Playing on 3D spatial distribution of Cu-Co (oxide) nanoparticles in inorganic mesoporous sieves: Impact on catalytic performance toward the cinnamaldehyde hydrogenation

The preparation of supported bimetallic materials based on transition metals has attracted much interest since their use as catalysts towards hydrogenation processes for the production of fine chemicals or environmental depollution processes. The synthesis procedure proposed in this study allows to obtain bimetallic materials with high dispersion of the active sites, control of the chemical composition and localization as well as good thermal resistance against sintering. In this line, a series of materials based on Cu and Co supported on SBA-15 were prepared by the optimization of the drying step during incipient wetness impregnation, the ratio of Cu-Co was studied and the monometallic materials were used for comparison. The physico-chemical properties of freshly calcined and reduced materials were investigated by ICP-EOS, nitrogen physisorption, ex-situ and in-situ XRD, TEM-EDX, TPR and XPS. The materials showed improved dispersion at low copper ratio, due to the stabilization of CuxCo(1-x)Co2O4 spinel phase, promoting a high dispersion of confined NPs of 9 nm within the large pores of the SBA-15. Subsequent stabilization of the Cu and Co NPs is observed by in situ-XRD, and the collected HAADF micrographs clearly evidence a high dispersion of the copper within the bimetallic NPs. However, when copper is exceeding the CuCo ratio of 4:1, larger NPs of CuO located outside the silica mesopores are observed. Subsequent catalytic performances were investigated in the hydrogenation reaction of cinnamaldehyde (CNA), in two different pressure regimes (1 bar and 10 bars). For the reaction under pressure, CuCo1:4 showed the highest conversion with 67 mol % after 150 min of reaction, while the selectivity to the cinnamyl alcohol (CNOL) was of 47 mol %. The same catalyst showed a conversion of 99 mol % in atmospheric pressure after 24 h of reaction and the selectivity to CNOL reached 72 mol %. Such results confirm that our modified IWI protocol using mild drying step is valuable towards the preparation of confined bimetallic nanoparticles within mesoporous sieves. High stability of such confined nanoparticles allow reduction of the active elements up to the metallic state, which strongly promotes the catalytic performance towards CNA hydrogenation reaction.

Automated summary

The preparation of bimetallic materials based on transition metals has attracted interest for their use as catalysts in hydrogenation reactions. The study successfully synthesized Cu and Co based bimetallic materials with high dispersion of active sites and thermal stability. CuCo1:4 exhibited the highest conversion and selectivity towards cinnamyl alcohol in the hydrogenation reaction.