Highly effective conversion of syngas to dimethyl ether over the hybrid catalysts containing high-silica HMCM-22 zeolites

Pure HMCM-22 zeolites with different SiO2/Al2O3 ratios were synthesized and characterized by XRD, N2 adsoption, 27Al MAS NMR, pyridine-FT-IR and NH3–TPD. The HMCM-22 samples were mechanically mixed with a methanol synthesis catalyst and then applied in the one-step synthesis of dimethyl ether from syngas (STD process). The results indicated that with the increase of SiO2/Al2O3 ratio of zeolites HMCM-22, selectivity to dimethyl ether increased and the selectivities of by-products decreased due to the weakening of their acidities. It is concluded that the high-silica HMCM-22 zeolite is an effective dehydration component of the hybrid catalyst for the STD process.