Novel catalytic behavior of Cu/Al 2O 3 catalyst against daily start-up and shut-down (DSS)-like operation in the water gas shift reaction

Abstract

Cu/Al 2O 3 catalysts (Cu/Al = 1/2) have been prepared by coprecipitation (CP-), homogeneous precipitation (HP-), sol–gel (SG-), and impregnation (IMP-) methods. Prepared Cu/Al 2O 3 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/Al 2O 3 catalysts showed a sustainable activity during DSS-like operation in the WGS reaction, whereas IMP-Cu/Al 2O 3 showed a quite low sustainability. CP-Cu/Al 2O 3 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/Al 2O 3 catalyst (MDC-7) even after 50 cycles of the DSS-like operation in the WGS reaction. In contrast, CP-Cu/Al 2O 3 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 CuAl 2O 4 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.