In this paper, three kinds of HZSM-5-supported transition metal (Cr, Fe, and Cu) oxide catalysts were prepared by the wet impregnation method, and their stability performances for catalytic combustion of dichloromethane (DCM) were investigated. Different behaviors were observed for these three catalysts during a 300 min catalytic reaction running at 320 °C. It was found that the Cr–O/HZSM-5 catalyst showed good catalytic stability, while both Fe–O/HZSM-5 and Cu–O/HZSM-5 suffered obvious deactivation. Characterizations using XRD, BET, XPS, O2-TG, O2-TP-MS, NH3–IR, and temperature-programmed surface reaction (TPSR) techniques were then carried out to disclose the deactivation mechanisms. The results revealed that the main cause of the deactivation over the Fe–O/HZSM-5 catalyst was coke formation, which could be mainly attributed to its lower deep oxidation capacity of the intermediate products, i.e., the methoxy groups, and it could also be obtained that the Cu–O/HZSM-5 catalyst was severely poisoned by chlorine species owing to the formation of stable Cu(OH)Cl species. Based on the results above, it could be concluded that the close proximity and synergy between acidic sites and active oxygen species were crucial to avoid coke deposition during the chlorinated volatile organic compound catalytic oxidation process.

In this paper, a sol–gel made Ce–O–P catalyst (referred to as Ce–O–P-SG) was employed for selective catalytic reduction (SCR) of NOx with NH3, which was directly compared with two other Ce–O–P samples as synthesized via hydrothermal and coprecipitation routes (referred to as Ce–O–P-HT and Ce–O–P-CP, respectively). Experimental results revealed that the Ce–O–P-SG catalyst yielded a more than 90% NO conversion at 200 °C in the presence of 10 vol % H2O, whereas Ce–O–P-HT and Ce–O–P-CP catalysts only showed 50% and 20% NO conversions under the same conditions, respectively. After subjected to a series of characterization technologies (e.g., XRD, BET-BJH, XPS, NH3-TPD, py-IR, and H2-TPR), it was found that more enriched surface Ce(4+) species were formed except for the two main CePO4 phases (monazite and rhabdophane phases) of the Ce–O–P-SG catalyst compared to the other two samples, resulting in the increase of surficial active oxygen ions content. This could lead to an enhancement in surface acidity and redox capacity of the Ce–O–P-SG catalyst, effectively promoting the NH3–SCR activity of the catalyst. Further analyses on SO2 and H2O tolerance revealed that the Ce–O–P-SG possessed a higher sulfur resistance than the other two samples, which could be attributed to the SO2 trapping effect by the abundant active oxygen species over Ce–O–P-SG catalyst.

The effects of four oxidation inhibitors (including ascorbic acid, formaldehyde, hydroquinone, and sodium thiosulfate) on mercury re-emission in simulated magnesium-based wet flue gas desulfurization solution were evaluated. Experimental results demonstrated that the addition of ascorbic acid significantly increased the mercury re-emission, whereas the formaldehyde and hydroquinone could slightly enhance this process at pH 6. Sodium thiosulfate was found to somewhat inhibit the bivalent mercury reduction owing to the strong binding between mercury and thiosulfate ions. pH variation showed dramatic effects on elemental mercury re-emission in the solution containing ascorbic acid or hydroquinone, and the mercury emission amount in 30 min increased about seven- and two-fold, respectively, when pH was adjusted from 6 to 8. These findings indicated that the ascorbic acid was an important reducer of mercury re-emission under acidic condition besides the sulfite ions, whereas it was the main reducer of mercury reduction under alkaline condition. In addition, the investigation on the effects of temperature and the presence of Cl– ions suggested that the mercury re-emission would be accelerated at elevated temperatures and could be suppressed in the presence of Cl– ions.

