Cu-Ni/Zn催化剂甲醇裂解机理原位XPS研究

In-situ XPS Study for Reaction Mechanism of Methanol Decomposition over Cu-Ni/Zn Catalyst

利用原位XPS和TPD-MS技术研究了Cu-Ni/Zn催化剂在甲醇裂解反应中的机理和活性中心.TPD-M脱附产物中仅检测到CH3OH、H2和CO,而未发现CH4和CH3OCH3、HCOOCH3等其它含氧物种,说明在CH3O裂解过程中仅包括O-H、C-H键的断裂,而不存在C-O键的断裂过程.In-situXPS的研究发现,在反应温度升高到200℃以上时,Cu/Zn催化剂中的Zn明显被还原,反映出Cu/Zn催化剂失活过程的Cu-Zn合金生成过程,而在Cu-Ni/Zn催化剂中未观察到Zn的还原,且表面出现Cu+/Cu0共存的现象.Cu+和Cu0很可能共同构成催化剂表面的活性中心,Cu+应该是在甲醇裂解反应过程中形成的中间态.产物氢从Cu-Ni/Zn催化剂表面脱附为反应的控速步骤.

In-situ XPS and TPD-MS techniques were used to study the reaction mechanism and the active center of Cu-Ni/Zn catalyst for methanol decomposition. Significant amount of CH3OH, H-2 and CO were detected during the methanol decomposition with TPD-MS, however no evidences of CH4, CH(3)OCHs and HCOOCH3 formation were obtained. TPD-MS results indicated that O - H and C - H bonds instead of C - O bond were broken in methanol decomposition on Cu/Zn/Ni catalyst. It was found that H-2 desorption from the surface of Cu-Ni/Zn catalyst was the rate control step, In-situ XPS studies confirmed that the Zn species was easily reduced when temperature was higher than 200 degreesC in Cu/Zn catalyst. However, similar reduction of Zn was not observed in Cu/Zn/Ni catalyst. Furthermore, both Cu+ and Cu-0 species were observed in Cu/Zn/Ni catalyst. Our study indicated that active center(s) in Cu/Zn/Ni catalyst may be Cu-0 and/or Cu+ species, in which Cu+ formed during the reaction.