The preparation of Pt and Mn-based composite catalysts and their influence on the catalytic oxidation of toluene

Abstract

Volatile Organic Compounds (VOCs) are a key contributor to atmospheric pollution, posing significant threats to both the environment and human health due to their diverse sources and high toxicity. Catalytic oxidation technology, known for its low-temperature, high-efficiency degradation and the absence of secondary pollution, has emerged as one of the most promising strategies for VOCs removal. The primary challenge lies in developing catalysts that combine high activity at low temperatures with long-term stability. Toluene, a typical VOC, is frequently used as a model pollutant to evaluate catalyst performance because of its structural features, which include both aromatic hydrocarbons and alkanes. This thesis focuses on one of representative reducible metal oxides-manganese oxide, and systematically investigates the impact of their interaction with the noble metal Pt as a support on the catalytic oxidation activity and reaction mechanism of toluene at first. Furthermore, by employing a doping modification strategy, the water resistance of manganese oxide catalysts was significantly enhanced, opening the possibility for their industrial application. Additionally, a facile and efficient method for synthesizing manganese oxide-based bimetallic catalysts was developed. The main research content and findings are as follows:
(1) α-MnO2 supports with varying exposed crystal planes were first synthesized by using hydrothermal method. Pt was then anchored onto the support surface through electrostatic adsorption, resulting in the formulation of a series of Pt/α-MnO2 catalysts. The influence of the crystal plane of supports on the catalytic oxidation performance of toluene was systematically examined. The findings revealed that modifying the primary exposed crystal plane of α-MnO2 significantly alters the oxygen vacancy concentration and the valence state distribution of the precious metals within the catalyst. Notably, Pt/α-MnO2-110 exhibited superior low-temperature catalytic activity. Further characterization analysis showed that, compared to the other samples, Pt/α-MnO2-110 has a higher Mn4+/Mn3+ ratio, a richer oxygen vacancy concentration, and a higher adsorbed oxygen content. These distinctive features not only promote the release of lattice oxygen but also facilitate the conversion of benzoate to phenol, driving its subsequent ring-opening reaction to yield formate species.
(2) A series of δ-MnO2 catalysts, doped with varying amounts of tin oxide (referred to as SM catalysts), were synthesized using the hydrothermal method. The research showed that an increase in Sn content triggered a phase transformation in δ-MnO2, shifting towards α-MnO2, and significantly enhanced its toluene oxidation activity and water resistance under humid conditions. Notably, the SM-4 catalyst, doped with 7% Sn, exhibited superior toluene oxidation activity, which can be attributed to its abundant acidic sites that promote toluene adsorption. The SM-4 catalyst features a unique dual crystal phase structure of δ-MnO2/α-MnO2 and retains stable catalytic activity across varying concentrations of external water vapor. Further analysis revealed that the introduction of tin modifies the adsorption and desorption behavior of water molecules on the MnO2 surface, thereby significantly enhancing the material’s hydrophobicity and improving the water resistance of the catalyst.
(3) A three-dimensional cobalt oxide (3D Co3O4) support was synthesized via a hydrothermal method, and a bimetallic Pta-(MnOx)b/3D Co3O4 catalyst was subsequently produced using a streamlined one-step hydrothermal procedure. This approach is notably more efficient and straightforward than conventional methods, which typically involve the initial synthesis of nanoparticles followed by their loading onto the support. Compared to monometallic catalysts, the Pt-MnOx bimetallic catalyst demonstrated markedly superior toluene oxidation activity. By optimizing the ratio of Pt and Mn precursors, the Pt1-(MnOx)1/3D Co3O4 catalyst achieved optimal performance. Characterization revealed that the presence of abundant oxygen vacancies on the Pt1-(MnOx)1/3D Co3O4 surface significantly enhanced the adsorption and activation of gaseous oxygen. This enhancement contributed to increased oxygen migration and storage capacity, thereby boosting the oxidation reaction of toluene.

Date of Award	15 Nov 2025
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Tao Wu (Supervisor), Hongfeng Yin (Supervisor), Mengxia Xu (Supervisor) & Sun Cheng-Gong (Supervisor)