NOx Removal Efficiency Research Articles

Enhanced performance on simultaneous removal of NOx-SO2-CO2 using a high-gravity rotating packed bed and alkaline wastes towards green process intensification

In order to intensify the gas-liquid absorption processes in the field of energy and environment, high-gravity rotating packed bed (HiGee RPB) has been successfully applied in the multiple air pollutants abatement and CO2 capture by mineralization. Since the mass transfer and chemical reaction through gas-liquid absorption were found to be the key factors affecting acid gas removal, a mass transfer model based on the two-film theory for simultaneous removal of NOx-SO2-CO2 in an RPB was developed in this study. The mass transfer parameters including overall gas-phase mass transfer coefficient (KGa), height of a transfer unit (HTU), liquid mass transfer rate (kL) and enhancement factor (E) were theoretically determined from the experimental data. The effect of key dimensionless operating factors such as high gravity factor (β), gas-to-liquid ratio (GLR), and liquid-to-solid ratio (LSR) on mass transfer parameters were evaluated. Based on the results obtained in this study, the enhancement of high gravity filed on mass transfer and removal efficiencies of NOx and CO2 were significantly higher than that of SO2. It was inferred that the carbonation reaction could compensate the removal efficiency of acid gaseous pollutants at the lower mass transfer rate. The relationship between mass transfer rate and energy consumption for the multiple air pollutant control via a HiGee process was established. The favorable operating factors for NOx-SO2-CO2 simultaneous removal in an RPB were suggested as β of 233.8, GLR of 69.5 and LSR of 40.

Study on efficient removal of SOx and NOx from marine exhaust gas by wet scrubbing method using urea peroxide solution

Marine exhaust gas is seriously harmful to the environment, and only using a single pollutant treatment device is difficult to meet the emission regulations. It is imperative to study integrated and efficient marine exhaust gas pollutant removal technology. This study proposes a novel process capable of removing NOx and SOx in marine exhaust gas, and this process can achieve higher NOx and SOx removal efficiency and lower nitrate concentration by using urea peroxide (CO(NH2)2·H2O2) combined with a countercurrent scrubber. The effects of reaction temperature, urea peroxide concentration, liquid-gas ratio (L/G), SO2 concentration and urea concentration in urea peroxide solutions on NO removal were investigated. The results showed that the temperature and liquid-gas ratio played the key role at a fixed urea peroxide concentration, and the NOx removal efficiency increased with the increase of temperature (from 23 ℃ to 80 ℃) and liquid-gas ratio (from 2 L/m3 to 6 L/m3). The NO removal efficiency of urea peroxide solution was really higher than that of mixed solution of urea and hydrogen peroxide. The NO removal efficiency can reach above 90% with proper operating parameters. The larger liquid-gas ratio can make the urea peroxide concentration decrease, and the NO removal efficiency still met the emission regulation. The use of onefold urea peroxide can not only achieve higher SOx and NOx removal efficiency, but keep lower nitrate concentration. This novel process can be applied in ships combined with exhaust gas cleaning (EGC) system.

NOx removal efficiency of urban photocatalytic pavements at pilot scale

Photocatalytic technology implemented in construction materials is a promising solution to contribute to alleviate air quality issues found in big cities. Photocatalysis has been proved able to mineralise most harmful contaminants. However, important problems associated with monitoring the efficiency of these solutions under real conditions still remain, including the lack of affordable analytical tools to measure NOx concentrations with enough accuracy. In this work, two pilot scale demonstration platforms were built at two different locations to assess the photocatalytic NOX removal efficiency of ten selected materials exposed outdoors for AQmesh low-cost sensor PODs were used to measure ground-level to measure NO and NO2 concentrations during nearly one year. The pollutant removal efficiency of the materials was then calculated based on a comparison with simultaneously concentration measurements carried-out on reference, non-active materials. It was found that the NO2 removal efficiency presented large variations across the seasons, with maxima during the warmer months, while NO efficiencies were comparatively steadier. Statistical analysis delivered evidence that the efficiencies significantly depend on different meteorological variables (irradiance and relative humidity) besides NO, NO2 ambient concentrations. Lower efficiencies were observed for higher concentration levels and vice versa. The influence of water vapour could be related to two different effects: a short-term contribution by the instantaneous air humidity and a long-term component associated with the hygroscopic state of the material. The contribution of wind to the pollutant removal efficiencies was principally related to the humidity of air masses moving above the location and to the advection of pollutants from specific emission sources.

