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  • MDPI AG  (7)
  • 1
    Online Resource
    Online Resource
    Single-Atom Catalysts: Preparation and Applications in Environmental Catalysis
    MDPI AG ; 2022
    In:  Catalysts Vol. 12, No. 10 ( 2022-10-14), p. 1239-
    Details
    In: Catalysts, MDPI AG, Vol. 12, No. 10 ( 2022-10-14), p. 1239-
    Abstract: Due to the expensive price and the low reserve of noble metals in nature, much attention has been paid to single-atom catalysts (SACs)—especially single-atom noble metal catalysts—owing to their maximum atomic utilization and dispersion. The emergence of SACs greatly decreases the amount of precious metals, improves the catalytic activity, and makes the catalytic process progressively economic and sustainable. However, the most remarkable challenge is the active sites and their stability against migration and aggregation under practical conditions. This review article summarizes the preparation strategies of SACs and their catalytic applications for the oxidation of methane, carbon monoxide, and volatile organic compounds (VOCs) and the reduction of nitrogen oxides. Furthermore, the perspectives and challenges of SACs in future research and practical applications are proposed. It is envisioned that the results summarized in this review will stimulate the interest of more researchers in developing SACs that are effective in catalyzing the reactions related to the environmental pollution control.
    Type of Medium: Online Resource
    ISSN: 2073-4344
    URL: Article
    DOI: 10.3390/catal12101239
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2662126-5
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  • 2
    Online Resource
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    Simultaneously Enhanced Potential Gradient and Nonlinearity of ZnO Varistor Ceramics by MnO Doping with Nano-Sized ZnO Powders
    MDPI AG ; 2021
    In:  Materials Vol. 14, No. 24 ( 2021-12-15), p. 7748-
    Details
    In: Materials, MDPI AG, Vol. 14, No. 24 ( 2021-12-15), p. 7748-
    Abstract: ZnO varistor ceramics with a high potential gradient, as well as a high nonlinear coefficient, were reported and analyzed in this paper. With the use of nano-sized ZnO powders, the average grain size was reduced to about 2.6 μm, which successfully raised the potential gradient to 1172 V/mm. Moreover, the nonlinear coefficient increased to 48, and the leakage current was decreased to 8.4 μA/cm2 by doping a moderate amount of MnO (0.9 mol%). This was proven to be caused by the high Schottky barrier height formed at the grain boundary, where the Mn element segregated and, consequently, led to the increased density of interface states. Therefore, this could be considered as a potential method to simultaneously enhance the potential gradient and the nonlinear coefficient of ZnO varistor ceramics.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma14247748
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2487261-1
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  • 3
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    Enhanced Performance of Supported Ternary Metal Catalysts for the Oxidation of Toluene in the Presence of Trichloroethylene
    MDPI AG ; 2022
    In:  Catalysts Vol. 12, No. 5 ( 2022-05-16), p. 541-
    Details
    In: Catalysts, MDPI AG, Vol. 12, No. 5 ( 2022-05-16), p. 541-
    Abstract: Chlorinated volatile organic compounds (CVOCs), even in small quantities, can cause Pt-based catalyst poisoning. Improving the low-temperature chlorine resistance of catalysts is of vital importance for industrial application, although it remains challenging. Considering actual industrial production, a TiO2-supported ternary metal catalyst was prepared in this work to study the catalytic oxidation of multicomponent VOCs (toluene and trichloroethylene (TCE)). Among all of the samples, PtWRu/TiO2 and PtWCr/TiO2 exhibited the best catalytic performance for toluene oxidation. In the mixed VOC oxidation, the PtWCr/TiO2 sample showed the best catalytic activity for toluene combustion (a toluene conversion of 90% was achieved at 258 °C and a space velocity of 40,000 mL g−1 h−1, and the specific reaction rate and turnover frequency at 215 °C were 44.9 × 10−6 mol gPt−1 s−1 and 26.2 × 10−5 s−1). The PtWRu/TiO2 sample showed the best catalytic activity for TCE combustion (a TCE conversion of 90% was achieved at 305 °C and a space velocity of 40,000 mL g−1 h−1, and the specific reaction rate and turnover frequency at 270 °C were 9.0 × 10−6 mol gPt−1 s−1 and 7.3 × 10–5 s−1). We concluded that the ternary metal catalysts could greatly improve chlorine desorption by increasing the active lattice oxygen mobility and surface acidity, thus reducing chlorinated byproducts and other serious environmental pollutants. This work may serve as a reasonable design reference for solving more practical industrial production emissions of multicomponent VOCs.
