Improved methanol synthesis from CO2 hydrogenation over CuZnAlZr catalysts with precursor pre-activation by formaldehyde

•FA pre-activation can convert Cu2+ to Cu+ in Cu-containing hydrotalcite.•Cu2O has a weak interaction with support oxides in Cu-based catalysts.•ZnO exhibits a synergetic effect with dispersed Cu in CO2 hydrogenation.•FA pre-activation is helpful to improving catalytic activity of methanol catalyst.