Gas phase esterification of acetic acid with ethanol over MoO3 supported on AlPO4 and the effect of modification with phosphomolybdic acid and Ce4+ ions

A series of AIPO₄–MoO₃ (APM) systems with various molybdena loadings (5–50) mol %, same modified with phosphomolybdic acid (PMA) and cerium ions, were prepared by an impregnation method and calcined at 400 °C, except for the samples modified with PMA which were calcined at 350 °C for 4 h. The catalysts were characterized by TG/DTG, XRD, IR spectroscopy, N₂ adsorption and electrical conductivity measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration–dehydrogenation of isopropyl alcohol. The catalytic esterification of acetic acid with ethanol was carried out in a convention fixed bed reactor. The results clearly revealed that the catalyst with a composition of 10 mol % MoO₃ (APM10) was the most active and selective catalyst for the production of ethyl acetate. Moreover, the yield of ethyl acetate increases on addition of PMA into APM10 while it decreases on the addition of Ce⁴⁺ ions. These results were correlated with structure, semiconductivity and the acid–base properties of the prepared catalysts. Copyright © 2003 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.     

Reactivity and surface properties of silica supported molybdenum oxide catalysts for the transesterification of dimethyl oxalate with phenol

A series of MoO₃/SiO₂ catalysts were prepared with Mo loadings ranging from 1 to 16 wt% and applied to the transesterification of dimethyl oxalate (DMO) with phenol. The results showed that the catalyst of MoO₃/SiO₂ with 1 wt% Mo content performed best, giving 54.6% conversion of DMO and 99.6% selectivity to target products, methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The surface properties were investigated by means of X-ray diffraction (XRD), X-ray photoelectron (XPS), BET specific surface area, temperature-programmed desorption (TPD) of ammonia, and FTIR analysis of adsorbed pyridine. XPS and XRD analyses indicated that Mo(VI) species was highly dispersed at low Mo loading and MoO₃ of the crystal structure appeared at higher loading. NH₃-TPD characterization and FTIR analysis of adsorbed pyridine demonstrated that only Lewis weak acids were present on catalyst surface and the amount of Mo loading has little effect on the strength of the surface acid on MoO₃/SiO₂. The catalytic results exhibited that the synergetic effect of Mo active centers with weak Lewis acid sites catalyzed transesterification of DMO with phenol.     

Thermal and catalytic upgrading of a biomass‐derived oil in a dual reaction system

The thermal and catalytic upgrsding of bio‐oil to liquid fuels was studied at atmospheric pressure in a dual reactor system over HZSM‐5, silica‐alumina and a mixed catalyst containing HZSM‐5 and silica‐alumina. This bio‐oil was produced by the rapid thermal processing of the maple wood. In this work, the intent was to improve the catalyst life. Therefore, the first reactor containing no catalyst facilitated thermal cracking of blo‐oil whereas the second reactor containing the desired catalyst upgraded the thermally cracked products. The effects of process variables such as reaction temperature (350°C to 410°C), space velocity (1.8 to 7.2 h^?1) and catalyst type on the amounts and quality of organic liquid product (OLP) were investigated, In the case of HZSM‐5 catalyst, the yield of OLP was maximum at 27.2 wt% whereas the selectivity for aromatic hydrocarbons was maximum at 83 wt%. The selectivities towards aromatics and aliphatic hydrocarbons were highest for mixed and silica‐alumina catalysts, respectively. In all catalyst cases, maximum OLP was produced at an optimum reaction temperature of 370°C in both reactors, and at higher space velocity. The gaseous product consisted of CO and CO₂, and C₁‐C₆ hydrocarbons, which amounted to about 20 to 30 wt% of bio‐oil. The catalysts were deactivated due to coking and were regenerated to achieve their original activity.     

Activity tests of various catalysts for hydrocracking of coal by means of high pressure differential thermal analysis

The activities of fourteen kinds of catalysts for the hydrocracking of Taiheiyo coal were examined by a high pressure differential thermal analytical method. Exothermic peaks appeared at low temperatures (420–430°C) when MoO₃TiO₂, NiY zeolite and CoY zeolite were used as catalysts, indicating that these catalysts are highly active compared with other catalysts including MoO₃CoOAl₂O₃. The qualitative analysis of gas and liquid products revealed that MoO₃TiO₂ and CoY are good catalysts for the liquefaction reaction. The hydrogenation ability of the catalyst is concluded to be more important than its acidic property.     

