Novel catalytic behavior of Cu/Al2O3 catalyst against daily start-up and shut-down (DSS)-like operation in the water gas shift reaction

摘要

Cu/Al2O3 catalysts (Cu/Al = 1/2) have been prepared by coprecipitation (CP-), homogeneous precipitation (HP-), sol–gel (SG-), and impregnation (IMP-) methods. Prepared Cu/Al2O3 catalysts were applied to the water gas shift (WGS) reaction. Effects of preparation method and calcination temperature on their activities for the WGS reaction and sustainability against the daily start-up and shut-down (DSS)-like operation between 323 and 473 K under steam treatment were investigated. CP-, HP-, and SG-Cu/Al2O3 catalysts showed a sustainable activity during DSS-like operation in the WGS reaction, whereas IMP-Cu/Al2O3 showed a quite low sustainability. CP-Cu/Al2O3 catalyst calcined at 823 K (CP-823) showed the highest activity and sustainability among the catalysts tested and almost similar to a commercial Cu/ZnO/Al2O3 catalyst (MDC-7) even after 50 cycles of the DSS-like operation in the WGS reaction. In contrast, CP-Cu/Al2O3 catalyst calcined at 1073 K (CP-1073) showed a low sustainability, although the initial activity was higher than that of CP-823. It was concluded that such prominent performances of the CP-823 catalyst is caused by (1) the formation of highly dispersed and stable Cu metal and (2) an important role of boehmite (AlO(OH)) phase formed during the DSS operation in inhibition of aggregation of Cu metal particles. For CP-1073, “in-situ” formation of boehmite phase did not proceed due to the formation of stable CuAl2O4 phase by calcination at high temperature. Therefore, the activity of CP-1073 remarkably decreased as a result of aggregation of Cu metal particles during the DSS-like operation