Fukun Bi

This review summarizes how various modification methods regulate ZSM-5 catalysts for oxidizing VOCs, NO _x , CO and flue gas pollutants. It links acidity, pore structure, redox sites and reaction conditions with activity, stability and deactivation.

Selective CO₂ hydrogenation over Ni-based catalysts requires control of the competing reverse water–gas shift (RWGS) and methanation pathways. Here, γ-Al₂O₃-supported Ni catalysts with nominal loadings of 5, 10, 15 and 20 wt% were prepared by wet impregnation. Structural, textural, reduction and surface analyses showed that Ni loading altered NiO crystallinity, pore accessibility, reducibility and the fitted surface Ni-state distribution. The 10%Ni/γ-Al₂O₃ catalyst reached 55% CO₂ conversion, approximately 90% CO selectivity and a CO production rate of 147.2 mmol CO·g_cat⁻¹·h⁻¹ at 600 °C. Increasing the H₂/CO₂ ratio from 1 to 4 at 500 °C raised conversion from 46% to 65% but decreased CO selectivity from 88% to 76%. The catalyst also maintained a nearly constant response during a 24 h time-on-stream test at 500 °C. In situ DRIFTS detected bicarbonate-, formate- and adsorbed-CO-related species, consistent with the participation of oxygenated intermediates in RWGS. Together, these results establish an internally controlled loading–structure–performance relationship and identify 10%Ni/γ-Al₂O₃ as providing the most favorable conversion–selectivity–productivity balance within the investigated series.

The development of highly efficient catalysts is important for the photothermal catalytic oxidation of volatile organic compounds (VOCs). Herein, MIL-100(Fe) was used as the sacrificial template to prepare MnFeO_x catalysts with different Mn contents through the impregnation–calcination method, and their performance in photothermal catalytic oxidation of toluene was investigated. The results show that the content of Mn significantly affects the crystal phase structure, pore properties, surface chemical state, and optical response of the catalyst. Among them, 30%MnFeO_x exhibits the best photothermal catalytic activity, with T₅₀ and T₉₀ being 211 and 237 °C, respectively, which are significantly lower than those of FeO_x (232 and 260 °C). Characterization results suggested that the introduction of Mn caused the bandgap of FeO_x to decrease from 1.96 to 1.67 eV. Meanwhile, the surface Fe²⁺, adsorbed oxygen (O_ads) species, and oxygen vacancies were increased, enhancing visible light absorption and gaseous oxygen species adsorption and activation, which promoted the photothermal catalytic oxidation of toluene. Additionally, the 30%MnFeO_x catalyst presented good thermal stability and water resistance. Furthermore, during the reaction process, the in situ activation of the catalyst’s surface induced the increase in surface Fe²⁺, Mn^3+, and O_ads species, which enhances the photothermal catalytic activity of the catalyst. Importantly, the in situ DRIFTS results further indicate that toluene is mainly oxidized along the path of toluene → benzyl alcohol → benzoate → maleic anhydride → CO₂ and H₂O. This work provides a theoretical basis for the construction of low-cost, non-precious-metal Mn–Fe-based photothermal catalysts.

MOF-based catalysts integrate high surface area, tunable structures, abundant active sites, low-temperature activity, and stability, enabling efficient thermocatalytic, photocatalytic, and photothermal VOC removal.

In this work, a series of defective Co₃O₄ catalysts (Al@Co₃O₄₋x, x = 4, 6, 8 mmol/L, representing the NaOH concentration) were prepared by Al doping and NaOH etching via hydrothermal method for ethyl acetate degradation. The results indicated that the Al@Co₃O₄-6 catalyst presented the optimal catalytic performance for ethyl acetate degradation (T₉₀ = 207 °C). The results of many characterizations, such as X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectra, Raman, and temperature-programmed H₂ reduction (H₂-TPR), etc., showed that the Al doping and NaOH etching induced the production of defects and oxygen vacancies in the catalyst, improved the surface area, boosted the low-temperature reducibility, and promoted the low-temperature oxygen species desorption, which enhanced ethyl acetate oxidation over Al@Co₃O₄-6. Importantly, the possible ethyl acetate degradation pathway was revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in the sense that the adsorbed ethyl acetate was gradually oxidized to ethanol and acetaldehyde, acetic acid, formate, and finally to CO₂ and H₂O.

The design of efficient catalysts is vital for the application of catalytic oxidation technology in the removal of gaseous pollutants. Herein, a series of MnO_x catalysts with the typical Mn₂O₃ crystal structure was synthesized via the high-temperature pyrolysis method by using Mn-based metal–organic frameworks (Mn-MOFs) with various morphologies as the precursors. The physicochemical properties of these Mn-MOF-derived MnO_x samples were investigated by various characterization techniques, including X-ray diffraction (XRD), thermogravimetry (TG), N₂ adsorption–desorption, scanning electron microscope (SEM), and H₂ temperature-programmed reduction (H₂-TPR), and their catalytic activity was evaluated for catalytic CO degradation. The results showed that the Mn-MOF with leaf-like morphology, derived MnO_x-Leaf, presented the optimal catalytic CO oxidation performance (T₉₈ = 214 °C), stability, and reusability. Characterization results showed that the different Mn-MOF-derived MnO_x catalysts possessed different physical–chemical properties. The superior catalytic activity of MnO_x-Leaf for CO degradation was ascribed to its large surface area and pore size, better low-temperature redox properties, and high H₂ consumption, which promoted the adsorption and activation of the CO and gaseous oxygen molecules, improving CO oxidation. Finally, the possible CO degradation pathway was evaluated by in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), which showed that gaseous CO and O₂ were adsorbed on the surface of the catalyst and oxidized to form surface carbon-related species (bicarbonate and carbonate), and finally converted to CO₂.

