ZnO supported on high-silica HZSM-5 as efficient catalysts for direct dehydrogenation of propane to propylene

Zn/HZSM-5 catalysts are well known in the conversion of propane to aromatics. Here we report that the HZSM-5 zeolite with high SiO2/Al2O3 ratio can be used to support ZnO catalysts for the reaction of direct dehydrogenation of propane to propylene (PDH). The 10%Zn/250HZSM-5 (SiO2/Al2O3 ratio is of 250) catalyst is much more selective and stable in PDH compared with that with lower SiO2/Al2O3 ratios, still presenting a high propane conversion of about 43% with a robust propylene selectivity of 93% after reaction for 10 h. As a result, the catalytic performance and reaction stability of the ZnO catalysts increase as rationally elevating the SiO2/Al2O3 ratio of HZSM-5 support. Comprehensive techniques including N2 sorption, XRD, SEM, TEM, DR UV–vis, XPS, C3H6-TPD, NH3-TPD and TGA jointly evidence that the high-silica HZSM-5 zeolite, with good textural properties, well-defined structure and well-adjusted acidity, is helpful for dispersing Zn species and reducing side reactions. Moreover, it is proposed that the small ZnO clusters directly connected with the framework of HZSM-5 zeolite are active phases, which are massively produced upon the zeolite support with fine structure condition and sparse Al sites. The ZnO catalysts supported on high-silica HZSM-5 is low-cost, toxicity-free and reusable, is thus of great promising to be used in industrial propylene production.