Chemiluminescence analyzer of NOx as a high-throughput screening tool in selective catalytic reduction of NO

Abstract

A chemiluminescence-based analyzer of NO_x gas species has been applied for high-throughput screening of a library of catalytic materials. The applicability of the commercial NO_x analyzer as a rapid screening tool was evaluated using selective catalytic reduction of NO gas. A library of 60 binary alloys composed of Pt and Co, Zr, La, Ce, Fe or W on Al₂O₃ substrate was tested for the efficiency of NO_x removal using a home-built 64-channel parallel and sequential tubular reactor. The NO_x concentrations measured by the NO_x analyzer agreed well with the results obtained using micro gas chromatography for a reference catalyst consisting of 1 wt% Pt on γ-Al₂O₃. Most alloys showed high efficiency at 275 °C, which is typical of Pt-based catalysts for selective catalytic reduction of NO. The screening with NO_x analyzer allowed to select Pt-Ce_(X) (X=1–3) and Pt–Fe₍₂₎ as the optimal catalysts for NO_x removal: 73% NO_x conversion was achieved with the Pt–Fe₍₂₎ alloy, which was much better than the results for the reference catalyst and the other library alloys. This study demonstrates a sequential high-throughput method of practical evaluation of catalysts for the selective reduction of NO.     

A scheme for solving strongly coupled chemical reaction equations appearing in the removal of SO2 and NOx from flue gases

The removal of NO_x from mixtures of NO-NO₂-N₂ and NO-NO₂-O₂-H₂O is discussed theoretically in this study, and the removal of ₂SO and xNO is further discussed when a gas system of NO_x-N₂-O₂-H₂O contains CO₂ and SO₂. The involved chemical reaction rate equations in the process of SO₂/NO_x removal are solved numerically using Treanor's method, in which a scheme separating chemical reactions into fast and slow groups has been proposed for improving the numerical stability. Numerical results show that the contribution of ion reactions to xNO removal is negligible, and that high temperature is not beneficial for the NO oxidation. However, high concentration of O₂ is conducive to the NO oxidation. Addition of water facilitates the NO_x removal, and increasing water vapor concentration enhances the NO_x removal efficiency; inclusion of CO₂ and SO₂ into the system favors the NO removal.     

Promotional effects of carbon nanotubes on V2O5/TiO2 for NOX removal

A series of V₂O₅/TiO₂-carbon nanotube (CNT) catalysts were synthesized by sol-gel method, and their activities for NO_X removal were compared. A catalytic promotional effect was observed by adding CNTs to V₂O₅/TiO₂. The catalyst V₂O₅/TiO₂-CNTs (10 wt.%) showed an NO_X removal efficiency of 89% at 300 °C under a GHSV of 22,500 h⁻¹. Based on X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, NH₃-temperature-programmed desorption, temperature-programmed reduction, Brunauer-Emmett-Teller surface area measurements, differential scanning calorimetry, and thermogravimetric analysis, the increased acidity and reducibility, which could promote NH₃ adsorption and oxidation of NO to NO₂, respectively, contributed to this promotion.     

Simultaneous absorption of NOx and SO2 from flue gas with pyrolusite slurry combined with gas-phase oxidation of NO using ozone

NO was oxidized into NO₂ first by injecting ozone into flue gas stream, and then NO₂ was absorbed from flue gas simultaneously with SO₂ by pyrolusite slurry. Reaction mechanism and products during the absorption process were discussed in the followings. Effects of concentrations of injected ozone, inlet NO, pyrolusite and reaction temperature on NO_x/SO₂ removal efficiency and Mn extraction rate were also investigated. The results showed that ozone could oxidize NO to NO₂ with selectivity and high efficiency, furthermore, MnO₂ in pyrolusite slurry could oxidize SO₂ and NO₂ into MnSO₄ and Mn(NO₃)₂ in liquid phase, respectively. Temperature and concentrations of injected ozone and inlet NO had little impact on both SO₂ removal efficiency and Mn extraction rate. Specifically, Mn extraction rate remained steady at around 85% when SO₂ removal efficiency dropped to 90%. NO_x removal efficiency increased with the increasing of ozone concentration, inlet NO concentration and pyrolusite concentration, however, it remained stable when reaction temperature increased from 20 °C to 40 °C and decreased when the flue gas temperature exceeded 40 °C. NO_x removal efficiency reached 82% when inlet NO at 750 ppm, injected ozone at 900 ppm, concentration of pyrolusite at 500 g/L and temperature at 25 °C.     

