Pd-Pt/HZSM-5催化剂的制备及催化低浓度甲烷燃烧性能

Preparation of Pd-Pt/HZSM-5 catalyst and catalytic combustion performance of low concentration methane

摘要:

以Pt(NH3)4Cl2和Pd(NO3)2·2H2O作为Pt和Pd的前驱体盐，以不同硅铝比〔n(SiO2)∶n(Al2O3)=38、200、800〕的HZSM-5分子筛为载体，采用浸渍法制备了Pd-Pt/HZSM-5催化剂，利用XRD、SEM、TEM、Raman、XPS、CO2-TPD和NH3-TPD等对催化剂的物相组成、孔隙结构、微观形貌、元素化学态以及表面酸碱性等进行表征，并通过固定床反应器测试了其催化低浓度（体积分数为0.5%）甲烷燃烧反应的活性。结果表明，不同硅铝比的Pd-Pt/HZSM-5催化剂活性有明显差异，其中以硅铝比为38的HZSM-5分子筛为载体的Pd-Pt/HZSM-5(38)催化剂表现出最好的催化性能，相比以硅铝比为800和200的HZSM-5分子筛为载体的Pd-Pt/HZSM-5(800)和Pd-Pt/HZSM-5(200)催化剂，Pd-Pt/HZSM-5(38)催化低浓度甲烷燃烧的起燃温度（T10）分别降低了27.54和30.92 ℃，完全转化温度（T90）分别降低了3.38和17.51 ℃。各种表征显示，Pd-Pt/HZSM-5(38)催化剂具有较小的Pd/Pt颗粒尺寸（6.3 nm），最多的PdO结晶、活性Pd/Pt物种和酸性位点，最高的n(Pd0)∶n(Pd2+)，以及最高的Pt质量分数（0.19%），这些可能是其具有最高催化活性的原因。稳定性测试中，Pd-Pt/HZSM-5(38)催化剂在360 ℃条件下，稳定运行150 h内，甲烷转化率为99.6%以上，活性无明显下降。

Abstract:

Using Pt(NH3)4Cl2 and Pd(NO3)2·2H2O as the precursor salts of Pt and Pd, Pd-Pt/HZSM-5 catalysts with different silicon-aluminum ratios 〔n(SiO2)∶n(Al2O3)=38, 200, 800〕 were prepared by impregnation method. The phase composition, pore structure, microstructure, chemical state and surface acidity and basicity of the catalysts were characterized by XRD, SEM, TEM, Raman, XPS, CO2-TPD and NH3-TPD, and the catalytic activity of the catalyst for low concentration (0.5% by volume fraction) methane combustion was tested by a fixed bed reactor. The results showed that the activity of Pd-Pt/HZSM-5 catalysts with different silica-alumina ratios was significantly different, and the Pd-Pt/HZSM-5(38) catalyst supported by HZSM-5 molecular sieve with Si/Al ratio of 38 showed the best catalytic performance. Compared with Pd-Pt/HZSM-5(800) and Pd-Pt/HZSM-5(200) catalysts supported by HZSM-5 molecular sieve with Si/Al ratio of 800 and 200, the ignition temperature (T10) of Pd-Pt/HZSM-5(38) catalyzed low concentration methane combustion decreased by 27.54 and 30.92 ℃, respectively, and the complete conversion temperature (T90) decreased by 3.38 and 17.51 ℃, respectively. Various characterization showed that Pd-Pt/HZSM-5(38) catalyst had smaller Pd/Pt particle size (6.3 nm), the most PdO crystals, active Pd/Pt species and acidic sites, the highest n(Pd0):n(Pd2+), and the highest Pt mass fraction (0.19%). These may be the reasons for its highest catalytic activity. In the stability test, the methane conversion rate of Pd-Pt/HZSM-5(38) catalyst was more than 99.6% and the activity did not decrease significantly within 150 h of stable operation at 360 ℃.