Enhancement of low-temperature NH3-SCR catalytic activity and H2O & SO2 resistance over commercial V2O5-MoO3/TiO2 catalyst by high shear-induced doping of expanded graphite

Influence of carbon content and irradiation modes on the antibiotic removal from water using VIS-activated TiO2/expanded graphite composite photocatalysts

TiO2/expanded graphite (TiO2/EG) composite films were applied to water treatment for sulfadiazine (SDZ) degradation in a continuous flat plate photochemical reactor. The films were synthesized by sol-gel method and deposited on borosilicate glass by airbrush spray coating technique, forming a TiO2/C heterojunction. Increasing the amount of carbon promoted more efficient photocatalytic removal of SDZ under simulated sunlight, which increased from 9.1% in the absence of carbon to 49.8% for the material containing 7.5% C. From the formation of the TiO2/C heterojunction, morphological modifications, changes in the electronic structure and reduction of the band gap energy were observed. Type-II heterojunction formation was observed. Foreground and background irradiation modes were investigated, and a possible photocatalytic mechanism was proposed. TiO2/7.5 %-EG exhibited the best photocatalytic performance, with the possibility of reuse. The films showed good reusability in the SDZ degradation over 4 photocatalytic cycles. The influence of irradiation modes and the role of oxidizing species were discussed. The results showed that TiO2/EG hybrid films are a promising alternative for practical photocatalytic applications under sunlight.

Technological solutions for NOx, SOx, and VOC abatement: recent breakthroughs and future directions

NOx, SOx, and carbonaceous volatile organic compounds (VOCs) are extremely harmful to the environment, and their concentrations must be within the limits prescribed by the region-specific pollution control boards. Thus, NOx, SOx, and VOC abatement is essential to safeguard the environment. Considering the importance of NOx, SOx, and VOC abatement, the discussion on selective catalytic reduction, oxidation, redox methods, and adsorption using noble metal and non-noble metal-based catalytic approaches were elaborated. This article covers different thermal treatment techniques, category of materials as catalysts, and its structure-property insights along with the advanced oxidation processes and adsorption. The defect engineered catalysts with lattice oxygen vacancies, bi- and tri-metallic noble metal catalysts and non-noble metal catalysts, modified metal organic frameworks, mixed-metal oxide supports, and their mechanisms have been thoroughly reviewed. The main hurdles and potential achievements in developing novel simultaneous NOx, SOx, and VOC removal technologies are critically discussed to envisage the future directions. This review highlights the removal of NOx, SOx, and VOC through material selection, properties, and mechanisms to further improve the existing abatement methods in an efficient way.

Advances in air pollution control for key industries in China during the 13th five-year plan

Industrial development is an essential foundation of the national economy, but the industry is also the largest source of air pollution, of which power plants, iron and steel, building materials, and other industries emit large amounts of pollutants. Therefore, the Chinese government has promulgated a series of stringent emission regulations, and it is against this backdrop that research into air pollution control technologies for key industrial sectors is in full swing. In particular, during the 13th Five-Year Plan, breakthroughs have been made in pollution control technology for key industrial sectors. A multi-pollutant treatment technology system of desulfurization, denitrification, and dust collection, which applies to key industries such as power plants, steel, and building materials, has been developed. High-performance materials for the treatment of different pollutants, such as denitrification catalysts and desulfurization absorbers, were developed. At the same time, multi-pollutant synergistic removal technologies for flue gas in various industries have also become a hot research topic, with important breakthroughs in the synergistic removal of NO_x, SO_x, and Hg. Due to the increasingly stringent emission standards and regulations in China, there is still a need to work on the development of multi-pollutant synergistic technologies and further research and development of synergistic abatement technologies for CO₂ to meet the requirements of ultra-low emissions in industrial sectors.

