Key Laboratory of Catalysis and Materials Sciences of the Ministry of Education, South-Central University for Nationalities , Wuhan, 430074, People's Republic of China.
Chemistry Discipline, Queensland University of Technology , Brisbane, QLD 4001, Australia.
J Am Chem Soc. 2017 Oct 18;139(41):14775-14782. doi: 10.1021/jacs.7b08861. Epub 2017 Oct 9.
Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is one of the key reactions for producing chemical commodities from biomass and their derivatives. The challenge for this reaction is to develop an efficient catalytic process that can be conducted under mild conditions (room temperature and atmospheric pressure, using oxygen molecules in air as the oxidant) and a recyclable catalyst. Herein we report a photocatalyst of cobalt thioporphyrazine (CoPz) dispersed on g-CN (abbreviated as CoPz/g-CN), which exhibits excellent catalytic activity toward the selective oxidation of HMF into FDCA under simulated sunlight using oxygen molecules in air as a benign oxidant. For example, an FDCA yield of 96.1% in an aqueous solution at pH = 9.18 is achieved at ambient temperature and air pressure. At lower pH (4.01), the product generated is 2,5-diformylfuran. Hence, it is possible to control the reaction outcome by control of the pH of the reaction system. g-CN itself is not a suitable catalyst for the selective oxidation because under the experimental conditions g-CN generates hydroxyl radicals that initiate processes that oxidize HMF directly to CO and HO. CoPz on the other hand activates O to give singlet oxygen (O), which more controllably oxidizes HMF to FDCA albeit at a more moderate yield (36.2%). The strong interaction between the CoPz and g-CN in the CoPz/g-CN catalyst is experimentally evidenced, which not only improves accessibility of the CoPz sites and makes the catalyst recyclable but also disables the hydroxyl radical generation by g-CN and promotes O generation on the CoPz sites, significantly enhancing the catalytic performance. This study demonstrates the potential for efficient non-noble metal photocatalysts for organic transformations driven by sunlight.
5-羟甲基糠醛（HMF）选择性氧化为 2,5-呋喃二甲酸（FDCA）是从生物质及其衍生物生产化工产品的关键反应之一。该反应的挑战是开发一种高效的催化过程，该过程可以在温和条件（室温、大气压力，使用空气中的氧分子作为氧化剂）和可回收催化剂下进行。在此，我们报告了一种钴卟啉（CoPz）分散在 g-CN 上的光催化剂（简称 CoPz/g-CN），该光催化剂在模拟阳光下使用空气中的氧分子作为温和氧化剂，对 HMF 选择性氧化为 FDCA 表现出优异的催化活性。例如，在 pH = 9.18 的水溶液中，在环境温度和大气压力下，FDCA 的产率达到 96.1%。在较低的 pH（4.01）下，生成的产物是 2,5-二糠醛。因此，可以通过控制反应体系的 pH 来控制反应结果。g-CN 本身不是选择性氧化的合适催化剂，因为在实验条件下，g-CN 会产生羟基自由基，这些自由基会直接将 HMF 氧化为 CO 和 HO。而另一方面，CoPz 会激活 O 以产生单线态氧（O），尽管产率较低（36.2%），但 O 可以更可控地将 HMF 氧化为 FDCA。在 CoPz/g-CN 催化剂中，CoPz 与 g-CN 之间的强相互作用得到了实验证实，这不仅提高了 CoPz 位点的可及性并使催化剂可回收利用，而且还阻止了 g-CN 产生羟基自由基并促进了 O 在 CoPz 位点上的生成，显著提高了催化性能。这项研究展示了基于阳光驱动的有机转化的高效非贵金属光催化剂的潜力。
