Catalytic Ammonia Decomposition Over Ruthenium Nanoparticles Supported on Nano-Titanates

Nanosized Na₂Ti₃O₇, K₂Ti₆O₁₃ and Cs₂Ti₆O₁₃ materials were prepared and used as supports of ruthenium nanoparticles for catalytic ammonia decomposition. It is shown that these catalysts exhibit higher catalytic activity than ruthenium supported on TiO₂ nanoparticles promoted with cesium. The difference is attributed to the use of nanostructured materials with incorporated alkali metals in the crystal lattice, which apparently gives a higher effect of the promoter. All samples were characterized by X-ray powder diffraction, transmission electron microscopy and N₂ physisorption measurements. Furthermore, the effect of ruthenium loading on the catalytic decomposition of ammonia was investigated.     

Catalytic Hydrogenation of Aqueous Phase Nitrate Over Fe/C Catalysts

Catalytic hydrogenation of nitrate in water has been carried out over Fe/C catalysts at ambient temperature using batch and continuous reactors. In batch reaction nitrate reduction activity of 2.9 mmol g _metal ^?1  min^?1 with nearly 100% selectivity towards nitrogen was obtained. Column study shows nitrate reduction below 5 ppm for an initial concentration of 100 ppm. Break through capacity, to reach concentration of 45 mg L^?1, is more than 530 bed volumes. The catalysts were characterized using XRD, SEM–EDAX and XPS. With high selectivity and activity the catalytic system in present study could be a potential option for nitrate removal from water.     

Low-Temperature Catalytic Decomposition of N2O

Theoretical Foundations of Chemical Engineering - A series of oxide catalysts modified with potassium cations, 1–5% K2О/CoFe2O4, with a spinel structure were obtained via...     

Catalytic Methanol Decomposition Over Palladium Deposited on Mesoporous Cerium Oxide

Ultrafine palladium particles can be deposited on mesoporous cerium oxide by a deposition–precipitation method. After reduction with hydrogen at 300 °C, palladium on the mesoporous compound is cationic with a valence close to +1 whereas the particles have a metallic structure. The catalytic activity in selective methanol decomposition to hydrogen and carbon monoxide at 180 °C is significantly higher than that of palladium supported on non-porous cerium oxide, suggesting that the mesoporous structure is advantageous to the reaction. When the palladium content is high, part of mesopores are probably choked with large palladium particles, which will cause saturation of the activity.     

Production of COX Free Hydrogen by Catalytic Decomposition of Methane Over Ni/HY Catalysts

In this present paper, we report catalytic decomposition of methane over Ni/HY catalysts, with varying Ni loading at 550 °C and atmospheric pressure. The relationships between catalyst performance and characterization of the fresh and used form of catalysts are discussed from the data obtained by scanning electron microscopy, X-ray diffraction analysis, temperature programmed reduction, O₂ pulse chemisorption and carbon elemental analyses. It is observed that, the catalytic activity of Ni/HY catalysts is high at initial stages and gradually decreased with time and finally deactivated completely. The yield of hydrogen and carbon nanofibers is strongly dependent on Ni loading. It is found that 20 wt% Ni/HY catalyst showed higher hydrogen yield over the other loadings.     

Liquid-Phase Catalytic Decomposition of Novel Ammonia Precursor Solutions for the Selective Catalytic Reduction of NOx

Aqueous solutions of NH₃-precursor compounds (i.e. urea and methanamide) were catalytically hydrolyzed in the liquid phase by applying a pressure of 50 bar during contact with the catalyst in a heated tube. Methanamide could be hydrolyzed on an Au/TiO₂ catalyst to yield not only NH₃, but also H₂. Decomposition of urea under high pressure in the liquid phase could even be achieved without the addition of a catalyst. Due to the large excess of water present during decomposition, side products could be avoided. As the reactor tube is electrically heated, the presented method provides a possibility to reliably transform NH₃-precursor compounds into gaseous NH₃ independent of the engine exhaust gas temperature. The NH₃-flow can be added to the main exhaust duct to enable the selective catalytic reduction of NO_x at the light-off of the SCR catalyst.     

