Single-Atom and Sub-Nano Ruthenium Cluster Catalysts—Application to Biomass Upgrading into Biofuel Additive

Sub-nano metal clusters have important physicochemical features that lead to a wide range of applications. Herein, we point out an unfailing reproducible protocol to synthesize ruthenium single-atom catalysts and ultra-small clusters supported on various silica–alumina mixed oxides. The catalysts were synthesized via a dendrimer-free, sonication-assisted route, with ruthenium loadings up to 2 wt%. Raman spectroscopy mapping revealed a wide coverage of the materials’ surfaces by ruthenium, while HAADF-STEM evidenced that 100% of the ruthenium was at the sub-nano scale, with up to 74% of the single atoms and metal clusters having an average size between 0.3 and 0.7 nm, independently of the support or the metal’s loading. These materials exhibited highly selective size-dependent catalytic performances in upgrading biomass-derived furfural into transportation biofuel additive 2,2′-difurfurylether, with turnover frequencies up to 1148 h−1. Ruthenium single atoms and sub-nano clusters showed an exceptional resistance to sintering, with a size variation of ±0.1 nm before and after reaction, and no metal leaching was observed.