Investigation of Deoxidation Process of MoO3 Using Environmental TEM
In situ environmental transmission electron microscope (ETEM) could provide intuitive and solid proof for the local structure and chemical evolution of materials under practical working conditions. In particular, coupled with atmosphere and thermal field, the behavior of nano catalysts could be directly observed during the catalytic reaction. Through the change of lattice structure, it can directly correlate the relationship between the structure, size and properties of materials in the nanoscale, and further directly and accurately, which is of great guiding value for the study of catalysis mechanism and the optimization of catalysts. As an outstanding catalytic material in the application of methane reforming, molybdenum oxide (MoO3)-based materials and its deoxidation process were studied by in situ ETEM method. The corresponding microstructures and components evolution were analyzed by diffraction, high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectrum (EELS) techniques. MoO3 had a good directional deoxidation process accompanied with the process of nanoparticles crushing and regrowth in hydrogen (H2) and thermal field. However, in the absence of H2, the samples would exhibit different structural evolution.Get more news about
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Molybdenum (Mo)-based materials are often used as efficient catalysts for various heterogeneous gas-solid catalytic reactions [1,2]. Primarily, molybdenum oxide (MoO3)/molybdenum carbide (MoC) catalysts are widely used in the chemical industry due to their value in the carbon cycle catalysis [3,4], including methane reforming [5]. As an excellent catalytic and substrate material, MoC also perfectly compounds other materials to achieve better results. For example, Ding Ma et al. employed α-MoC in hydrogenation reaction, showing high selectivity and yield because α-MoC and nitrogen compounds preferentially activate the C=O and C−OH bonds over C=C and C−C [6]. Interestingly, MoO3 is also the raw material used to produce MoC [7]. Xinhe Bao and colleagues prepared a highly reactive Au/MoC catalyst using MoO3 and Au nanoparticles. In the process, the MoO3 to MoC transition and the intermediate states, such as MoOxCy and Au dispersion processes, were completed by the Strong Metal-Support Interaction (SMIS) [8]. The first step of the MoO3 deoxygenation process, both with MoO3/MoC catalysts and during the molybdenum carbide reaction, deserves to be explored in detail [9,10]. In addition, previous work pointed out the connection between deoxygenation sites and the active sites of the subsequent reaction, which helps explore the evolution of reaction sites [11]. Moreover, MoO3 and MoOx are two-dimensional materials widely used in devices, which is one of the significances of exploring MoO3 deoxidation [12,13].
It is of great significance to explore the generations of catalysts and process of reaction [14,15]. And there are many in situ methods, such as X-ray diffraction patterns (XRD), Fourier Transform Infrared (FTIR), and X-ray Absorption Fine Structure (XAFS) are widely used in catalytic research, also the thermodynamic experiments mostly analyze the structure from a macro perspective rather than directly observing the reaction [14]. At present, there are few means for direct observation of catalytic reactions [16]. However, the recent development of environmental transmission electron microscope (ETEM) makes it possible to observe the nanomaterials’ performances during chemical reactions at an atomic scale [17,18]. In situ techniques such as thermal, electrical, and force fields are used to study the dynamics under external conditions during catalyst evolution and track the catalyst motion at the atomic scale to observe the atomic dynamics in real-time [19]. Therefore, the structure-activity relationships and reasons for activity could be better understood. In catalysis, many catalytic mechanisms are not clearly comprehended. The catalytic experiment can only show that some reactions are promoted, but the reason for their activity is still unknown [18]. Moreover, selective exploration should also get enough attention at the atomic scale, to guide more targeted, cheaper, and sustainable new catalysts [14].
Investigation of Deoxidation Process of MoO3 Using Environmental TEM
