原子层沉积制备FeOx/ZSM-5催化剂及其甲烷液相氧化性能

Preparation of FeOx/ZSM-5 catalyst by atomic layer deposition for liquid phase oxidation of methane

利用原子层沉积(ALD)技术将FeOx沉积在ZSM-5沸石上制备出FeOx/ZSM-5催化剂,并考察了FeOxALD循环数对催化剂的过氧化氢液相氧化甲烷性能的影响。ICP分析结果表明,Fe的负载量随着FeOx ALD循环数的增加而线性增加,Fe沉积速度为0.015%(质量分数)每循环。FeOx ALD循环数与甲烷液相氧化活性呈现火山形关系,FeOx循环数为30时,性能达到最优,甲烷转化率为2.27%,水相中C1有机物选择性96%以上,甲醇/甲酸摩尔比达到15。此外,甲烷转化的TOF值则随FeOx负载量的降低而增加,10循环时TOF值最高,达到809.5 h^-1。由TEM、ICP、XRD、IR和XPS等表征可知,Fe物种的价态、ZSM-5的骨架结构不受ALD循环数的影响,而骨架Fe的比例随循环数提高逐渐降低。低循环时FeOx与表面硅羟基化学键合,形成高活性Fe^3+-O-Si物种,有利于甲烷的转化制甲醇。

FeOx/ZSM-5 catalysts were prepared by atomic layer deposition(ALD) of FeOxon the ZSM-5 zeolite, and the effect of FeOx ALD cycle number on the catalytic performance of the catalyst in H2O2 liquid-phase oxidation of methane was investigated. The results of ICP analysis showed that the load of Fe increased linearly with the increase of ALD cycle number, and the deposition rate of FeOx was 0.015% by mass per cycle. The catalytic activity has a volcanic relationship with the number of FeOx ALD cycles, and the FeOx/ZSM-5 prepared by 30 FeOx ALD cycles performed the highest selectivity(90%) of C1 organics with a methanol/formic acid molar ratio of 15 at a methane conversion of 2.27%. In addition, the TOF value of methane conversion increased with the decrease of the FeOxloading, and reached the highest value of 809.5 h^-1 at 10 cycles. The results of TEM, ICP, XRD, IR and XPS show that the valence state of Fe species and the framework structure of ZSM-5 are not affected by ALD cycle number, while the proportion of skeleton Fe decreases with the increase of cycle number. At low cycle number, FeOx is chemically bonded with the surface silicon hydroxyl groups to form highly active Fe^3+-O-Si species, which is favorable to the conversion of methane to methanol.