Selective oxidation reactions are extensively used in the chemical industry to provide many useful intermediates including monomers, pharmaceuticals, fine chemicals, agricultural chemicals, fragrances, and flavorings. These are important reactions, providing a route to functionalize simple hydrocarbon molecules, to make them more useful. More than 60% of the chemicals and intermediates synthesized via catalytic processes are products of oxidation.
Our current focus in oxidation catalysis is on metal oxides. Oxides have been an important class of catalysts for oxidation reactions for many years, but the precise role of oxygen in these systems is often hard to characterize and understand. The most commonly used oxidant is gaseous O2, but it is generally believed that gaseous oxygen must be converted to a more active form or be incorporated into an oxide matrix before it will appear in oxidation products. Several kinds of active oxygen species such as O-, O2-, and O2- have been detected on the surface of oxidation catalysts. The nature of these active oxygen species found on the catalyst surface depends strongly on the counter metal cation and structural conditions. Surface oxygen species can exist as mononuclear or molecular, neutral or charged. It is often assumed that adsorbed molecular oxygen can accept electrons one by one until ultimately forming O2- lattice ions.
Our research strives to understand the factors that control the selective and non-selective mechanisms in which oxygen, from the lattice or activated from the gas phase, can be inserted into the hydrocarbon, and several reaction steps advance ultimately to form carbon oxides. For selective catalysts, there should exist an optimal balance in the oxygen activity, acid-base characteristics, and lattice diffusivity.
Carbon dioxide transients obtained for an oxygen isotopic switch during propane oxidative dehydrogenation over molybendum oxide-based catalyst showing the effect of chlorine promotion.