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1.
Surface properties and catalytic behavior of MoO3/SiO2 in esterification of acetic acid with ethanol
Abd El‐Aziz A Said Mohamed MM Abd El‐Wahab 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(3):329-335
A series of MoO3/SiO2 catalysts was prepared by an impregnation method with Mo loadings ranging from 1 to 50 wt%. The original and calcined samples at 400 °C were characterized by thermogravimetry (TG), differential thermogravimetry (DTG), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), Fourier transform infra‐red (FTIR) spectroscopy, and nitrogen adsorption measurements. The surface acidity and basicity of the catalysts were investigated by the dehydration–dehydrogenation of isopropanol and the chemisorption of pyridine. The catalytic esterification of acetic acid with ethanol was carried out at 220 °C in a conventional fixed‐bed reactor at 1 atm using air as a carrier gas. The results clearly revealed that silica–molybdena catalysts were active and selective towards the formation of ethyl acetate. Moreover, the catalyst containing 20 wt% MoO3 was the most active and selective one. The results emphasize the importance of the surface acid sites together with the specific surface area of the prepared catalyst, towards ester formation. Copyright © 2005 Society of Chemical Industry 相似文献
2.
Amol P. Amrute Ankur Bordoloi Nishita Lucas K. Palraj S. B. Halligudi 《Catalysis Letters》2008,126(3-4):286-292
MoO3/SiO2 composite with varying amounts of MoO3 loading (1–20 wt.%) were prepared by sol–gel method and calcined at 500 °C. These catalysts were employed for the liquid phase condensation of anisole with paraformaldehyde. All the catalysts were characterized by N2 sorption, XRD, and NH3-TPD. The activities of synthesized MoO3/SiO2 catalysts were compared with p-toluene sulfonic acid (p-TSA), the most frequently used catalyst for the condensation reactions, and with a supported metal oxide (WO x /ZrO2). Under the similar reaction conditions, synthesized 10 wt.% MoO3/SiO2 catalyst calcined at 500 °C was found to be the most active in the condensation of anisole with paraformaldehyde. 相似文献
3.
Ji Chul Jung Howon Lee Dong Ryul Park Jeong Gil Seo In Kyu Song 《Catalysis Letters》2009,131(3-4):401-405
γ-Bi2MoO6 catalysts prepared by a co-precipitation method were calcined at various temperatures (425–675 °C), and were applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene in a continuous flow fixed-bed reactor. Conversion of n-butene and yield for 1,3-butadiene were high at low calcination temperature (425–475 °C), but were decreased with increasing calcination temperature (525–675 °C). Temperature-programmed reoxidation (TPRO) measurements revealed that the catalytic performance of γ-Bi2MoO6 was well correlated with the oxygen mobility of the catalyst. Yield for 1,3-butadiene was increased with increasing oxygen mobility of γ-Bi2MoO6 catalyst. Among the catalysts tested, γ-Bi2MoO6 catalyst calcined at 475 °C showed the best catalytic performance due to its facile oxygen mobility. 相似文献
4.
Weixing Li Yingxiang Ni Weiwei Liu Weihong Xing Nanping Xu 《Korean Journal of Chemical Engineering》2013,30(6):1222-1228
Sulfated zirconia catalysts are proposed for the reversible hydrolysis of ethyl lactate instead of liquid acids. Sulfated zirconia catalysts were prepared by precipitation-impregnation method. The zirconium hydroxide was produced from zirconium oxychloride by adding aqueous ammonia and then impregnated in sulfuric acid. The solid samples were obtained by filtration and evaporation of the mixtures, respectively. After the samples were calcined, the sulfated zirconia catalysts were prepared. The results showed that the catalyst prepared by evaporation has higher catalytic activity. The physicochemical characteristics of the sulfated zirconia catalysts were studied by thermal analysis, X-ray powder diffraction (XRD), temperature programmed desorption of ammonia (NH3-TPD) and N2 adsorption-desorption, respectively. By the precipitation-impregnation-evaporation method, the optimal sulfated zirconia catalyst of tetragonal phase was prepared under liquid-solid ratio of 5ml/g, 1 mol/L of H2SO4 and calcination at 650 °C for 3 h. The conversion of the ethyl lactate was 87.8% in 3 h at 85 °C with the catalyst loading 2 wt% and initial molar ratio of water to ethyl lactate 20: 1. 相似文献
5.
