Objective To address the dual challenges of environmental pollution stemming from the leather industry and the sustainable biomass transformation, this study integrated the upcycling of industrial solid waste with advanced biorefinery processes. An efficient and low-cost lignin hydrogenolysis catalyst was developed, thereby synergistically promoting the reduction and valorization of tannery waste alongside directed biomass conversion strategies. This work ultimately provides a sustainable paradigm for the circular economy and green chemistry.

Methods Using chrome-containing tannery waste as the primary raw material, the abundant nitrogen/oxygen-containing functional groups derived from natural collagen were employed as coordination supports for metal ions. A nitrogen-doped carbon-supported ruthenium-chromium oxide catalyst (Ru-CrO_x/NC) was synthesized via Ru³⁺ coordination combined with an oxygen-limited pyrolysis strategy, inducing the in-situ confined transformation of metal components during the carbonization process. The microscopic morphology, crystalline phase structure, and chemical valence states of the catalyst were systematically characterized using various advanced analytical techniques. Furthermore, its catalytic performance was rigorously evaluated in the depolymerization of both a representative lignin α-O-4 model compound and real lignocellulosic biomass.

Results Structural characterization indicated that the inherently high nitrogen content of the collagen-derived carbon matrix played a pivotal role in the anchoring and ultra-high dispersion of CrO_x and Ru species, thus forming a composite structure with robust metal-support interactions. Ru primarily existed in a near-metallic state, while Cr was transformed into highly dispersed CrO_x species; their close contact within the carbon matrix constituted abundant active interfaces. These two components maintained intimate contact within the nitrogen-doped carbon lattice, synergistically constituting abundant and highly active interfacial sites. In the hydrogenolysis of the lignin α-O-4 model compound (2-benzyloxyphenol), the Ru-CrO_x/NC catalyst exhibited extraordinary catalytic performance. Under reaction conditions of 230 ℃ and 1.0 MPa H₂ for a duration of 4 h, it achieved a remarkable substrate conversion rate of 98.9% and an aromatic monomer yield of 96.1%. Notably, the selectivity toward the primary products, toluene and catechol, was close to the theoretical maximum values. This performance underscores the catalyst's ability to efficiently cleave C-O bonds while precisely inhibiting the over-hydrogenation of aromatic rings, thereby preserving the high-value aromatic structure of the monomers. After five consecutive cycle tests, the catalyst still retained a substrate conversion of over 90%, highlighting its exceptional structural stability and potential for repeated industrial use. Furthermore, the practical application of the catalyst was further extended to the hydrogenolysis of real hardwood lignin (from Populus euramericana sawdust). Under comparable reaction conditions, the lignin monomer yield reached 26.4%, with phenolic monomers dominating the product distribution. This result demonstrates the superior selectivity for phenolic products and a robust adaptability to the complex, cross-linked architecture of natural lignin.

Conclusion This work successfully demonstrates the promising prospect of converting chrome-containing tannery waste into high-performance supports for lignin hydrogenolysis catalysts. The synthesized Ru-CrO_x/NC catalyst not only achieves the high-value utilization of hazardous tannery waste but also significantly expands the application scenarios for chrome-containing solid waste. Furthermore, it provides an efficient, stable, and low-cost catalytic system for the directional and high-value conversion of natural lignin under the "lignin-first" strategy. The findings offer valuable theoretical insights and technical guidance for the directed transformation of biomass, with profound environmental benefits, social impacts, and substantial potential for industrial-scale applications.