Cu-Zn-Al hydrotalcites as precursors of catalysts for the production of hydrogen from methanol

The possibility of a wide use of hydrogen as fuel of proton exchange membrane fuel-cells forces to the development of selective catalytic materials for the oxidative steam reforming of methanol (OSRM) to produce H, essentially free from CO. Cu/ZnO/Al2O3 catalysts of OSRM process have been obtained from hydrotalcite-like precursors with nominal formula Cut-(1-x-y) Zn-y Al-x(OH)(2)(CO3)(x/2) (x=0.23-0.42, y=0.31-0.58) and prepared by homogeneous precipitation from metal chlorides solutions in the presence of urea. The catalysts were obtained after thermal decomposition of the hydrotalcites at 450 degrees C, followed by in situ reduction with H,. X-ray powder diffraction (XRPD) patterns of the precursors showed the presence of the hydrotalcite phase with minor amounts of a Zn-rich paratacamite phase (Cu2-x,Zn-x(OH)(3)Cl) whose amount increases with increasing Cu content. XRPD patterns of thermally treated samples show only the lines of CuO and ZnO phases; Al2O3 and/or aluminates may be present as amorphous phases. The BET surface areas of the samples are in the range 110-220 m(2) and increase with increasing Al content. The catalytic activity in the OSRM process is appreciable from about 200-250 degrees C and methanol conversions up to 90-95% are obtained at temperatures of 300-400 degrees C. Hydrogen is the main product, and its yield reaches values tip to 2.7 mol/mol of methanol. Carbon monoxide content is under the detection limit (500 ppm) of the detector. (c) 2005 Elsevier B.V. All rights reserved.