Catalytic Reduction Method Research Articles

Facile synthesis of flake‐like MnO 2 /CNFs catalysts and their activity in low‐temperature NO reduction with NH 3

A series of MnO2/carbon nanofibres (CNFs) catalysts were prepared by a facile co-precipitation method for low-temperature selective catalytic reduction (SCR) of NO with NH3. These catalysts were characterised by the techniques of specific surface area measurements (BET), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR). The XRD, FESEM and TEM results showed that the CNFs were surrounded by MnO2 nanoflakes. Compared with the MnO x /CNFs catalyst prepared by the wet impregnation method, the MnO2/CNFs catalysts exhibited better low-temperature SCR activity at low temperature. The XPS results indicated that a higher concentration of Mn4+ and more surface oxygen species exited on the surface for 8% MnO2/CNFs catalyst. The H2-TPR profiles displayed that the 8% MnO2/CNFs catalyst presented stronger low-temperature reducibility than the MnO x /CNFs catalyst. Based on the abovementioned favourable properties, the 8% MnO2/CNFs catalyst has an excellent performance in the low-temperature SCR of NO with NH3.

SO2-tolerant and H2O-promoting Pt/C catalysts for efficient NO removal via fixed-bed H2-SCR

In this paper, Pt supports on carbon black powder (Vulcan XC-72) were synthesized via a hydrothermal method for selective catalytic reduction (SCR) of NO with H2 in the presence of 2vol% O2 over a wide temperature of 20-300°C. The results showed that the 3 and 5wt% Pt/C catalysts resulted in high NO conversion (>90%) over a temperature range of 120 to 300°C, and the maximum NO conversion of 98.6% was achieved over 5wt% Pt/C at 120°C. Meanwhile, the influence of SO2 and H2O on the catalyst performance of 3wt% Pt/C was investigated. The catalysts exhibited good SO2 poisoning resistance when the SO2 concentration was lower than 260ppm. Moreover, a positive effect on NO conversion was detected with the addition of 3 and 5vol% H2O in the feed gas stream. Graphical abstract TEM image and good NO conversion performance of the Pt/C catalysts.

An improved method for selective catalytic reduction of nitrogen oxides in exhaust gases

The selective catalytic reduction (SCR) of nitrogen dioxide in an air flow modeling the exhaust gas from an internal combustion engine is studied. Granulated V2O5 (13.5%)–MnO2 (0.7–1.0%)/Al2O3 powder (AVK-10M catalyst) and ammonia injected into a SCR catalytic cell are used as a heterogeneous catalyst of NO2 reduction and a reducing agent, respectively. If the efficiency of NO2 removal is high enough and satisfies the requirements of the State Sanitary Standards for the maximum permissible concentrations of substances emitted into the atmosphere ( $$MP{C_{N{O_2}}}$$ = 0.085 mg/m3), the reducing agent (ammonia) is not completely consumed during SCR, so a considerable amount of NH3 can be released into the atmosphere. Therefore, a strict control of both NO2 and unreacted ammonia emissions is needed. The dependences of the concentrations of [NH3] and [NO2] on the [NH3]/[NO2] ratio for the model air flow passed through the AVK-10M granular heterogeneous catalyst are measured. It is found that the maximum degree of removal of NO2 from the air takes place at [NH3]/[NO2] = 1.3. In the conventional process, the concentration of [NO2] drop from 530.00 to 0.07 mg/m3, i.e., below the $$MP{C_{N{O_2}}}$$ . At the same time, the ammonia concentration increases to [NH3] = 3.4 mg/m3, which becomes 85 times the $$MP{C_{N{O_2}}}$$ , 0.04 mg/m3. To remove unreacted ammonia from air flows, we developed [P–(SO3 -)2 · Me2+] sulfocationites, where Me are the Cu and/or Ca ions, P is a styrene–divinylbenzene copolymer. It is shown that the concentration of ammonia passed through the adsorption cell filled with a freshly sulfocationite drops below $$MP{C_{N{H_3}}}$$ = 0.04 mg/m3. The dependences of the dynamic exchange capacity (DEC) before ammonia breakthrough for the [P–(SO3 -)2 · Cu2+] delta-sulfocationite on the air flow rate, [NH3] concentration, and humidity are measured. The maximum value of the DEC, δ = 59.5 mg/cm3, is observed at an air flow velocity of 2.171 m/s, [NH3] = 0.0035 mg/L, and 75% humidity. To illustrate practical applications of the proposed improved SCR method, it is shown that a 3-L replaceable [P–(SO3 -)2 · Cu2+] sorbent cartridge in a SCR exhaust gas purifier for a car internal combustion engine does not need replacement more frequently than every 50000 km.