    Type of Medium: Online Resource
    ISSN: 2073-4344
    URL: Article
    DOI: 10.3390/catal12050541
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
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  • 4
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    Online Resource
    Catalytic Performance and Reaction Mechanisms of Ethyl Acetate Oxidation over the Au–Pd/TiO2 Catalysts
    MDPI AG ; 2023
    In:  Catalysts Vol. 13, No. 4 ( 2023-03-23), p. 643-
    Details
    In: Catalysts, MDPI AG, Vol. 13, No. 4 ( 2023-03-23), p. 643-
    Abstract: The development of efficient and stable catalysts is of great importance for the elimination of volatile organic pollutants (VOCs). In this work, AuPdx nanoparticles (NPs) were loaded on TiO2 through the electrostatic adsorption approach to generate the yAuPdx/TiO2 (i.e., 0.35AuPd0.46/TiO2, 0.34AuPd2.09/TiO2, and 0.37AuPd2.72/TiO2; x and y are Pd/Au molar ratio and AuPdx loading, respectively; x = 0.46–2.72; and y = 0.34–0.37 wt%) catalysts, and their catalytic activities for the oxidation of ethyl acetate were determined. The results showed that the 0.37AuPd2.72/TiO2 sample exhibited the best activity (T50% = 217 °C and T90% = 239 °C at SV = 40,000 mL/(g h), Ea = 37 kJ/mol, specific reaction rate at 220 °C = 113.8 µmol/(gPd s), and turnover frequency (TOFNoble metal) at 220 °C = 109.7 × 10−3 s−1). The high catalytic performance of the 0.37AuPd2.72/TiO2 sample was attributed to the good dispersion of AuPd2.72 NPs, the strong redox ability, the large ethyl acetate adsorption capacity, and the strong interaction between AuPdx and TiO2. Acetaldehyde, ethanol, and acetic acid are the main intermediates in the oxidation of ethyl acetate, and the loading of AuPdx NPs effectively reduces the formation of the toxic by-product acetaldehyde. The oxidation of ethyl acetate over the 0.34AuPd2.09/TiO2 sample might occur via the pathway of ethyl acetate → ethanol → acetic acid → acetate → CO2 and H2O. We believe that the obtained results may provide a useful idea for the design of bimetallic catalysts under industrial conditions and for understanding the VOCs oxidation mechanisms.
    Type of Medium: Online Resource
    ISSN: 2073-4344
    URL: Article
    DOI: 10.3390/catal13040643
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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  • 5
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    Online Resource
    Symmetry Control of Comfortable Vehicle Suspension Based on H∞
    MDPI AG ; 2022
    In:  Symmetry Vol. 14, No. 1 ( 2022-01-16), p. 171-
    Details
    In: Symmetry, MDPI AG, Vol. 14, No. 1 ( 2022-01-16), p. 171-
    Abstract: Suspension is an important part of intelligent and safe transportation; it is the balance point between the comfort and handling stability of a vehicle under intelligent traffic conditions. In this study, a control method of left-right symmetry of air suspension based on H∞ theory was proposed, which was verified under intelligent traffic conditions. First, the control stability caused by the active suspension control system running on uneven roads needs to be ensured. To address this issue, a 1/4 vehicle active suspension model was established, and the vertical acceleration of the vehicle body was applied as the main index of ride comfort. H∞ performance constraint output indicators of the controller contained the tire dynamic load, suspension dynamic stroke, and actuator control force limit. Based on the Lyapunov stability theory, an output feedback control law with H∞-guaranteed performance was proposed to constrain multiple targets. This way, the control problem was transformed into a solution to the Riccati equation. The simulation results showed that when dealing with general road disturbances, the proposed control strategy can reduce the vehicle body acceleration by about 20% and meet the requirements of an ultimate suspension dynamic deflection of 0.08 m and a dynamic tire load of 1500 N. Using this symmetrical control method can significantly improve the ride comfort and driving stability of a vehicle under intelligent traffic conditions.
