Preparation Of N₂O On Supported Pt-based Catalysts

As the saying goes,everything has two sides.On the one hand,laughing gas is an environmentally harmful gas that can indirectly cause the ozone hole or the greenhouse effect.On the other hand,laughing gas is widely used in medical,cosmetic,food,Chemical industry,military industry and other fields.The traditional laughing gas generation include NH3 oxidation,NO reduction,nitrate-concentrated sulfuric acid treatment of urea and NH4NO3 thermal decomposition.However,there are still many problems that remain to be solved.For example,there are many by-products such as NO during the oxidation of NH3,the thermal decomposition of NH4NO3 is prone to be explosive,the energy consumption of NO reduction is high,the nitrate-concentrated sulfuric acid treatment of urea can cause serious environmental pollution.Based on there are no currently low-cost and efficient production of laughing gas,and inspired by the SCR denitrification process,a series of Pt/CeO2 and Pt/TiO2 catalyst powders were generated by hydrothermal method combined with solid grinding method.The feasibility of preparing N2O by ammonia,NO and oxygen is discussed.The structure and performance of the Pt-based sample are tested by X-ray diffraction(XRD),inductively coupled plasma spectrometer(ICP),Brunner Ermmet Teller(BET),transmission electron microscopy(TEM),temperature programed reduction(TPR),X-ray photoelectron spectroscopy(XPS),and temperature programmed desorption(TPD).And the conditions of the reaction of laughing gas are controlled.The conclusions mainly include:(1)A series of Pt/CeO2 and Pt/TiO2 catalysts with high Pt dispersion were generated by hydrothermal method with solid grinding method.On both catalysts,the selectivity of N2O increases first and then decreases with the loading of Pt.Among them,Pt/CeO2 has the highest efficiency of generating N2O at 0.5%Pt loading.Pt/TiO2 has the highest catalytic efficiency at 1.0%loading.In addition,unlike Pt/CeO2,Pt/TiO2 still has higher efficiency for laughing gas production under anaerobic conditions.(2)It was found that both Pt/TiO2 and Pt/CeO2 have good NH3 and NOx adsorption properties through a series of characterization methods.During the process of N2O formation,NH3 and NO were present on the surface of the catalyst in the form of adsorption at a temperature not exceeding 400°C,which proved that the catalytic reaction of laughing gas production abide by the Langmuir-Hinshelwood mechanism.(3)Conditions during the reaction such as temperature,oxygen concentration,and gas ratio play a crucial role in the selectivity of laughing gas.For Pt/Ce02 catalysts,the suitable reaction conditions for the formation of N2O are:[NO]/[NH3]= 1/2,[O2]= 5 vol%and Temperature = 275℃.For Pt/TiO2 catalysts,the best factors during the reaction for the generation of N2O are:[NO]/[NH3]= 1/2,[O2]= 1 vol%and Temperature=250℃.