Few-Atom Pt Ensembles Enable Efficient Catalytic Cyclohexane Dehydrogenation for Hydrogen Production

Abstract

Identification of catalytic active sites is pivotal in the design of highly effective heterogeneous metal catalysts, especially for structure-sensitive reactions. Downsizing the dimension of the metal species on the catalyst increases the dispersion, which is maximized when the metal exists as single atoms, namely, single-atom catalysts (SACs). SACs have been reported to be efficient for various catalytic reactions. We show here that the Pt SACs, although with the highest metal atom utilization efficiency, are totally inactive in the cyclohexane (C 6 H 12 ) dehydrogenation reaction, an important reaction that could enable efficient hydrogen transportation. Instead, catalysts enriched with fully exposed few-atom Pt ensembles, with a Pt−Pt coordination number of around 2, achieve the optimal catalytic performance. The superior performance of a fully exposed few-atom ensemble catalyst is attributed to its high d-band center, multiple neighboring metal sites, and weak binding of the product.

Low-Temperature Acetylene Semi-Hydrogenation over the Pd1–Cu1 Dual-Atom Catalyst

“…To improve atom utilization efficiency of the “site-isolated” methods, our group and Li et al independently reported that atomically dispersed Pd catalysts are able to provide excellent ethylene selectivity while exhibiting the maximized atom utilization efficiency in the partial hydrogenation of alkynes. − The Pd atom of these Pd single-atom catalysts (SACs) normally anchors over oxide or carbon supports through Pd–O, Pd–N, or Pd–C bonds, resulting in the partially positive charge on Pd species. − It weakens the adsorption of products, that is, ethylene here, on the Pd atoms, leading to excellent selectivity. However, the weak adsorption of reactants, the sluggish H 2 dissociation dynamics, and the change of the reaction path due to the lack of ensemble metal sites of SACs − will reduce its hydrogenation reactivity, which is evidenced by the higher reaction temperature required to achieve the around 100% conversion for the Pd 1 catalyst than that for its nanoparticle counterparts (180 vs 20 °C) . Constructing a fully exposed cluster catalyst could have the benefit of a rich surface ensemble site, thus enabling different adsorption modes and reaction paths. ,, Particularly, decorating the core metal atom with a second metal atom can change the coordination environment and the electronic structure of the latter. − Meanwhile, we have reported recently that the supported Cu 1 atom could catalyze the semi-hydrogenation of acetylene, but the reaction temperature needed to reach the desired reactivity is even higher .…”

“…However, the weak adsorption of reactants, the sluggish H 2 dissociation dynamics, and the change of the reaction path due to the lack of ensemble metal sites of SACs − will reduce its hydrogenation reactivity, which is evidenced by the higher reaction temperature required to achieve the around 100% conversion for the Pd 1 catalyst than that for its nanoparticle counterparts (180 vs 20 °C) . Constructing a fully exposed cluster catalyst could have the benefit of a rich surface ensemble site, thus enabling different adsorption modes and reaction paths. ,, Particularly, decorating the core metal atom with a second metal atom can change the coordination environment and the electronic structure of the latter. − Meanwhile, we have reported recently that the supported Cu 1 atom could catalyze the semi-hydrogenation of acetylene, but the reaction temperature needed to reach the desired reactivity is even higher . Therefore, we herein propose that constructing a Pd 1 –Cu 1 dual-active site catalyst is a promising way to overcome the drawbacks of isolated active sites and to enhance the semi-hydrogenation reactivity as it not only combines two active metal atoms with acetylene semi-hydrogenation activity but also offers new surface adsorption sites/configurations, the metal electronic structure, and the reaction path, which are usually not available over single Pd 1 or Cu 1 sites.…”

Size Sensitivity of Supported Palladium Species on Layered Double Hydroxides for the Electro-oxidation Dehydrogenation of Hydrazine: From Nanoparticles to Nanoclusters and Single Atoms

“…The XRD diffraction of Pd NCs/NiFe was similar to those of Pd SAs/NiFe, the absence of Pd diffraction peaks can be caused by the evenly distributed of Pd species with small sizes. 20,21 In contrast, Pd NPs/NiFe with an average size of 3.76 nm (labeled in white circles in Figures 1c and S2e,f) showed a diffraction peak at 2θ = 40°, which can be attributed to the Pd NPs with relatively good crystallinity.…”

“…As a result, single Pt atoms exhibited poor catalytic performance for the CDH reaction. 20 Likewise, the intracluster interactions can endow catalysts with excellent performance for specific reactions. valence state than the Ru SA, which enabled strong interactions between the d-orbitals of Ru with the antibonding orbitals of N 2 , resulting in better capability in N 2 activation than that over of Ru SAs.…”

Supported Cu3 clusters on graphitic carbon nitride as an efficient catalyst for CO electroreduction to propene

“…Recently, supported metal clusters (SMCs) have emerged as a special class of electrocatalysts that consist of metal clusters as effective catalytic sites. 17,18 Compared with the widely studied single-atom catalysts (SACs), in addition to high atom utilization, SMCs can provide more adjacent unsaturated coordination sites to adsorb multiple reactants at the same time, 19,20 which is benecial to C-C coupling between CO reactants. In particular, the synergistic effect between the metal atoms within SMCs can tune the adsorption mode of some key intermediates and optimize the reaction pathways, leading to signicantly improved catalytic activity and selectivity.…”