The promoting/inhibiting effect of water vapor on the selective catalytic reduction of NOx

In the field of nitrogen oxides (NO_x) abatement, developing selective catalytic reduction (SCR) catalysts that can operate stably in the practical conditions remains a big challenge because of the complexity and uncertainty of actual flue gas emissions. As water vapor is unavoidable in the actual flue gas, it is indispensable to explore its effect on the performance of SCR catalysts. Many studies have proved that the effects of H₂O on de-NO_x activity of SCR catalysts were indeed observed during SCR reactions operated under wet conditions. Whether the effect is promotive or inhibitory depends on the reaction conditions, catalyst types and reducing agents used in SCR reaction. This review focuses on the effect of H₂O on SCR catalysts and SCR reaction, including promoting effect, inhibiting effect, as well as the effecting mechanism. Besides, various strategies for developing a water-resistant SCR catalyst are also included. We hope that this work can give a more comprehensive insight into the effects of H₂O on SCR catalysts and help with the rational design of water-resistant SCR catalysts for further practical application in NO_x abatement field.

Catalytic Performance and Sulfur Dioxide Resistance of One-Pot Synthesized Fe-MCM-22 in Selective Catalytic Reduction of Nitrogen Oxides with Ammonia (NH3-SCR)—The Effect of Iron Content

The catalytic performance of Fe-catalysts in selective catalytic reduction of nitrogen oxides with ammonia (NH₃-SCR) strongly depends on the nature of iron sites. Therefore, we aimed to prepare and investigate the catalytic potential of Fe-MCM-22 with various Si/Fe molar ratios in NH₃-SCR. The samples were prepared by the one-pot synthesis method to provide high dispersion of iron and reduce the number of synthesis steps. We have found that the sample with the lowest concentration of Fe exhibited the highest catalytic activity of ca. 100% at 175 °C, due to the abundance of well-dispersed isolated iron species. The decrease of Si/Fe limited the formation of microporous structure and resulted in partial amorphization, formation of iron oxide clusters, and emission of N₂O during the catalytic reaction. However, an optimal concentration of Fe_xO_y oligomers contributed to the decomposition of nitrous oxide within 250–400 °C. Moreover, the acidic character of the catalysts was not a key factor determining the high conversion of NO. Additionally, we conducted NH₃-SCR catalytic tests over the samples after poisoning with sulfur dioxide (SO₂). We observed that SO₂ affected the catalytic performance mainly in the low-temperature region, due to the deposition of thermally unstable ammonium sulfates.

Progress of selective catalytic reduction denitrification catalysts at wide temperature in carbon neutralization

With the looming goal of carbon neutrality and increasingly stringent environmental protection policies, gas purification in coal-fired power plants is becoming more and more intense. To achieve the NOx emission standard when coal-fired power plants are operating at full load, wide-temperature denitrification catalysts that can operate for a long time in the range of 260–420°C are worthy of study. This review focuses on the research progress and deactivation mechanism of selective catalytic reduction (SCR) denitration catalysts applied to a wide temperature range. With the increasing application of SCR catalysts, it also means that a large amount of spent catalysts is generated every year due to deactivation. Therefore, it is necessary to recycle the wide temperature SCR denitration catalyst. The challenges faced by wide-temperature SCR denitration catalysts are summarized by comparing their regeneration processes. Finally, its future development is prospected.

Effect of Bimetal Element Doping on the Low-Temperature Activity of Manganese-Based Catalysts for NH3-SCR

