Influence of preparation methods and Zr and Y promoters on Cu/ZnO catalysts used for methanol steam reforming

Binary Cu/ZnO catalysts were prepared using three different methods (coprecipitation, sequential precipitation and homogeneous precipitation) and tested in a methanol steam reforming reaction. Zirconium and yttrium were tested as promoters, and their effects were evaluated in the same reaction. The studied preparation methods influenced the surface area of the Cu-based catalysts and consequently their catalytic activity; however, we verified that surface area was not the only factor influencing activity. Different structural changes in the aurichalcite precursor resulted from the different preparation methods used, and these differences were also observed in the reduced catalysts. An expansion of the Cu lattice with an increase in microstrain were identified and attributed to the formation of a Cu–Zn alloy. Based on the correlation found between these structural changes and the catalytic activity, the Cu–Zn alloy was proposed as active site. We concluded that the preparation methods used influenced Cu dispersion and overall catalyst structure, and Cu–Zn alloy formation resulted from the incorporation of Zn atoms into the Cu lattice. This influence was more pronounced in the catalysts prepared by homogeneous precipitation and coprecipitation. The yttrium promoter did not provide textural or structural advantages. In contrast, the incorporation of Zr promoted both greater Cu dispersion and structural changes in the Cu lattice.