Photothermal catalysis has emerged as a promising approach for the efficient and cost-effective removal of volatile organic compounds (VOCs). Pt@MnO₂ catalysts have demonstrated excellent performance in the photothermal catalytic oxidation of VOCs. However, current research has predominantly focused on the interaction between Pt and MnO₂, while often overlooking the influence of the MnO₂ crystal phase. Therefore, in this study, we synthesized Pt supported on four crystal phases (α, β, γ, and δ) of MnO₂ and established the structure–activity relationships through performance evaluation and characterization. Among the prepared catalysts, Pt@Mn[δ] exhibited excellent performance and possessed outstanding stability. Crystal structure characterization revealed that the larger specific surface area and lower crystallinity of Pt@Mn[δ] exposed more active sites. XPS analysis indicated the transformation of Mn⁴⁺ to Mn³⁺ on Pt@Mn[δ], leading to the formation of oxygen vacancies. O₂-TPD and H₂-TPR further confirmed the activation of lattice oxygen and the promoted redox cycle of Pt@Mn[δ]. UV-Vis DRS and electrochemical measurements demonstrated that Pt@Mn[δ] exhibited the most pronounced visible-light absorption, the highest photocurrent density, the lowest charge transfer resistance and superior charge carrier mobility. TD-GC-MS analysis indicated that o-xylene underwent alkylation and isomerization, with subsequent oxidation following the Mars–van Krevelen (MvK) mechanism.

A series of Ce-doped α-MnO₂ catalysts (Ce_XMn_1−XO₂, x = 0.04, 0.07, 0.10) were synthesized by a simple in situ hydrothermal method. It was confirmed by characterization methods such as XRD, Raman, N₂ adsorption–desorption and SEM confirmed that the introduction of Ce significantly regulated the microstructure of α-MnO₂, specifically manifested as the reduction in grain size, the increase in defect sites, the increase in Mn-O bond length and altered morphological structure. H₂-TPR, O₂-TPD and XPS analyses further revealed the strong interaction between Mn and Ce, accompanied by significant electron transfer (Ce³⁺ + Mn⁴⁺ → Ce⁴⁺ + Mn³⁺), thereby promoting the formation of Mn³⁺ species. In the test of toluene catalytic oxidation performance, C_e0.07Mn_0.93O₂ exhibited the most excellent catalytic activity (T₁₀₀ = 280 °C), while also having good thermal stability and water resistance. Furthermore, the degradation pathways of toluene were analyzed by TD-GC-MS technology: Toluene → Benzene → Benzaldehyde → Maleic anhydride → CO₂ and H₂O.

Volatile organic compounds (VOCs) emitted from industry processes are often accompanied by the discharge of impurity gases, which would affect the active sites and further pose great influence on the catalytic performance, even inducing toxic byproduct formation, bringing more serious threat to human health and the ecological environment. Furthermore, VOCs degradation byproducts would be changed with the alteration of catalysts, especially metal-organic frameworks (MOFs)-based catalysts, over which various degradation byproducts could be generated due to the precursor residual. Herein, an acid-modified Zr-MOF, UiO-67, supported Pd catalyst was synthesized and optimized as an example to explore the influence mechanism of impurity gases (H₂O and CO) on o-xylene degradation intermediates. It was found that the impurity gases had a great influence on the generation of Cl-containing byproducts, which formed due to the presence of residual Cl in the frameworks. Meanwhile, the influence mechanism was experimentally and theoretically studied. It was revealed that the introduction of H₂O weakened the formation of energy barriers for Cl-containing byproduct generation, resulting in the spontaneous generation of Cl-containing byproducts. Conversely, the addition of CO improved the energy barrier of the Cl-containing byproduct formation rate-determined step, chlorine addition reaction (*C₆H₃CH₃CH₃ + Cl → *C₆H₃ClCH₃CH₃, *C₆H₄CH₃CH₂ + Cl → *C₆H₄CH₃CH₂Cl), inhibiting Cl-containing byproducts formation. This study may provide guidance for the application of MOFs-based catalysts for VOCs elimination in actual discharge conditions.

The regulation of the active sites of a catalyst is important for its application. Herein, a series of Ag₁Cu_x/SBA-15 catalysts with different molar ratios of Ag to Cu were synthesized via the impregnation method, and the active sites of Ag₁Cu_x were regulated via various pretreatment conditions. These as-prepared Ag₁Cu_x/SBA-15 catalysts were characterized by many technologies, and their catalytic performance was estimated through CO catalytic oxidation. Among these catalysts, Ag₁Cu_0.025/SBA-15, with a Ag/Cu molar ratio of 1:0.025 and pretreated under the condition of 500 °C O₂/Ar for 2 h, followed by 300 °C H₂ for another 2 h, presented optimal CO degradation performance, which could realize the oxidation of 98% CO at 34 °C (T₉₈ = 34 °C). Meanwhile, Ag₁Cu_0.025/SBA-15 also displayed great reusability. Characterization results, such as X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance spectra (UV-vis DRS), temperature-programmed H₂ reduction (H₂-TPR), and physical adsorption, suggested that the optimal catalytic performance of Ag₁Cu_0.025/SBA-15 was ascribed to its high interspersion of Ag nanoparticles, better low-temperature reduction ability, the interaction between Ag and Cu, and its high surface area and large pore volume. This study provides guidance for the regulation of active sites for low-temperature catalytic degradation.