Pt-Impregnated ZnO/HZSM-5 Catalyst for Aromatics Synthesis by CO2 Hydrogenation

A highly efficient bifunctional catalysts containing platinum-impregnated ZnO-loaded HZSM5 and its performance on direct hydrogenation of CO2 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 CO2 conversion and aromatics selectivity. NH3-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 10 wt%, led to creation of some ZnO clusters that decreased the catalyst stability. However, 0.1 wt% Pt-8 wt% Zn/HZSM5 catalyst denoted as (P(8)Z/HZ5) showed the best results for CO2 conversion (88.3%) and aromatics selectivity (69.2%) with low CO selectivity (9.8%) compared to other zeolites.