Catalytic Oxidation Of Ammonia Research Articles

산성 Fe-ZSM5 담체에 담지된 귀금속 촉매를 활용한 암모니아의 선택적 산화반응

본 연구에서는 산성을 갖는 Fe-ZSM5를 담체로 활용하여 Pd, Pt 등 귀금속을 담지한 후, 제조 촉매의 암모니아의 선택적 산화반응 활성을 평가하였다. 이들 중 Pt/Fe-ZSM5가 Pd/Fe-ZSM5 보다 높은 활성을 나타냈다. 또한 Pt/Fe-ZSM5 촉매에서 ZSM5 구조체 내 Fe의 이온교환량을 달리한 촉매의 실험을 수행하여, 암모니아의 선택적 산화반응에 가장 우수한 활성을 보이는 최적 조성비를 탐색하였다. 그 결과, Fe의 이온교환량이 적을수록 반응 활성이 증가하는 경향을 보였고, 저온 영역인 <TEX>$250^{\circ}C$</TEX>에서 100%의 암모니아 전환율을 나타냈다. 이와 같이 암모니아의 선택적 산화반응에 효과적인 Fe-ZSM5 담체에 대하여, ICP-AES, BET, XRD, <TEX>$NH_3$</TEX>-TPD 등과 같은 특성 분석을 수행하여 제조 촉매의 구조와 물성이 반응활성에 미치는 영향을 검토해보았다. In this study, we investigated the activity of Pd and Pt supported on acidic Fe-ZSM5 supports for selective catalytic oxidation of ammonia (<TEX>$NH_3$</TEX>-SCO). Among the catalysts, Pt/Fe-ZSM5 catalyst exhibited superior <TEX>$NH_3$</TEX>-SCO activity to Pd/Fe-ZSM5 catalyst. We also tested Pt/Fe-ZSM5 catalysts with different Fe loading using ion-exchange method to prepare Fe-ZSM5 supports, which resulted in the increased catalytic performance with smaller Fe content: <TEX>$NH_3$</TEX> was oxidized completely at low temperature (<TEX>$250^{\circ}C$</TEX>). The physicochemical properties of Fe-ZSM5 were investigated to figure out the relationship between the characteristics of the catalysts and the catalytic activity on <TEX>$NH_3$</TEX>-SCO by Inductively coupled plasma-atomic emissions spectrometer (ICP-AES), <TEX>$N_2$</TEX> sorption, X-ray diffraction (XRD), temperature programmed desorption of <TEX>$NH_3$</TEX> (<TEX>$NH_3$</TEX>-TPD) technique.

Selective catalytic oxidation of ammonia to nitrogen over CuO/CNTs: The promoting effect of the defects of CNTs on the catalytic activity and selectivity

CuO/CNTs were prepared as catalysts for the selective catalytic oxidation of ammonia and demonstrated high catalytic activity and N2 selectivity. The study results showed that the surface defects of carbon nanotubes (CNTs) could not only activate CuO, but also promote the electron transfer in the catalysis. Thus, along with increasing the defect density of the CNTs, the temperature for the complete ammonia oxidation could be decreased from 235°C to 189°C and the corresponding N2 selectivity increased from 93.8% to 98.7%. Moreover, there was no apparent decrease in the catalytic activity at prolonged reaction time, indicating CuO/CNT catalysts are promising for the selective catalytic oxidation of ammonia.

Selective catalytic oxidation of ammonia to nitrogen over ceria–zirconia mixed oxides

The selective catalytic oxidation of ammonia to nitrogen (NH 3-SCO) has been studied over ceria–zirconia mixed oxides (Ce 1− x Zr x O 2). The addition of Zr into ceria leaded to the phase transition from the cubic fluorite structure to the tetragonal structure and the generation of oxygen vacancies. The Ce 1− x Zr x O 2 (0.2 ⩽ x ⩽ 0.8) mixed oxide catalysts exhibited certain amount of moderate acid sites. Particularly, the Ce 0.4Zr 0.6O 2 catalyst achieved the largest amount of moderate acid sites and highest proportion of Ce 3+ (oxygen vacancies). Meanwhile, it showed the best NH 3 oxidation activity, and the complete conversion temperature was about 360 °C. In addition, numerical results also indicated that the higher zirconium content in Ce 1− x Zr x O 2 catalysts improved the N 2 selectivity which was about 100% with x > 0.4. The formation of N 2O was the main reason for low N 2 selectivity over these catalysts ( x ⩽ 0.4) proved by TPSR experiments. Meanwhile, the reaction mechanism of NH 3 with lattice oxygen was observed to be different from the gaseous oxygen, and the gaseous oxygen species was much more active than lattice oxygen for NH 3 oxidation.

