Heterogeneous molecular catalysis: Oxymoron or reality?

It has become common to call a molecular catalyst a single site catalyst. The intent is to stress that all sites of a molecular catalyst are identical in activity and selectivity. In this essay, three cases are examined. In each one the evidence is very strong that heterogeneous catalysts can be considered to be molecular catalysts. The first case is the cracking of alkanes on H-ZSM-5. The second is the oxidation of carbon monoxide on palladium. The third is ammonia synthesis on KMI, a multipromoted iron based commercial catalyst.