Catalysis by Transition Metal Modified Ceria and Ceria-Zirconia Mixed Oxides Prepared via Sol-Gel Route

The aim of catalysis research is to apply the catalyst successfully in economically important reactions in an environmentally friendly way. The present work focuses on the modification of structural and surface properties of ceria and ceria-zirconia catalysts by the incorporation of transition metals. The applications of these catalysts in industrially important reactions like ethylbenzene oxidation, alkylation of aromatics are also investigated.Sol-gel method is effective for the preparation of transition metal modified ceria and ceria-zirconia mixed oxide since it produces catalyst with highly dispersed incorporated metal. Unlike that of impregnation method plugging of pores is not prominent for sol-gel derived catalyst materials. This prevents loss of surface area on metal modification as evident for BET surface area measurements.The powder X-ray diffraction analysis confirms the cubic structure of transition metal modified ceria and ceria-zirconia catalysts. The thermal stability is evident from TGA/DTA analysis. DR UV-vis spectra provide information on the coordination environment of the incorporated metal. EPR analysis ofCr, Mn and Cu modified ceria and a ceria-zirconia catalyst reveals the presence of different oxidation states of incorporated metal.Temperature programmed desorption of ammonia and thermogravimetric desorption of 2,6-dimethyl pyridine confirms the enhancement of acidity on metal incorporation. High a-methyl styrene selectivity in cumene cracking reaction implies the presence of comparatively more number of Lewis acid sites with some amount of Bronsted acid sites. The formation of cyclohexanone during cyclohexanol decomposition confirms the presence of basic sites on the catalyst surface.Mn and Cr modified catalysts show better activity towards ethylbenzene oxidation. A redox mechanism through oxometal pathway is suggested.All the catalysts were found to be active towards benzylation of toluene and a-xylene. The selectivity towards monoalkylated products remains almost 100%. The catalytic activity is correlated with the Lewis acidity of the prepared systems.The activity of the catalysts towards methylation of phenols depends on the strength acid sites as well as the redox properties of the catalysts. A strong dependence of methylation activity on the total acidity is illustrated.

Synthesis, Characterization and Catalytic Activity of Nanocrystalline Ceria Modified With Zirconia

The use of catalysts in chemical and refining processes has increased rapidly since 1945, when oil began to replace coal as the most important industrial raw material. Catalysis has a major impact on the quality of human life as well as economic development. The demand for catalysts is still increasing since catalysis is looked up as a solution to eliminate or replace polluting processes. Metal oxides represent one of the most important and widely employed classes of solid catalysts. Much effort has been spent in the preparation, characterization and application of metal oxides. Recently, great interest has been devoted to the cerium dioxide (CeO2) containing materials due to their broad range of applications in various fields, ranging from catalysis to ceramics, fuel cell technologies, gas sensors, solid state electrolytes, ceramic biomaterials, etc., in addition to the classical application of CeO2 as an additive in the so-called three way catalysts (TWC) for automotive exhaust treatment. Moreover, it can promote water gas shift and steam reforming reactions, favours catalytic activity at the interfacial metal-support sites. The solid solutions of ceria with Group IV transitional-metals deserve particular attention for their applicability in various technologically important catalytic processes. Mesoporous CeO2−ZrO2 solid solutions have been reported to be employed in various reactions which include CO oxidation, soot oxidation, water-gas shift reaction, and so on. Inspired by the unique and promising characteristics of ceria based mixed oxides and solid solutions for various applications, we have selected ceria-zirconia oxides for our studies. The focus of the work is the synthesis and investigation of the structural and catalytic properties of modified and pure ceria-zirconia mixed oxide.

Surface electron properties and catalytic activity of cerium-zirconium mixed oxides

The electron donating properties, surface acidity/ basicity and catalytic activity of cerium - zirconium mixed oxides at various compositions have been reported at an activation temperature of 500 degree C. The catalytic activity for the esterification of acetic acid with n-butanol has heen correlated with electron donating properties and surface acidity/basicity of the oxides.

Alkylation of phenol with methanol over mixed oxides of tin with some rare earth elements

Alkylation of phenol with methanol has been carried out over Sn-La and Sn-Sm mixed oxides of varying compositions at 623 K in a vapour phase flow reactor. It is found that the product selectivity is greatly influenced by the acid-base properties of the catalysts. Ortho-cresol formation is favoured over catalysts with weak acid sites whereas formation of 2,6-xylenol occurs in the presence of stronger acid sites. The cyclohexanol decomposition reaction and titrimetric method using Hammett indicators have been employed to elucidate the acid-base properties of the catalysts.

