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

Content Provider	CUSAT-Thesis
Advisor	Dr.Sugunan, S
Researcher	Maya, G
Abstract	The aim of catalysis research is to apply the catalyst successfully in economicallyimportant reactions in an environmentally friendly way. The present work focuses on themodification of structural and surface properties of ceria and ceria-zirconia catalysts bythe incorporation of transition metals. The applications of these catalysts in industriallyimportant reactions like ethylbenzene oxidation, alkylation of aromatics are alsoinvestigated.Sol-gel method is effective for the preparation of transition metal modifiedceria and ceria-zirconia mixed oxide since it produces catalyst with highly dispersedincorporated metal. Unlike that of impregnation method plugging of pores is notprominent for sol-gel derived catalyst materials. This prevents loss of surface area onmetal modification as evident for BET surface area measurements.The powder X-ray diffraction analysis confirms the cubic structure oftransition metal modified ceria and ceria-zirconia catalysts. The thermal stability isevident from TGA/DTA analysis. DR UV-vis spectra provide information on thecoordination environment of the incorporated metal. EPR analysis ofCr, Mn and Cumodified ceria and a ceria-zirconia catalyst reveals the presence of different oxidationstates of incorporated metal.Temperature programmed desorption of ammonia and thermogravimetricdesorption of 2,6-dimethyl pyridine confirms the enhancement of acidity on metal incorporation. High a-methyl styrene selectivity in cumene cracking reaction impliesthe presence of comparatively more number of Lewis acid sites with some amount ofBronsted acid sites. The formation of cyclohexanone during cyclohexanoldecomposition confirms the presence of basic sites on the catalyst surface.Mn and Cr modified catalysts show better activity towards ethylbenzeneoxidation. A redox mechanism through oxometal pathway is suggested.All the catalysts were found to be active towards benzylation of toluene anda-xylene. The selectivity towards monoalkylated products remains almost 100%. Thecatalytic activity is correlated with the Lewis acidity of the prepared systems.The activity of the catalysts towards methylation of phenols depends on thestrength acid sites as well as the redox properties of the catalysts. A strongdependence of methylation activity on the total acidity is illustrated.
File Format	PDF
Language	English
Publisher Institution	Cochin University of Science and Technology
Access Restriction	Open
Subject Keyword	Ceria Ceria-Zirconia Catalysis Sol-gel Route Oxidation Friedel Crafts Benzylation Toluene Methylation Phenol Ethylbenzene Applied Chemistry
Content Type	Text
Educational Degree	Doctor of Philosophy (Ph.D.)
Resource Type	Thesis