Steam effect on NO x reduction over lean NO x trap Pt–BaO/Al2O3 model catalyst

The effect of steam on NO _x reduction over lean NO _x trap (LNT) Pt–Ba/Al₂O₃ and Pt/Al₂O₃ model catalysts was investigated with reaction protocols of rich steady-state followed by lean–rich cyclic operations using CO and C₃H₈ as reductants, respectively. Compared to dry atmosphere, steam promoted NO _x reduction; however, under rich conditions the primary reduction product was NH₃. The results of NO _x reduction and NH₃ selectivity versus temperature, combined with temperature programmed reduction of stored NO _x over Pt–BaO/Al₂O₃ suggest that steam causes NH₃ formation over Pt sites via reduction of NO _x by hydrogen that is generated via water gas shift for CO/steam, or via steam reforming for C₃H₈/steam. During the rich mode of lean–rich cyclic operation with lean–rich duration ratio of 60 /20 s, not only the feed NO, but also the stored NO _x contributed to NH₃ formation. The NH₃ formed under these conditions could be effectively trapped by a downstream bed of Co²⁺ exchanged Beta zeolite. When the cyclic operation was switched into lean mode at T < 450 °C, the trapped ammonia in turn participated in additional NO _x reduction, leading to improved NO _x storage efficiency.     

Propylene epoxidation in a microreactor with electric heating

Gas phase propylene epoxidation on gold catalysts has attracted wide attention from industry and academia due to its high selectivity. However, it suffers from low propylene conversion and rapid catalyst deactivation. Experiments showed that propylene conversion could be increased by raising H₂, O₂, or C₃H₆ concentration in the feed, but the feed compositions were within the explosion limit. It was also shown that the activity of the used catalyst could be fully recovered, but the regeneration temperature was 280 °C, much higher than that for reaction. Therefore a microchannel reactor was devised to suppress explosion and was constructed with Fecralloy, to raise the temperature rapidly for catalyst regeneration by electric heating. In two minutes the temperature of the reactor could be raised from 50 to 300 °C. Catalysts were coated on the alloy belt by dip coating, and the performance of the reactor was evaluated under different operating conditions. Results showed that in the microreactor the overall reaction rate was controlled mainly by the intrinsic reaction rate, and also influenced by film diffusion to a certain extent. The deactivated catalyst was regenerated in the microchannel reactor and the activity was fully recovered.     

Influence of vacuum impregnation pretreatment combined with IR drying on quince quality with shrinkage modeling by ANN

The effects of infrared power on drying behavior of quince slice were investigated. The samples were pretreated under vacuum impregnation (VI) and atmospheric pressure with sucrose sirup. The quality attributes measured included moisture content, bulk density rehydration, water loss, solid gain, texture, porosity, color, non-enzymatic browning, and effective moisture diffusivity. In addition, the modeling of shrinkage by ANN. VI increased the effective moisture diffusivity, bulk density, and softening of the dried fruit tissues while decreasing the time of drying (p?<?0.05). The highest porosity was observed for the control samples treated under VI and dried at 1200?W. The desired color was achieved in the osmotic samples treated under atmospheric conditions and dried at 800?W. The rate of rehydration was reduced in the osmotic samples under vacuum. MLP neural network was used to model the shrinkage of the best topology 3-3-1 by LM learning algorithm and threshold function of Tangent sigmoid function, with a correlation coefficient of 0.9963 and the error MSE of 0.000340.     

杂多酸改性V-Mo/Ti-W催化剂的宽温SCR脱硝性能

采用等体积浸渍法制备了一系列Keggin型杂多酸改性的V-Mo/Ti-W催化剂,并通过X射线衍射（XRD）、BET比表面分析（BET）、NH₃程序升温脱附（NH₃-TPD）、H₂程序升温还原（H₂-TPR）、X射线光电子能谱（XPS）和傅里叶变换红外光谱（FTIR）等表征方法对催化剂物化性质进行了表征分析。各项表征分析结果表明,杂多酸改性后的HPAs-V-Mo/Ti-W催化剂相比于改性前的催化剂,平均孔径尺寸更大,可抑制硫酸氢铵沉积,以提高催化剂抗硫性能;与V-Mo/Ti-W样品相比,改性后的催化剂具有更强的NH₃吸附能力、更好的还原性能和更多的化学吸附氧物种,从而表现出更优异的脱硝性能和N₂选择性。杂多酸改性后的催化剂在200~380℃温度范围内、150000h^-1高空速、高浓度SO₂和H₂O存在的模拟烟气中表现出高 NH₃-SCR活性、优异的抗SO₂性能,并保持几乎100%的N₂选择性,可作为燃煤电厂深度调峰的宽温催化剂,具备良好的工业应用价值。     

