Understanding the Role of Coordinatively Unsaturated Al3+ Sites on Nanoshaped Al2O3 for Creating Uniform Ni–Cu Alloys for Selective Hydrogenation of Acetylene

In this work, we report a synthesis approach for catalyst preparation using shape-controlled Al2O3 supports with enriched quantities of coordinatively unsaturated Al3+ centers. These centers can then induce ordering in bimetallic catalysts, even with a simple impregnation strategy and this is shown to be beneficial for selective hydrogenation of acetylene. Interestingly, nanorod Al2O3 induced a highly homogeneous and ordered Ni1Cu1 nanoalloy, mainly attributed to the coordination effect of unsaturated Al3+ sites that accelerate atomic diffusion and ordering (affirmed by molecular simulation). The as-obtained Ni–Cu/Al2O3-rod catalyst exhibited both satisfactory activity and ethylene selectivity of 86% under mild reaction conditions, which outperformed most of Ni-based catalysts reported to date. Through the combination of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies and computational modeling by density functional theory, it was found that a di-σ-adsorption mode of acetylene on the ordered Ni1Cu1 nanoalloy featuring alternating rows of Cu and Ni atoms played a key role in the improvement of selectivity.