Abd El‐Aziz A Said Mohamed M M Abd El‐Wahab Alian Mohamed Alian 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2007,82(6):513-523
Different ratios of phosphotungestic acid supported on silica gel were prepared by an impregnation method with PWA loadings ranging from 1 to 30% w/w and calcined at 350 and 500 °C for 4 h in a static air atmosphere. The catalysts were characterized by thermogravimety (TG), differential thermal analysis (DTA), X‐ray diffraction, FT‐IR spectroscopy and N2 adsorption measurements. The surface acidity and basicity of the catalyst were investigated by the dehydration–dehydrogenation of isopropanol and the adsorption of pyridine (PY) and 2,6‐dimethyl pyridine (DMPY). The gas‐phase estrification of acetic acid with ethanol was carried out at 185 °C in a conventional fixed‐bed reactor at 1 atm using air as carrier gas. The results clearly revealed that the catalyst containing 10% w/w PWA/SiO2 is the most active and delivers reaction selectively to ester with 85% yield. The Brønsted acid site resulting from hydroxylation of tungsten oxide plays the main role in the formation of ester. Copyright © 2007 Society of Chemical Industry 相似文献
6.
《Catalysis communications》2007,8(5):800-806
Benzylation of phenol with benzylalcohol was carried out in liquid phase over tungstophosphoric acid (TPA) supported on titania. The catalysts were prepared with different TPA (10–25%) loading by wet impregnation method, were calcined at 700 °C and characterized by XRD, surface area, FTIR and acidity of the catalysts was measured by temperature programmed desorption of NH3–TPD, FTIR pyridine adsorption. The catalysts have been represented by a general formula as xPTiO2−y (where x = wt%, P = TPA, and y = calcination temperature in °C). The 20PTiO2 catalyst calcined at various temperatures to know the effect of calcination temperature on activity of the catalyst and the 20PTiO2-700 showed highest activity in benzylation of phenol with benzylalcohol because it had highest acidity. The effects of temperature, catalyst weight, mole ratio of the reactants on conversion of phenol and product selectivities have been optimized. 20PTiO2-700 catalyst gave conversion of benzylalcohol (BA) 98% and the selectivity to benzyl phenol (BP) 83.6%, phenyl benzyl ether (PBE) 9.4%, benzylether (BE) 7% at 130 °C, phenol to benzylalcohol molar ratio 2 and in 1 h. 相似文献
7.
The catalysts were prepared from pseudo-boehmite mixed with dilute nitric acid and calcined at different temperatures. The
vapour-phase reaction of furan and hydrogen sulfide was performed in a fixed-bed flow in the presence of catalyst. The catalysts
were characterized by XRD, N2 adsorption, FT-IR techniques. The Al2O3 calcined at 550 °C has large surface areas which resulted in high yield of thiophene under the conditions: at atmosphere,
reaction temperature 500 °C, the ratio of H2S to Furan about 10 (mol) and LHSV 0.2 h−1. The reaction mechanism was proposed for the synthesis of thiophene from furan and hydrogen sulfide over Al2O3. 相似文献
8.
Geoffrey C. Bond Samih A. Halawy Khalafalla M. Abd El-Salaam Ehsan A. Hassan Hesham M. Ragih 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(2):181-191
The vapour-phase dehydration and dehydrogenation of isopropyl alcohol (IPA) have been carried out over pure MoO3 and Fe2O3, produced by calcination of ammonium heptamolybdate and of iron (III) nitrate respectively, as well as MoO3 mixed with 0·5 and 50 mol% Fe2O3, prepared from the same materials. All catalysts were calcined in air, in the temperature range 200–600°C for 5 h, and were characterized by thermal analysis (TG, DTA), XRD, IR and SBET. Surface areas decreased with increasing calcination temperature, and the catalytic activity of the pure oxides MoO3 and Fe2O3, as well as of MoO3–0.5 mol % Fe2O3, increased with their SBET. The activity of MoO3–50 mol % Fe2O3, which was independent of its SBET, could be attributed to the increased intensity of terminal Mo—O bonds as shown by IR spectra. The activation energies for the decomposition of IPA over catalysts calcined at 250 and 500°C are tabulated. 相似文献
9.