Synthesis and characterization of catalysts produced from paper mill sludge: I. Determination of NOx removal capability

Characteristics and catalytic properties of a series of carbon-based catalysts (CBCs) produced from paper mill sludge were evaluated. The major processes involved in the production of the catalysts were chemical activation, impregnation, pyrolysis, and post pyrolysis rinsing. The porous structure, catalytic activity and thermostability of the catalysts were tailored during the production stage by introducing hetero-atoms (zinc chloride, and ferric nitrate) in the carbon structure. Characterization of the produced CBCs included determination of the surface area, pore size, and pore size distribution (PSD) from standard N₂-adsorption isotherm data. The extent of graphitization and the presence of metal crystals were identified from X-ray diffraction (XRD). The limit of the catalyst gasification was estimated from thermogravimetric analysis (TGA) conducted in an oxidized environment. The NO_x reduction capability of the produced catalysts was evaluated in the presence of carbon monoxide using a fixed bed reactor. The reaction temperature ranged from 300 to 500°C. It was shown that paper mill sludge is an excellent precursor for the production of CBCs with NO_x removal capability of 66–94%. The catalytic capability of the produced CBCs varied according to the method of production, catalyst surface properties (surface area, pore structure, PSD), metal composition and reaction temperature. The highest NO_x removal capacity was observed for the catalytic reactions carried out at 400°C. The mesoporous catalyst produced with a Zn:Fe molar ratio of 1:0.5 exhibited the maximum NO_x removal catalytic activity of 94%.     

An integrated solution for NOx‐reduction and ‐control under lean‐burn conditions

Upcoming emission regulations order highly effective NO_x‐reduction systems in lean‐burn engines requiring new catalytic materials and integrated control of the reduction process. Thus, new approaches for NO_x‐reduction and its monitoring over an On‐Board‐Diagnostic (OBD) system are suggested throughout the globe. A promising attempt is the development of a catalytic system having an integrated NO_x‐sensor, based on selective catalytic reduction process and impedance sensors. The study displays the results achieved both with a perovskite type of self‐regenerative catalyst functioning by H₂‐reductant and with impedance NO_x‐sensors. The catalysts were tested at the temperature range of 150 °C to 360 °C yielding NO_x conversion rates of 92 % with high selectivity to N₂. Impedance sensors having NiCr₂O₄‐ and NiO‐SE and PYSZ‐ and FYSZ‐electrolytes are developed and tested at 600 °C under lean atmosphere (5 vol. % O₂). Better sensing behaviour towards NO and lower cross‐selectivity towards O₂, CO, CO₂ and CH₄ have been observed with sensors having NiO‐SE.     

Influence of synthesis conditions on NO oxidation and NOx storage performances of La0.7Sr0.3MnO3 perovskite-type catalyst in lean-burn atmospheres

Synthesis conditions of catalysts can significantly affect catalytic activities for a certain reaction. Here, a series of the La_0.7Sr_0.3MnO₃ perovskite-type catalysts was prepared by the sol–gel method under the different synthesis conditions. The faster calefactive velocities during calcination of the xerogel precursors would produce a lot of the impurities and cause the dropped amount of the excessive oxygen in perovskite, as well as the aggregated particles and the decreased surface areas; the higher calcination temperature would sinter the perovskite phases seriously; and the initial pH value of the precursor solution would greatly affect the morphology of the catalysts including the shape and the size, which directly linked to their NO_x storage capacity. Moreover, our findings revealed that the NO oxidation ability was determined by the amount of the excessive oxygen species in the perovskite. Here, the optimum synthesis conditions were achieved with the calcination temperature of 700 °C, the calefactive velocity of 2 °C min⁻¹, and the precursor solution of pH = 8. This catalyst presented the best performances for the NO oxidization and NO_x storage, i.e. the NO-to-NO₂ conversion of 70.2% and the NO_x storage capacity of 170.4 μmol g⁻¹.     

Diesel emission control system using combined process of nonthermal plasma and exhaust gas components' recirculation

A NO_x aftertreatment system, using nonthermal plasma (NTP) reduction and exhaust gas components' recirculation, is investigated. A pilot-scale system is applied to a stationary diesel engine. In this system, NO_x is first removed by adsorption, and subsequently, the adsorbent is regenerated by thermal desorption. NO_x desorbed is reduced by using nitrogen NTP. Moreover, NO_x, CO₂, and water vapor recirculated into the engine intake reduce NO_x. In this study, approximately 57% of the NO_x of the exhaust (NO_x: 240-325 ppm, flow rate = 300 NL/min) can be continuously treated for 58 h. A system energy efficiency of 120 g (NO₂)/kWh is obtained.     