A new weighted optimal combination of ANNs for catalyst design and reactor operation: Methane steam reforming studies

Catalyst design and evaluation is a multifactorial multiobjective optimization problem and the absence of well‐defined mechanistic relationships between wide ranging input‐output variables has stimulated interest in the application of artificial neural network for the analysis of the large body of empirical data available. However, single ANN models generally have limited predictive capability and insufficient to capture the broad range of features inherent in the voluminous but dispersed data sources. In this study, we have employed a Fibonacci approach to select optimal number of neurons for the ANN architecture followed by a new weighted optimal combination of statistically‐derived candidate ANN models in a multierror sense. Data from 200 cases for catalytic methane steam reforming have been used to demonstrate the veracity and robustness of the integrated ANN modeling technique. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2412–2427, 2012     

Performance of a protonated Co-contained silicate catalyst for NO reduction in equivalent conditions to diesel engine exhaust

Effects of co-existence of H₂O, CO₂, and SO₂ in the reaction gas on the catalytic performance of cobalt containing silicate having ZSM-5 (MFI) structure (Co-silicate) were studied. Water vapor retarded only the hydrocarbon conversion to CO₂ but no effect was observed on NO conversion. Addition of CO₂ or SO₂ did not affect the reaction. The stability of H-Co-silicate against H₂O, CO₂, and SO₂ was ascribed to the state of metallic active species which were stabilized by incorporation into the high siliceous MFI structure.     

应用软计算优化气辅注射成型工艺

气体辅助注射成型由于气体的引入使工艺更为复杂,增加了工艺变量,参数选取更为困难。本文基于CAE数值模拟试验结果,采用软计算方法,集成人工神经网络和生物进化遗传算法优化成型工艺,实现了气体辅助注射成型试验样品气体穿透长度的最大化。数值模拟与试验结果一致     

富氧条件下氢气选择催化还原汽车尾气氮氧化物的研究进展

汽车尾气中的氮氧化物（NO _x ）是大气主要污染物之一,严重危害了环境和人类健康。选择催化还原（SCR）消除技术是一种在富氧条件下能够高选择性消除NO _x 的技术。氢气选择催化还原氮氧化物（H₂-SCR）由于其低温高活性的优势备受关注。目前H₂-SCR研究中以Pt和Pd作活性组分催化剂使用较多,其中Pt基催化剂的研究最为广泛,本文介绍了催化剂载体类型、载体性质（如酸碱性、比表面积、孔道结构）、助剂和预处理方式等对催化活性的影响及影响机制,综述了反应条件参数（如反应气中O₂和NO₂浓度,杂质气体H₂O和SO₂）对催化剂催化活性的影响,认为反应气组分的影响在于各组分在催化剂上的竞争吸附以及对催化剂活性位的影响,最后展望了面向实际应用H₂-SCR技术未来的研究方向。     

Catalyst design using artificial intelligence: SO2 to SO3 case study

Catalyst design is key to the improvement of chemical process efficiency. The required work for the development of new catalysts can be supported through the proper application of artificial intelligence to identify optimal compositions. A generic methodology for the application of machine learning to catalysis research is therefore outlined in this work. The catalytic oxidation of SO₂ was used to exemplify the first iteration of this methodology. 1784 data points from 31 published papers were compiled into a databank. The inlet SO₂ concentration ranged from 0 to 66 mol%. An artificial neural network (ANN) was trained on the databank in order to predict SO₂ conversion based on the catalyst composition and the reactor operating conditions (temperature, pressure, catalyst mass: volumetric flowrate ratio (w/v), and feed composition). The model achieved a root-mean-square error of 6.6%. A preliminary screening step identified 3:1 V-Mg/SiO₂ catalysts as exhibiting high conversion at 648 K. A multi-objective optimization was then performed on a single catalyst to identify solutions exhibiting high conversion and high productivity at 648 K while minimizing the catalyst cost. The optimal solution was predicted to be a 2.9 wt% V/0.2 wt% Mg/SiO₂ catalyst operating at a w/v of 7.49 kg-cat · s/m³ STP, achieving 100% SO₂ conversion with a material cost among the bottom third of cost values. Artificial intelligence can then be employed to extract useful knowledge from published catalytic data and orient future search for novel catalyst development.     

