Na2SnO3系催化剂表面吸附氧的EPR研究

以Na_2SnO_3系甲烷氧化偶联催化剂中性能较好的5%Li_2SO_4-Na_2SnO_3样品为主要研究对象, 用电子顺磁共振(EPR)方法对表面吸附氧及其与甲烷的作用进行了研究, 实验表明: 样品在氧气氛中处理后,得到可归属为表面吸附超氧负离子O_2~-的顺磁信号, 在300 ℃以上温度条件下吸附氧后, 可产生这种表面氧物种, 该物种在室温、1.33×10~(-2) Pa真空条件下能稳定存在, 700 ℃与甲烷作用后顺磁信号显著减弱, 因而催化剂表面的O_2~-物种可能起着活化甲烷的作用.

THE STUDY OF ADSORBED OXYGEN SPECIES ON THE SURFACE OF A SERIES OF Na_2SnO_3 CATALYSTS BY EPR EXPERIMENTS

According to the results of investigation in a series of Na_2SnO_3 catalysts for oxidative coupling of methane, a sample (5 mol%Li_2 SO_4-Na_2SnO_3) with good catalytic properties was selected as the main research object. By using electron paramagentic resonance(EPR) method, the form of surface adsorbed oxygen has been investigated. The EPR results confirm that a signal with g value of 2.013 is from the species of surface adsorbed oxygen, and that it can be assigned to adsorbed superoxide species O_2~-. At 300 ℃ or the above this type of oxygen species can form on that catalyst sample.The species O_2~- is stable under conditions of room temperature and vacuum of 1.33×10~(-2) Pa. But at 700 ℃ the reaction between O_2~- and CH_4 occured, and at the same time the intensity of O_2~- signal considerably decreased. The resuls show that the surface species O_2~- might play an important role in activating CH_4 molecules in the oxidative coupling reaction of methane.