Mechanisms for Selective Catalytic Oxidation of Ammonia over Vanadium Oxides

Ministry of Science and Technology[2011CB808505, 2007CB815206]; National Natural Science Foundation of China[20973139, 20923004, 21033006, 21133004]; Program for Changjiang Scholars and Innovative Research Team in University[IRT1036]; Fundamental Research Funds for the Central Universities; Key Science and Technology Specific Projects of Fujian Province[2009HZ0002-1]; Natural Science Foundation of Fujian Province of China[2009J05035]

Selective Catalytic Oxidation (SCO) of Ammonia to Nitrogen over Hydrotalcite Originated Mg–Cu–Fe Mixed Metal Oxides

Mg–Cu–Fe oxide systems, obtained from hydrotalcite-like precursors, were tested as catalysts for the selective catalytic oxidation (SCO) of ammonia. Copper containing catalysts were active in low-temperature SCO processes; however, their selectivity to nitrogen significantly decreased at higher temperatures. The optimum composition of the catalyst to guarantee high activity and selectivity to N2 was proposed. Temperature-programmed experiments, SCO catalytic tests performed with various contact times and additional tests on the samples in the selective catalytic reduction of NO with ammonia showed that the SCO process over the studied calcined hydrotalcites proceeds according to the internal SCR mechanism and oxidation of ammonia to NO is a rate-determining step in the low-temperature range.

Preparation, Electrochemical Properties and Cytotoxicity Assessment of Nanosized CuO/La&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/CeO&lt;sub&gt;2&lt;/sub&gt; Composite for the Decomposition of Gaseous Ammonia

This work considers the CuO/La2O3/CeO2nano-rare earth composite materials were synthesized by coprecipitation method with aqueous solutions of copper nitrate, lanthanum nitrate and cerium nitrate. The performance of the selective catalytic oxidation of ammonia to N2(NH3-SCO) over a CuO/La2O3/CeO2nano-rare earth composite materials in a tubular fixed-bed reactor (TFBR) at temperatures from 423 to 673 K in the presence of oxygen was reported. The catalytic redox behaviors were determined by cyclic voltammetry (CV). Further, cell cytotoxicity and the percentage cell survival were determined by using MTS assay on human fetal lung tissue cell (MRC-5). The experimental results show that the CuO/La2O3/CeO2nanocomposite particles only minor cause cytotoxicity effect in cultured human cells.

Catalytic Oxidation of Ammonia to NO over Perovskite-type LaMnO3 and LaVO4 Catalysts

Catalytic oxidation of NH3 to NO + NO2 (NOX) over perovskite-type LaMnO3 and LaVO4 prepared by sol–gel was studied. X-ray diffractometry and scanning electron microscopy analyses confirmed that the prepared LaMnO3 and LaVO4 had perovskite-type porous structure, and a specific surface area of 33.58 m2/g and 1.2 m2/g for LaMnO3 and LaVO4 was measured by BET, respectively. The catalytic oxidation of ammonia to NOX was found to begin at 350 °C, and approximately 88 and 95% of NH3 was oxidized to NOX at 600 °C over LaMnO3 and LaVO4, respectively. The catalytic oxidation of ammonia to NO was found to begin at 350 °C, and approximately 88 and 95% of NH3 was oxidized to NO at 600 °C over LaMnO3 and LaVO4, respectively.

