Musti S. Rao

Oxidative dehydrogenation of propane over Cr2O3/Al2O3 and Cr2O3 catalysts: effects of loading, precursor and surface area

Several alumina supported chromium oxide catalysts were prepared by varying the chromium oxide loading, precursors and surface areas of the support. The prepared catalysts were characterized using BET, XRD, XPS and UV–VIS spectroscopic techniques. The monolayer limit was observed to be ∼9mol Cr/m 2 . Below monolayer limits, surface chromium oxide species were present irrespective of precursors and surface area of the support. The activity of the prepared samples was tested for ODH of propane. It was observed that the supported chromium oxide samples were active for the ODH reaction and that propene was the major product. The activity and selectivity increased with loading up to monolayer limits and decreased for higher loadings. Bulk Cr2O3 was also studied for the ODH reaction and found to behave differently than the Cr2O3/Al2O3 catalysts. The efficiency of each surface chromium oxide species on alumina to carry out the ODH of propane, the turn over frequency (TOF), was relatively independent of chromium oxide loading for the monolayer catalysts. However, it appears that a constant fraction of the surface chromium oxide species is active for the ODH of propane. This constant fraction of the surface chromium oxide phase is given by the polymeric chromium oxide species. The inactive fraction is given by the monomeric chromium oxide species that is not reducible.

Oxidative dehydrogenation of n-butane to butadiene: Effect of different promoters on the performance of vanadium-magnesium oxide catalysts

Abstract A detailed study has been performed on the effect of different promoters viz. Cr 2 O 3 , MoO 3 and TiO 2 , which are added to vanadium-magnesium oxide (V-Mg-O) catalyst used for the production of butadiene from n-butane via oxidative dehydrogenation. The results are compared with those obtained from unpromoted V-Mg-O catalyst. It was found that Cr 2 O 3 and MoO 3 promoters enhanced the activity of the catalyst, while TiO 2 enhanced the selectivity. Finally, a fifth V-Mg-O catalyst containing both Cr 2 O 3 and TiO 2 as promoters was prepared and the reaction was studied in detail over this catalyst. A maximum yield of butadiene of 35.5 mol-% was obtained with this catalyst. Electron paramagnetic resonance studies showed that VO 2+ is the active species involved in the reaction. On comparison with the unpromoted V-Mg-O catalyst, it was found that V-Mg-O, Cr 2 O 3 , TiO 2 gave a better yield of butadiene.

Niobium oxide as support material for the oxidative dehydrogenation of propane

Abstract The ability of using niobium oxide (Nb 2 O 5 ) as a support for preparing surface metal oxide species and testing the catalyst for the ODH of propane was done in the present study. Chromium oxide was used as the representative surface metal oxide species. To test the objective several loadings of Cr 2 O 3 /Nb 2 O 5 were prepared by the incipient wetness impregnation technique. Surface area analysis, Raman, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy and TPR studies were used to characterize the sample. It was observed that surface chromium oxide species are formed similar to those on other oxide supports and similar monolayer coverages were achieved. However, the reduction characteristic ( T max temperature) was different due to the change in the Cr–O–support bond. The ODH of propane over the Cr 2 O 3 /Nb 2 O 5 catalysts revealed that the activity increased up to monolayer coverage and then decreased due to the presence of Cr 2 O 3 crystals. Similar observations were seen for the V 2 O 5 /Nb 2 O 5 and MoO 3 /Nb 2 O 5 catalysts. The turnover frequency (TOF) was independent of coverage for the surface chromium, vanadium and molybdenum oxide species on Nb 2 O 5 . The constant TOF suggests the structure insensitivity of this type of reaction. The propene selectivities were high and relatively constant for the Cr 2 O 3 /Nb 2 O 5 catalysts revealing the higher yields that can be obtained on this series of catalysts compared to the Cr 2 O 3 /Al 2 O 3 and Cr 2 O 3 /TiO 2 catalysts. Additional studies involving tungsten and molybdenum oxide additives on 1% Cr 2 O 3 /Nb 2 O 5 reveal the effect of exposed support surface on the propene selectivities.

Phenol oxidation by copper-metallated 9-allyladenine-DVB polymer: reaction catalysis and polymer recycling

Oxidation of a monophenol and two o-diphenols catalyzed by a novel copper-metallated nucleobase polymeric matrix has been observed. This polymer is insoluble in common organic solvents, and thus, catalysis is heterogeneous in nature. Synthesis and characterization of metallated polymer, kinetic profile of catalytic oxidation of an activated monophenol and o-diphenols and catalyst recycling experiments are described.

Selective oxidation of n-butane to maleic anhydride: A comparative study between promoted and unpromoted VPO catalysts

Abstract A comparative study has been conducted between a promoted VPO catalyst (promoted with molybdenum and cerium added simultaneously) and an unpromoted VPO catalyst with respect to their characteristics and catalytic performance. It was observed that the promoted VPO catalyst produced higher yields of maleic anhydride (MA) as compared to the unpromoted one but at comparatively more severe conditions of operations (i.e., higher reaction temperature, higher contact time and higher inlet n-butane concentration). Characterization studies revealed that molybdenum prevents further reduction of V IV to V III , whose transformation was probably responsible for the production of oxides of carbon. As a result, promoted catalyst showed higher selectivity toward MA as compared to the unpromoted one.

