Surface properties and catalytic behavior of MoO3/SiO2 in esterification of acetic acid with ethanol

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     

Sol–Gel Synthesis of MoO3/SiO2 Composite for Catalytic Application in Condensation of Anisole with Paraformaldehyde

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.     

Effect of Calcination Temperature on the Catalytic Performance of γ-Bi2MoO6 in the Oxidative Dehydrogenation of n-Butene to 1,3-Butadiene

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.     

Preparation and properties of sulfated zirconia for hydrolysis of ethyl lactate

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.     

Catalytic performance of Brønsted acid sites during esterification of acetic acid with ethyl alcohol over phosphotungestic acid supported on silica

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     

Tungstophosphoric acid supported on titania: A solid acid catalyst in benzylation of phenol with benzylalcohol

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.     

Catalytic Synthesis of Thiophene from the Reaction of Furan and Hydrogen Sulfide

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.     

MoO3—Fe2O3 catalysts: Characterization and activity for isopropyl alcohol decomposition

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 S_BET. 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 S_BET. The activity of MoO₃–50 mol % Fe₂O₃, which was independent of its S_BET, 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.     

MoO3 supported on montmorillonite type pillared clays: Characterization, surface acidity and catalytic properties towards the oxidation of methanol

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.     

Interaction between ammonium heptamolybdate and NH4ZSM-5 zeolite: the location of Mo species and the acidity of Mo/HZSM-5

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.     

Catalytic dehydration of lactic acid to acrylic acid over dibarium pyrophosphate

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.     

Hydrocracking of n-heptane. Study of NiO—MoO3 catalysts supported on a HY ultrastable zeolite

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.     

Some Insights into the Preparation of Pt/γ-Al2O3 Catalysts for the Enantioselective Hydrogenation of α-Ketoesters

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.     

Synthesis of bio-additives: Acetylation of glycerol over zirconia-based solid acid catalysts

Acetylation of glycerol with acetic acid was investigated over ZrO₂, TiO₂–ZrO₂, WO_x/TiO₂–ZrO₂ and MoO_x/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 MoO_x/TiO₂–ZrO₂ combination exhibited highest conversion (~ 100%) with best product selectivity, and a high time-on-stream stability.     

Gas phase hydrogenation of maleic anhydride to γ-butyrolactone by Cu–Zn–Ti catalysts

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 (Cu^o) appeared in all Cu–Zn–Ti catalysts. Cu^o 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.     

Novel Highly Acidic Nanoporous Cage Type Materials and Their Catalysis

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.     

固体超强酸ZrO_2-SO_4~(2-)催化合成乙酸糠酯

以固体超强酸ZrO2 SO2 -4为催化剂合成了乙酸糠酯。得到了适宜的催化剂制备条件及反应条件 :以氨水沉淀ZrOCl2 ·8H2 O溶液 ,以 0 75mol/L硫酸溶液浸渍ZrO2 ,并于 60 0℃下焙烧 4h。 0 2 5mol乙酸、0 2 5mol糠醇和 80ml甲苯混合后加入 4 g催化剂 ,产品收率可达 92 %。催化剂可重复利用 6次     

Effect of Calcination Temperature on Structure and Properties of Sn–Nb2O5/α-Al2O3 Catalyst for Ethylene Oxide Hydration

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.     

The molybdenum species of MoO3/SiO2 and their catalytic activities for the epoxidation of propylene with cumene hydroperoxide

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.     

Esterification of high acidity vegetable oil catalyzed by tin-based catalysts with different sulfate contents: contribution of homogeneous catalysis

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.