Citation: Zhang, W.; Descorme, C.; Valverde, J.L.; Giroir-Fendler, A. Effect of Calcination Conditions on Co 3 O 4 Catalysts in the Total Oxidation of Toluene and Propane. Catalysts 2023, 13, 992. https:// doi.org/10.3390/catal13060992 Academic Editor: Hongxing Dai Received: 18 May 2023 Revised: 6 June 2023 Accepted: 7 June 2023 Published: 9 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). catalysts Article Effect of Calcination Conditions on Co 3 O 4 Catalysts in the Total Oxidation of Toluene and Propane Weidong Zhang 1,2 , Claude Descorme 2 , Jose Luis Valverde 3 and Anne Giroir-Fendler 2, * 1 School of Chemistry and Chemical Engineering, Anhui Province Key Laboratory of Coal Clean Conversion and High Valued Utilization, Anhui University of Technology, Ma’anshan 243002, China; weidong.zhang@ahut.edu.cn 2 University Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, 2 Avenue Albert Einstein, F-69622 Villeurbanne, France; claude.descorme@free.fr 3 Faculty of Chemical Science and Technology, University of Castilla-La Mancha, Avenida Camilo José Cela 12, 13005 Ciudad Real, Spain; joseluis.valverde@uclm.es * Correspondence: anne.giroir-fendler@ircelyon.univ-lyon1.fr Abstract: Co 3 O 4 catalysts were prepared via carbonate precipitation and subsequent calcination under specific conditions. The different catalysts were characterized as received using several techniques and tested in the total oxidation of toluene or propane. Calcination at low temperature or under dynamic conditions resulted in Co 3 O 4 catalysts with small crystallite sizes and large surface areas. The performances of the Co 3 O 4 catalysts appeared to be closely related to the low-temperature reducibility. The best catalyst, Co-350D, showed a toluene oxidation rate of 44.5 nmol g −1 s −1 at 200 ◦ C and a propane oxidation rate of 54.0 nmol g −1 s −1 at 150 ◦ C. Meanwhile, Co-350D exhibited excellent cycling stability and decent long-term durability in both reactions. Keywords: volatile organic compounds; Co 3 O 4 ; calcination; toluene oxidation; propane oxidation 1. Introduction Volatile organic compounds (VOCs), emitted from industrial manufacturing, automo- bile vehicles, and domestic activities and involved in the formation of ozone, photochemical smog, and secondary aerosols, are major contributors to air pollution [1]. Some of them are identified to be carcinogenic, teratogenic, and mutagenic, threatening human health [1]. Converting VOCs to harmless CO 2 and H 2 O by catalytic oxidation is one of the most promising solutions. As the leading catalysts in the catalytic oxidation of VOCs, noble metals have been widely studied in the last decades [2]. However, viewing from an economic and sustainable perspective, transition metal oxides that exhibit comparable activity to noble metals could be a better choice. Among transition metal oxides, Co 3 O 4 nanocatalysts have been proven to be very active in the total oxidation of toluene [3–11] and propane [12–20], two representative model VOCs. According to the well-accepted redox reaction mechanisms [21], the activity of Co 3 O 4 is mainly governed by its reducibility and oxygen mobility, and these redox properties are generally related to the crystallite size, strain, structural defects, and surface cobalt oxidation state of Co 3 O 4 . Rational design and control of these properties lie in the preparation process. Precipitation is a commonly used method for Co 3 O 4 synthesis with the advantages of simple steps, easy operation, and indus- trial scalability. The variation of precipitation conditions, such as precipitation agent [22], precipitation pH [23], or calcination procedure [24,25] could affect the physicochemical properties of Co 3 O 4 and, consequently, the catalytic performance. Recently, we have investigated the effect of the precipitation agent on Co 3 O 4 cata- lysts in the total oxidation of toluene and propane and demonstrated carbonate as the most promising agent [26]. Straight after, we further singled out the optimum precipita- tion pH, 9.5 [27]. In addition to these, calcination conditions may be another important Catalysts 2023, 13, 992. https://doi.org/10.3390/catal13060992 https://www.mdpi.com/journal/catalysts