分等级结构对锡氧化物负载Pt室温催化甲醛氧化性能的影响（英文）

发布时间：2018-12-25 18:37

【摘要】：甲醛是主要的室内空气污染物,气相中甲醛去除技术具有重要意义.常用的甲醛去除技术主要包括物理和化学吸附、光催化分解和热催化氧化,其中能在常温下进行的催化氧化最具发展和实用前景.能在室温下高效催化甲醛完全氧化的催化剂一般为负载型贵金属,如铂(Pt)、钯、金、银等.除了选择具有内在高活性的组分,通过提高贵金属分散度,增强贵金属-载体相互作用,增加载体的甲醛亲和性等方法也可提高甲醛催化分解活性.以上方法主要关注催化剂化学性质的改良;另一方面,催化剂的微观几何结构以及传质快慢对表观催化反应速率也有重要影响.近年来研究表明,分等级结构利于反应物在材料孔隙中的扩散输移,可大幅提高催化活性.因此,我们制备了具有分等级结构的花状锡氧化物(SnO_x)负载的Pt纳米颗粒,并研究其室温下催化分解甲醛的性能.花状SnO_x以氟化亚锡和尿素为原料,通过水热法制备;Pt通过浸渍、硼氢化钠还原法负载,制备Pt/SnO_x催化剂.另外,对SnO_x进行球磨处理破坏其分等级结构,制备g-SnO_x及Pt/g-SnO_x作为对照.通过场发射扫描电镜观察,制备的锡氧化物为具有分等级结构的花状微球,直径约1μm,由厚度约20 nm的花瓣状纳米片交错连接而成.X射线衍射(XRD)谱图对应四方相氧化亚锡(SnO,JCPDS 06-0395),但也观察到四方金红石相氧化锡(SnO_2,JCPDS 41-1445)的微弱特征峰.高分辨透射电镜(HRTEM)仅观察到四方相SnO的晶格条纹.根据X射线光电子能谱(XPS)结果,在花状锡氧化物的表面,锡元素的氧化态为正四价.综合以上表征结果表明:制备的锡氧化物主体为SnO,由于表面被空气氧化,含有少量SnO_2.通过透射电镜观察Pt/SnO_X催化剂发现,直径2-3 nm的Pt纳米颗粒高度分散负载于SnO_x纳米片表面;XPS结果表明,纳米颗粒中Pt的价态为0价,与HRTEM观测结果一致.甲醛分解测试采用静态测试系统,在体积为6 L的测试箱中加入一定浓度甲醛后开始反应,监测甲醛、二氧化碳(CO_2)和一氧化碳(CO)浓度随时间的变化.结果表明,花状SnO_x在室温下不具有催化甲醛氧化活性,仅能通过吸附作用去除少量甲醛;而负载0价金属态Pt纳米颗粒后,甲醛快速分解为CO_2和水,且无CO生成.在初始浓度170 ppm条件下,反应1h后,甲醛去除率达到87%.Pt/SnO_x催化剂的高活性表明,金属态Pt是催化甲醛氧化的活性组分.经球磨处理后制备的Pt/g-SnO_x,其催化活性远低于具有分等级结构的Pt/SnO_x;后者的二级反应速率常数为前者的5.6倍,证明分等级结构能有效加速甲醛催化氧化分解.本研究结果对于高效分解室内甲醛材料的设计、制备提供了一种指导性的新思路.
[Abstract]:Formaldehyde is the main indoor air pollutant. The commonly used formaldehyde removal technologies include physical and chemical adsorption, photocatalytic decomposition and thermal catalytic oxidation, among which the catalytic oxidation at room temperature has the most development and practical prospects. The catalysts that can efficiently catalyze the complete oxidation of formaldehyde at room temperature are supported noble metals such as platinum (Pt), palladium gold silver and so on. In addition to the selection of components with high intrinsic activity, the catalytic decomposition activity of formaldehyde can also be improved by increasing the dispersion of precious metals, enhancing the interaction between noble metals and carriers, and increasing the formaldehyde affinity of the support. The above methods mainly focus on the improvement of the chemical properties of the catalyst, on the other hand, the microstructure of the catalyst and the speed of mass transfer also have an important effect on the apparent catalytic reaction rate. Recent studies have shown that the hierarchical structure is conducive to the diffusion and transport of reactants in the pores of the materials and can greatly improve the catalytic activity. Therefore, Pt nanoparticles supported on flower-like tin oxide (SnO_x) with hierarchical structure were prepared and their catalytic decomposition of formaldehyde at room temperature was studied. The flower-like SnO_x was prepared by hydrothermal method from stannous fluoride and urea, and the Pt/SnO_x catalyst was prepared by impregnation and sodium borohydride reduction method. In addition, SnO_x was milled to destroy its grading structure, and g-SnO_x and Pt/g-SnO_x were prepared as control. Observed by field emission scanning electron microscope, the tin oxide is a flower-like microsphere with graded structure, and its diameter is about 1 渭 m. The X-ray diffraction (XRD) spectra correspond to tetragonal stannous oxide (SnO,JCPDS 06-0395), but tetragonal rutile tin oxide (SnO_2,) is also observed. The weak characteristic peak of JCPDS 41-1445). The lattice stripes of tetragonal SnO were observed only by high resolution transmission electron microscopy (HRTEM). According to the results of X-ray photoelectron spectroscopy (XPS), the oxidation state of tin is tetravalent on the surface of flower-like tin oxide. The results of the above characterization indicate that the main body of tin oxide prepared is SnO, which contains a small amount of SnO_2. because the surface is oxidized by air. The Pt nanoparticles with diameter 2-3 nm were found to be highly dispersed on the surface of SnO_x nanoparticles by transmission electron microscopy (TEM), and the XPS results showed that the valence state of Pt in the nanoparticles was zero, which was consistent with that observed by HRTEM. A static test system was used to test the decomposition of formaldehyde. After adding a certain concentration of formaldehyde into the test box of 6 L volume, the concentration of formaldehyde, carbon dioxide (CO_2) and carbon monoxide (CO) were monitored over time. The results showed that the flower-like SnO_x had no catalytic activity for formaldehyde oxidation at room temperature, and only a small amount of formaldehyde could be removed by adsorption. However, after loading 0 valent metal Pt nanoparticles, formaldehyde rapidly decomposed into CO_2 and water, and no CO was formed. Under the initial concentration of 170 ppm, the formaldehyde removal rate reached the high activity of 87%.Pt/SnO_x catalyst after 1 h reaction. The results showed that the metal Pt was the active component of formaldehyde oxidation. The catalytic activity of Pt/g-SnO_x, prepared by ball milling is much lower than that of Pt/SnO_x; with graded structure. The second order reaction rate constant of the latter is 5.6 times of that of the former, which proves that the hierarchical structure can accelerate the catalytic oxidation decomposition of formaldehyde effectively. The results of this study provide a new guiding idea for the design and preparation of efficiently decomposing indoor formaldehyde materials.
【作者单位】：武汉理工大学材料复合新技术国家重点实验室;东华理工大学放射性地质与勘探技术国防重点学科实验室;沙特阿卜杜勒阿齐兹国王大学科学部物理系;
【基金】：supported by the National Natural Science Foundation of China (51320105001, 51372190, 21573170, 51272199, 21433007) the National Basic Research Program of China (973 program, 2013CB632402) the Natural Science Foundation of Hubei Province (2015CFA001) the Fundamental Research Funds for the Central Universities (WUT: 2015-Ⅲ-034) Innovative Research Funds of SKLWUT (2015-ZD-1)~~
【分类号】：O643.36

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