Effects of metal promoters in bimetallic catalysts in hydrogenolysis of lignin derivatives into value‐added chemicals

Bimetallic polyoxometalates catalysts for efficient lignin depolymerization: Unlocking valuable aromatic compounds from renewable feedstock

Lignin, a complex and abundant polymer present in lignocellulosic biomass, holds immense potential as a renewable source for the production of valuable aromatic compounds. However, the efficient depolymerization of lignin into these compounds remains a formidable challenge. Here, we present a promising solution by harnessing polyoxometalates (POMs) catalysts, which exhibit improved catalytic performance and selectivity. We synthesized a series of NixCoy@POMs catalysts (POMs: CsPW or CsPMo) and explored their application in the depolymerization of pine lignin, aiming to investigate the influence of different metal species and doping ratios of POMs on catalytic performance. Through meticulous optimization of reaction conditions, we achieved significant yields of valuable aromatic compounds, including methyl vanillate, vanillin, and 4-hydroxy-3-methoxyacetophenone. Furthermore, the Ni0.75Co0.75@CsPMo catalyst demonstrated exceptional efficacy in catalyzing the cracking process of C-C and/or C-O bonds in a β-O-4 dimer model compound. Notably, our catalyst exhibited outstanding stability over five cycles, underscoring its suitability as an effective heterogeneous catalyst for cyclic lignin depolymerization. This study sheds light on the potential of POMs-based catalysts for advancing lignin valorization and offers new avenues for sustainable biomass conversion into valuable chemicals.

Pd-Based Nano-Catalysts Promote Biomass Lignin Conversion into Value-Added Chemicals

Lignin, as a structurally complex biomaterial, offers a valuable resource for the production of aromatic chemicals; however, its selective conversion into desired products remains a challenging task. In this study, we prepared three types of Pd-based nano-catalysts and explored their application in the depolymerization of alkali lignin, under both H₂-free (hydrogen transfer) conditions and H₂ atmosphere conditions. The materials were well characterized with TEM, XRD, and XPS and others, and the electronic interactions among Pd, Ni, and P were analyzed. The results of lignin depolymerization experiments revealed that the ternary Pd-Ni-P catalyst exhibited remarkable performance and guaiacols could be produced under H₂ atmosphere conditions in 14.2 wt.% yield with a selectivity of 89%. In contrast, Pd-Ni and Pd-P catalysts resulted in a dispersed product distribution. Considering the incorporation of P and the Pd-Ni synergistic effect in the Pd-Ni-P catalyst, a possible water-involved transformation route of lignin depolymerization was proposed. This work indicates that metal phosphides could be promising catalysts for the conversion of lignin and lignin-derived feedstocks into value-added chemicals.

Dual Nanozyme-Driven PtSn Bimetallic Nanoclusters for Metal-Enhanced Tumor Photothermal and Catalytic Therapy

Specific generation of reactive oxygen species (ROS) within tumors in situ catalyzed by nanozymes is a promising strategy for cancer therapeutics. However, it remains a significant challenge to fabricate highly efficient nanozymes acting in the tumor microenvironment. Herein, we develop a bimetallic nanozyme (Pt₅₀Sn₅₀) with the photothermal enhancement of dual enzymatic activities for tumor catalytic therapy. The structures and activities of PtSn bimetallic nanoclusters (BNCs) with different Sn content are explored and evaluated systematically. Experimental comparisons show that the Pt₅₀Sn₅₀ BNCs exhibit the highest activities among all those investigated, including enzymatic activity and photothermal property, due to the generation of SnO_2-x with oxygen vacancy (O_vac) sites on the surface of Pt₅₀Sn₅₀ BNCs. Specifically, the Pt₅₀Sn₅₀ BNCs exhibit photothermal-enhanced peroxidase-like and catalase-like activities, as well as a significantly enhanced anticancer efficacy in both multicellular tumor spheroids and in vivo experiments. Due to the high X-ray attenuation coefficient and excellent light absorption property, the Pt₅₀Sn₅₀ BNCs also show dual-mode imaging capacity of computed tomography and photoacoustic imaging, which could achieve in vivo real-time monitoring of the therapeutic process. Therefore, this work will advance the development of noble-metal nanozymes with optimal composition for efficient tumor catalytic therapy.

