Selective Cleavage of Chemical Bonds in Targeted Intermediates for Highly Selective Photooxidation of Methane to Methanol

Abstract

Restrained by the uncontrollable cleavage process of chemical bonds in methane molecules and corresponding formed intermediates, the target product in the reaction of methane selective oxidation to methanol would suffer from an inevitable overoxidation process, which is considered to be one of the most challenging issues in the field of catalysis. Herein, we report a conceptually different method for modulating the conversion pathway of methane through the selective cleavage of chemical bonds in the key intermediates to suppress the generation of peroxidation products. Taking metal oxides, typical semiconductors in the field of methane oxidation as model catalysts, we confirm that the cleavage of different chemical bonds in CH 3 O* intermediates could greatly affect the conversion pathway of methane, which has a vital role in product selectivity. Specifically, it is revealed that the formation of peroxidation products could be significantly prevented by the selective cleavage of C−O bonds in CH 3 O* intermediates instead of metal−O bonds, which is proved by the combination of density functional theory calculations and in situ infrared spectroscopy based on isotope labeling. By manipulating the lattice oxygen mobility of metal oxides, the electrons transferring from the surface to the CH 3 O* intermediates could directionally inject into the antibonding orbitals of the C−O bond, resulting in its selective cleavage. As a result, the gallium oxide with low lattice oxygen mobility shows a 3.8% conversion rate for methane with a high methanol generation rate (∼325.4 μmol g −1 h −1 ) and selectivity (∼87.0%) under room temperature and atmospheric pressure in the absence of extra oxidants, which is superior among the reported studies (reaction pressure: <20 bar).

Pauling‐Type Adsorption of O2 Induced by Heteroatom Doped ZnIn2S4 for Boosted Solar‐Driven H2O2 Production

“…In contrast, for the Yeager‐type O 2 adsorption on ZIS, there's a discernible endergonic challenge when it comes to activating oxygen molecules. The Pauling‐type adsorption of O 2 on P 2 ZIS appears primed for *OOH generation, attributable to the more facile energy barriers (0.11 eV) as opposed to the Yeager‐type configuration observed in ZIS (0.30 eV) [28] . This underscores the role of P atoms neighboring Zn active sites in transmuting the O 2 adsorption configuration from Yeager‐type to Pauling‐type.…”

“…The Pauling-type adsorption of O 2 on P 2 ZIS appears primed for *OOH generation, attributable to the more facile energy barriers (0.11 eV) as opposed to the Yeager-type configuration observed in ZIS (0.30 eV). [28] This underscores the role of P atoms neighboring Zn active sites in transmuting the O 2 adsorption configuration from Yeager-type to Pauling-type. Furthermore, these proximal P atoms around Zn active sites are theoretically adept at stabilizing the ratelimiting *OOH intermediates (while ZIS exhibits a tendency for oxygen-oxygen bond cleavage), thus affording a strategic advantage in modulating the selectivity and activity of H 2 O 2 in P 2 ZIS.…”

Preparation of Heterojunction Catalysts for Photocatalysis by in‐situ Synthesis: What We Should Do Next?

“…To verify the effect of the reaction pathways in the change of the CH 4 photooxidation performance, Zhou et al used the in-situ DRIFTS measurement to dynamically monitor the effect of different metal oxides on CH 4 photooxidation into CH 3 OH (Figure 21). [61] It is indicated that there are overoxidation products involving HCHO and CO 2 generated on the ZnO surface during the reaction process, no visible adsorption band assigned to CH 2 * detected on the P25 surface, but several adsorption bands assigned to the overoxidation product appear. Different from them, on Ga 2 O 3 only CH 3 O* intermediates are detected.…”

Highly Selective Photocatalytic Methane Coupling by Au-Modified Bi2WO6

“…Three key peaks were investigated: lattice oxygen (∼530.13 eV, bulk lattice oxygen is also involved), oxygen near the oxygen vacancies (∼531.30 eV), and hydroxyl groups or surface-adsorbed oxygen (∼532.30 eV). 37,44,45 It can be seen that Au modification measurably increased surface O v , which favors the activation of O 2 and the turnover of oxygen species through a reported evolutionary pathway of oxygen: 8,23,37,46 The existence of surface O v provided sites for the activation of O 2 , and as a result, more O 2− could be generated from O 2 and facilitate selective C−H activation upon photoexcitation.…”

“…This is further corroborated by theoretical calculations indicating a substantial decrease in the energy required for O v formation at interface sites in the presence of Au due to the effects of lower valence dopants, such as Au. , To further test this understanding, we next performed X-ray photoelectron spectroscopy (XPS, Figure c). Three key peaks were investigated: lattice oxygen (∼530.13 eV, bulk lattice oxygen is also involved), oxygen near the oxygen vacancies (∼531.30 eV), and hydroxyl groups or surface-adsorbed oxygen (∼532.30 eV). ,, It can be seen that Au modification measurably increased surface O v , which favors the activation of O 2 and the turnover of oxygen species through a reported evolutionary pathway of oxygen: O 2 ↔ O 2 – ↔ O 2 2– ↔ 2O – ↔ 2O 2– (surface lattice). ,,, The existence of surface O v provided sites for the activation of O 2 , and as a result, more O 2– could be generated from O 2 and facilitate selective C–H activation upon photoexcitation.…”