(81f) Hydrogenation of Lactic Acid to Propylene Glycol and Propanoic Acid: A Selectivity Challenge

Periodic, self-consistent Density Functional Theory (DFT) calculations are employed to analyze the hydrogenation of lactic acid^{1, 2} to propylene glycol (desired product) and propanoic acid (undesired product). A comprehensive reaction network is proposed and key surface intermediates are identified for both reactions. Detailed adsorption thermochemistry and activation energy barrier calculations are performed to probe the mechanisms on Pt(111) and energetically most favorable pathways for the formation of both products are identified. A thorough investigation of the thermochemistry of all possible elementary steps over several close-packed transition metal surfaces (Rh, Ir, Ni, Pd, Cu, Ag, Au) is then performed to establish reactivity trends among metals. The results from these calculations point to a specific metal which might be an efficient monometallic catalyst.

These DFT calculations, in combination with microkinetic modeling and experiments, will be used to screen for improved (active and selective) alloy catalysts for lactic acid hydrogenation. Our analysis is expected to not only help with identifying improved ways for the manufacture of propylene glycol from biomass-derived lactic acid, but is also expected to capture the qualitative features of the vapor phase hydrogenation of oxygenated biomass-derived feed stocks.

References

1.         Cortright RD, Sanchez-Castillo M, & Dumesic JA. Conversion of biomass to 1,2-propanediol by selective catalytic hydrogenation of lactic acid over silica-supported copper. Applied Catalysis B-Environmental 2002; 39: 353-359.

2.         Simonov MN, Simakova IL, & Parmon VN. Hydrogenation of lactic acid to propylene glycol over copper-containing catalysts. Reaction Kinetics and Catalysis Letters 2009; 97: 157-162.