A green organic, solvent-free, subcritical water-CO (subW-CO) system was proposed for the production of furfural from the main hemicellulose's sugar, xylose. Despite subW itself showed potential for furfural generation due to its catalytic properties under subcritical conditions; when CO was added into the system as pressurization agent, higher yields were reached due to its effect as a Brønsted acid when dissolved in water. Furthermore, its combination with different Lewis acidic catalysts showed a synergistic effect, further improving furfural yield. In a batch configuration, five homogeneous and four heterogeneous catalysts were tested at 180 °C and 5.5 MPa and compared for the first time in a subW-CO reaction medium. Different furfural production paths were determined for the two catalysts types, with higher xylose isomerization rates to xylulose when homogeneous trivalent metal catalysts were used. CrCl and resin were selected as best catalysts from each of the groups due to higher furfural production rates (51.9 ± 0.9 % yield/h) and higher furfural selectivity (60.9 %), respectively. Furthermore, catalytic activity remained unchanged after 10 runs at 180 °C. The green subW-CO system furfural yields were comparable to water-organic solvent biphasic ones, proving to be a promising green alternative.

中文翻译：

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无溶剂绿色加压反应介质（亚临界水-CO2）中糖源生物质生产糠醛的均相和非均相催化策略的评估


提出了一种绿色有机、无溶剂、亚临界水-CO (subW-CO) 系统，用于从主要半纤维素的糖、木糖生产糠醛。尽管 subW 本身由于其在亚临界条件下的催化特性而显示出生成糠醛的潜力；当将CO作为加压剂添加到系统中时，由于其溶解在水中时作为布朗斯台德酸的作用，可以达到更高的产率。此外，其与不同路易斯酸性催化剂的组合表现出协同效应，进一步提高了糠醛收率。在批量配置中，五种均相催化剂和四种非均相催化剂在 180 °C 和 5.5 MPa 下进行了测试，并首次在 subW-CO 反应介质中进行了比较。确定了两种催化剂类型的不同糠醛生产路径，当使用均相三价金属催化剂时，木糖异构化为木酮糖的速率更高。由于较高的糠醛生产率（51.9±0.9%产率/小时）和较高的糠醛选择性（60.9%），CrCl和树脂分别被选为各组中的最佳催化剂。此外，在 180 °C 下运行 10 次后，催化活性保持不变。绿色 subW-CO 系统糠醛产量与水-有机溶剂双相体系相当，被证明是一种有前途的绿色替代品。