Tin
Development of cobalt catalysts for the steam reforming of naphthalene as a model compound of tar derived from biomass gasification by Takeshi Furusawa; Atsushi Tsutsumi (pp. 195-205).
The catalytic performances of Co/MgO catalysts for the steam reforming of naphthalene were investigated. The results of characterizations (TPR, XRD, CO adsorption, and CO-TPD) showed that large-sized Co metal particles were formed over the catalysts pre-calcined at 873K with high Co loading via reduction of Co3O4 and MgCo2O4 phases. A few Co metal particles were obtained over the catalysts pre-calcined at 1173K with all Co loading values after reduction.The catalytic performances data showed that 12wt.% Co/MgO catalyst pre-calcined at 873K exhibited the best catalytic performance (conv., 23%, 3h) for the steam reforming of naphthalene among the catalysts tested in this study, due to the existence of Co metal and the low amounts of coke deposition. On the other hand, the data also revealed that the reaction of steam reforming of naphthalene proceeds over all Co-loaded catalyst pre-calcined at 1173K initially; however, the deposition of the polymer of C nH m radicals and the oxidation of catalysts by H2O led to the decrease of activity.It should be noted that 12wt.% Co/MgO catalyst pre-calcined at 873K showed high and stable activity under the low steam/carbon mole ratio (0.6), with H2 and CO2 as main products. These two excellent advantages serve to increase the overall biomass gasification system energy efficiency and allow using the product gas for fuel cell system. Thus, Co catalyst is a promising system for the steam reforming of naphthalene derived from biomass gasification as a second fixed catalytic bed.
Keywords: Cobalt catalyst; Steam reforming; Naphthalene; Biomass; Tar
Comparison of Co/MgO and Ni/MgO catalysts for the steam reforming of naphthalene as a model compound of tar derived from biomass gasification by Takeshi Furusawa; Atsushi Tsutsumi (pp. 207-212).
The catalytic performances of 12wt.% Co/MgO catalyst pre-calcined at 873K and of Ni catalysts for the steam reforming of naphthalene were investigated. The results of characterizations (TPR, XRD, and CO adsorption) for Ni catalysts showed that Ni metal particles were formed over the catalysts pre-calcined at 873K with high Ni loading via reduction of NiO–MgO phases. A few Ni metal particles were obtained over the catalysts pre-calcined at 1173K with all Ni loading values.The catalytic performance data showed that Co/MgO catalyst had higher activity (conv., 23%, 3h) than any kinds of Ni/MgO catalysts tested in this study, under lower steam/carbon mole ratio (0.6) and higher concentration of fed naphthalene (3.5mol%) than those used in the other works. The steam reforming of naphthalene proceeded when there was a stoichiometric ratio between the carbon atoms of naphthalene and H2O over Co catalyst; however, the activation of excess H2O happened over the Ni catalyst and this phenomenon can lead to having lower activity than Co catalyst. We concluded that these observations should be attributed to different catalytic performances between Co/MgO and Ni/MgO catalysts.
Keywords: Cobalt catalyst; Nickel catalyst; Steam reforming; Naphthalene; Biomass; Tar
The influence of preparation method on the properties of NiMo sulfide catalysts supported on ZrO2 by Meiling Jia; Pavel Afanasiev; Michel Vrinat (pp. 213-221).
Highly loaded supported (Ni)Mo sulfide catalysts prepared using different methods have been studied. Two zirconia supports of high specific surface area were used, including amorphous or tetragonal ZrO2 solids. The order of active components introduction as well as thermal treatment conditions were varied. The best performance in the reactions of hydrodesulfurisation of thiophene and hydrogenation of tetralin was shown by the coimpregnated systems sulfidized without calcination of the oxide precursor. Crystallized ZrO2 support always provides higher activities in both reactions, than amorphous zirconia, despite very high specific surface area of the last. The differences between variously treated systems were explained using the results of characterizations including laser Raman spectroscopy, XPS spectroscopy and temperature programmed reduction.
Keywords: NiMo sulfide; Hydrodesulfurisation; Thiophene
Impact of the support on the heat of adsorption of the linear CO species on Pt-containing catalysts by Prisca Pillonel; Salim Derrouiche; Abdennour Bourane; François Gaillard; Philippe Vernoux; Daniel Bianchi (pp. 223-231).
