K.S. Rama Rao

Ammoxidation of 3-picoline over V2O5/TiO2 (anatase) system. II. Characterisation of the catalysts by DTA, SEM, FTIR, ESR and oxygen and ammonia chemisorption

Abstract In an earlier communication the ammoxidation activity of V 2 O 5 /TiO 2 catalysts with V 2 O 5 loadings in the range 0.4–9.9 mol% was correlated to the average oxidation number of vanadium in the catalysts. In the present work, these catalysts were characterised by SEM, FTIR, ESR, DTA techniques and chemisorption of NH 3 and O 2 . The scanning electron micrographs of the catalysts indicate that deposition of vanadium is taking place inside the mesopores of titania (anatase) up to 3.4 mol% V 2 O 5 corresponding to a monolayer coverage. Beyond this loading neddle-like and bulk structures of vanadia appear probably on the external surface of the catalysts. The bands at 1010–1020 cm −1 appearing in the FTIR spectra of fresh catalysts are characteristic of highly dispersed monomeric VO x units and two-dimensional structures. The FTIR spectra of the used catalysts are altogether different from those of the fresh catalysts suggesting that the active phase has been drastically modified during the course of the reaction. The ESR spectrum of 0.4 mol% V 2 O 5 shows an eightfold well resolved hyperfine structure indicating that V 4+ is in diluted conditions on anatase surface. As V 2 O 5 content increases the hyperfine structure of ESR spectrum gets progressively smeared out due to strong coupling between V 4+ dipoles. The results indicate that vanadium is in a highly dispersed distorted octahedral or square pyramidal geometry at 3.4 mol% corresponding to a monolayer coverage. The DTA curves contain endothermic peaks at 100–150°C and 630–675°C corresponding to desorption of adsorbed water and melting of vanadia particles and loss of oxygen from vanadia. Chemisorption of NH 3 and O 2 is observed to exhibit maximum at the monolayer V 2 O 5 loading just as the ammoxidation activity of the catalysts.

Ammoxidation of 3-picoline over V2O5/TiO2 (anatase) system : I. Relationship between ammoxidation activity and oxidation state of vanadium

Abstract A series of titania (anatase)-supported vanadia catalysts ranging in V 2 O 5 content from 0.4 to 9.9 mol% was prepared by wet impregnation technique, characterized by BET surface area measurement and X-ray diffraction, and evaluated for ammoxidation of 3-picoline. The average oxidation number of vanadium in the fresh and used catalysts was determined by titrimetric methods. The ammoxidation activity and the average oxidation number were observed to increase with vanadia loading up to 3.4 mol% in the catalyst which corresponds to a monolayer coverage. The phase transformation of anatase to rutile after the reaction was observed at a V 2 O 5 loading of 5.9 mol%. The slow decrease of ammoxidation activity beyond 3.4 mol% V 2 O 5 was attributed to the coverage of active monomeric VO x species on the support by bulk vanadia and by other oxides, and also to compound formation with ammonia.

Effect of support modification by carbon coverage in the dehydrogenation activity of Cu/Al2O3 catalyst

Gamma alumina and carbon covered gamma alumina supported Cu catalysts were prepared and characterized by adsorptive decomposition of N2O, NH3 chemisorption and temperature-programmed reduction. The decrease in interaction of copper species with alumina of carbon covered alumina has influence on the conversion and selectivity of the reaction of cyclohexanol to cyclohexanone.Gamma alumina and carbon covered gamma alumina supported Cu catalysts were prepared and characterized by adsorptive decomposition of N2O, NH3 chemisorption and temperature-programmed reduction. The decrease in interaction of copper species with alumina of carbon covered alumina has influence on the conversion and selectivity of the reaction of cyclohexanol to cyclohexanone.

Calcined Mg–Al, Mg–Cr and Zn–Al hydrotalcite catalysts for tert-butylation of phenol with iso-butanol—a comparative study

Calcined hydrotalcites (CHTs) are studied for the tert-butylation of phenol using iso-butanol in the temperatures ranging from 350 to 500 °C. The major products of this reaction on calcined magnesium–aluminium hydrotalcites (CMA-HTs) are O-tert-butyl phenol (tert-butyl phenyl ether, OTBP) and 2-tert-butyl phenol (o-tert-butyl phenol, 2TBP) with O-butenyl phenol (butenyl phenyl ether, OBP) and 2-butenyl phenol (o-butenyl phenol, 2BP) as useful by-products. With a view to understand the reaction mechanism and the reaction path, tert-butylation of phenol is studied by changing both Mg[M(II)] and Al[M(III)] ions with Zn2+ and Cr3+, respectively. Thus, Mg–Al (MA), Mg–Cr (MC) and Zn–Al (ZA) hydrotalcites (with M2+:M3+ ratio=2) are prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS), differential thermal analysis/thermo gravimetric analysis (DTA/TG), BET-surface area (BET-SA) and acidity–basicity measurements (temperature-programmed desorption (TPD) of NH3 and CO2). Mixed oxides obtained from CHTs are found to be more active over their individual oxides for the tert-butylation of phenol. The butylation activities of the three different CHTs are in the order CMA-HT>CZA-HT>CMC-HT. A different product distribution is obtained over calcined Mg–Cr and Zn–Al hydrotalcites for the tert-butylation of phenol showing the influence of acid–base properties on the activity of the catalysts. A probable mechanism based on the experimental observations has been proposed in order to explain the formation of butenyl phenols.

