TiO_2、La_2O_3、ZrO_2改性Pd／SiO_2催化剂吸氢性能及反应

STUDIES ON H_2 CHEMISORPTION AND METHANOL DECOMPOSITION ON Pd/SiO_2 CATALYSTS PROMOTED BY TiO_2、La_2O_3、and ZrO_2

ＴｉＯ＿２、Ｌａ＿２Ｏ＿３和ＺｒＯ＿２以单层形式分布在ＳｉＯ＿２上制得了Ｐｄ催化剂。经４７３Ｋ（ＬＴＲ）及７７３Ｋ（ＨＴＲ）Ｈ＿２处理后，进行Ｈ＿２－Ｏ＿２滴定反应，测定催化剂对Ｈ＿２的吸附能力。结果表明，Ｐｄ／ＴｉＯ＿２／ＳｉＯ＿２，Ｐｄ／Ｌａ＿２Ｏ＿３／ＳｉＯ＿２及Ｐｄ／ＺｒＯ＿２／ＳｉＯ＿２的吸氢能力高于单一载体Ｐｄ催化剂的吸氢能力，说明ＳｉＯ＿２骨架经徐层氧化物的改性，Ｐｄ得到较好的分散。Ｐｄ与载体之间相互作用为：Ｐｄ／ＴｉＯ＿２＞Ｐｄ／Ｌａ＿２Ｏ＿３＞Ｐｄ／Ｔ１Ｏ＿２／ＳｉＯ＿２＞Ｐｄ／Ｌａ＿２Ｏ＿３／ＳｉＯ＿２＞Ｐｄ／ＳｉＯ＿２＝Ｐｄ／ＺｒＯ＿２＝Ｐｄ／ＺｒＯ＿２／ＳｉＯ＿２。ＴＰＲ、ＴＰＤ实验结果与Ｈ＿２－Ｏ＿２滴定的结果基本一致。ＴＰＤ的结果进一步证实，易于受Ｈ＿２还原温度影响的Ｐｄ／ＴｉＯ＿２、Ｐｄ／Ｌａ＿２Ｏ＿３催化剂改性为Ｐｄ／ＴｉＯ＿２／ＳｉＯ＿２、Ｐｄ／Ｌａ＿２Ｏ＿３／ＳｉＯ＿２后，此时，Ｈ＿２脱附位基本上不受Ｈ＿２还原温度影响，主要显示了骨架ＳｉＯ＿２及ＴｉＯ＿２、Ｌａ＿２Ｏ＿３涂层氧化物对金属Ｐｄ起的作用。最后考察了甲醇分解反应，结果证实，改性Ｐｄ／ＴｉＯ＿２／ＳｉＯ＿２、Ｐｄ?

Two wt. percent Palladiun1 were supported on pure supports(SiO_2、TiO_2、La_2O_3 and ZrO_2 )and coated supports(TiO_2/SiO_2、 ZrO_2/SiO_2、 La_2O_3/SiO_2 ). After reducing at473K(LTR) and 773K(HTR ) by hvdrogen,the samples were characterized by hydrogen-Oxygen titration,temperature programmed desorption(TPD)of hydrogen and methanol de-composition reaction.All the samples except Pd/SiO_2、Pd/ZrO_2 and Pd/ZrO_2/SiO_2 show de-pressed chemisorption of H_2 when treated at HTR , compared to the results of LTR. Thesamples Pd/TiO_2/SiO_2、Pd/La_2O_3/SiO_2 and Pd/ZrO_2 /SiO_2 have stronger H_2 chemisorptionthan samples prepared from pure supports(Pd/SiO_2 , Pd/TiO_2 , Pd/ZrO_2 and Pd/La_2O_3), in-dicating that in the promoted catalysts , Pd is better dispersed. The order of SMSI detectedin these samples is at follows :Pd/TiO_2>Pd/La_2O_3>Pd/TiO_2/SiO_2>Pd/La_2O_3/SiO_2>Pd/SiO_2=pd/ZrO_2 = pd/ZrO_2/SiO_2. In TPR tests thereduction peaks of promoted Pd/SiO_2 sam-ples appeared at lower temperatures with higher intensity than in the case of pure Pd/SiO_2.Differences in TPD profiles between LTR and HTR samples agree well with differences in H_2-O_2 titration data, Compared to Pd on pure TiO_2 and La_2O_3 , the samples Pd/TiO_2/SiO_2 andPd/La_2O_3/SiO_2 are not sensitive to HTR with respect to H_2 chemisorption. At given reactionconditions,Pd/TiO_2 /SiO_2、Pd/La_2O_3/SiO_2 and Pd/ZrO_2/SiO_2 have high activity for methanoldecomposition and they are not affected by reduction temperature.