Properties of pumice aggregate concretes at elevated temperatures and comparison with ANN models

The mechanical properties and thermal conductivity of concretes including pumice aggregate (PA) exposed to elevated temperature were analyzed by thermal conductivity, compressive strength, flexure strength, dynamic elasticity modulus (DEM) and dry unit weight tests. PA concrete specimens were cast by replacing a varying part of the normal aggregate (0–2 mm) with the PA. All concrete samples were prepared and cured at 23 ± 10C lime saturated water for 28 days. Compressive strength of concretes including PA decreased that reductions were 14, 19, 25 and 34% for 25, 50, 75 and 100% PA, respectively. The maximum thermal conductivity of 1.9382 W/mK was observed with the control samples containing normal aggregate. The tests were carried out by subjecting the samples to a temperature of 0, 100, 200, 300, 400 500, 600 and 700 °C for 3 h, then cooling by air cooling or in water method. The results indicated that all concretes exposed to a temperature of 500 and 700 °C occurred a significant decrease in thermal conductivity, compressive strength, flexure strength and DEM. An artificial neural network (ANN) approach was used to model the thermal and mechanical properties of PA concretes. The predicted values of the ANN were in accordance with the experimental data. The results indicate that the model can predict the concrete properties after elevated temperatures with adequate accuracy. Copyright © 2016 John Wiley & Sons, Ltd.     

Modeling mass transport with microkinetics in monolithic NO x storage and reduction catalyst

A 2D axisymetric model of a NO _x storage and reduction catalyst monolith channel combining mass transport with a detailed kinetic model was created to evaluate the importance of mass transport in a Pt/BaO/Al₂O₃ washcoat. Results show that there are small radial gradients in stored species concentration early during transients. The Sherwood number calculated during the transient storage phase will not be constant in time nor space as a film correlation would predict, but instead shows a region of higher Sherwood number propagating through the channel as the storage reaches completion. It is concluded that incorporating detailed mass transport provides a better spatially resolved picture of the dynamics of the proposed reaction mechanism and minimises the risk of arriving at false intrinsic kinetics during the development of a microkinetic model.     

Sol-gel Ag + Pd/SiO2 as a catalyst for reduction of NO with CO

A catalyst with an ultra high iridium load was prepared using a method involving multiple impregnations. The obtained iridium catalyst contained between 29 and 35 wt% of 2 nm-sized nanoparticles dispersed on a support such as reinforced alumina, bauxite and precipitated alumina. XAFS suggested a possible structural model of Ir₄ surrounded by oxygen. The decomposition of hydrazine hydrate to its elements was used as a probe reaction. The results showed that a catalyst support with a high mechanical strength such as reinforced alumina and bauxite is essential for sustaining the decomposition reaction of hydrazine hydrate where there is a high degree of mechanical and thermal shock. The decomposition reaction of hydrazine monohydrate (N₂H₄ · H₂O) proceeded rapidly to generate a CO_x-free hydrogen-rich gas through contact with the iridium catalyst at room temperature.     

NO reduction by isobutene, in the presence of oxygen, on platinum and copper, a comparative study

The reaction of NO, oxygen and isobutene was studied under conditions close to stoichiometric, on a platinum and on a copper disk in order to better understand the role of each metal, free of any support and dispersion effects. The products of the reaction were analysed by mass spectrometry and an XPS characterization of the surface was carried out at different stages of the reaction. A correlation between the catalytic activity for NO conversion and the presence of adsorbed intermediates has been clearly demonstrated on platinum. On copper, a redox cycle of the metal is necessary to activate the catalyst. On platinum, oxygen is necessary to initiate the reaction, clean the surface and form reactive intermediates; the reaction is strongly sensitive to oxygen concentration, whereas on copper, oxygen does not directly participate in the reaction mechanism.     

An acid catalyzed step in the catalytic reduction of NO x to N2

Contact of adsorbed ammonium nitrite, NH₄NO₂, with HCl vapor or a solid acid such as the zeolite HY, significantly lowers the temperature of its decomposition to N₂ + H₂O. Protonated NH₄NO₂ decomposes at room temperature. The decomposition of ammonium nitrite is one of the steps in the catalytic reduction of NO _x with ammonia or other reductants.     

ANN Analysis of a Roller Compaction Process in the Pharmaceutical Industry

Dry granulation via a roller compactor was simulated based on the artificial neural network (ANN) methodology. Two process parameters, including roll force and screw speed, were considered as input of the simulation whereas ribbon density was considered as output. Experimental work was carried out using an industrial‐scale roller compactor. The results showed an excellent agreement between simulation and experiments. The findings were compared as well with the results obtained in a previous study employing the Johanson model, which is the predominant model for the simulation of a roller compaction process. The overall deviation observed for the developed ANN model was found to be significantly improved in comparison with the deviation obtained for the Johanson model. The results demonstrated a very good capability and robustness of the developed ANN model in design and optimization of the roller compaction process.     

