First-Principles Investigations of Phenylacetylene Semihydrogenation Catalyzed by Ni-Containing FAU Zeolite

The semihydrogenation of phenylacetylene to styrene is a critical process for styrene purification, and the rational design of catalysts with high activity and selectivity remains a key challenge. Transition metal containing zeolite catalysts offer unique advantages in semihydrogenation, while the reaction mechanism remains unclear, thereby hindering the performance optimization of catalysts. Using density functional theory calculations, a representative Ni@FAU catalyst, with Lewis pairs comprising a FAU six-membered ring-confined Ni(II) ions and adjacent framework oxygen atoms as the active sites, are investigated for phenylacetylene semihydrogenation. At 0 K, H2 fails to dissociate directly at clean Lewis pairs, but phenylacetylene preadsorption (PhC≡CH_Ni*) at Ni sites promotes H2 dissociation at the classical Lewis pairs, forming [H_Oz+H_Ni]* intermediates. These intermediates can convert to [H_Oz+H_Oz]* via hydride/proton transfer, with PhC≡CH_Ni* stabilizing both [H_Oz+H_Ni]* and [H_Oz+H_Oz]* intermediates and facilitating hydrogen transfer. Analysis of four phenylacetylene hydrogenation pathways shows that ethylbenzene formation is suppressed by a high barrier (2.46–2.71 eV) for the second H2 dissociation (rate-determining step) due to steric hindrance. In contrast, styrene formation is kinetically favorable, with Pathway 3 (α-carbon first, then β-carbon) being optimal, featuring a low rate-determining step barrier (0.67 eV) for proton transfer. This work clarifies how the Ni@FAU catalyst achieves high styrene selectivity by inhibiting overhydrogenation to ethylbenzene, aligning well with experimental observations, and further deepens mechanistic understandings of phenylacetylene semihydrogenation over the Ni@FAU catalyst for the rational design of selective hydrogenation catalysts.