Effect of modifiers on the reactivity of Cr2O3/Al2O3 and Cr2O3/TiO2 catalysts for the oxidative dehydrogenation of propane

Chromium oxide supported on alumina and titania supports was modified with oxides of sodium, vanadium and molybdenum. The modified and unmodified chromium oxide catalysts were characterized by several techniques. The presence of surface chromium oxide and surface molybdenum and vanadium oxide species was detected in the unmodified and molybdenum and vanadium oxide modified supported chromium oxide catalysts. The reducibility (Tmax and H/Cr ratio) of the surface chromium species was not affected for the vanadium and molybdenum oxide modified catalysts; however, the reducibility changed noticeably for sodium modified supported chromium oxide catalysts. Studies of the reactivity of the ODH of propane revealed the effect of modifiers on the reactivity properties of the surface chromium oxide species. The activity and propene selectivity decreased for sodium modified supported chromium oxide catalysts. However, the activity increased for vanadium oxide modified catalysts and was similar for molybdenum oxide modified catalysts irrespective of the support. The propene selectivity was higher for molybdenum oxide modified chromium oxide catalysts. However, the propene selectivity for vanadium oxide modified catalysts depends on the support since it appears that the inherent selectivity of the surface vanadium oxide species is reflected.

Statistical techniques in modeling of complex systems: Single and multiresponse models

An exposition of statistical techniques in modeling complex systems (single and multiresponse models) that are representative of recent work on modeling systems is provided. The paper begins with several basic concepts related to linear and nonlinear models. The authors then examine four representative techniques of model discrimination which deal with use of nonintrinsic and intrinsic parameters, use of Bayesian methods, and likelihood discrimination. Next they examine multiresponse models with issues dealing with design of experiments for parameter estimation and model discrimination. A case study on sequential model discrimination in multiresponse models is also discussed. Finally an overview on estimating parameters in models of a dynamical system is briefly discussed. The paper concludes with a summary of unresolved issues, and with suggestions on the future role of modeling in the complex situation.

Influence of the fuel used in the microwave synthesis of Cr2O3

The synthesis and physico-chemical characterization of chromium oxide (Cr2O3) is reported. Samples were prepared by a novel microwave technique using two different fuels, i.e., tetraformaltrisazzine (TFTA) and urea. The physical characterization of the synthesized chromium oxides was achieved using XRD, IR, Raman, BET surface area and pore size distribution (PSD) techniques. The XRD and IR and Raman spectroscopy studies reveal that crystalline Cr2O3 is the only phase formed. The XRD, surface area and particle size analysis reveal that the samples prepared using TFTA as the fuel possess a larger surface area, smaller crystalline size, smaller particle size and larger pore diameter. Both samples were calcined at 600 °C for 6 h so that they could be used for the catalytic oxidation of LPG. Catalytic runs on the Cr2O3 samples revealed that the two samples possess different activity and selectivity. The Cr2O3 sample prepared by using TFTA as the fuel gave rise to more dehydrogenation and cracking compared to the sample prepared by using urea as the fuel, which gave more combustion products.

Thermal characteristics of synthetic sodium zeolites prepared with silica from rice-husk ash

The differential thermal analysis and thermogravimetric data on the synthetic sodium zeolite species NaX, Pc, HS, Z-21 and analcime, prepared with silica from rice-husk ash, are presented. The DTA curves revealed the presence of an initial endotherm for dehydration, followed by an exotherm at around 800 to 850°, representing the structural change and dissociation of all these species, except in the case of zeolite Z-21. For the latter, the initial endotherm was followed by an endotherm in the 900° region. The structural changes inferred on the basis of the DTA curves were confirmed by X-ray diffraction analysis.ZusammenfassungDifferentialthermoanalytische und thermogravimetrische Daten von den synthetischen, unter Verwendung von Reisschalenasche als Siliciumdioxidquelle hergestellten Na-Zeolithen NaX, Pc, HS, Z-21 und Analcim werden angegeben. Die DTA-Kurven zeigen anfangs einen der Dehydratisierung zuzuschreibenden endothermen Peak, dem bei 800–850° ein exothermer folgt, der auf den Zusammenbruch der Zeolithstruktur zurückzuführen ist. Nur im Falle von Z-21 tritt dieser exotherme Peak erst bei 900° auf. Die mittels DTA festgestellten strukturellen Veränderungen wurden röntgendiffraktometrisch verifiziert.РезюмеДизельные топлива с р азличным содержание м вокса были исследова ны усовершенствованны м методом дифференци ального термического анализ а (ДТА), согласно стандартным тестовы м методам. Из ДТА-кривы х были измерены следующие п араметры: начало температурно го пика, максимум темп ературного пика и площадь пика. Ис следовано изменение этих парам етров в зависимости о т таких стандартных характе ристик дизельных топлив, как температу ры помутнения, застыв ания, закупорки фильтра на холоду и содержанием воска и найдена для ни х линейная корреляци я. Коэффициенты коррел яции были вычислены согласно установлен ным уравнениям, котор ые были также использованы д ля определения стандартных парамет ров других образцов д изельного топлива на основе их Д ТА-кривых. Пределы точности усо вершенствованного м етода ДТА найдены удовлетвори тельными.