Design of SA-FLP Dual Active Sites for Nonoxidative Coupling of Methane

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.