The Enhancing Effect of Brønsted Acidity of Supported MoO_<i>x</i> Species on their Activity and Selectivity in Ethylene/<i>trans</i>‐2‐Butene Metathesis

Abstract

Abstract Supported catalysts with a nominal Mo surface density of 0.15 and 1.5 Mo atoms nm −2 were synthesized by impregnation of alumina, silica, and alumina–silica supports with silica content between 1 and 70 wt %. They were tested for their activity and selectivity in the metathesis of ethylene and trans ‐2‐butene to propene between 343 and 603 K at 125 kPa. The catalysts were characterized by UV/Vis, Raman, and IR spectroscopy, XRD and H 2 temperature‐programmed reduction for elucidating the distribution, degree of polymerization, reducibility, and acidity of MoO x species. We established that Brønsted acidity of highly dispersed tetrahedral and polymerized octahedral MoO x species is required to ensure high metathesis activity. The acidic character of these species is influenced by their structure and support. Tetrahedral MoO x species with Brønsted acidic character are only formed on supports possessing such acidity, whereas Brønsted acidic octahedral MoO x is also created on supports without such acidic sites.