甲烷在SrO-La_2O_3/CaO催化剂上的氧化偶联 Ⅱ.反应动力学的研究

OXIDATIVE COUPLING OF METHANE OVER SrO-La_2O_3/CaO CATALYSTS Ⅱ.A COMPARATIVE STUDY ON REACTION KINETICS

在20％La_2O_3/CaO(LC)催化剂中添加SrO(添加SrO的LC以SLC表示)明显地提高了反应活性和C_2选择性。反应动力学研究表明,LC和SLC催化剂在甲烷氧化偶联反应中,在表观活化能和表观反应级数上存在很大的差异。LC催化剂在CH_4转化以及C_2和CO_x形成过程中,表观活化能大于SLC催化剂,而SLC催化剂的指前因子小于LC体系,两者存在着补偿现象。SLC催化剂的反应速率常数比kc_2/k_(CH4)大于LC,而k_(COX)/k_(CH4)小于LC催化剂。保留时间的实验表明:LC催化剂上的甲烷氧比偶联,CO,C_2H_6是初始产物;而在SLC催化剂上,CO,CO_2和C_2H_6是初始产物,CO,CO_2同时产生且两者存在着平衡关系。LC催化剂在CH_4转化过程中,CH_4和O_2的表观反应级数均为一级左右,而在SLC催化剂上CH_4的表观反应级数接近二级,而O_2的表观反应级数为一级左右。

There was obvious increase in activity and C2 selectivity with the addition of SrO to La2O3/CaO(LC) catalyst.Kinetic analysis shows that there are obvious differences in apparent activation energy, apparent reaction order and the formation of CO, over LC and SLC (20%SrO-20% La2O3/CaO)catalysts.The apparent activation energies for CH4 conversion and C2,COx formation over LC are higher than those over SLC catalyst, while the pre-exponential factors for CH4 conversion and C2, COx formation are in reverse.The value of kc2/kCH4 of SLC is larger than that of LC.On the contrary, the value of KCOx/KCH4 of SLC is smaller than that of LC.This suggests that the SrO plays a role in suppression of the total oxidation of methane and results in higher C2 selectivity.The influence of W/F on activity and C2 selectivity suggests that CO and C2H6 are primary products over LC,while CO, CO2 and C2H6 are primary products and there is an equilibrium between CO and CO2 over SLC.The apparent reaction orders with respect to CH4 and O2 are close to one in CH4 conversion over LC, while it is nearly 2 with respect to CH4 and is about one with respect to O2 over SLC.