低负载Pd/Al2O3催化剂的制备及其对CO室温催化性能研究

采用等体积浸渍法和还原法结合制备了Pd/Al_2O_3催化剂,通过N_2吸附-脱附、SEM、TEM、X射线衍射、X射线光电子能谱和CO原位漫反射傅里叶变换红外光谱等表征手段对制备的样品微观结构进行了系统分析,考察了不同Pd负载量和测试条件下CO催化氧化性能。实验结果表明,水合肼还原法实现了Pd在Al_2O_3载体上的均匀分散,Pd颗粒的直径在9 nm左右,且为Pd单质;负载后的催化剂呈现明显的中孔结构特征,有利于气体分子的扩散。在0.2%～0.5%的低负载质量分数下,CO的催化性能随着Pd负载量的增加而增加,随着CO进口浓度和空速的升高而逐渐降低,在进口浓度为0.05%,空速为4 017 h~(-1)时,不同负载量的催化剂均能使CO完全催化;温度对催化剂的催化效果影响显著,从常温到50℃催化剂的性能变化显著;湿度增加对催化有一定的促进作用。Pd负载质量分数0.5%的催化剂稳定性测试表明,催化剂能够在100 h内保持92%以上的稳定转化率。

Preparation of Pd/Al2O3 catalyst with low Pd loading amount for CO oxidation at room temperature

Pd/Al₂O₃ catalysts were prepared by the combination of incipient-wetness impregnation method and reduction method.The physicochemical properties of the catalysts were characterized by N₂ adsorption-desorption,scanning electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy and CO in-situ diffuse reflection using Fourier transform spectroscopy.The effects of Pd loading amount and catalytic reaction conditions on the CO catalytic oxidation performance were investigated.The results show that Pd could be uniformly dispersed on the Al₂O₃ support with the particle size of 9 nm in an elemental state.After Pd loading,the catalyst still possesses obvious mesoporous structure,which could facilitate the diffusion of gas molecules.During low Pd mass fraction of 0.2%-0.5%,the CO catalytic oxidation performance increases with the loading amount and decreases with the increasing import CO concentration and space velocity.CO could be completely converted for different loading amount at the inlet concentration of 0.05% with a space velocity of 4 017 h^-1.Temperature has a significant influence on the catalytic performance,and the performance of the catalyst improves significantly from room temperature to 50 ℃.Humidity has a promoting effect on the CO catalytic oxidation performance of Pd/Al₂O₃.The stability test of catalyst with 0.5% Pd mass fraction shows that the catalyst could maintain a relatively stable conversion of more than 92% for 100 h.