B. Mahipal Reddy

Dispersion and activity of molybdena-alumina catalysts prepared by impregnation and solid/solid wetting methods

Alumina-supported molybdena catalysts were prepared by both the standard incipient wetness method and by mixing MoO{sub 3} and Al{sub 2}O{sub 3} (solid/solid wetting), followed by thermal treatment of 500 C under dry or wet O{sub 2} atmospheric conditions. These catalysts were characterized by means of O{sub 2} chemisorption at {minus}78 C, CO{sub 2} uptake at ambient temperature, X-ray diffraction (XRD), and electron spin resonance (ESR) techniques. Activities of the catalysts were determined for partial oxidation of methanol and hydrodesulfurization of thiophene at atmospheric pressure. XRD results suggest high dispersion of Mo-oxide on alumina support irrespective of their method of preparation. However, O{sub 2} and CO{sub 2} uptake measurements reveal partial coverage of the Al{sub 2}O{sub 3} support surface by the Mo-oxide phase and appear to depend on the gas atmosphere (wet or dry O{sub 2}) during heat treatments in case of solid/solid wetting method. ESR, oxygen and carbon dioxide uptakes and the catalytic properties clearly demonstrate that spontaneous spreading of MoO{sub 3} on the Al{sub 2}O{sub 3} support at 500 C in the presence of wet O{sub 2} is a most effective alternative method for preparing molybdenum-alumina catalysts.

Reactivity of V2O5 with TiO2ZrO2 mixed oxide: An X-ray diffraction study☆

Abstract The reactivity of vanadia with TiO 2 ZrO 2 mixed oxide support was investigated by the X-ray powder diffraction technique. TiO 2 ZrO 2 mixed oxide was prepared by the technique of precipitation from homogeneous solution. Ammonium metavanadate was used as a source of vanadia, and V 2 O 5 contents varied from 2 to 16 wt%. Calcination of Ti- and Zr-hydroxides at 773 K result in the formation of an amorphous phase, and further heating at 873 K converts this amorphous phase into a crystalline TiO 2 · ZrO 2 compound. This compound is quite stable in the absence of V 2 O 5 . Addition of V 2 O 5 and heating of the samples beyond 873 K result in the formation ZrV 2 O 7 , with the simultaneous presence of TiO 2 rutile phase. Quantities of these phases increase with increasing in V 2 O 5 content.

Oxygen chemisorption and activity studies on alumina- and carbon-supported hydrodesulphurization catalysts

Abstract Co Mo and a series of Mo catalysts were prepared on alumina and carbon supports and were characterized by low temperature oxygen chemisorption (LTOC) at−78°C. The reactivity of sulphided catalysts for thiophene hydrodesulphurization (HDS) and cyclohexene hydrogenation (HYD) were measured in a flow microreactor at atmospheric pressure. Three commercial HDS catalysts were also subjected to these studies for comparison. A good correlation was found between HDS activity and oxygen uptake. Carbon-supported catalysts had a much higher HDS activity and lower HYD activity than alumina-supported catalysts. The improved HDS activity was related to the better dispersion of the molybdenum sulphide phase on the carbon support.

Influence of MoO3 and WO3 on the dispersion and activity of V2O5 in vanadia-silica catalysts

Abstract A series of silica-supported vanadia and molybdenum- and tungsten-promoted vanadia catalysts have been prepared and were characterized by means of low temperature oxygen chemisorption, 1 H magic angle spinning nuclear magnetic resonance, X-ray diffraction, and electron spin resonance techniques. Reactivities of these catalysts for partial oxidation of methanol were also determined under atmospheric pressure in a flow microreactor. These results suggest the formation of the “patchy monolayer” phase of V oxide at lower loadings and on top of it bulk V 2 O 5 at higher vanadium loadings. The presence of molybdenum increases the activity of the catalyst, whereas tungsten has the opposite effect. The improved activity of molybdena-vanadia catalyst was related to the better dispersion of the V oxide phase in the presence of Mo on silica surface.

