An atomic level engineering of catalytic surface is critical to understand and to design heterogeneous catalysts satisfying high selectivity and activity. To address these desires in bimetallic systems, it is urgent to precisely control the bimetallic surface and to correlate such surface to specific catalytic pathways. Alloys are widely used as heterogeneous catalysts. However, alloys usually have randomly arranged structures, which can complicate the active surface as well as reduce the selectivity. Intermetallic compounds (IMCs) are thus ideal catalysts with well-defined structures to enhance the selectivity. IMCs have stoichiometric compositions and their crystal structures are stable and ordered at an atomic level. The major synthesis obstacle of IMC nanoparticles (NPs) is the NP aggregation during the high temperature annealing essential for the phase transition. We developed a seeded growth strategy to prepare a series of Pt-based alloy/IMC NPs encapsulated in single mesoporous silica shells (PtM, Pt3M@mSiO2, M=Sn, Zn, Pb, Co, Ni, Cu and Pd), starting from Pt@mSiO2 seeds. The strategy can precisely tune secondary metal compositions with high incorporation efficiency, and can also show high flexibility to precursors and solvents. Due to the mSiO2 protection, these PtM@mSiO2 NPs show high thermal stabilities up to 700 °C. We can easily tune Pt/M ratios, and calcine/anneal them to induce the clean and atomically homogenous IMC surface. Chemoselective hydrogenation of various nitroarenes was studied over IMC PtSn, IMC Pt3Sn and Pt catalysts. IMC PtSn shows over 99% selectivity to desired products in contrast to their Pt3Sn and Pt counterparts with poor selectivity. IMC PtZn and IMC PtPb were also evaluated as selective hydrogenation catalysts. Further kinetic studies demonstrate that catalytic pathways can be readily altered upon different IMC structures. This study emphasizes the critical relationship between the surface structure of IMCs and their catalytic properties.

Atomic control of intermetallic surfaces towards chemoselective hydrogenation of nitroarenes to functionalized anilines

253rd National Meeting (2017)

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