Regulation of Double Bond Location in Skeletal Isomerization of Light Liquid Olefins by Combining the Novel Active Sites of Zno and Zsm-22 Zeolites: From Internal to Terminal Location

Abstract

The catalytic conversion of internal olefins to terminal ones is still a challenging subject, let alone the regulation of double bond location from internal to terminal during the skeletal isomerization of olefins. Herein, the combination of novel active sites of ZnO and ZSM-22 zeolites is used to regulate the location of double bond during the skeletal isomerization of 2-pentene. The ZnO clusters are proved to catalyze the transformation of 2-Methyl-2-Butene (2M2B) to 2-Methyl-1-Butene (2M1B). Combining with Brønsted acid sites, it lowers the activation energy of cleavage of methyl and ethyl group in methyl and ethyl shift intermediate route where the 2-pentene is directly converted into 2M1B. The ZnOH+ enhances transformation of 2M1B to 2M2B, while the variation of acid amount has limited effect on the ratio of 2M1B/2M2B. The cooperation of ZnO and acid sites endows the Zn/ZSM-22 the highest isopentene yield (67.4%) reported at the same reaction temperature, and the 2M1B/2M2B ratio reaches as high as 0.47. This work not only contributes to skeletal isomerization of olefins, but also provides a reference for catalyst design for production of terminal olefins from internal ones.

Keywords: Zn/ZSM-22 catalysts, olefin isomerization, internal olefins, terminal olefins