Ni-Based Alloy Catalysts for Liquid Organic Hydrogen Storage: Mechanistic Insights from First-Principles Calculations

The development of high-efficiency dehydrogenation catalysts for methylcyclohexane, a key medium for liquid organic hydrogen storage, is crucial for advancing the hydrogen economy. This study systematically investigates the dehydrogenation performance of methylcyclohexane (MCH) by DFT calculations, including eight types of Ni_<i>x</i>Rh_<i>y</i> surface and bulk alloys along with six Ni₃M₁ (M = Ru, Rh, Pd, Os, Ir, or Pt) alloy catalysts. The study reveals that the optimal catalytic activity is achieved at a Ni:M ratio of 3:1, with the top-performing catalysts Ni₃Rh₁, Ni₃Ir₁, Ni₃Os₁, and Ni₃Ru₁ exhibiting remarkably low reaction energy barriers of 0.70, 0.73, 0.75, and 0.78 eV, respectively. It is further found that the valence electron counts of doped metals and the <i>d</i>-bandwidth of modified Ni-based catalysts collectively affect dehydrogenation energy barriers. Notably, a distinct Brønsted-Evans-Polanyi (BEP) relationship exists between the Gibbs free energy change (Δ<i>G</i>) of the rate-determining step (RDS) in MCH dehydrogenation and the activation energy barrier for the first dehydrogenation step (Δ<i>G</i>_a). Based on these correlations, a two-parameter descriptor incorporating valence electron counts and <i>d</i>-bandwidth was established, which can enable the rapid screening of high-performance catalysts. Meanwhile, microkinetic simulations further confirmed that the four optimal catalysts maintain excellent reactivity and high turnover frequencies even under low hydrogen coverage. These findings elucidate the electronic structure modulation mechanism of Ni-based alloys for catalytic MCH dehydrogenation, providing fundamental theoretical guidance for the rational design of cost-effective and high-performance dehydrogenation catalysts.