Green and scalable approaches for synthesis and encapsulating clean metal nanoclusters inside cerium MOFs for efficient glycerol carboxylation with CO2

In the pursuit of CO₂-neutral renewable energy solutions, biofuels have emerged as one of the key strategies. However, biodiesel production generates a surplus of crude glycerol (GL), creating a need for efficient valorization pathways. The conversion of GL into value-added chemicals represents a sustainable approach to address this issue. Metal nanoclusters (NCats) embedded within metal-organic frameworks (MOFs) constitute a promising class of hybrid catalysts for GL–CO₂ coupling, yet their controlled synthesis remains limited to a few MOF systems. Herein, we present a clean, scalable, and efficient method for the synthesis of ultra-small, surfactant-free Cu, Ag, and Pd NCats encapsulated in cerium-based MOFs. The resulting catalysts were evaluated in the direct carboxylation of crude GL with CO₂. Among them, the Pd₁Cu₁@MOF1 composite demonstrated outstanding performance, achieving > 73 % yield and a TOF > 100 h⁻¹ with pure GL, and > 14 % yield with a TOF of 30 h⁻¹ using crude GL. The method also enabled successful incorporation of trimetallic PdAgCu NCats, highlighting its potential for the sustainable synthesis of multimetallic NCats-MOF catalytic systems. • Low-cost, green, and scalable synthesis of ultra-small, uniform metal nanoclusters (NCats) in aqueous media. • In-situ encapsulation of NCats within Ce-MOFs achieved without aggregation or external surface deposition. • Formation of high-surface-area core–shell NCats@Ce-MOF composites with well-preserved framework integrity and purity. • Pd₁Cu₁@MOF1 exhibits superior catalytic efficiency in the direct carboxylation of glycerol with CO₂. • Direct carboxylation of crude glycerol yielded > 14 % GLC with a turnover frequency (TOF) > 30 h⁻¹ . • The protocols are extendable to multimetallic systems, offering potential for broader CO₂ conversion applications.