Continuous on-site electrochemical production of hydrogen peroxide (H 2 O 2 ) can provide an attractive alternative to the present anthraquinone-based H 2 O 2 production technology. A major challenge in the electrocatalyst design for H 2 O 2 production is that O 2 adsorption on the Pt surface thermodynamically favors "side-on" configuration over "end-on" configuration, which leads to a dissociation of O−O bond via dominant 4-electron pathway. This prefers H 2 O production rather than H 2 O 2 production during the electrochemical oxygen reduction reaction (ORR). In the present work, we demonstrate that controlled coating of Pt catalysts with amorphous carbon layers can induce selective end-on adsorption of O 2 on the Pt surface by eliminating accessible Pt ensemble sites, which allows significantly enhanced H 2 O 2 production selectivity in the ORR. Experimental results and theoretical modeling reveal that 4-electron pathway is strongly suppressed in the course of ORR due to a thermodynamically unfavored end-on adsorption of O 2 (the first electron transfer step) with 0.54 V overpotential. As a result, the carbon-coated Pt catalysts show an onset potential of ∼0.7 V for ORR and remarkably enhanced H 2 O 2 selectivity up to 41%. Notably, the produced H 2 O 2 cannot access the Pt surface due to the steric hindrance of the coated carbon layers, and thus no significant H 2 O 2 decomposition via disproportionation/ reduction reactions is observed. Furthermore, the catalyst shows superior stability without considerable performance degradation because the amorphous carbon layers protect Pt catalysts against the leaching and ripening in acidic operating conditions.

Designed catalyst poisons can be deliberately added in various reactions for tuning chemoselectivity. In general, the poisons are "transient" selectivity modifiers that are readily leached out during reactions and thus should be continuously fed to maintain the selectivity. In this work, we supported Pd catalysts on a thermochemically stable crosslinked polymer containing diphenyl sulfide linkages, which can simultaneously act as a catalyst support and a "permanent" selectivity modifier. The entire surfaces of the Pd clusters were ligated (or poisoned) by sulfide groups of the polymer support. The sulfide groups capping the Pd surface behaved like a "molecular gate" that enabled exceptionally discriminative adsorption of alkynes over alkenes. H 2 /D 2 isotope exchange revealed that the capped Pd surface alone is inactive for H 2 (or D 2 ) dissociation, but in the presence of coflowing acetylene (alkyne), it becomes active for H 2 dissociation as well as acetylene hydrogenation. The results indicated that acetylene adsorbs on the Pd surface and enables cooperative adsorption of H 2 . In contrast, ethylene (alkene) did not facilitate H 2 −D 2 exchange, and hydrogenation of ethylene was not observed. The results indicated that alkynes can induce decapping of the sulfide groups from the Pd surface, while alkenes with weaker adsorption strength cannot. The discriminative adsorption of alkynes over alkenes led to highly chemoselective hydrogenation of various alkynes to alkenes with minimal overhydrogenation and the conversion of side functional groups. The catalytic functions can be retained over a long reaction period due to the high thermochemical stability of the polymer.

Hydrogen spillover has been one of the most debated concepts in the field of heterogeneous catalysis due to limited ways of studying it. The main controversies in hydrogen spillover, especially from the viewpoint of its catalytic functions, can be mainly attributed to the absence of well‐defined model catalysts that can provide direct proof of the catalytic functions of hydrogen spillover. In this article, we will provide an overview of the recent progress made with encapsulated metal catalysts, which can act as an ideal model catalyst for proving the existence and catalytic functions of hydrogen spillover. We will also demonstrate unique opportunities of using the encapsulated metal catalysts for designing advanced hydroprocessing catalysts with enhanced activity, distinct chemoselectivity, and increased catalyst durability.

Direct synthesis of hydrogen peroxide (H2O2) from hydrogen (H2) and oxygen (O2) has been widely investigated as an attractive way for small-scale/on-site H2O2 production. Among various catalysts, carbon-supported AuPd catalysts have been reported to exhibit the most promising H2O2 productivity and selectivity. In this work, to better understand the catalytic role of the surface properties and porous structures of the carbon supports, we systematically investigated AuPd catalysts supported on various nanostructured carbons including activated carbon, carbon nanotube, carbon black, and ordered mesoporous carbons. The results showed that a high density of oxygen functional groups on the carbon surface was essential for synthesizing highly dispersed bimetallic catalysts with effective AuPd alloying, which is a prerequisite for achieving high H2O2 selectivity. Regarding porous structure, a solely mesoporous carbon support was superior to microporous ones. Microporous carbons such as activated carbon suffered from diffusion limitation, leading to significantly slower H2 conversion than mesoporous catalysts. Furthermore, H2O2 produced from AuPd catalyst in the micropores was more prone to subsequent disproportionation/hydrogenation into H2O due to retarded diffusion of the H2O2 out of the microporous structure, which led to decreased H2O2 selectivity. The present study showed that solely mesoporous carbons with high surface oxygen content are most desirable as a support for AuPd catalyst in order to achieve high H2O2 productivity and selectivity.

To achieve high catalytic selectivity towards H2O2 from a H2/O2 mixture, HH bonds should be dissociated and OO bonds should be kept intact in the course of the reaction. A major dilemma in catalyst design, however, is that the metal catalysts that dissociate HH bonds have a thermodynamic preference for the dissociation of OO bonds. In this work, the selective dissociation of H2 over O2 was realized by the deposition of H2‐selective carbon diffusion layers on a Pt catalyst. Because O2 cannot access the carbon‐coated Pt surface, O2 hydrogenation occurs at the carbon surface from spilt‐over hydrogen rather than at the Pt surface on which OO dissociation is likely. This leads to the great suppression of OO dissociation, which allows the highly selective synthesis of H2O2. Notably, N‐doping of the carbon diffusion layer could increase the selectivity towards H2O2 significantly because of the stabilization of the hydroperoxy radical on the carbon surface.