制备及反应条件对Pt/Al_2O_3蜂窝状催化剂性能的影响

Effect of preparation and reaction conditions on catalytic performances of honeycomb Pt/Al_2O_3

采用多次涂层 浸渍法制备了蜂窝状Pt Al2 O3 催化剂 .并对焙烧温度和焙烧时间等不同制备条件和反应温度、O2 浓度和空速等不同反应条件下NOx 的选择性催化还原性能进行了研究 .实验表明 ,蜂窝状Pt Al2 O3 催化剂上NOx 转化率在反应温度为 30 0℃左右时出现最高值 .而随反应温度的升高 ,达到最高转化率所需的O2 浓度不断减小 ,分别为 8% ,6 %和 4 % .这可能是由于在高温下O2 会与NO发生竞争吸附 ,从而阻碍了NO催化还原反应的进行 ;同时随着空速的依次增加 ,催化剂的活性逐渐下降 ,催化剂活性曲线的峰值依次向高温方向移动 .实验还说明 ,在过高的焙烧温度和较长的焙烧时间的制备条件下 ,蜂窝状Pt Al2 O3 的催化性能明显下降 .这是因为高的焙烧温度和较长的焙烧时间能够导致蜂窝状Pt Al2 O3 催化剂的表面发生烧结现象 ,使得催化剂的比表面减小 ,从而导致活性降低 .

A honeycomb Pt/Al_2O_3 catalyst was prepared by mult-coating and wet impregnation method. The performance for NO_x selective catalytic reduction under the conditions of different calcinations time, calcinations temperature, O_2 concentration and space velocity was studied. The results showed that the honeycomb Pt/Al_2O_3 exhibited the highest value for NO_x conversion at about 300℃. With rising of temperature, the O_2 concentration decreases when NO_x conversion reaches the top value. With rising of O_2 concentration, the catalytic activity declined at higher temperature. It may be attributed that the decomposition of NO_x on the catalyst surface was inhibited by superfluous O_2 at higher temperature. The results also indicated that catalytic activity of honeycomb Pt/Al_2O_3 declined at higher calcinations temperature and longer calcinations time, because the catalyst can be sintered under this condition and results in reduction of its surface area.