摘要
在常压流动反应装置上评价了一系列La_2O_3/CaO催化剂和SrO-La_2O_3/CaO催化剂。实验表明:La_2O_3/CaO体系是很好的甲烷氧化偶联催化剂。在1073K和CH_4:O_2:He=4:1:5(总流速120ml/min)的实验条件下,20％La_2O_3/CaO催化剂上的甲烷转化率为26％,C_2选择性为53％;加入助剂SrO(15—20％)后,在同样实验条件下,甲烷转化率为29％,C_2选择性为66％。表明SrO对La_2O_3/Cao催化剂有明显的促进作用。用XRD,XPS和TPD(CO_2-TPD和O_2-TPD)技术表征了SrO-La_2O_3/CaO催化剂体系,结合反应评价结果,认为SrO的促进作用可以归结为:(1)调变了催化剂的碱性强度分布,提高了催化剂表面强碱中心的数目;(2)提高了La_2O_3的分散度;(3)抑制了催化剂的低温氧吸附物类。
A series of La2O3/CaO and SrO-La2O3/CaO catalysts were 'evaluated in a flowing fixed-bed reactor with a catalyst charge of 50 mg. The combination of La2O3 and CaO results in a good catalyst for the oxida-tive coupling of methane, the conversion of methane is 26% and the selectivity for ethylene and ethane is 53% at 1073K and -the total flow rate of 120 ml/min with the volumetric ratio of CH4:O2:He- 4= 1:5. When SrO (15-20%) incorporated into La2O3/CaO, the conversion of methane raises to 29% and C2 selectivity to 66%. Combining XRD, XPS and TPD (CO2- and CK-TPD) characterizations with the reaction results, it is suggested that the promotive effect of SrO additive can be attributed to (1 ) the modification of the distribution of basicity on the catalyst surface, ( 2 ) an increase in the dispersion degree of La2O3, and ( 3 ) the suppression of the oxygen species released at relatively low temperature, which is supposed to be responsible for the total oxidation of methane.
基金
中国科学院大连化学物理研究所1990年所长基金
关键词
氧化镧
氧化钙
甲烷
氧化偶联
Lanthanum oxide,calcium oxide,supported catalyst,strontium oxide,cocatalyst,methane,oxidative coupling
