Supported Metal Oxide Catalysts: Their Activity to Vapor Phase Oxidation of Ethylbenzene

Mesoporous MCM-41 and Al-MCM-41 (Si/Al = 99 and 158) molecular sieves were synthesized hydrothermally and characterized by low-angle X-ray powder diffraction (XRD), nitrogen adsorption isotherms, FT-IR, and TG-DTA techniques. Monometallic manganese and cobalt oxides and also their bimetallic forms impregnated Si-MCM-41 and AlMCM-41 catalysts were prepared by wet method and characterized by XRD, AAS, DRS UV-vis, and ESR techniques. The presence of Mn2+ and Co3+ in the mono- and bimetal impregnated catalysts was evident through DRS studies. The analysis with DRS-UV-vis spectroscopy showed independent existence of manganese and cobalt 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 catalytic activity of the impregnated catalysts was studied for the vapor phase oxidation of ethylbenzene with air (CO2-free) at 250, 300, 350, 375, and 400 (degree) C. The major products were found to be acetophenone, benzaldehyde, and styrene. The ethylbenzene conversion was found to be higher over Mn-MCM-41 than CoMCM-41. The results with bimetallic catalysts showed the absence of any new chemical compound between manganese and cobalt. The selectivity to acetophenone, which was the principally aimed product in this study, was found to be higher than that of the others. The activities of catalysts follow the order Mn,Co-MCM-41 > Mn,Co-AlMCM-41 (99) > Mn,CoAlMCM-41 (158) > Mn-MCM-41 > Mn-AlMCM-41 (99) > Mn-AlMCM-41 (158) > Co-MCM-41 > Co-AlMCM-41 (99) > Co-AlMCM-41 (158). The effect of weight hourly space velocity and time on stream was also studied on conversion and products selectivity, and the results are discussed.