Structured cobalt oxide catalyst for VOC combustion. Part I: Catalytic and engineering correlations

Structured reactors based on metallic carriers for catalysts of highly enhanced transport properties can be an interesting alternative to monolithic converters. In this study the carriers based on wire gauze have been shown to improve the efficiency of the VOC combustion simultaneously decreasing the converter length. A successful application of metallic microstructures needs proper methods of catalyst layering. This study focuses on non-equilibrium plasma (NEP) deposition technique which is referred to Langmuir–Blodgett (LB) film deposition and to wet impregnation. The cobalt oxide catalyst deposited on wire gauze and steel sheets were characterised by XPS and Raman microscopy and tested in n-hexane oxidation in tubular and gradientless (jet-stirred) reactors. The model cobalt catalysts showed sufficiently high activity in relation with Pt reference catalysts. The most important factor affecting the catalyst activity was the type of the carrier. The best performance was achieved for the catalysts deposited on wire gauzes.     

Control of a reverse flow reactor for VOC combustion

A flow reversal reactor for VOC combustion is controlled by the linear quadratic regulator (LQR), which uses dilution and internal electric heating as controls to confine the hot spot temperature within the two temperature limits, in order to ensure complete conversion of the VOC and to prevent overheating of the catalyst. Three phases of operation, i.e., dilution phase, heating phase and inactive phase, are identified. In dilution and heating phases, the cost functions of the LQR control are defined in quadratic forms. In the inactive phase, the controllers are inactivated. A linear model is derived by linearization of a countercurrent pseudo-homogeneous model at two nominal operating conditions in the dilution phase and the heating phase, respectively. The feed concentration and the temperature profile are estimated on-line by using a high-gain observer with three temperatures measurements and are used in the LQR feedback control. Experiments are carried out on a medium-scale reversed flow reactor to demonstrate the proposed LQR control strategy. Results show that the LQR controller is highly efficient in maintaining normal operation of the reactor.     

Efficiency of catalytic processes for the reduction of CO and VOC emissions from wood combustion in domestic fireplaces

Pollutant characterization of domestic fireplaces, according to two paces of functioning (normal and low-charge phase) was performed. Two catalysts supported on cordierite or metal were placed in the exhaust of two domestic fireplaces (old and new generation) in order to reduce gaseous pollutants. Active phase of catalysts is composed of noble metals (Pd, Pt) and cerium. Methane was the dominant compound of the released Volatile Organic Compounds (VOC, 80% b. v.). Products resulting from incomplete combustion (CO and other VOC) did not represent more than 6% of the initial carbon content in wood. Lower concentration of CO in the exhaust was obtained with the new generation fireplace as compared to the older one with mean concentrations of CO normalized for 13% oxygen b.v. equal to 0.12% and 0.3%, respectively. Emission of VOC is also drastically reduced for new generation fireplace. The presence of a catalyst induced a decrease of the CO and VOC emission factors during ignition and low-charge phases by factors ranging from 65% to 70%. The abatement of VOC for the old generation fireplace was better in the presence of metal as compared to cordierite, with efficiency values of 65% and 30%, respectively. The new fireplace was the one on which the addition of the cleanup implements had most impact. Besides the introduction of a catalyst, a heating system of the fume was set up below the catalyst. This heating system allowed a faster activation of the catalyst, particularly during ignition and low-charge phases. Best abatements were obtained with the heated metallic support with values close to 80% and 94% for VOC and CO respectively.     

Catalytic activation of ceramic filter elements for combined particle separation, NOx removal and VOC total oxidation

The development of a catalytically active filter element for combined particle separation and NO_x removal or VOC total oxidation, respectively, is presented. For NO_x removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO₂–V₂O₅–WO₃ catalyst system was developed on a ceramic filter element. Different TiO₂ sols of tailor-made mean particle size between 40 and 190 nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO₂-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3 m²/g. Selected TiO₂-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V₂O₅ and WO₃ precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300 °C, a filtration velocity of 2 cm/s and an NO inlet concentration of 500 vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO₂-impregnated filter element support was catalytically activated with a Pt/V₂O₅ system. Complete oxidation of propene with 100% selectivity to CO₂ was achieved at 300 °C, a filtration velocity of 2 cm/s and a propene inlet concentration of 300 vol.-ppm.     