The Effect of Cordierite-Platinum SCR Catalyst on the NOx Removal Efficiency in an Engine Fueled with Diesel-Ethanol-Biodiesel Blends

Today, vehicles especially diesel engines emitted a large amount of NOx in the urban areas. So, it is required to find ways such as SCR catalysts to reduce this hazard pollutant emission. In this work, a 3D model of cordierite/Pt SCR catalyst has been developed by using AVL FIRE software to analyze the NOx conversion efficiency. The simulation was performed based on experimental tests conducted on a single-cylinder engine. The exhaust gas from the engine that appears at the inlet of the catalyst was measured for E20B50D30 (20% ethanol, 50% biodiesel, 30% diesel) D100, E10D90, E20D80, B25D75 and B50D50 fuel blends at the engine speeds of 1800, 2150 and 2500 rpm under full load. The results showed that an increase in the engine’s rotational speed resulted in a reduction of NOx conversion, and the conversion rate reaches its minimum value at speed of 2500 RPM for all fuel mixtures. Moreover, increasing the ammonia mass flow rate resulted in higher NOx conversion for all fuel mixtures. However, the effect of increasing ammonia flow rate from 0.2 to 0.3 kg/h on the NOx conversion is lower than that when the ammonia mass flow changes from 0.1 to 0.2 kg/h. The maximum NOx conversion rate was observed for the mixture containing 20% ethanol and 80% diesel at the rotational speed of 1800 RPM while the lowest conversion rate is observed for pure diesel fuel. According to the results, it was seen that the SCR catalytic process for fuel blends contained ethanol have a better performance to reduce the NOx pollutant compared to the mixtures containing biodiesel at lower engine speeds; but at higher rotational speeds ethanol and biodiesel has not a positive effect on the NOx conversion.

Perovskite-Based Catalysts as Efficient, Durable, and Economical NOx Storage and Reduction Systems

Diesel engines operate under net oxidizing environment favoring lower fuel consumption and CO2 emissions than stoichiometric gasoline engines. However, NOx reduction and soot removal is still a technological challenge under such oxygen-rich conditions. Currently, NOx storage and reduction (NSR), also known as lean NOx trap (LNT), selective catalytic reduction (SCR), and hybrid NSR–SCR technologies are considered the most efficient control after treatment systems to remove NOx emission in diesel engines. However, NSR formulation requires high platinum group metals (PGMs) loads to achieve high NOx removal efficiency. This requisite increases the cost and reduces the hydrothermal stability of the catalyst. Recently, perovskites-type oxides (ABO3) have gained special attention as an efficient, economical, and thermally more stable alternative to PGM-based formulations in heterogeneous catalysis. Herein, this paper overviews the potential of perovskite-based formulations to reduce NOx from diesel engine exhaust gases throughout single-NSR and combined NSR–SCR technologies. In detail, the effect of the synthesis method and chemical composition over NO-to-NO2 conversion, NOx storage capacity, and NOx reduction efficiency is addressed. Furthermore, the NOx removal efficiency of optimal developed formulations is compared with respect to the current NSR model catalyst (1–1.5 wt % Pt–10–15 wt % BaO/Al2O3) in the absence and presence of SO2 and H2O in the feed stream, as occurs in the real automotive application. Main conclusions are finally summarized and future challenges highlighted.

Low temperature selective catalytic reduction of NOx by NH3 over Cu modified V2O5/TiO2–carbon nanotube catalyst

A set of CuO–V2O5/TiO2–carbon nanotubes catalysts were prepared by sol–gel method and the structural characteristics of the prepared catalyst were examined by scanning electron microscope, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller surface area measurements, X-ray diffraction, X-ray photoelectron spectroscopy and temperature programmed desorption (TPD) analyses. It was observed from the results that vanadium particles were highly dispersed on the CNTs wall and the promotional effects of CuO over V2O5/TiO2–CNTs catalyst were also investigated. The positivity of the catalytic activity was attributed to the diameter of the CNTs used. Among the catalysts, V–Cu1/Ti–C10 (1 wt% Cu & 10 wt% CNTs) with CNTs having an outer diameter of 10–15 nm attained a NOx removal efficiency of 94% at 300 °C under a gas hourly space velocity of 30,000 h−1. The existence of copper species in the form of small CuO clusters and Cu2+ ions in the catalyst enhanced the redox properties of the catalyst. The presence of CNTs improved catalytic activity and provides better resistance to SO2 and H2O at the low reaction temperatures.

