Influence of method of preparation on pore structure and dehydrogenation activity of chromia catalysts

Abstract

Amorphous and crystallite chromia catalysts have been prepared by <i>in situ </i> reduction of Cr(VI) oxide and by decomposition of Cr(NO₃)₃ respectively, characterized by several techniques and evaluated for dehydrogenation of cycIohexane to benzene. The catalysts are found to be mesoporous and macroporous with average pore diameters of 108 Å and 470 Å respectively. The surface area of amorphous chromia is found to be 5.2 times larger than that of crystalline chromia. In the reduced form, the oxygen chemisorption capacity of the former is 8.3 times higher than that of the latter. The ratio of the dehydrogenation rates over the two catalysts is also found to be almost equal to that of their O₂ uptakes. The intrinsic activities of the two morphologies of chromia calculated on the-basis of irreversible O₂ uptakes and the activities are found to be equal (3.61 x 10^-1). All these observations suggest that the dehydrogenation of cyclohexane is a structure insensitive reaction on chromia catalysts.