Preparation And Catalytic Performance Of 3DOM CoFe₂O₄-and 3DOM LaMnAl₁₁O₁₉-Supported Noble Metal Alloy Catalysts For Methane Oxidation

Natural gas is considered as the main complementary energy in the 21 century.As the main composition,direct combustion of methane needs high temperatures,generating atmosphere pollutants.Catalytic methane combustion technology can decline the light-off temperatures and peak temperatures of fuel combustion and improve the utilization efficiency of methane combustion,in which the key issue is the availability of high-performance catalysts.In recent years,spinel-type?AB₂O₄?cobalt ferrites and hexaaluminates have gained much attention due to their cheapness and stability.It has been reported that the CoFe₂O₄ materials with different morphologies?e.g.,nanoparticles and meso-or macropores?and hexaaluminate nanoparticles were successfully prepared.To the best of our knowledge,no works related to the use of 3DOM AB₂O₄ and 3DOM LaMnAl₁₁O₁₉ for CH₄ combustion have been reported in the literature.In this thesis,3DOM CoFe₂O₄,3DOM LaMn Al₁₁O₁₉,zMnO_x/3DOM CoFe₂O₄?z=4.99-12.3 wt%,MnO_x=Mn₂O₃ or MnO₂?,yPd-Pt/6.70MnO_x/3DOM CoFe₂O₄?y=0.44-1.81 wt%?,and xAuPd_y/3DOM LaMn Al₁₁O₁₉?x=0.44-1.91 wt%;y=1.80-1.86?catalysts were prepared using the polymethyl methacrylate?PMMA?-templating,incipient wetness impregnation,and gas bubble-assisted polyvinyl alcohol?PVA?-protected reduction strategies.Physicochemical properties of the samples were characterized by means of various techniques,such as inductively coupled plasma-atomic emission spectroscopy?ICP-AES?,X-ray diffraction?XRD?,N₂ adsorption–desorption?BET?,scanning or transmission electron microscopy?SEM or TEM?,photoelectron spectroscopy?XPS?,and H₂ temperature-programmed reduction?H₂-TPR?.Catalytic performance of the samples was measured for methane combustion.The main results obtained in the thesis are as follows:?1?3DOM CoFe₂O₄,zMnO_x/3DOM CoFe₂O₄?z=4.99-12.30 wt%?,and yPd-Pt/6.70 wt%MnO_x/3DOM CoFe₂O₄?y=0.44-1.81 wt%;Pd/Pt molar ratio=2.1-2.2?were prepared using the PMMA-templating,incipient wetness impregnation,and gas bubble-assisted PVA-protected reduction methods,respectively.It is shown that the as-prepared samples exhibited a high-quality 3DOM structure?103±20 nm in pore size?,the CoFe₂O₄ in the samples was cubic in crystal structure,and the samples displayed a surface area of 19-28 m²/g.The MnO_x nanoparticles?NPs,18.0-20.0 nm in diameter?and noble metal or alloy NPs with a size of 2.2-3.0 nm were uniformly dispersed on the macropore wall surface of the support.The1.81Pd_2.1Pt/6.70MnO_x/3DOM CoFe₂O₄ sample showed the highest catalytic activity(T_10%=255 ^oC,T_50%=301 ^oC,and T_90%=372 ^oC at a space velocity of 20,000 mL/?g h?).Itisconcludedthattheexcellentcatalyticperformanceof1.81Pd_2.1Pt/6.70MnO_x/3DOM CoFe₂O₄ was associated with its well-dispersed Pd-Pt alloy NPs,high adsorbed oxygen species concentration,good low-temperature reducibility,and strong interaction between MnO_x or Pd-Pt NPs and 3DOM CoFe₂O₄.?2?3DOM LaMnAl₁₁O₁₉ and xAuPd_y/3DOM LaMnAl₁₁O₁₉?x=0.44-1.91 wt%;y=1.80-1.86?were prepared via the PMMA-templating and gas bubble-assisted PVA-protected reduction routes.The La MnAl₁₁O₁₉ in the samples were hexagonal in crystal structure,and all of the samples showed a good-quality 3DOM architecture with a surface area of 24.4-28.2 m²/g.The Au-Pd NPs with a size of about 2.8 nm were uniformly dispersed on the wall surface of 3DOM LaMnAl₁₁O₁₉.The1.91AuPd_1.80/3DOM LaMnAl₁₁O₁₉ sample performed the best(T_50%=342 ^oC and T_90%=402 ^oC at a space velocity of 20,000 mL/?g h?).The good catalytic activity of1.91AuPd_1.80/3DOM LaMnAl₁₁O₁₉ was associated with its high adsorbed oxygen species concentration,good low-temperature reducibility,and strong interaction between Au-Pd alloy NPs and 3DOM LaMnAl₁₁O₁₉.