Effects of Adding CeO2 to Ag/Al2O3 Catalyst for Ammonia Oxidation at Low Temperatures

The effects of adding CeO 2 to Ag/Al 2 O 3 on the selective catalytic oxidation of ammonia to nitrogen were investigated by activity test and N 2 physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis diffuse-reflectance spectroscopy, high resolution transmission electron microscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy of NH 3 adsorption, and O 2 -pulse adsorption. Adding a suitable amount of CeO 2 improved the catalytic activity of Ag/Al 2 O 3 for NH 3 oxidation at temperatures below 160 °C, and slightly influenced N 2 selectivity by improving the catalyst's ability to adsorb and activate O 2 and the adsorption and activation of NH 3 . 摘要：采用活性测试和氮气吸附、X 射线衍射、X 射线光电子能谱、紫外-可见漫反射吸收光谱、高倍透射电镜、原位漫反射傅里叶变换红外光谱和 O 2 脉冲吸附等研究了铈添加对 Ag/Al 2 O 3 催化剂低温氨氧化性能的影响. 结果表明, 适量铈的添加可以明显促进 Ag/Al 2 O 3 催化剂的低温氨氧化活性, 且对催化剂的选择性影响不大. 添加铈不仅可以促进 Ag/Al 2 O 3 催化剂表面吸附和活化 O 2 的能力, 而且可促进催化剂表面对氨的解离吸附和活化. 这是铈促进 Ag/Al 2 O 3 催化剂低温氨氧化活性的主要原因. Adding CeO 2 to Ag/Al 2 O 3 enhanced O 2 uptake and promoted the dissociative adsorption of NH 3 to -NH 2 and -NH, which improved the selective catalytic oxidation of ammonia at low temperatures.

New Insights into Reaction Mechanism of Selective Catalytic Ammonia Oxidation Technology for Diesel Aftertreatment Applications

New Insights into Reaction Mechanism of Selective Catalytic Ammonia Oxidation Technology for Diesel Aftertreatment Applications

Catalytic decomposition of ammonia in simulated coal-derived gas over supported nickel catalysts

As a hot gas clean-up technology for integrated coal gasification combined-cycle (IGCC) power plants, the catalytic decomposition of ammonia using simulated coal-derived gas was studied. Based on the selective catalytic oxidation of ammonia to nitrogen and water, the characteristics of five kinds of supported nickel catalysts were investigated. Ammonia decomposition experiments were carried out at 0.9 MPa, and the surface properties of the catalysts were investigated through surface area measurement, the temperature programmed desorption of ammonia (NH 3-TPD), carbon analysis, XRD analysis, and transmission electron microscope (TEM) observation. The results showed that a nickel catalyst supported on ZSM-5 zeolite has the highest activity and selectivity for ammonia decomposition to nitrogen without carbon deposition from 250–400 °C among the tested catalysts.

Rare earth oxide modified Cu-Mn compounds supported on TiO 2 catalysts for low temperature selective catalytic oxidation of ammonia and in lean oxygen

Selective catalytic oxidation (SCO) of ammonia was carried out over Cu-Mn compounds catalysts modified with trivalent rare earth oxide Ce 2O 3 and La 2O 3 respectively. TiO 2 was used as support and different ratio of O 2 were tested in order to find an appropriate O 2 concentration (vol.%), and the results showed that 1%O 2 (vol.%) was propitious to SCO of ammonia. The effects of the two rare earth oxides modified catalysts Ce 2O 3-Cu-Mn/TiO 2 and La 2O 3-Cu-Mn/TiO 2 on the catalytic activity and selectivity of ammonia oxidation were investigated under the reaction condition of 500 ppm ammonia, 1%O 2 (vol.%), at the temperature from 125 to 250 °C. The results revealed the beneficial role of Ce 2O 3 and La 2O 3 in catalytic activity at low temperature and lean oxygen concentration, while the modification with Ce 2O 3 and La 2O 3 led to the negative influence on N 2 selectivity. For the catalysts modified with Ce showed lower NO and N 2O selectivity than the catalysts modified with La, then the effects of different Ce loadings on catalytic activity and selectivity were also considered, in combination with catalysts preparation methods, which include incipient wet impregnation, sol-gel method and co-precipitation. Results revealed that the catalysts prepared by sol-gel method obtained preferable catalytic activity compared with the others, reaching 99% ammonia at 200 °C, whereas 96% NO was detected. It also indicated that different catalyst preparation method significantly determined production distribution.

