Preparation Of The New M（Ru,Pt）-CeO₂ Based Catalyst And Its Application In The Degradation Of Typical VOCs

Noble metal-cerium based[M（Pd,Pt,Ru,Rh etc.）-CeO₂]catalysts are widely used in the study of catalytic oxidation.Due to the excellent ability of CeO₂ to store and transport oxygen and the strong interaction between noble metal and CeO₂,the introduction of CeO₂ can significantly improve the catalytic reaction process and even change the catalytic oxidation pathway.At present,M-CeO₂ based catalysts supported on high-performance materials have become a hot research topic in the field of catalysis.A series of physicochemical properties of supports,such as specific surface area,pore structure,surface acidity,thermal stability,chemical stability and interaction with precious metals,significantly affect the dispersion state of precious metal nanoparticles The high temperature stability and the diffusion of reactants and products significantly affect the catalytic activity and a series of catalytic performance of noble metal based catalysts.In this work,two new M（Ru,Pt）-CeO₂ based catalysts were designed and applied to the catalytic oxidation of VOCs.Their catalytic combustion performance and oxidation mechanism were explored,and a series of meaningful research results were obtained:（1）Firstly,nano-flower sheet-like alumina（NF-Al₂O₃）was synthesized by hydrothermal method,and then a series of Ru-CeO_x supported nano flak nano-flower sheet-like alumina catalysts（Ru-CeO_x/NF-Al₂O₃）were synthesized by deposition precipitation method for the total oxidation of propane.The activity and stability of the series of catalysts were evaluated,and characterized by XRD,Raman,XPS,NMR,electron microscopy and so on.The results show that the 90%conversion temperature(T₉₀)of Ru-Ce₇/NF-Al₂O₃ is as low as 207 ^oC,and the apparent activation energy of Ru-Ce₇/NF-Al₂O₃ is as low as 56.7 k J mol^-1 in the kinetic conditions of mass and heat transfer are excluded.Compared with conventional Ru/Al₂O₃-Con catalysts,NF-Al₂O₃ rich in penta coordinated Al³⁺(Al³⁺_penta)supported Ru catalysts have higher total propane oxidation performance and lower apparent activation energy（Ea）,and the introduction of Ru-CeO_x interface further improves its catalytic activity.In addition,Ru-CeO_x/NF-Al₂O₃ also showed excellent water resistance,sulfur resistance,carbon dioxide resistance and recycling performance.The excellent catalytic performance of Ru-CeO_x/NF-Al₂O₃ for propane oxidation is not only due to the introduction of Ru-CeO_x interface with rich active oxygen,but also due to the rich mesopores of NF-Al₂O₃ support,which greatly improves the mass transfer efficiency.Equally important,NF-Al₂O₃ is rich in unsaturated pentacoordinated Al³⁺anchor sites.The anchoring effect of Al³⁺_penta on metal active units can effectively promote the dispersion of Ru-CeO_x active species and stabilize the electronic valence of Ru⁰,which is the main reason for its excellent propane degradation performance.Finally,the in situ DRIFTS confirmed that the mechanism of propane oxidation catalyzed on Ru-CeO_x/NF-Al₂O₃ was consistent of the Mars van Krevelen（MVK）mechanism,and the active oxygen species on the Ru-CeO_x interface participated in the whole redox cycle.（2）A core-shell structure Pt-CeO_x@S-1 catalyst with multistage pore structure was successfully synthesized by temperature programmed dry gel crystallization without mesoporous template.The activity and stability of the series of catalysts were evaluated and characterized by XRD,Raman,XPS,electron microscopy and other testing techniques.The 90%conversion temperature(T₉₀)is as low as 207 ^oC,and the apparent activation energy is as low as 56.7 k J mol^-1.HRTEM and UC-HAADF-STEM clearly demonstrated the Pt-CeO_x@S-1 The Pt-CeO_x are uniformly distributed in the mesopores.The catalytic activity of Pt-CeO_x@Si O₂ was significantly higher than that of Pt@Si O₂,which was attributed to the excellent ability of CeO₂ to store and transport oxygen,so that the active interface was improved.The catalytic activity of Pt-CeO_x@S-1 after transcrystallization was further improved significantly,The reasons were as follows:firstly,the in situ concentration/catalytic bifunctional strategy significantly accelerates the reaction process;secondly,the mass transfer effect of reactant and product molecules was enhanced by the presence of a large number of intragranular mesopores;Thirdly,the presence of a large number of surface hydroxyl groups（-OH）provides more reactive oxygen species[O]and speeding up the reaction.In addition,Pt-CeO_x@S-1 showed excellent recycling performance,long-term stability performance,water resistance performance and high temperature sintering resistance performance,which is mainly due to the existence of multi-stage pore structure and the confinement effect on active components.Finally,the in situ DRIFTS showed that the mechanism of Pt-CeO_x@S-1 catalytic toluene oxidation conforms to the Mars van Krevelen（MVK）mechanism,and the O-from the Pt-CeO_x interface and the reactive oxygen species[O]from the surface hydroxyl group were involved in the whole redox cycle.