Preparation of three-dimensionally ordered macroporous La0.6Sr0.4Fe0.8Bi0.2O3−δ and their excellent catalytic performance for the combustion of toluene

Potential Strategy to Control the Organic Components of Condensable Particulate Matter: A Critical Review

More and more attention has been paid to condensable particulate matter (CPM) since its emissions have surpassed that of filterable particulate matter (FPM) with the large-scale application of ultralow-emission reform. CPM is a gaseous material in the flue stack but instantly turns into particles after leaving the stack. It is composed of inorganic and organic components. Organic components are an important part of CPM, and they are an irritant, teratogenic, and carcinogenic, which triggers photochemical smog, urban haze, and acid deposition. CPM organic components can aggravate air pollution and climate change; therefore, consideration should be given to them. Based on existing methods for removing atmospheric organic pollutants and combined with the characteristics of CPM organic components, we provide a critical overview from the aspects of (i) fundamental cognition of CPM, (ii) common methods to control CPM organic components, and (iii) catalytic oxidation of CPM organic components. As one of the most encouraging methods, catalytic oxidation is discussed in detail, especially in combination with selective catalytic reduction (SCR) technology, to meet the growing demands for multipollutant control (MPC). We believe that this review is inspiring for a fuller understanding and deeper exploration of promising approaches to control CPM organic components.

Thermally Inducing Viscous Fluids to Generate Co-Based Perovskites Enriched with Active Species for the Removal of VOCs

Various Co-based perovskites are synthesized through thermally driving viscous fluids. In this process, rare earth salts, cobalt salts, and citric acid do not require homogeneous mixing but only need to be heated until they melt into a molten viscous slurry. The physicochemical properties of cobalt-based perovskites were examined using techniques such as X-ray diffraction (XRD), electron paramagnetic resonance (EPR), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-Mapping-EDS), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), and N2 adsorption-desorption. The results indicate that the surface-active species can be controlled by altering the A-site elements of cobalt-based perovskites. All catalysts synthesized through the thermal treatment of viscous mixtures exhibited a low activation temperature and a low apparent activation energy for the catalytic oxidation of toluene. Among all cobalt-based perovskites, LaCoO3 demonstrated the most outstanding catalytic activity, primarily attributed to its capacity to expose a larger number of surface-active sites and oxygen species, as well as its superior reducibility. Furthermore, the formation process of optimal LaCoO3 was monitored using thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), and the byproducts of the low-temperature catalytic oxidation of toluene by the catalyst were identified using gas chromatography-mass spectrometry (GC-MS). The possible mechanism of toluene oxidation was inferred by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Moreover, LaCoO3 exhibits a predominant resistance to high-temperature hydrothermal conditions. This work provides a scalable and innovative approach to fabricating exceptionally effective catalysts for the efficient purification of VOCs.

Three-dimensionally macroporous MnZrOx catalysts for propane combustion: Synergistic structure and doping effects on physicochemical and catalytic properties

Three-dimensionally macroporous (3DM) MnZrO_x catalysts were fabricated to reveal the structure and Zr-doping effects on both physicochemical properties and propane combustion behaviors. The increasing addition of zirconium is favorable for the formation of 3DM structure and amorphous Mn-Zr solid solution, leading to tunable physicochemical properties. The significant activity improvement after zirconium addition was originally attributable to the superior redox ability, higher oxygen mobility and more abundant oxygen vacancy. The excellent catalytic activity, cycling stability and water resistant ability over 3DM Mn_0.6Zr_0.4O_x make it a promising material for hydrocarbons elimination. The comparative TPSR, in situ DRIFTs and kinetics study over 3DM and bulk catalysts emphasize the advantageous function of 3DM architecture on promoting propane adsorption, oxidation and lattice oxygen mobility.