The promotional effect of Ce on CuFe/beta monolith catalyst for selective catalytic reduction of NOx by ammonia

The Cu3Fe3/beta and Cu3Fe3/Ce/beta catalysts were prepared by incipient wetness impregnation method, their activity, hydrothermal stability and C3H6 resistance for selective catalytic reduction of NOx with ammonia (NH3-SCR) were investigated systematically. The experimental results indicated that Cu3Fe3/Ce/beta performed better NH3-SCR performance, because the dispersion of Fe and/or Cu species of Cu3Fe3/Ce/beta was higher than that of Cu3Fe3/beta. In addition, the hydrothermal stability of Cu3Fe3/beta was improved by the addition of Ce. The results of N2 adsorption-desorption, XRD and NH3-TPD, showed that the change of the texture, structure and acid density of Cu3Fe3/Ce/beta was slighter than that of Cu3Fe3/beta after hydrothermal aging, the results of UV–vis DRS indicated that the aggregation of metal ions during hydrothermal aging process was inhibited by the introduction of Ce. Furthermore, compared to Cu3Fe3/beta, less amount of C3H6/O2 was adsorbed on Cu3Fe3/Ce/beta, thus, the C3H6 resistance of Cu3Fe3/Ce/beta was better than that of Cu3Fe3/beta. In conclusion, the catalytic activity, hydrothermal stability and C3H6 resistance of Cu3Fe3/beta were improved by the addition of Ce.

Promotional Effect of Molybdenum Additives on Catalytic Performance of CeO2/Al2O3 for Selective Catalytic Reduction of NOx

A series of CeO2/Al2O3 and CeMoxOy/Al2O3 catalysts were prepared by an extrusion method for selective catalytic reduction of NOx, and were characterized by techniques of XRD, XPS, N2-BET, H2-TPR and NH3-TPD. Promotional effects of molybdenum additives on catalytic performances and tolerances toward SO2 and H2O poisoning of the catalysts were comparatively studied. Results showed that the CeO2/Al2O3 catalyst with the Ce/Al molar ratio of 1:5 exhibited the best catalytic performance; molybdenum additives greatly improved catalytic performance of the CeMoxOy/Al2O3 catalysts, and the catalyst with the Al/Ce/Mo molar ratio of 5:1:0.15 calcinated at 550 °C exhibited the highest catalytic activity above 95 % in active temperature window of 250–430 °C under the gas hourly space velocity (GHSV) of 7200 h−1. Moreover, molybdenum additives broadened the range of the active temperature, and significantly enhanced the anti-sulfur poisoning ability. Analysis showed that the promotional effects of molybdenum additives were attributed to the improvement of specific surface area, increment of surface acidity and the enhancement of the redox properties. The molybdenum additives significantly increase the catalytic performance of CeO2/Al2O3 for selective catalytic reduction of NOx and greatly broaden the range of the active temperature. The reasons mainly due to molybdenum additives improve the specific surface area, increase the proportion of Ce3+/(Ce4++Ce3+) and Oα/(Oα + Oβ) on the surface, and enhance the amount of the Lewis acid sites.

Chromium(VI) reduction in aqueous medium by means of catalytic membrane reactors

A novel method for catalytic reduction of chromium(VI) to chromium(III) in model and real water is proposed in this work. Hydrogen was used as a reducer. Three different catalytic membrane reactors were prepared and employed in the studied reaction. The catalytic membrane reactors were prepared using commercial corundum hollow fiber membranes. The active phases, palladium, cerium oxide, iron oxide or combinations of them, were incorporated by incipient wetness impregnation of the corresponding water-soluble salts followed by calcination and reduction. The catalytic tests were performed in semi-batch mode at ambient conditions. A mass flow controller was used to supply hydrogen to one end of the membrane whilst the other end was kept closed. The reactors were submerged into a vessel containing the chromate solution. The concentration of the chromate was continuously monitored following a standard analytical method. The initial chromate concentration was varied between 0.5 and 18mgL−1. In order to completely reduce the Cr(VI) to Cr(III), it was necessary to decrease the pH of the solution to 3. In the end of the tests the final solutions were neutralized to pH 8 and filtered. The content of chromium in the final solutions and in the precipitates was determined by inductively coupled plasma (ICP) technique. It was demonstrated that for the studied reaction the presence of palladium is essential. In all experiments, with synthetic and real water adjusted to pH 3, the catalytic membrane reactors containing palladium (0.3–0.9w/w%) effectively reduced the chromium to levels below 0.03mgL−1 without losing activity in repetitive runs. The results from ICP analyses demonstrated that the chromium can be completely eliminated from the water after neutralization and filtration.