It has been previously shown that the individual heats of adsorption of each adsorbed CO species (linear, bridged and three-fold coordinated) on Pt/Al2O3 catalysts can be obtained from the change of their characteristic IR bands with the adsorption temperature Ta (in the range of 300–800K) at a constant CO partial pressure Pa according to a procedure denoted adsorption equilibrium infrared spectroscopy. In the present study, this procedure is used to reveal the impact of the nature of the support TiO2, CeO2 and Y2O3/ZrO2 (two solids with high (104m2/g) and low (14m2/g) BET surface area) on the heat of the adsorption of the L CO species that dominates the CO adsorption. These reducible supports have been selected because of their expected interactions with Pt particles according to different SMSI effects. In the wavenumber range characteristic of the L CO species on Pt sites, the FT-IR spectra are dependent on the nature of the support: two strongly overlapped IR bands are detected with an intensity ratio depending on the support. However, it is shown that the nature of the support only has a slight impact on the average heats of adsorption of the L CO species (<20kJ/mol as compared to Pt/Al2O3).
Keywords: Heat of adsorption; Linear CO species; FT-IR spectra; Platinum catalysts
Silica aerogel supported catalysts for Fischer–Tropsch synthesis by Brian C. Dunn; Paul Cole; Daniel Covington; Matthew C. Webster; Ronald J. Pugmire; Richard D. Ernst; Edward M. Eyring; Naresh Shah; Gerald P. Huffman (pp. 233-238).
Cobalt catalysts supported on silica aerogel have been prepared using sol–gel chemistry followed by drying under supercritical ethanol conditions. Three different loadings of cobalt were synthesized: 2, 6, and 10% by weight. Transmission electron micrographs indicate that the metallic cobalt exists as discrete particles 50–70nm in diameter for the 2 and 6% loadings. The 10% catalyst shows long needles of cobalt. BET and BJH measurements indicate that the catalysts retain the silica aerogel properties of high surface area (∼800m2/g), large pore volume (∼5cm3/g), and an average pore diameter in the mesoporous regime (∼25nm). The catalysts were evaluated for Fischer–Tropsch activity in a laboratory-scale packed bed reactor. All three catalysts were active with the 10% Co catalyst achieving more than 20% CO conversion which corresponds to a rate of 1.53g CO per g-cat per hour. The catalysts were selective for the C10+ hydrocarbons with more than 50% of the carbon contained within this fraction. A significant portion of the C9–C15 hydrocarbon product was observed as 1-olefins which reflects the enhanced mass transport within the very porous aerogel support.
Keywords: Silica aerogel; Cobalt catalysts; Fischer–Tropsch synthesis; Mesoporous supports
XPS and EXAFS study of supported PtSn catalysts obtained by surface organometallic chemistry on metals by Guillermo J. Siri; José M. Ramallo-López; Mónica L. Casella; José L.G. Fierro; Félix G. Requejo; Osmar A. Ferretti (pp. 239-249).
In this work, well defined alumina and silica supported Pt and PtSn catalysts were prepared by surface organometallic reactions and were characterized by TEM, XPS and EXAFS. These catalysts were tested in the catalytic dehydrogenation of isobutane. XPS results show that tin is found under the form of Sn(0) and Sn(II,IV), being the percentage of Sn(0) lower for alumina supported than for silica supported catalysts. Tin modified platinum catalysts, always show a decrease of approximately 1eV in the BE of Pt, what would be indicative of an electron charge transfer from tin to platinum. When the concentration of Sn(0) is high enough, in our case Sn(0)/Pt∼0.3, EXAFS experiments demonstrated the existence of a PtSn alloy diluting metallic Pt atoms, for both PtSn/γ-Al2O3 and PtSn/SiO2. This PtSn alloy seems to be not active in the dehydrogenation reaction; however, it is very important for selectivity and stability, inhibiting cracking and coke formation reactions. The ensemble of our catalytic, XPS and EXAFS results, show that bimetallic PtSn/γ-Al2O3 catalysts, prepared via SOMC/M techniques, can be submitted to several sequential reaction–regeneration cycles, recovering the same level of initial activity each time and that the nature of the catalytic surface remains practically without modifications.
Keywords: PtSn catalysts; Organometallic chemistry; Isobutane hydrogenation; Catalyst regeneration
Room temperature direct oxidation of benzene to phenol using hydrogen peroxide in the presence of vanadium-substituted heteropolymolybdates by Jin Zhang; Ying Tang; Guiying Li; Changwei Hu (pp. 251-261).
