(778f) Kinetics Studies On the Hydrodeoxygenation of Propionic Acid Over Supported Monometallic and Bimetallic Catalysts

The unceasing demand of energy and the need to develop a more efficient process for the conversion of biomass to bio-fuels, has prompted a move towards novel catalytic techniques. We report a catalytic gas-phase hydrodeoxygenation (HDO) of carboxylic acid (i.e. Propionic Acid), to produce hydrocarbons over two different Pd catalysts supported on carbon and silica, and a series of bimetallic systems of Ag-Pd. The reaction studies were carried out in a single-pass plug flow reactor, where PAc is co-fed with hydrogen at temperatures ranges of (200-400ºC) and atmospheric pressure. Pd/C showed high activity and selectivity towards ethane, indicating that the reaction favored the C-OH bond cleavage based on decarbonylation (DCN) and decarboxylation (DCX) reactions.  Similarly, Pd/SiO₂, showed to be selective towards ethane and propionaldehyde, indicating DCN and hydrogenation reactions. The TOF values decrease in the following the order: Pd/SiO₂ >Pd/C, suggesting that the particle size and/or support plays an important role in the activity of the catalyst. A detailed kinetic study for the HDO of PAc showed that both Pd/C and Pd/SiO₂, exhibited an apparent reaction order for PAc and H₂ of half and zero order, respectively. The corresponding activation energies of Pd/C was higher (17 ± 0.6 kcal/mole) compared to Pd/SiO₂ (12 ± 0.7 kcal/mole), due to a higher catalytic activity. A series of bimetallic systems were examined, to explore the structure and activity for the HDO of PAc. The addition of Ag, has a significant ensemble size effect for Pd/C and Pd/SiO₂ catalysts.  A correlation between the structural properties and the catalytic performance at different coverage of Ag was established. The catalysts were characterized utilizing Fourier transform infrared spectroscopy (FTIR), Transmission Electron Microscopy (TEM), Temperature Programmed Oxidation and Reduction TPO/TPR, Atomic Absorption and H₂ titration of oxygen pre-covered catalyst.