Why Is Alloying a Prerequisite for Interstitial Carbon Playing a Promotional Role in Selective Acetylene Hydrogenation?
The thermodynamic−kinetic origin of why alloying is a prerequisite for interstitial carbon playing a promotional role in selective acetylene hydrogenation over Ni-based catalysts remains elusive. Moreover, catalytic mechanisms are frequently studied on pristine or bare surface models, overlooking the realistic surface states and coverage effects under operando conditions. Herein, we establish a realistic surface-state research paradigm, integrating global optimization, ab initio thermodynamic phase diagrams, constrained ab initio molecular dynamics, and coverage self-consistent calculations. We reveal that pure Ni thermodynamically rejects subsurface carbon (ΔEinc = −0.41 eV) with a prohibitively high kinetic barrier (3.75 eV), while Ga/Zn alloying switches the thermodynamics to favorable (ΔEinc = −3.61 eV) and lowers the penetration barrier by ∼0.95 eV via lattice expansion and electronic activation. Coverage-dependent calculations demonstrate that adsorbate−adsorbate interactions adjust the free energy profiles, and the coverage self-consistent microkinetic modeling and reactor simulations align well with experimental trends of Ni-based catalysts. The excellent performance of Ni3GaCx and Ni3ZnCx originates from interstitial carbon within the alloy matrix. Synergistic ligand and geometric effects tuning Ni-based carbic to the summit of a predictive selectivity volcano that simultaneously suppresses overhydrogenation and oligomerization, where electronic modulation optimizes intermediate adsorption strength while adjacent Ni atoms stretching creates selective advantage sites. This work transforms the understanding of interstitial carbon from a phenomenological observation into a quantitative, descriptor-based design map that can guide future rational catalyst design via controlled interstitial modification engineering.