Synergy effect of highly dispersed palladium and Ni-SiW polyoxometalate-based metal-organic framework (POMOF) for highly efficient and selective nitroaromatics hydrogenation

Abstract

The Pd/Ni-SiW catalysts with different Pd loadings (weight percent-0.77%, 1.41%, and 2.52%) are prepared by room-temperature precipitation method, which are with the Pd nanoclusters highly dispersed in Ni-SiW POMOF. These as-prepared catalysts show high catalytic activity for the hydrogenation of nitroaromatics under mild condition (hydrogen pressure-3.0 MPa and reaction temperature-40 ℃). Among them, the 1.41%Pd/Ni-SiW catalyst has 99% conversion, 100% selectivity and 255.5 h−1 TOF for p-nitroacetophenone hydrogenation to p-aminoacetophenone. The Pd nanoclusters are highly dispersed in the pores of Ni-SiW POMOF, resulting in appropriate size of the Pd nanoclusters making H2 much better dissociation, and the substrate is easily adsorbed at the Ni-SiW POMOF by the interaction of Ni-SiW POMOF-NO2 group. There is a synergistic effect between the Pd and Ni-SiW, which the existence of a two-dimensional framework composed of 4,4′-bipyridine and nickel nodes increases the adsorption capacity of nitro groups, thus preferentially adsorbing nitro groups.