Co-αAl_2O_3-Cu as shaped catalyst in NaBH_4 hydrolysis

摘要

A study about catalytic films of Co-supported-over-αAl_2O_3 fabricated by electrophoretic deposition (EPD) is reported, the as-prepared shaped catalysts being intended to catalyze NaBH_4 hydrolysis. Co-αAl_2O_3 supported over Cu substrate can be prepared by a 2-step route: (ⅰ) preparation of the supported catalyst Co-αAl_2O_3 (in powder form) by wet impregnation of CoCl_2 over αAl_2O_3, followed by a reduction, and (ⅱ) fabrication of Co-αAl_2O_3-Cu (thin film over Cu) by EPD. Both types of catalysts, whatever their form, are highly efficient in hydrolyzing NaBH_4, conversions of 100% and HGRs of tens of mL(H_2) min~(-1) being achieved at 60-80 ℃. The Co-αAl_2O_3-Cu catalysts are even more reactive than the Co-αAl_2O_3 catalysts because the surface of the former materials becomes much more acid than that of the latter ones in the course of the EPD process. The respective rate laws and reaction kinetics have been determined. Independently on the catalyst form, apparent activation energies of about 52 kJ mol~(-1) and positive reaction orders versus the initial NaBH_4 concentration (i.e. 0.3-0.7) were calculated, suggesting that the EPD does not affect the reaction mechanisms. Besides, it is showed that the hydrolysis is really catalytic as well as typical of a heterogeneous process. For example, an apparent reaction order versus the Co content of 0.9 was calculated. All of these results among others are reported and discussed in the present article.