KGa-priderite and related compound for the selective reduction of nitrogen monoxide with propylene

The catalytic activity of KGa-priderite, K_1.6Ga_1.6Ti_6.4O₁₆, and its related compound KGa₈Ga₉Ti₁₅O₅₆ was investigated for the selective reduction of nitrogen monoxide (NO) with propylene (C₃H₆) in the presence of high oxygen concentrations. The KGa-priderite showed significant activity during this reaction, but the related compound showed only a little activity. These compounds are quite different from the conventional catalysts for NO_x selective reduction and are characterized by the fact that their properties are free from the effects of solid acidity and support metals. This difference was attributable to the NO desorption rate at the surface of these compounds. It has become clear that the KGa-priderite catalyst remarkably adsorbed NO, and it is suggested that the amount of NO adsorbed and the amount of catalytic activity are able to be increased by the design of priderite structure.     

原位漫反射红外光谱研究NO和NH3在MnOx/TiO2催化材料上的吸附行为及反应机理

MnO_x/TiO₂催化材料在选择性催化还原过程中表现出了较好的低温催化活性,为了深入了解其作用机理,进一步改善催化活性,本工作采用原位漫反射红外光谱法系统地分析了NO和NH₃在MnO_x/TiO₂催化材料上的单吸附和共吸附行为。分析认为,该催化材料表面发生的选择性催化还原过程符合Eley-Ridal机理,催化反应发生在吸附态的NH₃和气态NO之间,而吸附态的NO及后续生成的硝酸盐、亚硝酸盐等物质会占据催化材料的活性位点,影响其对NH₃的吸附,进而导致脱硝活性下降。     

Selective catalytic reduction of NOx by CO (CO-SCR) over metal-supported nanoparticles dispersed on porous alumina

The selective catalytic reduction of NO_x by CO (CO-SCR) was investigated over metals supported on porous alumina. The Pt, Co, Fe and Ni nanoparticles were dispersed on the alumina and characterized by XRD, textural properties, FTIR spectroscopy, chemical analyses, Py adsorption followed by FTIR measurements, HRTEM and SEM-EDS. Among the solids studied, the Pt/Al₂O₃ and NiPt/Al₂O₃ catalysts exhibited improved performance due to the interaction and synergy between the Pt(Ni) nanoparticles and the support. In other words, the electron transfer facility between the PtO_x(Ni) and chlorined Pt species on the support provided a more active solid in the CO-SCR reaction. The surface acidity of Lewis acid sites and the porous features of the Pt/Al₂O₃ and NiPt/Al₂O₃ catalysts also contributed significantly to the high performance of these materials in the NO_x conversion. The Pt/Al₂O₃ and NiPt/Al₂O₃ catalysts were tolerant to the poisoning by SO₂ and H₂O and depicted a superior catalytic performance, compared to the other solids.     

Oxide Catalysts with Ultrastrong Resistance to SO2 Deactivation for Removing Nitric Oxide at Low Temperature

Nitrogen oxides are one of the major sources of air pollution. To remove these pollutants originating from combustion of fossil fuels remains challenging in steel, cement, and glass industries as the catalysts are severely deactivated by SO₂ during the low‐temperature selective catalytic reduction (SCR) process. Here, a MnO_X/CeO₂ nanorod catalyst with outstanding resistance to SO₂ deactivation is reported, which is designed based on critical information obtained from in situ transmission electron microscopy (TEM) experiments under reaction conditions and theoretical calculations. The catalysts show almost no activity loss (apparent NO_X reaction rate kept unchanged at 1800 µmol g^?1 h^?1) for 1000 h test at 523 K in the presence of 200 ppm SO₂. This unprecedented performance is achieved by establishing a dynamic equilibrium between sulfates formation and decomposition over the CeO₂ surface during the reactions and preventing the MnO_X cluster from the steric hindrance induced by SO₂, which minimized the deactivation of the active sites of MnO_X/CeO₂. This work presents the ultralong lifetime of catalysts in the presence of SO₂, along with decent activity, marking a milestone in practical applications in low‐temperature selective catalytic reduction (SCR) of NO_X.     

