Tailoring Supported Pt-based Catalysts For Efficient Toluene Catalytic Combustion

Volatile organic compounds（VOCs）are the crucial precursors to form secondary organic aerosol and ozone,which is deleterious to the health of human beings.It is urgent to develop effective elimination technologies to restrain the emissions of VOCs to reduce the atmosphere pollution.Catalytic combustion plays an essential role in the treatment of VOCs due to its advantages of high efficiency and minimal secondary pollution.The biggest challenge is to develop highly active catalysts for the low-temperature combustion of VOCs.Supported Pt catalysts exhibit outstanding catalytic performance for VOCs combustion.However,the scarcity and high cost of Pt-based catalysts are the main concerns hindering the wide application of supported Pt catalysts.Hence,the design of highly efficient low Pt-content supported Pt catalysts is the main challenge of the VOCs catalytic combustion.In this thesis,the supported Pt catalysts were designed by tailoring the structure and chemical state of the Pt.Low-content Pt catalysts with excellent low temperature catalytic performance were developed and the structure-activity relationship of the catalysts was well studied.The toluene combustion mechanism over the as-prepared Pt catalysts was revealed by the in situ diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）.The major results are given below:（1）Pt nanoparticles（NPs）with uniform particle size were prepared by ethylene glycol reduction method and loaded on BN（Pt NPs/BN-E）.Comparing with the impregnation method（Pt/BN-E）,the Pt NPs prepared by ethylene glycol reduction method had better dispersity.The excellent distribution of Pt NPs on Pt NPs/BN sample made it easy to be reduced by H₂,and thus Pt NPs/BN possessed more active Pt⁰ species which could promote the activation and oxidation of toluene.However,it was difficult for the Pt on Pt/BN-E to be reduced by H₂,due to agglomeration of Pt.The inert Pt²⁺species on Pt/BN-E blocked the catalytic combustion of toluene at low temperature.In situ DRIFTS connecting with mass spectrometry was conducted to investigate the reaction mechanism of toluene over Pt/BN catalyst.The inert Pt²⁺species on Pt/BN-E hindered the conversion of benzaldehyde to benzoic acid and inhibited the ring opening of benzene,resulting in poor catalytic activity.However,the active Pt⁰ species on Pt NPs/BN could accelerate the oxidation of benzaldehyde and the ring-opening process of benzene in toluene oxidation.Therefore,Pt NPs/BN shown high activity for the toluene catalytic combustion.（2）Exploring highly efficient and low-cost supported Pt catalysts is attractive for the application of VOCs combustion.Herein,efficient catalytic combustion of toluene at low temperature over Pt/γ-Al₂O₃catalysts has been demonstrated by tailoring active Pt species spatially.Pt/γ-Al₂O₃catalyst with low Pt-content（0.26 wt%）containing both interfacial Pt-Al（OH）_x and surficial metallic Pt（Pt⁰）species exhibited super activity and water-resistant stability for toluene oxidation.The strong metal-support interaction located at the Al-OH-Pt interfaces elongated the Pt-O bond and contributed to the oxidation of toluene.Meanwhile,the OH group at the Al-OH-Pt interfaces had the strongest adsorption and activation capability for toluene and the derived intermediate species were subsequently oxidized by oxygen species activated by surficial Pt⁰ to yield carbon dioxide and water.（3）γ-Al₂O₃ was modified with Ni by co-precipitation method,and Ni Al₂O₄ spinel was successfully prepared.A certain size of Pt NPs（0.25 wt%）was supported on as preparedγ-Al₂O₃ and Ni Al₂O₄ by one-step ethanol impregnation method.The presence of Ni effectively enhanced the metal-support interaction between Pt and Ni Al₂O₄.The strong metal-support interaction between Pt and Ni Al₂O₄ improved the oxidation capability of the Pt-M（OH）_x（M=Al,Ni）species and the lattice oxygen of Pt/Ni Al₂O₄-E,which facilitated the oxygen storage and oxygen activation capacity of Pt/Ni Al₂O₄-E.Therefore,Pt/Ni Al₂O₄-E displayed excellent catalytic performance for toluene combustion at low temperature.In situ DRIFTS revealed the mechanism of catalytic combustion of toluene over Pt/Ni Al₂O₄-E.The Pt-M（OH）_x and lattice oxygen in Pt/Ni Al₂O₄-E could promote the oxidation process of benzaldehyde to benzoic acid and accelerate the ring-opening of toluene at low temperature.