Two different MoO3 catalysts (30 wt%) supported on montmorillonite type pillared clays have been synthesized by (i) impregnation with an ammonium molybdate solution (sample Mo-APC-i) and (ii) mechanical mixing with MoO3 (sample Mo-APC-m). After preparation both catalysts were calcined at 400°C. It has been established by X-ray phase analysis, temperature programmed reduction and IR spectroscopy that impregnation leads to a better dispersion of molybdenum oxide on the support, which ensures (i) a higher concentration of Brønsted acid sites (measured by adsorption of pyridine) and (ii) a higher catalytic activity in methanol oxidation of the Mo-APC-i catalyst. 相似文献
10.
Mo/HZSM-5 catalysts show high reactivity and selectivity in the activation of methane without using oxidants. Mo/HZSM-5 catalysts with Mo loading ranging from 0 to 10% were prepared by impregnation with an aqueous solution of ammonium heptamolybdate (AHM). The samples were dried at 393 K, and then calcined at different temperatures for 4 h. The interaction between Mo species and NH4ZSM-5 zeolite was characterized by FT-IR spectroscopy, differential thermal analysis (DTA) and temperature programmed decomposition (TPDE) and NH3-TPD at different stages of catalyst preparation. The results showed that if Mo/HZSM-5 catalysts were calcined at a proper temperature, the Mo species will interact with acid sites (mainly with BrØnsted acid sites) and part of the Mo species will move into the channel. The Mo species in the form of small MoO3 crystallites residing on the external surface and/or in the channel, and interacting with BrØnsted acid sites may be responsible for the methane activation. Strong interaction between Mo species and the skeleton of HZSM-5 will occur if the catalyst is calcined at 973 K. This may lead to the formation of MoO
4
2–
species, which is detrimental to methane activation. 相似文献
11.
Barium phosphate catalysts were prepared by a precipitation method. The catalysts were calcined at 500 °C for 6 h in air atmosphere and characterized by SEM for morphological features, by XRD for crystal phases, by N2 sorption for specific surface area, by TPD–NH3 for acidity and by TG for thermal stability. The dibarium pyrophosphate catalyst was found to have the best catalytic performance, ascribing to weak acidity on the surface. Under the optimal reaction conditions, 99.7% of the lactic acid conversion and 76.0% of the selectivity to acrylic acid were achieved over the dibarium pyrophosphate catalyst. 相似文献
12.
The hydrocracking of n-heptane in the temperature range of 573 to 623 K and at 2.45 × 106 Pa pressure has been employed as a test reaction for the study of Ni—Mo bifunctional catalysts supported on a HY ultrastable zeolite. Two groups of catalysts containing 8 and 12 wt% of MoO3 and different amounts of NiO have been studied. In both series a maximum in the activity has been obtained for catalysts with a Ni/Mo atomic ratio of 0.8-1.0. The order of the impregnation of the oxides can have little influence on the activity. The most active catalyst has been obtained when the zeolite is exchanged with NH+4 ions until the Na+ level is less than 2% of the original and calcined at 823 K to obtain a HY ultrastable zeolite. Using this catalyst the rate controlling step could be the transformation of the carbonium ion on the acid sites. 相似文献
13.
