(541b) Lactic Acid Hydrogenation: DFT, Microkinetic Modeling and Experiments

Lactic Acid is the smallest organic compound that contains a methyl, a hydroxyl and a carboxylic acid functional group, and hence can be considered as an ideal model molecule for highly oxygenated biomass derived feed stocks. To date, only a few attempts to describe the selective hydrogenation ^[1] of carboxylic acids have been published, and the mechanism for this important class of reactions is not well established.

We present a systematic study for selective lactic acid hydrogenation that combines first principles calculations, experiments and microkinetic modeling to provide insights into its reaction mechanism. In particular, periodic self-consistent Density Functional Theory (DFT) calculations are employed to probe the thermochemistry on several close-packed transition metal surfaces. Detailed activation energy barrier calculations are then performed for all the elementary steps on Cu(111). A DFT based mean-field microkinetic model is then employed to compare the calculated reaction rates and selectivity with the experimentally measured ^[2] values. A careful comparison between the DFT derived parameters and those obtained upon fitting the microkinetic model provides valuable insights into the nature of active site on Cu catalysts. This study is then extended to Pt catalysts (modeled as Pt(111)). We also employ our microkinetic model to develop trends across metals, and to identify the promising (active and selective) alloy catalysts for this reaction.

References

1.         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.

2.         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.