The methanol oxidation reaction is a promising route to eliminating trace amount of methanol in exhaust gases which aroused serious environmental concern. In this work, a novel Pd/MgAl 2 O 4 catalyst was prepared to construct the metal-support interface and employed in the methanol oxidation reaction. The reaction results show that the Pd/MgAl 2 O 4 catalyst could achieve 100% methanol oxidation at 198 ℃ over the Pd/MgO and Pd/Al 2 O 3 catalysts. The high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), CO-chemisorption, H 2 temperature programmed reduction (H 2 -TPR), and CO diffuse reflectance infrared Fourier transformed spectroscopy (CO-DRIFTS) show that the Pd was uniformly distributed over the MgAl 2 O 4 support due to strong interaction between Pd and MgAl 2 O 4 . The mechanism studies show that the abundant Pd-MgAl 2 O 4 interfaces significantly contributed to the reaction enhancement. The Pd-MgAl 2 O 4 interfaces could greatly enhance the oxidation reaction at a lower temperature with the assistance of oxygen vacancies compared with traditional oxide catalysts, which was confirmed by methanol temperature program surface reaction (MeOH-TPSR) experiments. In-situ DRIFTS is carried out to elucidate the reaction mechanism and establish the structure − activity relationship: the methanol could be effectively absorbed on the MgAl 2 O 4 support with oxygen vacancies to form bidentate formate, then the Pd species assisted the intermediates converting to CO 2 product. The Pd/MgAl 2 O 4 catalyst and its enhancement mechanism investigation provided a potential strategy in the VOCs removal catalysis development. Graphical Abstract
Jie Li,Jieying Cai,Yan Zhang,Peng Wang,Xuehai Wang,Xiangchen Fang,Yunbo Yu,Wenpo Shan
Mesoporous MgAl 2 O 4 is synthesized via a novel sol–gel combustion method and the concentration of oxygen defects on the surface is modulated through varying the calcination temperature (850, 900, 1000, and 1100 °C). Notably, the 1Pd/MgAl 2 O 4 -1000 catalyst exhibits superior catalytic activity and stability. The turnover frequency (TOF) for 1Pd/MgAl 2 O 4 -1000 is 0.079 and 0.058 s −1 under dry conditions (300 °C) and wet conditions (380 °C), respectively. The results of H 2 temperature-programmed reduction and X-Ray photoelectron spectroscopy reveal that the principal active species within the Pd/MgAl 2 O 4 -y catalyst is PdO. Specifically, the Pd–MgAl 2 O 4 -1000 catalyst exhibits the lowest temperature reduction peak (120 °C) and the highest redox capability. Additionally, O 2 temperature-programmed oxidation further elucidates that PdO x species in the Pd/MgAl 2 O 4 -1000 catalyst is prone to decomposition and the resultant palladium metal is readily reoxidized. Consequently, the rapidity of the redox cycle between PdO and Pd 0 emerges as a pivotal factor in CH 4 catalytic combustion. Furthermore, a correlation analysis among catalyst particle size, oxygen defect concentration, and TOF is conducted. The findings illustrate a distinct volcano-shaped curve in the relationship between oxygen defect concentration and TOF for the 1Pd/MgAl 2 O 4 −y catalysts. A comparable trend is also evident in the correlation between Pd particle size and TOF.
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