In nitrostyrene hydrogenations, Pt@Silicalite-1 greatly enhances the selectivity to aminostyrene whereas Pt/SiO2 mainly formed overhydrogenation products. Experiments with model substrates and adsorption followed by DRIFTS reveal that the enhanced selectivity of Pt@Silicalite-1 is primarily determined by its lower polarity, which enhances preferential adsorption of NO2 and NH3 groups. In addition, the small Pt size obtained due to encapsulation is less active in the C=C hydrogenation, thus maintaining selectivity at higher conversions.

Encouraged by these results, we explored other reactions using the Pt@Silicalite-1 catalyst and obtained excellent selectivity for Pt-based catalysts in the hydrogenation of cinnamaldehyde to hydrocinnamaldehyde (98%). An apolar environment originating from low polarity of Silicalite-1 and the solvent (toluene) enhances selectivity. In addition, Pt(111) face sites decrease selectivity to C=C hydrogenation because flat adsorption of cinnamaldehyde becomes unfavorable. Thus, smaller Pt particles remain important in obtaining high selectivity at high conversions.