The liquid-phase direct catalytic oxidation of benzene to phenol was studied at room temperature using vanadium-substituted heteropolyacids as catalysts. Glacial acetic acid was employed as the solvent for the first time, while hydrogen peroxide was used as the oxidant. A yield of 26% and a selectivity of 91%, respectively, were obtained. The as-prepared phenol was separated by column chromatography and was characterized by infrared and mass spectrometry. The catalysts have been characterized by elemental analysis, thermal gravimetric analysis, infrared spectroscopy, UV–vis spectroscopy, X-ray diffraction, and31P NMR and51V NMR techniques. The effects of various reaction parameters, such as solvent, reaction temperature, reaction time and the amount of hydrogen peroxide used, were studied. The effects of different vanadium species on the catalytic performance were also studied. Glacial acetic acid was found to be the most suitable solvent among the solvents used in present work. An appropriate molar ratio of H2O2 to benzene of 1.7, and a favorable reaction time of 100min were optimized. H4PMo11VO40·13H2O was found to be the most active in terms of turnover based on vanadium atom and the most stable catalyst.The liquid-phase direct catalytic oxidation of benzene to phenol was studied at room temperature using vanadium-substituted heteropolyacids as catalysts. A yield of 26% and a selectivity of 91% were obtained. An appropriate molar ratio of H2O2 to benzene was 1.7, and a favorable reaction time was 100min. H4PMo11VO40 showed the highest activity in term of turnover based on vanadium atom and the highest stability. ▪
Keywords: Heteropolyacids; Oxidation of benzene; Phenol; Acetic acid
Oxovanadium(IV) complexes as homogeneous catalyst—aerobic epoxidation of olefins by Sajjad Mohebbi; Davar M. Boghaei; Ali Hossien Sarvestani; Abdollah Salimi (pp. 263-267).
The novel N2O2 unsymmetrical tetradentate Schiff bases complexes are used as catalysts for the selective aerobic oxidation of cyclohexene. In general, conversion percentages decrease with increasing Δ Ep and decreasingEredox0′. Catalytic activity increases with decrease of the number of electron-donating groups and the catalytic selectivity varies according to the types of substituents in the ligands. The catalytic system described here is an inexpensive method for selective oxidation of olefins, with advantages of high activity, selectivity, re-usability and short reaction times. Analysing GC and redox potential results shows a moderate correlation between selectivity and activity.
Keywords: Aerobic selective oxidation; Selective epoxidation; Catalytic oxidation of olefins; Vanadyl tetradentate Schiff base complexes; Oxovanadium(IV) complexes
Oxidation of hydrophobic alcohols using aqueous hydrogen peroxide over amphiphilic silica particles loaded with titanium(IV) oxide as a liquid–liquid phase-boundary catalyst by Kwang-Min Choi; Shigeru Ikeda; Satoru Ishino; Keita Ikeue; Michio Matsumura; Bunsho Ohtani (pp. 269-274).
Phase-boundary catalysis (PBC), a new concept of a heterogeneous catalytic system for oxidation of various hydrophobic alcohols with aqueous hydrogen peroxide (H2O2), has been investigated. A part the external surface of silica (SiO2) particles loaded with titanium(IV) oxides was modified with hydrophobic alkyl groups to obtain amphiphilic particles, having both hydrophobic and hydrophilic surfaces on each particle. The amphiphilic particles were spontaneously assembled at interfaces between dual phase mixtures of aqueous solutions and water-immiscible organic compounds. Upon addition to a dual phase mixture of aqueous H2O2 and toluene-containing hydrophobic alcohols, these particles acted as an efficient catalyst for the reaction, to produce corresponding aldehydes and ketones selectively. Notable features of the PBC system are that the oxidation proceeds even without agitation and that only a few percent of titanium species was detected as dissolved species. Productions of aldehydes and ketones were also observed when titanium loaded SiO2 without modification with alkyl groups was employed for the reaction. However, a large amount of titanium loaded on the material was leached during the reaction. These results indicate that surface-covered alkyl groups not only bring about effective contact with hydrophobic alcohols in the organic phase but also give stability against leaching, leading to heterogeneous catalytic functions.
Keywords: Liquid-phase oxidation; Hydrophobic alcohols; Asymmetric surface modification; Amphiphilic solid catalyst; Phase-boundary; Titanium; Leaching