CFD modeling of mixing intensification assisted with ultrasound wave in a T-type microreactor

This paper aims to demonstrate the effect of ultrasound wave on mixing in a T-type microreactor. In order to create vibration in this microreactor, a low frequency (42 kHz) piezoelectric transducer was used. A well-known parallel-competitive reaction (Villermaux–Dushman reaction) was employed to study the mixing in the microreactor and the segregation index values were found for layouts with and without sonication. Results show that the ultrasound waves have a significant favorable influence on product distribution and the segregation index at various total flow rates. In all cases, the segregation index decreased with increase in total flow rate. The results reveal that the segregation index improved up to 10–20% by consuming a low energy (2.45 W Kg⁻¹) by the piezoelectric transducer. Finally, the computational fluid dynamics (CFD) modeling was carried out to explain the observed experimental results.     

The Effects of CO2 and H2O on the NO x Destruction Performance of a Model NO x Storage/Reduction Catalyst

The effects of CO₂ and H₂O on the NO _x storage and reduction characteristics of a Pt/Ba/Al₂O₃ catalyst were investigated. The presence of CO₂ and H₂O, individually or together, affect the performance and therefore the chemistry that occurs at the catalyst surface. The effects of CO₂ were observed in both the trapping and reduction phases of the experiments, whereas the effect of H₂O seems limited to the trapping phase. The data also indicate that multiple types of sorption sites (or mechanisms for sorption) exist on the catalyst. One mechanism is characterized by a rapid and complete uptake of NO _x . A second mechanism is characterized by a slower rate of NO _x uptake, but this mechanism is active for a longer time period. As the temperature is increased, the effect of H₂O decreases compared to that of CO₂. At the highest temperatures examined, the elimination of H₂O when CO₂ is present did not affect the performance.     

Ir基催化剂用于CO选择性催化还原NO的研究进展

针对具有烟温低、氧含量高和CO浓度大等特征的固定源烟气（钢铁烧结/球团烟气和焦化烟气等）脱硝领域,CO选择性催化还原NO _x （CO-SCR）技术具有良好的发展前景。Ir基贵金属催化剂因其在CO-SCR反应体系中表现出了良好的抗氧能力和较高的催化活性成为催化脱硝领域研究的热点之一。本文重点总结了单一载体、复合载体与复合活性组分三类Ir基催化剂在CO-SCR脱除NO _x 中的催化性能,同时从制备条件和反应条件两大方面归纳了其对Ir基催化剂的CO-SCR脱硝性能的影响,简要阐述了Ir基催化剂表面反应机理,并对未来研究工作进行了展望,指出采用多种手段对催化剂进行改性,并通过降低Ir负载量、反应温度窗口以及提升其催化活性等方式来降低成本,为实现Ir基催化剂CO-SCR工业化应用提供借鉴。     

化工过程的智能混合建模方法及应用

随着人工智能技术和配套数据系统的快速发展,化工过程建模技术达到了新的高度,将多个机理模型和数据驱动模型以合理的结构加以组合的智能混合建模方法,可以综合利用化工过程的第一性原理及过程数据,结合人工智能算法以串联、并联或者混联的形式解决化工过程中的模拟、监测、优化和预测等问题,建模目的明确,过程灵活,形成的混合模型有着更好的整体性能,是近年来过程建模技术的重要发展趋势。本文围绕近年来针对化工过程的智能混合建模工作进行了总结,包括应用的机器学习算法、混合结构设计、结构选择等关键问题,重点论述了混合模型在不同任务场景下的应用。指出混合建模的关键在于问题和模型结构的匹配,而提高机理子模型性能,获取高质量宽范围的数据,深化对过程机理的理解,形成更有效率的混合建模范式,这些都是现阶段提高混合建模性能的研究方向。     

Catalytic performance of a novel ceramic-supported vanadium oxide catalyst for NO reduction with NH3

A novel TiO₂/Al₂O₃/cordierite honeycomb-supported V₂O₅–MoO₃–WO₃ monolithic catalyst was studied for the selective reduction of NO with NH₃. The effects of reaction temperature, space velocity, NH₃/NO ratio and oxygen content on SCR activity were evaluated. Two other V₂O₅–MoO₃–WO₃ monolithic catalysts supported on Al₂O₃/cordierite honeycomb or TiO₂/cordierite honeycomb support, two types of pellet catalysts supported on TiO₂/Al₂O₃ or Al₂O₃, as well as three types of pellet catalysts V₂O₅–MoO₃–WO₃–Al₂O₃ and V₂O₅–MoO₃–WO₃–TiO₂ were tested for comparison. The experiment results show that this catalyst has a higher catalytic activity for SCR with comparison to others. The results of characterization show, the preparation method of this catalyst can give rise to a higher BET surface area and pore volume, which is strongly related with the highly active performance of this catalyst. At the same time, the function of the combined carrier of TiO₂/Al₂O₃ cannot be excluded.