Metal-free carbon catalysis of toluene on activated coke and its active sources

Abstract

In this work, toluene removal by activated coke (ACK) was investigated. For the first time, metal-free carbon catalytic oxidation of toluene on ACK was experimentally demonstrated. On this basis, the active sources of carbon catalytic oxidation of toluene on ACK, including surface defects, pore grading degree (V${}_{mes+mac}$/V${}_t$), and surface oxygen functional groups, were identified in combination with characterization tests. The catalytic effects of different oxygen-containing functional groups (C=O, COO-, C-O-) on toluene oxidation were analyzed. The carbon catalytic oxidation reaction path of toluene on ACK has been determined as follows: toluene $\to$ benzyl alcohol $\to$ benzaldehyde $\to$ benzoic acid $\to$ maleic anhydride $\to$ carbon dioxide and water. It can be divided into three steps: initial oxidation of toluene to benzyl alcohol and benzaldehyde on C=O; deep non-mineralized oxidation of benzyl alcohol and benzaldehyde on C=O, COO-, C-O-; and mineralized oxidation of intermediate products on C-O- to produce CO${}_2$. The gradual oxidation of toluene promotes the interconversion of C=O, COO-, and C-O-, with the assistance of O${}_2$ and reactive oxygen species (O${}^{\ast }$) generated by activation of O${}_2$ and adsorbed water.