Green Synthesis of Cu and Pd Catalysts Using Mexican Oregano (Lippia graveolens) Extract and Their Application in the Conversion of a Biomass-Derived Molecule

This work reports the synthesis of two monometallic catalysts, Cu/Al2O3, and Pd/Al2O3, using a green approach based on Mexican oregano (Lippia graveolens), a common food condiment. Its extract has been largely overlooked as a high-technology reactive for synthesizing catalysts, metallic or oxide nanoparticles, unlike other green leaf plants. The green synthesis was compared with a conventional catalyst synthesis methodology using commercial chemical reducing agents. Oregano extract shows promise for novel applications extending beyond its culinary use, valorizing it as a chemical reducer to produce catalysts. Thus, this kind of application could significantly elevate the value of oregano, empowering communities that rely on its cultivation for economic benefit and transforming the plant from a low-profit agro-industrial product to a high-added-value crop. The reduction kinetics involved in the formation of nanoparticles were monitored up to the first stage of nucleation and a first-order model adequately described the data. Activation energy analysis showed that the chemical reaction mechanism has a dominant role in controlling the reaction, compared to mass transfer effects. Notoriously, the Pd/Al2O3 green synthesis catalyst showed the smallest mean particle size (4.85 ± 1.30 nm). These findings underscore the potential of green synthesis as an economically viable and environmentally friendly alternative for producing catalysts. Concerning the 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) as a biomass-derived molecule, its oxidation with H2O2 using both Pd/Al2O3 catalysts (by green and chemical synthesis methods) exhibited significantly higher selectivity toward 2,5-diformylfuran (DFF) compared to Cu/Al2O3 catalysts, suggesting a possible inhibitory effect.