Support effects in hydrogenation of cinnamaldehyde over carbon nanofiber-supported platinum catalysts: Kinetic modeling

Carbon nanofiber-supported platinum catalysts with a narrow and stable platinum particle size distribution (1–2 nm) were prepared, one with a considerable amount of oxygen support surface groups (PtCNF, 2.8 acidic O atoms/nm2atoms/nm2) and one with a much smaller amount (PtCNF973, 0.06 acidic O atoms/nm2atoms/nm2). Their catalytic performance was compared in a series of liquid-phase cinnamaldehyde hydrogenation experiments at 383 K using hydrogen pressures of 2.8–6.8 MPa and a cinnamaldehyde concentration in the range 14–345mol/m3. These results showed a different hydrogen dependency of the reaction rate for the two catalysts, demonstrating a change in the adsorption of hydrogen on platinum. Using a single-site model including both Langmuir–Hinshelwood kinetics and mass transfer effects we found that the intrinsic reaction rate increased up to a factor of 120 with the removal of the oxygen-containing surface groups. Also the adsorption constants increased significantly, indicating that adsorption on PtCNF973 is stronger than on PtCNF. These results suggest that hydrogenation is assisted by adsorption of the benzene ring of cinnamaldehyde on the non-polar CNF support surface after removal of the oxygen-containing groups.