Low temperature selective catalytic reduction of NO by NH3 over V2O5 supported on TiO2–SiO2–MoO3

The V₂O₅ catalysts supported on TiO₂–SiO₂–MoO₃ (TSM) prepared by the coprecipitation method were investigated for the selective catalytic reduction (SCR) of NO by NH₃ at low temperatures. The V₂O₅/TSM catalyst with 7–13 wt% SiO₂ was found to exhibit a superior SCR activity and a good sulfur tolerance at low temperatures (<250 °C). The presence of highly active polymeric vanadates formed by the incorporation of MoO₃ to TiO₂–SiO₂ and superior redox properties seems to enhance SCR activity, and furthermore the very lower SO₂ oxidation activity due to the higher acidity leads to the remarkable improvement of sulfur tolerance.     

ESR, FT-Raman spectroscopic and ethanol partial oxidation studies on MoO3/SnO2 catalysts made by metal oxide vapor synthesis

A series of SnO₂-supported MoO₃ catalysts were prepared by the metal oxide vapor synthesis (MOVS) technique. ESR studies indicated the presence of highly dispersed Mo⁵⁺ species in both octahedral and tetrahedral coordination environments at all the loadings studied. At the highest MoO₃ loading of 12 wt%, the formation of MoO₃ microcrystallites was indicated from the lower intensity of the ESR signal. Raman studies also showed the presence of well dispersed surface molybdate species up to 4.4 wt% MoO₃ loading, and the peaks corresponding to microcrystallites of molybdena were observed at 12 wt% MoO₃ loading. The ethanol partial oxidation activities of the catalysts increased with increase in MoO₃ loading and the catalyst with 4.4 wt% molybdena content showed the highest activity; all the MOVS catalysts showed 100% selectivity to acetaldehyde at low conversions. This revised version was published online in July 2006 with corrections to the Cover Date.     

A General Method for Preparation of PVP-Stabilized Noble Metal Nanoparticles in Room Temperature Ionic Liquids

Catalysts based on a physical mixture of Ga₂O₃ and MoO₃ have been prepared and evaluated for propane partial oxidation to propene. The Ga₂O₃/MoO₃ catalysts demonstrated propene yields greater than a 6 wt% V₂O₅/TiO₂ catalyst, which is known to be active for the reaction. The higher yield of propene was achieved by the alkane activation properties of Ga₂O₃ and the selective oxidation function of MoO₃ combining in a synergistic manner.     

Selective Furfural Hydrogenation to Furfuryl Alcohol Using Cu-Based Catalysts Supported on Clay Minerals

Copper supported on clay minerals (bentonite and sepiolite) catalysts, with copper loading between 15 and 60 wt%, have been synthesized by precipitation-deposition, calcination and subsequent reduction. The catalysts were characterized by X-ray diffraction, H₂ temperature programmed reduction (H₂-TPR), N₂ adsorption–desorption at ?196?°C and X-ray photoelectron spectroscopy, being detected spherical metal Cu-particles with variable size, mainly located on the surface of clays. The evaluation of their catalytic performance in the furfural (FUR) hydrogenation in gas phase has demonstrated that the use of bentonite as support allows attaining conversion values of 83% for 45Cu-Bent, whereas only a 52% is reached by the 45Cu-Sep catalyst. All catalysts were highly selective towards furfuryl alcohol (FOL), reaching yields of 72% for 45Cu-Bent and 45% for 45Cu-Sep after 5 h of time-on-stream (TOS) at 210?°C, by using a H₂:FUR molar ratio of 11.5 and a WHSV of 1.5 h^?1. However, all catalysts suffer a progressive deactivation with TOS, by deposition of reactants and product (FOL and FUR), as well as the oxidation of the active phase.     

Effect of the metal oxide loading on the activity of silica supported MoO3 and V2O5 catalysts in the selective partial oxidation of methane

Precipitated silica catalysts loaded with either MoO₃ (0.2–4.0 wt%) or V₂O₅ (0.2–5.3 wt%) have been studied in the selective partial oxidation of methane to formaldehyde with molecular oxygen at 520 °C. The functionality of the SiO₂ surface towards the formation of HCHO is significantly promoted by V₂O₅, while it is depressed by the MoO₃.     