CePO4 catalyst (termed Ce–P–O) was for the first time employed to capture elemental mercury (Hg0) under simulated coal-fired flue gas conditions. As compared with commercial SCR catalyst (i.e., V–W–Ti), the Ce–P–O catalyst showed a much better performance in Hg0 removal. The high Hg0 adsorption capacity, abundant active oxygen species, and excellent SO2 poisoning resistance account for the performance of the Ce–P–O catalyst. When the catalyst was subjected to individual flue gas component conditions, it was found that the presence of NO can significantly improve the Hg0 removal efficiency over the Ce–P–O catalyst; however, HCl did not show promotion effect. It is proposed that the former occurs because the generated NO2 (originated from NO oxidation) could react with Hg0 ad-species (e.g., Hg2O), regenerating the HgO and hence enhancing the Hg0 chemisorption. The latter was found to be due to the absence of the Deacon reaction over the catalyst.

Cl species transformation and deactivation effects on ceria (111) model catalysts were investigated in the first-principles framework. Conventionally, the strong adsorption of Cl atom in the oxygen vacancy of ceria was believed to be the dominant deactivation factor. However, under the typical conditions of chlorinated volatile organic compounds (CVOCs) catalytic combustion, the deactivation was found to be hindered because of the high O2/Cl ratio in the reactants’ feed. Then, the possible formation pathways of Cl2 and HCl during CVOCs catalytic abatement reaction were proposed. It was identified that the H-bond interaction between surface hydroxyls and Cl species was the key factor to control the selectivity in the final product of Cl species (HCl or Cl2). By introduction of H2O or other H resources, the coverage of surface OH radicals could be increased, which in turn benefits the conversion to HCl over Cl2. However, the competitive adsorption between H2O and oxygen on vacancy would lead to somewhat of a loss of low-temperature catalytic activity.

•Both thiocyanate and sulfide ions would have inhibiting effects on mercury re-emission.•The inhibition by thiocyanate ions was due to the formation of HgSO3SCN− and HgSCNX−(X–2).•Different inhibition mechanism by sulfide ions existed under acidic or alkaline conditions.•The inhibition effect of mercury reduction by sulfide ions was enhanced at high pH value.In this paper, elemental mercury (Hg0) re-emissions from simulated wet flue gas desulfurization (WFGD) solutions were evaluated in the presence of thiocyanate ions (SCN−) or sulfide ions (S2− and HS−). Experimental results revealed that both thiocyanate ions and sulfide ions could inhibit the reduction of oxidized mercury to Hg0. The inhibition effect of SCN− was mainly attributed to the formation of HgSO3SCN− and HgSCNX−(X–2) (X = 2–4). It was found that the mercury reduction process in the presence of sulfide ions followed different mechanism under acidic or alkaline condition, though the formation of stable HgS could be ascribed to the main inhibition reason. Under acidic condition, the bivalent mercury ions may not directly combine with sulfide ions to form HgS. This had led to a weaker inhibition effect under the acidic condition compared to that under alkaline condition.

One-step synthesized sulfonic-acid-functionalized SBA-15 (denoted as αSSBA-15) impregnated with polyethyleneimine (PEI) was used for CO2 capture in this study. The resulted sorbents were characterized via a range of analytical techniques, including transmission electron microscopy (TEM), 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR), infrared (IR), thermogravimetry–differential scanning calorimetry (TG–DSC), etc. Experimental results showed that the incorporation of propanesulfonic acid groups into the inner structure of the silica support had brought dramatic improvement in CO2 adsorption capacity, of which PEI/5SSBA-15 showed the highest CO2 adsorption amount. The main reason of this increased capacity could be attributed to the enhanced CO2 diffusion into bulk networks of PEI polymers because of its better dispersion in the pores of support, where the extended propanesulfonic acid groups on the inner surface could spatially disperse the subsequent loaded PEI molecules. Furthermore, the PEI/5SSBA-15 also exhibited superior stable cyclic adsorption/desorption performance compared to PEI/SBA-15, especially after 5 cycles. This was assumed because the enhanced surface acidity of PEI/5SSBA-15 anchored the NH2/NH groups through acid–base interaction, reducing the loss of active sites.