BaFe1-xCuxO3 Perovskites as Active Phase for Diesel (DPF) and Gasoline Particle Filters (GPF)

BaFe_1−xCu_xO₃ perovskites (x = 0, 0.1, 0.3 and 0.4) have been synthetized, characterized and tested for soot oxidation in both Diesel and Gasoline Direct Injection (GDI) exhaust conditions. The catalysts have been characterized by BET, ICP-OES, SEM-EDX, XRD, XPS, H₂-TPR and O₂-TPD and the results indicate the incorporation of copper in the perovskite lattice which leads to: (i) the deformation of the initial hexagonal perovskite structure for the catalyst with the lowest copper content (BFC1), (ii) the modification to cubic from hexagonal structure for the high copper content catalysts (BFC3 and BFC4), (iii) the creation of a minority segregated phase, BaO_x-CuO_x, in the highest copper content catalyst (BFC4), (iv) the rise in the quantity of oxygen vacancies/defects for the catalysts BFC3 and BFC4, and (v) the reduction in the amount of O₂ released in the course of the O₂-TPD tests as the copper content increases. The BaFe_1−xCu_xO₃ perovskites catalyze both the NO₂-assisted diesel soot oxidation (500 ppm NO, 5% O₂) and, to a lesser extent, the soot oxidation under fuel cuts GDI operation conditions (1% O₂). BFC0 is the most active catalysts as the activity seems to be mainly related with the amount of O₂ evolved during an. O₂-TPD, which decreases with copper content.

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

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 (O_latt/O_ads = 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.

Ordered meso- and macroporous perovskite oxide catalysts for emerging applications

Hierarchically ordered perovskite materials which have potential applications in chemistry, energy and materials science.

Preparation and high catalytic performance of Au/3DOM Mn2O3 for the oxidation of carbon monoxide and toluene

Three-dimensionally ordered macroporous (3DOM) Mn2O3 and its supported gold (xAu/3DOM Mn2O3, x=1.9-7.5wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Mn2O3 and xAu/3DOM Mn2O3 samples exhibited a surface area of 34-38m(2)/g. The Au nanoparticles (NPs) with a size of 3.0-3.5nm were uniformly dispersed on the skeletons of 3DOM Mn2O3. The 5.8Au/3DOM Mn2O3 sample performed the best, giving the T90% (the temperature required for a conversion of 90%) of -15°C at space velocity (SV)=20,000mL/(gh) for CO oxidation and 244°C at SV=40,000mL/(gh) for toluene oxidation. The apparent activation energies (30 and 54kJ/mol) over 5.8Au/3DOM Mn2O3 were much lower than those (80 and 95kJ/mol) over 3DOM Mn2O3 for CO and toluene oxidation, respectively. The effects of SV, water vapor, CO2, and SO2 on catalytic activity were also examined. It is concluded that the excellent catalytic performance of 5.8Au/3DOM Mn2O3 was associated with its high oxygen adspecies concentration, good low-temperature reducibility, and strong interaction between Au NPs and 3DOM Mn2O3 as well as high-quality porous architecture.

Au/3DOM Co3O4: highly active nanocatalysts for the oxidation of carbon monoxide and toluene

Three-dimensionally ordered macroporous Co3O4 (3DOM Co3O4) and its supported gold (xAu/3DOM Co3O4, x = 1.1-8.4 wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Co3O4 and xAu/3DOM Co3O4 samples exhibited a surface area of 22-27 m(2) g(-1). The Au nanoparticles with a size of 2.4-3.7 nm were uniformly deposited on the macropore walls of 3DOM Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO and toluene oxidation. Among 3DOM Co3O4 and xAu/3DOM Co3O4, the 6.5Au/3DOM Co3O4 sample performed the best, giving a T90% (the temperature required for achieving a conversion of 90%) of -35 °C at a space velocity of 20 000 mL g(-1) h(-1) for CO oxidation and 256 °C at a space velocity of 40 000 mL g(-1) h(-1) for toluene oxidation. The effect of water vapor was more significant in toluene oxidation than in CO oxidation. The apparent activation energies (26 and 74 kJ mol(-1)) over 6.5Au/3DOM Co3O4 were lower than those (34 and 113 kJ mol(-1)) over 3DOM Co3O4 for CO and toluene oxidation, respectively. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and 3DOM Co3O4 were responsible for the excellent catalytic performance of 6.5Au/3DOM Co3O4.