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Study of Air Quality Objectives (AQOs) and long-term changes of air pollution plays a decisive role in formulating and refining pollution control strategies. In this study, 10-year variations of six major air pollutants were analyzed at seven monitoring sites in Hong Kong. The continuous decrease of annual averaged concentrations of NO

In the process of catalytic destruction of chlorinated volatile organic compounds (CVOCs), the catalyst is prone to chlorine poisoning and produce polychlorinated byproducts with high toxicity and persistence, bringing great risk to atmospheric environment and human health. To solve these problems, this work applied phosphate to modify K-OMS-2 catalysts. The physicochemical properties of catalysts were determined by using X-ray powder diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), hydrogen temperature programmed reduction (H

The adsorption characteristics of dichloromethane (DCM), toluene (MB), and ethyl acetate (EAC) vapors on hypercrosslinked polymeric resins (NDA-88) were studied. It showed that the NDA-88 exhibited promising adsorption and regeneration properties.

In this study, a series of cordierite monolithic catalysts with Ru species supported on different low-cost available carriers were prepared and investigated for the degradation of CVOCs.

The spatially isolated Ni2P and NiO dual-cocatalysts synergistically promoted CO2 photocatalytic conversion of CN, and the in situ formed Ni0 during photocatalytic reactions endowed the catalyst with sustainably efficient CO2 reduction activity.

Herein, a series of niobium oxide supported cerium nanotubes (CeNTs) catalysts with different loading amount of Nb2O5 (0–10 wt.%) were prepared and used for selective catalytic reduction of NOx with NH3 (NH3-SCR) in the presence of CH2Cl2. Commercial V2O5-WO3-TiO2 catalyst was also prepared for comparison. The physcial properties and chemical properties of the Nb2O5 loaded cerium nanotubes catalysts were investigated by X-ray diffractometer, Transmission electron microscope, Brunauer-Emmett-Teller specific surface area, H2-temperature programmed reduction, NH3-temperature programmed desorption and X-ray photoelectron spectroscopy. The experiment results showed that the loading amount of Nb2O5 had a significant effect on the catalytic performance of the catalysts. 10 wt.% Nb-CeNTs catalyst presented the best NH3-SCR performance and degradation efficiency of CH2Cl2 among the prepared catalysts, due to its superior redox capability, abundant surface oxygen species and acid sites, the interaction between Nb and Ce, higher ratio of Nb4+/(Nb5++ Nb4+) and Ce3+/(Ce3+ + Ce4+), as well as the special tubular structure of cerium nanotube. This study may provide a practical approach for the design and synthesis of SCR catalysts for the simultaneously removal NOx and chlorinated volatile organic compounds (CVOCs) emitted from the stationary industrial sources.

To investigate impact factors and source area of secondary organic aerosols in the Yangtze River Delta (YRD) region, a world-class urban agglomeration in China, long-term measurements of organic carbon (OC) and elementary carbon (EC) in particulate matter of less than 2.5 µm (PM2.5) with hourly time resolution were conducted at a regional site in Shanghai from 2016 to 2020. Based on the 5-year measurements, the interannual, monthly, seasonal, and diurnal variations in OC and EC, as well as OC subtypes, i.e. secondary OC (SOC) and primary OC (POC), apportioned by the novel statistical model of the minimum R2 method, and the formation pathways of SOC, are presented. By examining the relationship between SOC and temperature, as well as relative humidity (RH), we show that SOC formation is greatly enhanced at high temperatures (> 30 ∘C), whereas it correlates inversely with RH. In particular, we show that the photochemical formation of SOC is the major formation pathway even in winter, when solar radiation was supposedly less intense than in summer, which is different from that in the north China plain, where aqueous phase chemistry is found to be an important SOC formation pathway. Moreover, increased SOC concentrations are also found to be associated with high wind speed (> 5 m s−1) in winter, which is increased by 29.1 % (2.62 µg m−3) when compared with that during lower winds, suggesting regional sources of SOC in winter. By analysing the potential source regions using the concentration-weighted trajectory (CWT), the geographic regions of SOC are found to be mainly associated with transport from outside Shanghai (SOC > 3.5 µg m−3) including central and southern Anhui, Zhejiang, and Fujian. The results from this study provide critical information about the long-term trend of carbonaceous aerosol, in particular, SOC, in one of the largest megacities in the world, and are helpful for developing pollution control measures from a long-term planning perspective.

