Continuous Homogeneous Catalytic Oxidation of C–H Bonds by Metal-Free Carbon Dots with a Poly(ascorbic acid) Structure
Xiao Wang, Shaoang Chen, Yurong Ma, Tianyang Zhang, Yu Zhao, Tiwei He, Hui Huang, Shitong Zhang, Junfeng Rong, Chunfeng Shi, Kangjian Tang, Yang Liu, Zhenhui Kang
Abstract
The activation of the C–H bond, a necessary step to get high-value-added compounds, is one of the most important issues in modern catalysis. Combining the advantages of both homogeneous and heterogeneous catalysis, a certain continuous homogeneous process should be one of the ideal routes for the catalytic activation of C–H bonds. Here, through machine learning (ML), we predicted and fabricated metal-free carbon dot (C-Dot) homogeneous catalysts for C–H bond oxidation. These C-Dots have an ascorbic acid unit based polymer-like structure with a polymerization degree in the range of 3–10. With C-Dots as the catalyst, three groups (aliphatic, aromatic, and cycloalkanes) of 10 hydrocarbon molecules were tested, proving its generality for the catalytic oxidation of the C–H bond. A typical example of cyclohexane that was selectively oxidized to adipic acid (AA) by using a circulation and phase-transfer process demonstrates its critical advantages, such as the continuous and large-scaled producing ability of the homogeneous catalysis process. The one-pass conversion efficiency of cyclohexane to AA reaches 77.49% with selectivity up to 84.24% in 4 h. The yield of 16.32% per hour is about 4 times over that of modern technology. Theoretical calculations suggested that the O2 activation on C-Dots plays a crucial role in determining the reaction rate of the entire catalytic oxidation process of cyclohexane.