Vapor phase deoxygenation of heptanoic acid over silica-supported palladium and palladium-tin catalysts

Silica-supported Pd and PdSn catalysts were prepared by ion exchange or incipient wetness impregnation and characterized with H2 chemisorption, X-ray diffraction, in situ Sn K-edge X-ray absorption near edge structure (XANES), and scanning transmission electron microscopy. The activity of the catalysts was evaluated in the deoxygenation of vapor-phase heptanoic acid at 0.1 MPa and 573 K. A Pd catalyst synthesized via ion exchange formed nanoparticles of 1.1 ± 0.4 nm and was more stable in heptanoic acid conversion compared to a Pd catalyst synthesized via incipient wetness impregnation having nanoparticles of 2.4 ± 0.5 nm. The addition of Sn to a Pd catalyst by either co-impregnation of precursors or physical mixing of supported monometallic catalysts improved the overall catalyst stability. Moreover, Sn addition expanded the reaction network from primarily decarbonylation over Pd to include dehydration and decarboxylative ketonization over PdSn. Electron microscopy confirmed the physical migration of Sn during catalytic reaction. In situ XANES analysis during the deoxygenation of a carboxylic acid suggests that partially reduced SnOx is the active Sn phase associated with Pd nanoparticles under reaction conditions.