(568b) Theoretical Studies of the Effects of Structure and Composition On the Activity and Selectivity of Zeolite-Catalyzed Reactions

Zeolites widely used as catalysts for the conversion of petroleum to transportation fuels and for the synthesis commodity and specialty chemicals. The effects of the composition and structure of zeolites on their catalytic activity and selectivity have largely been revealed through experimental studies, but advances in theoretical methods and computer speed have opened the door for exploring the influence of zeolite composition and structure theoretically. This talk will demonstrate that a hybrid quantum mechanics/molecular mechanics (QM/MM) approach can be used to determine the energetic of species adsorption and formation of transition states with an accuracy approaching that of experimental measurements. QM/MM can also be used to determine the free energy of activation for elementary processes and the dynamics of reactions as they proceed towards product states. The latter type of calculations has revealed that multiple products can be formed from a given transition state and that the distribution of final products depends on a complex interplay of entropic and enthalpic effects. Examples of what can be learned from theoretical analysis of zeolite-catalyzed reactions will be illustrated with the cracking of alkanes, the methylation of alkenes by methanol, the oligomerization of alkenes, and the carbonylation of ethers.