Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/γ-Al2O3 Catalysts

Low-temperature oxidative removal of benzene from the air using titanium carbide (MXene)-Supported platinum catalysts

MXenes are an emerging class of two-dimensional (2D) inorganic materials with great potential for versatile applications such as adsorption and catalysis. Here, we describe the synthesis of a platinized titanium carbide MXene (Pt@Ti3C2) catalyst with varying amounts of platinum (0.1%-2 wt.%) for the low-temperature oxidation of benzene, an aromatic volatile organic compound often found in industrial flue gas. A 1% formulation of Pt@Ti3C2-R allowed near-complete (97%) oxidation of benzene to CO2 at 225 °C with a steady-state reaction rate (r) of 0.119 mol g-1·h-1. This low-temperature catalytic oxidation reaction was promoted by an increase in the lattice oxygen (O*)/Pt2+ species (active sites) of 1%Pt@Ti3C2-R from 45.3/34.6% to 71.0/61.1% through pre-thermal reduction under H2 flow, as revealed by X-ray photoelectron spectroscopy, temperature-programmed reduction, and in situ diffuse reflectance infrared Fourier transform spectroscopy analyses. The cataltyic activity of 1% Pt@Ti3C2-R against benzene was assessed under the control of the key process variables (e.g., catalyst mass, flow rate, benzene concentration, relative humidity, and time-on-stream) to help optimize the oxidation reaction process. The results provide new insights into the use of platinum-based 2D MXene catalysts for low-temperature oxidative removal of benzene from the air.

Discovering the key role of MnO2 and CeO2 particles in the Fe2O3 catalysts for enhancing the catalytic oxidation of VOC: Synergistic effect of the lattice oxygen species and surface-adsorbed oxygen

Highly active mesoporous Fe-Mn-Ce catalysts with high specific surface area (S_BET) were synthesized by a modified precipitation process for catalyzing toluene oxidation. The Fe_0.85Mn_0.1Ce_0.05 catalyst presents richer surface oxygen species (OS), a higher proportion of Mn⁴⁺ and Ce⁴⁺, a higher concentration of lattice defects and oxygen vacancies, the highest O_ads/O_latt ratio, and a superior low-temperature redox property compared with the Fe-Mn binary oxide and Fe₂O₃ and MnO₂ catalysts. The properties contribute to a high catalytic activity to achieve T₉₀% of toluene conversion at 264 °C and 185 °C with a gas hourly space velocity (GHSV) at 180,000 and 20,000 mL/(g∙h), respectively. The introduction of a slight quantity of Ce and Mn onto the Fe₂O₃ catalyst is the key to enhancing the synergistic effect of the lattice OS and surface-adsorbed oxygen, contributing to the activation oxidation procedure of toluene. In-situ DRIFTS analysis reveals that the rich oxygen vacancy concentration of catalysts accelerates the key steps for the generation and activation of oxidized products. These catalysts with rich oxygen vacancies can efficiently diminish the accumulation of a small number of the intermediary species (phenolate, C₆H₅-OH) produced during the catalytic oxidation of toluene.

Combined experimental and theoretical study of o-xylene elimination on Fe-Mn oxides catalysts

The development of low-cost and easily accessible catalysts to realize the practical applications of catalytic combustion of volatile organic compounds remains a challenge. In this work, a series of Fe-Mn oxides catalysts were prepared via a facile redox-precipitation route for the elimination of o-xylene. Among the synthesized catalysts, Fe3Mn1-RP exhibited excellent activity for o-xylene elimination with a T₅₀ and T₉₀ of 223 °C and 236 °C, respectively (o-xylene concentration = 500 ppm, WHSV = 36,000 mL g^-1 h^-1). Characterization results demonstrated that superior catalytic activity could be achieved from large specific surface area, good reducibility and high proportion of Mn⁴⁺. Besides, high Fe contents proved beneficial in generating additional oxygen vacancies, thereby improving the performance of the catalyst. The stable crystal structures and surface electron density distributions of the catalysts, and adsorption sites of o-xylene on the catalyst surface, were also determined through density functional theory (DFT) calculations to provide an in-depth mechanism on how the o-xylene oxidation occurred. Moreover, analysis of the energy barrier during the oxidation process proved that the ring-opening reaction on the surface of Fe3Mn1-RP with an activation energy as low as 2.46 eV would more likely occur via oxygen vacancies.

