Solvent effects in the hydrogenolysis pathways of propionic acid

Ab initio density functional theoretical calculations were carried out to explore different mechanisms in the hydrogenolysis of propionic acid to propanol over Ru(0001) in vapor as well as aqueous phase. Effectiveness of transition-metal-based bimetallic catalysts (Ru-Re) was also studied. To determine the energetically most favorable path for the overall hydrogenation of propionic acid on (Ru(0001), a series of elementary paths were probed. Based on reaction energies, the reaction pathway involving the formation of the acetyl intermediate was the most favorable. The acetyl surface intermediate reacted with surface bound hydrogen to form propanoldehyde, which in turn reacted with surface hydrogen in succession via the Horiuta-Polanyi mechanism to form propanol. The presence of water lowered the activation barriers for the elementary steps by stabilizing the transition state intermediates, and also provided alternate pathways. The adsorption of propionic acid and other intermediates in solution proceeded in a similar manner but required the desorption or displacement of at least one water molecule on the surface. This is an abstract of a paper presented at the 2007 AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).