Investigation of product selectivity and kinetics of poplar sawdust catalytic pyrolysis over bi-metallic Iron-Nickel/ZSM-5 catalyst

Py-GC/MS and thermogravimetric analysis were carried out to systematically explore product selectivity and kinetics of poplar sawdust catalytic pyrolysis over bi-metallic Fe-Ni/ZSM-5. The results showed that the Fe-Ni/ZSM-5 exhibited an additive effect on the production of monocyclic aromatic hydrocarbons compared to mono-metallic catalysts (Fe/ZSM-5 or Ni/ZSM-5). Fe-Ni/ZSM-5 further increased the yield of toluene (17.28 mg g^-1), which was 41.4% and 80.9% higher than Fe/ZSM-5 and Ni/ZSM-5, respectively. According to the kinetic analysis, the average activation energy obtained from catalytic pyrolysis with Fe-Ni/ZSM-5 using the methods of Friedman, Starink, Flynn-Wall-Ozawa, and Kissinger-Akahira-Sunose was 156.19, 152.39, 154.30, and 152.11 kJ mol^-1, respectively. Fe-Ni/ZSM-5 addition lowered the activation energy compared to non-catalytic pyrolysis at the conversion rate of 0.15-0.75. The overall catalytic pyrolysis process of poplar sawdust follows the diffusion and nucleation models. The thermodynamic parameters (enthalpy and entropy) showed positive and negative values, respectively, indicating non-spontaneous reactions during the catalytic pyrolysis process.

More than a support: the unique role of Nb2O5 in supported metal catalysts for lignin hydrodeoxygenation

How does Nb2O5 in supported catalysts affect the hydrodeoxygenation of lignin? This article discusses the effects of Nb2O5 in detail, including the promotion of C–O bond cleavage, the improvement of water resistance and the enhancement of durability.

Lignin-to-chemicals: Application of catalytic hydrogenolysis of lignin to produce phenols and terephthalic acid via metal-based catalysts

Lignin is the only renewable aromatic material in nature and contains a large number of oxygen-containing functional groups. High-value and green utilization of "lignin-to-chemicals" can be realized via using lignin to produce fine chemicals such as phenols and carboxylic acids, which can not only reduce the waste of lignin in the process of lignocellulosic biomass treatment, but gradually make the substitution of traditional fossil fuels come true. The hydrogenolysis process under catalysis of metal catalyst has high product selectivity and less impurity, which is suitable for the production of same type or single fine chemicals. Hydrogenolysis of lignin via metal catalysts to produce lignin oil, and further modification of functional groups (e.g. methoxyl, alkyl and hydroxyl group) of depolymerized monomers in the bio-oil to yeild phenols and terephthalic acid are reviewed, and catalytic mechanisms are briefly summarized in this paper. Finally, the problems of lignin catalytic conversion existing currently are investigated, and the future development of this field is also prospected.

Vacancy Engineering in Transition Metal Sulfide and Oxide Catalysts for Hydrodeoxygenation of Lignin-Derived Oxygenates

The catalytic hydrodeoxygenation (HDO) of lignin has long been a hot research topic and vacancy engineering is a new means to develop more efficient catalysts for this process. Oxygen vacancies and sulfur vacancies are both widely used in HDO. Based on the current research status of vacancies in the field of lignin-derived oxygenates, this Minireview discusses in detail design methods for vacancy engineering, including surface activation, synergistic modification, and morphology control. Moreover, it is clarified that in the HDO reaction, vacancies can act as acidic sites, promote substrate adsorption, and regulate product distribution, whereas for the catalysts, vacancies can enhance stability and reducibility, improve metal dispersion, and improve redox capacity. Finally, the characterization of vacancies is summarized and strategies are proposed to address the current deficiencies in this field.

Regulation mechanism of three key parameters on catalytic characterization of molybdenum modified bimetallic micro-mesoporous catalysts during catalytic fast pyrolysis of enzymatic hydrolysis lignin

Novel preparation of molybdenum modified bimetallic micro-mesoporous catalyst was proposed innovatively to conduct catalytic fast pyrolysis of enzymatic hydrolysis lignin. The optimal catalytic characterization of the prepared catalyst was attributed to appropriate porous structure, the interaction between zeolite support and metal species, and the synergetic and stable mechanism of bimetallic active sites. With the incorporation of metal species into micro-mesoporous catalyst, the distribution of active sites experienced a regulation, which contributed to MAHs production and cracking of oxygen-containing substances. NiMo/AZM catalyst exhibited the most obvious coke inhibition effect (8.47 wt% of mass yield) and converted more high-ordered graphite carbon to low-ordered one, so as to make it easier to remove and prolong the catalyst lifetime, and obtained the highest mass yield of MAHs (13.15 wt%) as well as the minimum selectivity of bulky oxygenates (3.82%), which was the joint contribution of three key parameters.

Stepped M@Pt(211) (M = Co, Fe, Mo) single-atom alloys promote the deoxygenation of lignin-derived phenolics: mechanism, kinetics, and descriptors

HDO of lignin-derived phenolics on stepped M@Pt(211) (M = Co, Fe, Mo) single-atom alloy was computationally explored. Either C–O bond length or *OH binding energy was confirmed as an effective catalytic descriptor for predicting HDO performance.