No abstract

Direct conversion of methane to value-added chemical products under nonoxidative conditions is one of the most effective routes but still faces eminent challenges due to thermodynamic constraints and the lack of efficient catalysts. Herein, we propose to construct “Single-Atom”-“Frustrated Lewis Pair” (SA-FLP) dual-active-site catalysts for nonoxidative coupling of methane (NOCM). The single-atom site is created by doping a Pt atom at the Ce site of the CeO2 surface. The FLP site is fabricated by removing oxygen atom(s) adjacent to Pt atoms. Density functional theory (DFT) calculations reveal that SA-FLP dual active sites can simultaneously activate two methane molecules and notably enhance the coupling of hydrocarbon species to generate C2 products. The SA-FLP sites with two oxygen vacancies show the best performance for methane activation with a low energy barrier of 0.32 and 0.71 eV at SA and FLP sites, respectively. The coupling of two methyl groups to further generate ethane and ethylene only needs to surpass the highest barrier of 1.31 eV. Microkinetic analysis demonstrates that on the designed SA-FLP sites, CH4 consumption can reach a high turnover frequency (TOF) of 0.3014 s–1 under the conditions of 1200 K and a CH3 partial pressure of 8.0 × 10–3 bar, which is nearly two orders of magnitude higher than the experimentally reported value (3.8 ∼ 5.5 × 10–3 s–1) on traditional Pt/CeO2 catalysts. Importantly, the main product on the SA-FLP sites is shown to be the desired ethane with a TOF of 0.2535 s–1 under the conditions mentioned above. This study not only provides a strategy for designing efficient catalysts for NOCM but also offers insights into C–C coupling to generate oriented C2 products.

Isotope substitution, a compelling tool of physical chemistry, has been broadly applied in the research field of heterogeneous catalysis. In general, upon the differences in mass-related atomic vibrational frequencies and...

The discovery of naturally frustrated Lewis pairs (FLPs) on wurtzite-structured surfaces provides a shortcut to obtain dense and stable surface FLPs without complex surface engineering. However, the catalytic performance and potential applications in the catalysis of natural FLPs have not been thoroughly investigated. Herein, the heterolytic dissociation of hydrogen is studied at the natural FLPs of wurtzite-structured GaN, ZnO, and SiC surfaces by using theoretical methods. Compared with classical Lewis pairs (CLPs), the FLPs show lower activation barriers ranging from 0.07 to 0.16 eV but higher reaction energies in the heterolytic dissociation of hydrogen. By splitting the energy into different items via a chemical–physical model, the optimal substrate–surface interaction and the decreasing stability of lone pair electrons on N atoms are recognized as the main reason for the lower activation energy and the higher reaction energy at FLPs, respectively. Because of the relatively favorable kinetics and unfavorable thermodynamics in hydrogen dissociation, FLPs present superior performance in the selective hydrogenation of acetylene to ethylene, reflected by the lower activation energy by 0.89 eV in the rate-determining step than CLPs. Overall, this study not only provides mechanistic insights into the heterolytic dissociation of hydrogen at FLPs but also unfolds the advantages of FLPs in hydrogenation reactions.

The direct, nonoxidative conversion of methane achieved a breakthrough with the development of a silica-confined single-atom iron catalyst (Fe©SiO2). However, improving the catalyst from high temperature and harsh conditions is still required. Here we designed a two-atom single-cluster catalyst denoted as Fe2C©SiO2 and revealed its performance on the nonoxidative conversion of methane by density functional theory (DFT) calculations. The results demonstrate that the dual Fe–Fe sites provide a unique dissociation channel for methane, which reduces the activation barrier of methane dissociation by 0.42 eV. On the designed Fe2C©SiO2 catalyst, the target product (ethylene) is preferentially generated via the surface coupling mechanism rather than the gas-phase mechanism, indicated by the lower top point of the free energy profile (2.85 eV vs 3.94 eV) and the lower activation barrier of the rate-determining step (2.12 eV vs 2.32 eV). The coke-resistance ability of Fe2C©SiO2 was evaluated by the deep dehydrogenation of methyl (CH3*), which shows that the dehydrogenation of methyl to methylene (CH2*) is readily to occur, but its deep dehydrogenation to poisonous methine (CH*) or naked carbon (C*) is significantly more difficult than the competing CH2* coupling reactions, demonstrating the remarkable coke-resistant behavior of the catalyst.