Pt/γ-Al2O3 catalysts were prepared by two different impregnation methods and characterized by XRD, TEM, and CO chemisorption. The Pt particle sizes ranged in 2.4–23.3 nm for these 5.0 wt% Pt/γ-Al2O3 catalysts. The catalysts were also characterized by FT-IR spectroscopy using CO as a probe molecule before and after the chiral modification with cinchonidine. Two IR bands (2078 and 2060 cm-1) due to CO linearly adsorbed on the Pt/γ-Al2O3 catalyst, calcined at 500 °C before reduction in sodium formate solution were observed, whereas only one IR band at ~2070 cm-1 was observed for other catalysts. A red shift of the IR band was observed after chiral modification of all the catalysts, except the one with the largest Pt particle size and lowest Pt dispersion. The catalytic performance of the cinchonidine-modified Pt/γ-Al2O3 catalysts was tested for the enantioselective hydrogenations of ethyl pyruvate and ethyl 2-oxo-4-phenylbutyrate (EOPB). A 95% ee value was obtained for the ethyl pyruvate hydrogenation and about 83% ee was achieved for the enantioselective hydrogenation of EOPB under the optimized preparation and reaction conditions. It is deduced that the interaction of Pt with γ-Al2O3 is a crucial factor for obtaining high activity and that the adsorption abilities (adsorption of reactant, solvent and chiral modifier molecules) of the catalyst surface affect the catalytic performance significantly. 相似文献
14.
《Catalysis communications》2011,12(15):1224-1228
Acetylation of glycerol with acetic acid was investigated over ZrO2, TiO2–ZrO2, WOx/TiO2–ZrO2 and MoOx/TiO2–ZrO2 solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bio-additives for petroleum fuels. The prepared catalysts were characterized by means of XRD, BET surface area, ammonia-TPD and FT-Raman techniques. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt.% and time-on-stream were studied to optimize the reaction conditions. Among various catalysts investigated, the MoOx/TiO2–ZrO2 combination exhibited highest conversion (~ 100%) with best product selectivity, and a high time-on-stream stability. 相似文献
15.
《Catalysis communications》2007,8(2):193-199
Cu–Zn–Ti catalysts were prepared by coprecipitation method. The calcined and reduced Cu–Zn–Ti catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and N2 adsorption. The calcined Cu–Zn–Ti catalysts were composed of CuO, ZnO, and amorphous TiO2. There were two kinds of CuO species present in the calcined Cu–Zn–Ti catalyst. At a lower copper content, CuO species interacted with ZnO and TiO2; at a higher copper content, both the surface-anchored and bulk CuO species were present. After reduction, metallic copper (Cuo) appeared in all Cu–Zn–Ti catalysts. Cuo produced by reduction of the surface-anchored CuO favored the deep hydrogenation of maleic anhydride. ZnO and TiO2 had synergistic effect on the catalytic activity of Cu–Zn–Ti catalysts in hydrogenation of maleic anhydride. 相似文献
16.
Dhanashri Prakash Sawant Veerappan Vaithilingam Balasubramanian Josena Justus Shivappa Basappa Halligudi Arumugam Chandra Bose Katsuhiko Ariga Toshiyuki Mori Ajayan Vinu 《Topics in Catalysis》2009,52(1-2):111-118
Acylation of aromatic compounds such as veratrole (1,2-dimethoxybenzene), anisole, isobutyl benzene, and 2-methoxynaphthalene with acetic anhydride (Ac2O) has been investigated over different solid acid catalysts such as MWW, BEA, FAU, MOR, and MFI. MWW catalysts have been characterized by X-ray diffraction, N2 adsorption–desorption isotherm, and HR-FESEM characterization techniques. The reaction is studied in the temperature range 313–353 K under N2 atmosphere. Among the catalysts tested, MWW was found to be more active than other zeolites. This is mainly due to its three dimensional porous structure with excellent textural characteristics. The effect of veratrole/Ac2O molar ratio, catalyst concentration, and reaction temperature has been optimized to get higher conversion of Ac2O. Under the optimized reaction conditions, MWW gave the Ac2O conversion of 64.3% with a selectivity to acetoveratrone (3′,4′-dimethoxyacetophenone) (100%). It was also found that the structural features and acidity play an important role in the conversion and product distribution in the acylation of different aromatic substrates like anisole, isobutyl benzene, and 2-methoxy naphthalene. MWW catalyst has been reused in few cycles after regeneration by washing with ethyl acetate followed by calcination at 500 °C for 4 h without loss in its activity. The reaction kinetics of the catalyst was also studied and the results are discussed in detail. 相似文献
17.
