High-resolution electron microscopic, spectroscopic, and catalytic studies of intentionally sulfided Pt/ZrO2-SO4 catalysts
High-resolution electron microscopic, spectroscopic, and catalytic studies of intentionally sulfided Pt/ZrO2-SO4 catalysts
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DOI：
10.1016/j.jcat.2003.11.014
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发表时间：
2004-03
影响因子：
7.3
通讯作者：
M. Appay;J. Manoli;C. Potvin;M. Muhler;U. Wild;O. Pozdnyakova;Z. Paâl
中科院分区：
文献类型：
--
作者：
M. Appay;J. Manoli;C. Potvin;M. Muhler;U. Wild;O. Pozdnyakova;Z. Paâl
用H2S/H2（10%v/v混合物）处理“新鲜”（干燥）以及“使用”状态（在煅烧和在20巴H2和300托正己烷下在高压釜中使用后）的Pt（3wt%）/硫酸化氧化锆（Pt/SZ）。采用X射线衍射（XRD）、X射线光电子能谱（XPS）、高分辨透射电子显微镜（HRTEM）等分析手段，研究了硫的形态、结构变化以及硫的化学状态。XPS检测到硫酸盐（BE = 169.5 eV）作为未硫化催化剂中S的唯一化学形式。两种样品在硫化后的S2 p区均出现了硫化物S2 p组分（BE = 162.5eV）.其量与Pt含量相关。几乎所有的“硫化物”成分消失，从X射线光电子能谱准原位氢处理。离子散射光谱（ISS）发现部分“嵌入”在硫化催化剂中的Pt，并增加了硫信号。H2S处理几乎完全去除了表面碳杂质。模拟的Pt 4f峰的金属Pt（Pt 0），PtOads，和PtS的人工复合光谱表明，Pt是目前作为一个混合物的Pt 0在密切的相互作用与支持氧（和/或与吸附的O覆盖层）和硫化后的PtS。使用HRTEM在未硫化的催化剂中检测到几个小的扁平Pt 0颗粒。硫化后，Pt 0和PtS颗粒共存。硫化催化剂在苯和环己烯加氢反应中失活，但在573 K下的氢处理使催化剂重新活化用于后一反应。因此，铂表面容纳了一些失活的化学吸附的硫，但是，更多的S没有形成，一个紧凑的表面覆盖层，但出现作为结晶PtS相具有可辨别的晶格距离。通过HRTEM观察到的单独的PtS颗粒由小Pt 0颗粒的总硫化或由表面PtS实体从较大的Pt微晶迁移到支撑体产生。
Pt (3 wt%)/sulfated zirconia (Pt/SZ) was treated with H2S/H2(10% v/v mixture) in the “fresh” (dried) as well as in the “used” state (after calcination and use in an autoclave run under 20 bar H2and 300 Torr n-hexane). Morphological and structural changes as well as the chemical state of sulfur were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM). XPS detected sulfate (BE ∼169.5 eV) as the only chemical form of S in the unsulfided catalysts. A sulfide S 2p component (BE ∼162.5 eV) appeared in the S 2p region after sulfidation of both samples. Its amount correlated with the Pt content. Almost all “sulfide” components disappeared from the X-ray photoelectron spectra quasi in situ hydrogen treatment. Ion scattering spectroscopy (ISS) uncovered partly “embedded” Pt in sulfided catalysts and increased the sulfur signal. The H2S treatment almost completely removed surface carbon impurities. Simulation of the Pt 4f peaks by artificial composite spectra of metallic Pt (Pt0), PtOads, and PtS showed that Pt was present as a mixture of Pt0in close interaction with support oxygens (and/or with an adsorbed O overlayer) and PtS after sulfidation. Using HRTEM several small flat Pt0particles were detected in unsulfided catalysts. After sulfidation distinct flat Pt0and PtS particles coexisted. Sulfided catalysts were inactive in benzene and cyclohexene hydrogenation but hydrogen treatment at 573 K reactivated the catalyst for the latter reaction. Thus, the platinum surface accommodated some deactivating chemisorbed sulfur; more S did not, however, form, a compact surface overlayer but appeared as a crystalline PtS phase with discernible lattice distances. Separate PtS particles seen by HRTEM were produced either by total sulfidation of small Pt0particles or by migration of surface PtS entities from larger Pt crystallites to the support.