Highly dispersed Pd nanoparticles confined in ZSM-5 zeolite crystals for selective hydrogenation of cinnamaldehyde

Selective hydrogenation of α,β-unsaturated aldehyde catalyzed by supported Pd nanoparticles (NPs) is challenging, especially under harsh reaction conditions. Here, we report a facile method to prepare a catalyst composed of highly dispersed Pd NPs (∼2.6 nm) confined in zeolite ZSM-5 crystals. When used in the hydrogenation of cinnamaldehyde, the prepared catalyst (Pd@SG-ZSM-5) exhibited excellent performance for the selective production of hydrocinnamaldehyde (HCAL) due to the confinement effect. Compared with the traditional supported Pd catalyst prepared by impregnation, Pd@SG-ZSM-5 showed a 2.5-fold enhancement in the HCAL selectivity (73% vs. 30%). Liquid adsorption combined with infrared spectroscopy characterization revealed that compared with the traditional catalyst, Pd@SG-ZSM-5 adsorbed much less reactant as well as product molecules and desorbed the generated HCAL quickly, thereby suppressing the formation of by-products and leading to high selectivity of HCAL. Cinnamaldehyde was selectively hydrogenated to hydrocinnamaldehyde (∼73% selectivity) over Pd NPs confined in ZSM-5 zeolite compared to 30% over Pd-supported catalyst. [Display omitted] •Pd NPs (∼2.6 nm) with good dispersion confined in zeolite ZSM-5 crystals.•High selectivity of hydrocinnamaldehyde (HCAL) obtained due to the confinement effect.•The prepared Pd@SG-ZSM-5 catalyst exhibited good reusability.•Fast desorption of HCAL and low adsorption capacity suppressing by-products formation.