High-performance CeO2/halloysite hierarchical catalysts with promotional redox property and acidity for the selective catalytic reduction of NO with NH3

Earth-abundant and environmental-friendly ceria with excellent redox ability, rich surface oxygen vacancies and high oxygen storage capacity was wildly used as catalysts for NH3-SCR. A high-performance deNOx catalyst based on CeO2 decorated halloysite (HAT) synthesized via a conventional solvothermal method was originally designed and developed in this work. The CeO2/HAT exhibited a high NOx removal efficiency of > 95% and N2 selectivity of > 98% over a wider temperature range (275–400 °C) under a high gas hourly space velocity of 177,000 h−1. As revealed by XPS and LT-ESR, HAT fabrication contributed to the enrichment of active oxygen species and vacancies according to the hydroxyl-riched octahedral sheet (Al-OH) groups as well as the defect-riched nano-ceria synthesized via the constrained effects of steric hindrance. The enriched oxygen vacancies led to the reducibility strengthen of ceria, benefiting NH3 activation and avoiding the over-oxidation. In situ DFRITS demonstrated that HAT fabrication resulted in the great enrichment of Brønsted acidity and a rapid reactivity of NH3-intermediates, leading to the high NOx removal efficiency and N2 selectivity even at high temperatures.

Prediction of voltage required for nonthermal plasma based diesel exhaust treatment for removal of nitrogen oxides.

A prior prediction of voltage required for the nonthermal plasma (NTP)-based diesel exhaust treatment toward removal of nitrogen oxides, i.e., NOX (sum of NO and NO2) would help the researchers to plan for the resources required for the treatment. In this present study, experimental data set of 4032 number of input-output pairs have been collected by taking flow rate (Fr), temperature (T), discharge gap (Dg), initial NOX concentration (NOXi), and NOX removal efficiency (ηr) as the 5 inputs and the voltage required for the treatment (Vrt) as the output. Then, an attempt has been made to predict Vrt for achieving particular ηr, while other input parameters have fixed values, using multivariable linear and quadratic polynomial regression techniques. The performances of these two predictive models have been assessed during training and testing. The root mean square error (RMSE) between experimental and predicted values of Vrt with both the models has been compared, where quadratic polynomial regression-based model has been found to be performing well with an RMSE of 0.85kV for a test data of 1210 sets. This study shows that the voltage required for the treatment, to achieve a particular amount of NOX removal from the exhaust, can be predicted with very good accuracy so that the necessary arrangements for the treatment can be made by the researchers.

Computer simulation of NOx removal from diesel engine off-gases under electron beam and wet scrubber system

NOx emission from diesel engine off-gases in marine transportation sector is still an environmental issue to be solved in present day. Electron beam (EB) followed by a seawater wet scrubber method to removal NOx has been experimentally studied (Chmielewski et al., 2018). In this work numerical simulation of NOx reduction using EB followed by a water scrubber system has been carried out. The first stage was to calculate NOx removal versus dose under EB irradiation. Computer code “KINETIC” and Gear method were used, the model has been improved based our previous work (Zwolinska E. et al., 2015) and verified by the experimental results. The calculation results of NOx removal efficiency was 4.9% at 10.9 kGy dose under EB irradiation, which was a little higher than experimental value (3.5%). Computer program MATLAB was used to study NOx absorption in water. The NOx removal efficiency was increased by 17.5% at 10.9 kGy dose for inlet concentration of NOx being 1333 ppm after EB-water absorption process. At the end, NOx reduction in the simulated marine off-gas using microwave plasma was simulated using computer program Chemical Workbench. Less than 20% NOx was removed from the off-gases in microwave plasma reactor even at 9000 kGy dose for the inlet concentration of NOx being 1500 ppm. EB is more energy efficient than microwave plasma for NOx removal.