A series of novel Mn₆Zr_1-xCo_x denitrification catalysts were prepared by the co-precipitation method. The effect of co-modification of MnO_x catalyst by zirconium and cobalt on the performance of NH₃-SCR was studied by doping transition metal cobalt into the Mn₆Zr₁ catalyst. The ternary oxide catalyst Mn₆Zr_0.3Co_0.7 can reach about 90% of NO_x conversion in a reaction temperature range of 100–275°C, and the best NO_x conversion can reach up to 99%. In addition, the sulfur resistance and water resistance of the Mn₆Zr_0.3Co_0.7 catalyst were also tested. When the concentration of SO₂ is 200ppm, the NO_x conversion of catalyst Mn₆Zr_0.3Co_0.7 is still above 90%. 5 Vol% H₂O has little effect on catalyst NO_x conversion. The results showed that the Mn₆Zr_0.3Co_0.7 catalyst has excellent resistance to sulfur and water. Meanwhile, the catalyst was systematically characterized. The results showed that the addition of zirconium and cobalt changes the surface morphology of the catalyst. The specific surface area, pore size, and volume of the catalyst were increased, and the reduction temperature of the catalyst was decreased. In conclusion, the doping of zirconium and cobalt successfully improves the NH₃-SCR activity of the catalyst.

PTFE-Modified Mn-Co-Based Catalytic Ceramic Filters with H2O Resistance for Low-Temperature NH3-SCR

Mn-Co-based catalysts were loaded to ceramic filters element by impregnation for the coprocessing of dust and nitrogen oxide (NOx) in flue gas. The influence of the Mn/Co ratio and loading on the catalytic performance was investigated. The Mn-Co-based catalytic ceramic filter with a Mn/Co molar ratio of 2/1 can achieve 99% NO conversion by selective catalytic reduction of NOx with NH3 (NH3-SCR) in the temperature range of 100−180 °C, but its resistance to H2O was relatively poor. The filter element was modified by PTFE to improve the H2O resistance. After modification, the catalytic ceramic filter showed superior resistance to H2O and SO2 at low temperatures (100–180 °C) and satisfactory self-cleaning performance.

Low-Temperature SCR Catalyst Development and Industrial Applications in China

In recent years, low-temperature SCR (Selective Catalytic Reduction) denitrification technology has been popularized in non-power industries and has played an important role in the control of industrial flue gas NOx emissions in China. Currently, the most commonly used catalysts in industry are V2O5-WO3(MoO3)/TiO2, MnO2-based catalysts, CeO2-based catalysts, MnO2-CeO2 catalysts and zeolite SCR catalysts. The flue gas emitted during industrial combustion usually contains SO2, moisture and alkali metals, which can affect the service life of SCR catalysts. This paper summarizes the mechanism of catalyst poisoning and aims to reduce the negative effect of NH4HSO4 on the activity of the SCR catalyst at low temperatures in industrial applications. It also presents the outstanding achievements of domestic companies in denitrification in the non-power industry in recent years. Much progress has been made in the research and application of low-temperature NH3-SCR, and with the renewed demand for deeper NOx treatments, new technologies with lower energy consumption and more functions need to be developed.

One-step synthesis by redox co-precipitation method for low-dimensional Me-Mn bi-metal oxides (Me=Co, Ni, Sn) as SCR DeNOx catalysts

In this research, one-step synthesis of redox co-precipitation method (using sodium lauryl sulfate, KMnO₄, and metal precursor) was well applicable in universally preparing low-dimensional Me-MnOx nanosheet catalysts with different metal doping (Me=Co, Ni, or Sn). NH₃-SCR activity was explored to the relationship with structure morphology and physio-chemical properties via the characterization techniques of SEM, XRD, XPS, H₂-TPR, and NH₃-TPD. It was found that Ni-MnOx has a relatively poor activity at low-down temperature but was improved as the reaction temperature rising. Co-MnOx presented a relatively stable catalytic activity of which the NOx conversion rate can be maintained 80~90% in a wide temperature window of 100-250 °C with relatively better N₂ selectivity. Compared with Co- or Ni-modified MnOx, Sn-MnOx catalyst has an excellent low-temperature catalytic activity (93% NOx conversion at 100 °C) that was maintained > 80% before 200 °C but with poor selectivity to N₂. Due to its nanosheet-structured solid solution structure, Sn-MnOx promoted the interaction between MnOx and SnO₂ with the increased contents of adsorbed oxygen and also the numbers of surface Lewis acid sites, which integrally promoted the NH₃-SCR reaction at low temperature and also contributed to an acceptable resistances to water and sulfur. High content of adsorbed oxygen was beneficial to improve the catalytic activity at lower temperatures, while the electron cycle interaction of different metal valence ions will play a more important role with the increase of reaction temperature.