In this paper, we investigated the primary reduction and oxygen replenishing processes over Mn substitutionally doped CeO2(111) surfaces by density functional theory with the on-site Coulomb correction (DFT + U). The results indicated that Mn doping could make the surface much more reducible and the adsorbed O2 could be effectively activated to form superoxo (O2−) and/or peroxo species (O22−). The Mn doping induced the Mn 3d–O 2p gap state instead of Ce 4f acting as an electrons acceptor and donor during the first oxygen vacancy formation and O2 replenishing, which helped to lower the formation energy of the first and second oxygen vacancies to −0.46 eV and 1.40 eV, respectively. In contrast, the formation energy of a single oxygen vacancy in the pure ceria surface was 2.08 eV and only peroxo species were identified as the O2 molecule adsorbed. Our work provides a theoretical and electronic insight into the catalytic redox processes of Mn doped ceria surfaces, which may help to understand the enhanced catalytic performances of MnOx–CeO2 oxides, as reported in previous experimental works.

In this paper, protonated titanate nanotubes (PTNTs) were modified with polyethyleneimine (PEI) by wet impregnation method for CO2 adsorption. Their micro-morphology and structural properties were characterized by a range of analytical techniques, including XRD, TEM, SEM, N2 adsorption etc. Experimental results revealed that the functionalized PTNTs with 50 wt.% PEI loaded exhibited a high CO2 adsorption capacity of 130.8 mg/g-sorbent at 100 °C. Only a minor loss of its capacity was observed after five consecutive adsorption–desorption runs. The PEI was existed both in the internal and external mesoporous pores of PTNTs via chemical combination between amino group and enriched protons, which accounted for their good thermal stability at elevated temperatures. The results present herein imply that the PEI modified PTNTs could be appealing materials for capturing CO2 from power plant flue gas.Graphical abstractHighlights► Novel PEI modified PTNTs materials were proposed for adsorption of CO2. ► PEI–PTNTs showed superior CO2 adsorption capacity of around 130 mg/g at ∼100 °C. ► PEI–PTNTs also exhibited better thermal stability compared with PEI–MCM-41. ► The well thermal stability corresponded to the interactions between PEI and PTNTs.

Six transition metal oxides were added in ceria-modified titania using a sol-gel method for catalytic oxidation of toluene. An MnOx based catalyst was found to be the most active one, with which toluene could be decomposed completely at 200 °C. The greatest Mn/Ti and molar ratio of the mobile oxygen to the total oxygen concentration, together with a large surface area and a low reduction peak-starting temperature, would result in its best activity in toluene oxidation.

A series of MnOx/TiO2 composite nanoxides were prepared by deposition-precipitation (DP) method, and the sample with the Mn/Ti ratio of 0.3 showed a superior activity for NO catalytic oxidation to NO2. The maximum NO conversion over MnOx(0.3)/TiO2(DP) could reach 89% at 250 °C with a GHSV of 25,000 h−1, which was much higher than that over the catalyst prepared by conventional wet-impregnation (WI) method (69% at 330 °C). Characterization results including XRD, HRTEM, FTIR, XPS, H2-TPR, NO-TPD and Nitrogen adsorption–desorption implied that the higher activity of MnOx(0.3)/TiO2(DP) could be attributed to the enrichment of well-dispersed MnOx on the surface and the abundance of Mn3+ species. Furthermore, DRIFT investigations and long-time running test indicated that NO2 came from the decomposition of adsorbed nitrogen-containing species.Graphical abstractMnOx/TiO2 composite nanoxides prepared by deposition-precipitation method showed much higher activity for NO catalytic oxidation than that prepared by wet-impregnation method due to well-dispersion of MnOx and abundant Mn3+ species.Research highlights► MnOx(0.3)/TiO2(DP) showed much higher activity than MnOx(0.3)/TiO2(WI) for NO catalytic oxidation to NO2. ► DP method made MnOx better dispersed on the support surface and produced more trivalent Mn species with respect to WI method. ► Trivalent Mn species was more favorable than tetravalent Mn species for NO catalytic oxidation. ► NO2 comes from the decomposition of nitrogen-containing species generated during the co-adsorption NO and O2.

