Catalytic partial oxidation of methanol:: H2 production for fuel cells

In this work Cu/ZnO and Cu/ZnO/Al2O3 catalysts have been studied for the partial oxidation of methanol with O-2 to produce H-2. These Cu-Zn based catalysts showed high activity for the partial oxidation of methanol and with activity directly related to the Cu metal area. In the series Cu-Zn with copper relative content of 20-70 wt%, the catalyst Cu40Zn60 (Cu 40 wt% and Zn 60 wt%), which showed the highest Cu area, gave the best results for the partial oxidation of methanol. The activation energies and TOF (turnover frequencies) varied with the Cu-Zn catalyst composition. For catalysts with low Cu loading very high E-a and TOF were obtained (for Cu30Zn70 E-a=482 kJ/mol and TOF ca. 200 min(-1) at 497-499 K) whereas for higher Cu contents the E-a and TOF decreased tending to constant values (for Cu70Zn30 E-a=71 kJ/mol and TOF=160 min(-1) at 497-499 K). These results are discussed in terms of a possible effect of the Cu-ZnO interaction which depends on the catalyst composition. Catalytic experiments with Cu40Zn55Al5 showed that the presence of Al has an inhibiting effect producing slightly lower methanol conversion. On the other hand, higher selectivities for H-2 and CO2 were obtained with only traces of the undesirable CO. Moreover, the Al is very important for catalyst stability and life-time experiments showed that Cu40Zn55Al5 is stable during the partial oxidation of methanol with no significant change in activity and selectivity even after 110 h of operation at 503 K. Overall, the results seem to indicate that Cu-0 is active for partial oxidation of methanol to H-2 and CO2 whereas Cu+ favors the formation of H2O and CO.