Effects of potassium on the reaction pathway of C3H7 species over Mo2C/MO (100)

被引:7
作者
Farkas, A. P.
Koos, A.
Bugyi, L.
Solymosi, F.
机构
[1] Univ Szeged, Inst Solid State & Radiochem, H-6701 Szeged, Hungary
[2] Hungarian Acad Sci, React Kinet Res Grp, H-6701 Szeged, Hungary
关键词
alkyl iodide; molybdenum carbide; reaction of propyl; thermal desorption; X-ray photoelectron spectroscopy; high resolution electron energy loss spectroscopy;
D O I
10.1016/j.susc.2006.03.037
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The adsorption and surface reactions of propyl iodide on clean and potassium-modified Mo2C/Mo(100) surfaces have been investigated by thermal desorption spectroscopy (TPD), X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) in the 100-1200 K temperature range. This work is strongly related to the better understanding of the catalytic effect of Mo2C in the conversion of hydrocarbons. Potassium was found to be an effective promoter: it induced the rupture of C-I bond in the adsorbed C3H7I even at 100 K. The extent of C-I bond scission varied approximately linearly with the concentration of K coverage at the adsorption temperature of 100 K. As revealed by HREELS and TPD measurements the primary products of the dissociation are C3H7 and I. The former one was stabilized by potassium and underwent dehydrogenation and hydrogenation to give propene and propane. The desorption of both compounds is reaction-limited process. A fraction of propyl groups was converted into di-sigma-bonded propene, which was stable up to similar to 380 K. The coupling reaction of propyl species was also facilitated by potassium and resulted in the formation of hexane and hexene with T-p similar to 230-250K. Hydrogen was released with T-p = 390 K, indicative of a desorption limited process. The effect of potassium was explained by the extended electron donation to adsorbed propyl iodide in one hand. and by the direct interaction between potassium and I on the other hand. This was reflected by the shift of the desorption of potassium from the coadsorbed layer at and above 1.0 ML to higher temperature, and by the coincidal T, values (similar to 700 K) of potassium and iodine. The formation of KI was also supported by the appearance of a loss feature at 650 cm(-1) in the HREEL spectra attributed to a phonon mode of KI. (c) 2006 Elsevier B.V. All rights reserved.
引用
收藏
页码:2355 / 2363
页数:9
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