Geometrically embedding dispersive Pt nanoparticles within silicalite-1 framework for highly selective alpha, beta-unsaturated aldehydes hydrogenation via oriented C = O adsorption configuration

The issue for thermodynamically favored C = C hydrogenation needs to be overcome in the hydrogenation of alpha, beta-unsaturated aldehydes to unsaturated alcohols. Herein, we employ confinement effect in the catalyst-designing engineering to orient the C = O adsorption by the zeolitic microchannel, where highly dispersed Pt nanoparticles are homogeneously well-embedded within the silicalite-1 framework (Pt@S-1). Comprehensive characterizations, such as HAADF-STEM, H-2-TPR, FT-IR of CO adsorption and XPS are carried out to demonstrate the geometric, confinement and electronic properties of metal species. In the hydrogenation of alpha, beta-unsaturated aldehydes with suitable molecular size, Pt@S-1 displays preferential C = O hydrogenation. For example, Pt@S-1 gives conversion of 99.8% and meanwhile the aiming cinnamal alcohol selectivity of 98.7% in the hydrogenation of cinnamaldehyde, outperforming larger Pt nanoparticles ill-suitedly embedded within silicalite-1 (Pt@S-1-is) and highly dispersed Pt nanoparticles supported on the silicalite-1 surface (Pt/S-1). For the hydrogenation of smaller 3-methyl-2-butenal, though the confinement effect boosts the C = O hydrogenation to some extent, the synergetic electronic effect via introducing Fe species effectively increases the unsaturated alcohol selectivity. Investigations on the adsorption configuration by in-situ FT-IR spectroscopy clearly indicate that the unsaturated aldehyde with suitable molecular size is preferentially adsorbed on Pt sites of Pt@S-1 via the oxygen atom of C = O with on-top eta(1) mode, thus favoring high unsaturated alcohol selectivities, while the d(i)-sigma(CO)eta(2) and eta(4) adsorption modes on Pt@S-1-is and Pt/S-1 are relatively adverse for prioritized C = O hydrogenation.