Tailoring perovskite surface composition to design efficient lean NOx trap Pd–La1-xAxCoO3/Al2O3-type catalysts (with A = Sr or Ba)

Here we report the influence of surface composition on the NOx removal efficiency of lean NOx trap Pd–La1-xAxCoO3/Al2O3-type catalysts. Three catalysts were prepared by the sequential impregnation of 30 wt.% of La1-xAxCoO3-type perovskites and 1.9 wt.% of Pd over alumina. The following perovskite compositions were used: La0.7Sr0.3CoO3, La0.7Ba0.3CoO3 or La0.5Ba0.5CoO3. The results of X-Ray diffraction, N2 adsorption-desorption at −196 °C, electron microscopy, temperature programmed techniques, and Raman and X-ray photoelectron spectroscopies demonstrated that lanthanum partial substitution by barium promoted the presence of Ba-based phases homogeneously distributed at the surface. This fact together with the higher basicity of Ba than Sr led to an increase of the surface basicity for Ba-doped samples. Likewise, Ba doping also favors the formation of small PdO particles homogenously distributed over the surface in close contact with the perovskite phase. Hence, the interactions between Pd and surface basic sites were also promoted. As a result, 1.9 wt.% Pd–30 wt.% La0.5Ba0.5CoO3/Al2O3 catalyst exhibited the highest NOx adsorption and reduction efficiency. Specifically, the NO global conversion and nitrogen production were as high as 90 % and 72 % at 350 °C, respectively. The enhancement of NOx storage capacity during the lean period is mainly assigned to the displacement of gas/solid equilibrium between NO2 and the available NOx adsorption sites due to the presence of higher concentration of basic sites at the surface. Meanwhile, the promotion of the NOx reduction capacity is due to the higher strength of NOx adsorbed species, which slows down the decomposition rate of NOx adsorbed species. Furthermore, the high proximity of Pd and perovskite phase favors the intermediate compounds diffusion. These results confirmed the excellent NOx removal efficiency of the 30 wt.% La0.5Ba0.5CoO3-based catalyst, even above than Pt-based model catalyst.

A preliminary study on effect of additive in the removal of NOx and SO2 by electron beam irradiation

In this study, an electron beam (EB) was used to remove target compounds (NOx and SO2), which exist in flue gas that is emitted from fossil fuel combustion. In order to improve the removal efficiency of NOx and SO2, we investigated various influencing factors such as type (H2O, NH4OH, NaCl, NaOH, Ca(OH)2, CaCl2, NaClO2, and HA–Na (C9H8Na2O4)) and injection amount of additive, and absorbed dose (5, 10, and 20 kGy). When NaOH solution was added to EB treatment process, the removal efficiencies of all target gases (NOx and SO2) were the highest. When NaOH was used as additive, the removal efficiencies of NOx and SO2 were additionally increased up to 60 and 18.5%, respectively, compared to electron beam only process. As the amount of injected additive increased, the removal efficiency also increased. The removal efficiencies of SO2, NO, and NO2 at 10 kGy were 100, 79.8, and 83.9%, respectively, when the stoichiometric ratio (reaction ratio) between target compounds and NaOH was 1:2. Also, the removal efficiencies of SO2, NO, and NO2 increased gradually as absorbed dose increased.

Synthesis of oxygen functionalized carbon nanotubes and their application for selective catalytic reduction of NO x with NH3.

Oxygen functionalized carbon nanotubes synthesized by surface acid treatment were used to improve the dispersion properties of active materials for catalysis. Carbon nanotubes have gained attention as a support for active materials due to their high specific surface areas (400–700 m2 g−1) and chemical stability. However, the lack of surface functionality causes poor dispersion of active materials on carbon nanotube supports. In this study, oxygen functional groups were prepared on the surface of carbon nanotubes as anchoring sites for decoration with catalytic nanoparticles. The oxygen functional groups were prepared through a chemical acid treatment using sulfuric acid and nitric acid, and the amount of functional groups was controlled by the reaction time. Vanadium, tungsten, and titanium oxides as catalytic materials were dispersed using an impregnation method on the synthesized carbon nanotube surfaces. Due to the high density of oxygen functional groups, the catalytic nanoparticles were well dispersed and reduced in size on the surface of the carbon nanotube supports. The selective catalytic reduction catalyst with the oxygen functionalized carbon nanotube support exhibited enhanced NOx removal efficiency of over 90% at 350–380 °C which is the general operating temperature range of catalysis in power plants.

