The effect of the preparation on the catalytic activity of ZnO/TiO2 in the methanol steam reforming reaction

ZnO/TiO2 catalysts, with different compositions, have been synthesized by wetness impregnation of TiO2 in Zn(NO3)(2) water solution and by precipitation of ZnCO3 in the presence of TiO2, characterized by X-ray diffraction and surface area measurements and tested in the methanol steam reforming reaction. The methanol conversion, the hydrogen yield and the CO selectivity were compared for composition, for synthesis methods and for surface area. The activity resulted proportional to the surface area for both kind of preparations. Precipitated catalyst had higher surface area. Nevertheless, impregnation method gave better performances, in term of methanol conversion, hydrogen yield and CO selectivity. XRD gave evidence of a more crystalline structure for impregnated catalysts than for precipitated ones. This higher crystallinity allows for better electronic interactions between ZnO and TiO2, which is probably responsible for the better catalytic performance. Using GHVS(CH3OH) = 5 x 10(4) h(-1) impregnated catalyst with chi(Zn) <= 0.22 reached methanol conversion completeness at T = 400 degrees C with CO selectivity = 2% and gave GHVS(H2) = 14.5 x 10(4) h(-1) at 400 degrees C and 4.5 x 10(4) h(-1) at 350 degrees C. CO selectivity resulted invariant with respect to methanol conversion, giving information about possible reaction pathway.