Hydrocarbon fuel synthesis from sorbitol over bifunctional catalysts: Association of tungstated titania with platinum, palladium or iridium (original) (raw)
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New bifunctional catalytic systems for sorbitol transformation into biofuels
Applied Catalysis B: Environmental, 2014
Tungstated oxides were prepared from several supports and characterized. The tungsten surface repartition and availability depends on the initial support. The acidity in water was evaluated through a model compound reaction, cyclohexanol dehydration. The results show that acidity in water is completely different from gas phase acidity (from NH 3-TPD), evidencing the crucial role of water in the acid catalytic activity. The tungstated oxides were then mixed with Pt/ZrO 2 to obtain a bifunctional catalytic system, which was used for transforming sorbitol in water. The activity and selectivity is highly dependent on the acid phase. TiO 2-WO x led to increased activity and higher selectivity for long chain hydrocarbons (C5-C6 alkanes) which can be valorized as biofuels, when compared to traditional sorbitol transformation catalyst. Al 2 O 3-WO x is not acid in water but produces short alcohols by C C cleavage. These results provide an incentive for further catalysts preparation.
Sorbitol can be selectively transformed into liquid alkanes over a bifunctional catalytic system Pt/ZrO 2 + TiO 2 –WO x. In this paper, we investigated the reaction mechanism by carefully analyzing the numerous products issued from sorbitol and by studying the reactivity of some identified intermediates (1-hexanol 2-hexanol, 2-hexanone, 2,5-dimethyltetrahydrofuran, 1,2-hexanediol and 1,2,6-hexanetriol). This led us to propose that CAC cleavage reactions occur on terminal CAC bonds and mainly consist of dehydroge-nation–decarbonylation reactions. The limiting steps of the sorbitol transformation are the isosorbide and mono-oxygenated intermediate transformations, especially the hydrogenation of ketones. It is also assessed that diols or triols with n carbon atoms are mainly converted in compounds with n À 1 carbon atoms. Short compounds (1 to 3 carbon atoms) are obtained via a dehydrogenation-retro-aldol reaction pathway and not from isosorbide conversion.
Catalytic Performance of Acid Catalysts for Sorbitol Dehydration to Isosorbide
Journal of the Japan Institute of Energy
This research studied dehydration of sorbitol in aqueous solution to isosorbide over heterogeneous catalysts (Amberlyst-15, Purolite CT269, and H-beta) and a homogeneous catalyst (sulfuric acid). The dehydration of sorbitol was carried out in a high-pressure reactor under a nitrogen gas atmosphere at a fixed initial pressure of 2 MPa. It was found that the Purolite CT269 catalyst gave the highest sorbitol conversion of 100% and an isosorbide selectivity of 42% after 6 h at 453 K. The results showed that an increase in the reaction temperature gave rise to sorbitol conversion. However, the solid-compound was formed during the reaction at high temperature by polymerization of the product. The high acidity could catalyze the dehydration process; however, strong acid such as sulfuric acid gave low selectivity to isosorbide. Thus, the acidity of the catalyst plays a vital role in catalytic performance for the sorbitol dehydration to isosorbide.
Advances in the Catalytic Production and Utilization of Sorbitol
Recently, research on the production and transformation of sorbitol has become exciting in chemical industry and in catalysis studies for its broad applications. It opens up a new path for achieving sustainable energy supply and chemicals production. Here we mainly review the catalytic routes for the synthesis of sorbitol and conversion of sorbitol into high valueadded compounds such as lower alcohols, paraffins, isosorbide, and other derivatives. Meanwhile, some promising and valuable research directions are suggested based on the major challenges emerged in current research, such as the development of efficient magnetic catalysts, microwave heating, and other hydrogen sources.