In situ electron-induced reduction of NOx via CNTs activated by DBD at low temperature

In this study, a new in situ electron-induced process is presented with carbon nanotubes (CNTs) as a reduction agent activated by dielectric barrier discharge (DBD) for nitrogen oxide (NOx) abatement at low temperature (< 407 K). Compared with a single DBD system and a DBD system with activated carbon (DBD-AC), a DBD system with carbon nanotubes (DBD-CNT) showed a significant promotion of NOx removal efficiency and N2 selectivity. Although the O2 content was 10%, the NOx conversion and N2 selectivity in the DBD-CNT system still reached 64.9% and 81.9% at a specific input energy (SIE) of 1424 J/L, and these values decreased to 16.8%, 31.9% and 43.2%, 62.3% in the single DBD system and the DBD-AC system, respectively. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were utilized to investigate surface changes in the CNTs after activation by DBD to explore the NOx reduction abatement mechanism of this new process. Furthermore, the outlet gas components were also observed via Fourier transform infrared spectroscopy (FTIR) to help reveal the NOx reduction mechanism. Experimental results verified that carbon atoms excited by DBD and the structure of CNTs contributed to the synergistic activity of the DBD-CNT system. The new deNOx process was accomplished through in situ heterogenetic reduction reactions between the NOx and carbon atoms activated by the plasma on the CNTs. In addition, further results indicated that the new deNOx process exhibited acceptable SO2 tolerance and water resistance.

NOx reduction by CO over Fe/ZSM-5: A comparative study of different preparation techniques

Abstract Fe/ZSM-5 catalysts were prepared by three kinds of ion exchange methods: aqueous ion-exchange (AI), hydrothermal ion-exchange (HI) and solid-state ion-exchange (SI). Their catalytic activities were tested for NOx reduction by CO in a separated NOx adsorption-desorption process. In this paper, performances of adsorption, reduction and dynamic adsorption-reduction were all investigated. All three catalysts exhibited good reduction activity at above 300 °C. Fe/ZSM-5(SI) exhibited excellent NOx removal efficiency in the dynamic adsorption-reduction experiments. However, in the dynamic process the adsorption efficiency of Fe/ZSM-5(AI) and the reduction efficiency of Fe/ZSM-5(HI) is not very good. The catalysts were further characterized by SEM, BET, XRD, XRF, XPS and TPD. It was found that the Fe content of the Fe/ZSM-5(SI) was the highest. Further, Fe is supported in the form of Fe2O3 particles. Bronsted acid sites were also playing a major role in the high catalytic activity. TPD and in situ DRIFT experiments show that more Fe loading in α acid sites could result in a higher NOx removal efficiency.

Highly efficient WO3-FeOx catalysts synthesized using a novel solvent-free method for NH3-SCR

WO3-FeOx catalysts with various WO3 contents were synthesized through a facile solvent-free method, satisfying the selective catalytic reduction of NO (NH3-SCR). Strikingly, the optimum 30 %WO3-FeOx catalyst with the largest surface area exhibited the most outstanding catalytic activity, achieving the nearly 100 % NOx removal efficiency in a wide temperature window between 225−500 °C, which was better than that of Fe-W series catalysts reported in other studies. In addition, Raman and XPS results proved that the introduction of WO3 altered the electronic environment of Fe2O3, inducing the formation of Fe3O4 (Fe2+) and surface adsorbed oxygen. In situ DRIFTS demonstrated that the interaction between WO3 and Fe2O3 not only promoted the adsorption capacity of NH3 on the catalyst, but also contributed to the formation of adsorbed NOx species. NOx reduction reaction on WO3-FeOx catalyst proceeded via the Eley-Rideal and Langmuir-Hinshelwood mechanism synchronously. All of these factors, jointly, accounted for the superior catalytic activity and N2 selectivity of WO3-FeOx catalysts.

Removal of simulated NOx from motor vehicle exhaust by high-voltage pulsed discharge coupled with LaMn1-xFexO3 catalyst

High-voltage pulsed discharge coupled with LaMn1-xFexO3 catalyst was used to remove simulation NOx from motor vehicle exhaust. A self-made line-tube pulsed discharge reactor was adopted. Several important parameters such as diameter of stainless steel cylinder of pulsed discharge reactor and diameter of the high-voltage pole were determined. The catalysts were prepared by citric acid-EDTA method, which were characterized by X-ray photoelectron spectroscopy (XPS), electron microscopy (SEM), X-ray diffraction (XRD) and BET. The characteristic results showed that the LaMn1-xFexO3 catalysts could be synthesized successfully. Besides, the effect of calcination temperature, catalyst dosage, gas temperature, and methane addition on removal efficiency of NOx was investigated. The results indicated that the removal efficiency could reach 62.2 % within 20 min treatment.

