摘要
以H_2S为毒物,用浸渍法制备了一系列不同载体的钯催化剂(Pd/Al_2O_3、Pd/MgO和Pd/TiO_2)以Na_2S与催化剂机械混合的方式,在载体上引入S^(2-),用H_2—O_2混合气对含硫的催化剂进行处理。藉XPS和IR谱对不同载体的催化剂上硫的吸附及转化进行了研究。结果表明,载体酸碱性对其上担载的贵金属的电子状态有一定的影响。酸性较强的载体对贵金属的分散作用较强,H_2S在这种载体的催化剂上的吸附和转化能力较差。在碱性较强的载体的催化剂上,结果相反。此外,载体上晶格氧的活性不同,对H_2S的转化能力也有差异。在Pd/Al_2O_3催化剂运行过程中,H_2S在A1_2O_3载体上主要发现为一种物理的吸附-脱附过程;而在MgO和TiO_2载体上,不仅存在H_2S的吸附过程,且有H_2S转化为SO_2或SO_4^(2-)的过程。结果还表明,载体性质对催化剂的自身再生能力具有较大影响。
A series of supported palladium catalysts (Pd/Al2O3, Pd/MgO and Pd/TiO2 ) were prepared by impregnation and treated with H2S, H2+O2 or O2, respectively. The S2- species in the supports was introduced by means of mechanically mixing Na2S with the supports or catalysts. XPS and IR spectroscopy were used to investigate the catalysts and supports. The results show that on MgO and TiO2 whose acidities are weak, there exist two kinds of oxygen : the lattice oxygen, and the active oxygen species in the form of adsorbed OH-. The latter can oxidize the S2- into SO42- even at room temperature. Because of the weak acidities and smaller specific surface areas of MgO and TiO2, they show low ability to disperse the supported palladium. The electronic density was thus relatively high, so the metal can donate electron to the adsorbed sulfur easily and S2- was adsorbed. On the other hand the S2- adsorbed is also easy to transform into SO42-. But in the case of A12O3 its acidity is rather strong, and its surface oxygen species is not so active as that in TiO2 or MgO.H2S on A12O3 experiences only physical adsorption-desorption. In Pd/Al2O2, the electronic density of palladium particles was somewhat lower, and the palladium was not so easy to adsorb and transform S2- as that in Pd/TiO2 or Pd/MgO.
出处
《分子催化》
EI
CAS
CSCD
1991年第4期308-315,共8页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金