铁改性分子筛直接催化分解一氧化二氮

采用以离子交换法制备的Fe-ZSM-5、Fe-MCM-22和Fe-Beta分子筛催化剂,系统地考察了分子筛构型、酸性和酸中心分布对N2O直接催化分解的影响.采用N2吸附、红外光谱仪(FT-IR)、NH3程序升温脱附实验(NH3-TPD)、H2程序升温还原实验(H2-TPR)和原位漫反射红外光谱(in situ DRIFTS)等方法考察了铁离子负载量、Si与Al摩尔比和分子筛构型对N2O催化分解的影响.结果表明,价键补偿Fe3 离子是N2O分解的主要活性组分;分子筛活性随Si和Al摩尔比的减少和铁离子负载量的增加而增加;Fe-Beta分子筛的催化活性明显高于Fe-ZSM-5和Fe-MCM-22分子筛;分子筛酸性和酸中心分布影响铁离子的分布,从而导致不同构型分子筛催化分解N2O的活性具有明显差异.     

Fe2O3/AC催化剂的低温选择性催化还原脱硝性能

以活性焦(AC)为载体、Fe2O3为活性组分,采用等体积浸渍法制备Fe2O3/AC催化剂,研究了Fe含量对Fe2O3/AC催化剂低温脱硝性能的影响. 结果表明,当Fe负载量为6wt%时能获得比其它负载量更佳的NOx转化率,尤其在240℃时NOx转化率达93.9%,当分别有120?10?6(vol) SO2和3.5vol H2O存在时,脱硝率分别稳定在约86%和74%;催化剂孔径≤4 nm,随Fe负载量增加,孔径呈增大趋势;催化剂较稳定;Fe主要以γ-Fe2O3分散在催化剂表面,负载适量Fe2O3使表面吸附氧Oβ和Fe3+增多,为催化剂提供更多活性位,提高了Fe2O3/AC催化剂的低温选择性催化还原脱硝活性.     

Catalytic Dehydrogenation of C4 Hydrocarbons Over Chromia-Alumina

Reactions involving hydrogenation and dehydrogenation are employed particularly in the petrochemical industry. Among these the dehydrogenation of butane over chromia-alumina catalysts plays an important role, because it represents the most important process for obtaining butenes and butadiene. Due to their practical interest, such processes have been the object of extensive investigations. The aim of these researches on dehydrogenation reactions is not confined to the solution of technological problems, however, and the results have allowed important contributions to some aspects of the theory of heterogeneous catalysis to be obtained.     

Catalytic Dehydrogenation of C4 Hydrocarbons Over Chromia-Alumina

Reactions involving hydrogenation and dehydrogenation are employed particularly in the petrochemical industry. Among these the dehydrogenation of butane over chromia-alumina catalysts plays an important role, because it represents the most important process for obtaining butenes and butadiene. Due to their practical interest, such processes have been the object of extensive investigations. The aim of these researches on dehydrogenation reactions is not confined to the solution of technological problems, however, and the results have allowed important contributions to some aspects of the theory of heterogeneous catalysis to be obtained.     

Catalytic decomposition of propellant N2O Over Ir/Al2O3 catalyst

N₂O, as a green propellant alternative to N₂H₄, shows potential application in satellite propulsion system. The state of Ir species and the reaction behaviors on Ir/Al₂O₃ in the oxidative environment during N₂O decomposition were identified here. Two types of Ir sites existed in this catalyst and affected the process of N₂O decomposition. The strong Ir sites facilitated the dissociative adsorption of N₂O to form N₂ and adsorbed O atoms with adsorption heat of as high as 281 kJ/mol, which promoted the desorption of adsorbed O atoms and favored the self‐sustaining decomposition of N₂O by raising the catalyst bed temperature. The other Ir sites interacted weakly with O atoms but facilitated their combination to form O₂. The Ir/Al₂O₃ catalyst then exhibited an excellent performance in initiating the decomposition of N₂O at low temperature of 200°C and good stability in 0.1 N microthruster for orbit adjustment and attitude control of satellite. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3973–3981, 2016     

蒸氨、氨分解工艺设备优化改造

通过对蒸氨、氨分解系统一段时间的运行操作分析,发现原料氨水在蒸氨塔内经蒸汽蒸吹后的氨汽在分缩器的冷却过程和氨汽在分解炉中经高温和催化剂的作用被催化分解,生成氮、氢和一氧化碳的过程中存在的问题,针对这些问题采取了优化改造。     

