Akula Venugopal

The Water-Gas Shift Reaction Over Au-Based, Bimetallic Catalysts. The Au-M (M=Ag, Bi, Co, Cu, Mn, Ni, Pb, Ru, Sn, Tl) on Iron(III) Oxide System

The bimetallic Au-M/Fe2O3 catalysts were prepared by deposition coprecipitation method with Au/M atomic ratio of 1. All the catalysts were measured for WGS reaction and characterized by TPR/TPO studies. Ruthenium- and nickel-modified catalysts showed higher WGS activities compared to the other systems including unmodified Au/Fe2O3 at low temperature (100 °C). At higher temperature (240 °C), ruthenium-, nickel-, bismuth-, lead-, copper-, silver-, thallium- and tin-modified catalysts were more active than unmodified Au/Fe2O3. Manganese- and cobalt-modified catalysts were less active than unmodified Au/Fe2O3. TPR analyses indicated a shift in reduction temperature in the bimetallic catalysts, suggesting a degree of interaction between gold and the second metal.

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.

N-Alkylation of amines with alcohols over nanosized zeolite beta

Direct N-alkylation of amines with alcohols was successfully performed by using nanosized zeolite beta, which showed the highest catalytic activity among other conventional zeolites. This method has several advantages, such as eco-friendliness, moderate to high yields, and simple work-up procedure. The catalyst was successfully recovered and reused without significant loss of activity and only water is produced as co-product. In addition, imines were also efficiently prepared from the tandem reactions of amines with 2-, 3- and 4-nitrobenzyl alcohols using nanosized zeolite beta.

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.

An investigation on the influence of support type for Ni catalysed vapour phase hydrogenation of aqueous levulinic acid to γ-valerolactone

Ni (20 wt%) supported on SiO2, γ-Al2O3 and ZrO2 catalysts was examined for hydrogenation of aqueous levulinic acid (LA) to γ-valerolactone (GVL) at 270 °C and ambient pressure. The band intensities of Bronsted (BAS: 1540 cm−1) and Lewis acid sites (LAS: 1450 cm−1) estimated by pyridine adsorbed DRIFT spectra revealed a lower ratio of BAS/LAS over the Ni/SiO2 catalyst than over the Ni/ZrO2 and Ni/γ-Al2O3 catalysts. The rate of angelica lactone (AL) formation was lower than the rate of AL hydrogenation over the Ni/SiO2 catalyst. The poisoning and regeneration of the Ni/SiO2 catalyst using pyridine and 2,6-dimethylpyridine demonstrated that Lewis acid sites influenced the conversion of LA to AL and subsequent hydrogenation of AL to GVL occurred on surface Ni sites. In contrast, Bronsted acid sites were responsible for the ring opening of GVL to valeric acid (VA). Kinetic data emphasized that the hydrogenation activity and product distribution were dependent on the type of acid site, and the Ni sites in close proximity to Bronsted acid sites are prone to hydrogenolysis of GVL to valeric acid and hydrocarbons.

Catalytic decomposition of CH4 over Ni-Al2O3-SiO2 catalysts: Influence of pretreatment conditions for the production of H2

Abstract This article reports the production of CO x free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al 2 O 3 -SiO 2 catalysts. The influence of reaction temperature, pretreatment temperature, and effect of reductive pretreatment on the decomposition of methane activity is investigated. The physico-chemical characteristics of fresh and deactivated samples were characterized using BET-SA, XRD, TPR, SEM/TEM, CHNS analyses and correlated with the methane decomposition results obtained. The Ni-Al-Si (4:0.5:1.5) catalyst reduced with hydrazine hydrate produced better H 2 yields of ca . 1815 mol H 2 /mol Ni than the catalyst reduced with 5% H 2 /N 2 .

Selective hydrogenation of levulinic acid to γ-valerolactone over a Ru/Mg–LaO catalyst

Ruthenium supported on magnesium–lanthanum mixed oxide (Ru/Mg–LaO) obtained from Mg–La hydrotalcite (a base support) catalyzes the hydrogenation of biomass derived levulinic acid (LA) to γ-valerolactone (GVL). The conversion of LA to GVL in toluene was found to be 92% with the selectivity >99% at 80 °C and 0.5 MPa hydrogen pressure in 4 h. It is the first example on the basic support under mild reaction conditions. The Ru nanoparticles on the Mg–LaO support exhibited excellent GVL yields for 5 cycles, making it a sustainable process.

A Pd(II)/Mg–La mixed oxide catalyst for cyanation of aryl C–H bonds and tandem Suzuki–cyanation reactions

A palladium(II)/magnesium–lanthanum mixed oxide (Pd(II)/Mg–La) catalyst is a reusable catalyst for cyanation of aromatic C–H bonds by using the combination of NH4HCO3 and DMSO as the ‘‘CN’’ source. Moderate to good yields of aromatic nitriles were obtained. An excellent regioselectivity was achieved using the present protocol. A tandem process involving Suzuki coupling followed by a cyanation reaction was also developed using the heterogeneous (Pd(II)/Mg–La) catalyst. This cascade process resulted in the formation of aromatic nitrile from simple 2-halopyridine. The catalyst was recovered by centrifugation and reused for three consecutive cycles with nearly consistent activity and selectivity.