High-Performance Materials from Bio-based Feedstocks. Группа авторов

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High-Performance Materials from Bio-based Feedstocks - Группа авторов


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catalysts [1]. In order to develop more industrially friendly catalysts, many investigations have advanced the use of different bio‐based carbon materials for a wide range of catalytic applications. The studied bio‐based carbon catalysts and supports initially started with biochar, activated carbon, carbon nanotubes (CNTs), mesoporous carbons, and sugar catalysts, but have now been extended to include graphene and its derivatives. The crucial target for these developments is the upgrading of bio‐based carbon materials into direct catalysts or as catalyst supports to maximize catalytic efficiency. A simple process for the preparation of bio‐based carbon materials as well as achieving high conversion and highly desired product yield under mild reaction conditions are aimed for.

      An understanding of the mechanisms of heterogeneous catalysis could address the appropriate characteristics of bio‐based carbonaceous catalysts. Generally, a heterogeneous catalytic reaction takes place through the following steps: (1) dispersion of the substrate from the bulk fluid to the pore entrance on the external catalyst surface; (2) diffusion of the substrate from the pore entrance into the internal catalyst pore; (3) adsorption of the substrate on the active catalyst site; (4) reaction of the substrate on the active site to generate a product; (5) desorption of the product from the active site; (6) diffusion of the product from the internal catalyst pore to the external surface of the catalyst; and (7) dispersion of the product from the external surface of catalyst into the bulk fluid [78].

      An overview of high‐performance bio‐based carbon materials as catalysts and as carbon‐supported catalysts in various reactions are discussed here to present state‐of‐the‐art bio‐based carbon materials in a wide range of catalysis applications.

      2.5.1 Biochar

      Biochar is a carbonaceous solid product created by thermochemical conversion of biomass in an oxygen‐free or oxygen‐poor atmosphere by carbonization, pyrolysis and gasification. Among the various bio‐based carbon materials, biochar has promising characteristics allowing it to be used as a heterogeneous catalyst and as catalyst support in numerous reactions. As discussed in Section 2.3.1, biochars have been gaining increased attention in catalysis applications due to their low cost, high porosity, stability, easy regeneration, and being more environmentally safe than other synthetic carbon materials. Biochars were reported to exhibit good catalytic performance in biodiesel production, steam reforming, pyrolysis, photocatalysis, bio‐oil upgrading processes, and biomass conversions into fuels and chemicals [4,6–9, 79].

Schematic illustration of examples of chemical reactions catalyzed by biomass-derived carbons.

      The existence of organic compounds in the renewable resource matrix, particularly animal wastes, brings about occurring minerals and inorganic alkalis in the structure of the produced biochar, such as K, Ca, Mg, N, P, and S [85–88]. These elements may be present in the form of chemical compounds such as CaCO3, KCl, or SiCl4 [8]. These minerals and inorganic alkalis can behave like a natural promoter of biochar activity in some catalyzed reactions. For example, the alkali and alkali earth metallic species could markedly promote the catalytic activity of biochar in tar reforming during biomass gasification [89]. An increasing biomass pyrolysis temperature resulted in enhanced fixed carbon and mineral contents in the produced biochar [83]. However, the number of surface functional groups within


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