Non‐oxidative Coupling of Methane: N‐type Doping of Niobium Single Atoms in TiO₂–SiO₂ Induces Electron Localization

Abstract

Photodriven nonoxidative coupling of CH4 (NOCM) is an attractive potential way to use abundant methane resources. Herein, an n‐type doped photocatalyst for NOCM is created by doping single‐atom Nb into hierarchical porous TiO2–SiO2 (TS) microarray, which exhibits a high conversion rate of 3.57 μmol g−1 h−1 with good recyclability. The Nb dopant replaces the 6‐coordinated titanium on the (1 0 1) plane and forms shallow electron‐trapped surface polarons along [0 1 0] direction and the comparison of different models proves that the electron localization caused by the n‐type doping is beneficial to both methane activation and ethane desorption. The positive effect of n‐type dopant on CH4 conversion is further verified on Mo‐, W‐ and Ta‐doped composites. In contrast, the doping of p‐type dopant (Ga, Cu, Fe) shows a less active influence.

Light‐Induced Nonoxidative Coupling of Methane Using Stable Solid Solutions

“…It should be noted that, except for Ga 2 O 3 , [18] most of the other metal oxide semiconductors can be easily reduced under the NOCM conditions, and therefore are not suitable as robust catalytic supports. As shown in Figure 1 a and Table S1, almost all the previously reported NOCM photocatalysts are constructed based on stable insulators, such as Al 2 O 3 , SiO 2 , and molecular sieves, while the photocatalytic properties are accessed by introducing isolated photoactive species into the insulators [19–25] . Compared to these “quantum photocatalysts”, the development of robust semiconductor photocatalysts with much more superior light‐harvesting ability is expected to greatly boost the efficiency of light‐driven methane conversion reactions.…”

Defect Engineering in Photocatalytic Methane Conversion

“…[ 23–25 ] More importantly, the presence of defects can induce localized carrier trapping centers, resulting in the positively or negatively charged sites for electrostatic adsorption or C—H bond polarization of methane molecule, which can greatly weaken the inert C—H bond of methane. [ 26 ] Furthermore, the adsorption configuration of methane molecules on the surface of photocatalyst can be rationally modulated by regulating the parameters of defects, which is highly beneficial for efficiently converting methane into desired products. [ 27 ]…”

Photocatalytic Conversion of Methane: Recent Advancements and Prospects

“…So far, many catalytic materials such as metal ion (Zn + , Ga 3+ )d oped zeolites,S iO 2 ,G aN,Z nO,a nd TiO 2 composites have been successfully applied to the photocatalytic NOCM. [37,44,66,132,[134][135][136][137][138] Currently,t he predominant C 2 product of photocatalytic NOCM is C 2 H 6 ,with only traces of C 2 H 4 produced as aby-product. Lang et al have so far achieved the highest C 2 H 6 production rate of 81.7 mmol g À1 h À1 over Au/ TiO 2 .…”