【作者】 陈霄榕；

【导师】 李永丹；

【作者基本信息】 天津大学 ， 工业催化， 2001， 博士

【摘要】 杂多酸在乙烷、丙烷部分氧化反应中的应用已展现较好的苗头，但仍需进行深入研究。本文以负载在SiO₂上的杂多酸为催化剂，以O₂为氧化剂，对乙烷氧化脱氢，丙烷部分氧化反应进行了研究。 采用经典酸化和乙醚萃取相结合的方法制备了Keggin型杂多酸，并以SiO₂为载体，采用等量浸渍的方法制备了不同煅烧温度、不同负载量的负载型杂多酸催化剂。采用IR、XRD、TPD、TPR、BET、TG、DTA等方法对催化剂进行了表征。采用常压固定床反应器，在烷／氧为2，空速为1500h^-1的条件下，测定了上述负载型杂多酸的催化活性。运用XRD、TPD、TPR、XPS等手段对反应后的催化剂进行了表征，并对相关反应机理和具体反应途径进行了探讨。 实验证明用经典酸化法和乙醚萃取法可以制备出具有Keggin型结构的杂多酸。杂多酸负载在SiO₂上能提高其热稳定性。载体的引入及制备条件的改变并不改变其Keggin型结构，但对负载型杂多酸的酸性和TPR特性曲线产生影响。 在负载型杂多酸上进行的乙烷氧化脱氢反应主要产物是乙烯、一氧化碳和二氧化碳。反应以自由基反应为主，同时伴随着表面反应的发生。其催化活性受弱酸性和TPR曲线特性的影响较大：弱酸位与乙烷在杂多酸表面的吸附有关，酸性越强，引发自由基反应的起燃温度越高。催化剂的TPR曲线特性与其催化活性有关，具有适宜TPR还原峰温的H₆PMo₉V₃O₄₀／SiO₂（350℃煅烧，20wt％）乙烷氧化脱氢活性最好。 在负载型杂多酸上进行的丙烷部分氧化反应的高低温活性不同，低温下丙烷转化率较低，但有利于部分氧化产物的生成，高温下转化率较高，但COx较多。低温下丙烷以表面反应方式进行，丙烷在催化剂表面存在M-O—C₃H₈和M—C₃H₈两种吸附方式，第一种吸附方式有利于部分氧化产物的生成，第二种吸附方式COx生成量较多。在弱酸性较强、TPR还原峰温较低的HPMo₁₂O₄₀／SiO₂（350℃煅烧，20wt％）上丙烷以M-O—C₃H₈吸附方式为主，其部分氧化产物选择性最好。高温下存在气相和表面反应两种反应途径，此时丙烷以M—C₃H₈方式吸附在催化剂表面，产物中CO_x较多。更多还原

【Abstract】 Heteropoly acids （HPA） are promising catalysts for ethane and propane partial oxidation. Silica supported heteropoly acids were adopted here to investigate the ethane oxidative dehydrogenation and propane partial oxidation with molecular oxygen as oxidant.A conventional acidification method incorporated with an ether extraction technique was used to prepare HPA with Keggin structure. An incipient wetness method was employed to prepare silica supported HPA. The supported HPAs were characterized by IR 、XRD 、 TPD 、 TPR 、 BET 、 TG 、 DTA , and their catalytic performance was examined in an atmospheric fixed-bed reactor at a feed ratio of C₂H₆/O₂ （C₃H₈/O₂）=2 and a space velocity of 1500h^-1. Catalyst samples after reaction were characterized by XRD 、 TPD 、 TPR and XPS. The reaction mechanism and pathways were also discussed.It has been found that HPAs with a Keggin structure can be prepared successfully by method employed. The support SiO₂ improves the thermal stability of HPAs. The calcination temperature, the amount of loading on the support and V, W substitution into the Keggin structure influence the acidity and redox property of supported HPAs.It was observed that there exists a light off temperature for ethane reaction. When the reaction was carried out at below this temperature, the conversion is very low, while over this temperature, the reaction was controlled by a free radical gas phase mechanism. Above the light off temperature, the main products of ethane oxidative dehydration were ethene, carbon monoxide and carbon dioxide. Gas phase radical reaction was the main pathway, but the surface reaction took place simultaneously. The acidity of HPA controls the ethane adsorption on the surface. The stronger the acidity was, the higher the light-off temperature of radical reaction was. The redox property influences also the catalytic performance. H₆PMo₉V₃O₄₀/SiO₂ with a suitable redox property gave the best result of ethane oxidative dehydrogenation.The partial oxidation of propane on supported HPA showed different catalytic performance at lower and higher reaction temperatures respectively. The conversion of propane was relatively low at low temperatures, but it is beneficial for the production of partial oxidation products. The conversion of propane was high at high temperatures, but the amount of CO_X in the product was relatively high. At low temperatures, only the surface reaction took place. It is proposed that propane be adsorbed in two manners: M-O—C₃H₈ and M—C₃H₈. The former one is beneficial for the production of partial oxidation products, while the latter one is for the production of CO_x At H₃PMo₍12_O40/SiO₂ （calcined at 350°C. 20wt% on SiO₂ ）, propane was mainly adsorbed in a M-O—C₃H₈ manner, so it gives a good result. At high temperatures, there were two pathways: gas phase radical reaction and surface reaction. At this temperature, propane was mainly adsorbed on the surface in M—C₃H₈ manner, so it gives a lot of CO_x.更多还原