Unraveling the synergistic mechanism of multimetals in Ni3Cu–Sn catalysts for selective hydrogenation of phenylacetylene†

Abstract

The selective hydrogenation of phenylacetylene plays an important role in purifying the styrene monomer. Non-noble Ni₃Cu–Sn trimetallic catalysts have demonstrated high styrene selectivity at an acceptable reaction rate in phenylacetylene hydrogenation. However, the synergistic mechanism of Ni, Cu, and Sn in complex Ni–Cu–Sn alloys remains unclear, restricting the design and development of more efficient trimetallic catalysts. Herein, we explore the interactions among the three metals by employing relatively simple Ni₃Cu_(1−y)Sn_y pseudo-binary alloys, based on the similarity in crystal structure between Ni₃CuSn_x/SBA-15 and Ni₃Cu_(1−y)Sn_y/SBA-15 catalysts. Density functional theory calculations reveal that Ni and Cu atoms directly contribute to the adsorption of phenylacetylene, styrene and hydrogen at trimer sites, while Sn atoms modulate the electronic and geometric properties of Ni. As the degree of Cu substitution by Sn in cubic Ni₃Cu_(1−y)Sn_y planes increases, the Ni–Ni bond lengthens and Ni atoms become more electron-rich, thereby weakening styrene adsorption. Nevertheless, more Sn substitution induces a cubic-to-hexagonal crystal structure transformation, leading to an adverse effect. This trend is supported by experimental results: styrene selectivity on Ni₃Cu_(1−y)Sn_y/SBA-15 increases with y up to 0.5, but decreases with further Sn substitution due to the crystal structure transformation. The hydrogenation activity of the catalysts consistently deceases with increasing y, likely owing to a reduction in the concentration of Ni trimers, which serve as the primary adsorption sites for reactants. Therefore, the key to achieving high styrene selectivity is increasing the degree of Cu substitution by Sn in Ni₃Cu–Sn catalysts until the cubic-to-hexagonal transformation occurs.