Ji Hong-bing, Xu Jian-hua, Xie Jun-feng, Chen Qing-lin
Key Laboratory of Enhanced Heat Transfer and Energy Conservation of Ministry of Education, South China University of Technology, Guangzhou 510640, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2008 Jun;28(6):1246-50.
8%Ru-5%Ce/gamma-Al2O3 catalyst exhibited excellent catalytic performance for low temperature activation of methane. Although the conversion rates of methane were 25.3% for exothermal partial oxidation of methane, and 0.8% for endothermal carbon dioxide reforming, whose activity was rather low, 38.8% of conversion rate of methane could be obtained for the obtained coupling reaction at 500 degrees C owing to the coupling intensification between endothermal carbon dioxide reforming reaction and exothermal partial oxidation of methane. The mechanism of coupling partial oxidation of methane and carbon dioxide reforming on supported Ru catalyst was investigated by in-situ DRIFTS. The adsorption of CO on 8%Ru-5%Ce/gamma-Al2O3 showed that two kinds of doublet peaks which were characteristic adsorption of the gaseous CO at 2167 cm(-1) (2118 cm(-1)) to form Ru(CO)2 at 2031 cm(-1) (2034 cm(-1)) to form Ce(CO)2 were observed. These CO adsorption species wee easy to be desorbed from the surface of the catalyst at high temperature. The results of in-situ DRIFTS showed that carbonate, formal (formate) and carbon monoxide formed on the surface of catalyst, and formal (formate) was intermediate for the methane partial oxidation. This intermediate was formed through the combination of the adsorption species of methane CHx and the lattice oxygen adsorption species on the surface of catalyst, and syngas was produced through the splitting of this intermediate. The DRIFTS researching on carbon dioxide reforming showed that there was no new adsorption species on the surface of the catalyst, which indicated that the mechanism for carbon dioxide reforming was through the dissociation of the adsorbed methane and carbon dioxide. During the reaction of the coupling of carbon dioxide reforming reaction and partial oxidation of methane, there was hydroxyl adsorption species on the surface of catalyst. The mechanism of coupling methane, carbon dioxide and oxygen might be composed of the above two reaction mechanism and the bridging hydroxyl group adsorption species Ru-(OH)2 might contribute to the coupling reaction.
8%Ru-5%Ce/γ-Al2O3催化剂对甲烷低温活化表现出优异的催化性能。尽管甲烷的转化率对于甲烷的放热部分氧化为25.3%，对于吸热二氧化碳重整为0.8%，其活性相当低，但由于吸热二氧化碳重整反应与甲烷放热部分氧化之间的耦合强化，在500℃下进行的耦合反应可获得38.8%的甲烷转化率。通过原位漫反射红外傅里叶变换光谱（in-situ DRIFTS）研究了负载型Ru催化剂上甲烷耦合部分氧化和二氧化碳重整的机理。8%Ru-5%Ce/γ-Al2O3上CO的吸附表明，观察到两种双峰，分别是气态CO在2167 cm(-1)（2118 cm(-1)）处的特征吸附以形成Ru(CO)2，以及在2031 cm(-1)（2034 cm(-1)）处形成Ce(CO)2。这些CO吸附物种在高温下易于从催化剂表面脱附。原位漫反射红外傅里叶变换光谱的结果表明，催化剂表面形成了碳酸盐、甲醛（甲酸盐）和一氧化碳，且甲醛（甲酸盐）是甲烷部分氧化的中间体。该中间体是通过甲烷CHx吸附物种与催化剂表面晶格氧吸附物种的结合形成的，合成气通过该中间体的分解产生。对二氧化碳重整的漫反射红外傅里叶变换光谱研究表明，催化剂表面没有新的吸附物种，这表明二氧化碳重整的机理是通过吸附的甲烷和二氧化碳的解离。在二氧化碳重整反应与甲烷部分氧化的耦合反应过程中，催化剂表面存在羟基吸附物种。甲烷、二氧化碳和氧气耦合的机理可能由上述两种反应机理组成，桥连羟基吸附物种Ru-(OH)2可能有助于耦合反应。
