La_2O_3、CeO_2、MgO对镍催化剂的α-Al_2O_3载体表面的改性效应

EFFECTS OF La_2O_3, CeO_2 AND MgO ON THE PROPERTIES OF α-Al_2O_3 SUPPORTS FOR NICKEL CATALYSTS

分别用 La_2O_3、CeO_2和MgO对α-Al_20_3处理制得改性载体,然后浸镍制得催化剂.研究结果表明,以上三种氧化物均能抑制尖晶石NiA1_2O_4的生成,并不同程度地增大了载体的比表面,降低了催化剂的表面酸性;提高了轻油-水蒸气转化制氢的催化活性,其中尤以La_2O_3为最佳.还发现La_2O_3和CeO_2削弱了NiO与Al_2O_3的相互作用,使NiO的还原温度降低,而MgO则与NiO在α-Al_2O_3表面上生成镍镁固溶体,使NiO的还原温度大幅度地升高,La_2O_3和CeO_2抑制镍晶粒的长大作用比MgO强,对催化剂活性的稳定有利.

α-Al2O3 support was treated by means of impregnation followed by decompositiontwice or three times with nitrate solution of lanthanum, cerium and magnesium respectively.Nickel oxide was then supported on these treated supports, and their structure and propertieswere determined. The results showed that (1) the surface area of supports increased; (2) theformation of spinel NiAl2O4 was inhibited by La2O3, CeO2 and MgO; (3) the surface activityof the nickel catalysts decreased, and (4)the activity of the nickel catalysts for naphtha-steamreforming was enhanced, in which the effect of La2O3 was the most remarkable. In addition,the growth of nickel crystallite in size was significantly retarded by La2O3 and CeO2, thecatalytic activity can maintain a higher level for a long period, and the reduction temperatureof nickel oxide on MgO-containing support increased due to the formation of NiO-MgO solidsolution. On the contrary, the temperature of reduction are much lower for La2O3-and CeO2-containing supports.