The conversion of carbon dioxide (CO2) into high-value-added chemicals by photocatalysis is recognized as a potential method to ease the greenhouse effect and the global energy crisis simultaneousl...

Municipal solid waste incineration and the iron and steel smelting industry can simultaneously discharge NOx and chlorinated organics, particularly polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). Synergistic control of these pollutants has been considered among the most cost-effective methods. This work combined experimental and computational methods to investigate the reaction characteristics of a catalytically synergistic approach and gives the first insight into the effect of arsenic (As) on the multipollutant conversion efficiency, synergistic reaction mechanism, and toxic byproduct distribution over a commercial V2O5-WO3/TiO2 catalyst. The loaded As2O3 species were shown to distinctly decrease the formation energy of an oxygen vacancy at the V-O-V site, which likely contributed to the extensive formation of more toxic polychlorinated byproducts in the synergistic reaction. The As2O5 species strongly attacked neighboring V═O sites forming the As-O-V bands. Such an interaction deactivated the deNOx reaction, but led to excessive NO being oxidized into NO2 that greatly promoted the V5+-V4+ redox cycle and in turn facilitated chlorobenzene (CB) oxidation. Subsequent density functional theory (DFT) calculation further reveals that both the As2O3 and As2O5 loadings can facilitate H2O adsorption on the V2O5-WO3/TiO2 catalyst, leading to competitive adsorption between H2O and CB, and thereby deactivate the CB oxidation with water stream.

Ceria-based catalysts have been investigated extensively for their good activities at low–medium temperatures for selective catalytic reduction of NO with ammonia (NH3–SCR). In considering the usua...

In this work, various Co3O4-ZSM-5 catalysts were prepared by the microwave hydrothermal method (MH-Co3O4@ZSM-5), dynamic hydrothermal method (DH-Co3O4@ZSM-5), and conventional hydrothermal method (CH-Co3O4/ZSM-5). Their catalytic oxidation of dichloromethane (DCM) was analyzed. Detailed characterizations such as X-ray diffractometer (XRD), scanning microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), H2 temperature-programmed reduction (H2-TPR), temperature-programmed desorption of O2 (O2-TPD), temperature-programmed desorption of NH3 (NH3-TPD), diffuse reflectance infrared Fourier-transform spectra with NH3 molecules (NH3-DRIFT), and temperature-programmed surface reaction (TPSR) were performed. Results showed that with the assistance of microwave, MH-Co3O4@ZSM-5 formed a uniform core-shell structure, while the other two samples did not. MH-Co3O4@ZSM-5 possessed rich surface adsorbed oxygen species, higher ratio of Co3+/Co2+, strong acidity, high reducibility, and oxygen mobility among the three Co3O4-ZSM-5 catalysts, which was beneficial for the improvement of DCM oxidation. In the oxidation of dichloromethane, MH-Co3O4@ZSM-5 presented the best activity and mineralization, which was consistent with the characterizations results. Meanwhile, according to the TPSR test, HCl or Cl2 removal from the catalyst surface was also promoted in MH-Co3O4@ZSM-5 by their abundant Bronsted acid sites and the promotion of Deacon reaction by Co3O4 or the synergistic effect of Co3O4 and ZSM-5. According to the results of in situ DRIFT studies, a possible reaction pathway of DCM oxidation was proposed over the MH-Co3O4@ZSM-5 catalysts.