Preparation and characterization of nano-rare earth composite materials: application in selectivity catalytic oxidation of ammonia and its cytotoxicity study

The manufacture, physical characterization, environmental applications and cytotoxicity properties of nanocomposites consisting of CuO/CeO 2 nano-rare earth composite materials prepared using the coprecipitation method at molar ratio of 6:4 with aqueous solutions of copper nitrate and cerium nitrate were reported. The performance of the selective catalytic oxidation of ammonia to N 2 (NH 3-SCO) over a CuO/CeO 2 nano-rare earth composite materials in a tubular fixed-bed reactor (TFBR) at temperatures from 423 to 673 K in the presence of oxygen was elucidated. The catalytic redox behavior was determined by cyclic voltammetry (CV). The nanocomposite particles were characterized by TEM, with a tiny particle size around 10 nm with high dispersion phenomena. Further, cell cytotoxicity and the percentage cell survival were determined by using 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenol)-2-(4-sulfophenyl)-2H-tetra-zolium (MTS) assay on human lung MRC-5 cell line. Experimental results showed that no apparent cytotoxicity was observed when the MRC-5 was exposed to the CuO/CeO 2 nanocomposite materials.

Use of microtechnologies for intensifying industrial processes

The use of new technologies based on microstructured reactors in industrial processes, including the obtainment of hydrogen peroxide, the catalytic oxidation of ammonia, the utilization of rocket fuels, fine organic synthesis, polymerization, and phase transfer catalysis, were considered. The transition to microtechnologies considerably increases the performance of the process; at the same time, the product yield increases as compared with periodically operating reactors, which allows for a reduction of costs at the separation stage of the reaction mixture and the extraction of the reaction products.

Characterization and performance of Pt-Pd-Rh cordierite monolith catalyst for selectivity catalytic oxidation of ammonia

This work considers the oxidation of ammonia (NH 3) by selective catalytic oxidation (SCO) over a Pt-Pd-Rh cordierite monolith catalyst in a tubular fixed-bed flow quartz reactor (TFBR) at temperatures between 423 and 623 K. A Pt-Pd-Rh cordierite monolith catalyst was prepared by incipient wetness impregnation with aqueous solutions of H 2PtCl 6, Pd(NO 3) 3 and Rh(NO 3) 3 that were coated on cordierite substances. The catalysts were characterized using XRD, PSA and SEM. The experimental results show that around 99.0% NH 3 removal was achieved during catalytic oxidation over the Pt-Pd-Rh cordierite monolith catalyst at 623 K with oxygen content of 4%. N 2 was the main product in the NH 3-SCO process over the Pt-Pd-Rh cordierite monolith catalyst. These results also verify that the Pt-Pd-Rh metals on cordierite monolith surfaces, resulting in the formation of catalytically active sites at the metal-support interface in the reduction of NH 3 in the process.

Cordierite-supported Pt–Pd–Rh ternary composite for selective catalytic oxidation of ammonia

This study elucidates ammonia (NH 3) oxidation by selective catalytic oxidation (SCO) over a Pt–Pd–Rh ternary composite cordierite substrate catalyst in a tubular fixed-bed flow quartz reactor (TFBR) at temperatures of 423–623 K. A Pt–Pd–Rh ternary composite cordierite substrate catalyst was prepared by incipient wetness impregnation with aqueous solutions of H 2PtCl 6, Pd(NO 3) 3 and Rh(NO 3) 3 that were coated on cordierite ceramic honeycomb substances. Experimental data indicate that high NH 3 reduction activity was achieved during catalytic oxidation over the Pt–Pd–Rh cordierite substrate catalyst at 623 K with an oxygen content of 4%. Notably, N 2 was the predominant product of the NH 3–SCO process over the Pt–Pd–Rh cordierite substrate catalyst. These experimental results also confirm that an initial high concentration of NH 3 influent decreases ammonia removal efficiency. Further, catalysts were characterized by SEM, TGA–DTA, FTIR and TEM. Analytical results indicate that catalytic behavior is associated with the Pt–Pd–Rh ternary composite and cordierite ceramic honeycomb substrate.

Selective catalytic oxidation of ammonia to nitrogen over mesoporous CuO/RuO2 synthesized by co-nanocasting-replication method

A new type of catalyst for ammonia selective catalytic oxidation, mesoporous CuO/RuO2 with well-crystallized framework and ordered mesoporous structure, has been synthesized by a co-nanocasting-replication method. Various techniques have been employed for the material characterization. The prepared mesostructured bimetal oxides demonstrated high catalytic activity and N2 selectivity toward NH3 oxidation reaction in the presence of excess oxygen. The temperature for the complete ammonia oxidation was as low as 180 °C on the mesoporous 10 wt.% CuO/RuO2 composite, and there was no apparent decrease in the catalytic activity at prolonged reaction time. Both high ammonia conversion up to 100% and high N2 selectivity (>95%) were achieved on the mesoporous 5–15 wt.% CuO/RuO2 composites. A synergetic catalytic mechanism between copper and ruthenium component was proposed to understand the promoted catalytic effect, especially the achievement of both high conversion and high selectivity for N2 by CuO.

