Oxidative dehydrogenation of isobutane at short contact times Original Research Article

The oxidative dehydrogenation of isobutane over noble metal coated ceramic foam monoliths selectively produces isobutylene with high conversions and yields at short contact times in an autothermal reactor at atmospheric pressure and temperatures of ∼800–900°C. Maximum selectivity of ≤71% to total olefins is achieved with O2 and reactant preheat of 350°C at a fuel/oxygen ratio of 1.7. Operation at a constant fuel/oxygen ratio of 1.2 while varying the space velocity from 8×104 to 8×105 h−1 increases selectivities to C4-olefins and decreases selectivities to C2-olefins by ∼8%, although the fuel conversion drops from 80% to 40%.To investigate the effects of the physical and chemical nature of the catalyst, Pt, Rh, Ir, Pd, and Pt–Sn catalysts were examined, with Pt being optimal for olefin production and catalytic activity decreasing in the order Pt>Pd>Rh>Ir. Pt–Sn deactivated by carbon formation and metal loss while Pd deactivated by rapid carbon formation. Monolithic catalysts with various pore sizes (20, 45, 80 ppi) show that in the fuel lean regime, smaller pores (80 ppi), as compared to catalysts with more open channels (20 ppi), lead to 20% higher fuel conversion but 10–15% lower selectivity to olefins.