Mesoporous single-atom and nano-confined catalysts: Enabling low-energy integrated CO2 capture and direct conversion

Mesoporous architecture confinement engineering has become an effective approach to address major limitations of single-atom catalysts (SACs) and integrated CO2 capture-conversion systems. These techniques may provide enhanced control of the spatial distribution, local microenvironment and pore size to attain high activity, selectivity and permanence in photocatalytic and electrocatalytic CO2 reduction. The recent trends in confinement mechanisms that have been highlighted in the present paper include two step space-confinement pyrolysis, hierarchical porosity in MOFs, single-micelle assembly and defect engineering. These methods enable the fabrication of well-defined nanoreactors, allowing synergistic reactions between photoactive and catalytic species, cascade reactions, tremendous charge separation and carrier lifetimes. Mesoporous supports with both single-atom and dual-atom sites are given special consideration, where tunable coordination environments and dynamic structural evolution under operating conditions play critical roles in dictating selectivity to high value C1 or C2 products at low over potentials. When mesoporous SAC systems are compared with traditional amine-based sorbents and nanoparticle catalysts, it can be seen that mesoporous materials have clear advantages in regard to regeneration energy, humidity resistance, cycling stability, and combined capture-conversion efficiency. Physical confinement and electronic modulation (with a state-of-the-art inverse design and Bayesian optimization) offers the paradigm of scalable, energy-efficient use of CO2. Finally, low active-site density, long-term stability, and industrial translation have been identified as key issues and a roadmap to the future that incorporates the development of hierarchical multi-scale porous structures to host both SACs, full CCUS loops with renewables, and technologies that produce negative emissions using the sun as the power source have been discussed.