NOx储存催化剂Pt/BaAl2O4-Al2O3的XAFS研究

采用共沉淀-浸渍法在不同载体焙烧温度下,制备了不同Al/Ba原子比的Pt/BaAl2O4-Al2O3系列样品.用XRD, XANES, EXAFS,以及NSC (NOx storage capacity）测定等手段对样品的微观结构和NOx储存性能进行了详细的表征.样品中Ba物种是以BaAl2O4和BaCO3两种混合物相的形式存在,且伴随着载体焙烧温度和Ba含量的降低, BaAl2O4物相的分散度变高, NOx储存活性也随之提高,这表明BaAl2O4相的分散度与样品的NOx储存性能密切相关,小颗粒的BaAl2O4相是NOx的主要储存活性中心.在样品中, Pt物种以金属原子簇形式存在,分散度很高,其Pt－Pt壳层配位数较标样Pt粉有显著下降, Pt－Pt键长变短,出现了纳米收缩现象.高分散的小颗粒金属Pt原子簇为捕获和氧化NOx的主要活性中心.     

Bi2O3—Y2O3系阻抗谱研究

本文用交流阻抗法研究了Bi_2O_3-Y_2O_3系的阻抗谱。呈现特有的Warburg阻抗及其相关阻抗。在高氧分压下,电极过程由氧原子在三相线发生反应后直接进入电解质步骤控制;低氧分压下,由上述步骤和界面浓差极化共同控制,或仅由浓差极化控制。在氧分压为1.01×10~(-10)～1.01×10~5Pa内时,Bi_2O_3-Y_2O_3系表现为纯氧离子导体。     

Activity Enhancement of Pt/Ba/Al2O3 Mixed with Mn/Ba/Al2O3 for NOx Storage-reduction by Hydrogen

The storage and reduction of nitrogen oxides has attracted much attention as an efficient way to reduce NOx emission of lean-burn gasoline and diesel engines1-5. At present, NOx storage and reduction (NSR) catalysts based on Pt and Ba have been extensivel…     

Mn/Ba/Al2O3催化剂的NOx氧化-储存和耐硫性能

采用分步等体积浸渍法制备了Mn/Ba/Al2O3催化剂, 并用XRD和TPD等方法进行表征. 考察了催化剂在不同温度下NOx氧化-储存特性和NOx脱附行为. 结果表明, Mn/Ba/Al2O3催化剂具有较高的催化NO氧化活性和较大的NOx储存容量. BaMnO3是主要的活性组分；Mn能够催化NO的氧化反应, 且具有一定的NOx储存能力; Ba是主要的储存组分, 将NOx以硝酸盐的形式储存; 硝酸盐在300～600 ℃分解, 释放出NOx. Mn/Ba/Al2O3催化剂在800 ℃老化6 h后, NO氧化活性和NOx储存能力稍有下降. 低含量的SO2对催化剂的NO氧化活性和NOx储存能力没有明显影响; 高含量的SO2使催化剂的NO氧化活性降低, NOx储存量减小, 最终导致催化剂失活.     

Bi2O3／γ—Al2O3系助燃剂的性能研究

负载性Pt助燃剂已被广泛应用。由于助燃剂能促进CO的转化成CO_2,对焦炭本身的燃烧速度无明显影响,故欲强化催化剂再生过程应提高其表面结焦的燃烧速度。我们制备了一系列Bi_2O_3/γ-Al_2O_3助燃剂以取代较为昂贵的Pt系助燃剂,并考察了Bi系助燃剂的物相结构、表面吸附性能、抗硫性及CO催化氧化活性和烧碳速度。结果表明,在高温实用区域,Bi系和Pt系对CO催化氧化活性相近,Bi系尚具有较好的去焦性能,有利于催化剂再生。     

燃煤在O2／CO2方式下NOx生成特性的研究

O2／CO2方式是一种能有效控制CO2、SO2和NOx排放的新型高效清洁的煤燃烧技术,在自行设计的实验装置上研究了三种不同煤质特性的燃煤在这种方式下NOx的生成与排放特征。主要研究结果表明当温度为700℃及900℃时,O2／CO2方式下NOx的排放量较空气气氛下大为降低,研究结果还表明O2／CO2方式下温度、煤质特性、钙基吸收剂的加入对NOx的生成特性有着重要影响。     