    Type of Medium: Online Resource
    ISSN: 2073-8994
    URL: Article
    DOI: 10.3390/sym14010171
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2518382-5
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  • 6
    Online Resource
    Online Resource
    Methane Combustion over Zeolite-Supported Palladium-Based Catalysts
    MDPI AG ; 2023
    In:  Catalysts Vol. 13, No. 9 ( 2023-08-29), p. 1251-
    Details
    In: Catalysts, MDPI AG, Vol. 13, No. 9 ( 2023-08-29), p. 1251-
    Abstract: The emission of methane leads to the increase in the methane concentration in the atmosphere, which not only wastes resources but also intensifies the greenhouse effect and brings about serious environmental problems. Catalytic combustion can completely convert methane into carbon dioxide and water at low temperatures. However, the catalytic activities of the conventional supported palladium catalysts (e.g., Pd/Al2O3 and Pd/ZrO2) are easy to decrease or the two catalysts can even be deactivated under actual harsh reaction conditions (high temperatures, steam- and sulfur dioxide-containing atmospheres, etc.). Recently, noble metal catalysts supported on zeolites with ordered pores and good thermal stability have attracted much attention. This review article summarizes the recent progress on the development and characteristics of zeolite-supported noble metal catalysts for the combustion of methane. The effects of framework structures, silica/alumina ratios, acidity, doping of alkali metals or transition metals, particle sizes and distributions, and their locations of/in the zeolites on methane combustion activity are discussed. The importance of developing high-performance catalysts under realistic operation conditions is highlighted. In addition, the related research work on catalytic methane combustion in the future is also envisioned.
    Type of Medium: Online Resource
    ISSN: 2073-4344
    URL: Article
    DOI: 10.3390/catal13091251
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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  • 7
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    Pt/CeMnOx/Diatomite: A Highly Active Catalyst for the Oxidative Removal of Toluene and Ethyl Acetate
    MDPI AG ; 2023
    In:  Catalysts Vol. 13, No. 4 ( 2023-03-30), p. 676-
    Details
    In: Catalysts, MDPI AG, Vol. 13, No. 4 ( 2023-03-30), p. 676-
    Abstract: Pt nanoparticles and a CeMnOx composite were loaded on the surface of the natural diatomite material to generate the Pt/CeMnOx/diatomite using the redox precipitation and impregnation methods. The physicochemical properties of the catalysts were characterized by means of various techniques. The catalytic properties and resistance to H2O and SO2 of the catalysts were measured for the oxidation of typical volatile organic compounds (i.e., toluene and ethyl acetate). Among all of the as-prepared samples, Pt/CeMnOx/diatomite exhibited the highest catalytic activity: the temperatures (T90%) at a toluene or ethyl acetate conversion of 90% were 230 and 210 °C at a space velocity (SV) of 20,000 mL g−1 h−1, respectively, and the turnover frequency (TOFPt) at 220 °C was 1.04 μmol/(gcat s) for ethyl acetate oxidation and 1.56 μmol/(gcat s) for toluene oxidation. In particular, this sample showed a superior catalytic activity for ethyl acetate oxidation at low temperatures, with its T50% being 185 °C at SV = 20,000 mL g−1 h−1. In addition, the Pt/CeMnOx/diatomite sample possessed good sulfur dioxide resistance during the toluene oxidation process. In the presence of SO2, some of the SO2 molecules were adsorbed on diatomite, which protected the active sites from being poisoned by SO2 to a certain extent. The pathways of ethyl acetate and toluene oxidation over Pt/CeMnOx/diatomite or Pt/CeMnOx were as follows: The C–C and C–O bonds in ethyl acetate are first broken to form the CH3CH2O* and CH3CO* species or toluene is first oxidized to benzaldehyde and benzoic acid, and all of these intermediates are then converted to CO2 and H2O. This work can provide a strategy to develop efficient catalysts with high catalytic activity, durability, low cost, and easy availability under actual working conditions.
    Type of Medium: Online Resource
    ISSN: 2073-4344
    URL: Article
    DOI: 10.3390/catal13040676
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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