Potassium Coordination Stabilized Ru^δ+ State on Potassium Titanate Nanowire for Efficient Photothermal CO₂ Methanation.

Abstract

Photothermal CO₂ methanation offers a solution to achieve both the decarbonization targets and the substitution of fossil fuel feedstocks using renewable energy. The slightly oxidized Ru (Ru^δ+) site is an active site for low-temperature CO₂ activation. However, the susceptibility of Ru^δ+ to reduction under the photothermal reaction process is a key limitation to the stabilization. Herein, the K₂RuO₃ with high Ru─O bond strength via potassium coordination stabilized onto K₂Ti₆O₁₃ is constructed (KTO-Ru^δ+/Ru⁰). Benefiting from reducing activation energy by the Ru^δ+ as Lewis active sites, the CO₂ hydrogenation path for KTO-Ru^δ+/Ru⁰ tends to favor a more advantageous formate pathway. In addition, K ions in K₂RuO₃ and K₂Ti₆O₁₃ as alkaline promoters facilitate the adsorption of CO₂ and suppress dehydration to stablize the Ru^δ+. The KTO-Ru^δ+/Ru⁰ exhibits remarkable photothermal CO₂ methanation activity (CH₄ yield of 526 ± 5.5 mmol g_cat ^-1 h^-1), and CH₄ selectivity reaches over 99.9%. Taking advantage of thin KTO-Ru^δ+/Ru⁰ inorganic porous paper, the flow reactor system with the efficient contact among the KTO-Ru^δ+/Ru⁰, flowing gas and the solar illumination obtains an ultrahigh photothermal CH₄ production rate of 0.99 mol g_cat ^-1 h^-1 at a gas flow rate of 35 mL min^-1 (gas hourly space velocity of 210 000 mL g_cat ^-1 h^-1) with ≈96.6% CH₄ selectivity. This work suggests alternative perspectives for designing stabilized oxidation-state photothermal catalysts for flow photothermal CO₂ methanation.