•Bimetallic Pt-Pd/MCM-41 catalysts were prepared by one-step synthesis method.•Co-doping of Pt and Pd induced smaller metal size and higher surface Pt(0) content.•The synergistic effect enhanced oxygen adsorption capacity and the reducibility.The catalytic performances of Pt-Pd/MCM-41 bimetallic catalysts prepared by one-step synthesis method were investigated for total toluene oxidation in this paper. The experimental results demonstrated that Pt-Pd/MCM-41 was of superior catalytic activity comparing to the monometallic Pt/MCM-41 or Pd/MCM-41 catalysts with the same metallic content, yielding an almost 100% conversion at 180 °C. The following characterization results indicated that the bimetallic catalyst possessed a higher surface Pt(0) content and smaller doped metal size owing to the synergistic effect of the two noble metals, resulting in the improvement of oxygen adsorption capacity and the reducibility.Download high-res image (319KB)Download full-size image

V2O5 was loaded on the surface of C-doped TiO2 (C-TiO2) by incipient wetness impregnation in order to enhance the visible light photocatalytic performance. The physicochemical properties of the C-TiO2/V2O5 composite were characterized by XRD, Raman, TEM, XPS, UV–vis diffuse reflectance spectra, and PL in detail. The result indicated that a heterojunction between C-TiO2 and V2O5 was formed and the separation of excited electron–hole pairs on C-TiO2/V2O5 is greatly promoted. Thus, this composite photocatalyst exhibited enhanced visible light photocatalytic activity in degradation of gas-phase toluene compared with the pristine C-TiO2.

A series of nanosized ion-doped TiO2 catalysts with different ion content (between 0.1 at.% and 1.0 at.%) have been prepared by wet impregnation method and investigated with respect to their behavior for UV photocatalytic oxidation of nitric oxide. The catalytic activity was correlated with structural, electronic and surface examinations of the catalysts using X-ray diffraction analysis (XRD), ultraviolet-visible (UV-Vis) absorption spectroscopy, transmission electron microscopy (TEM), energy disperse spectrometer (EDS) and high resolution-transmission electron microscopy (HR-TEM) techniques. An enhancement of the photocatalytic activity was observed for Zn2+ doping catalyst ranged from 0.1 at.% to 1.0 at.% which was attributed to the lengthened lifetime of electrons and holes. The improvement in photocatalytic activity could be also observed with the low doping concentration of Cr3+ (0.1 at.%). However, the doping of Fe3+,Mo6+,Mn2+ and the high doping concentration of Cr3+ had no contribution to photocatalytic activity of nitric oxide.

In this paper, we investigated the primary reduction and oxygen replenishing processes over Mn substitutionally doped CeO2(111) surfaces by density functional theory with the on-site Coulomb correction (DFT + U). The results indicated that Mn doping could make the surface much more reducible and the adsorbed O2 could be effectively activated to form superoxo (O2−) and/or peroxo species (O22−). The Mn doping induced the Mn 3d–O 2p gap state instead of Ce 4f acting as an electrons acceptor and donor during the first oxygen vacancy formation and O2 replenishing, which helped to lower the formation energy of the first and second oxygen vacancies to −0.46 eV and 1.40 eV, respectively. In contrast, the formation energy of a single oxygen vacancy in the pure ceria surface was 2.08 eV and only peroxo species were identified as the O2 molecule adsorbed. Our work provides a theoretical and electronic insight into the catalytic redox processes of Mn doped ceria surfaces, which may help to understand the enhanced catalytic performances of MnOx–CeO2 oxides, as reported in previous experimental works.