Cu,Zn,Al layered double hydroxides as precursors for copper catalysts in methanol steam reforming - pH-controlled synthesis by microemulsion technique

By co-precipitation inside microemulsion droplets a Cu-based catalyst precursor was prepared with a Cu : Zn : Al ratio of 50 : 17 : 33. A pH-controlled synthesis was applied by simultaneous dosing of metal solution and precipitation agent. This technique allows for continuous operation of the synthesis and enables easy and feasible up-scaling. For comparison conventional co-precipitation was applied with the same composition. Both techniques resulted in phase pure layered double hydroxide precursors and finally (after calcination and reduction) in small Cu nanoparticles (8 nm) and ZnAl2O4. By applying the microemulsion technique smaller Cu/ZnAl2O4 aggregates with less embedded Cu particles were obtained. The microemulsion product exhibited a higher BET and specific Cu surface area and also a higher absolute catalytic activity in methanol steam reforming. However, the Cu surface area-normalized, intrinsic activity was lower. This observation was related to differences in interactions of Cu metal and oxide phase.