Insights into the mechanism of ethanol conversion into 1,3-butadiene on Zr-β zeolite

Abstract

1,3-butadiene is an important monomer in the production of rubber, resin and engineering plastics. In recent years, ethanol to 1,3-butadiene (ETB) has been widely studied. Zr-β molecular sieves have been paid more attention to because of their relatively good catalytic properties. However, there is still a lack of specific understanding of the microscopic properties of Zr-β closed and open sites and their synergistic effects in the catalytic process of ETB. In this work, density functional theory (DFT) calculations were used to study the structural properties of open and closed site on Zr-β zeolite and the mechanism of ETB reaction. The results show that the key reaction species are adsorbed more strongly at Zr-β open site, and the proton transfer step is the highest barrier step (Ea = 1.79 eV) for the ETB process at closed site, which is similar to the process on the zirconium oxide surface. At open site, based on the cycle mechanism that Zr-OH participates in the proton transfer step of the ETB process proposed in this study, Zr-OH assists the proton transfer, which reduces the energy barrier of the proton transfer step. As a result, Meerwein-Ponndorf-Verley (MPV) reaction at open site is the rate-limiting step (Ea = 0.78 eV). So Zr-β open site exhibits relatively better catalytic performance than closed site and zirconia. For the conclusion that the number of Zr-β open site is positively correlated with catalytic performance, the explanation of the elementary reaction mechanism has been put forward.