The effect of P modification on the acidity of HZSM-5 and P-HZSM-5/CuO-ZnO-Al2O3 mixed catalysts for hydrogen production by dimethyl ether steam reforming

Abstract

Dimethyl ether steam reforming (DME SR) was catalyzed by a CuO-ZnO-Al2O3 (CuZnAlO) catalyst mixed with P-modified HZSM-5 for the production of H2. The effect of P modification on the acidity and activity of the P-HZSM-5/CuZnAlO mixed catalyst for DME SR was investigated. P-HZSM-5/CuZnAlO gave a higher CO2 selectivity and also higher stability during DME SR compared to the mixed catalyst with HZSM-5. N2 desorption, X-ray diffraction, temperature-programmed oxidation (TPO), NH3 temperature-programmed desorption (NH3-TPD), Fourier transform infrared spectroscopy (FT-IR), and solid-state 31P magic angle spinning nuclear magnetic resonance (31P MAS NMR) were used for catalyst characterization. NH3-TPD results showed that both the acid quantity and strength of HZSM-5 were significantly changed after P modification. With increased P content, the density of strong acid sites decreased, while the weak acid sites changed little. TPO results indicated that catalyst deactivation was mainly caused by the deposition of coke. The catalyst with 5% P exhibited much better stability than the parent HZSM-5 due to the disappearance of strong acid sites after P modification. The FT-IR spectra of pyridine adsorption clearly revealed that with increased P content, there was an obvious decrease of Lewis acid sites and slight decrease of Brönsted acid sites. From the results of 31P MAS NMR, NH3-TPD and FT-IR of adsorbed pyridine, a description of the effect of phosphorus modification on HZSM-5 was proposed.