Ca-Promoted Alumina for CO2 Capture and Combined Capture and Conversion

Abstract

The development of efficient materials for CO2 capture and integrated capture and conversion processes is essential for advancing low-temperature carbon utilization technologies. In this work, CaO-modified γ-alumina sorbents were synthesized from boehmite precursors and systematically evaluated to elucidate the effects of calcination temperature and Ca loading on structural evolution and CO2 adsorption performance. Progressive dehydroxylation and phase transformation from boehmite to γ-alumina increased the density of strong Lewis acid–base pairs, while Ca incorporation further enhanced surface basicity and strengthened CO2 binding. Among the investigated materials, 15 wt % CaO/γ-alumina exhibited the highest CO2 uptake and the most thermally stable carbonate species, as confirmed by BET analysis, TGA, in situ FTIR, and XPS. Isosteric heat measurements indicated predominantly physisorptive behavior, with mild chemisorption emerging at higher Ca loadings. To enable combined capture and conversion, 5 wt % Ru was incorporated into the optimized sorbent to form a dual-function material (DFM). The resulting 5% Ru/15% CaO/γ-alumina demonstrated stable performance over ten consecutive CO2 adsorption-methanation cycles at 200 °C, maintaining 58.8–64.5% CH4 conversion with minimal deactivation. Importantly, the overlap between CO2 adsorption/desorption and methanation at the same temperature eliminates the need for thermal swings, providing a clear energy-efficiency advantage. Overall, the synergy between CaO-enhanced CO2 capture and Ru-catalyzed methanation establishes this material as a promising candidate for integrated CO2 capture and utilization.