研究目的
Investigating the phase changes and catalytic activity of mesoscopic and nanosized CoO catalysts during CO oxidation using operando techniques to understand the active phases under reaction conditions.
研究成果
The study shows that nanosized CoO undergoes easier and more complete oxidation to Co3O4 under CO oxidation conditions compared to mesoscopic CoO, leading to higher catalytic activity. Operando techniques are crucial for identifying active phases, revealing dynamic surface adjustments dependent on grain size and morphology.
研究不足
The mesoscopic CoO's large grain size limited the detection of surface oxidation by bulk-sensitive techniques like XAS, requiring surface-sensitive methods. Vacuum reduction might not fully represent industrial conditions. The study focused on model reactions and may not directly apply to real-world catalytic systems without further optimization.
1：Experimental Design and Method Selection:
The study used operando X-ray absorption spectroscopy (XAS) and near-ambient pressure X-ray photoemission spectroscopy (NAP-XPS) to monitor structural and electronic changes during CO oxidation, complemented by ex situ transmission electron microscopy and diffraction (TEM/SAED) for structural characterization. Catalytic performance was assessed using mass spectrometry (MS) and gas chromatography.
2：Sample Selection and Data Sources:
Two types of CoO catalysts were used: commercial mesoscopic CoO (particle size ~1 μm) and nanosized CoO prepared by vacuum reduction of commercial Co3O4 (particle size 20-50 nm). Specific surface areas were measured using BET analysis.
3：List of Experimental Equipment and Materials:
Equipment included an ASAP 2020 instrument for BET surface area measurements, a Philips X'Pert diffractometer for XRD, a TECNAI F20 for HRTEM and SAED, a fixed-bed quartz reactor for catalytic tests, an HP-PLOT Q column with flame-ionization detector for gas chromatography, a reaction cell at MAX-lab II for operando XAS, and a NAP-XPS setup at BESSY II. Materials included CoO and Co3O4 powders, quartz powder, BN diluent, and tantalum grids.
4：Experimental Procedures and Operational Workflow:
For mesoscopic CoO, pretreatments involved heating in He or synthetic air, followed by CO oxidation in a flow reactor with temperature ramping. Operando XAS was performed during heating in reaction mixtures. For nanosized CoO, vacuum reduction of Co3O4 was done, followed by operando NAP-XPS and NEXAFS during CO oxidation. TEM and SAED were conducted ex situ on pretreated samples.
5：Data Analysis Methods:
XRD data were analyzed with HighScore Plus and TOPAS for phase identification and refinement. XAS spectra were processed with Athena software for energy alignment and normalization. XPS and NEXAFS data were calibrated and interpreted based on binding energies and spectral features. Catalytic activity data were analyzed for conversion temperatures.
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