The Role of Activated Carbon Supported CeO_x and VO_x Phases during Oxidative Dehydrogenation of Propane to Propylene Using CO2 As a Soft Oxidant

摘要

Two parallel and independent reaction pathways occur: propane CO2-ODH which is related to participation of lattice oxygen, and propane cracking to methane, H2 and carbon. Ethylene is formed only in trace amounts suggesting fast C=C bond cleavage. Activation of propane is associated with lattice oxygen abstraction and catalyst reduction. Based on the C3H8-TPR and CO2-TPO results we can postulate that that bulk CeVO4 formation contains negligible activity for propane and CO2 activation. The ability of bulk crystalline V2O5 catalyst to activate CO2 is very limited leading to a progressive decline of its CO2-ODH activity. Bulk CeO2 acts favorably towards catalyst re-oxidation with CO2 already at 450°C. Presence of vanadium species strongly changes the redox and catalytic performance of CeO2, hindering its CO2 activation ability. Finely dispersed, non-crystalline VO_x species appear as the ones mainly responsible for propane activation, leading to propylene formation.