Assembly of hydrolysis, activation and reforming sites boosting steam reforming of DME over ZnO/TiO2 catalysts

Abstract

Steam reforming of dimethyl ether (DME SR) through the tandem reactions of DME hydrolysis to methanol and methanol steam reforming (MSR) is a promising process for feeding hydrogen to fuel cells. Herein, we synthesize a series of ZnO/TiO2 catalysts with different Zn contents for DME SR. We discover that TiO2 exhibits excellent methanol activation ability by forming a large amount of methoxy species, and adjacent ZnO sites can directly utilize them for the substantial steam reforming. Compared with TiO2 and ZnO alone, the MSR reaction rate over the 2ZnO/TiO2 catalyst (with a Zn content of 2 wt%) at 340 °C increases by 56 and 38 times, respectively. For DME SR, DME hydrolysis could occur on strong acidic sites of the TiO2 support to generate methanol molecules to subsequently involve in MSR. The synergy as described above significantly enhances the DME SR activity. Additionally, the adsorption strength of the oxygenated intermediates formed on the ZnO/TiO2 catalysts is weaker than that on TiO2, which then inhibits the reactions of methanation and methanol/DME decomposition. The 2ZnO/TiO2 catalyst exhibits low CO (2.8%) and CH4 (0.3%) selectivity with DME conversion of 92% in DME SR at 400 °C.