Citation: Almithn, A.; Alghanim, S.N.; Mohammed, A.A.; Alghawinim, A.K.; Alomaireen, M.A.; Alhulaybi, Z.; Hossain, S.S. Methane Activation and Coupling Pathways on Ni 2 P Catalyst. Catalysts 2023, 13, 531. https://doi.org/10.3390/ catal13030531 Academic Editors: Tamer S. Saleh, Nesreen S. Ahmed and Mohamed Mokhtar M. Mostafa Received: 3 January 2023 Revised: 13 February 2023 Accepted: 24 February 2023 Published: 6 March 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). catalysts Article Methane Activation and Coupling Pathways on Ni 2 P Catalyst Abdulrahman Almithn * , Salem N. Alghanim, Abdullah A. Mohammed, Abdullah K. Alghawinim, Mazen A. Alomaireen, Zaid Alhulaybi and SK Safdar Hossain Department of Chemical Engineering, College of Engineering, King Faisal University, Al Ahsa 31982, Saudi Arabia * Correspondence: aalmithn@kfu.edu.sa Abstract: The direct catalytic conversion of methane (CH 4 ) to higher hydrocarbons has attracted considerable attention in recent years because of the increasing supply of natural gas. Efficient and selective catalytic conversion of methane to value-added products, however, remains a major challenge. Recent studies have shown that the incorporation of phosphorus atoms in transition metals improves their selectivity and resistance to coke formation for many catalytic reactions. In this work, we report a density function theory-based investigation of methane activation and C 2 product formation on Ni 2 P(001). Our results indicate that, despite the lower reactivity of Ni 2 P relative to Ni, the addition of phosphorus atoms hinders excessive dehydrogenation of methane to CH* and C* species, thus reducing carbon deposition on the surface. CH 3 * and CH 2 * moieties, instead, are more likely to be the most abundant surface intermediates once the initial C–H bond in methane is activated with a barrier of 246 kJ mol −1 . The formation of ethylene from 2CH 2 * on Ni 2 P is facile with a barrier of 56 kJ mol −1 , which is consistent with prior experimental studies. Collectively, these findings suggest that Ni 2 P may be an attractive catalyst for selective methane conversion to ethylene. Keywords: methane activation; dehydrogenation; nickel phosphides; ethylene; density functional theory 1. Introduction Recent years have seen a dramatic increase in catalytic studies focusing on the trans- formation of methane (CH 4 ) into value-added products [1–9]. Conversion of methane into high-value chemicals at low operating conditions is a critical process to utilize the increasing production of natural gas, as well as to mitigate greenhouse gas emissions. Methane is considered a major contributor to global warming along with carbon dioxide. Currently, longer alkanes and olefins are produced from methane indirectly using Fischer- Tropsch synthesis [10]. It involves the catalytic oxidation of methane to syngas (CO and H 2 ) followed by production of methanol and other valuable products. However, the high operating pressures and temperatures required for this process make it energy-intensive and economically costly. It is also possible to convert methane directly and efficiently into higher hydrocarbons through selective activation and coupling in a single-step process [9], but this remains a major challenge in the field of heterogenous catalysis because methane has a high C–H bond activation energy (439 kJ mol −1 ), which requires extreme conditions to activate (temperatures > 700 ◦ C) [11]. Moreover, once the initial C–H bond is cleaved, which is the most difficult step, subsequent C–H bond activation steps can occur rapidly due to the high temperature and cannot be controlled to selectively produce high-value chemicals. Instead, coke formation becomes prevalent, which severely impacts catalyst performance and stability. Many different catalysts have been experimentally and theoretically investigated for oxidative and non-oxidative coupling of methane. In the oxidative coupling process, first reported by Keller and Bhasin [12], methane is converted into ethane or ethylene at temperatures higher than 700 ◦ C according to the following equations: Catalysts 2023, 13, 531. https://doi.org/10.3390/catal13030531 https://www.mdpi.com/journal/catalysts