Incorporating Catalytic Units into Nanomaterials: Rational Design of Multipurpose Catalysts for CO2 Valorization

ConspectusCO₂ conversion to valuable chemicals is effective at reducing CO₂ emissions. We previously proposed valorization strategies and developed efficient catalysts to address thermodynamic stability and kinetic inertness issues related to CO₂ conversion. Earlier, we developed molecular capture reagents and catalysts to integrate CO₂ capture and conversion, i.e., in situ transformation. Based on the mechanistic understanding of CO₂ capture, activation, and transformation at a molecular level, we set out to develop heterogeneous catalysts by incorporating catalytic units into nanomaterials via the immobilization of active molecular catalysts onto nanomaterials and designing nanomaterials with intrinsic catalytic sites.In thermocatalytic CO₂ conversion, carbonaceous and metal-organic framework (MOF)-based catalysts were developed for nonreductive and reductive CO₂ conversion. Novel Cu- and Zn-based MOFs and carbon-supported Cu catalysts were prepared and successfully applied to the cycloaddition, carboxylation, and carboxylative cyclization reactions with CO₂, generating cyclic carbonates, carboxyl acids, and oxazolidinones as respective target products. Reductive conversion of CO₂, especially reductive functionalization with CO₂, is a promising transformation strategy to produce valuable chemicals, alleviating chemical production that relies on petrochemistry. We explored the hierarchical reductive functionalization of CO₂ using organocatalysts and proposed strategies to regulate the CO₂ reduction level, triggering heterogeneous catalyst investigation. Introducing multiple active sites into nanomaterials opens possibilities to develop novel CO₂ transformation strategies. CO₂ capture and in situ conversion were realized with an N-doped carbon-supported Zn complex and MOF materials as CO₂ adsorbents and catalysts. These nanomaterial-based catalysts feature high stability and excellent efficiency and act as shape-selective catalysts in some cases due to their unique pore structure.Nanomaterial-based catalysts are also appealing candidates for photocatalytic CO₂ reduction (PCO₂RR) and electrocatalytic CO₂ reduction (ECO₂RR), so we developed a series of hybrid photo-/electrocatalysts by incorporating active metal complexes into different matrixes such as porous organic polymers (POPs), metal-organic layers (MOLs), micelles, and conducting polymers. By introducing Re-bipyridine and Fe-porphyrin complexes into POPs and regulating the structure of the polymer chain, catalyst stability and efficiency increased in PCO₂RR. PCO₂RR in aqueous solution was realized by designing the Re-bipyridine-containing amphiphilic polymer to form micelles in aqueous solution and act as nanoreactors. We prepared MOLs with two different metallic centers, i.e., the Ni-bipyridine site and Ni-O node, to improve the efficiency for PCO₂RR due to the synergistic effect of these metal centers. Sulfylphenoxy-decorated cobalt phthalocyanine (CoPc) cross-linked polypyrrole was prepared and used as a cathode, achieving the electrocatalytic transformation of diluted CO₂ benefiting from the CO₂ adsorption capability of polypyrrole. We fabricated immobilized 4-(t-butyl)-phenoxy cobalt phthalocyanine and Bi-MOF as cathodes to promote the paired electrolysis of CO₂ and 5-hydroxymethylfurfural (HMF) and obtained CO₂ reductive products and 2,5-furandicarboxylic acid (FDCA) efficiently.