Enhanced direct air capture of CO2 and catalytic methanation by forming K-dawsonite on γ-Al2O3 support combined with Ni impregnated catalyst

Abstract

K2CO3-based sorbents are promising for direct air capture (DAC), but their performance depends strongly on the stabilization of potassium species on the support. Here, we show that DAC performance is governed by a support-dependent interfacial transition that is enabled uniquely by γ-Al2O3. Systematic support screening shows that γ-Al2O3, unlike TiO2, CeO2, activated carbon or SiO2, drives potassium species toward a K-dawsonite-related K–O–Al adsorption environment that provides additional CO2-reactive sites beyond bulk-like K2CO3. This interfacial phase forms only after calcination at ≥ 550 °C and is further promoted by controlled water addition during physical mixing. The optimized sorbent achieved a CO2 uptake of 1.58 mmol g−1 under real-air DAC conditions. Mechanistic analysis shows that pretreatment decomposes synthesis-derived K-dawsonite into K2CO3 and interfacial K–O–Al species, while subsequent humid-air DAC re-forms K-dawsonite-related phase in parallel with KHCO3 formation. After Ni impregnation for CO2 utilization, this reversible interfacial adsorption environment further enhances DAC capacity to 2.62 mmol g−1 and increases CH4 selectivity to 27.9% in sequential DAC–methanation. These findings establish synthesis-controlled K-dawsonite formation and re-formation as a key design principle for high-performance K2CO3/γ-Al2O3 sorbents and dual-functional DAC–conversion materials. © 2026 Elsevier B.V.