Control of dual-function amphiphilic biochar-MoO3-x catalysts with abundant oxygen vacancies for efficient extractant-free oxidative desulfurization

Abstract

The development of an efficient dual-function catalytic-sorption system, which seamlessly integrates reaction and separation into a single step for extractant-free systems, represents a transformative advancement in oxidative desulfurization (ODS) process. In this work, we introduce a novel dual-function amphiphilic biochar (Mo/CBC) catalyst, functionalized with MoO_3-x featuring abundant oxygen vacancies, for highly effective extractant-free ODS. The polarity of the biochar was precisely tailored by varying the amount of KOH, leading to the creation of amphiphilic carriers. Subsequent ball milling facilitated the successful loading of MoO_3-x onto the biochar surface via an impregnation-calcination route leveraging carbon reduction, resulting in the synthesis of amphiphilic Mo/CBC catalysts. The amphiphilic nature of these catalysts ensures their stable dispersion within the oil phase, while also facilitating their interaction with the oxidant H₂O₂ and the adsorption of sulfur-containing oxidation products. Characterization techniques, including EPR, XPS, and in situ XRD, verified the existence of abundant oxygen vacancies obtained by carbon reduction on the amphiphilic Mo/CBC catalysts, which significantly boosted their activity in an extractant-free ODS system. Remarkably, the amphiphilic Mo/CBC catalyst displayed exceptional catalytic performance, achieving a desulfurization efficiency of 99.6% in just 10 min without extraction solvent. DFT theoretical calculations further revealed that H₂O₂ readily dissociates into two •OH radicals on the O_vac-MoO₃, overcoming a low energy barrier. This process was identified as a key contributor to the catalyst's outstanding ODS performance. Furthermore, other biochar sources, such as rice straw, bamboo, rapeseed oil cake, and walnut oil cake, were investigated to produce Mo-based amphiphilic biochar catalysts, which all showed excellent desulfurization performance. This work establishes a versatile and highly efficient dual-function catalytic-sorption system by designing amphiphilic biochar catalysts enriched with oxygen vacancies, paving the way for the development of universally applicable ODS catalysts for industrial applications.