低温甲烷氧化偶联纳米SrTi_(0.975)Li_(0.025)O_(3-δ)催化剂的原位ESR和TPSR表征

In situ ESR and TPSR measurements of SrTi_(0.975)Li_(0.025)O_(3-δ) nanocatalysts for oxidative coupling of methane at low temperature

采用溶胶-凝胶法制备纳米钙钛矿型复合氧化物催化剂SrTi1-xLixO3-δ（x=0、0.025、0.050）,用微型催化反应评价装置结合XRD、TEM、原位ESR和程序升温表面反应（TPSR）等方法,研究甲烷氧化偶联（OCM）纳米SrTi1-xLixO3-δ催化剂结构和催化性能。结果表明,B位掺杂适量的低价Li＋离子可优化纳米SrTiO3催化剂低温（~650℃）甲烷氧化偶联催化性能,Li＋掺杂量为0.025时获得最高的甲烷转化率和C2选择性。与柠檬酸法制相同组成的常规催化剂相比,SrTi0.975Li0.025O3-δ纳米催化剂具有较优良的低温OCM催化性能和相同温度下更高的C2选择性。SrTi0.975Li0.025O3-δ纳米催化剂优良的催化性能与其表面原子配位不饱和存在F中心相关。

Perovskite-type SrTi1-xLixO3-δ（x = 0,0.025,0.050） nano catalyst was prepared by using sol-gel method.Its structure was characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM）,in-situ electron spin resonance（ESR）,and temperature-programmed surface reaction（TPRS）;its catalytic performance for oxidative coupling of methane（OCM） was measured in a microreactor.The results indicated that the OCM catalytic performance at low temperature（about 650 ℃） is enhanced by doping Li＋ cation to the B site of perovskite-type SrTiO3 nano catalysts;the SrTi1-xLixO3-δ nano catalyst with x = 0.025 performs best.Compare with the conventional catalysts of the same composition prepared by citric acid method,SrTi0.975Li0.025O3-δ nano catalyst performs much better for OCM reaction at low temperature;higher C2 selectivity is achieved at the same temperature.In-situ ESR results showed that there exist O-with ESR signal at g = 2.043 0 and F center with ESR signal at g = 2.008 0 in the nano SrTi0.975Li0.025O3-δ catalyst,while the conventional SrTi0.975Li0.025O3-δ catalyst shows O2-with the ESR signals at g∥ = 2.014 and g⊥ = 1.990 6.The high catalytic performance of SrTi0.975Li0.025O3-δ nano catalyst is related to F centers due to the low coordination surface atoms on the nano oxide particles.F center may activate CH4 at lower temperature and lead to the formation of C2 hydrocarbons with higher selectivity.