Insights into the selective hydrogenation of cinnamaldehyde on low-loading Pd based catalysts

Abstract

This study explores how catalysts containing a low palladium loading (0.5 wt%) contribute to the selective hydrogenation of cinnamaldehyde. High specific surface area (SSA) mesoporous (2 wt%) TiO₂ – SiO₂ (UVM-7) materials were prepared by two different approaches: a one-step procedure, in which titania and silica precursors were added from the beginning to generate Ti₂@UVM-7 support, and a two-step procedure, where TiO₂ was deposited onto the UVM-7 silica surface via wet impregnation technique (Ti₂/UVM-7). Both types of supports were decorated with Pd nanoparticles (NPs) through the deposition–precipitation technique. The obtained catalysts were thoroughly characterized by using different techniques, including XRD, N₂ adsorption–desorption isotherms at liquid N₂ temperature, ATR-FTIR, TEM-EDX, SEM-EDX, and XPS. Characterization data revealed that one-step procedure largely preserves the textural and structural properties of the support following the deposition–precipitation of the noble metal, whereas the two-step procedure slightly alters the UVM-7 morphology. Moreover, the preparation method of the supports impacts the Pd particle sizes and the metal-support interaction (MSI). The one-step procedure tends to promote the growth of larger Pd NPs, likely due to the TiO₂ species being well embedded within the SiO₂ matrix. In contrast, the two-step procedure yields well-dispersed Pd NPs smaller than 2 nm, due to the confinement of TiO₂ nanodomains within the UVM-7 cavities, which enhances the MSI. Consequently, enhanced catalytic performance and stability were achieved with 0.5Pd/Ti₂/UVM-7 (∼99% hydrocinnamaldehyde yield, TOF 4.81 s⁻¹), due to the formation of very small Pd nanoparticles on the support that promote the MSI.