High yields of olefins and hydrogen from decane in short contact time reactors: rhodium versus platinum

The partial oxidation of n-decane to produce H2, ethylene, and α-olefins has been compared over Rh and Pt in autothermal reactors at short contact times. Over Rh it is shown that the addition of an alumina wash coat and small foam pore size give higher H2 selectivity (>85%), while the absence of wash coat and larger pore size give more olefins (up to 60%). In contrast, Pt is unsatisfactory for producing either H2 or olefins because the conversion of both n-decane and O2 is lower. Pt produces essentially no H2 (<0.1% under any conditions). Ignition and autothermal operation over Pt also occur only over a narrow range of composition and flow rate. A catalyst consisting of Pt–Rh gave higher olefin selectivity (89%) than either metal, while producing little H2. We interpret these results as caused by the high activity of Rh that removes all O2 early in the catalyst, leaving homogeneous pyrolysis to produce olefins. The lower activity of Pt appears to be caused by its inability to completely dissociate n-decane, leaving fragments on the surface that inhibit reaction and produce a less active surface.