Residual sodium effect on the catalytic activity of Cu/ZnO/Al2O3 in methanol synthesis from CO2 hydrogenation

The effect of residual Na on the co-precipitated Cu/ZnO/Al2O3 catalyst has been investigated in connection with the characteristics of active component and methanol synthesis activity in CO2 hydrogenation. As revealed by XRD and N2O surface titration, NaNO3 present in calcined catalysts inhibits the interaction of CuO phase with ZnO matrix and thus decreases Cu-dispersion. During reduction treatment, NaNO3 seems to be converted to a basic compound of Na, which leads to a strong chemisorption of CO2 on the sodium incorporated catalysts. Characterization by TPR indicated that high incorporation of Na made the reduction of CuO phase difficult. The reaction results showed that activities for methanol formation and CO formation decreased markedly with increasing sodium content. From the correlation between catalytic activity and Cu surface area, the sharp decrease in catalytic activity by Na incorporation can be interpreted mainly in terms of low Cu surface area, a result of poor dispersion.