Kinetics of Hydrogenation of Serine and Glutamic Acid in Aqueous Solution over a Ru/C Catalyst

Two amino acids, serine (SE, 2-amino-3-hydroxypropanoic acid) and glutamic acid (GA, 2-amino-pentanedioic acid), are widely regarded as attractive, renewable platform chemicals. Catalytic hydrogenation of these amino acids to amino alcohols is a crucial step in making many useful products. In this work, the kinetics of hydrogenation of aqueous solutions of SE and GA was investigated over a heterogeneous Ru/C catalyst. Hydrogenation trials were performed in the kinetics-control regime in a batch reactor at 383 and 403 K. Serinol (2-amino-1,3-propanediol) and 2-amino-1,5-pentanediol were the major hydrogenation products, correspondingly. The effects of the concentrations of the reactants (viz. amino acid and H2) and catalyst on the rates of disappearance of the acids and hence the turnover frequency (TOF) were studied. Also, the influence of addition of phosphoric acid on the hydrogenation process was investigated. From power-law kinetics, the apparent energy of activation for the reactions with SE and GA was 42.3 and 53.9 kJ/mol, respectively. A Langmuir–Hinshelwood–Hougen–Watson-type model was considered as well. A model that presumed a slow, dual-site surface reaction between competitively adsorbed amino acid and atomic H2 was used.