Selective Dissociation of Dihydrogen over Dioxygen on a Hindered Platinum Surface for the Direct Synthesis of Hydrogen Peroxide

Abstract

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.

Hydrogen Spillover in Encapsulated Metal Catalysts: New Opportunities for Designing Advanced Hydroprocessing Catalysts

“…Very recently,o ur group prepared several model catalysts meeting this requirement and used them to obtain af undamental understanding of hydrogen spillover and also to explore the catalytic functions of spilt-over hydrogen. [4,5] These works not only provided strong evidences of the existence of hydrogen spillover,b ut also showedt he unique possibility of using the encapsulatedmetal catalysts in the design of chemoselectivea nd highly durable catalysts. By virtue of advanced materialc hemistry,s everal other groupsh ave also reported interesting model catalysts andc learly showed ap otential use of hydrogen spillover for the design of advanced hydrogenation catalysts.…”

“…[5] The major hurdle for the direct H 2 O 2 synthesis is the existence of diversec ompeting reactions such as the simultaneous formation of H 2 O( H 2 combustion), and the consecutive decomposition/hydrogenation of the produced H 2 O 2 into H 2 O( Scheme 5a). All of these competing reactions are thermodynamically more favorable than H 2 O 2 formation,t husg enerally resulting in al ow H 2 O 2 production selectivity.T oa chieve ah igh catalytic selectivity towards H 2 O 2 , one clear constraint for catalyst design is that HÀHb onds in H 2 should be activated, while OÀObonds in O 2 must be preserved in the course of the reaction.…”

“…[22] The addition of mineral acid with halide poisons [49][50][51] and the alloying of inactive Au with Pd catalysts [48,52] in earlier researches may be understood as as trategy to selectively poison or block energetic active sites, whichc an kinetically retard OÀOd issociation. In our recent work, [5] an ew concept Pt-based catalyst was prepared, which can selectively produce H 2 O 2 in the absence of corrosivep oison additives. The key design concept is to coat the Pt/SBA-15 (mesoporousS iO 2 )c atalyst with nanoscale amorphous carbon layers that can selectively allow the diffusion of H 2 which has as mall kinetic diameter (0.29 nm), over O 2, which has al arger kinetic diameter (0.35 nm) (Scheme 5c).…”

“…The DFTcalculation suggested that nitrogen doping on the carbon layer could significantly increase the selectivity towards H 2 O 2 due to the stabilization of the hydroperoxyr adical (HOOC)o nt he carbon surface. [5] When chemisorbed on the N-doped carbon surface(NC), the non-hydrogenated oxygen of HOO* can selectively react with second spilt-over hydrogen, leading to the selective production of H 2 O 2 (Figure5). In contrast, on the pure carbon surface( C) with no specific binding site for HOOC,t he second spilt-over hydrogen can stochastically react with both the non-hydrogenated oxygen and the hydrogenated oxygen of HOOC,o wing to the dynamic motions of the non-chemisorbed intermediate species.…”

“…[4] In "Hydrogen spillover in carbon" section, we saw that the selective activation of H-H while keeping OÀOb ond intact couldl ead to the selective formation of H 2 O 2 over H 2 O from an H 2 /O 2 mixture. [5] 2) If the metals are encapsulated in ad ense support matrix that selectively allows the diffusion of H 2 ,the reaction between target reactant and activated hydrogen should take place at the externals urface of the support. This means that catalytic properties are mainly determined by the adsorption mode of the target reactants on the 'support surface' rather than the 'metal surface'.Therefore, chemicalmodification of the support surfacec an lead to ad ramatic changei nc atalytic properties.…”