Emission Control Diesel Power Plant for Reducing Oxides of Nitrogen through Selective Catalytic Reduction Method using Ammonia

Background/Objectives : The major pollutant that comes out from engine exhaust of Diesel Power Plant (DPP) is Nitrogen Oxide (NO x )as well as Sulphur oxides (SO x ). Since NOx concentration level is higher it affects our environment to great extent. Our main objective of our project is to reduce NO x concentration level to lower rate of parts per million (ppm). Methods/Statistical Analysis : The NO x concentration level is higher in DPP as they didn’t install any NO x control methods. We suggested using Selective Catalytic Reduction (SCR) method for controlling NO x emission. Ammonia (NH 3 ) is making use of reagent in SCR technique and it is inject to the exhaust stream. Findings: NH 3 reacts with NO x present in the exhaust and it is converted into Nitrogen (N 2 ) and water (H 2 O). It is proposed that, if SCR system is installed in Diesel Power Plant, NOx concentration level is expected to reduce from 1100 ppm to 132 ppm. Application/Improvements: If The proposed system is implemented successfully in the power plant, then NOx concentration level could be reduced to approximately 132ppm (<2 g / kWh).

Building Selectivity for NO Sensing in a NOx Mixture with Sonochemically Prepared CuO Structures

Several technologies are available for decreasing nitrogen oxide (NOx) emissions from combustion sources, including selective catalytic reduction methods. In this process, ammonia reacts with nitric oxide (NO) and nitrogen dioxide (NO2). As the stoichiometry of the two reactions is different, electrochemical sensor systems that can distinguish between NO and NO2 in a mixture of these two gases are of interest. Since NO and NO2 can be brought to equilibrium, depending on the temperature and the surfaces that they are in contact with, the detection of NO and NO2 independently is a difficult problem and has not been solved to date. In this study, we explore a high surface area sonochemically prepared CuO as the resistive sensing medium. CuO is a poor catalyst for NOx equilibration, and requires temperatures of 500 C to bring about equilibration. Thus, at 300 C, NO and NO2 retain their levels after interaction with CuO surface. In addition, NO adsorbs more strongly on the CuO over NO2. Using these two concepts, we can detect NO with minimal interference from NO2, if the latter gas concentration does not exceed 20% in a NOx mixture over a range of 100–800 ppm. Since this range constitutes most of the range of total NOx concentrations in diesel and other lean burn engines, this sensor should find application in selective detection of NO in this combustion application. A limitation of this sensor is the interference with CO, but with combustion in excess air, this problem should be alleviated.

Organocatalyzed Reduction of Tertiary Phosphine Oxides

AbstractA novel selective catalytic reduction method of tertiary phosphine oxides to the corresponding phosphines has been developed. Notably, the reaction proceeds smoothly with low catalyst loadings of 1–5 mol% even at low temperature (70 °C). Under the optimized conditions various phosphine oxides could be selectively reduced and the desired phosphines were usually obtained in excellent yields above 90%. Furthermore, we have developed a one‐pot reaction sequence for the preparation of valuable phosphine⋅borane adducts. Simple addition of BH3⋅THF subsequent to the reduction step gave the desired adducts in yields up to 99%.magnified image

Porous bimetallic Mn2Co1Ox catalysts prepared by a one-step combustion method for the low temperature selective catalytic reduction of NOx with NH3

The porous Mn2Co1Ox catalysts are prepared by a one-step combustion (CB) method for low temperature deNOx process. This catalyst displays an excellent NH3-SCR activity, achieving 100% NOx conversion at 150–300°C. In addition, the catalyst shows high N2 selectivity, wide operating temperature window, high stability, and high H2O and SO2 resistance. The crystalline phase of CoMn2O4, porous structure and large specific surface areaare beneficial for the deNOx activity. The catalyst exists abundant Mn4+, Co3+ and surface adsorbed oxygen species, which improve the catalyst's redox ability. Plenty of acid sites from the strong interaction of manganese and cobalt oxide enhance the catalyst performance.