Electrochemical promotion of toluene combustion on an inexpensive metallic catalyst

Electrochemical promotion of the complete catalytic oxidation of toluene at 310 °C is reported, using a Ag/YSZ/Ag two electrode system where Ag films were deposited on YSZ from AgNO₃ aqueous solution followed by reduction in H₂. After on-stream activation, a non-negligible conversion (about 30%) at OCV is reached and then the rate of the catalytic toluene conversion into CO₂ and H₂O can be multiplied by a factor higher than 1.5, by application of a small negative current (about—4 μA cm⁻²). The associated Faradaic efficiency is very high and may exceed −13,000.     

Microstructural evolution of supra-nanostructure Al2O3/ZrO2 eutectic powders by combustion synthesis-spray cooling

Eutectic powders with fine microstructure are difficult to synthesize by crushing eutectic bulk because of the damage of crystal structure and the introduction of milling media during preparation process. In this work, a novel combustion synthesis-spray cooling (CSSC) method is developed to fabricate supra-nanostructure Al₂O₃/ZrO₂ eutectic powders. CSSC is a kind of self-heating technique, which simplifies operations, reduces costs and supplies ultra-high cooling rate. The phase composition and the microstructural evolution are investigated using experiment studies and ANSYS simulation. During the process, the t-ZrO₂ are stabilized at room temperature because of the solubility of Al₂O₃ in ZrO₂. The ultra-high cooling rate greatly refined eutectic structure. Although the eutectic structure coarsens with increases in particle size, the interphase spacing of all particles reaches supra nanoscale. The work provides a route for preparing supra-nanostructure Al₂O₃/ZrO₂ eutectic powders and for better understanding the microstructural evolution.     

The effect of the nature of vanadium species on benzene total oxidation

The nature of the vanadium species present on V₂O₅/Al₂O₃ catalysts was investigated by using solid state ⁵¹V NMR, diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD) and temperature programmed reduction (TPR). ⁵¹V NMR and DRS analyses indicated the presence of V⁵⁺ in tetrahedral symmetry at low vanadium loading. A surface polymeric vanadium species and/or the bulk crystalline V₂O₅ were mainly observed at high vanadium loading as also detected by XRD. The positions of the absorption edges determined through the UV–VIS spectra allowed distinguishing between various tetrahedral symmetries. After TPR, the average oxidation state of vanadium depended on the vanadium content. The nature of vanadium species was related to the catalyst behavior on the benzene oxidation reaction. The catalysts containing high vanadium content were more active suggesting that a high amount of V⁴⁺ is responsible for the higher activity.     

Mn Salophen/A12O3高压催化环己烯合成环己烯酮

介绍了催化荆MnSalophen/A12O3的制备方法,并对其结构进行了表征.然后以自制的MnSalophen/A12O3为催化剂,以分子氧为氧化剂,研究了催化剂用量、反应时间、反应温度以及反应压力对环己烯转化率和环己烯酮收率的影响.结果表明,在催化剂用量:50 mg,反应时间:8 h,反应温度:100℃,反应压力:1.5 MPa的条件下,环己烯酮的收率可达50.3%.     

不同ZnO／Al2O3的LZAS系微晶玻璃的显微结构和性能

采用DTA、XRD、SEM、TEC(热膨胀系数)等测试方法研究了不同ZnO/A12O3的LZAS玻璃体系的显微结构和热膨胀性能.结果表明:随着ZnO/A12O3减小,基础玻璃的转变温度、第一放热峰温度和重熔温度逐渐增大;晶化温度为650℃时,各试样的主晶相均为γⅡ-LZS,并且热膨胀系数较大;750℃时,各试样的主晶相转变为γ0-LZS、β-石英固溶体和β-锂辉石固溶体,并且膨胀系数变小,晶体结构致密.同时发现,这两个温度的热膨胀系数在ZnO/A12O3≈1.0～1.5(mol比)时发生较大变化.     

低温燃烧法制备纳米La2O2CO3

采用低温燃烧合成法,以尿素为燃烧剂,以聚乙二醇为活化剂,加入少量的柠檬酸做引发剂,通过与硝酸镧反应制备碳酸氧镧,以XRD、TG-DTA、TEM等分析手段进行表征,系统考察焙烧时间、焙烧温度等工艺参数对最终产物的组成和粒径的影响,确定最佳的工艺条件.实验结果表明,以尿素为燃烧剂制备纳米碳酸氧镧是可行的,制备碳酸氧镧的最佳...     

