Combustion performance of sub-nanometer Pd/S-1 catalyst for ventilation air methane
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摘要: 煤矿开采导致乏风瓦斯的大量排出，不仅对环境造成较大影响，而且与我国“双碳”理念相违背。本研究通过一锅水热法制备了一种封装在Silicalite-1分子筛载体中的亚纳米Pd团簇催化剂。通过XRD、BET、SEM、XPS和TEM对催化材料的物相组成、孔结构参数、微观形貌、元素化学态以及活性组分Pd的存在状态进行表征，探讨了活性组分负载量、空速和反应温度对催化性能的影响。研究结果表明：采用一锅水热法成功将Pd团簇封装在Silicalite-1分子筛载体孔道内，制备出高分散度的亚纳米Pd团簇催化剂；随着Pd负载量的增加，催化性能呈现先升高后降低的趋势，这是由于Pd原子间产生团聚效应，导致部分Pd原子被包覆，降低了活性组分与反应物间的接触面积；以Silicalite-1分子筛为载体，可以促进活性位点骨架氧向表面羟基转化，有助于甲烷催化氧化。对比现有甲烷催化氧化工艺，本研究制备的催化剂具有催化活性高、制备方法简单、处理成本低等优点。
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关键词:
- 甲烷催化氧化 /
- Pd团簇催化剂 /
- Silicalite-1分子筛 /
- 催化机理
Abstract: Coal mining leads to ventilation air methane emission, which not only pollutes the environment but also runs counter to "carbon neutral, carbon peaking" in China.This study prepared a sub-nanometer Pd cluster catalyst encapsulated in the Silicalite-1 molecular sieve support by the one-pot hydrothermal method, which has excellent catalytic activity and stability in methane catalytic oxidation reaction.The physical phase composition, pore structure parameters, microscopic morphology, chemical state and the present state of the active component Pd of the catalytic material were characterized by XRD, BET, SEM, XPS and TEM.This study then investigated the effects of active component loading, air velocity, reaction temperature and other conditions on the catalytic performance.The experimental results showed that the one-pot hydrothermal method successfully encapsulate Pd clusters within the pores of Silicalite-1 molecular sieve carriers to prepare highly dispersed sub-nanometer Pd cluster catalysts; the catalytic performance first increases and then decreases with the increase of Pd loading.This was due to the agglomeration effect between Pd atoms, resulting in the encapsulation of some Pd atoms and reducing the contact area between the active component and the reactants; in addition, using Silicalite-1 molecular sieve as a carrier can promote the conversion of active site skeletal oxygen to surface hydroxyl groups, which contributes to the catalytic oxidation of methane.The catalyst in this study excels existing methane catalytic process for its high catalytic activity, simple preparation, and low processing cost. -
图 1 亚纳米Pd/S-1催化剂制备示意图
Figure 1. Preparation schematic diagram of sub-nanometer Pd/S-1 catalyst
图 3 S-1纯硅分子筛与不同负载量催化剂XRD图谱
Figure 3. XRD of S-1 molecular sieve and catalysts with different loadings
图 4 S-1纯硅分子筛与不同负载量催化剂吸/脱附曲线和孔径分布
V—材料孔体积，cm3；W—材料质量，g
Figure 4. Adsorption/desorption curve and pore size distribution diagram of S-1 molecular sieve and catalysts with different loadings
图 5 S-1纯硅分子筛与0.75 % Pd/S-1催化剂的SEM图像
Figure 5. SEM image of S-1 molecular sieve and 0.75 % Pd/S-1 catalyst
图 6 0.75 % Pd/S-1催化剂的HADDF-STEM图像
Figure 6. HADDF-STEM image of 0.75 % Pd/S-1 catalyst
图 7 0.75 % Pd/S-1催化剂在Ar+刻蚀前后Pd 3d的XPS图谱
Figure 7. XPS spectra of Pd 3d of 0.75 % Pd/S-1 catalyst before and after Ar+etching
图 8 不同Pd负载量催化剂在不同空速下的甲烷转化率
Figure 8. Methane conversion rate of catalysts with different Pd loadings at different airspeed
图 9 不同Pd负载量催化剂空速为100 000 mL/(g·h)时的Arrhenius图与0.75 % Pd/S-1催化剂在不同空速、450 ℃条件下的稳定性测试图
Figure 9. Arrhenius of catalysts with different Pd loadings at 100 000 mL/(g·h), and stability diagram of 0.75 % Pd/S-1 catalyst at different airspeed and 450 ℃
图 10 甲烷在Pd/S-1催化剂上的催化机理
Figure 10. Catalytic mechanism diagram of methane on Pd/S-1 catalyst
表 1 催化实验条件
序号 甲烷浓度/% Pd负载量/% 空速/(mL·g-1·h-1) 催化燃烧温度/℃ 1 1 0，0.5，0.75，1 50 000 200~500 2 1 0，0.5，0.75，1 80 000 200~500 3 1 0，0.5，0.75，1 100 000 200~500 4 1 0.75 50 000，80 000，100 000 200~500 
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表 2 不同Pd负载量在不同空速下的甲烷转化温度
Table 2. Methane conversion temperature with different Pd loading at different airspeed
空速/(mL·g-1·h-1) 0.5% Pd/S-1 0.75% Pd/S-1 1% Pd/S-1 T50%/℃ T90%/℃ T50%/℃ T90%/℃ T50%/℃ T90%/℃ 50 000 350 400 320 350 320 380 80 000 355 415 320 350 325 395 100 000 360 460 325 370 325 390
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