摘要
采用原位红外和原位显微 Raman光谱技术及 XPS、吡啶 (Py)吸附的漫反射 UV谱、Py-TPD、CO2 - TPD等方法对含氟稀土基催化剂上甲烷氧化偶联 (OCM)反应活性氧物种、催化剂表面酸碱性进行了考察 .在 O2 预处理和 /或工作条件下的 Sr F2 / L a2 O3 ,Sr F2 / Nd2 O3 ,L a OF,Ba F2 / L a OF和 Ba F2 / Ce O2 等催化剂上原位观测到超氧物种 (O-2 ) ,并在其中前 4种催化剂上检测到 O-2 物种与CH4 反应生成的气相 C2 H4 ,CO2 和表面碳酸盐等 OCM反应主、副产物 .这些结果为 O-2 是相应催化剂上 OCM反应的活性氧物种首次提供了直接的光谱证据 .研究结果还表明 ,催化剂的 OCM反应性能与其表面酸碱性的强弱并无简单的对应关系 .采用原位时间分辨红外光谱和原位显微 Raman光谱技术对 Si O2 和γ- Al2 O3 负载的 Rh、Ru催化剂上甲烷部分氧化 (POM)制合成气反应的研究表明 ,由 CH4 直接氧化生成 CO和 H2 是 Rh/ Si O2 上 POM反应的主要途径 ,而燃烧 -重整机理是 Ru/ γ-Al2 O3 和 Ru/ Si O2 上 CO和 H2 生成的主要途径 ,反应条件下催化剂表面氧 (O2 -)物种浓度的差异很可能是导致这两种催化剂体系上 POM反应机理不同的主要原因 ,其本质可能源于 Rh和 Ru对氧的亲合力的不同 .
Active oxygen specie and surface acid/base properties of fluoride containing rare earth based catalysts for methane oxidative coupling (OCM) reaction were studied using in situ IR and in situ microprobe Raman spectroscopies, XPS, UV spectra of pyridine (Py) adsorption, Py and CO 2 TPD. O - 2 species was detected over O 2 and/or CH 4/O 2 pretreated SrF 2/La 2O 3, SrF 2/Nd 2O 3, LaOF, BaF 2/LaOF and BaF 2/CeO 2 catalysts at OCM reaction temperature, and the reactions between O - 2 species and CH 4 to form C 2H 4 and corresponding side products of OCM reaction such as CO 2 and surface carbonate were observed over SrF 2/La 2O 3, SrF 2/Nd 2O 3, LaOF, BaF 2/LaOF catalysts. These results, for the first time, provide direct spectroscopic evidences which suggest that O - 2 is the active oxygen species for OCM reaction over the corresponding catalysts. It is also found that the surface basicity is not always a requisite attribute for a good OCM catalyst. The results of in situ time resolved FTIR and in situ microprobe Raman spectroscopic characterizations on the partial oxidation of methane (POM) reaction indicate that direct oxidation of CH 4 to synthesis gas is the main pathway of POM reaction over Rh/SiO 2 catalyst, while the combustion reforming scheme is the dominant pathway of synthesis gas formation over Ru/γ Al 2O 3 and Ru/SiO 2 catalysts. The significant difference in the reaction schemes of POM reaction over SiO 2 and γ Al 2O 3 supported Rh and Ru catalysts may be related to the difference in surface concentration of oxygen species (O 2- ) over the catalysts under the reaction conditions mainly due to the difference in oxygen affinity of the two metals
出处
《厦门大学学报（自然科学版）》
CAS
CSCD
北大核心
2001年第2期349-359,共11页
Journal of Xiamen University：Natural Science
基金
国家重点基础研究发展规划!(G19990 2 2 4 0 8)
高等学校博士学科点专项科研基金资助项目
关键词
甲烷
氧化偶联
部分氧化
氧物种
反应机理
原位红外光谱
原位显微Raman光谱
含氟稀土
基催化剂
methane
oxidative coupling
partial oxidation, synthesis gas
oxygen species
acid/base properties
reaction mechanism
in situ (time resolved) FTIR, in situ microprobe Raman, fluoride containing rare earth based catalyst, Rh/SiO 2,Ru/γ
