Tandem Hydrogenolysis-Hydrogenation of Lignin-Derived Oxygenates over Integrated Dual Catalysts with Optimized Interoperations

Stable and Antisintering Tungsten Carbides with Controllable Active Phase for Selective Cleavage of Aryl Ether C-O Bonds

Transition-metal carbides are important materials in heterogeneous catalysis. It remains challenging yet attractive in nanoscience to construct the active phase of carbide catalysts in a controllable manner and keep a sintering-resistant property in redox reactions, especially hydroprocessing. In this work, an integrated strategy was presented to synthesize stable and well-defined tungsten carbide nanoparticles (NPs) by assembling the metal precursor onto carbon nanotubes (CNTs), wrapping a thin polymeric layer, and following a controlled carburization. The polymer served as a soft carbon source to modulate the metal/carbon ratio in the carbides and introduced amorphous carbons around the carbides to prevent the NPs from sintering. The as-built p-W_xC/CNT displayed high stability in the hydrogenolysis of aryl ether C-O bond in guaiacol for more than 150 h. Its activity was more than two and six times higher than those prepared via typical temperature-programmed reduction with gaseous carbon (W_xC/CNT-TPR) and carbothermal reduction with intrinsic carbon support (W_xC/CNT-CTR), respectively. Our p-W_xC/CNT catalyst also achieved high efficiency for selective cleavage of the aryl ether C-O bonds in lignin-derived aromatic ethers, including anisole, dimethoxylphenol, and diphenyl ether, with a robust lifespan.

Lignin valorization by bacterial genus Pseudomonas: State-of-the-art review and prospects

The most prominent aromatic feedstock on Earth is lignin, however, lignin valorization is still an underrated subject. The principal preparatory strategies for lignin valorization are fragmentation and depolymerization which help in the production of fuels and chemicals. Owing to lignin's structural heterogeneity, these strategies result in product generation which requires tedious separation and purification to extract target products. The bacterial genus Pseudomonas has been dominant for its lignin valorization potency, owing to a robust enzymatic machinery that is used to funnel variable lignin derivatives into certain target products such as polyhydroxyalkanotes (PHAs) and cis, cis-muconic acid (MA). In this review, the potential of genus Pseudomonas in lignin valorization is critically reviewed along with the advanced genetic techniques and tools to ease the use of lignin/lignin-model compounds for the synthesis of bioproducts. This review also highlights the research gaps in lignin biovalorization and discuss the challenges and possibilities for future research.