Theoretical Study Of Isomerization Of Butene Catalyzed By Zeolite Acidic Sites

The reaction mechanism of double-bond isomerization of 1 -butene to cis, trans-2-butene and skeletal isomerization of cis, trans-2-butene to isobutene with 3T cluster models simulating zeolites have been systematically studied by using density-functional theory (DFT). Moreover, in comparison of butene isomerization with and without catalyst in the same calculation level, it was found that butene isomerization with zeolite-catalysis may lower the activation barriers. In addition, the reaction path and variational rate constants of the reaction of CH₂O with CH3/OH have been studied using the QCISD method of quantum chemistry. The main results and contribution are summarized as follows.The adsorption properties of trans-2-butene in 12-ring- pore structure, zeolite 3T cluster model (3Ta and 3Tb) have been investigate at the ONIOM (B3LYP/6-31G(d):PM3) and B3LYP/6-31G(d) level,respectively. It is found that three geometry structure of adsorption molecule is similar, and the adsorption energies are 33.06. 28.14 and 4.37 kJ/mol, respectively. The slight discrepancy shows the catalysis function take place on the nearby atoms of acidic site and 3T cluster model can explain the catalysis of zeolites, so 3T cluster model is used to study the reaction mechanism of butene.At the B3LYP/6-31G(d,p) level, the double-bond isomerization of 1-butene to cis, trans-2-butene catalyzed by zeolites was studied. Using a Plank's 3Ta and a new 3Tb cluster model simulating zeolites catalyst, the full geometry optimization and activation energy calculation were studied. It was found that the process include three steps, adsorption —> chemical reaction —? desorption in this four double-bond isomerization. Firstly, the OH group of acidic site of zeolite adsorbs the double-bond of 1-butene and forms a Ti-complex, then the side C atom of double-bond of 1 -butene draws the proton of zeolite acid site and simultaneously, the neighboring basic O atom of the cluster abstracts a hydrogen atom from the butene molecule, restoring the zeolite active site and yielding adsorbs /r