Characterization and activity of alkaline earth metals loaded CeO2–MOx (M = Mn,Fe) mixed oxides in catalytic reduction of NO

Nanocrystalline CeO₂–MO_x mixed oxides (M = Mn, Fe) with different M/(M + Ce) molar ratio are prepared by sol–gel combustion method. X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Temperature Programmed Reduction with H₂ (H₂-TPR) and N₂-adsorption (BET) analyses are conducted to characterize the physical–chemical properties of the catalysts. The activity of catalysts for reduction of NOx with ammonia has been evaluated. The CeO₂–MnO_x catalysts showed better low temperature activity than CeO₂–FeO_x. The superior activity of CeO₂–MnO_x with Mn/(Mn + Ce) molar ratio of 0.25 respect to other catalysts (with 83% NO conversion and 68% N₂ yield at 200 °C) is associated to nanocrystalline structure, reducibility at low temperature and synergistic effect between Ce and Mn that are observed by XRD, TEM and H₂-TPR. The CeO₂–FeO_x catalysts were found to be active at high temperature, being Ce–Fe the best catalyst yielded 82% NO conversion at 300 °C. The effect of alkaline earth metals (Ca, Mg, Sr and Ba) loading on the structure and catalytic activity of cerium mixed oxides are also investigated. Loading of Ba enhanced the NO reduction activity of mixed oxides due to the increase of number of basic sites. Highest performance with 91% NO conversion and 80% N₂ yield attained over CeO₂–MnO_x (0.25)-Ba (7%) catalyst at 200 °C.     

High-throughput technology for novel SO2 oxidation catalysts

We review the state of the art and explain the need for better SO₂ oxidation catalysts for the production of sulfuric acid. A high-throughput technology has been developed for the study of potential catalysts in the oxidation of SO₂ to SO₃. High-throughput methods are reviewed and the problems encountered with their adaptation to the corrosive conditions of SO₂ oxidation are described. We show that while emissivity-corrected infrared thermography (ecIRT) can be used for primary screening, it is prone to errors because of the large variations in the emissivity of the catalyst surface. UV-visible (UV-Vis) spectrometry was selected instead as a reliable analysis method of monitoring the SO₂ conversion. Installing plain sugar absorbents at reactor outlets proved valuable for the detection and quantitative removal of SO₃ from the product gas before the UV-Vis analysis. We also overview some elements used for prescreening and those remaining after the screening of the first catalyst generations.     

Wurtzite-derived ternary I–III–O2 semiconductors

Ternary zincblende-derived I–III–VI₂ chalcogenide and II–IV–V₂ pnictide semiconductors have been widely studied and some have been put to practical use. In contrast to the extensive research on these semiconductors, previous studies into ternary I–III–O₂ oxide semiconductors with a wurtzite-derived β-NaFeO₂ structure are limited. Wurtzite-derived β-LiGaO₂ and β-AgGaO₂ form alloys with ZnO and the band gap of ZnO can be controlled to include the visible and ultraviolet regions. β-CuGaO₂, which has a direct band gap of 1.47 eV, has been proposed for use as a light absorber in thin film solar cells. These ternary oxides may thus allow new applications for oxide semiconductors. However, information about wurtzite-derived ternary I–III–O₂ semiconductors is still limited. In this paper we review previous studies on β-LiGaO₂, β-AgGaO₂ and β-CuGaO₂ to determine guiding principles for the development of wurtzite-derived I–III–O₂ semiconductors.     

NOX reduction over paper-structured fiber composites impregnated with Pt/Al2O3 catalyst for exhaust gas purification

Pt/Al₂O₃ catalyst powder was successfully incorporated in a microstructured paper-like matrix composed of a ceramic fiber network, by use of a simple papermaking technique. As-prepared composite, denoted paper-structured catalyst, was applied to the reduction of nitrogen oxide (NO _X ) in the presence of propene, for exhaust gas purification. The paper-structured catalyst demonstrated higher NO _X reduction efficiency and more rapid thermal responsiveness than a conventional Pt-loaded honeycomb catalyst, indicating that the paper-like structure with interconnected pore spaces contributes to effective transport of heat and reactants to the catalyst surfaces. Furthermore, the paper-structured catalyst with the appearance of flexible paperboard has a high degree of utility. The efficiency of utilization of Pt catalyst was improved by using hierarchically assembled paper-structured catalysts with preferential location of Pt catalyst in the upper part. The paper-structured catalyst composite with paper-like utility and porous microstructure is thought to be a promising catalytic material for efficient NO _X gas purification.     

