Catalytic Reaction Rates Controlled by Metal Oxidation State: C−H Bond Cleavage in Methane over Nickel‐Based Catalysts

Abstract

The role of low concentrations of carbon complexes in hydrocarbon decomposition over transition metal surfaces has been a topic of much debate over the past decades. It is also a mystery as to whether or not electric fields can enhance hydrocarbon conversion in an electrochemical device at lower than normal reforming temperatures. To provide a “bottom‐up” fundamental insight, C−H bond cleavage in methane over Ni‐based catalysts was investigated. Our theoretical results show that the presence of carbon or carbide‐like species at the interface between the Ni cluster and its metal‐oxide support, as well as the application of an external positive electric field, can significantly increase the Ni oxidation state. Furthermore, the first C−H bond cleavage in methane is favored as the local oxidation state of Ni increases. Thus, the presence of a low concentration of carbon species, or the addition of a positive electric field will improve the hydrocarbon activation process.

Significant Advances in C1 Catalysis: Highly Efficient Catalysts and Catalytic Reactions

“…221−223 The dispersion/chemical state of noble metal NPs critically impacts the adsorption behavior of the reactants and the subsequent conversion of reaction intermediates. 224,225 However, the support can affect the chemical state of noble metal nanoparticles in a manner that differs from a substrate for metal dispersal. 226,227 Controlling the metal size, especially the size uniformity, remains a major challenge for supported metal catalysts.…”

Reducing Reaction Temperature, Steam Requirements, and Coke Formation During Methane Steam Reforming Using Electric Fields: A Microkinetic Modeling and Experimental Study

“…One classical explanation for such a field effect on the C−H bond cleavage of methane is that the direction of a positive electric field aligns with the dipole moment of methyl species on Ni(111) (see inset picture in Figure 6), leading to a lower potential energy ( = − ⃗ • ⃗ U d F) of such a system as compared to the scenario in the absence of an electric field or in the presence of a negative field, which is in agreement with our previous calculations of the reaction barriers using DFT. 73 This further suggests that, when the Ni surface is positively charged in the presence of a positive electric field, the methane gas molecule decomposes more readily into the methyl species, while the effects are opposite when a negative electric field (the Ni surface is negatively charged) is applied on the decomposition of methane. 73 Overall, a positive electric field polarizes the Ni surface to be positively charged, which can accelerate the ratelimiting step (CH 4 (gas) + 2* → CH 3 * + H*) of the MSR-over-Ni reaction.…”

“…73 This further suggests that, when the Ni surface is positively charged in the presence of a positive electric field, the methane gas molecule decomposes more readily into the methyl species, while the effects are opposite when a negative electric field (the Ni surface is negatively charged) is applied on the decomposition of methane. 73 Overall, a positive electric field polarizes the Ni surface to be positively charged, which can accelerate the ratelimiting step (CH 4 (gas) + 2* → CH 3 * + H*) of the MSR-over-Ni reaction. 73 Evidence also suggests that the first C−H bond cleavage in methane is facilitated as the local oxidation state of Ni increases, which had been validated from our previous work.…”

Catalytic Methane Pyrolysis with Liquid and Vapor Phase Tellurium

“…Despite considerable research on methane activation, the scope of catalysts studied has been limited to several elements and compounds already known to be active, and the development of new catalysts is still largely based on trial and error, due to the lack of a clear correlation between the intrinsic properties of catalysts and their methane-activation activity. However, there have been reports of a positive correlation between the electron affinity (or equivalent) of catalysts and their catalytic activity for methane. ,− Tellurium is a metalloid with the highest electron affinity and electronegativity among the common low-melting-point elemental solids and therefore might be active. Tellurium has been shown to be a dehydrogenation catalyst for several polynuclear hydrocarbons, − but to our knowledge, it has not been studied as a catalyst for C–H bond activation in methane or CH 4 pyrolysis.…”