To date, investigations onto the regulation of reactants mass transfer has been paid much less attention in environmental catalysis. Herein, we demonstrated that by rationally designing the adsorption sites of multi-reactants, the pollutant destruction efficiency, product selectivity, reaction stability and secondary pollution have been all affected in the catalytic chlorobenzene oxidation (CBCO). Experimental results revealed that the co-adsorption of chlorobenzene (CB) and gaseous O2 at the oxygen vacancies of CeO2 led to remarkably high CO2 generation, owning to their short mass transfer distance on the catalyst surface, while their separated adsorptions at Bronsted HZSM-5 and CeO2 vacancies resulted in a much lower CO2 generation, and produced significant polychlorinated byproducts in the off-gas. However, this separated adsorption model yielded superior long-term stability for the CeO2/HZSM-5 catalyst, owning to the protection of CeO2 oxygen vacancies from Cl poisoning by the preferential adsorption of CB on the Bronsted acidic sites. This work unveils that design of environmental catalysts needs to consider both of the catalyst intrinsic property and reactant mass transfer; investigations of the latter could pave a new way for the development of highly efficient catalysts towards environmental pollution control.

A sequence of CuCeOx-HZSM-5 composite catalysts at different Cu-Ce loading synthesized by the citric acid complex impregnation method were evaluated for the catalytic oxidation of acetonitrile. Among which, the 2CuCeOx-HZSM-5 sample exhibited the best degradation efficiency. In the temperature range of 225–350 °C, its activity and mineralization rate were approximately 100%, and the N2 selectivity remained more than 93%. The characterization results revealed that all the samples showed an existence of isolated Cu2+ species. And more Cu-Ce mixed oxides covered on HZSM-5 at an elevated Cu-Ce content, leading to the enhanced reducibility. In situ DRIFTS results showed that both oxidation and hydrolysis reaction routes proceeded during the degradation of acetonitrile over the composite catalysts. Their synergism was crucial to guarantee both high activity and N2 selectivity. The highly dispersed CuOx species ensured the superior activity of the 2CuCeOx-HZSM-5 sample. And Cu2+ exchanged HZSM-5 zeolite would be beneficial to N2 selectivity owing to the improved internal SCR (Selective Catalytic Reduction) reaction to reduce NOx from oxidation routes. Additionally, the mineralization rate was lowered with the formation of carbonaceous products like CH4 and CO for the catalysts at low Cu-Ce loading due to the lack of redox capacity.

This study compared the reaction behaviors of dichloromethane (DCM) catalytic combustion over Cu/HZSM-5 (H form of Zeolite Socony Mobil-5) nanoporous catalysts at different copper loadings. Among t...

Industrial catalysis is confronted with the common problem of catalyst deactivation. For the field of chlorinated volatile organic compound (Cl-VOC) elimination, it is hard to find an effective solution for the regeneration and re-use of deactivated catalysts within industrial settings. In this work, the performance of a metal-exchanged H-zeolite (Cu–Nb/HZSM-5) catalyst is tested for chlorobenzene (CB) combustion by different catalyst regeneration strategy. By confirming the related reaction mechanism via in situ DRIFTS, GC-MS, and PR-IR, the catalysts were analyzed in terms of their carbon deposition, surface elemental content, and acidity, before and after the regeneration. It was found that humid air exhibited an excellent catalyst restoration effect at a temperature of 400 °C, the adsorbed coke and chlorine on the surface of the deactivated catalyst were mostly removed, and the catalytic performance was recovered to 100% of that of the fresh catalyst.

