Oxidative Conversion of Glucose to Formic Acid as a Renewable Hydrogen Source Using an Abundant Solid Base Catalyst

New understanding on iota-carrageenan oxidation by hydrogen peroxide with or without copper sulphate and the properties of oxidized iota-carrageenan

To explore the oxidation mechanism of iota-carrageenan (IC) and the potential applications of oxidized IC (OIC), a series of OIC samples were firstly synthesized under hydrogen peroxide or hydrogen peroxide/copper sulphate, their purification process, chemical composition, chemical structure, molecular weight, physical property, biosafety and antibacterial activity were systematically evaluated. Our results firstly found that only the combination of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) pre-treatment and dialysis could realize successful purification of OIC due to the strong electrostatic attractions between positive copper ions and negative sulphate ions. The introduction of copper ions could effectively speed up the oxidation of OIC, enhancing the content of aldehyde and carboxyl groups, resulting in the hydrolysis of the ether bonds in IC, inhibiting the detachment of sulphate, decreasing the molecular weight, thermal stability, characteristic temperature (i.e. gelling and melting temperature). It was worth mentioning that K+ and Zn2+ could also inhibit the de-sulfation during the oxidation via the chelating interactions. In addition, purified OIC samples possessed excellent cytocompatibility and blood compatibility, which could also promote the proliferation and migration of fibroblast cells. Meanwhile, all OIC samples possessed antibacterial activity. In summary, our investigations shed new lights on OIC synthesis, purification, properties and potential applications.

Conversion of Cellobiose to Formic Acid as a Biomass-Derived Renewable Hydrogen Source Using Solid Base Catalysts

Formic acid is considered a promising hydrogen carrier. Biomass-derived formic acid can be obtained by oxidative decomposition of sugars. This study explored the production of formic acid from cellobiose, a disaccharide consisting of d-glucose linked by β-glycosidic bonds using heterogeneous catalysts under mild reaction conditions. The use of alkaline earth metal oxide solid base catalysts like CaO and MgO in the presence of hydrogen peroxide could afford formic acid from cellobiose at 343 K. While CaO gave 14 % yield of formic acid, the oxide itself was converted to a harmful metal peroxide, CaO2 after the reaction. In contrast, MgO could produce formic acid without the formation of the metal peroxide. The difficulty in selectively synthesizing formic acid from cellobiose using these solid base catalysts was due to the poor conversion of cellobiose to glucose. Using a combination of solid acid and base catalysts, a high formic acid yield of 33 % was obtained under mild reaction conditions due to the quantitative hydrolysis of cellobiose to glucose by a solid acid followed by the selective decomposition of glucose to formic acid by a solid base.

Facile Synthesis of Microporous Carbons from Biomass Waste as High Performance Supports for Dehydrogenation of Formic Acid

Formic acid (FA) is found to be a potential candidate for the storage of hydrogen. For dehydrogenation of FA, the supports of our catalysts were acquired by conducting ZnCl₂ treatment and carbonation for biomass waste. The texture and surface properties significantly affected the size and dispersion of Pd and its interaction with the support so as to cause the superior catalytic performance of catalysts. Microporous carbon obtained by carbonization of ZnCl₂ activated peanut shells (C_PS-ZnCl₂) possessing surface areas of 629 m²·g⁻¹ and a micropore rate of 73.5%. For ZnCl₂ activated melon seed (C_MS-ZnCl₂), the surface area and micropore rate increased to 1081 m²·g⁻¹ and 80.0%, respectively. In addition, the introduction of ZnCl₂ also caused the increase in surface O content and reduced the acidity of the catalyst. The results represented that C_MS-ZnCl₂ with uniform honeycomb morphology displayed the best properties, and the as-prepared Pd/C_MS-ZnCl₂ catalyst afforded 100% hydrogen selectivity as well as excellent catalytic activity with an initial high turnover number (TON) value of 28.3 at 30 °C and 100.1 at 60 °C.