Enhancement of catalytic activity over TiO2-modified AI2O3 and ZnO-Cr2O3 composite catalyst for hydrogen production via dimethyl ether steam reforming

摘要

The dimethyl ether steam reforming (DME SR) was carried out over the composite catalyst of ZnO-Cr2O3 coupled with Al2O3, TiO2 or TiO2-Al2O3 in the microreactor. The results showed that the catalytic activities were greatly enhanced over the composite catalyst of ZnO-Cr2O3 combined with TiO2-Al2O3 (ZnCr-TiAl) in comparison to those combined with Al2O3 or TiO2 in DME SR. By evaluating the catalytic activity of solid acids in DME hydrolysis, it was proposed that the better performance of TiO2-Al2O3 in DME hydrolysis contributed to the superior activity of ZnCr-TiAl in DME SR, indicating a higher DME hydrolysis activity favored DME SR. In view of the characterization of N2 physisorption, scanning electron microscope, X-ray diffraction and NH3 temperature-programmed desorption, the promotion effect of TiO2 on both DME hydrolysis and steam reforming was discussed in terms of the modification effect of TiO2 on the acid properties of Al2O3 surface. The acid strength or total acid amount was enhanced by the addition of different TiO2 content. In the 150 h medium stability test, there was no obvious deactivation for ZnCr-TiAl catalyst with the H2 production rate of 345 mol h~(-1) kg_(cat)~(-1) and the CO selectivity in the dry reformate remained below 6%. The characterization results of the used catalyst revealed that no change in the crystalline phase and size occurred on the spent catalyst.