Rational Design of the Catalysts for the Direct Conversion of Methane to Methanol Based on a Descriptor Approach

Abstract

The direct oxidation of methane to methanol as a liquid fuel and chemical feedstock is arguably the most desirable methane conversion pathway. Currently, constructing and understanding linear scaling relationships between the fundamental physical or chemical properties of catalysts and their catalytic performance to explore suitable descriptors is crucial for theoretical research on the direct conversion of methane to methanol. In this review, we summarize the energy, electronic, and structural descriptors used to predict catalytic activity. Fundamentally, these descriptors describe the redox properties of active sites from different dimensions. We further explain the moderate principle of descriptors in methane-to-methanol catalyst design and provide related application work. Simultaneously, the underlying activity limitation of methane activation and active species generation is revealed. Based on the selectivity descriptor, the inverse scaling relationship limitation between methane conversion and methanol selectivity is quantitatively understood. Finally, multiscale strategies are proposed to break the limitation and achieve the simultaneous enhancement of activity and selectivity. This descriptor-based review provides theoretical insights and guidance to accelerate the understanding, optimization, and design of efficient catalysts for direct methane-to-methanol conversion.

Recent Advances in the Use of Controlled Nanocatalysts in Methane Conversion Reactions

“…Methane 2024, 3, FOR PEER REVIEW 4 nanoscale catalysts, providing insights into key factors governing catalytic performance [29,30]. Experimental and computational approaches have been employed to characterize the structure-activity relationships of nanocatalysts and identify the optimal catalyst formulations for enhanced methane conversion efficiency and selectivity [31,32].…”

“…Significant progress has been made in recent years towards the development and application of controlled nanocatalysts for methane conversion reactions. Fundamental studies have elucidated the mechanisms of methane activation and transformation on nanoscale catalysts, providing insights into key factors governing catalytic performance [29,30]. Experimental and computational approaches have been employed to characterize the structureactivity relationships of nanocatalysts and identify the optimal catalyst formulations for enhanced methane conversion efficiency and selectivity [31,32].…”

“…In Figure 3, methane activation is depicted as being dependent on the interaction between methane and the surface, occurring through either a radical or surface-stabilizer pathway. The methane conversion process involves the initial breaking of the C-H bond [30]. In Figure 3A, a homolytic radical mechanism is illustrated.…”

“…In Figure 3A, a homolytic radical mechanism is illustrated. This mechanism proceeds through hydrogen abstraction via active oxygen species in the M-O active site, resulting in the formation of a hydrogen atom adsorbed on the catalyst surface (M-OH) and a free methyl radical (*CH 3 ) with sp 2 hybridization and a trigonal planar geometry [30,34,35]. The *CH 3 radical does not form M-C bonds with active sites, and the *H exhibits a weak interaction forming OH groups.…”

“…The *CH 3 radical does not form M-C bonds with active sites, and the *H exhibits a weak interaction forming OH groups. Additionally, a one-electron redox process occurs, leading to the oxidation of the carbon center from the −4 state to the −3 state and the corresponding reduction of the active sites [29,30]. This process requires strong oxidants, such as H 2 O 2 and N 2 O, and high metal oxidation states to form electron-deficient species, such as O − and O 2− , thereby promoting the homolytic dissociation of C-H bonds [5,29,30,34,36].…”