整体式Co3O4/YSZ-Y-Al2O3+CYZ催化剂上的甲烷催化燃烧

用质量比为32的YSZ-γ-Al2O3和CeO2-Y2O3-ZrO2的混合物(以YSZA+CYZ表示)作载体,制备了不同Co3O4含量的整体式甲烷燃烧催化剂,同时制备了分别以YSZA和CYZ为载体的催化剂作为对比,研究了它们老化前后的反应性能,并用BET,XPS,XRD,TPR等研究了催化剂的比表面、表面状态、晶相结构和还原性能.结果表明,YSZ-γ-Al2O3和CeO2-Y2O3-ZrO2混合载体能有效地抑制CoAl2O4的生成,并能充分发挥各自的优点,因此负载一定量的钴后表现出很高的甲烷催化燃烧活性和抗老化性,尤其是含8 wt%Co3O4的样品性能最佳,有望成为实用的甲烷燃烧催化剂之一.     

Ce0.67Zr0.33O2对CH4燃烧催化剂Fe2O3/Al2O3的改性作用

固定n（Ce）／n（Zr）比为0．67／0．33,用共沉淀法制得一系列CeO2-ZrO2-Al2O3固溶体,采用这些固溶体作载体,以Fe2O3为活性组分,用浸渍法制备了一系列催化剂,BET结果显示,将适量Ce0.67Zr0．33O2引入到Al2O3载体中有助于催化剂保持较高的比表面积,TPR结果显示,载体中引入适量的Ce0．67Zr0.33O2可以改善催化剂的氧化还原性能,XRD结果表明,Fe2O3在CeO2-ZrO2-Al2O3载体上呈现出良好的分散状况,老化前后催化剂的晶相结构基本无明显变化,特别是当载体中m（Ce0.67Zr0.33O2）：m（Al2O3）的值为1：2时,Fe2O3／CeO2-ZrO2-Al2O3催化剂在甲烷催化燃烧中显示出最佳的催化性能和抗高温老化性能。     

CH_2(~3B_1)自由基与N_2O反应的研究

CH2是燃烧和大气光化学中重要的自由基之一[1]．在燃烧过程中,CH2自由基由碳氢化合物分子热解或由O原子和C2H2等反应生成．这种高活性的中间体,又可进一步与燃烧过程中其它重要物质如NOx（NO、NO2、N2O）发生反应．在低温燃烧过程中,N2O是NOx存在的主要形式,所以,研究CH2自由基与N2O的反应,对于了解燃烧机制有重要意义．就我们所知,关于CHZ和N20的反应,国内外还未见文献报导．本文从态-态反应的层次上,开展基电子态CH2（X3B1）自由基与N2O反应的实验研究．我们利用351um紫外激光光解CH2CO产生CH2自由基,这种方法…     

Yb2O3对Bi2O3-MoO3催化剂性能的影响

在Bi2O3-MoO3复合氧化物催化剂中加入Yb2O3，可明显提高异丁烯转化率和生成甲基丙烯醛的选择性，用XRD、FT-Raman光谱和SEM技术研究了催化剂的组成和性质，Bi2O3—MoO3催化剂的成分主要是α-Bi2Mo3O12，添加镱后出现了Yb2Mo3O12的吸收峰；且Bi2O3-MoO3-Yb2O3催化剂的FT—Raman光谱图在363cm^-1处出现了Yb—O伸缩振动峰，同时既Bi2O3-MoO3催化剂的铝-氧振动发生红移，表明镱的加入使铝-氧键的振动减弱，使Bi2O3-MoO3-Yb2O3催化剂有较高传递晶格氧给予异丁烯的能力，导致异丁烯转化率和生成甲基丙烯醛的选择性均显著提高。     

