Enhancing the performance of SBA-15-supported copper catalysts by chromium addition for the chemoselective hydrogenation of trans-cinnamaldehyde

SBA-15-supported copper-chromium mixed oxide nanoparticles (CuCr/SBA-15) were prepared by incipient wetness impregnation followed by mild drying at 25 degrees C and calcination. The Cu:Cr weight ratios were 1:1, 5:1, and 10:1, at a constant total loading of 5 wt%. Monocomponent SBA-15-supported Cu-oxide (Cu/SBA-15) and Cr-oxide (Cr/SBA-15) were prepared as reference samples. The materials were systematically characterized by XRD at low and high angles, N-2 physisorption, DR UV-vis, FT-IR, and XPS spectroscopies, and TPR. XRD at low angles and N-2 physisorption confirmed the preservation of the mesoporous structure of the SBA-15 support after impregnation and calcination. In the case of monocomponent samples, CuO appeared poorly dispersed, while the Cr species (Cr2O3, mono- and polychromates) appeared highly dispersed on the surface of the SBA-15 support. The progressive addition of chromium to copper had positive effects on the average crystallite size of CuO, which decreased from similar to 28 nm (Cu/SBA-15) to similar to 3 nm (CuCr/SBA-15; Cu:Cr = 1:1), and on reducibility, as well. Metallic active phases were obtained by reducing of the oxide phases under a hydrogen flow at 350 degrees C. By comparison to the monometallic catalysts, the reduced CuCr/SBA-15 materials were active in the hydrogenation of cinnamaldehyde and chemoselective towards cinnammyl alcohol (>50 mol%). The activity can be correlated with the particle size of copper, whereas the high selectivity to unsaturated alcohol can be associated with the presence of dual Cu-0-Crn+ sites.