New insight into the preparation of copper/zirconia catalysts by sol-gel method

Cu/ZrO2 catalysts prepared by the sol-gel method were characterized by XRD, N2 adsorption, DTA/TG, TPR and N2O dispersion measurements and tested as catalysts for the oxidative steam reforming of methanol (OSRM). Two synthesis procedures, based on the Cu precursors Cu(CH3COO)2.H2O (A-ZrCu samples) and Cu(NO3)2 .2.5H2O (N-ZrCu samples) respectively, were compared to investigate the consequence of synthesis parameters on the physical and chemical properties of the prepared materials. The adopted procedures resulted in remarkable differences in thermal behaviour: the crystallization of tetragonal ZrO2 was shifted to higher temperature in N-ZrCu samples in comparison with pure ZrO2, while this effect was not observed in A-ZrCu. XRD data indicated that Cu2+ ions were incorporated into the ZrO2 lattice in N-ZrCu samples. Though both synthesis lead to very high surface areas, the textural properties of the reduced samples suggested the existence of different interactions between Cu ions and the ZrO2 matrix in A-ZrCu and in N-ZrCu. The Cu/ZrO2 systems showed noticeable catalytic activity for the oxidative steam reforming of methanol, even without the pre-reduction treatment, but the catalytic response is drastically affected by the preparation procedure and the pre-treatments. N-ZrCu samples gave higher methanol conversion and yield to H2. Moreover, the distribution of secondary products was completely different: N-ZrCu produced a lot of CO, while A-ZrCu gave large amounts of CH2O and (CH3)2O