Catalytic reactions of n-Alkanes on β-W 2C and WC: The effect of surface oxygen on reaction pathways

Abstract

Tungsten carbide powders with WC and β-W 2C structures catalyze alkane hydrogenolysis reactions. Alkanes adsorb on fresh carbide surfaces strongly, leading to rapid deactivation by carbon fragments and to high selectivity to hydrogenolysis products. n-Hexane isomerization or dehydrocyclization products were not observed on fresh carbides. Chemisorbed oxygen lowers the binding energy of adsorbed intermediates and decreases both hydrogenolysis and deactivation rates. Oxygen-exposed carbides catalyze n-hexane and n-heptane isomerization with high selectivity (74–99%). Isomerization involves methyl-shift pathways that require alkene intermediates. These results and the well-known acid properties of WO x , surface species suggest that oxygen-exposed tungsten carbides catalyze bifunctional (dehydrogenation/carbenium-ion) alkane isomerization pathways.