采用水热法合成了小晶粒的SAPO-34.MnSAPO-34和CuSAPO-34分子筛,并以它们为载体采用浸渍法制备了一系列不同Pd含量的催化剂用于催化CO氧化反应.结果表明:分子筛载体、催化剂制备条件、反应条件、Pd含量及预还原等对催化剂的活性影响较大.催化剂活性随焙烧温度的增加而降低,而随着反应温度的升高而提高,担载在SAPO-34上Pd含量为1.35%时性能最佳.X射线衍射和透射电镜结果表明Pd物种高度分散于催化剂上,粒子粒径在2～8 nm;X射线光电子能谱及氢气程序升温还原结果表明,高度分散的Pd~(2+)物种是CO氧化反应活性位.随着反应进行被还原为Pd~0物种,因而导致催化剂活性下降.H2预还原处理催化剂致使活性下降的实验结果也支持了这一结论.
SAPO-34, MnSAPO-34, and CuSAPO-34 were synthesized by the hydrothermal method. A series of supported Pd catalysts were prepared by the impregnation method. The effects of calcination temperature, Pd content, prereduction of the catalyst, and reaction temperature on CO oxidation were studied. The catalytic activity decreased with increasing calcination temperature. The higher reaction temperature or Pd content resulted in the higher catalytic performance for CO oxidation; however, H_2 prereduction of the catalyst led to a lower catalytic performance. The results of X-ray diffraction and transmission electron microscopy analysis showed that Pd species are highly dispersed on SAPO-34 zeolite, and the Pd dispersion of the catalysts depends on the pretreatment temperature and reaction conditions. The characterization of X-ray photoelectron spectroscopy and H_2 temperature-programmed reduction reveals that Pd~(2+) species are the active sites for CO oxidation.
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