Plasmon‐Induced Radical‐Radical Heterocoupling Boosts Photodriven Oxidative Esterification of Benzyl Alcohol over Nitrogen‐Doped Carbon‐Encapsulated Cobalt Nanoparticles

Abstract

Selective oxidation of alcohols under mild conditions remains a long‐standing challenge in the bulk and fine chemical industry, which usually requires environmentally unfriendly oxidants and bases that are difficult to separate. Here, a plasmonic catalyst of nitrogen‐doped carbon‐encapsulated metallic Co nanoparticles (Co@NC) with an excellent catalytic activity towards selective oxidation of alcohols is demonstrated. With light as only energy input, the plasmonic Co@NC catalyst effectively operates via combining action of the localized surface‐plasmon resonance (LSPR) and the photothermal effects to achieve a factor of 7.8 times improvement compared with the activity of thermocatalysis. A high turnover frequency (TOF) of 15.6 h−1 is obtained under base‐free conditions, which surpasses all the reported catalytic performances of thermocatalytic analogues in the literature. Detailed characterization reveals that the d states of metallic Co gain the absorbed light energy, so the excitation of interband d‐to‐s transitions generates energetic electrons. LSPR‐mediated charge injection to the Co@NC surface activates molecular oxygen and alcohol molecules adsorbed on its surface to generate the corresponding radical species (e.g., ⋅O2−, CH3O⋅ and R‐⋅CH‐OH). The formation of multi‐type radical species creates a direct and forward pathway of oxidative esterification of benzyl alcohol to speed up the production of esters.

Recent Applications of Photothermal Conversion in Organic Synthesis

“…While previous examples use metallic species which have strong plasmonic capabilities, a 2023 report from the Zhang group designed a new photothermal nanoparticle (Figure 6c). 47 They wanted to improve the photothermal properties of Co species, which typically suffer from low absorption coefficients, limiting potential applicability. However, improvements in light absorption were made by encapsulating the Co nanoparticles with organic ligands.…”

The plasmonic effect of Cu on tuning CO2 reduction activity and selectivity

“…3,4 After light irradiation, plasmons decay through non-radiation pathways, enhancing surface electromagnetic field, forming hot carriers (electron–hole pairs), and inducing photothermal effects. 5–8 Plasmonic metals, such as noble metal gold (Au) and silver (Ag), are recognized as efficient mediators for utilizing solar energy due to their exceptional capability in harvesting a broad spectrum ranging from the ultraviolet-visible (UV-vis) to near-infrared (NIR) region, and are thereby widely researched in water splitting, 9–12 ethylene epoxidation, 13,14 NH 3 decomposition, 15 and so on. 16–19 However, the scarcity of Au and Ag metals hinders their practical applications.…”

Solvent‐Free Oxidation of Benzyl Alcohol Using Modified Zeolitic Imidazolate Frameworks‐8 (ZIF‐8) Catalysts

“…Appropriate catalyst selection can significantly influence the success of attaining the desired product yield. Some heterogeneous catalysts that have been employed in the alcohol oxidation reaction include Au−Pd nanoparticles, [7] perovskite LaMO 3 (M=Cr, Mn, Co, Ni, and Fe), [8] high‐entropy oxides (e. g. HP‐(FeCrCoNiCu) x O y , HE‐MOF, MW‐HEO), [9–11] Ce Oxysulfate Clusters (MCe 70 , M=Ce, Cu, Ni, Co, and Fe), [12] as well as porous materials like zeolites, [13] nitrogen‐doped carbon‐encapsulated metallic Co nanoparticles, [14] and Metal‐Organic Frameworks (MOFs) [15] …”