高催化活性2D/2D Ti3C2/Bi4O5Br2纳米片异质结的构建及其可见光催化去除NO

This study concentrated on the production of a two-dimensional and two-dimensional (2D/2D) Ti₃C₂/Bi₄O₅Br₂ heterojunction with a large interface that applied as one of the novel visible-light-induced photocatalyst via the hydrothermal method. The obtained photocatalysts enhanced the photocatalytic efficiency of the NO removal. The crystal structure and chemical state of the composites were characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that Ti₃C₂, Bi₄O₅Br₂, and Ti₃C₂/Bi₄O₅Br₂ were successfully synthesized. The experimental results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the prepared samples had a 2D/2D nanosheet structure and large contact area. This structure facilitated the transfer of electrons and holes. The solar light absorptions of the samples were evaluated using the UV-Vis diffuse reflectance spectra (UV-Vis DRS). It was found that the absorption band of Ti₃C₂/Bi₄O₅Br₂ was wider than that of Bi₄O₅Br₂. This represents the electrons in the Ti₃C₂/Bi₄O₅Br₂ nanosheet composites were more likely to be excited. The photocatalytic experiments showed that the 2D/2D Ti₃C₂/Bi₄O₅Br₂ composite with high photocatalytic activity and stability. The photocatalytic efficiency of pure Bi₄O₅Br₂ for the NO removal was 30.5%, while for the 15%Ti₃C₂/Bi₄O₅Br₂ it was 57.6%. Moreover, the catalytic reaction happened in a short period. The concentration of NO decreased exponentially in the first 5 min, which approximately reached the final value. Furthermore, the stability of 15%Ti₃C₂/Bi₄O₅Br₂ was favorable: the catalytic rate was approximately 50.0% after five cycles of cyclic catalysis. Finally, the scavenger experiments, electron spin resonance spectroscopy (ESR), transient photocurrent response, and surface photovoltage spectrum (SPS) were applied to analyze the photocatalytic mechanism of the composite. The results indicated that the 2D/2D heterojunction Ti₃C₂/Bi₄O₅Br₂ improved the separation rate of the electrons and holes, thus enhancing the photocatalytic efficiency. In the photocatalytic reactions, the photogenerated electrons (e⁻) and superoxide radical (·O₂⁻) were critical active groups that had a significant role in the oxidative removal of NO. The in situ Fourier-transform infrared spectroscopy (in situ FTIR) showed that the photo-oxidation products were mainly NO₂⁻ and NO₃⁻. Based on the above experimental results, a possible photocatalytic mechanism was proposed. The electrons in Bi₄O₅Br₂ were excited by visible light. They jumped from the valence band (VB) of Bi₄O₅Br₂ to the conduction band (CB). Then, the photoelectrons transferred from the CB of Bi₄O₅Br₂ to the Ti₃C₂ surface, which significantly promoted the separation of the electron-hole pairs. Therefore, the photocatalytic efficiency of Ti₃C₂/Bi₄O₅Br₂ on NO was significantly improved. This study provided an effective method for preparing 2D/2D Ti₃C₂/Bi₄O₅Br₂ nanocomposites for the photocatalytic degradation of environmental pollutants, which has great potential in solving energy stress and environmental pollution.     

TiO2/Bi2O3纳米复合体的制备及可见光催化产氢性能

首先采用相分离的水解-溶剂热法制备了Bi₂O₃纳米粒子,然后利用简单的湿化学法在Bi₂O₃表面负载不同比例的TiO₂纳米颗粒,进而得到TiO₂/Bi₂O₃纳米复合体。通过气氛调控的表面光电压谱(SPS)等测试表明,表面负载适量的TiO₂后能够提高Bi₂O₃光生电荷分离。可见光催化产氢和降解污染物测试结果进一步证明,表面负载适量的TiO₂后可显著提高其可见光催化活性,其中Ti/Bi摩尔比为7%时具有最高的光催化活性。这主要归因于TiO₂具有较为合适的导带能级位置,可以接收Bi₂O₃在可见光激发下所产生的高能级电子,从而抑制光生电子-空穴对复合,并且维持了高能级电子较高的还原能力。     

Pt/Al2O3催化剂用于丙烯选择性还原NO

分别采用浸渍法(IM)和溶胶-凝胶法(SG)制备了一系列不同铂负载量的催化剂,在固定床反应器上用C3H6作还原剂,测试了选择性还原NO_x的活性,结果发现,在IM法和SG法制备的催化剂中,活性组分铂最佳负载质量分数分别为0.5%和2%.针对两种催化剂,分别考察了氧浓度、丙烯浓度及反应气流量对选择性催化还原NO_x性能的影响,催化活性随丙烯浓度的增大而上升.2%Pt/Al₂O₃(SG)催化剂的抗SO₂性能好于0.5%Pt/Al₂O₃(IM)催化剂,H₂O的存在可明显拓宽活性温度范围,并向高温区间移动,在200～400℃范围内可有效净化NO_x.     

