A series of CeaMnOx hollow microsphere like arbutus with hierarchical structure are prepared by redox co-precipitation method and applied for catalytic toluene combustion. The Ce0.03MnOx shows a better catalytic performance for toluene combustion with high stability, water resistance, even under the condition of 5vol.% H2O. The results of XRF, XRD, Raman, N2 adsorption-desorption, SEM, TEM prove that the doping of Ce can affect the structure of CeaMnOx such as much smaller particle size and higher specific surface area. The characterizations of H2-TPR, O2-TPD, XPS certify the strong interaction between Ce and Mn oxides that leads to more surface adsorbed oxygen and Mn4+ species due to oxidation reduction cycle of Mn3+ + Ce4+ ↔ Mn4+ + Ce3+ after Ce addition. Meanwhile, the Toluene-TPD in different conditions confirms the introduction of water promoted the catalytic oxidation of toluene. In situ DRIFTS is used to investigate the reaction process of toluene oxidation. And the results reveal that the Ce0.03MnOx catalyst has much stronger ability to adsorb and activate toluene compared with MnOx catalyst, especially under with H2O. That may be the main reason that the Ce0.03MnOx catalyst exhibits the special catalytic activity for toluene combustion.

Synthesis of CeaMnOx hollow microsphere with hierarchical structure and its excellent catalytic performance for toluene combustion

Herein, a series of rod-like MnCeOx are synthesized by pyrolyzing Mn/Ce-BTC for toluene oxidation. The 3Mn2Ce catalyst exhibits superior catalytic performance and stability under high humidity (10 % H2O). XRD, Raman, H2-TPR, O2-TPD, XPS and EXAFS results confirm that the formation of solid solution between Ce and Mn species and better reducibility play a key role in toluene oxidation. H2O-TPD, toluene-TPD, toluene-TPSR, in situ DRIFTS in different conditions and TD-GC–MS confirm that the introduction of water can promote toluene mineralization. H2O-TPD indicates that oxygen vacancies adsorbed H2O to provide HOH active sites and promote the conversion of Oads to Olatt. The degradation pathway of toluene was toluene→benzaldehyde→benzoate→CO2 and H2O. Additionally, the water promotion is also confirmed by DFT calculations. The promotion of water vapor is that the water vapor is conducive to the adsorption of toluene, benzaldehyde and oxygen, and promotes the activation of oxygen.

The promoting effect of H2O on rod-like MnCeOx derived from MOFs for toluene oxidation: A combined experimental and theoretical investigation

Catalytic combustion technology is one of the effective methods to remove VOCs such as toluene from industrial emissions. The decomposition of an aromatic ring via catalyst oxygen vacancies is usually the rate-determining step of toluene oxidation into CO2. Series of CeO2 probe models were synthesized with different ratios of surface-to-bulk oxygen vacancies. Besides the devotion of the surface vacancies, a part of the bulk vacancies promotes the redox property of CeO2 in toluene catalytic combustion: surface vacancies tend to adsorb and activate gaseous O2 to form adsorbed oxygen species, whereas bulk vacancies improve the mobility and activity of lattice oxygen species via their transmission effect. Adsorbed oxygen mainly participates in the chemical adsorption and partial oxidation of toluene (mostly to phenolate). With the elevated temperatures, lattice oxygen of the catalysts facilitates the decomposition of aromatic rings and further improves the oxidation of toluene to CO2.

Roles of Oxygen Vacancies in the Bulk and Surface of CeO2 for Toluene Catalytic Combustion

Carbon deposit during the catalytic oxidation of volatile organic compounds (VOCs) is a key factor to restrict long-term stability of catalysts. Herein, a modified ordered porous catalyst with high coke-resistance performance was developed by introducing oxygen vacancies (OVs) into CeO2 through simple redox and steam treatment (ARCeO2), and applied in efficiently photothermocatalytic degradation of VOCs. Abundant OVs in ARCeO2 leads to enhanced light absorption, improved charge separation and increased reactive oxygen generation, and then promote its photothermocatalytic performance. Moreover, no obvious decrease was observed in the photothermocatalytic activity of ARCeO2 at 200 °C for 25 h reaction. Its superior photothermocatalytic stability can be attributed to the less intermediates and limited coke accumulation onto ARCeO2. This work provides a facile and cost-effective strategy for the design and fabrication of CeO2 catalyst with strong coke-resistance potential and highlights the significance of OVs engineering for improving the photothermocatalytic performance of VOCs degradation.

Introduce oxygen vacancies into CeO2 catalyst for enhanced coke resistance during photothermocatalytic oxidation of typical VOCs

The crystalline phase of manganese dioxide catalysts shows strong influence on its catalytic performance, and the construction of hierarchically nanostructured materials with active interface and oxygen vacancy is an effective approach to develop the enhanced functionality. Herein, nanosized MnO 2 catalysts with α-, β- and hierarchically α@β-crystal phases were synthesized. α@β-MnO 2 catalysts showed the excellent activity than pure MnO 2 in toluene combustion, either α-MnO 2 or β-MnO 2. The catalytic activity was strongly related with the ratio of α-MnO 2 and β-MnO 2 in α@β-MnO 2 catalyst, and α@β-MnO 2 (1:1) exhibited the highest activity for toluene oxidation and toluene can be completely oxidized to CO 2 and H 2 O at about 205 °C with a space velocity (GSHV) of 30,000 h −1 . HRTEM, Raman and XPS demonstrated that α@β-MnO 2 owned the abundant defects due to the mixed phase interfacial structure. The strong synergistic effect in α@β-MnO 2 catalyst with larger specific area enhanced and facilitated the adsorption and activation of toluene molecules and oxygen species. The mobility of oxygen species and low-temperature reducibility compared with pure MnO 2 were significantly enhanced. When the ratio of α-MnO 2 and β-MnO 2 was 1:1, α@β-MnO 2 reached the maximum biphase interface content, formed large amount of oxygen vacancy, and showed the strongest synergistic effect and activation ability for reactants. Thus it was thought that the formation of the special biphase structure of α@β-MnO 2 was beneficial to the improvement of toluene catalytic oxidation activity.

