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 H2 essentially free from CO. Cu/ZnO/Al2O3 catalysts of OSRM process have been obtained from hydrotalcite-like precursors with nominal formula Cu1-x-yZnyAlx(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°C, followed by in situ reduction with H2. 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-xZnx(OH)3Cl) 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 m2 g-1 and increase with increasing Al content. The catalytic activity in the OSRM process is appreciable from about 200–250°C and methanol conversions up to 90–95% are obtained at temperatures of 300–400°C. Hydrogen is the main product, and its yield reaches values up to 2.7 mol/mol of methanol. Carbon monoxide content is under the detection limit (500 ppm) of the detector