Effect of composition and pretreatment parameters on activity and stability of Cu-Al catalysts for water-gas shift reaction

We investigated various Cu species responsible for highly efficient Cu-Al oxide catalyst for the water-gas shift reaction (WGSR). The formation of various Cu species was achieved by systematically varying the Cu-Al composition in the coprecipitated mixed Cu-Al oxides. The Cu-Al composition of 70:30 (Cu-Al-7) was the best for WGSR using the reformate gas composition. In addition, the Cu-Al-7 catalyst reduced under 100 % H₂, was relatively stable with time on stream of 100 h, at higher gas hourly space velocity of 36 201 h ^-1.The structural investigation of our coprecipitated catalysts with varying Cu-Al compositions revealed the formation of nonzero oxidation state copper and metallic Cu to be essential for the observed WGSR activity. In addition, the highest activity and stability of Cu-Al-7 catalysts reduced under 100 % H₂ at lower temperature was attributed to particle-size stabilization and a lower extent of Cu aggregation by Cu₂O and boehmite phases, respectively, along with the formation of various Cu species during the activation protocol for 12 h. Complete CO₂ selectivity without methanation was observed for all the Cu-Al compositions irrespective of their pretreatment conditions. Teamwork brings success: The coexistence of various nonzero oxidation state and metallic copper species in a Cu-Al catalyst with 70 atom % Cu yields the highest CO conversion with a stable time on stream (TOS) of 100 h in the water-gas shift reaction (WGSR). PEM=proton-exchange membrane.