Oxide-modified HZSM-5 for efficient production of hydrogen via steam reforming of dimethyl ether

Abstract

The parent HZSM-5 was modified with oxide M (M = Fe, Cu, La, P) via the incipient impregnation method by using ferric nitrate, copper nitrate, lanthanum nitrate and diammonium hydrogen phosphate as precursors to prepare a series of oxide M modified HZSM-5 (M/HZSM-5). And the M/HZSM-5 used as solid acid was physically mixed with commercial Cu/ZnO/Al₂O₃ to obtain bifunctional catalysts for steam reforming of dimethyl ether (SRD) reaction. The samples were systematically characterized by XRD, FTIR, N₂ adsorption–desorption, and NH₃-TPD techniques. The results showed that HZSM-5 structure remained basically unchanged after it was modified by oxide M; however, its specific surface area, pore volume, total acid amount, especially strong acid amount was decreased, and then affecting the DME conversion, H₂ yield and carbon-containing product selectivity of the corresponding bifunctional catalyst. Among them, the bifunctional catalyst composed of Cu/ZnO/Al₂O₃ and La/HZSM-5 with the larger specific surface area and lower strong acid sites showed best SRD performance, and the dimethyl ether conversion and H₂ yield reached 90.4% and 73.9% at TOS of 10 h under the conditions of reaction temperature 300 °C, pressure 0.1 MPa, space velocity 5000 mL/(g h), respectively.