Preparation Of Ni-CeO₂/SiO₂ Nanocomposite And Study On The Catalytic Property Of Methane Dry Reforming

Methane reforming with carbon dioxide can not only make use of natural gas,but also reduce the emission of greenhouse gas,and the syngas produced has a wide application prospect in industry.Among all kinds of catalysts for methane reforming with carbon dioxide,catalysts participated with noble metal have good catalytic performance,but they are not suitable for large-scale industrial applications because of the scarcity of limited reserves,high price and property of sintering loss at high temperature.Among non-noble metal catalysts,nickel-based catalysts are more active than catalysts participated with noble metal,but their anti-coking performance is bad,which easily leads to coke deposition of the catalyst surface and deactivation.Therefore,improving the resistance ability of deposited carbon and enhancing the activity of catalysts and durability of nickel-based catalysts have become the key to our research.In this paper,the catalytic performance of Ni-CeO2/SiO2 catalyst for methane reforming with carbon dioxide was studied:1.Ni-CeO₂/SiO₂ with different proportions were prepared by Ni?NO₃?₂,Na₂SiO₃,Ce?NO₃?₃,HNO₃ and NH₃·H₂O through precipation method.Catalysts were characterized by ICP-OES,XRD,N₂ adsorption/desorption,TEM and HAADF-STEM,EDX mapping,XPS and UV-VIs-NIR spectrophotometer.The results show that Ni-CeO₂/SiO₂ catalyst is mesoporous silica supported Ni nanocrystals modified by ceria clusters.2.The thermalcatalytic activity and durability of Ni-CeO₂/SiO₂ samples with different proportions for methane reforming with carbon dioxide were studied by WFS-2015 gas-phase reactor and GC9560 gas chromatograph.It was found that the catalytic activity of 5%Ni-5%CeO₂/SiO₂ catalyst was the highest between 400 and 750,which was significantly higher than that of the comparative Ni/SiO₂ catalyst.We selected 5%Ni-5%CeO₂/SiO₂ catalyst for thermal stability experiment.381 h after the reaction,the activity of the catalyst decreased slightly at 700,but still show a high conversion of CH₄ and CO₂.The results of TG-MS showed that there was almost no deposited carbont in the samples after the test of durability,which indicated that the Ni nanocrystals modified by CeO₂ clusters effectively inhibited deposited carbon in methane reforming with carbon dioxide,and this property made the catalyst have good thermalcatalytic durability.3.The photothermalcatalytic activity and durability of Ni-CeO2/SiO2 catalysts in methane reforming with carbon dioxide were studied by simulating sunlight with Xe lamp.Ni-CeO2/SiO2 exhibits excellent photothermalcatalytic activity for methane reforming with carbon dioxide under focused UV-visible-infrared and visible-infrared illumination,with a photothermal conversion efficiency of 27.4%.The high photocatalytic activity of Ni-CeO2/SiO2 is due to its high thermalcatalytic activity and high photothermal conversion under UV-visible-infrared illumination.100 h after the reaction,Ni-CeO2/SiO2 catalyst shows good photothermalcatalytic durability and activity,because Ni nanocrystals modified by CeO₂ clusters obviously inhibits the carbon deposition on Ni nanocrystals.The modification of CeO₂ clusters was obtained and confirmed by DFT calculation and isotope labeling experiments.The values of the activation energies?Ea?of C*and CH*oxidation of the intermediate products of the reaction were significantly reduced?from 1.61 and 1.43 to 0.59 and 1.30 eV?,which could inhibit carbon deposition on nickel nanocrystals.Finally,a new photoactivation effect of Ni-CeO₂/SiO₂ in methane reforming with carbon dioxide was revealed,the surface activation energy values(E_{a and ap})of Ni-CeO₂/SiO₂ in methane reforming with carbon dioxide were significantly reduced by illumination.