Mechanism of selective catalytic oxidation of ammonia to nitrogen over Ag/Al 2O 3

The mechanism of selective catalytic oxidation (SCO) of NH 3 over Ag/Al 2O 3 was studied by NH 3 temperature-programed oxidation, O 2-pulse adsorption, and in situ DRIFTS of NH 3 adsorption and oxidation. The essence which affects the low temperature activity of Ag/Al 2O 3 has been elucidated through the mechanism study. Different Ag species on Ag/Al 2O 3 significantly influence O 2 uptake by catalysts; while different oxygen species affect the activity of NH 3 oxidation at low temperature. The activated –NH could react with the atomic oxygen (O) at low temperatures (<140 °C); however, the –NH could also interact with the O 2 at temperatures above 140 °C. At low temperatures (<140 °C), NH 3 oxidation follows the –NH mechanism. However, at temperatures above 140 °C, NH 3 oxidation follows an in situ selective catalytic reduction (iSCR) mechanism (two-step formation of N 2 via the reduction of an in situ-produced NO x species by a NH x species).

Theoretical Investigation of the Mechanism of the Selective Catalytic Oxidation of Ammonia on H-Form Zeolites

The selective catalytic oxidation (SCO) of ammonia has been investigated on a portion of the H-ZSM5 framework which contains 5T atoms by using density functional theory, representing H-form zeolites. The mechanism was subdivided into three main blocks: (I) the direct reaction of NH3 with oxygen, leading either to HNO or to NH2OH, (II) the decay of nitroxyl (HNO), and (III) the decay of intermediately produced hydroxylamine (NH2OH). For the decay of HNO and NH2OH the catalyst is active for reactions with both NO and HNO, which leads to a reaction network with several energetically similar and accessible pathways. The initial reaction of oxygen with adsorbed ammonia exhibits the highest energy barrier in the mechanism and thus is likely to be the rate-limiting step. For all three parts, the crossing of potential energy surfaces was considered if necessary. The investigation of potential reaction pathways of N2O with NH3 and NO reveals a low activity of H-ZSM5 for them, and thus, they only have a minor relev...

The role of silver species on Ag/Al 2O 3 catalysts for the selective catalytic oxidation of ammonia to nitrogen

The role of Ag species on Ag/Al 2O 3 catalyst for the selective catalytic oxidation (SCO) of NH 3 to N 2 was studied using 10 wt% Ag/Al 2O 3 catalysts prepared with impregnation, incipient wetness impregnation and sol–gel methods. The catalyst characterization was preformed using N 2 adsorption–desorption, UV/Vis, TEM and XRD. O 2-chemisorption and H 2–O 2 titration were measured to confirm the metal dispersion on the catalyst. The Ag species state and Ag particle size have significant influence on the Ag/Al 2O 3 activity and N 2 selectivity of the SCO of NH 3 at low temperature. Ag 0 is proposed to be an active species on the H 2 pretreated catalyst at low temperature (<140 °C). It is evident that well-dispersed and small particle Ag 0 enhances catalytic activity at low temperature, whereas large particle Ag 0 is relate to a high N 2 selectivity. In contrast, Ag + could also be the active species at temperatures above 140 °C.

Potentials of gas chromatography in the determination of reaction products in the catalytic oxidation of ammonia to nitrogen(II) oxide

Peculiarities of the determination of nitrogen oxides and ammonia in the reaction products of ammonia oxidation are studied by gas chromatography. Particular attention was paid to the sampling problem. It is shown that in the course of the transportation of samples containing nitrogen(II) oxide and oxygen, the oxidation of nitrogen(II) oxide to nitrogen(IV) oxide takes place in the vapor phase. The conditions were found for suppressing or even eliminating the gas-phase reaction of NO oxidation to NO2. A procedure for the gas-chromatographic analysis of the reaction products in the catalytic oxidation of ammonia is proposed using several samples and packed columns, including the determination of NO with respect to NO2 formed in the gas-phase oxidation of NO.