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采用热分解法制备了SnO2载体,并用浸渍法制备了Pd/SnO2催化剂.同时,采用X射线衍射仪(XRD)、透射电镜(TEM)、扫描电镜(SEM)及BET比表面积仪等对所制载体和催化剂材料进行了分析表征.结果表明,热分解法和浸渍法都能够获得纳米材料,SnO2及Pd/SnO2的粒径均在9～10nm左右,比表面积分别达到144.99m·2g-1和147.36m·2g-1.在以甲酸为还原剂的Pd/SnO2催化还原硝酸盐体系中,在Pd与SnO2负载比为2%～7%,反应温度为20～50℃和甲酸投加量4.0～24.0mmol·L-1的条件下,催化活性为0.70～9.48mg·min-·1g-1,且催化活性随着负载比、温度和甲酸投加量的增大而增大,随着pH的升高先升后降,最佳pH为3.反应温度升高及pH降低都能够提高Pd/SnO2的选择性.甲酸-Pd/SnO2催化还原硝酸盐体系中还原反应的调控策略为:反应温度宜控制在40～50℃内,这样可同时获得较高的催化活性和选择性,温度过高对催化活性和选择性影响很小,温度过低则会同时降低催化活性和选择性;控制pH为3时,可以获得最大的催化活性及较好的选择性,pH升高会降低Pd/SnO2的催化活性和选择性,pH降低会导致催化活性迅速降低,但对选择性影响不大;甲酸与硝酸盐的物质的量比宜大于4:1,此时可以有效地抑制pH的上升,同时获得较高的催化活性和选择性,甲酸与硝酸盐的物质的量比小于4:1时,会同时降低Pd/SnO2的催化活性和选择性.
The SnO2 carrier was prepared by thermal decomposition method and the Pd / SnO2 catalyst was prepared by impregnation method.At the same time, XRD, TEM, SEM and BET specific surface area The results show that both the thermal decomposition method and the impregnation method can obtain nanomaterials, the particle sizes of SnO2 and Pd / SnO2 are about 9 ~ 10nm, and the specific surface areas are 144.99m · 2g-1 and 147.36m · 2g-1. In the Pd / SnO2 catalytic reduction nitrate system with formic acid as reductant, the Pd / SnO2 loading ratio was 2% ~ 7%, the reaction temperature was 20 ~ 50 ℃ and the dosage of formic acid 4.0 ~ 24.0mmol·L-1, the catalytic activity was 0.70-9.48mg · min-1g-1, and the catalytic activity increased with the increase of the loading ratio, temperature and the amount of formic acid. With the increase of pH , The optimum pH was 3. The reaction temperature and the pH decreased the selectivity of Pd / SnO2.The control strategy of the reduction reaction in the formic acid-Pd / SnO2 catalytic reduction nitrate system was as follows: the reaction temperature should be appropriate Controlled at 40 ~ 50 ℃, so that both high catalytic activity and selectivity, the temperature is too high for the catalytic activity and selectivity When the pH is 3, the maximum catalytic activity and good selectivity can be obtained. The increase of pH will decrease the catalytic activity and selectivity of Pd / SnO2 , the decrease of pH will lead to the rapid decrease of the catalytic activity but little effect on the selectivity. The ratio of formic acid to nitrate should be greater than 4: 1, which can effectively inhibit the increase of pH and achieve higher catalytic activity And selectivity, the ratio of formic acid to nitrate mass ratio of less than 4: 1 will reduce the catalytic activity and selectivity of Pd / SnO2.