Bifunctional catalysts of Cu center dot ZnO supported on modified gamma-Al2O3 were prepared and tested in the direct hydrogenation of CO2 to methanol and dimethyl ether (DME). The gamma-Al2O3 modification was carried out using a solution of (NH4)(2)SiF6, aiming to incorporate Si atoms in the alumina structure. The metals were added to the support by wet impregnation. The catalysts were characterized by the Brunauer-Emmett-Teller area, chemical composition, Si-29 and Al-27 magic angle spinning nuclear magnetic resonance, acidity, and temperature-programmed reduction. All of the prepared catalysts were able to convert CO2 into methanol and DME in the temperature range of 270-290 degrees C and 30 and 50 bar of pressure. The yield of DME was higher over the catalyst supported on gamma-Al2O3 containing more incorporated Si atoms. The results were interpreted in terms of the acid strength of the supports.