The effect of electrostatic field on the catalytic properties of platinum clusters confined in zeolite for hydrogenation

Abstract

The electrostatic field of a dielectric cavity is powerful for modulating many aspects of confined metal clusters. Here we report that the catalytic properties of Pt_n clusters confined in X-zeolite cages are strongly tuned by altering the zeolitic field, which is achieved by using different cations (Na⁺, Cs⁺, Ca²⁺ or La³⁺) to balance the negative framework of the zeolite. Compared with Pt_n@LaX, for example, Pt_n@CsX shows a surprising ∼5500% enhancement in TOF value for phenol hydrogenation to cyclohexanol. Electrostatic field modulation leads to gradual changes of electronic properties such as the Fermi levels/d-band centers of the Pt_n clusters, as revealed by DFT calculations and experimental characterizations. The decreases in Fermi levels of the Pt_n clusters benefit the hydrogenation of –CCH groups (phenylacetylene and acetylene) and –NO₂ groups (nitrobenzene, o-nitroanisole and o-chloronitrobenzene) but are detrimental for aromatic ring hydrogenation (phenol). These findings are important for the design of high performance catalysts.