A Series of NiM (M = Ru, Rh, and Pd) Bimetallic Catalysts for Effective Lignin Hydrogenolysis in Water

Abstract

In this paper, NiRu, NiRh, and NiPd catalysts were synthesized and evaluated in the hydrogenolysis of lignin C− O bonds, which is proved to be superior over single-component catalysts. The optimized NiRu catalyst contains 85% Ni and 15% Ru, composed of Ni surface-enriched, Ru−Ni atomically mixed, ultrasmall nanoparticles. The Ni 85 Ru 15 catalyst showed high activity under low temperature (100 °C), low H 2 pressure (1 bar) in β-O-4 type C−O bond hydrogenolysis. It also exhibited significantly higher activity over Ni and Ru catalysts in the direct conversion of lignin into monomeric aromatic chemicals. Mechanistic investigation indicates that the synergistic effect of NiRu can be attributed to three factors: (1) increased fraction of surface atoms (compared with Ni), (2) enhanced H 2 and substrate activation (compared with Ni), and (3) inhibited benzene ring hydrogenation (compared with Ru). Similarly, NiRh and NiPd catalysts were more active and selective than their singlecomponent counterparts in the hydrogenolysis of lignin model compounds and real lignin.

Heterogeneously catalyzed lignin depolymerization

“…It was proposed that the improved yield from combining Raney Ni with a zeolite arose from the latter hindering the reaction between the parent lignin and other more reactive lignin fragments that could together to produce high molecular weight oligomers. Bimetallic NiM (M = Ru, Rh, Pd, Au, Mo) catalysts have also been studied for lignin hydrogenolysis [33,34], [35] [36], wherein NaOH addition proved beneficial, promoting the formation of aromatic compounds and supressing arene hydrogenation. Konnerth et al [37] also observed increased Organosolv lignin depolymerization via NaOH addition to the aqueous reaction mixture containing an Ni 7 Au 3 Fig.…”

Isolation of Functionalized Phenolic Monomers through Selective Oxidation and CO Bond Cleavage of the β‐O‐4 Linkages in Lignin

“…A key advantage of our lignin depolymerization method is the retention of functional groups in the major phenolic product 8, as these groups are frequently lost in other lignin depolymerization processes. [13,17] Future studies will focus on integrating methods to recover and recycle both the organic solvents used and the solubilized zinc salts in the aqueous waste stream. The environmental and cost implications of using a halogenated organic catalyst, such as DDQ, will also be assessed.…”

High Catalytic Efficiency of Lignin Depolymerization over Low Pd-Zeolite Y Loading at Mild Temperature

“…Then a sample was acquired from the organic phase for GC-MS analysis. For GC-MS analysis, the response factor for each product was standardized with the use of efficient carbon number (Scanion and Willis, 1985;Zhang et al, 2014b), which enabled the analysis of compounds without pure standards.…”