MoO2(acac)2 immobilized on polymers as catalysts for cyclohexene epoxidation: Effect of the degree of crosslinking

Crosslinked poly(4‐vinylpyridine‐co‐styrene) used as support for a immobilized oxomolybdenum complex was synthesized by radical polymerization. As crosslinking agent, 1,4‐divinylbenzene (DVB) was incorporated at 2, 4, and 6 mol %. Catalysts having similar MoO₂(acac)₂ loading on different resins were obtained by refluxing a solution of the complex with the polymeric supports at 70°C. FTIR, specific surface area, and XPS techniques were used for characterization. It was found that a significant increase in the surface area occurs as the degree of crosslinking increases, presumably due to the development of branched polymers having higher porosity. XPS showed that the complex is anchored to the pyridinic nitrogen on the resin and that that Mo was present essentially as Mo(VI) species. The Mo/C atomic surface ratio exhibits a maximum for the catalyst with medium crosslinking degree. The epoxidation of cyclohexene was studied in the temperature range 40–60°C by using tert‐butyl hydroperoxide as oxidant agent. The catalysts were active and selective to the corresponding epoxide and almost no leaching of the active phase was observed. The highest catalytic activity of the studied solids was displayed by the one supported on the resin with intermedium degree of crosslinking. The results are explained in terms of the access to the active sites and surface composition. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1602–1608, 2004     

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.     

Surface Modification of Pd/α-Si3N4 Catalysts Through the Solvent Used During Synthesis. Implications on the CO Chemisorption Properties and Catalytic Performances

Palladium catalysts supported on α-Si₃N₄ were prepared by impregnation with Pd(II)-acetate dissolved either in toluene or in water. The mean metal particle size of ~0.5 wt% Pd catalysts was similar (~5 nm) and independent of the way of preparation. Nevertheless, the two catalysts present very different chemisorption behaviour chemisorptive and catalytic properties. Fourier transformed infrared (FTIR) spectra of adsorbed CO at different temperatures (ranging from room temperature to 300 °C) show a very different behaviour for both catalysts. While the CO adsorption states on the Pd/α-Si₃N₄ prepared in toluene are very similar to those generally measured for silica and/or alumina supported palladium catalysts, CO chemisorbs less strongly on Pd/α-Si₃N₄ prepared in water and on different adsorption sites. The Pd/α-Si₃N₄ catalyst obtained by aqueous impregnation is much less efficient for the methane total oxidation. It is less active and less stable: it deactivates strongly after 3 h on stream at 650 °C. The two catalysts present about the same activity for the 1,3-butadiene hydrogenation after stabilisation at 20 °C. But, the catalyst prepared in water shows a much better selectivity to butenes. The results are discussed in terms of the possible migration of silicon atoms from the silicon nitride support to the surface of the palladium particles, when the catalyst is prepared in water. This is not the case when prepared in an organic solvent.     

Selective Oxidation of Ethane Over Mo–V–Al–O Oxide Catalysts: Insight to the Factors Affecting the Selectivity of Ethylene and Acetic Acid and Structure-activity Correlation Studies

Catalysts of general formula, MoVAlO _x were prepared with the initial elemental composition of 1:0.34:0.167 (Mo:V:Al) at a pH value in the range of 1–4. The elemental analysis showed that the final composition of the catalysts is pH dependant. The performance of the catalysts was tested for selective oxidation of ethane to give ethylene and acetic acid. While all of them were active for ethane oxidation with a moderate conversion, the catalyst prepared at pH 2 showed a highest activity with 23% ethane conversion and a combined selectivity of 80.6% to ethylene and acetic acid. The catalyst prepared at pH 4 was least selective to ethylene and acetic acid. Various techniques like powder XRD, SEM, Raman, UV–Vis and EPR were used to characterize the catalysts and to identify the active phases responsible for the selective oxidation of ethane. The powder XRD data showed that the catalysts prepared at pH 1 and 2 contain mainly of MoO₃ and MoV₂O₈ along with traces of Mo₄O₁₁. The amount of MoO₃ was slightly higher in the catalyst prepared at pH 1. However, the catalyst prepared at pH 3 contains mainly of MoV₂O₈ with no trace of MoO₃. The catalyst prepared at pH 4 showed V₂O₅ as the major phase along with MoVAlO₄ phase. The Raman data corroborated the XRD results. EPR and UV–Vis studies indicated the presence of traces of V⁴⁺ in pH 1 and 2 catalysts and significant amount of Mo⁵⁺ in all the catalysts. Thus, the high activity and selectivity to ethylene and acetic acid are attributed to the presence of MoV₂O₈ phase and other reduced species like Mo₄O₁₁ phase supported on MoO₃. The presence of V and Mo ions in a partially reduced form seems to play a crucial role in the selective oxidation of ethane.     

