Heterolytic Dissociation of H₂ in Heterogeneous Catalysis

Abstract

H2 dissociation plays crucial roles in catalytic hydrogenation reactions and hydrogen storage. Metal-nanoparticle-based heterogeneous catalysts often dissociate H2 via a homolytic pathway. The heterolytic H2 dissociation pathway was identified in several heterogeneous catalytic systems, including single-atom catalysts, metal–support interfaces, and bulk metal oxides/sulfides/nitrides/phosphides. The active site structures of these heterogeneous catalysts resemble homogeneous catalysts where the metal centers (Lewis acids) are coordinated with O/S/N/P atoms (Lewis bases). These Lewis acid–base pairs dissociate H2 molecules heterolytically into proton–hydride pairs, which favor the hydrogenation of polar functional groups in unsaturated hydrocarbons. In this review, we summarize the common structural features of heterogeneous, homogeneous, and enzyme catalysts in the heterolytic dissociation of H2. The active sites, Lewis acid–base pairs, are discussed throughout this review. The energy barriers and kinetic contributions of heterolytic and homolytic H2 dissociation pathways in heterogeneous catalytic systems are discussed. The spectroscopic evidence of the heterolytic H2 dissociation pathways is critically reviewed.

Synergy of metal nanoparticles and organometallic complex in NAD(P)H regeneration via relay hydrogenation

“…Correspondingly, homogenous organometallic complexes (M) and supported metal nanoparticles (NPs) are the most widely used catalysts for each process,respectively 1 . Both types of catalysts are well-developed and hold unique merits, such as the high regio/stereo-selectivity for M 9 – 11 and the easy recovery and strong H 2 dissociation ability for supported metal NPs 1 , 12 , which make each of them irreplaceable and yet not universal 13 , 14 . Traditionally, homogenous and heterogeneous catalysts were applied separately and rarely catalyzed a target reaction synergistically.…”

“…Actually, the H 2 -driven NAD(P)H regeneration has been explored using M 23 , 40 or supported metal NPs 31 , 33 as catalysts. However, the M usually gives lower activity, which is probably related to their lower H 2 dissociation ability 12 . The supported metal NPs suffer from the poor NAD(P)H selectivity arising from the non-oriented adsorption modes of NAD(P) + on the active sites 31 .…”

Metal surfaces catalyze polarization-dependent hydride transfer from H2

“…Thus, this quantitative relationship provides a paradigm for predicting the thermochemistry and reactivity of hydride transfer steps embedded within more complex reaction sequences such as the (de)hydrogenation or hydrogenolysis of polar bonds and the activation of small molecules such as CO2. [22][23][24][25][26][27][28][29][30][31][32][33]47…”

“…Nonetheless, surface hydride transfers have been invoked as part of polar (de)hydrogenation/hydrogenolysis and CO2 reduction reactions. [22][23][24][25][26][27][28][29][30][31][32][33] Additionally, the electrochemical Heyrovsky step (M−H + H + + e − → H2) in the HER can be equivalently viewed either as a proton-coupled electron transfer (PCET) to surface M−H, 21 or alternatively as an interfacial hydride transfer to a proton in solution. Given the rich ability of metal surfaces to generate surface M−H species via PCET or H2 dissociative adsorption, a deeper exploration of the hydride transfer reactivity of surface M−H could offer new mechanistic insights and enable the development of novel surfacecatalyzed transformations.…”

The Role of Hydrogen Adsorption Site Diversity in Catalysis on Transition Metal Phosphide Surfaces

“…On a TMP surface, H2 is more likely to be cleaved heterolytically similar to what is observed on other binary materials. [66][67][68] This difference results in the presence of Had with various HBEs on TMP surfaces after exposure to H2.…”