In situ IR studies of Co and Ce doped Mn/TiO2 catalyst for low-temperature selective catalytic reduction of NO with NH3

The Mn–Co–Ce/TiO2 catalyst was prepared by wet co-impregnation method for selective catalytic reduction of NO by NH3 in the presence of oxygen. The adsorption and co-adsorption of NH3, NO and O2 on catalysts were investigated by in situ FTIR spectroscopy. The results suggested that addition of cobalt and cerium oxides increased the numbers of acid and redox sites. Especially, the cobalt oxide produced lots of Brønsted acid sites, which favor to the adsorption of coordinated NH3 through NH3 migration. Ce addition improved amide ions formation to reach best NO reduction selectivity. A mechanistic pathway over Mn–Co–Ce/TiO2 was proposed. At low-temperature SCR reaction, coordinated NH3 reacted with NO2−, and amide reacted with NO (ad) or NO (g) to form N2. NO2 was related to the formation of nitrite on Co-contained catalysts and the generation of NH2− on Ce-contained catalysts. At high temperature, the other branch reaction also occurred between the coordinated NH3 and nitrate species, resulting in N2O yield increase.

MoO3 modified CeO2/TiO2 catalyst prepared by a single step sol–gel method for selective catalytic reduction of NO with NH3

A MoO3 modified CeO2/TiO2 catalyst was prepared by a single step sol–gel method for selective catalytic reduction of NO with NH3. The experimental results indicates that MoO3 modified CeO2/TiO2 catalyst exhibited higher SCR activity and resistance to 10% H2O and 1000ppm SO2. From the characterization results, it can be concluded that good physical properties, highly dispersed active species of Ce and Mo, more appearance of Ce3+ and chemisorbed oxygen, strong interaction among ceria, molybdenum and titania, and high oxygen storage capacity might contribute to the excellent deNOx performance of CeO2–MoO3/TiO2 catalyst prepared by a single step sol–gel method.

Activity and characterization of a Ce–W–Ti oxide catalyst prepared by a single step sol–gel method for selective catalytic reduction of NO with NH3

A Ce–W–Ti mixed oxide catalyst prepared by a single step sol–gel method exhibited excellent SCR activity and high resistance to H2O and SO2. The excellent catalytic performance might be attributed to the improved dispersion of Ce species on TiO2, the increase in the amount of Ce3+ and chemisorbed oxygen and the strong interaction among ceria, tungsten and titania owing to the addition of WO3.

A Density Functional Theory Study of NO Reduction by C3H8 Aided Selective Catalytic Reduction Method

In this theoretical work sequential adsorption of H2 and O2 on a Ag 7 + cluster surface is first studied and Ag 7 + H2O2 cluster co-complex thereby obtained is used for the NO reduction process. This cationic charged silver nano cluster simulates small Ag crystals experimentally detected on γ-Al2O3 support. For NO reduction, three different mechanisms and intermediate steps of these mechanisms reported in experimental literature are examined. Energy profiles, activation barriers and transition states of the reaction steps involved are studied. Some intermediate steps turned out to have high activation barriers. Hence a combined mechanism selected from the favorable steps found in these three mechanisms is proposed. By using this combined mechanism, reduction of NO to N2 is achieved.

Synthesis, Characterization and NH&lt;sub&gt;3&lt;/sub&gt;-SCR Activity of MnSAPO-34 Molecular Sieves

采用水热合成方法制备含锰的SAPO-34分子筛（MnSAPO-34）催化剂,考察了锰投加量、焙烧温度及晶化时间对催化剂氨选择性催化还原（SCR）氮氧化物反应活性的影响,并通过X射线光电子能谱（XPS）、程序升温还原（TPR）、程序升温脱附（TPD）等多种分析手段对催化剂进行表征.活性测试结果表明,当MnO与P_2O_5的摩尔比n_（MnO）/n_（P_2O_5）=0.1,采用6h晶化时间,550℃焙烧制备的MnSAPO-34分子筛具有最佳SCR活性NO_x转化率接近100%,N_2选择性高于80%.分析结果表明,Mn的引入对分子筛的晶体及多孔结构有较大影响过多的引入会降低结晶度及产生非骨架锰氧化物,同时还会降低分子筛的比表面积和孔容,但焙烧温度的降低以及晶化时间的缩短可以提高分子筛的比表面积和孔容.高温焙烧后分子筛表面出现了高氧化态锰物种,以Mn（4＋）为主,而提高Mn（3＋）的比例则有利于提高催化活性.在适当的合成条件下,Mn的引入可增强分子筛对NO和NH_3分子的吸附,而强吸附态NO及强吸附态NH_3的相互作用可能是催化活性快速提高的原因。