Washcoating of metallic monoliths with a MnCu catalyst for catalytic combustion of volatile organic compounds

A ready-made MnCu catalyst showing a good performance in the combustion of volatile organic compounds has been deposited on FeCrAlloy^® metallic monoliths by means of washcoating. With the aim of depositing a homogeneous and well-adhered layer of catalyst on the monoliths, the effects of a pre-coating with colloidal alumina as a primer, the solid concentration in the slurry, the addition of a stabilizer to the slurry, and the immersions number of the monolith in the slurry were studied. The addition of a stabilizer to the slurry was necessary to prevent sedimentation and to achieve reproducible washcoatings. The pre-coating of the monolith with the primer improved the washcoating adherence obtained with one impregnation but a better adherence did not compensate a lower solid load due to a lower surface roughness. A higher amount of deposited material was obtained with the slurry at 35 wt% making two impregnations. The obtained monoliths showed excellent catalytic activity in the combustion of ethyl acetate and toluene. The activity as well as the surface area and pore volume of each monolith increased with the amount of retained solid.     

搅拌速率对Pd/Al_2O_3催化剂CH_4催化燃烧性能的影响

为了考察搅拌速率在Pd/Al2O3催化剂制备过程中的作用,通过对不同搅拌速率制备的Pd/Al2O3催化剂进行XRD、H2-TPR和XPS表征及CH4催化燃烧活性测试,研究搅拌速率对Pd/Al2O3催化剂活性的影响。结果表明,低搅拌速率[(200~300)r·min-1]条件制备的催化剂,Pd O粒径较大,Pd分散度高,表面Pd与Pd O物质的量比=0.55~0.56,催化剂的CH4催化反应活化能与无搅拌时相比降低,在200 r·min-1达到最低;随着搅拌速率增加,高搅拌速率[(400~600)r·min-1]抑制了Pd O晶粒的生长,导致Pd O粒径变小,Pd分散度降低,并使表面Pd O含量增大,Pd与Pd O物质的量比=0.41~0.52,提高了CH4催化燃烧反应的活化能。     

两级A/O工艺处理生活污水脱氮除磷试验

针对传统A2/O工艺存在的泥龄矛盾,将脱氮和除磷分置于前后2套不同的A/O系统中,第一级A/O采用活性污泥法除磷;第二级A/O采用生物膜法脱氮。以生活污水为处理对象进行试验研究。结果表明,在泥龄为6 d、水温为22～28℃,进水NH3-N、TP、COD的质量浓度分别为40～70、2.0～6.0、150～320 mg/L条件下,出水NH3-N、TP、COD的平均质量浓度分别为5.9、1.0、40 mg/L,均达到了城镇污水处理厂污染物排放标准(GB18918-2002)中的一级排放标准,其去除率分别为82.5%、69.7%、83.1%。     

Optimization of structured catalyst carriers for VOC combustion

Typical catalytic afterburners do not offer sufficient mass transport properties for volatile organic compounds (VOC) combustion. Therefore, displaying highly increased transport properties, short-channel microstructures of various geometries and wire gauze structures have been designed and evaluated as an alternative to monoliths. The structures have been deposited with Pd promoted cobalt oxide catalyst using Langmuir–Blodgett technique. The catalyst has proved to meet the specific requirements of VOC combustions and also not to change the microstructure geometry. According to the models of mass transfer proposed in this study, short-channel and gauze structures have up to 15 times higher mass transfer coefficients, and up to 90 times higher volumetric coefficients than standard monoliths. The results of experiments performed using the stacked wire gauze structure were in accordance with the results derived from modelling giving high convergence for higher Reynolds number values (>15). According to the evaluation criteria proposed by us, the majority of short-channel microstructures have shown very high mass transfer efficiency both in diffusional regime (40 times higher than monoliths) and in levelled diffusional and kinetic regime (over 20 times higher).     

过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧性能的影响

考察过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧活性的影响以及过渡金属负载量及循环条件对甲烷降解性能的影响,采用扫描电镜、N_2吸附-脱附以及H_2程序升温还原技术对催化剂进行表征。结果表明,过渡金属Ni的添加对催化剂在(375~475)℃下的甲烷催化燃烧活性产生影响。催化剂经多次重复使用后,催化燃烧活性提高。分析原因为经过渡金属Ni改性后,可与载体形成NiAl_2O_4尖晶石,促进活性组分形成较小晶粒,并改善活性组分分散度,提高催化剂催化活性。     

