Regulating the Spin State of Single Noble Metal Atoms by Hydroxyl for Selective Dehydrogenation of CH₄ Direct Conversion to CH₃OH

Abstract

The key scientific challenge for methane (CH 4 ) direct conversion to methanol (CH 3 OH) is considered to be the prevention of overoxidation of target products, which is restrained by the difficulty in the well-controlled process of selective dehydrogenation. Herein, we take single noble metal atomanchored hexagonal boron nitride nanosheets with B vacancies (M SA /B 1−x N) as the model materials and first propose that the dehydrogenation in the direct conversion of CH 4 to CH 3 OH is highly dependent on the spin state of the noble metal. The results reveal that the noble metal with a higher spin magnetic moment is beneficial to the formation of the spin channels for electron transfer, which boosts the dissociation of C−H bonds. The promoted process of dehydrogenation will lead not only to the effective activation of CH 4 but also to the easy overoxidation of CH 3 OH. More importantly, it is found that the spin state of noble metals can be regulated by the introduction of hydroxyl (OH), which realizes the selective dehydrogenation in the process of CH 4 direct conversion to CH 3 OH. Among them, Ag SA /B 1−x N exhibits the best performance owing to the dynamic regulation spin state of a single Ag atom by OH. On the one hand, the introduction of OH significantly reduces the energy barrier of C−H bond dissociation by the increase in the spin magnetic moment. On the other hand, the high spin magnetic moment of a single Ag atom during the process of subsequent dehydrogenation can be modulated to nearly zero. As a result, the spin channel for electron transfer between the adsorbed CH 3 OH and reactive sites is broken, which hinders its overoxidation. This work opens a new path to designing catalysts for selective dehydrogenation by tuning the spin state of local electronic structures.

Methane Photooxidation with Nearly 100 % Selectivity Towards Oxygenates: Proton Rebound Ensures the Regeneration of Methanol

“…As mentioned above, the dehydrogenation process on the BN surface is quite different from that on ZnO and P25, affecting the stabilization of CH 3 * and CH 3 O* intermediates, which are the important intermediates in the process of CH 3 OH generation [20] . Hence, a different dehydrogenation process might be the main factor affecting the product selectivity of CH 4 photooxidation into CH 3 OH over BN, ZnO, and P25 samples.…”

Methane Photooxidation with Nearly 100 % Selectivity Towards Oxygenates: Proton Rebound Ensures the Regeneration of Methanol

“…Previous studies have reported that the reaction process could take place on the in‐plane surface, armchair edge, or zigzag edge of BN nanosheets [17, 20, 27] . Hence, three types of calculated modes are constructed in Figure S24.…”

“…As mentioned above, the dehydrogenation process on the BN surface is quite different from that on ZnO and P25, affecting the stabilization of CH 3 * and CH 3 O* intermediates, which are the important intermediates in the process of CH 3 OH generation. [20] Hence, a different dehydrogenation process might be the main factor affecting the product selectivity of CH 4 photooxidation into CH 3 OH over BN, ZnO, and P25 samples. It is generally believed that during the photocatalysis process, the photoinduced carriers generated by semiconductors under light illumination may transfer to the surface to participate in the activation of the reactant and the further conversion process.…”

“…Previous studies have reported that the reaction process could take place on the in-plane surface, armchair edge, or zigzag edge of BN nanosheets. [17,20,27] Hence, three types of calculated modes are constructed in Figure S24. As shown in Figure 7a,b and Figures S25-S28, the Gibbs free energy change (ΔG) of HCHO conversion into CHO* intermediates on the in-plane BN surface is 189.0 kJ mol À 1 , which is much higher than that of CH 3 OH formation (ΔG = À 528.0 kJ mol À 1 ).…”

Recent advances and future perspectives in MOF-derived single-atom catalysts and their application: a review

“…), atomic layer deposition method (ALD), 7,8 pyrolysis method, and mass-separation soft landing method. 9 Currently, various metal-based SACs have been successfully developed, incorporating metals such as platinum, 10 cobalt, 11 iron, 12 copper, 13,14 bismuth, 15 palladium, 16 ruthenium, 17 nickel, 10 and silver, 18 and their various applications are also introduced. For the characterization of SACs, it is tough to efficiently distinguish the existence of single metal atoms.…”