Energy & Fuels, 2008
The effect of the temperature of calcination of the support on the structural properties of ZrO 2 and on the activity of the acid and metal functions of a Pt/WO x-ZrO 2 catalyst used in the isomerization-cracking of medium length paraffinic C 8-C 12 cuts was studied. n-Octane was used as model molecule. The calcination temperature was varied in order to change the metal/acid balance and to increase the yield of the reaction to isoparaffins of high octane number. Four supports were prepared by impregnating Zr(OH) 4 with ammonium metatungstate (15% W) and then they were calcined at 500, 600, 700, and 800°C. These supports were then impregnated with H 2 Cl 6 Pt (1% Pt) and calcined in air at 500°C. They were characterized by means of chemical analysis, XRD, N 2 adsorption, pyridine TPD, hydrogen chemisorption, temperature-programmed reduction, and infrared spectroscopy of adsorbed CO. The catalytic activity of the catalysts was evaluated with the test reactions of n-octane (300°C, 1 atm, WHSV) 1, H 2 /n-C 8) 6), n-butane (350°C, WHSV) 1, H 2 /n-C 4) 6), and cyclohexane (300°C, 1 atm, WHSV) 12.6, H 2 /CH) 1.4). The results reveal a strong influence of the calcination temperature on the final metal/acid balance of the catalysts. At 5 min time on stream, all catalysts produce a RON gain of 55 points. In general, the higher the calcination temperature the higher the promoting action of W for generating strong acid sites and the higher the concentration of Pt δ+ of the metal function. The highest liquid yield and isoparaffin yield were obtained with the sample calcined at 700°C. The sample calcined at 800°C had the highest cracking activity and the maximum yield of isobutane and propane.
Liquid-phase dehydration of sorbitol to isosorbide using sulfated zirconia as a solid acid catalyst
Applied Catalysis A: General, 2013
Sulfated zirconia catalysts have been prepared with zirconium (IV) hydroxide and sulfuric acid as the sources of zirconia and sulfate group, respectively. In this study, liquid-phase dehydration of sorbitol to isosorbide is investigated in the presence of the catalysts under various reaction conditions including reaction temperature, time, catalyst dosage and sulfur content/acidity of the catalysts. The results show that sulfated zirconia, with high sulfur content and a tetragonal crystalline structure, is a promising solid acid catalyst that can be used at least four times in the dehydration of sorbitol to isosorbide.
Applied Catalysis A: General, 2004
In order to elucidate the influence of the crystal structure of zirconia on the properties of the metallic and acid function of Pt/SO 4 2− -ZrO 2 , catalysts with different zirconia crystal phases were synthesized, fully tetragonal, fully monoclinic, and with a mixture of the tetragonal and monoclinic phases. Their catalytic properties were studied in the metal-catalyzed reaction of cyclohexane dehydrogenation (300 • C, 0.1 MPa, WHSV = 10 h −1 , H 2 /C 6 H 12 = 30), the acid-catalyzed isomerization of n-butane (350 • C, 0.1 MPa, WHSV = 1 h −1 , H 2 /C 4 H 10 = 6), and the bifunctional hydroconversion of n-octane (300 • C, 1.5 MPa, WHSV = 4 h −1 , H 2 /C 8 H 18 = 6). TPR, XRD and FTIR of chemisorbed CO were also used in order to characterize the catalysts. The results showed a strong influence of the crystal phase on the activity of the acid function. A less marked effect was found for the metal-catalyzed reaction. An opposite relation between the two functions was seen with respect to this crystal structure influence. Among the sulfated catalysts, monoclinic Pt/SO 4 2− -ZrO 2 had the lowest activity in n-C 4 isomerization and the highest activity in cyclohexane dehydrogenation. Tetragonal Pt/SO 4 2− -ZrO 2 catalysts were the most active in isomerization of n-butane. They had the lowest activity in cyclohexane dehydrogenation and their metal properties were negligible. They were also the most active in n-C 8 conversion, producing mainly i-C 4 . Monoclinic catalysts had low cracking activity and produced mainly isooctane. Mixed phase catalysts had an intermediate behavior.
Applied Catalysis A: General, 2015
Ethanol dehydration was investigated (423-773 K, 1 atm, 1.43 h −1 WHSV in nitrogen) over titania, zirconia, as such and after impregnation with WO3. As for comparison, data on other WO3-free and WO3-containing catalysts will be also discussed, considered a strong Lewis acid (alumina), a covalent oxide (silica) and a basic material (calcined hydrotalcite). The catalysts were characterized using FT-IR of adsorbed pyridine and of wolframate species, and by UV-Vis spectroscopy. The results presented here show that WO3/ZrO2 and WO3/TiO2 are excellent catalysts for ethanol dehydration. Their performances may compete with those of zeolites and alumina both for conversion to diethyl ether and to ethylene. The addition of WO3 to both ZrO2 and TiO2 introduces strong Brønsted acid sites that are supposed to represent the active sites in the reaction, but also inhibits the formation of byproducts, i.e. acetaldehyde and higher hydrocarbons. This is attributed to the poisoning of basic sites and of reducible surface Ti and Zr centers, respectively.