Pt-Impregnated ZnO/HZSM-۵ Catalyst for Aromatics Synthesis by CO۲ Hydrogenation

A highly efficient bifunctional catalysts containing platinum-impregnated ZnO-loaded HZSM۵ and its performance on direct hydrogenation of CO۲ to aromatics was investigated. Methanol-mediated pathway was applied for hydrogenation reactions. ZnO was introduced to the zeolite structure through hydrothermal synthesis and illustrated gradual enhancement in surface area and pore volume of the zeolite. Pt was added to the zeolite by post treatment partial vacuum impregnation technique. The amount of zeolite acidity indicated a key role in CO۲ conversion and aromatics selectivity. NH۳-TPD analysis suggested that introduction of both ZnO and Pt increased the strong acid sites and conversly decreased the weak acid sites. Furthermore, some new acidic sites were appeared in zeolite structure after ZnO loading. Furthermore, XPS results proposed that most of the zinc species located on the surface of the zeolite as oxide form, whereas, the platinum is located in the catalysts in both metallic and oxide form. Increasing the amount of zinc load to ۱۰ wt%, led to creation of some ZnO clusters that decreased the catalyst stability. However, ۰.۱ wt% Pt-۸ wt% Zn/HZSM۵ catalyst denoted as (P(۸)Z/HZ۵) showed the best results for CO۲ conversion (۸۸.۳%) and aromatics selectivity (۶۹.۲%) with low CO selectivity (۹.۸%) compared to other zeolites.

Keywords:

ZnO/HZSM۵ catalysts , Pt impregnation , CO۲ hydrogenation , Aromatics