Electron donating properties and catalytic actiVity of cerium oxide and its mixed oxides with alumina

The electron donating properties of Ce02 and its mixed oxides with alumina have been determined from the studies of adsorption of electron acceptors of various electron affinities on the surface of these oxides. The catalytic activity of these oxides towards some reactions such as oxidation of alcohols and reduction of ketones have been Correlated with their surface electrondonor properties. The surface acidity/basicity of these oxides have also been determined by titration method using a set of Hammett indicators.

Basicity and electron donor properties of lanthanum oxide and its mixed oxides with alumina

The electron donating properties of La2O3 activated at 300, 500 and 800·C and its mixed oxides with alumina are reported from the studies on adsorption of electron acceptors of varying electron affinity on La203. The electron acceptors with their electron affinity values given in parenthesis are: 7,7,8,8-tetracyanoquinodimethane (2.84 eV), 2,3,5,6-tetrachloro-I,4-benzoquinone (2.40 eV) and p-dinitrobenzene(l.77eV). The basicity of the oxide has been determined by titration with n-butylamine and Ho.max values are reported. The limit of electron transfer from the oxide to the electron acceptor is between 2.40 and 1.77 eV. It is observed that La203 promotes the surface electron properties of alumina without changing its limit of electron transfer.

Acid-base, electron-donating and magnetic properties of Nd2O3 and its mixed oxides with alumina catalysts

The electron donor properties of Nd2O3 activated at 300, 500 and 800°C were investigated through studies on the adsorption of electron acceptors of various electron affinities - 7, 7, 8,8-tetracyanoquinodimethane (2.84 eV). 2, 3, 5, 6-tetrachloro-l , 4-benzoquinone (2.40 eV). p-dinitrobenzene (1.77 eV), and m-dinitrobenzene (1.26 eV) in solvents acetonitrile and 1, 4-dioxan. The extent of electron transfer during adsorption has been found from magnetic measurements and electronic spectral data. The corresponding data on mixed oxides of neodymium and aluminium are reported for various. compositions. The acid-base properties of catalysts were also determined using a set of Hammett indicators.

Surface acidity/basicity of yttria and its mixed oxides with alumina catalysts

Acid/base strength distribution of Y2O3 and its mixed oxides with alumina catalysts are measured on Hammett acidity function scale and expressed in terms of H0max value. Basicity of Y2O3 increases with increase in activation temperature and for mixed oxides the basicity increases with increase in concentration of Y2O3, in the catalyst.

Electron Donating Property and Catalytic Activity of Perovskite-type Mixed Oxides (ABO3 ) Consisting of Rare Earth and 3d Transition Metals

The catalytic activity of Perovskite-type mixed oxides (LaCo03 . PrCo03 and SmCo03 ) for the reduction of cyclohexanone to cyclohexanol with 2-propanol (Meerwein-Ponndorf-Verley reduction) has been studied. The data have been correlated with the surface electron donor properties of these mixed oxides.

Surface Electron Donor Properties of Dy2O3,Y2O3 and Their Mixed Oxides with Alumina Catalyst

The limit of electron transfer in electron affinity from the oxide surface to the electron acceptor (EA) are reported from the adsorption of EA on DY203, mixed oxides of DY203 with alumina and mixed oxides of Y203 with y-alumina. The extent of electron transfer is understood from magnetic measurements.

Catalytic activity of some of the perovskite-type mixed oxides (ABO3) consisting of rare earth and 3d transition metals

The catalytic activity of some of the ABO3 (A = La, Pr and Sm, B= Cr, Mn, Fe, Co and Ni) perovskite-type oxides for the liquid phase reduction of ketone and oxidation of alcohol in 2-propanol medium has been studied. The data have been correlated with the surface electron donor properties of these oxides. The surface electron donor properties have been determined from the adsorption of electron acceptors of varying electron affinities on the oxide surface.

Surface acidity/basicity and catalytic activity of mixed oxides of Zr, La and Al

The surface acidity/basicity of binary oxides of Zr and La and the ternary oxides of Zr, La and Al are reported. The data have been correlated with their catalytic activity towards liquid phase reduction of cyclohexanone.

Acidity, basicity and catalytic activity of La−Zn mixed oxides

Surface acidity/Basicity of mixed oxides of La and Zn activated at three different temperatures were determined. The data have been correlated with the catalytic activity for liquid phase reduction of cyclohexanone in isopropanol.