The reactions of ethylene, propene, and acetylene with two different zeolite models are computationally characterized using both semiempirical and ab initio methods. The MP2/6-31G* level calculations give activation energies which appear too high in comparison with the estimated experimental values. The DFT values seem more reasonable. The AM1 and PM3 transition state structures appear dubious with respect to both ab initio results and generally accepted intuitive descriptions.

Three different model clusters simulating the acid site in zeolites are employed to explore the stability of the hydrogen bonded adsorption complex and silyl−ether addition compounds on adsorption of the carbonyls formaldehyde, acetaldehyde, and acetone at the Brönsted acid site. Ab initio calculations are performed at the Hartree−Fock level and post-Hartree−Fock. Optimization along a reaction coordinate in the case of these carbonyls exhibits a competition between two stable structures, hydrogen bonded and addition complexes. The relative stabilities of these two complexes are shown to be very much dependent on the nature of the cluster model. Effects of basis set superposition error and correlation are also discussed.

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