Du Shuangli, Zhang Huan, Deng Cunbao, Wang Xuefeng, Zhai Ruicong, Wen Zhijie
College of Safety and Emergency Management Engineering, Taiyuan University of Technology Taiyuan 030024 China.
Key Laboratory of Mining Disaster Prevention and Control Qingdao 266590 China
RSC Adv. 2022 Oct 26;12(47):30549-30556. doi: 10.1039/d2ra05493k. eCollection 2022 Oct 24.
Catalytic combustion technology is an efficient and green method to deal with low concentration methane. Gas adsorption over the catalyst surface is a key step in the catalytic combustion process, which has attracted much interest. In this work, the first-principles density functional theory calculation method has been applied to explore the adsorption processes of CH and O molecules on the surface of cryptomelane type manganese oxide octahedral molecular sieves (OMS-2). In addition, the effect of K concentration in the OMS-2 tunnel on the adsorption of the two gaseous molecules has also been investigated. The results of adsorption energy and structural characteristics show that the adsorption energies of CH and O molecules over the catalyst surface are favorable. Adsorption sites of CH are the K and O sites, among which the K site is the most stable adsorption site. In addition, Mn sites are favorable for adsorbing O molecules. The interactions between the catalyst and the adsorbed CH and O are enhanced with the increasing tunnel potassium ions. It should be noted that with the increasing strength of the adsorption energies, equilibrium distances from the two gaseous molecules to the active sites become shorter and the bond lengths of C-H and O-O bonds become longer. Moreover, the adsorption sites of CH on the catalyst surface increase with the increasing K concentration. Bader charge and cohesive energy calculations reveal that the tunnel K can balance charges and help strengthen the structural stability of OMS-2. Interestingly, the electronegativity of the catalyst has been altered after introducing K, which leads to better adsorption of gaseous CH and O. The microscopic mechanism of the effect of K concentration on the adsorption of CH and O over the catalyst surface paves the way for further deciphering the mechanism underlying the catalytic oxidation process and helps design more efficient catalysts for methane utilization.
催化燃烧技术是处理低浓度甲烷的一种高效且绿色的方法。气体在催化剂表面的吸附是催化燃烧过程中的关键步骤，这引起了人们的广泛关注。在本工作中，采用第一性原理密度泛函理论计算方法，探究了CH和O分子在隐钾锰矿型锰氧化物八面体分子筛（OMS - 2）表面的吸附过程。此外，还研究了OMS - 2孔道中K浓度对这两种气体分子吸附的影响。吸附能和结构特征结果表明，CH和O分子在催化剂表面的吸附能是有利的。CH的吸附位点是K位和O位，其中K位是最稳定的吸附位点。此外，Mn位有利于吸附O分子。随着孔道钾离子的增加，催化剂与吸附的CH和O之间的相互作用增强。需要注意的是，随着吸附能强度的增加，两种气体分子到活性位点的平衡距离变短，C - H键和O - O键的键长变长。而且，CH在催化剂表面的吸附位点随K浓度的增加而增加。Bader电荷和内聚能计算表明，孔道中的K可以平衡电荷并有助于增强OMS - 2的结构稳定性。有趣的是，引入K后催化剂的电负性发生了改变，这导致对气态CH和O的吸附更好。K浓度对催化剂表面CH和O吸附影响的微观机制为进一步解读催化氧化过程的机理铺平了道路，并有助于设计更高效的甲烷利用催化剂。