Ti-Al复合载体载锰催化剂同时脱硝脱汞实验

采用溶胶-凝胶法制备了一系列TiO₂、TiO₂-Al₂O₃（TiAl）、MnO₂/TiO₂（MnTi）和MnO₂/TiO₂-Al₂O₃（MnTiAl）样品,在固定床实验装置上研究了MnTi和MnTiAl催化剂的脱硝、脱汞性能,并对相应的样品进行了BET、XRD、H₂-TPR、XPS表征分析。表征结果表明,Al₂O₃掺入TiO₂后能极大提高载体的比表面积,提升催化剂氧化还原性能,且有利于高价态锰离子（Mn³⁺和Mn⁴⁺）和化学吸附氧（O*）在催化剂表面富集。固定床实验结果表明,在反应温度范围内,MnTiAl催化剂脱硝、脱汞性能均优于MnTi催化剂,MnTiAl催化剂在200℃时脱硝、脱汞效率分别高达88.5%和96.1%。MnTiAl脱除烟气Hg⁰过程中,将Hg⁰氧化为Hg²⁺的同时,催化剂表面Mn³⁺、Mn⁴⁺和O*浓度均被消耗,同时烟气中的O₂能将催化剂表面较低价态的锰离子（Mn²⁺和Mn³⁺）重新氧化为高价态锰离子（Mn³⁺和Mn⁴⁺）,并且能补充催化剂表面的化学吸附氧（O*）,进而实现催化剂催化氧化Hg⁰过程。     

Comparison of wash‐coated monoliths vs. microfibrous entrapped catalyst structures for catalytic VOC removal

Head‐to‐head experimental performance comparisons for flow through pleated microfibrous structures (flat‐, V‐, and W‐shaped) were made with wash‐coated monolith of different cells per square inch (230 and 400). Microfibrous entrapped catalyst (MFEC) was prepared by entrapping support particles (γ‐Al₂O₃, 150–250 μm diameter) into nickel microfibers. Pleated structures of MFECs and wash‐coated monoliths containing Pd‐Mn/γ‐Al₂O₃ were investigated systematically for volatile organic compound (e.g., ethanol) removal at various face velocities (ca. 3–30 m/s) and at low temperatures (≤473 K). The experimental studies showed that pleated MFEC (W‐shaped) had shown significantly improved performance in VOC removal in terms of conversion and pressure drop than tested monolith for high face velocity system. The flexibility of pleating lowered the effective velocity inside the media that resulted lower pressure drop and higher conversion. Furthermore, a reaction kinetic model was developed for pleated MFEC considering the Peffer's model to substantiate the experimental results. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3814–3823, 2014     

BaO对Al_2O_3的改性及MnO_x/BaO-Al_2O_3对甲烷燃烧的催化活性

以Mn(CH3COO) 2 ·4H2 O为前驱体 ,制备了MnOx/Al2 O3 和MnOx/BaO Al2 O3 系列催化剂 ,用X 射线衍射 (XRD)和程序升温还原 (TPR)进行了表征 ,考察了加入BaO对Al2 O3 的热稳定性及对MnOx/BaO Al2 O3 还原性能的影响。以甲烷燃烧为模型反应 ,考察了MnOx/BaO Al2 O3的催化活性。结果表明BaO Al2 O3 负载MnOx 催化剂对甲烷燃烧的活性比MnOx/Al2 O3 有明显提高 ,Ba在Al2 O3 中的最佳质量分数为 5 %     

O2／CO2燃烧技术研究进展

O2／CO2燃烧技术不仅有效收集烟气中的CO2,还能减少NOx和SO2的排放,是一种新型的洁净煤燃烧技术。介绍了其应用、发展历程以及在燃烧、传热和污染物排放的研究进展,指出了这一技术领域中存在的问题,并对下一步的研究方向给出了建议。     

Preparation of mesoporous silica fiber matrix for VOC removal

A novel method for the preparation of the mesoporous silica fiber matrix was introduced for a removal of volatile organic compounds (VOCs). Paper making technology was applied to make a sheet of mesoporous silica fiber matrix. Reinforcing the mesoporous silica fiber with the ceramic fibers (50 wt.%) increased the mechanical strength of the matrix. Mesoporous silica fibers using TMOS (tetramethoxysilane) as a silica source and CTAC (cetyltrimethyl-ammoniumchloride) as a surfactant were drawn by the spinning method. The spinning process increased both the crystallinity and the fraction of mesopores (1.9 nm) of the fiber. As the spinning rate was increased both the crystallinity and the specific area of the mesoporous silica fiber increased, but the diameter of fiber decreased. We could control the size and morphology of mesoporous silica fiber matrix by changing the shape of substrates. This leads to easy fabrication of honeycomb-structured adsorbent which can be used for the VOC removal.