Preparation And Catalytic Properties Of Biomass-based Catalysts

Synthetic chemistry is closely related to the survival and development of human beings, and its main task is to develop efficient methods of forming carbon-carbon or carbon-heteroatom bonds, as well as functional groups conversion strategies. Among them, the transition metal-catalyzed organic reaction is one of the most important areas in modern synthetic chemistry and has been widely used in chemical and medicine industries. However, not only the cost of traditional homogeneous catalysis and chemical industries is high, but also the emission of catalysts, in particular, transition metal ions and phosphine ligands, could cause serious environmental pollution and ecological damage. By contrast, heterogeneous catalysts can not only overcome the limitations of homogeneous catalyst including the difficulties of separation, recovery and recycling, but also ealized industrialisation production. Accordingly, it has become a hot research field in green chemistry.Biomass-based materials have great potentials as functional materials, which can replace traditional materials, reducing the dependence on fossil resources and environmental pollution. Meanwhile, the biomass materials possess many attracting characteristics, such as high specific surface area, stability in most organic solvents, especially abundant functional groups, which are capable of chelating with metal ions or nanoparticles, thereby providing the required stability. Owing to their abundance in nature, renewability, biodegradability, and non-toxicity, biomass materials are regarded as an ideal alternative for the preparation of heterogeneous catalysts. Therefore, the design and development of biomass as catalyst carriers has very important significance.In this paper, several biomass-based catalysts were synthesized, and their catalytic performance for organic synthesis was studied. The results were as followed:(1) By in situ reduction-deposition of metal palladium nanoparticles(Pd NPs) on the surface of xylan hemicelluloses(XH), xylan hemicellulose loaded nanometer palladium catalyst(Pd NPs@XH) was successfully prepared. Its morphology, composition and stability were characterized and the applications of Pd NPs@XH in carbon-carbon bond cross-coupling reactions were investigated in detail. Under relatively mild conditions, the catalyst can efficiently catalyze the Suzuki, Heck, Sonogashira cross-coupling reactions between aryl halides(iodides, bromides, respectively) and organic boric acid, alkenes, alkynes and the yield could be up to 82-99%. The catalyst could be easily recovered from the reaction mixtures by a simple filtration and reused at least six times without significant loss of its catalytic activity.(2) A novel xylan hemicellulose supported palladium-terpyridine complex catalyst were prepared by modifying xylan hemicelluloses extracted from Dendrocalamus membranaceus Munro(Dm M) with terpyridine, before liganding to palladium salt, and its application for the Suzuki–Miyaura cross-coupling reaction was studied. The novel catalyst possessed high catalytic activity for the reaction between aryl halides and organic boronic acid derivatives in alcohol solvent system at room temperature with a yield of 78~98%. Additionally, the reusability of the catalyst was also investigated. The catalyst could be easily and quantitatively recovered from the reaction mixtures by a simple filtration and reused at least six times without significant loss of its catalytic activity, exhibiting good catalytic stability.(3) A novel cooperative catalytic system, composed of bagasse with abundant hydroxyl groups(served as hydrogen bond donor), and potassium iodide was used for catalyzing cycloaddition reaction of various epoxides and aziridines with CO2 under solvent-free condition. The effect of reaction factors, such as temperature, time, and pressure on the catalytic activity of the cycloaddition reaction was investigated, as well as the synergetic effect between bagasse and alkali salts. In addition, a series of cyclic carbonate and oxazolidinone derivatives were successfully prepared by expanding corresponding reaction substrates. Meanwhile, the reusibility of the catalyst was also studied and the results showed that the catalyst could be readily recovered by a simple distillation process, and reused at least five times without significant loss of its catalytic activity, showing excellent catalytic activity and stability. The cooperative catalytic system possessed potentially practical applications for the capturing of carbon dioxide in the preparation of propylene carbonate.(4) Lignosulfonic acid catalyst, derived from lignin sulfonate was prepared by a simple ion exchange process. Their application for the catalyzing the condensation reaction among aldehyde, β-naphthol, and 1,3-cyclohexanedione derivates under solvent-free condition was studied, and the yield of produced benzoxanthene derivates was 82~93% under the optimal condition i.e., 20 mg of the catalyst, 2 h of reaction time at 90 oC. Also the recycling performance of the catalyst was investigated and the catalyst could be recovered by simple filtration, and used directly. The yield could still remain 82% after being continuously reused for four times. On the basis of the good catalytic performance, the type of catalyzed reaction was further expanded, applying to catalyzing the condensation reaction among aldehyde, β-naphthol, and amides derivates for the preparation of amidoalkyl naphthol derivates, Hantzsch and Strecker reaction. The results showed that this catalyst was widely applicabe to a variety of multicomponent reactions.(5) A novel biomass-based solid acid catalysts derived from bagasse was synthesized via a combination method of partial carbonization and subsequent sulfonation and their application for catalyzing 1,3-dipolar cycloaddition of nitroolefins and sodium azide was investigated. The catalyst possessed high catalytic activity for cycloaddition reaction at 60 oC in DMF system, giving 4-Aryl-NH-1,2,3-triazoles in high yields ranging from 65% to 95%. In addition, this novel cycloaddition reaction tolerated a wide range of functional groups including methyl, methoxy, cyano, ester, halogen, proving to be a general method for the synthesis of 4-Aryl-NH-1,2,3-triazoles. The results showed that the reaction activities of reaction substrates with electron-donating groups were higher than those of substrates with electron withdrawing ones in the catalytic system. Furthermore, the stronger electron-withdrawing effect was, the lower the catalytic activity was and accordingly the reaction activity of substrate was dependent on the position of substituent group, i.e., para > meta > ortho. Meanwhile, the reusability of the catalyst was also investigated. After being reused for five times in succession, the catalyst still exhibited excellent catalytic activity and stability, achieving a yield up to 84%.