Oxidation of ethane and cyclohexane over vanadia-niobia- silica catalysts

The conversion of ethane and cyclohexane in the presence of oxygen has been investigated on vanadia-silica (VS), niobia-silica (NS) and 1:1 vanadia-niobia-silica (VNS) catalysts. Vanadia-silica is an active catalyst for the production of ethylene from ethane and of benzene from cyclohexane. Selectivity to ethylene near 60% is obtained at near 10% ethane conversion near 820 K. Selectivity to benzene declines from above 70 to 40% when conversion of cyclohexane grows up to 40%. Cyclohexene is produced only after total oxygen conversion. Niobia-silica is much less active than vanadia-silica, and the selectivities to ethylene and to benzene grow by increasing conversion up to approach those obtained in the empty reactor at very high temperatures (above 900-1000 K). The vanadia-niobia-silica catalyst behaves quite like the vanadia-silica catalyst. Raman, UV-Vis and XRD characterization experiments show that V2O5 particles are present both in vanadia-silica and in niobia-vanadia-silica. On the contrary niobium oxide is present as amorphous phase and traces of V-Nb mixed oxide are found in the V-Nb-silica catalyst. (C) 2003 Elsevier Science B.V. All rights reserved.