(147e) Active Sites for Olefin Metathesis On WO3 Catalysts : A Density Functional Theory Study | AIChE

(147e) Active Sites for Olefin Metathesis On WO3 Catalysts : A Density Functional Theory Study

Authors 

Cheng, Z. - Presenter, Washington University
Lo, C. S. - Presenter, Washington University in St. Louis


Industrial demand for polypropylene has spurred research on improved catalysts and mechanisms for propylene production. Recently, WO3was reported to exhibit high activity for the metathesis of ethylene and 2-butylene to form propylene. This study investigates active sites for this metathesis reaction on WO3surfaces, using first-principles calculations based on density functional theory. For the WO3 orthorhombic crystal, the (001) surface has been found to be the most stable with sixfold coordinated tungsten sites W6cand fivefold coordinated tungsten sites W5c. The whole process is divided into two stages: 1. Initiation - the formation of active W-carbene species from the W-oxo precursor, and 2. Propagation - the metathesis reaction on these active sites to yield propylene. The oxidation states of W on the surface have a great influence on the adsorption of ethylene and 2-butylene. It is more favorable for W5c sites to adsorb ethylene while it is more favorable for W6c sites to adsorb 2-butylene, which were the compromising results of electrophilic and steric effects. The formations of the W-carbene species from ethylene and 2-butylene were found to follow different pathways. These study results reveal the relationship between WO3surface structure and metathesis activities, which is significant in guiding the preparation of more suitable WO3 catalysts for the production of propylene.