摘要
用高分辨电子能量损失谱（ＨＲＥＥＬＳ），热脱咐谱（ＴＤＳ）在１４０Ｋ—７００Ｋ温度范围内研究了清洁和氧改性Ｐｄ（１００）面上ＣＨ_３ＯＨ的吸咐与分解机理。ＨＲＥＥＬＳ结果表明：在１４０Ｋ吸咐甲醇能形成分子吸咐层；当加热甲醇分子层时，甲醇在１８５Ｋ先分解为ＣＨ_３Ｏ_（ａｄ）和Ｈ_（ａｄ），在２００Ｋ以上温度ＣＨ_３Ｏ_（ａｄ）逐步分解为ＣＯ_（ａｄ）和Ｈ_（ａｄ）；预吸咐氧后表面有甲酸物种生成。ＴＤＳ研究表明；除有少量甲醇在１８５Ｋ脱咐外，甲醇分解的主要脱咐产物为Ｈ_２（３２０Ｋ）和ＣＯ（４４０Ｋ）；次要脱附产物为甲烷（２００Ｋ—２１０Ｋ）。综合ＨＲＥＥＬＳ和ＴＤＳ研究指出，在清洁表面甲醇主要通过Ｏ—Ｈ键断裂，经甲氧基中间物种分解为ＣＯ和Ｈ_２，还有部分甲醇通过Ｃ—Ｏ键断裂分解为甲烷，预吸附氧后甲醇的分解除了存在以上两种方式外，氧的存在一方面能够转移ＣＨ_３Ｏ_（ａｄ）中的氢原子在表面形成一定量的甲酸中间物种，另一方面能够稍许提高少量ＣＨ_３Ｏ_（ａｄ）的热稳定性。
The adsorption and decomposition of methanol on clean and oxygen preadsorbed Pd (100) in a temperature range of 140-700 K has been studied using high resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). HREELS spectra characterized by a v_(OH) stretch at 3300 cm￣(-1) indicate that methanol adsorbs molecularly on Pd (100) at 140 K. Heating the sample to 185 K, the desorption of molecular methanol is observed by TDS. Both on clean and oxygen preadsorbed Pd (100) the conversion of methoxy species to carbon monoxide and hydrogen1 occurs above 200 K. The TDS profiles of methanol show that the main products of methanol decomposition are H_2(320 K) and CO(440 K), and the minor product is methane (200 K-210 K) while a small amount of methanol desorbs at 185 K. It suggests that both the O-H bond and the C-O bond cleavage take place in the decomposition of methanol. The different structures of preadsorbed oxygen affect the course of methanol decomposition differently. One type of oxygen attacks the hydrogen of methoxy to form formate species on the surface. The loss peak at 1328 cm￣(-1) on oxygen preadsorbed Pd (100) surface implies the formation of formate species , while another type of oxygen enhances slightly the thermal stability of the methoxy species.
出处
《分子催化》
EI
CAS
CSCD
1994年第1期1-7,共7页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金
关键词
甲醇
吸附
分解
钯
Adsorption, Decomposition of methanol, Pd(100), High Resolution Electron Energy Loss Spectroscopy (HREELS),Thermal Desorption Spectroscopy (TDS) .