Herein, a facile in situ sulfation strategy was employed for modifying Cu/TiO2 catalysts using CuSO4 as the precursor to enhance the performance of dichloromethane (DCM) catalytic combustion. The experimental results revealed that the modified samples exhibited superior DCM conversion and COx yield compared to the pristine Cu/TiO2 catalyst. Among these, the 1CuSO4/TiO2 sample showed the best activity with near 90% conversion during 50 h of reaction at 275 °C. Characterization results showed that the in situ sulfation modification could considerably improve the catalyst acidity, benefiting the dissociative adsorption of DCM with C–Cl rupture. Notably, the surface sulfate groups provided abundant Bronsted acidic sites that release surface Cl species in the form of HCl at relatively low temperatures, preventing the surface Cu species from chloride poisoning. With excess CuSO4 addition, the intermediates derived from DCM dechlorination could not be decomposed in time due to the decreased reducibility, leading to their deactivation due to coke deposition. The superior performance of 1CuSO4/TiO2 is attributed to the balance achieved between acidity and redox capacity for DCM catalytic decomposition. Moreover, it was found that CuSO4/TiO2 could partially replace noble-metal Ru/TiO2 catalysts and achieve comparable performances. The findings of this study will aid the development of CVOCs catalytic combustion catalysts with good activity and stability.

To investigate impact factors and source area of secondary organic aerosols in the Yangtze River Delta (YRD) region, a world-class urban agglomeration in China, long-term measurements of organic carbon (OC) and elementary carbon (EC) in particulate matter of less than 2.5 μm (PM2.5) with hourly time resolution were conducted at a regional site in Shanghai from 2016 to 2020. Based on the five-year measurements, the interannual, monthly, seasonal, and diurnal variations in OC and EC, as well as OC subtypes, i.e., secondary OC (SOC) and primary OC (POC), apportioned by the novel statistical model of the minimum R2 method, and the formation pathways of SOC, are presented. By examining the relationship between SOC and temperature, as well as relative humidity (RH), we show that SOC formation is greatly enhanced at high temperatures (>30 °C), while it is inversely correlated with RH. In particular, we show that the photochemical formation of SOC is the major formation pathway even in winter when solar radiation was supposedly less intense than in summer, which is different from that in north China plain where aqueous phase chemistry is found to be an important SOC formation pathway. Moreover, increased SOC concentrations are also found to be associated with high wind speed (>5 m s−1) in winter, which is increased by 29.1 % (2.62 μg m−3) when compared to that during lower winds, suggesting regional sources of SOC in winter. By analyzing the potential source regions using the concentration weighted trajectory (CWT), the geographic regions of SOC are found to be mainly associated with transport from outside Shanghai (SOC > 3.5 μg m−3) including central and southern Anhui, Zhejiang, and Fujian. The results from this study provide critical information about the long-term trend of carbonaceous aerosol, in particular SOC, in one of the largest megacities in the world and are helpful to develop pollution control measures from a long-term planning perspective.

For the nitrogen oxide removal processes, high performance gas mixer is deeply needed for the injection of NH3 or O3. In this study, a new type of double swirl static mixer in gas mixing was investigated using computational fluid dynamics (CFD). The results obtained using Particle Image Velocimetry (PIV) correlated well with the results obtained from simulation. The comparisons in pressure loss between the experimental results and the simulation results showed that the model was suitable and accurate for the simulation of the static mixer. Optimal process conditions and design were investigated. When L/D equaled 4, coefficient of variation (COV) was

Herein, K-OMS-2 catalysts with different levels of Ca2+ loading were synthesized to investigate the influence of Ca2+ deposition on the catalytic oxidation of CB. The micromorphology, redox ability, oxygen species, and surface acidity of the prepared catalysts were analyzed via SEM, HR-TEM, H2-TPR, O2-TPD, Py-IR, and GC–MS. After the Ca addition, CB conversion on the catalyst was achieved at

In an attempt to achieve the selective oxidation of NOx, a hybrid catalyst of single-atom-anchored metal organic frameworks (MOF, NH2-UiO-66) and MnO2 was constructed and used in the plasma catalyt...

