Single Ru Sites-Embedded Rutile TiO₂ Catalyst for Non-Oxidative Direct Conversion of Methane: A First-Principles Study

Abstract

Non-oxidative direct methane conversion provides a potentially economic and environmental friendly route for the use of natural gas and shale gas, but this process suffers the disadvantages of low activity and selectivity and harsh operating conditions. Using density functional calculations, we develop the relations in heats of adsorption of CH x (x = 0−4) species and catalytic performance of conventional Fe, Ru, and Co-based catalysts and identify the key factors that affect the activity and selectivity as methane adsorption and the relative strength of CH 2 and CH adsorption. Based on the analysis, we design the single Ru sites embedded in rutile TiO 2 (110) catalyst, which tunes the adsorption strength of CH x compared with the traditional Ru-based catalyst, particularly weakening CH adsorption relative to CH 2 adsorption, thus leading to increased activity, improved selectivity toward ethylene, and strong resistance toward coking. This work highlights the impact of surface coordination environment, achieving fundamental insight that can be used to design and develop improved catalysts for direct methane conversion and other important reactions of technological interest.

Breaking Simple Scaling Relations through Metal–Oxide Interactions: Understanding Room-Temperature Activation of Methane on M/CeO2 (M = Pt, Ni, or Co) Interfaces

“…Methane (CH 4 ) is the simplest, most stable, and most abundant alkane molecule in our planet . It is the main component of natural gas and a major problem in the atmosphere due to its contribution to greenhouse warming. − There is broad interest in the activation and conversion of methane into value-added chemicals (aromatics, olefins, and oxygenates). , This is a real challenge because of the high C–H bond strength (104 kcal/mol for the first bond dissociation energy), the absence of low-energy empty orbitals, and the presence of high-energy occupied orbitals. , With respect to the activation of methane, several descriptors and scaling relations have been examined for the cleavage of the first C–H bond in the hydrocarbon. − In general, these descriptors and scaling relations provide guidelines for comparing and predicting the performance of potential new catalysts with that of existing materials used for C–H bond activation. ,, They can be used to quickly determine whether a new material of interest can successfully activate methane and should be examined further. ,, Computational volcanos have become the gold standard in the design of catalysts, and scaling relations are generally considered to have a universal validity. ,, In the case of methane activation, volcano plots have been presented for metal or oxide systems. ,, In this work, we investigate how to use metal–support interactions to enhance chemical reactivity for methane activation, breaking existing scaling relations, , and moving into a different dimensional space.…”

Recent advances in heterogeneous catalysis for the nonoxidative conversion of methane

“…Results from recent theoretical studies provided an indepth mechanistic understanding of the elementary steps. [86][87][88][89][90] In the work conducted by Bao and colleagues, 15 a gas-phase reaction mechanism was proposed based on preliminary theoretical calculations and VUV-SPI-MBMS analysis. It was proposed that methane was rst activated over the single Fe atom center, resulting in the C-H bond cleavage of CH 4 with the dissociated H and methyl being adsorbed at the C and Fe sites, respectively.…”

Metal–Support Interactions and C1 Chemistry: Transforming Pt-CeO2 into a Highly Active and Stable Catalyst for the Conversion of Carbon Dioxide and Methane

“…6,8 When dealing with the activation of CO2 and CH4 on metal and oxide surfaces, several descriptors and scaling relations have been examined for the controlled cleavage of the C-O or CH bonds in these molecules. [7][8][9][10][11][12][13][14][15] But, what types of systems can activate simultaneously CO2 and CH4? It has become clear that single metals alone are not efficient for the MDR process [16][17] and better results can be obtained when one uses metalmetal or metal-oxide interfaces where different sites cooperate in the activation of CO2 and CH4.…”

“…In the second reaction, the reverse water-gas shift (RWGS), is often seen at high temperature. The MDR process is a real challenge due to the high stability and the nonpolar nature of both CO 2 and CH 4 . ,− Heterogeneous catalysts are frequently used to accomplish this task and the activation of C–O and C–H bonds must be done in a concerted manner to avoid carbon deposition and subsequent deactivation of the catalyst. , When dealing with the activation of CO 2 and CH 4 on metal and oxide surfaces, a set of scaling relations and descriptors have been evaluated for the controlled cleavage of the C–O or C–H bonds in these molecules. − However, what types of systems can simultaneously activate CO 2 and CH 4 ? It has become clear that single metals alone are not efficient for the MDR process , and better results can be obtained when one uses metal–metal or metal-oxide interfaces where different sites cooperate in the activation of CO 2 and CH 4 . ,− …”