Co and Mn impregnated MCM-41: their applications to vapour phase oxidation of isopropylbenzene

The mesoporous molecular sieves Si-MCM-41 and Al-MCM-41 (Si/Al = 99) were synthesized and their structures were elucidated by XRD, N-2-adsorption isotherm and TG-DTA technique. Monometallic cobalt and manganese oxides and also their bimetallic forms impregnated Si-MCM-41 and Al-MCM-41 catalysts were prepared by wet method and characterised by XRD, AAS, DRS-UV-vis and ESR techniques. The presence of Co3+ and Mn2+ in the mono and bimetal impregnated catalysts was evident through DRS studies. The analysis with DRS-UV-vis-spectroscopy showed independent existence of cobalt and manganese oxides in the bimetallic catalysts. AAS analysis showed higher loading of manganese than cobalt and the same difference was also observed for bimetal impregnated catalysts. The vapour phase oxidation of isopropylbenzene with CO2-free air was studied over cobalt and manganese oxide impregnated Si-MCM-41 and Al-MCM-41 catalysts. Isopropylbenzene conversion increased with increase in temperature from 200 to 300 degreesC, but at 325 degreesC it decreased. Formation of coke has been noted at all the temperatures. Cumene hydroperoxide, 1,2-epoxy isopropylbenzene, acetophenone and styrene were the products observed in this reaction. Among the products, cumene hydroperoxide was found to have more selectivity than other products over all the catalysts. Both cobalt and manganese oxide impregnated catalysts were found to have nearly the same activity. The study of time-on-stream indicated decrease in conversion with stream due to coke formation. (C) 2004 Published by Elsevier B.V.