CO2 capture and utilisation and the integration, Conversion of CO2 into chemicals and fuels

Abstract

CO2 capture and utilization (CCU) is a sustainable process that can partially close the carbon cycle. It is attractive to store the excess and uncertain supply of energy from renewable sources to stable chemical energy. Increasing studies have been carried out on integrated CO2 capture and utilization (ICCU) to reduce the cost of the overall process by eliminating transportation and storage of the CO2. ICCU could achieve in-situ CO2 adsorption, separation and conversion using dual-function catalysts (DFMs), consisting of CO2 adsorbents and catalysts. ICCU avoid temperature swing sorbent regeneration, which is considered an energy-intensive process. Integrating CO2 capture and utilization via reverse water-gas shift reaction (ICCU-RWGS) is particularly attractive due to the important industrial value of syngas. Furthermore, the in-situ CO2 utilization can outperform conventional RWGS in relation to CO2 conversion and CO selectivity. Herein, we achieved very promising ICCU-RWGS performance by CaO-alone and functionalizing CaO using active transition metals (e.g. Ni and Fe). Excellent CO2 adsorption and extremely efficient CO2 conversion can be achieved with simple materials, outperforming traditional separated CO2 capture and catalytic conversion processes. Currently, the conversion of captured CO2 into value-added chemicals or fuels is considered a key strategy to mitigate the yet increasing anthropogenic CO2 emissions, in particular when combined with H2 obtained using renewable energy. Depending on the catalyst and the reaction conditions used, thermocatalytic CO2 hydrogenation can give CO, methanol, dimethyl ether (DME), methane, or heavier hydrocarbons. MXene materials, that is, a family of two-dimensional (2D) carbides, nitrides and carbonitrides with the general formula of Mn +1XnTx (where M is an early transition metal, n = 1, 2, 3, X is C and/or N and T are surface –O–, –OH and/or –F groups), are currently emerging in thermocatalytic applications as catalysts or supports with reactive metal–support interactions. Enabled by the scalable synthesis of MXenes, we report a gram-scale synthesis of a phase-pure multilayered hexagonal 2D-Mo2C material with only Mo-terminated basal planes. 2D-Mo2C is by a factor of six per mass of catalyst more active for CO formation than the reference β-Mo2C catalyst and shows no deactivation on stream for more than 100 h. We also report that silica-supported, dispersed, reducible nanosheets of a delaminated molybdenum MXene, Mo2CTx, can be used to engineer a Cu/Mo2CTx interface that shows an at least six times increased intrinsic formation rate of methanol by the direct hydrogenation of CO2 compared to Cu/SiO2.