18.
Yingcheng Li Shirun Yan Weimin Yang Zaiku Xie Qingling Chen Bin Yue Heyong He 《Catalysis Letters》2008,124(1-2):85-90
Sn–Nb2O5/α-Al2O3 catalysts were prepared by impregnation and tested for ethylene oxide (EO) hydration to form ethylene glycol. The effect of the calcination temperature on the structure, acidity, H2O and EO adsorption properties and catalytic performance of the catalyst were investigated by using XRD, TG-DTA, IR, NH3-TPD and EO-TPD. It was found that the phase compositions, acidity, the EO adsorption strength and water adsorption capacity of the Sn–Nb2O5/α-Al2O3 catalyst were markedly influenced by the calcination temperature. The catalyst calcined at a temperature between 350 and 400 °C showed the best catalytic performance. A correlation between catalytic performance and characterization was proposed. 相似文献
19.
Yongxia Miao Guanzhong Lu Xiaohui Liu Yanglong Guo Yanqin Wang Yun Guo 《Journal of Industrial and Engineering Chemistry》2010,16(1):45-50
The MoO3/SiO2 catalysts containing different surface molybdenum species were prepared by a sol–gel method, and the effects of the preparation condition and MoO3 loading on the surface molybdenum species and property of MoO3/SiO2 were studied. The XRD, FT-IR, UV–vis and Raman spectroscopies were used to characterize the surface molybdenum species, and temperature-programmed desorption of NH3 adsorbed on a catalyst was used to detect the surface acidic properties. The results show that, there were the dispersed polymolybdate, α-MoO3, β-MoO3, monomeric molybdenum species and silicomolybdic acid on the MoO3/SiO2 catalyst, and their distributions and subsistence states were affected by the preparation condition and MoO3 loading. Different molybdenum species exhibit different catalytic activities for the epoxidation of propylene with cumene hydroperoxide. In the 15 wt% MoO3/SiO2 catalyst synthesized at pH 9.1 and dried appropriately, there are the small size β-MoO3 and monomeric molybdenum species that they are mainly effective catalyst components for the epoxidation of propylene. Using this catalyst, the ~100% conversion of cumene hydroperoxide and ~100% selectivity to propylene oxide can be obtained in the tert-butyl alcohol solvent at 2.6 MPa and 80 °C for 4 h. 相似文献
20.
Camila O. P. Teixeira Kelly C. N. R. Pedro Thais L. A. P. Fernandes Cristiane A. Henriques 《Chemical Engineering Communications》2019,206(2):169-181
Biodiesel production costs can be significantly reduced by using nonrefined feedstock. Sulfated solid catalysts have been proposed for producing biodiesel from acid oils by esterification reactions. Nevertheless, leaching of sulfate species to the reaction medium may occur, but often it is not considered. In this article, a commercial tin sulfate (SnSO4) was used as a catalyst for the esterification of a feedstock with high content of free fatty acid in order to assess the contribution of the homogeneous catalysis in different situations. SnSO4 was calcined at different temperatures (300, 400, 500 and 700?°C) and converted into SnO2 after calcination at temperatures higher than 300?°C. Homogeneous catalysis seems possible to occur with all of the catalysts, but it was clearly observed for the uncalcined catalyst (SnSO4) and for that calcined at 300?°C (SnSO4(300)). For these catalysts, an important leaching of the sulfate species was confirmed. Higher conversions were obtained with the uncalcined SnSO4. Reactions at the same conditions using sulfuric acid as catalyst at concentrations of 0.1% were performed and confirmed conversions higher than 80%. Heterogeneous catalysis plays a significant role only with the catalyst that present the highest specific surface areas and acidity (SnSO4(400)). As some small amount of sulfate species is retained in the structure or surface of the calcined catalysts (even after calcination at 700?°C), we cannot exclude the possibility that these species are also leached during reaction. Thus, a possible contamination of biodiesel through the use of sulfated catalysts cannot be ruled out. 相似文献