PARTIAL OXIDATION OF ALKANES OVER NOBLE-METAL COATED MONOLITHS

The production of olefins and synthesis gas (CO and H-2) from CH4, C2H6, C3H8, and n-C4H10 in the presence of air or O-2 at atmospheric pressure has been examined over monoliths coated with various metals at residence times between 10(-3) and 10(-2) s. Experiments are carried out by feeding gases at atmospheric pressure and 25 degrees C into an autothermal monolith reactor operating between 800 and 1200 degrees C. In CH4 oxidation, > 90% selectivity to syngas is achieved over Ph at > 90% CH4 conversion, while Pt forms more H2O, Ir sinters, and Ni volatilizes. In C2H6 oxidation, Pt forms up to 70% selectivity to C2H4, while Ph gives up to 70% selectivity to syngas, and Pd forms solid carbon. Carbon formation is suppressed under conditions where graphite formation is predicted on some metals, but forms readily on others. The C2H6 results can be interpreted quite simply in terms of hydrogen abstraction by adsorbed oxygen to form the alkyl, followed by beta-hydrogen elimination to yield the olefin (Pt) or pyrolysis to yield syngas (Ph) or carbon (Pd). When C3H8 and n-C4H10 are used, considerable cracking to ethylene plus alkane is also observed.