研究报告
郭燕妮,胡勇有,程建华.Pd/TiO2-SnO2催化还原硝酸盐效能及反应调控[J].环境科学学报,2011,31(9):1887-1893
Pd/TiO2-SnO2催化还原硝酸盐效能及反应调控
- Catalytic efficiency of Pd/TiO2-SnO2 in reduction of nitrate and control of the reaction
- 基金项目：国家科技重大专项 (No. 2008ZX07211-005)
- 作者
- 单位
- 郭燕妮
- 华南理工大学环境科学与工程学院,工业聚集区污染控制与生态修复教育部重点实验室,广州 510006
- 胡勇有
- 1. 华南理工大学环境科学与工程学院,工业聚集区污染控制与生态修复教育部重点实验室,广州 510006;
2. 华南理工大学制浆造纸工程国家重点实验室,广州 510640
- 程建华
- 1. 华南理工大学环境科学与工程学院,工业聚集区污染控制与生态修复教育部重点实验室,广州 510006;
2. 华南理工大学制浆造纸工程国家重点实验室,广州 510640
- 摘要：采用共沉淀法制备了掺杂TiO2的复合载体TiO2-SnO2;浸渍法制备了单金属负载型催化剂Pd/TiO2-SnO2.用X射线衍射(XRD)、X射线光电子能谱(XPS)、比表面仪(BET)和透射电镜(TEM)表征表明Pd和TiO2在SnO2上成单层或亚单层分散,增加了反应活性位.催化剂分散性良好,比表面积为100.8 m2 · g-1,是平均粒径为9.1 nm的纳米颗粒.常压下考察了甲酸-Pd/TiO2-SnO2-硝酸盐催化还原反应体系的主要影响因素.结果表明,Pd/TiO2-SnO2催化活性与负载比、甲酸量正相关;在15~45℃内,随温度升高催化活性先升后降;增加催化剂量可提高反应速率.Pd/TiO2-SnO2的选择性与催化剂量正相关,与负载比、甲酸量及温度负相关.该反应的调控策略为:催化剂量宜为0.1mg以上,有利于保持较高的选择性;甲酸与硝酸盐的摩尔比宜大于4 ∶ 1,可以有效抑制pH上升而获得较高的催化活性和选择性,若小于4 ∶ 1,则硝酸盐不能完全转化;反应温度宜控制在25~35 ℃,温度>45 ℃会使催化剂失活,温度<25 ℃会降低催化活性,延长反应时间.反应过程中形成的铵根可采用离子交换工艺完全去除.
- Abstract：The monometallic catalyst Pd/TiO2-SnO2 was prepared by impregnating Pd on the surface of a composite support of TiO2-SnO2, which was prepared by coprecipitation. The prepared sample was characterized by X-ray diffraction (XRD), specific surface area analysis (BET) and transmission electron microscopy (TEM) as nano-sized particles with average size of 9.1 nm and specific surface area of 100.08 m2 · g-1. The Pd and TiO2 were dispersed on the surface of the SnO2 support in one monolayer, resulting in an increase of catalytic active sites. The catalytic performance of the Pd /TiO2-SnO2 catalyst for reduction of nitrate was investigated under normal atmosphere, with formic acid used as reducing agent. The results showed that the catalytic activity of the Pd/TiO2-SnO2 was positively related to load ratio and initial formic acid concentration but fluctuated with the temperature over the range of 15~45℃. With the temperature increasing, the catalytic activity initially increased then decreased. Increasing the amount of catalyst accelerated the reaction rate. The selectivity of Pd/TiO2-SnO2 was positively related to catalyst amount, but negatively related to load ratio, initial formic acid concentration and temperature. Strategies for control of the catalytic reduction of nitrate based on the formic acid- Pd/TiO2-SnO2 system are as follows: 1 To maintain high catalytic selectivity, the catalyst amount should be more than 0.1 mg. 2 To restrain pH rise and keep higher catalytic activity and selectivity, the molar ratio of formic acid and nitrate should be higher than 4 ∶ 1; otherwise, the nitrate cannot be completely converted. 3 The temperature should be controlled at the range of 25~35 ℃, since higher temperature (>45 ℃) will cause catalyst deactivation while lower temperature (< 25 ℃) will reduce the catalytic activity and extend the reaction time. The ammonium formed during the catalytic reduction of nitrate can be completely removed by a cation-exchange process.
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