Effects of Oxidation/Reduction and Oxychlorination/Reduction Cycles on CO Adsorption by Pt–Re/Al2O3 Catalysts
Effects of Oxidation/Reduction and Oxychlorination/Reduction Cycles on CO Adsorption by Pt–Re/Al2O3 Catalysts
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DOI：
10.1006/jcat.1999.2433
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发表时间：
1999-05
影响因子：
7.3
通讯作者：
Geomar J. Arteaga;J. Anderson;C. H. Rochester
中科院分区：
文献类型：
--
作者：
Geomar J. Arteaga;J. Anderson;C. H. Rochester
本文采用CO化学吸附和FTIR研究了由无Cl前体制备的含0.30wt%Pt和0、0.15、0.30和0.45wt%Sn的Pt-Sn/Al_2 O_3催化剂在六次氧氯化-还原循环或六次氧化-还原循环后再进行氧氯化-还原循环中的CO吸附。还报道了氧氯化后CO在各催化剂上的光谱。在氧氯化后，催化剂含有暴露的Pt位点，以Pt°（被O-吸附原子覆盖）、Pt（II）、Pt（IV）氧化物、PtCl 2（与CO形成PtCl 2 CO和PtCl 2（CO）2）和PtOxCly存在，这些物质的相对比例随Sn含量而变化。锡阻碍了氧化过程中的催化剂烧结和氧氯化过程中的再分散。随后还原后氧化催化剂的IR结果与分散在Sn（II）改性的氧化铝表面上的Pt°相容。然而，氯的加入促进了Pt和Sn之间更大的亲密度，后者阻止了低配位Pt位点，并降低了暴露的Pt原子系综的尺寸。由草酸锡和酒石酸锡制备的两种Pt（0.3%）-Sn（0.3%）/Al_2 O_3催化剂得到了不同的结果，强调了催化剂性质对制备过程的敏感性。
Abstract Pt–Sn/Al2O3catalysts containing 0.30 wt% Pt and 0, 0.15, 0.30, and 0.45 wt% Sn and prepared from Cl-free precursors have been studied by CO chemisorption and FTIR of adsorbed CO after each cycle in a series of six oxychlorination–reduction cycles or six oxidation–reduction cycles followed by oxychlorination–reduction. Spectra of CO on each catalyst directly after oxychlorination are also reported. After oxychlorination catalysts contained exposed Pt sites present as Pt° (covered with O-adatoms), Pt(II), Pt(IV) oxide, PtCl2(forming PtCl2CO and PtCl2(CO)2with CO), and PtOxCly, the relative proportions of these species varying with Sn content. Tin hindered both catalyst sintering during oxidation and redispersion during oxychlorination. The IR results for oxidised catalyst after subsequent reduction were compatible with Pt° dispersed over a Sn(II)-modified alumina surface. However, addition of chlorine promoted greater intimacy between Pt and Sn with the latter blocking low coordination Pt sites and reducing the size of exposed ensembles of Pt atoms. Two Pt(0.3%)–Sn(0.3%)/Al2O3catalysts prepared from tin(II) oxalate and tin(II) tartrate gave different results emphasising the sensitivity of catalyst character to preparation procedure.