沉淀法制备Bi2O3的晶相转变过程及其光催化性能

以硝酸铋为原料,氨水为沉淀剂,通过液相沉淀法制得前驱体Bi(OH)₃,并将Bi(OH)₃分别在不同温度和时间下焙烧。利用X射线衍射(XRD)、拉曼光谱、热重(TG)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)及紫外-可见漫反射光谱(UV-Vis DRS)详细研究了Bi(OH)₃转变为Bi₂O₃的过程及相变过程中粒子形貌、大小、光吸收性质等。结果表明,前驱体Bi(OH)₃经过焙烧之后,发生了如下的转变过程:Bi(OH)₃→Bi₅O₇NO₃→β-Bi₂O₃/Bi₅O₇NO₃→β-Bi₂O₃/Bi₅O₇NO₃/α-Bi₂O₃→α-Bi₂O₃,而且转变过程伴随着粒子长大。在上述转变过程中,与Bi₅O₇NO₃向β-Bi₂O₃转变的过程相比,从β-Bi₂O₃到α-Bi₂O₃相变过程更为迅速。此外,以光催化降解罗丹明B(RhB)为模型反应,考察了不同晶相的Bi₂O₃光催化活性,结果表明Bi₅O₇NO₃和β-Bi₂O₃材料具有优异的光催化性能,而α-Bi₂O₃具有较低的光催化活性。     

富含光诱导氧空位Bi12O17Br2的制备及其高效光催化固氮性能

采用一步水热法制备了Bi₁₂O₁₇Br₂光催化剂,其平均微片尺寸为1.2μm,比表面积约为29 m²·g^-1。Bi₁₂O₁₇Br₂的禁带宽度为2.42 eV,能够响应可见光。值得注意的是,在光照条件下Bi₁₂O₁₇Br₂表面能够产生氧空位;光诱导氧空位不仅能促进氮气在催化剂表面的吸附,而且对吸附的氮气分子的活化起到至关重要的作用。实验结果表明在可见光照射下,Bi₁₂O₁₇Br₂光催化剂上的氨生成速率为337.6μmol·g^-1·h^-1。在可见光的驱动下,Bi₁₂O₁₇Br₂光催化剂能够实现氮气与水反应生成氨的过程。     

掺加Nd和K改性对Co3O4催化分解N2O活性的影响

用水热法和共沉淀法分别制备了Nd-Co₃O₄催化剂,催化分解N₂O。其中,水热法制备的Nd-Co₃O₄催化活性较高。在不同组成的Nd-Co₃O₄中,优化出了较高活性的0.01Nd-Co₃O₄催化剂,在其表面浸渍K₂CO₃溶液制备K改性催化剂（K/Nd-Co₃O₄）。用X射线衍射（XRD）、N₂物理吸附、扫描电镜（SEM）、X射线光电子谱（XPS）、程序升温还原（H₂-TPR）、O₂程序升温脱附（O₂-TPD）等技术表征催化剂结构。结果表明,Nd-Co₃O₄和K改性催化剂均为尖晶石结构;K改性弱化了催化剂表面Co-O键,有利于表面氧的脱除,提高了催化剂活性。有氧有水气氛350 ℃连续反应40 h,K/Nd-Co₃O₄催化剂上的N₂O分解率超过90%,稳定性较好。     