A New Strategy for Improving the Efficiency of Low-temperature Selective Catalytic Reduction of NOx with CH4via the Combination of Non-thermal Plasma and Ag2O/TiO2 Photocatalyst

In the present work, a remarkable combination of non-thermal plasma and photocatalyst was developed to widen the operating temperature window of selective catalytic reduction(SCR) of NOx with CH4, especially to im-prove the low-temperature removal efficiency of NOx. It was shown that the operating temperature window was significantly widened. Among all the catalysts prepared, 1%Ag2O/TiO2 showed the highest catalytic activity for NOx removal due to the utilization of near ultraviolet light. The conversion of NOx to N2 over the in-plasma 1%Ag2O/TiO2 photocatalyst at 60 and 300 °C could achieve 31.8% and 53.0%, respectively. The combination mode of plasma and catalyst affected NOx removal efficiency greatly, the in-plasma catalysis outperformed the post-plasma catalytic mode remarkably, signifying the contribution of photocatalytic processes on the catalysts. Meanwhile, the characterizations of the catalyst demonstrated that the morphology and structure of the Ag2O/TiO2 catalyst were unchanged throughout the non-thermal plasma and photocatalytic processes, implying the superior stability of the catalyst.

Active sites assembly effect on CeO2-WO3-TiO2 catalysts for selective catalytic reduction of NO with NH3

Each active site on catalysts with multiple active sites is vital important to their catalytic performance, how to assemble these active sites to obtain the best performance is an attractive spot. In this work, the CeO2-WO3-TiO2 (CeWTi: Ce-W/Ti, Ce/W/Ti and W/Ce/Ti) catalysts with different loading sequence of CeO2 (redox site) and WO3 (acidic site) were prepared to investigate the active sites assembly effect on their catalytic performance for NH3-SCR reaction. Catalytic activity evaluation proposed that active sites assembly effect depends largely on the ratio of CeO2/WO3 and had a significantly influence on NOx removal efficiency over CeWTi catalysts (espeicially for Ce0.1W0.1Ti0.8 (mass weight)). From the analysis of surface properties, different assemble of active sites would affect the redox and acid properties of CeWTi catalysts. Reaction process study by in situ DRIFT suggested that the reaction over CeWTi catalysts followed Langmuir-Hinshelwood (L–H) mechanism at low temperature but Eley–Rideal (E–R) mechanism at high temperature. Based on the analysis of the reaction process, it was concluded that the control step of NH3-SCR reaction over Ce0.1W0.1Ti0.8 catalysts was the adsorption and activation of NH3. Through this study, we constructed a study strategy of active sites assembly effect that might contribute to understand the catalytic mechanism over catalysts with multiple active sites.

Using dielectric barrier discharge and rotating packed bed reactor for NOx removal

Nitrogen oxides (NOx) are the main cause of photochemical smog and acid rain, which seriously endangers the ecological environment and human health. This phenomenon is particularly serious in developing countries like China. In this work, it is the first time to combine a dielectric barrier discharge (DBD) and a rotating packed bed (RPB) for NOx removal from the simulated flue gas. A DBD is employed to oxide part of NO to the soluble NO2, which is conducive to the following absorption process using the RPB with (NH2)2CO used as the absorbent and NaClO2 as the effective additive. NOx oxidation degree can reach more than 50% under the NOx concentration of 1000 ppm. Absorption results show that the NOx removal efficiency (η) dramatically increases with the increase of the NOx oxidation degree. Additionally, it increases with the enhancement of NaClO2 concentration and rotational speed of the RPB. As a result, NOx removal efficiency can reach more than 85% at the optimal conditions. The obtained results forecast a bright prospect in the NOx removal from flue gas by combining DBD with RPB.

NOx degradation by photocatalytic mortars: The underlying role of the CH and C-S-H carbonation

This study aims to understand the impact of carbonation mechanism of C-S-H and CH in photocatalytic mortars on NOx removal efficiency. Changes in surface chemistry and microstructure induced by the carbonation of portlandite and C-S-H (AFm/AFt) were correlated with the photocatalytic efficiency of the mortars doped with three types of titania-based photocatalysts. Furthermore, the influence of cementitious matrix on the photocatalytic selectivity was evaluated by studying the capacity of hydration/carbonation products to adsorb NO2. The study revealed that in terms of both photocatalytic efficiency and selectivity, mortars with microsilica addition exhibit superior properties over the pure cement-based mortars upon carbonation. Carbonation of C-S-H (AFm/AFt) gel results in the formation of capillary pores between10–50 nm, which outbalances the shielding effects of carbonates formed, leading to the enhanced photocatalytic properties. Moreover, C-S-H gel maintains its high NO2 adsorption capacity even after carbonation, resulting in the high selectivity of the photocatalysis.