Maya, G; Dr.Sugunan, S(Cochin University of Science and Technology, December , 2006)
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Abstract:
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.
Description:
Department of Applied Chemistry,
Cochin University of Science and Technology