Superior performance of α@β-MnO2 for the toluene oxidation: Active interface and oxygen vacancy

Surface species and oxygen vacancies were studied in MnO x (0.4)-CeO 2 toward repeated soot oxidation. MnO x (0.4)-CeO 2 catalysts prepared by the citric acid complex method were repeatedly used in a 10% O 2 /Ar gas flow and showed favorable activity and satisfactory durability toward soot oxidation. X-ray diffraction (XRD), N 2 adsorption/desorption, Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and in situ visible/UV Raman characterization methods were utilized to investigate the structural features of fresh and reused catalysts. The irreversible conversion of high valence manganese species as well as the reduction of Frenkel-type oxygen vacancies and lattice oxygen could be clearly observed in the reused samples, which were associated with the slight deactivation. Spectators and participators were two existing forms of Frenkel-type oxygen vacancies. It was noteworthy that the participators almost fully regenerated after each reaction cycle, which ensured the ability to activate O latt in repeated soot oxidation process. Therefore, the catalysts maintained favorable activity and satisfactory durability, which was mainly because the relatively stable level of participators.

The key surface species and oxygen vacancies in MnOx(0.4)-CeO2 toward repeated soot oxidation

Enhanced oxygen vacancies to improve ethyl acetate oxidation over MnOx-CeO2 catalyst derived from MOF template

3D geometric modeling analysis of contact probability effect in carbon black oxidation over MnOx-CeO2 catalysts

A series of CeO2–MnOX catalysts with different Ce contents was prepared using Mn–BTC MOF as a sacrificial template for toluene oxidation. Interestingly, the performance of CeO2–MnOX increased rapidly only when the Ce content lower than 5%. The 1%-, 3%- and 10%-Ce-content samples exhibited the T90 value of 325 °C, 291 °C and 277 °C, respectively. XRD shows that the catalyst phase changes significantly before (Mn3O4 only) and after (Mn2O3, Mn3O4 and CeO2) 3% Ce loading. All other results indicated that the Ce–Mn interface properties of different Ce content composite oxides was quite distinguishable in terms of removal and energy efficiency. XRD and XPS results further showed that there a Ce monolayer dispersion threshold existed on the interface of MnOX (3.2 wt%, confirmed by XPS), which caused the difference in performance increment. The dispersed Ce could be divided into a monolayer dispersion state (1–3%) and a crystalline phase state (>3%), according to the existence form, which corresponded to the significant and minor enhancements of toluene conversion rate. Importantly, the Ce in monolayer dispersion state obviously improved the redox properties of catalysts interface, while the Ce in crystal state not. The interfaces with monolayer dispersion Ce result in more abundant metal ion states, oxygen vacancies, better electron transfer performance and catalytic activity.

Interfaces in MOF-Derived CeO2–MnOX Composites as High-Activity Catalysts for Toluene Oxidation: Monolayer Dispersion Threshold

The invention discloses a controllable circular concentration paint spraying waste gas treatment system The controllable circular concentration paint spraying waste gas treatment system comprises a paint spraying chamber, a painting mist filtering assembly, a waste gas purification assembly, a waste gas circular assembly and a testing and automatic control system assembly The painting mist filtering assembly is used for removing particles such as painting mist in the paint spraying waste gas pumped out of the paint spraying chamber; the waste gas purification assembly is used for purifying and discharging organic waste gas filtered through the painting mist filtering assembly; the waste gas circular assembly is used for receiving the waste gas at an outlet of the painting mist filtering assembly and sending the waste gas back to the paint spraying chamber; and the testing and automatic control system assembly is used for testing the painting mist concentration and the blast capacity of the outlet of the painting mist filtering assembly and selectively starting or stopping a draught fan of the waste gas circular assembly and opening or closing a valve of the waste gas circular assembly or reminding an operator according to a set value According to the controllable circular concentration paint spraying waste gas treatment system, through a testing and automatic control system, energy consumption of a waste gas treatment technology can be reduced, the operating cost is reduced, safety in the waste gas treatment process is improved, and paint spraying waste gas is practically and effectively treated

Jingheng Gao

Papers

The key surface species and oxygen vacancies in MnOx(0.4)-CeO2 toward repeated soot oxidation

Enhanced oxygen vacancies to improve ethyl acetate oxidation over MnOx-CeO2 catalyst derived from MOF template

3D geometric modeling analysis of contact probability effect in carbon black oxidation over MnOx-CeO2 catalysts

Interfaces in MOF-Derived CeO2–MnOX Composites as High-Activity Catalysts for Toluene Oxidation: Monolayer Dispersion Threshold

Controllable circular concentration paint spraying waste gas treatment system