Deciphering Particle Morphology Effects in Cinnamaldehyde Hydrogenation over Palladium Nanostructures

Chemoselective hydrogenation of α-β unsaturated hydrocarbons is a widely studied chemical transformation. In this study, hydrogenation of cinnamaldehyde (CAL) to the corresponding products, viz hydrocinnamaldehyde (HCAL) and hydrocinnamyl alcohol (HCOL) and cinnamyl alcohol (COL), over the different exposed facets of a Pd-based catalyst is studied. The Pd octahedra having (111) facet shows 90% selectivity toward HCAL with 100% conversion in a short duration (45 min). Pd cube having (100) facet shows selectivity (55%) toward HCOL, while Pd spheres show initial selectivity toward HCAL but to HCOL over a prolonged reaction period. The experimental results are corroborated by density functional theory (DFT) calculations, wherein we observe a lower activation barrier E_a = 51 kJ/mol for HCAL formation on the Pd(111) surface. However, an alternative route through the COL intermediate is more prominent on the Pd(100) surface.