The promotional effect of surface Ru decoration on the catalytic performance of Co-based nanocatalysts for guaiacol hydrodeoxygenation

Green catalyst for clean fuel production via hydrodeoxygenation

The development of new fuel sources to replace nonrenewable fossil fuels has received substantial attention due to the ongoing demand for fossil fuels. Biomass and raw waste materials are crucial sources to produce suitable alternative fuels instead of nonrenewable fuels and offer a greener approach. Therefore, improving the fuel properties of biooils produced from the thermochemical conversion of biomass and raw waste materials is critical as it is used as an alternative to nonrenewable fuel. Developing an economical and eco-friendly method to produce sustainable and renewable oil by improving biooil containing large amounts of phenolic compounds has become imperative. One of the most intriguing and promising technologies for refining biooil to produce renewable fuels of comparable quality to conventional fossil fuels is the hydrodeoxygenation (HDO)-based process for converting biooil to renewable fuels. This method is almost one of the best improving methods described in the literature. At this point, it is of great importance that the HDO process is carried out catalytically. Carbon materials are preferred for both designing catalysts for HDO and supporting metal nanoparticles by providing chemically inert surfaces and tunable functional groups, high surface area and active sites. The HDO of biomass and raw waste materials has significantly advanced thanks to carbon-based catalysts. In this review, the effect of the surface character and catalytic ability of the carbon support, especially prepared by the green synthesis technique, on the HDO reaction during biooil improvement is discussed. Moreover, HDO reaction parameters and recent studies have been investigated in depth. Thus, green carbon catalysts' role in clean fuel production via the HDO process has been clarified.

Cobalt-Graphene Catalyst for Selective Hydrodeoxygenation of Guaiacol to Cyclohexanol

Herein, cobalt-reduced graphene oxide (rGO) catalyst was synthesized with a practical impregnation-calcination approach for the selective hydrodeoxygenation (HDO) of guaiacol to cyclohexanol. The synthesized Co/rGO was characterized by transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM (HAADF-STEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), and H₂ temperature-programmed reduction (H₂-TPR) analysis. According to the comprehensive characterization results, the catalyst contains single Co atoms in the graphene matrix and Co oxide nanoparticles (CoO_x) on the graphene surface. The isolated Co atoms embedded in the rGO matrix form stable metal carbides (CoC_x), which constitute catalytically active sites for hydrogenation. The rGO material with proper amounts of N heteroatoms and lattice defects becomes a suitable graphene material for fabricating the catalyst. The Co/rGO catalyst without prereduction treatment leads to the complete conversion of guaiacol with 93.2% selectivity to cyclohexanol under mild conditions. The remarkable HDO capability of the Co/rGO catalyst is attributed to the unique metal-acid synergy between the CoC_x sites and the acid sites of the CoO_x nanoparticles. The CoC_x sites provide H while the acid sites of CoO_x nanoparticles bind the C-O group of reactants to the surface, allowing easier C-O scission. The reaction pathways were characterized based on the observed reaction-product distributions. The effects of the process parameters on catalyst preparation and the HDO reaction, as well as the reusability of the catalyst, were systematically investigated.

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.