Tuning the material and catalytic properties of SUZ-4 zeolites for the conversion of methanol or methane

Abstract

This work describes the synthesis and investigation of improved SUZ-4 catalysts (SZR framework) and their application in methanol-to-olefins and methane-to-methanol conversion. We report boron containing, dealuminated and desilicated SUZ-4 catalysts. Ammonia and pyridine probe molecules enabled the assignment of acid site densities to the 10-MR and 8-MR pores, respectively. The difference in between the theoretically expected and the for the probes accessible acid site density is a good descriptor for the accessibility of pores and acid sites. The access to the 8-MR SUZ-4 pores is sterically hindered by counter ions as well as extra framework aluminum (EFAl) species that account for up to 15% of the aluminum. Dealumination and desilication were successfully applied to optimize the diffusion properties and resulted in outstandingly high BET surface area, nSi/nAl-ratios and potassium exchange degrees. The improved accessibility led to an up to 2-fold increased MTO conversion capacity of the catalysts. Cu-exchanged SUZ-4 was applied in the selective oxidation of methane to methanol. By operando X-ray absorption spectroscopy (XAS) we showed that CuII ions are mainly coordinated in 2Al sites of 6-MR motifs and inhibited for redox-reactions.