微波液相法一步合成H3PW12O40/Bi2WO6光催化剂及其脱氮性能

采用微波液相法一步合成了固载型H₃PW₁₂O₄₀/Bi₂WO₆光催化剂. 通过紫外-可见漫反射光谱(UV-Vis)、 场发射扫描电子显微镜(SEM)、 表面积及孔隙度(BET)测定、 氨气程序升温脱附(NH₃-TPD)、 吡啶吸附红外光谱(Py-FTIR)和X射线衍射(XRD)对所合成催化剂的结构和性质进行了考察, 并以吡啶浓度为15 mg/g的模拟油对光催化剂的脱氮效果进行评价. 结果表明, 与传统浸渍固载法相比, 微波液相一步法不仅能高效合成H₃PW₁₂O₄₀/Bi₂WO₆光催化剂, 且所合成的催化剂能被低能量的光激发. 固载H₃PW₁₂O₄₀不但能提高Bi₂WO₆纳米颗粒的表面酸量, 还能通过改变Bi₂WO₆前驱液的酸强度来调控催化剂形貌. 在H₃PW₁₂O₄₀固载量为15%(质量分数), 微波功率为800 W, 反应时间为90 min条件下得到的H₃PW₁₂O₄₀/Bi₂WO₆的光催化脱氮活性最高, 在催化剂与模拟油质量比为1/300, 500 W氙灯光照60 min的最佳光催化反应条件下, 模拟油脱氮率达到92.63%.     

N2O Decomposition Catalyzed by K+-doped Bi0.02Co

K⁺-doped Bi_0.02Co was investigated as catalyst for N₂O decomposition. It was found that the catalytic performance of the Bi_0.02Co catalyst, which was prepared by coprecipitation method, can be effectively modified by potassium cations via impregnation. The optimized K_0.01Bi_0.02Co catalyst exhibited much higher activity compared with Bi_0.02Co and K_0.01Co for the reaction in feed gas 0.2% N₂O/Ar, irrespective of the presence or absence of impurity gas(volume fraction) 5%O₂, 2%H₂O, 0.12%NO and 10%CO₂. Characterization of the catalysts with H₂ temperature programmed reduction(H₂-TPR) and O₂ temperature programmed desorption(O₂-TPD) indicate that the Co-O bond in Bi_0.02Co was weakened by the K⁺doping, and hence the K_0.01Bi_0.02Co catalyst has much higher turnover frequency(TOF) than Co₃O₄ spinel and Bi_0.02Co for the reaction.     

还原-氧化预处理对Co_3O_4催化分解N_2O性能的影响

采用液相沉淀法制备了Co_3O_4催化剂,并对其进行还原-氧化预处理制得Co_3O_4-RO。通过XRD、N_2-physisorption、Raman、H_2-TPR、XPS和O_2-TPD等技术对催化剂进行表征,在连续流动微反应装置上考察了催化剂催化分解N_2O性能。结果表明,经过还原-氧化预处理,与Co_3O_4催化剂相比,Co_3O_4-RO结晶度变差,晶粒粒径减小,尤其是尖晶石结构重构过程削弱了Co-O键,增强了催化剂表面的氧物种脱附能力,降低了催化分解N_2O反应的活化能,因而显著提高了催化剂的催化活性。同时,Co_3O_4-RO对原料气中的O_22%(体积分数)和H_2O 2. 3%(体积分数)表现出较强的耐受性。     

Photocatalytic conversion of NOx on AgCl/Al2O3 catalyst

The rate of NO conversion under UV illumination was evaluated over Ag/Al₂O₃ and AgCl/Al₂O₃ catalysts at room temperature. The AgCl/Al₂O₃ catalyst is highly active for the conversion of NO_x. The conversion is enhanced in the presence of O₂ and further enhanced when oxygen coexists with hydrocarbons. Diffuse reflectance spectra of AgCl/Al₂O₃ and Ag/Al₂O₃ show an absorption band at 250 nm, and a weak and broad band at 230 nm, respectively. The high photocatalytic NO_x conversion is achieved over the AgCl/Al₂O₃ catalyst. The conversion level of NO_x is maintained above 60% over 5 h in the presence of O₂ and hydrocarbons under UV-irradiation. The absorption band at 250 nm is ascribed to the band gap energy of crystallized AgCl particles on Al₂O₃. These results suggest that high photocatalytic NO_x conversion proceeds on crystallized AgCl particles formed on Al₂O₃.