In situ XPS investigation of Pt(Sn)/Mg(Al)O catalysts during ethane dehydrogenation experiments
- 作者：Anastasia Virnovskaia ; Sissel Jø ; rgensen ; Jasmina Hafizovic ; Ø ; ystein Prytz ; Evgueni Kleimenov ; Michael Hä ; vecker ; Hendrik Bluhm ; Axel Knop-Gericke ; Robert Schlö ; gl ; Unni Olsbye
- 关键词：X-ray photoelectron spectroscopy ; Catalysis ; Platinum ; Tin ; Alkanes ; Alkenes
- 刊名：Surface Science
- 出版年：2007
- 期刊代码：104_00396028
- 类别：ch
- 出版时间：1 January 2007
- 卷：601
- 期：1
- 页码：30-43
- 文件大小：992 K
摘要
Calcined hydrotalcite with or without added metal (Mg(Al)O, Pt/Mg(Al)O and Pt,Sn/Mg(Al)O) have been investigated with in situ X-ray photoelectron spectroscopy (XPS) during ethane dehydrogenation experiments. The temperature in the analysis chamber was 450 °C and the gas pressure was in the range 0.3–1 mbar. Depth profiling of calcined hydrotalcite and platinum catalysts under reaction, oxidation and in hydrogen–water mixture was performed by varying the photon energy, covering an analysis depth of 10–21 Å. It was observed that the Mg/Al ratio in the Mg(Al)O crystallites does not vary significantly in the analysis depth range studied. This result indicates that Mg and Al are homogeneously distributed in the Mg(Al)O crystallites. Catalytic tests have shown that the initial activity of a Pt,Sn/Mg(Al)O catalyst increases during an activation period consisting of several cycles of reduction–dehydrogenation–oxidation. The Sn/Mg ratio in a Pt,Sn/Mg(Al)O catalyst was followed during several such cycles, and was found to increase during the activation period, probably due to a process where tin spreads over the carrier material and covers an increasing fraction of the Mg(Al)O surface. The results further indicate that spreading of tin occurs under reduction conditions.
A PtSn2 alloy was studied separately. The surface of the alloy was enriched in Sn during reduction and reaction conditions at 450 °C. Binding energies were determined and indicated that Sn on the particle surface is predominantly in an oxidised state under reaction conditions, while Pt and a fraction of Sn is present as a reduced Pt–Sn alloy.