Higher order fuzzy logic in controlling selective catalytic reduction systems

Abstract This paper presents research on applications of fuzzy logic and higher-order fuzzy logic systems to control filters reducing air pollution [1]. The filters use Selective Catalytic Reduction (SCR) method and, as for now, this process is controlled manually by a human expert. The goal of the research is to control an SCR system responsible for emission of nitrogen oxide (NO) and nitrogen dioxide (NO2) to the air, using SCR with ammonia (NH3). There are two higher-order fuzzy logic systems presented, applying interval-valued fuzzy sets and type-2 fuzzy sets, respectively. Fuzzy sets and higher order fuzzy sets describe linguistically levels of nitrogen oxides as the input, and settings of ammonia valve in the air filter as the output. The obtained results are consistent with data provided by experts. Besides, we show that the type-2 fuzzy logic controllers allows us to obtain results much closer to desired parameters of the ammonia valve, than traditional FLS.

Effect of Cerium on Manganese Base Catalysts by Co-Precipitation for Low-Temperature SCR of NO with NH&lt;sub&gt;3&lt;/sub&gt;

Catalysts of Mn/TiO2 and Mn-Ce /TiO2 prepared by co-precipitation method for low temperature selective catalytic reduction (SCR) of NO with NH3 were investigated in this study. The experimental results showed that co-precipitation method after improvement, the NO conversion of Mn-Ce/TiO2 catalyst increased sharply. Meanwhile, the addition of cerium has significant effects on the catalytic activity. Characterizations of catalysts were carried out by XRD, BET and H2-TPR. The characterized results indicated that co-precipitation method after improvement, in temperature windows 150 to 300 °C, showed higher NOx conversion.

ChemInform Abstract: Copper‐Catalyzed Reduction of Alkyl Triflates and Iodides: An Efficient Method for the Deoxygenation of Primary and Secondary Alcohols.

We describe an effective method for catalytic reduction of 1° alkyl sulfonates, and 1° and 2° iodides in the presence of a wide range of functional groups. This Cu-catalyzed reaction provides a means for the effective deoxygenation of alcohols, as demonstrated by the highly selective reduction of 1° alcohols using a triflation/reduction sequence. A preliminary study of the reaction mechanism suggests that the reduction does not involve free-radical intermediates.

Microwave-assisted catalytic reduction of NO into N2 by activated carbon supported Mn2O3 at low temperature under O2 excess

The catalytic reduction of NO by AC with high activity and selectivity to N2 at low temperature under O2 excess is a challenge. Herein, we report a novel method for selective catalytic reduction of NO into N2 by activated carbon supported Mn2O3 in the microwave catalytic reaction mode. Furthermore, the effects of a series of reaction parameters, including microwave heating behavior, reaction temperature, outlet gas temperature, Mn2O3 loading, microwave input power and O2 concentration have been investigated. Novel results were observed that microwave-assisted catalytic reduction of NO into N2 over Mn2O3/AC is of high efficiency with 98.7% NO conversion and 99.8% NO selectivity to N2 at temperature as low as 300°C under O2 excess. We also found that microwave irradiation exhibited microwave selective effect in the microwave catalytic reaction mode. The microwave catalytic reaction mode is a viable and promising method for flue gas control using selective catalytic reduction of NO by AC compared with the conventional reaction mode.

Influence of the Re introduction method onto Pd/TiO2 catalysts for the selective hydrogenation of succinic acid in aqueous-phase

Bimetallic Re-Pd catalysts were prepared by addition of Re onto a Pd/TiO2 monometallic catalyst, either by a catalytic reduction method or by successive impregnation. The physical and chemical properties of the bimetallic catalysts were evaluated by several characterization techniques, including analysis by transmission electronic microscopy, hydrogen chemisorption, temperature programmed reduction and X-ray photoelectron spectroscopy to explain their different catalytic performances in the selective hydrogenation of succinic acid to 1,4-butanediol in aqueous solution. The localization of the Re deposit on the parent Pd catalyst surface varied according to the Re introduction mode. The catalytic reduction method induced a selective Re deposit at the Pd–TiO2 interface compared to a random distribution obtained by successive impregnation. The oxidation state of the Re species (Re3+, Re0) on the reduced bimetallic samples was also linked to their preparation mode.