摘要
制备了负载型Pd/Al_2O_3和Pd/MgO催化剂,借助于CO探针分子,用原位FT-IR研究了不同状态的硫对催化剂上活性组分的影响,结果表明,吸附在多位活性中心上的硫(一般是不可逆吸附硫)除了屏蔽本身所在的活性点外,对周围单活性中心还具有电子效应;吸附在单活性中心上的硫(主要为可逆吸附硫),主要以屏蔽效应影响催化剂的性质,载体上的硫对活性组分的电子状态具有一定的影响。
Sulfur as a poison adsorbed on noble metal catalysts is known to have two forms: reversibly and irreversibly adsorbed sulfur. They display two different effects upon the catalysts, i. e. geometric blocking effects and electronic effect. In this paper, in-situ FT-IR with the aid of CO as probe molecule was employed to study the S poisoning on supported Pd catalysts. The results show that sulfur adsorbed on the catalysts decreases greatly the ability of the catalysts to adsorb CO (both linear form and bridge one) and causes 'blue shift 'of the vibration frequencies of adsorbed CO, particularly of the bridge form. After the sulfur-poisoned catalysts were treated with H2 +O2+Ar at 200 ℃ for 10 min, some reversible sulfur was removed. As a consquence, the CO adsorbed was found to increase considerably, particularly so for that in the linear form. But the adsorbed bands are almost the same as those obtained with the untreated catalysts. A new CO linear adsorbtion at 2143 cm-1 appears and the relative intensity of the two bridge forms changes with the sulfur content on the support. All these phenomena are rationalized as follows:
The sulfur adsorbed on the multi-active sites, where CO is adsorbed in bridge form, is irreversibly adsorbed sulfur and results in the decrease in CO adsorbtion strength. This appears to be an electronic effect. The sulfur adsorbed on the single active sites is reversibly adsorbed sulfur which exhibits mainly a geometric blocking effect. Sulfur on the support can affect the supported metal components electronically to some extent.
出处
《分子催化》
EI
CAS
CSCD
1992年第1期1-7,共7页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金资助项目
关键词
硫中毒
机理
负载型
钯
催化剂
Mechanism, Sulfur poisoning, Supported palladium catalysts,Pd/Al2O3, Pd/MgO, Pd/TiO2