Current progress on catalytic oxidation of toluene: a review

Toluene is one of the pollutants that are dangerous to the environment and human health and has been sorted into priority pollutants; hence, the control of its emission is necessary. Due to severe problems caused by toluene, different techniques for the abatement of toluene have been developed. Catalytic oxidation is one of the promising methods and effective technologies for toluene degradation as it oxidizes it to CO₂ and does not deliver other pollutants to the environment. This paper highlights the recent progressive advancement of the catalysts for toluene oxidation. Five categories of catalysts, including noble metal catalysts, transition metal catalysts, perovskite catalysts, metal-organic frameworks (MOFs)-based catalysts, and spinel catalysts reported in the past half a decade (2015-2020), are reviewed. Various factors that influence their catalytic activities, such as morphology and structure, preparation methods, specific surface area, relative humidity, and coke formation, are discussed. Furthermore, the reaction mechanisms and kinetics for catalytic oxidation of toluene are also discussed.

Effect of Molybdenum on the Activity Temperature Enlarging of Mn-Based Catalyst for Mercury Oxidation

The MnO2/TiO2 (TM5) catalyst modified by molybdenum was used for mercury oxidation at different temperatures in a fixed-bed reactor. The addition of molybdenum into TM5 was identified as significantly enlarging the optimal temperature range for mercury oxidation. The optimal mercury oxidation temperature of TM5 was only 200 °C, with an oxidation efficiency of 95%. However, the mercury oxidation efficiency of TM5 was lower than 60% at other temperatures. As for MnO2–MoO3/TiO2 (TM5Mo5), the mercury oxidation efficiency was above 80% at 200–350 °C. In particular at 250 °C, the mercury oxidation efficiency of TM5Mo5 was over 93%. Otherwise, the gaseous O2, which could supplement the lattice oxygen in the catalytic reaction, played an important role in the process of mercury oxidation over TM5Mo5. The results of X-ray photoelectron spectroscopy (XPS) suggested that mercury oxidized by O2 over TM5Mo5 followed the Mars–Maessen mechanism.

Catalytic removal of toluene over manganese oxide-based catalysts: a review

It is necessary to control the emissions of toluene, which is hazardous to both human health and the atmosphere environment and has been classified as a priority pollutant. Manganese oxide-based (Mn-based) catalysts have received increased attention due to their high catalytic performance, good physicochemical characteristic, availability in various crystal structures and morphologies, and being environmentally friendly and low cost. These catalysts can be classified into five categories, namely single manganese oxide, Mn-based composite oxides, Mn-based special oxides, supported Mn-based oxides, and Mn-based monoliths. This review focused on the recent progress on the five types of Mn-based catalysts for catalytic removal of toluene at low temperature and further systematically summarized the strategies improving catalysts, including improving synthetic methods, incorporating MnO_x with other metal oxides, depositing Mn-based oxides on proper supports, and tuning the supports. Moreover, the effect of coexisting components, the reaction kinetics, and the oxidation mechanisms toward the removal of toluene were also discussed. Finally, the future research direction of this field was presented.

An integrative process of the simultaneous catalytic oxidation of NO, Hg0 and toluene from sintering flue gas by the natural ferrous manganese ore

An integrative process of the simultaneous catalytic oxidation of NO, Hg⁰ and toluene from sintering flue gas by the natural ferrous manganese ore was studied in fixed bed reactor and in situ DRIFTS.