Heterogeneous CuH-Catalyzed Reductions

Catalysts such as copper chromite, first prepared and utilized for carbonyl 1,2-reductions back in 1931 [47], have given way to more modern reagents for effecting 

Concentrated NH4OH was added to a solution of Cu(N03)2-3H20 (25 mL, 160 g/L) until pH = 9 was reached, the support (silica, 10 g) was then added, and the mixture was slowly diluted to 3 L in order to allow hydrolysis of the Cu[NH3]4+ complex and deposition of the finely dispersed product to occur. The solid was separated hy filtration, washed with water, dried overnight at 120 °C, and calcined in air at 350 °C for 3 hours. In this way, 8% Cu samples, 308 m /g BET surface area, were obtained. The catalyst was reduced with H2 at 270 °C at atmospheric pressure, the water formed being removed under reduced pressure, before the hydrogenation reaction. 

A fascinating study on the surface science of copper hydride on Si02, as well as on AI2O3, ceria (cerium oxide), and ZnO, has appeared [50]. Pure, yet thermally unstable, CuH can be precipitated as a red-brown solid from aqueous cupric sulfate and hypophosphorous acid in the presence of H2SO4, and has been characterized by powder X-ray diffraction (PXRD) (Eq. 5.25). Transmission electron microscopy (TEM) data suggest that it is most stable when deposited on acidic Si02. 

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