Novel calcined Mg-Cr hydrotalcite supported Pd catalysts for the hydrogenolysis of CCl2F2

Pd supported on calcined Mg-Cr hydrotalcite, MgO and Cr2O3 are prepared and tested for the hydrogenolysis of CCl2F2. It is found that 6 wt.% Pd loading is optimum on MgO-Cr2O3 hydrotalcite. The hydrogenolysis activities for CCl2F2 are found in the order: Pd/HT>Pd/MgO>Pd/Cr2O3. While Pd/HT is yielding deep hydrogenation product (CH4) with more selectivity, Pd/MgO is yielding dechlorination product (CH2F2). Pd/Cr2O3 is showing poor activity. It is observed that calcined Mg-Cr hydrotalcite has shown synergy when used as a support for Pd and used for the hydrogenolysis of CCl2F2.

Microwave irradiation: an effective method for the preparation of low dispersed Pd/Al2O3 catalysts used in the hydrodechlorination of CCl2F2 to CH2F2

Microwave irradiation is found to be a faster method for the preparation of low dispersed Pd/Al2O3 catalysts with higher activity and selectivity to CH2F2 in the hydrodechlorination of CCl2F2.

Highly active titania supported ceria catalysts for ammoxidation of picolines

TiO2 supported ceria catalysts with 20 wt% CeO2 were prepared by impregnating rutile and anatase polymorphs in aqueous solution of ammonium ceric nitrate [(NH4)2Ce(NO3)6], characterized by BET surface area measurement and low temperature oxygen chemisorption (LTOC) at −78°C and evaluated for ammoxidation of β- and γ-picolines. Anatase supported catalyst has exhibited higher ammoxidation activities than rutile supported one and pure ceria. Turnover frequencies calculated from ammoxidation rates and irreversible O2 uptakes in respect to a particular picoline isomer were almost equal for pure supports on one hand and for supported ceria catalysts on the other. The two structural isomers, β- and γ-picolines seem to have exhibited marked steric effect in their reactivity in catalysis on the catalysts.

Oxidative dehydrogenation of ethane to ethylene on Cr2O3/Al2O3–ZrO2 catalysts: the influence of oxidizing agent on ethylene selectivity

Abstract Oxidative dehydrogenation of ethane to ethylene was investigated on Al2O3, ZrO2 and Al2O3–ZrO2 mixed oxide supported Cr2O3 catalysts taking O2 and CO2 as oxidants. The catalysts were characterized by nitrogen adsorption, X-ray diffraction, temperature-programmed reduction, and X-ray photoelectron spectroscopy. The catalytic activity depended on the chromium species formed on the surface. However, the selectivity to ethylene was influenced by the oxidizing agent (O2 or CO2). Temperature-programmed desorption of ethylene was employed to confirm the role of oxidant in deciding ethylene selectivity.

Selective hydrogenolysis of dichlorodifluoromethane (CCl2F2) over CCA supported palladium bimetallic catalysts

Abstract La, Bi, Sb, Sn, Ba, and Zn are chosen for addition on carbon covered alumina (CCA) supported Pd catalyst. The effect of these second metals on supported Pd catalysts has been studied for the hydrogenolysis activity of CCl 2 F 2 . Bi and Sb promoters have been found to improve not only the thermal stability but also selectivity towards CH 2 F 2 . Sn bimetallic catalyst exhibited high selectivity towards CHClF 2 . This may be explained on the basis of the metal–metal interactions that influence the reducibility of the palladium. These improved properties arise due to inter-metallic compound formation as evidenced from the XRD and TPR data on CCA supported bimetallic palladium catalysts. The effect of addition of second metal on Pd/CCA catalyst is screened in terms of partial dehalogenation ability and thermal stability for hydrodechlorination activity of CCl 2 F 2 to maximize the CH 2 F 2 yield.

Highly selective zirconium oxychloride modified Pd/C catalyst in the hydrodechlorination of dichlorodifluoromethane to difluoromethane

Zirconium oxychloride modified active carbon supported palladium catalyst appears to be a promising system in the hydrodechlorination of CCl2F2 to yield CH2F2 in greater yields; showing an altogether different product distribution compared to Pd/C and Pd/ZrO2 catalysts. The catalysts have been characterized by BET-surface area, CO-chemisorption, X-ray diffraction (XRD), temperature programmed reduction (TPR) analysis and fluorine contents in used catalysts. The interaction of Zr species with Pd and the formation of fluorinated zirconium species during the course of reaction led to the higher selectivity towards CH2F2.