Since the discovery of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the process of municipal solid waste incineration (MSWI), a large number of researches have been conducted to reveal their formation mechanisms and emission characteristics. As one of national priority control pollutants, chlorinated organics are inclined to transfer into PCDD/Fs in the heterogeneously catalyzed process, which has been considered to be one of great challenges in environmental catalysis. However, so far direct evidences to support such a conversion process are insufficient, and the reaction mechanisms are lack of exploration. This study investigated the catalytic elimination of chlorobenzene (CBz) over a range of industrially applied active species including Pt, Ru, V, Ce and Mn oxides, and explored their reaction byproducts, chlorine adsorption/desorption behaviors and PCDD/F formations. We found that all of these species could generate the PCDD/Fs, amongst which, Mn species were the most active for PCDD/F formation. Approximately 140 ng I-TEQ g−1 PCDD/Fs were detected on the Mn-CNT surface after ageing at 250 °C for 30 h. Even using the dichloromethane (DCM) as a precursor, significant PCDD/Fs were still detected. The Ru and V species were shown to generate much less polychlorinated byproducts and PCDD/Fs, owning to their sufficiently high abilities in Cl desorption, which were through the semi-Deacon and Bronsted H reactions, respectively.

Low-medium temperature NH3-SCR technology has been applied for years in municipal solid wastes incineration (MSWI) to control the emissions of nitrogen oxides. Unlike coal-fired flue gases, the tail gas from MSWI contains high levels of heavy metals in fly ash, especially the zinc species, which may harm SCR catalysts. As such, in this paper, the deactivation mechanism of different zinc species (ZnO, ZnSO4 and ZnCl2) on the Sb-CeZr2Ox catalysts and the co-effects of zinc species and gas-phase pollutants (including SO2 and HCl) were investigated. The experimental results indicated that the deactivation rate of various poisoning zinc species was in the order of ZnCl2 > ZnSO4 > ZnO. Moreover, the interactions between zinc and antimony species would disrupt the structure of the Sb-Ce mixed oxides to decrease the redox ability, consequently suppressing the ammonia activation and NO adsorption. Furthermore, such damaging effects on catalyst structures would promote the formation of bulk-like sulfate species in the presence of SO2, resulting in a decreased mobility of surface oxygen species, which significantly decrease the sulfur resistance. However, the presence of HCl did not show an evident co-effect on the Zn poisoned sample owing to the limited coverage of the chlorine deposition.

Photocatalytic reduction of carbon dioxide (CO2) under visible light irradiation for producing high-value fuel has attracted tremendous attention in recent years. In this study, titanium carbide MXene (Ti3C2) was used as a noble metal-free co-catalyst by simply mixing graphitic carbon nitride (g-C3N4) and alkalized Ti3C2. The carbon monoxide evolution rate of the optimized composite (5%TCOH-CN) from photocatalytic reduction of CO2 was 5.9 times higher than that of pure g-C3N4. Alkalized Ti3C2 was responsible for the superior photocatalytic activity due to its excellent electrical conductivity and large CO2 adsorption capacity. Furthermore, the separation of the photo-induced electron–hole pairs was greatly enhanced because of the large Fermi level difference between alkalized Ti3C2 and pure g-C3N4. This work demonstrates the potential of MXenes as noble metal-free co-catalyst for photocatalysis processes such as carbon dioxide reduction reaction and nitrogen reduction reaction.

Mn-based catalysts are extensively used; herein, the poisoning mechanism of Pb2+ and SO2 on the γ-MnO2 catalyst during the combustion of chlorobenzene (CB) was studied. The oxidizability/reducibility, surface acidity and water activation property of the Pb/SO42- modified γ-MnO2 were analyzed by using XPS, H2-TPR/O2-TPD, NH3-TPD/Pyridine-IR and H2O-TPD. Catalytic performance and byproduct selectivity towards CB combustion were explored, indicating that Pb2+ and SO2 both impacted CB conversion and CO2 selectivity as indicated by the loss of oxidation properties and surface acidity. Analysis of the byproducts showed that Pb2+ and SO2 induced the formation of more toxic polychlorinated byproducts, thereby introducing new secondary environmental pollution risks.