Electronic Interface Interaction on Al 2 O 3 /Ag Inverse Catalysts for Enhanced Catalytic Reduction of 4-NP

Electronic interface interaction (EII) plays an important role in regulating the structure-function relationship of metal/oxide heterogeneous catalytic systems. In this work, we prepared Al2O3/Ag inverse oxide/metal catalysts with a facile synthetic method without using any organic ligand. The composites were supported by well-defined silver nanocubes (Ag NCs) and covered by an oxide layer with variable coverage as confirmed by transmission electron microscopy (TEM) and high-sensitivity low-energy ion scattering spectroscopy (HS-LEIS) characterizations. The catalytic performance toward the reduction of 4-nitrophenol (4-NP) in excess NaBH4 obviously enhanced with increasing coverage of alumina overlayer; the composite principally provided more surface adsorption sites for reactants, confirmed by the increasing saturated adsorption capacity toward 4-NP. In comparison with pristine Ag NCs and bulk Al2O3, optimized Al2O3/c-Ag showed superior catalytic performance with about complete conversion of 4-NP within 2 min, keeping high stability for six cycles; the reaction possessed lower apparent activation energy (35.0 kJ/mol), and the corresponding pseudo-first-order kinetic rate constant (2.11 min-1) was about 3.27 times greater than that of Ag NCs (0.65 min-1). In addition, X-ray photoelectron spectroscopy (XPS) characterization indicated that overall Ag 3d peaks shifted to lower binding energy with increasing percentage of oxide layer, indicating an inclination of metal-oxide interface electron transfer, and Ag NCs acted as a charge contributor, thus directly influencing the catalytic performance in such an electron inducing reaction. This report provides a profound understanding of the electronic interaction between metal and nonreducible oxides, helping to construct a more efficient and stable silver-based catalyst for catalytic reduction of aromatic nitro compounds.