SiO_2、Al_2O_3上涂载TiO_2、ZrO_2、La_2O_3制备Pd

STUDY ON SILICA AND ALUMINA COATED WITH TITANIA,ZIRCONIA AND LANTHANA AS SUPPORTS FOR PALLADIUM CATALYSTS

采用浸渍法制备了Ｌａ＿２Ｏ＿３、ＴｉＯ＿２、ＺｒＯ＿２以单层状态分散在ＳｉＯ＿２、Ａｌ＿２Ｏ＿３上的改性载体。用ＸＰＳ求得它们的最大单层分散阈值为：０．２２ｇＬａ＿２Ｏ＿３／１００ｍ￣２ＳｉＯ＿２，０．２７ｇＬａ＿２Ｏ＿３／１００ｍ￣２，０．０４ｇＴｉＯ＿２／１００ｍ￣２ＳｉＯ＿２，０．０３６ｇＴｉＯ＿２／１００ｍ￣２Ａｌ＿２Ｏ＿３，０．０７ｇＺｒＯ＿２／１００ｍ￣２ＳｉＯ＿２，０．０８ｇＺｒＯ＿２／１００ｍ￣２Ａｌ＿２Ｏ＿３。Ｌａ＿２Ｏ＿３可以完全铺满ＳｉＯ＿２、Ａｌ＿２Ｏ＿３载体表面，而ＴｉＯ＿２、ＺｒＯ＿２仅仅覆盖ＳｉＯ＿２（Ａｌ＿２Ｏ＿３）表面的４０％及５０％。在以涂层氧化物为载体的Ｐｄ催化剂制备过程中，通过ＸＰＳ的氩离子刻蚀技术，确定了Ｐｄ分布在以ＳｉＯ＿２（Ａｌ＿２Ｏ＿３）为骨架的涂层氧化物的表面上，与Ｌａ＿２Ｏ＿３、ＴｉＯ＿２、ＺｒＯ＿２在ＳｉＯ＿２（Ａｌ＿２Ｏ＿３）骨架上的分布基本一致，没有进入ＳｉＯ＿２（Ａｌ＿２Ｏ＿３）晶格内部。ＸＲＤ衍射图则说明在Ｐｄ催化剂配制过程中，ＴｉＯ＿２、ＺｒＯ＿２、Ｌａ＿２Ｏ＿３没有形成结晶相，也没有与ＳｉＯ＿２（Ａｌ＿２Ｏ＿３）发生反应，仍以单层分散形式存在?

Lanthana,Titania and Zirconia were coateed on Silica and Alumina by the im-pregnation of Silica and Alumina with solutions of the corresponding salts, followed by dry-ing and ealcination. The threshold values for monolayer spreading of the oxides were esti-mated by XPS. They were 0.22g La_2O_3/100m￣2 SiO_2,0.27g La_2O_3/100m￣2 Al_2O_3,0.04g TiO￣2/100m￣2 SiO_2,0.036g TiO_2/100m￣2 Al_2O_3,0. 07g ZrO_2/100m￣2 SiO_2,and 0.08g ZrO_2/100m￣2 Al_2O_3.Calculation based on the simple close-packed monolayer model, shows thatlanthana can cover up all of the Silica and Alumina surface,and the throshold coverages ofTitania and Zirconia are only about 40% and 50% respectively. Argon ion etching of samplesprepared by impregnating the coated supports with PdCl_2 indicated that Pd deposited on thecoated oxide surfaces in agreement with the dispersion of lanthana、titania and zirconia onsilica and Alumina. It was verified by XRD results that in the preparing procedure of Pd cat-alysts,Titania,lanthana and Zirconia neither formed crystal phases nor reacted with the sili-ca and Alumina. These coating oxides existed on the surfaces of silica and Alumina by mono-layer spreading.