Control in Local Coordination Environment Boosting Activating Molecular Oxygen with an Atomically Dispersed Binary Mn–Co Catalyst

Abstract

Activation of molecular oxygen plays a crucial role in natural organisms and the modern chemical industry. Herein, we report a Mn–Co dual-single-atom catalyst that exerts a specific synergy in boosting O2 activation by collaboration between two distinct types of activation sites. Taking the oxidative esterification of the biomass platform 5-hydroxymethylfurfural (HMF) as the model reaction, the activation of O2 is demonstrated through transforming O2 into a reactive superoxide anion radical (O2 •–) on Co–N4 sites and, meanwhile, by reversible consumption and supplement of coordinated surface oxygen as a new type of reactive oxygen species (ROS) on N,O-coordinated single-atom Mn sites (Mn–N x O y ). EXAFS analysis results show a longer average Mn–O bond distance at near 2.19 Å, which makes the breaking and formation of surface Mn–O bonds easier to cycle. Control experiments support that such Mn–O bonding conditions could facilitate H-elimination of C–H in HMF. The co-existence of two types of ROS effectively matches the oxidation of hydroxyl and aldehyde groups, and thus, the overall reaction is boosted in excellent yield of diester (95.8%) with an extremely high carbon balance. This study represents a rare example of taking advantage of the synergy of the diatomic catalyst for activating O2 by two types of activation pathways.

Leveraging Pt/Ce1–xLaxO2−δ To Elucidate Interfacial Oxygen Vacancy Active Sites for Aerobic Oxidation of 5-Hydroxymethylfurfural

“…Accordingly, a possible mechanism could be proposed (Figure ) for the alcohol oxidation step (HMFCA→FFCA) over Pt/3D-Ce 1– x La x O 2−δ , where the mono-substituted interfacial asymmetric oxygen vacancy sites of Pt/La-□(-Ce) 2 served as both reversible active sites for O 2 activation and adsorption sites for oxygen-containing groups of reactants. Firstly, the interfacial Pt/La-□(-Ce 3+ ) 2 sites can boost O 2 adsorption through the electron donation from Ce 3+ to the π* antibonding orbitals of O 2 to form active oxygen species, such as · O 2 – and · O 2 2– (Figure a) . After the desorption of active oxygen species, the resulting Pt/La-□(-Ce 4+ ) 2 sites can work as the adsorption sites for alcohol hydroxyl groups of HMFCA (Figure b).…”

“…The pieces of evidence from a variety of in-situ and ex-situ characterizations discussed above proved that the monosubstituted interfacial oxygen vacancy sites of Pt/La-□(-Ce) 2 played a crucial role in promoting O 2 adsorption and 11a). 66 After the desorption of active oxygen species, the resulting Pt/La-□(-Ce 4+ ) 2 sites can work as the adsorption sites for alcohol hydroxyl groups of HMFCA (Figure 11b). The O atoms of hydroxyl groups would fill up the oxygen vacancy to generate Pt δ+ /La-O(-Ce 4+ ) 2 , on which the cleavage of O−H takes place under the assistance of active oxygen species • O 2 − to form • OOH (Figure 11c).…”

Industry-oriented method for the aqueous phase oxidation of crude 5-hydroxymethyl furfural (HMF) to 2,5-furandicarboxylic acid (FDCA)

“…Literature reports suggest that oxidation over mixed metal oxides generally proceeds through Mars-van Krevelen mechanism. [76][77][78] In one of the report, insights on the role of oxygen vacancy over Mn-based catalyst is predominantly discussed. 76 In another report, the activation of oxygen is suggested through the formation of superoxide anion radical through EXAFS analysis.…”

“…76 In another report, the activation of oxygen is suggested through the formation of superoxide anion radical through EXAFS analysis. 77 The adsorption of HMF over Lewis acid site (Mn 4+ ) by the sharing of lone pair of electrons from the oxygen in HMF (hydroxyl) is also mentioned in the literature for the activation of HMF. 78 Later, the hydrogen atom is suggested to be interact with the Lewis base site (O 2 − ) present on the catalyst.…”

Gold/Substituted Hydroxyapatites for Oxidative Esterification: Control of Thin Apatite Layer on Gold Based on Strong Metal–Support Interaction (SMSI) Results in High Activity

“…The base-free oxidative esterification of aldehydes has been attracting attention in particular for the production of methyl methacrylate (MMA) from methacrolein and methanol. ,,− However, the oxidative esterification of aliphatic aldehydes and alcohols with long alkyl chains ,,− is more challenging than that of benzylic and allylic ones ,− owing to the low reactivity of the former and results in low conversion or requires harsher reaction conditions even in the presence of a base. − Although Au catalysts show high catalytic activity and product selectivity when methanol is used to produce methyl esters, the synthesis of ethyl esters also generally yields unsatisfactory results because ethanol is less nucleophilic and more oxidizable than methanol, forming acetates such as ethyl acetate as byproducts. The synthesis of aromatic ethyl esters has been reported using Au NP catalysts with ,− and without a base .…”