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     

Selective Production of C4 Hydrocarbons from Syngas Using Fe‐Co/ZrO2 and SO42—/ZrO2 Catalysts

Modified Fischer‐Tropsch (MFT) syntheses were carried out to convert synthesis gas to C₄ hydrocarbons over Fe‐Co/ZrO₂ (FT) and SO₄^2—/ZrO₂ (SZ) catalysts in a dual reactor system, keeping the FT to SZ catalysts ratio at 1:1.5. Five Fe‐Co/ZrO₂ catalysts with different Fe and Co loading, and SZ with 15 wt% SO₄^2— were prepared and extensively characterized using various physico‐chemical methods. The FT synthesis process was initially performed using a Fe‐Co/ZrO₂ catalyst in a single reactor and the effects of Fe and Co mass ratio, reaction temperature, space velocity on the production of C₄ hydrocarbons and C₂‐C₄ olefins were investigated. Results indicated that a 3.71% Fe—8.76% Co/ZrO₂ mixed oxide catalyst alone at 260°C and 5 h^—1 gave high selectivities of C₂‐C₄ olefins (～26.1 wt%) and total C₄ hydrocarbon product (～16.2 wt%). The MFT process 150°C gave higher C₄ (～31.6 wt%), isobutane (～22.9 wt%) and C₂‐C₄ (31.1 wt%) selectivities.     

WO3 and MoO3 addition effect on V2O5/TiO2 as promoters for removal of NOx and SOx from stationary sources

As an attempt to improve the catalytic activity at higher reaction temperatures between 300-450°C, various mole ratios of WO₃ were added to V₂O₅/TiO₂ catalytic systems. And also, in order to suggest a new mixed oxide catalyst system for simultaneous removal of NO_x and SO_x, from stationary sources, MoO₃-V₂O₅/TiO₂catalysts were prepared by a conventional impregnation method together with a newly introduced method of surface fixation (non-aqueous solution method). In case of WO₃ addition, at higher reaction temperature range (300–450°C), WO₃ and WO₃-V₂O₅/TiO₂ catalysts showed significant high conversion in NO reduction with NH₃ while V₂O₅/TiO₂ catalyst showed a significant change in selectivity mainly due to the excess side reaction of NH₃ oxidation. This difference in selectivity due to NH₃ oxidation at high temperature is supposed to be associated with the difference in values of surface excess oxygen between WO₃ and V₂O₅ on titania. The surface acidities of tested catalysts were relatively well correlated with the % conversion of NO at 400°C. In case of MoO₃ addition, the catalytic activity for the simultaneous removal of NO_x and SO_x were quite enhanced by the addition of MoO₃ into V₂O₅/TiO₂ catalysts. The enhanced activities were responsible for the formation of Mo=O bond on the intermediate species produced by solid solutions on MoO₃-V₂O₅/TiO₂ (aqueous). However, in the case of MoO₃-V₂O₅/TiO₂ (non-aqueous), the exact source of active site was not able to detect in IR spectra in spite of more enhanced activity was obtained in this study. After SO₂ contact, VOSO₄ is newly formed on the surface of catalyst, which supposed to be associated with the activity enhancement.     

Alkylation of phenol with methanol over molybdenum oxide supported on NaY zeolite

A series of MoO₃/NaY catalysts were prepared with Mo loadings ranging from 2 to 16 wt% and characterized by X-ray diffraction (XRD), BET specific surface area and temperature-programmed desorption (TPD) of ammonia. XRD results revealed that the crystallinity of NaY zeolite was found to decrease with increase in Mo loading in the catalysts. The total acidity measured by ammonia TPD of the catalysts was found to decrease with increase in Mo loading. The catalytic properties were evaluated for the vapor phase alkylation of phenol with methanol and the results were correlated with results obtained from different characterization techniques. The conversion of phenol decreases as Mo loading increases in the catalyst. With increase in Mo loading on NaY zeolite the selectivity for the formation of C-alkylated compounds was decreased. However, the selectivity towards the formation of O-alkylated products was increased.     

Characterization and reactivity of MoO3 supported on AlPO4

A series of MoO₃/AlPO₄ catalysts with molybdena content varying from 2 to 16 wt% were prepared and characterized by low temperature oxygen chemisorption (LTOC), ammonia chemisorption, X-ray diffraction (XRD) and electron spin resonance (ESR). Maximum O₂ uptake was observed at 6 wt% MoO₃ loading indicating the completion of monolayer. The ESR results are in conformity with LTOC and XRD data. The activities of the catalysts were tested in methanol partial oxidation and are correlated with their surface characteristics wherever possible.IICT Communication No. 3188.