Fe2O3/CNTs的制备及其对RDX热分解的催化机理

采用溶胶-凝胶法制备了纳米Fe2O3/CNTs催化剂,通过正交实验优化了工艺参数,用SEM、TEM、XRD对Fe2O3/CNTs复合粒子进行了表征,DSC研究了Fe2O3/CNTs对RDX热分解性能的影响.结果表明,纳米级Fe2O3颗粒均匀包覆在CNTs表面,当其加入量为RDX质量的5%时,Fe2O3/CNTs复合粒子使RDX的分解温度降低了14.1℃;通过Kissinger法计算发现,Fe2O3/CNTs复合粒子的加入使RDX的分解反应活化能降低了38.5%.     

Spectroscopic Evidence for a Nitrite Intermediate in the Catalytic Reduction of NOx with Ammonia on Fe/MFI

The mechanism of selective catalytic reduction (SCR) of NO_x with NH₃ over Fe/MFI was studied using in situ FTIR spectroscopy. Exposing Fe/MFI first to NH₃ then to flowing NO + O₂ or using the reversed sequence, invariably leads to the formation of ammonium nitrite, NH₄NO₂. In situ FTIR results in flowing NO + NH₃ + O₂ at different temperatures show that NH₃ is strongly adsorbed and reacts with impinging NO_x. The intensity of the NH₄NO₂ bands initially increases with temperature, but passes through a maximum at 120 °C because the nitrite decomposes to N₂ + H₂O. The mechanistic model rationalizes that the consumption ratio of NO and NH₃ is close to unity and that the effect of water vapor depends on the reaction temperature. At high temperature H_2O enhances the rate because it is needed to form NH₄NO₂. At low temperature, when adsorbed H₂O is abundant it lowers the rate because it competes with NO_x for adsorption sites.     

Competitive Reaction During Decomposition of Hexachlorobenzene Over Ultrafine Ca–Fe Composite Oxide Catalyst

The decomposition of hexachlorobenzene (HCB) has been investigated over ultrafine Ca–Fe composite oxide catalyst (Ca/Fe atomic ratio was 3.4), CaO and α-Fe₂O₃ by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Adsorption experiments on the surface of oxides monitored by in situ DRIFTS showed that partial oxidation products, i.e., phenolate and acetate species were formed on the surface of Ca–Fe composite oxide. The further studies indicated that Ca–Fe composite oxide catalyst was easier to induce the rupture of C–Cl bond and C–C bond of aromatic rings. The best catalytic activity of Ca–Fe composite oxide may be related to the acidity, which was determined by NH₃–TPD. The products after reaction have been analyzed by XRD and chloride selective electrode. Ca–Fe composite oxide exhibited the highest extent of mineralization for organic chlorine among the different oxides tested. The combined results of current and previous experiments demonstrated that two competitive reactions took place during the decomposition process of HCB: (1) hydrodechlorination resulting in the formation of lower chlorinated benzenes and (2) oxidation of aromatic rings leading to the rupture of aromaticity and the formation of oxidation products. The latter is the major process in the coexisted competitive reaction. A possible decomposition pathway was discussed.     

负载型氨分解催化剂的载体——高岭土的研究

为了拓展高岭土在化工领域的应用,研究了将其作为催化剂载体应用于氨分解的可行性。通过正交实验确定了高岭土载体制备过程中最大影响因素,进而确定最佳制备条件。将其制备成负载型Ni基催化剂,进行氨分解活性评价,结果表明,与工业MgO载体比较,自制高岭土载体可以达到工业MgO载体的同等水平,在氨分解反应中可替代工业MgO载体。     

纳米固体超强酸SO2-4/Fe2O3的催化性能

引言 目前的工业催化反应大部分属于酸催化反应,而固体超强酸[SO2- 4/MxOy(M代表金属)]和液体酸相比,具有活性和选择性高、不腐蚀、无污染及产物易分离等特点[1],是一种较理想的绿色催化剂.自1979年Hion首例制备SO2- 4/Fe2O3固体超强酸以来,它就成为人们研究的热点[2～5],并广泛地应用于石油炼制和有机合成工业.但有关纳米固体超强酸的研究报道还不多.