Synthesis of isobutyraldehyde from methanol and ethanol over mixed oxide supported vanadium oxide catalysts

Abstract A one step synthesis of isobutyraldehyde from methanol and ethanol over mixed oxide (TiO2-Al2O3, TiO2-SiO2, TiO2-ZrO2 and TiO2-SiO2-ZrO2) supported vanadium oxide catalysts was investigated at atmospheric pressure and 350 °C. The V2O5/TiO2-SiO2 catalyst showed a better performance in terms of total conversion and product selectivity than the other catalyst systems.

Phase transformation study of titania in V2O5TiO2 and MoO3TiO2 catalysts by X-ray diffraction analysis

The effect of the presence of vanadia or molybdena and the thermal treatment on the phase transformation of titania in V2O5/TiO2 and MoO3/TiO2 catalysts was investigated using X-ray powder diffraction (XRD) analysis. The titania support used was a commercial sample from Harshaw containing anatase together with a small quantity of graphite. The XRD results suggest that when the TiO2 support is calcined at 973 K, anatase is partially transformed into rutile, whereas at 1273 K it is totally converted to rutile. In the presence of V2O5 the temperature of partial conversion is reduced to 813 K, and a total transformation is noted already at 973 K. MoO3 also induces this transformation, but is less effective than V2O5. XRD results further show that when the V2O5/TiO2 catalyst is subjected to calcination at 973 K, no crystalline V2O5 phase is present. The same is not true for MoO3, which is present in a crystalline state at this calcination temperature. This study reveals clearly that vanadia and molybdena behave differently when impregnated on the same titanium dioxide support.

Titration of active sites for partial oxidation of methanol over V2O5/SnO2 and MoO3/SnO2 catalysts by a low-temperature oxygen chemisorption technique

Abstract The amount of oxygen chemisorbed at − 78°C on V 2 O 5 /SnO 2 and MoO 3 /SnO 2 catalysts has been found to correlate directly with the conversion of methanol at 175°C. These catalysts have shown high selectivity for the formation of formaldehyde, selectivities being over 95% for V 2 O 5 /SnO 2 and ca. 90% for MoO 3 /SnO 2 .

Solvent-free aerobic oxidation of ethylbenzene over supported Ni catalysts using molecular oxygen at atmospheric pressure

Abstract We investigated the aerobic oxidation of ethylbenzene in the absence of solvent or any additive carried out over Ni on different types of supports namely SiO2, hydroxyapatite, SBA-15, and USY Zeolites. The oxidation of ethylbenzene activities was measured in a round bottom flask immersed in oil bath at known reaction temperature. The physicochemical characteristics of the catalysts were examined by BET surface area, XRD, FT-IR and the oxidation activities were correlated with the acidities of the catalysts obtained by TPD of NH3. It was observed that both hydroxyapatite and USY (13% Na2O) supported Ni catalysts displayed higher ethylbenzene conversion and 80% selectivity towards acetophenone.

A single-step synthesis of isobutyraldehyde from methanol and ethanol over CuO–ZnO–Al2O3 catalyst

Selective synthesis of isobutyraldehyde from methanol and ethanol in a single step over CuO–ZnO–Al2O3 catalyst is reported.

A study of tin dioxide and antimony tetroxide supported vanadium oxide catalysts by solid-state 51V and 1H NMR techniques

A series of vanadia catalysts with various V2O5 loadings supported on SnO2 and alpha-Sb2O4 are investigated by the application of X-ray diffraction and solid-state 51V and 1H NMR techniques. XRD results show no evidence for the formation of a crystalline vanadia phase on both supports. However, the 51V NMR spectra of the catalysts reveal the existence of two types of vanadia species on the surface of the support: one due to a dispersed vanadia phase at lower vanadia loadings and the other due to a crystalline vanadia phase at higher vanadium content. The quantity of the dispersed vanadia phase, however, depends on the nature of the support material. The 1H NMR results provide evidence for the existence or non-existence of a metal oxide support interaction through the support surface hydroxyl groups.