Mechanism of Asymmetric “Ru–B” Double Site Synergy in Breaking C–C Bonds of Lignin Derivatives in Bio-char

The ring opening of an aromatic ring is the key step of lignin depolymerization (LD) to obtain high-value-added fatty alcohol compounds. Bio-char catalysts with nonmetallic boron (B) and d-p hybrid of C-Ru sites were prepared by an amino-assisted coordination strategy, and used for lignin derivatives conversion in supercritical ethanol systems. Metal-nonmetal interface sites composed of Ru clusters and Csp3-N-BO3 exhibited the optimal orbital energy level and active electronic state. In Ru and B interface sites, the attraction of Ru empty d orbitals to π electron clouds of the benzene ring, along with electron exchange between B anti-bonding orbitals and hydroxyl oxygen of the benzene ring side chain, was synergically coupled. This coupling led to a reduction in the stability of π electron clouds within the benzene ring and easy opening, ultimately achieving a conversion rate of 99.2% for lignin derivatives. During the adsorption process, d-band centers of Ru and enhanced localization of B-site electronic states led to a certain directionality of the benzene ring transformation, thereby effectively enhancing the catalytic selectivity toward 1-hexanol, with a yield of 29.7%. This study elucidates the criteria for designing efficient LD catalysts by synergistically utilizing metal d orbitals and non-metal antibonding orbitals.