Catalysis in CO reactions: A homogeneous catalyst chemist's view of heterogeneous catalysis

Organic and inorganic chemists study homogeneous catalysis while physical chemists, surface physicists and chemical engineers turn to heterogeneous catalysis. There is a continuum from simple metal complexes through metal clusters to surface catalysis. Terminology used by each group differs enough so that homogeneous and heterogeneous catalyst people find it difficult to communicate. It is relevant as to whether metals react by associative mechanisms in which the metal increases its coordination number (''oxidative-addition'') or whether they react by dissociative mechanisms in which vacant sites are created (''reductive-elimination''). It is relatively easy to discover new soluble catalysts whose structures can be elucidated. Mechanisms involved in homogeneous catalysis, involving CO, can usually be carried out using conventional techniques. In heterogeneous catalysis, it is difficult even to reproduce the catalyst or to gain insights into reaction mechanisms. Homogeneous catalysis of CO reactions have provided evidence for species that might exist on heterogeneous surfaces. In turn, heterogeneous catalytic studies have forced homogeneous investigators to attempt to verify the existence of surface species that might help explain certain heterogeneous catalytic reactions. Modern techniques of surface science should result in better communication. This paper endeavors to compare views from the different vantage points.