Promoting Low‐Temperature Hydrogenation of CO Bonds of Acetone and Acetaldehyde by using Co–Pt Bimetallic Catalysts

The catalytic hydrogenation of carbonyl groups is one of the most useful and widely applicable reaction routes for organic synthesis. For instance, the selective hydrogenation of the C=O bond in a,b-unsaturated aldehydes to unsaturated alcohols is of growing interest for the production of fine chemicals. More recently, C=O bond hydrogenation has been considered as an important initial step in catalytic conversion of cellulose biomass. Owing to the toxicity of many a,b-unsaturated aldehydes and the complex structures of cellulose, in the current study, we use acetone and acetaldehyde as probe molecules to identify novel bimetallic catalysts for the low temperature (between 308 and 343 K) hydrogenation of carbonyl groups. In addition to being a useful probe reaction, acetone hydrogenation is also an important reaction that can be used to produce 2-propanol and methyl isobutyl ketone. 7] Furthermore, the facile hydrogenation of acetaldehyde and acetone is of interest for use in the ethanol-acetaldehydehydrogen and isopropanol-acetone-hydrogen chemical heatpump systems. Bimetallic catalysts often show properties that differ distinctly from those of the parent metals, offering the opportunity to obtain novel catalysts with enhanced activity and/or selectivity. 10] Many investigations have been performed to correlate the electronic and catalytic properties by combining fundamental surface-science studies and theoretical calculations. For example, it has been demonstrated that a Pt-terminated Pt-Co-Pt(111) surface, which represents a subsurface bimetallic structure with Pt on the topmost surface layer and Co residing in the subsurface region, shows a much higher activity for the hydrogenation of cyclohexene than a Co-terminated Co-Pt-Pt (111) surface and corresponding monometallic surfaces. 14] The low temperature hydrogenation pathway on the subsurface of these bimetallic structures has been correlated to the presence of weakly bonded adsorbates, owing to the modification of the electronic properties of Pt by the subsurface Co atoms. 14] More recently, these surface science results have been extended to g-Al2O3-supported bimetallic Co–Pt catalysts, which exhibit significantly higher activity than monometallic Co and Pt catalysts for the hydrogenation of cyclohexene, benzene, and butadiene at low temperatures. The main objective of the present work is to extend the C=C hydrogenation activity of g-Al2O3 supported Co–Pt bimetallic catalysts to the low temperature hydrogenation of the carbonyl group by using batch and flow reactors. Similar to the correlation established previously for the hydrogenation of C=C bonds, the facile C=O bond hydrogenation on Co–Pt can also be correlated to the weaker binding energies of acetone and acetaldehyde on the bimetallic surface, as determined by using density functional theory (DFT) calculations. The hydrogenation activity of acetone over the Co–Pt bimetallic and Co and Pt monometallic catalysts in batch reactor studies is compared in Figure 1. The sum of gas-phase concen-