Catalytic Oxidation of VOCs over SmMnO₃ Perovskites: Catalyst Synthesis, Change Mechanism of Active Species, and Degradation Path of Toluene

Abstract

Highly active samarium manganese perovskite oxides were successfully prepared by employing self-molten-polymerization, coprecipitation, sol–gel, and impregnation methods. The physicochemical properties of perovskite oxides were investigated by XRD, N2 adsorption–desorption, XPS, and H2-TPR. Their catalytic performances were compared via the catalytic oxidation of toluene. The perovskite prepared by self-molten-polymerization possessed the highest catalytic capacity, which can be ascribed to its higher oxygen adspecies concentration (Olatt/Oads = 0.53), higher surface Mn4+/Mn3+ ratio (Mn4+/Mn3+ = 0.95), and best low-temperature reducibility (H2 consumption = 0.27; below 350 °C). The most active catalyst also exhibited good cycling and long-term stability for toluene oxidation. After a multistep cycle reaction and a long-term reaction of 42 h, the toluene conversion maintained above 99.9% at 270 °C. Mechanistic study hinted that lattice oxygen was involved in toluene oxidation. The oxidation reaction was dependent on the synergism of lattice oxygen, adsorbed oxygen, and oxygen vacancies. The degradation pathway of toluene, researched by diffuse reflectance infrared Fourier transform spectroscopy and online mass spectrometry technologies, demonstrated that a series of organic byproducts existed at a relatively low temperature. This work provides an efficient and practical method for selecting highly active catalysts and for exploring the catalytic mechanism for the removal of atmospheric environmental pollution.

Synthesis, characterization and photoluminescence properties of Tm3+-doped Ca2YTaO6 blue-emitting phosphors

“…And the low CRI was due to the lack of red composition [8][9][10]. Method (2) was mixing the tricolor (RGB) emission phosphors with a near-UV chip [11][12][13]. The quest for blue-emitting phosphors for lighting is an important and urgent challenge for investigators.…”

The Influence of the Chemical Potential on Defects and Function of Perovskites in Catalysis

“…The dominant oxidation state of manganese in perovskites is Mn 3+ , accompanied by smaller proportions of Mn 2+ and Mn 4+ (Figure 4). (Levasseur and Kaliaguine, 2008;Liu et al, 2018b;Liu et al, 2019) Mn 2+ species were already present in the fresh Sm 0.96 MnO 3 catalyst (Koch et al, 2020) balanced by about 5% Mn 4+ resulting in an average oxidation state of 3.03. After heating in 20% O 2 , the average oxidation state decreased to 3.00.…”

“…Defect-rich structures are of particular importance with respect to the application of perovskites in heterogeneous catalysis (Royer et al, 2014;Najjar and Batis, 2016). In addition to the increasing interest in perovskites as catalysts for oxygen reduction and oxygen evolution reactions (Suntivich et al, 2011;Gupta et al, 2016;Zhu et al, 2019), this class of materials is also widely used in photocatalysis (Grabowska, 2016;Tasleem and Tahir, 2020) or total oxidation to remove volatile organic and hazardous compounds (Gil et al, 2004;Liu et al, 2018a;Liu et al, 2018b;Liu et al, 2019). However, perovskites are also suitable catalysts for selective oxidations at low temperatures (Polo-Garzon and Wu, 2018;Kamata, 2019), especially for the oxidative dehydrogenation of propane (Koch et al, 2020).…”

Effect of Acid Treatment on the Catalytic Activity and Mechanical Stability of SmMnO3/Cordierite Monolithic Catalysts

“…Among a series of transition metal oxide catalysts, the perovskite-type oxides (general formula of ABO 3 ) have attracted wide attention for VOC oxidation, in which samarium manganese perovskite show oxygen mobility and high thermal stability, and resulting in better activity in oxidation of toluene. [21] Nevertheless, the applications of perovskite oxides often suffer from the obstacle of low specific surface area results from high-temperature calcination. One of the solutions is to disperse ABO 3 on supports which have a high surface area, such as Al 2 O 3 , TiO 2 , CeO 2 , SiO 2 , zeolite at al.…”

“…The recent explosive growth in research on non‐noble mental catalysts with low cost and good thermal stability offers a great potential to significantly increase catalytic activity. Among a series of transition metal oxide catalysts, the perovskite‐type oxides (general formula of ABO 3 ) have attracted wide attention for VOC oxidation, in which samarium manganese perovskite show oxygen mobility and high thermal stability, and resulting in better activity in oxidation of toluene [21] …”