Ethylenediamine-assisted solvothermal synthesis of one-dimensional CdxZn(1−x)S solid solutions and their photocatalytic activity for nitrobenzene reduction

A series of one-dimensional Cd_xZn_(1−x)S semiconductor alloys were prepared via a hydrothermal method with the assistance of ethylenediamine at 180 °C for 12 h. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption/desorption and Fourier transform infrared techniques. With the value of x increased, the band gap of Cd_xZn_(1−x)S semiconductor alloys gradually decreased indicating that catalysts were exchanged to visible-light response. Photocatalytic reduction results showed that Cd_0.73Zn_0.27S exhibited the highest photocatalytic activity toward photo production of aniline via nitrobenzene reduction under visible irradiation respectively. The reaction mechanism was also discussed.     

Engineering Bimetallic Ag–Cu Nanoalloys for Highly Efficient Oxygen Reduction Catalysts: A Guideline for Designing Ag‐Based Electrocatalysts with Activity Comparable to Pt/C‐20%

Development of highly active and stable Pt‐free oxygen reduction reaction catalysts from earth‐abundant elements remains a grand challenge for highly demanded metal–air batteries. Ag‐based alloys have many advantages over platinum group catalysts due to their low cost, high stability, and acceptable oxygen reduction reaction (ORR) performance in alkaline solutions. Nevertheless, compared to commercial Pt/C‐20%, their catalytic activity still cannot meet the demand of commercialization. In this study, a kind of catalysts screening strategy on Ag_x Cu_100?x nanoalloys is reported, containing the surface modification method, studies of activity enhancement mechanism, and applied research on zinc–air batteries. The results exhibit that the role of selective dealloying (DE) or galvanic displacement (GD) is limited by the “parting limitation”, and this “parting limitation” determines the surface topography, position of d‐band center, and ORR performance of Ag_x Cu_100?x alloys. The GD‐Ag₅₅Cu₄₅ and DE‐Ag₂₅Cu₇₅ catalysts alloys present excellent ORR performance that is comparable to Pt/C‐20%. The relationship between electronic perturbation and specific activity demonstrates that positive shift of the d‐band center (≈0.12 eV, relative to Ag) for GD‐Ag₅₅Cu₄₅ is beneficial for ORR, which is contrary to Pt‐based alloys (negative shift, ≈0.1 eV). Meanwhile, extensive electrochemical and electronic structure characterization indicates that the high work function of GD‐Ag₅₅Cu₄₅ (4.8 eV) is the reason behind their excellent durability for zinc–air batteries.     

Effects of particulates, heavy metals and acid gas on the removals of NO and PAHs by V2O5–WO3 catalysts in waste incineration system

This study investigated the activities of prepared and commercial V₂O₅–WO₃ catalysts for simultaneous removals of NO and polycyclic aromatic hydrocarbons (PAHs) and the influences of particulates, heavy metals, SO₂, and HCl on the performances of catalysts. The experiments were carried out in a laboratory-scale waste incineration system equipped with a catalyst reactor. The DREs of PAHs by prepared and commercial V₂O₅–WO₃ catalysts were 64% and 72%, respectively. Increasing the particulate concentrations in flue gas suppressed the DRE of PAHs, but increasing the carbon content on surface of catalysts promotes the NO conversions. The DRE of PAHs by the catalysts was significantly decreased by the increased concentrations of heavy metal Cd, but was promoted by high concentration of Pb. The influence level of SO₂ was higher than HCl on the performances of V₂O₅–WO₃ catalysts for PAHs removal, but was lower than HCl for NO removal. Prepared and commercial V₂O₅–WO₃ catalysts have similar trends on the effects of particulates, heavy metals, SO₂, and HCl. The results of ESCA analysis reveal that the presences of these pollutants on the surface of catalysts did not change the chemical state of V and W.     

Surface Tension Measurements on Industrial Alloys by the Drop-Weight Method

The drop-weight method has been successfully applied to a representative set of industrial alloys (W–Re₂₆, Mo–Re₅₀, Pt–Rh₁₀, Pt–Rh₃₀, Ti–Al₆–V₄, AISI 316 L stainless steel, INCONEL 182 and 600 alloys), with the result that very reproducible surface tension measurements ( /<0.5%) have been established for these materials at the liquidus temperature. This work supports the idea that the simplicity of the drop-weight method should attract much more attention for production control or to provide reference values at the liquidus temperature, although it cannot be used for temperature coefficient measurements of the surface tension.