Active oxygen species and oxidation mechanism over Ce-doped LaMn0.8Ni0.2O3/hierarchical ZSM-5 in pentanal oxidation

• 作者: Jian Li Yingjie Shi Xiaoheng Fu Yun Shu Jiayu Huang Jinwei Zhu Gang Tian Jingnan Hu
• 来源期刊: 稀土学报（英文版）
• 年，卷（期）: 2021,（9）
• 所属期刊栏目: RARE EARTH CATALYSIS
• 页码范围: 1062-1072
• 页数: 11页
• 语种: 英文

摘要

Hierarchical ZSM-5 (HZ) molecular sieves based on fly ash were synthesized using a method combining water heat treatment with step-by-step calcination. The coupling catalysts between La1-xCexMn0.8-Ni0.2O3 (x ≤ 0.5) perovskites and HZ were prepared through the impregnation method, which were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution trans-mission electron microscopy (HRTEM), N2 adsorption, X-ray photoelectron spectroscopy (XPS), NH3-temperature programmed desoprtion (NH3-TPD), H2-temperature programmed reduction (H2-TPR) and O2-TPD techniques and investigated regarding pentanal oxidation at 120-390 °C to explore the effects of Ce doping on the catalytic activity and the active oxygen species of the coupling catalysts, meanwhile, the reaction mechanism and pathway of pentanal oxidation were also studied. The results reveal that Ce substitution at La sites can change the electronic interactions between all the elements and promote the electronic transfer among La, Ce, Ni, Mn and HZ, influencing directly the physicochemical characteristics of the catalysts. Moreover, the amount and transfer ability of surface adsorbed oxygen (O2- and O-) regarded as the reactive oxygen species and the low temperature reducibility are the main influence factors in pentanal oxidation. Additionally, La0.8Ce0.2Mn0.8Ni0.2O3/HZ exhibits the best catalytic activity and deep oxidation capacity as well as a better water resistance due to its larger amount of surface adsorbed oxygen species and higher low temperature reducibility. What's more, appropriate Ce substi-tution can significantly enhance the amount of O2- ions, which can distinctly enhance the catalytic ac-tivity of the catalyst, and moderate acid strength and appropriate acid amount can also facilitate the improvement of the pentanal oxidation activity. It is found that there is a synergic catalytic effect be-tween surface acidity and redox ability of the catalyst. According to the in situ DRIFTS and GC/MS ana-lyses, pentanal can be oxidized gradually to CO2 and H2O by the surface oxygen species with the form of adsorption in air following the Langmuir-Hinshelwood (L-H) reaction mechanism. Two reaction path-ways for the pentanal oxidation process are proposed, and the conversion of the formates to carbonates may be one of the main rate-determining steps.