Mesoporous calcium oxide–silica and magnesium oxide–silica composites for CO2 capture at ambient and elevated temperatures

Abstract

Incorporation of basic metal species (oxides) such as magnesium oxide and calcium oxide into porous materials is a logical strategy for enlarging the uptake of acidic greenhouse gases such as CO₂. This work reports the development of ordered mesoporous silica (OMS) with incorporated magnesium and calcium oxides for CO₂ sorption at ambient and elevated temperatures. These materials were prepared by using the sol–gel method in the presence of the triblock copolymer Pluronic P123 in acidic medium followed by evaporation-induced self-assembly (EISA). The resulting magnesium oxide (MgO)- and calcium oxide (CaO)-OMS materials were used for CO₂ sorption at low (0, 15 °C), ambient (25 °C), and elevated (120 °C) temperatures. Temperature programmed desorption (TPD) was used to measure the CO₂ sorption capacities for the mesostructures studied at 120 °C. These sorbents exhibited relatively high adsorption capacity (0.63–2.61 mmol g⁻¹) under low (0, 15 °C) and ambient conditions (25 °C, 1 atm) and remarkably high sorption uptake (3.11–4.71 mmol g⁻¹) at 120 °C. The observed high CO₂ uptake by CaO–SiO₂ and MgO–SiO₂ composites under ambient conditions is caused by enhanced physisorption of CO₂ in micropores. Amazingly high CO₂ uptake at elevated temperatures by OMS sorbents with incorporated CaO and MgO is mainly due to the chemisorption of CO₂. The well-developed porous structure together with high surface area, basic surface properties and high thermal and chemical stabilities of CaO–SiO₂ and MgO–SiO₂ composites increase their prospects for high temperature capture of CO₂ from industrial emissions.