Intrinsic mechanism insight of the interaction between lead species and the Vanadium-based catalysts based on First-principles investigation

Lead (Pb) species trigger serious poisoning of selective catalytic reduction (SCR) catalysts. To improve the Pb resistance ability, revealing the impact mechanism of Pb species on the commercial SCR catalysts from a molecular level is of great significance. Herein, first-principles calculations were applied to unveil the Pb adsorption mechanism on the vanadium-based catalysts, the results were also compared with the previous experimental findings. The intrinsic interaction mechanism between Pb and catalyst components was interpreted by clarifying the change of the catalyst electronic structures (including charge transfer, bond formation situations, and active sites reactivities). It is found that the adsorption of Pb species belongs to chemisorption, evident electron transfer with the catalyst surface is inspected and intense charge transfer indicates strong adsorption. A remarkable interaction with the V = O active sites occurs and stable Pb-O bonds are formed, which significantly changes the electronic structures of the V = O sites and inhibits the NH₃ adsorption, thus suppressing the SCR activity. Finally, thermodynamic analysis was applied to elucidate the temperature influence on Pb adsorption. It is found that Pb adsorption on catalysts cannot proceed spontaneously over 500 K. At higher temperatures the adsorption is inhibited and the Pb species become less stable, which partially explains why the Pb-poisoning effect at high temperatures is relatively moderate than that at low temperatures.

Improved SO2 Tolerance of Cu-SAPO-18 by Ce-Doping in the Selective Catalytic Reduction of NO with NH3

The Ce-Cu-SAPO-18 catalysts were prepared using the ion exchange method. The impact of sulfur dioxide on catalytic performance of Ce-Cu-SAPO-18 for the selective catalytic reduction (SCR) of NO with NH3 was examined. Detailed characterization of the fresh and sulfur-poisoning Cu-SAPO-18 and Ce-Cu-SAPO-18 samples was conducted. XRD and BET results show that SO2 treatment of the Ce-doped Cu-SAPO-18 (Ce-Cu-SAPO-18-S) sample did not induce a remarkable change in structure, as compared with that of the fresh counterpart. According to in situ DRIFT, H2-TPR, SEM, and EDS results, it is found that the sulfation species attached preferentially to the cerium species, rather than the isolated Cu2+ species. In particular, the TG/DSC results confirm that the sulfate species on the Ce-Cu-SAPO-18-S sample was easier to decompose than that on the Cu-SAPO-18-S sample. The catalytic active sites of Ce-Cu-SAPO-18 were less influenced after SO2 treatment, as demonstrated by the TPR and XPS results. All of the above results show that the Ce-Cu-SAPO-18 sample exhibited better sulfur-resistant performance than the Cu-SAPO-18 sample.

Spinel-structured Mn–Ni nanosheets for NH3-SCR of NO with good H2O and SO2 resistance at low temperature

High specific surface area, more NH₃ adsorption ability and efficient electronic interaction over Mn–Ni spinel nanosheet leaded to good SCR activity, and Ni-outside with active Mn-inner spinel configuration and nanosheet morphology relieved SO₂-poisoning.

A new V2O5–MoO3–TiO2–SO42−nanostructured aerogel catalyst for diesel DeNOxtechnology

A new V₂O₅–MoO₃–TiO₂–SO₄²⁻nanostructured aerogel catalyst exhibits superior SCR activity compared to the V₂O₅–WO₃/TiO₂commercial catalyst (EUROCAT) at high temperatures (375–500 °C).