Novel monolithic catalysts for VOCs removal: A review on preparation, carrier and energy supply

Efficient photocatalytic NO removal with inhibited NO2 formation and catalyst loss over sponge-supported and functionalized g-C3N4

Though photocatalytic purification of NO has been widely studied, how to avoid secondary pollution during gas-solid reaction is still a challenge, especially in inhibiting the formation of toxic intermediates (NO2) and avoiding the blow away of powdery photocatalyst. Herein, we proposed a one-step solvothermal method to prepare melamine sponge (MS) supported and functionalized g-C3N4 (CN), which simultaneously realizes the inhibition of NO2 formation and catalyst loss. Sodium hydroxide, which plays a dual role, has been introduced during the preparation of supported photocatalyst. Specifically, sodium atom, as the modifier of performance, could facilitate the randomly distributed charge of pristine CN to be converged, which accelerates the adsorption/activation of reactants for efficient and deep NO oxidation. Hydroxyl group, as the binder between CN and MS, induces the interaction by forming hydrogen bonds, which contributes to the firm immobilization of powdery photocatalyst. The supported sample exhibits outstanding NO removal rate (58.90%) and extremely low NO2 generation rate (1.41%), and the mass loss rate of photocatalyst before and after reaction is less than 1%. The promotion mechanism of performance also has been elaborated. This work takes environmental risks as a prerequisite to propose a feasible strategy for perfecting the practical application of photocatalytic technology.

Catalytic Oxidation of Acetone on SmMn2O5: Effect of Acid Etching and Loading Treatment

The key of catalytic oxidation technology is to develop a stable catalyst with high activity. It is still a serious challenge to achieve high conversion efficiency of acetone with an integral catalyst at low temperature. In this study, the SmMn₂O₅ catalyst after acid etching was used as the support, and the manganese mullite composite catalyst was prepared by loading Ag and CeO₂ nanoparticles on its surface. By means of SEM, TEM, XRD, N₂-BET, XPS, EPR, H₂-TPR, O₂-TPD, NH₃-TPD, DRIFT, and other characterization methods, the related factors and mechanism analysis of acetone degradation activity of the composite catalyst were discussed. Among them, the CeO₂-SmMn₂O₅-H catalyst has the best catalytic activity at 123 and 185 °C for T₅₀ and T₁₀₀, respectively, and shows excellent water and thermal resistance and stability. In essence, the surface and lattice defects of highly exposed Mn sites were formed by acid etching, and the dispersibility of Ag and CeO₂ nanoparticles was optimized. Highly dispersed Ag and CeO₂ nanoparticles have a highly synergistic effect with the support SmMn₂O₅, and the reactive oxygen species provided by CeO₂ and the electron transfer brought by Ag further promote the decomposition of acetone on the carrier SMO-H. In the field of catalytic degradation of acetone, a new catalyst modification method of high-quality active noble metals and transition metal oxides supported by acid-etched SmMn₂O₅ has been developed.

Redox-Induced In Situ Growth of MnO2 with Rich Oxygen Vacancies over Monolithic Copper Foam for Boosting Toluene Combustion

Catalytic combustion has been known to be an effective technique in volatile organic compound (VOC) abatement. Developing monolithic catalysts with high activity at low temperatures is vital yet challenging in industrial applications. Herein, monolithic MnO₂-O_v/CF catalysts were fabricated via the in situ growth of K₂CuFe(CN)₆ (CuFePBA, a family of metal-organic frames) over copper foam (CF) followed by a redox-etching route. The as-synthesized monolith MnO₂-O_v-0.04/CF catalyst displays a superior low-temperature activity (T_90% = 215 °C) and robust durability for toluene elimination even in the presence of 5 vol % water. Experimental results reveal that the CuFePBA template not only guides the in situ growth of δ-MnO₂ with high loading over CF but also acts as a source of dopant to create more oxygen vacancies and weaken the strength of the Mn-O bond, which considerably improves the oxygen activation ability of δ-MnO₂ and consequently boosts the low-temperature catalytic activity of the monolith MnO₂-O_v-0.04/CF toward toluene oxidation. In addition, the reaction intermediate and proposed mechanism in the MnO₂-O_v-0.04/CF mediated catalytic oxidation process were investigated. This study provides new insights into the development of highly active monolithic catalysts for the low-temperature oxidation of VOCs.

Co/SBA-16 coating supported on a 3D-printed ceramic monolith for peroxymonosulfate-activated degradation of Levofloxacin

This study reports a simple method for anchoring dispersed Co nanoparticles on SBA-16 mesoporous molecular sieve coating grown on the 3D-printed ceramic monolith (i.e., Co@SBA-16/ceramic). The monolithic ceramic carriers with a designable versatile geometric channel could improve the fluid flow and mass transfer but exhibited a smaller surface area and porosity. The SBA-16 mesoporous molecular sieve coating was loaded onto the surface of the monolithic carriers using a simple hydrothermal crystallization strategy, which can increase the surface area of the monolithic carriers and facilitate the loading of active metal sites. In contrast to the conventional impregnation loading method (Co-AG@SBA-16/ceramic), dispersed Co₃O₄ nanoparticles were obtained by directly introducing Co salts into the as-made SBA-16 coating (containing a template), accompanied by conversion of the Co precursor and removal of the template after calcination. These promoted catalysts were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller theory, and X-ray photoelectron spectroscopy. The developed Co@SBA-16/ceramic catalysts exhibited excellent catalytic performance for the continuous removal of levofloxacin (LVF) in fixed bed reactors. Co/MC@NC-900 catalyst exhibited a ∼ 78% degradation efficiency in 180 min compared to that of Co-AG@SBA-16/ceramic (17%) and Co/ceramic (0.7%). The improved catalytic activity and reusability of Co@SBA-16/ceramic was because of the better dispersion of the active site within the molecular sieve coating. Co@SBA-16/ceramic-1 exhibits much better catalytic activity, reusability and long-term stability than Co-AG@SBA-16/ceramic. After a 720 min continuous reaction, the LVF removal efficiency of Co@SBA-16/ceramic-1 in a 2 cm fixed-bed reactor was stable at 55%. Using chemical quenching experiments, electron paramagnetic resonance spectroscopy, and liquid chromatography-mass spectrometry, the possible LVF degradation mechanism and degradation pathways were proposed. This study provides novel PMS monolithic catalysts for the continuous and efficient degradation of organic pollutants.