Oxidation Mechanism And Experimental Studies Of Carbon-based Single Atom Iron Catalyst For Removal Of Formaldehyde

Indoor air quality is an important factor affecting human health.Formaldehyde（HCHO）is one of the most common indoor air pollutants,has been the subject of concern.Staying indoors with low concentration of HCHO for a long time will cause great health threat to human body.Catalytic oxidation method is a promising method for effectively removing indoor HCHO.Generally,noble metal catalysts can catalyze the oxidation of HCHO at room temperature,but the high cost of noble metals limits their wide application.Metal oxide catalysts have cost advantages,but their activity at low temperatures cannot meet the requirements.The development of low-cost,high-activity HCHO oxidation catalysts is still an important research direction.Therefore,based on the high activity and high metal utilization rate of the single atom catalysts,this thesis innovatively proposed the use of Fe-N doped carbon-based single atom catalysts for catalytic oxidation of HCHO.Density functional theory（DFT）calculations and fixed-bed activity evaluation experiments were used to study the performance of Fe-N doped carbon-based single atom catalysts for the catalytic oxidation of HCHO.The reaction mechanism of HCHO catalytic oxidation was revealed,and the effects of temperature and humidity on the conversion of HCHO were studied.It provides a new idea and theoretical guidance for the development of new carbon-base single atom catalysts for the catalytic oxidation of HCHO.Firstly,three kinds of Fe-N doped single-vacancy（SV）and double-vacancy（DV）models,Fe/SV-N3,Fe/DV-N4 and Fe/DV-N4.5,were established and optimized in this thesis,and their structural stability was verified.The adsorption characteristics of HCHO,O₂,H₂O and CO₂ on the surface of three kinds of catalysts were analyzed.And the results show that the stability order of the three is Fe/DV-N4.5>Fe/DV-N4>Fe/SV-N3,the order of adsorption performance is Fe/SV-N3>Fe/DV-N4>Fe/DV-N4.5.Then,based on the Langmuir-Hindhelwood（L-H）and Eley-Rideal（E-R）mechanisms,the oxidation reaction mechanisms of HCHO on the surfaces of the three catalysts were studied.In detail,the possible reaction paths of HCHO oxidation were searched,including the structure and energy of each reaction step.And the effect of temperature on reaction rate was analyzed.The results show that the dominant reaction mechanism of Fe/SV-N3 is L-H mechanism,and the latter two are both E-R mechanism.The highest energy barriers for the rate determining steps are1.09 eV,0.66 eV and 0.58 eV,respectively.And temperature has a promoting effect on the reaction rate.In view of the high activity of Fe/DV-N4.5 and the weak physical adsorption of H₂O and CO₂,Fe/DV-N4.5 was determined as the experimental research object.Finally,Fe-N-C catalyst sample was synthesized using pyrolytic organometallic frame material.And the results of powder X-ray diffraction and X-ray absorption fine structure spectroscopy show that the catalyst sample is consistent with the predicted Fe/DV-N4.5 configuration.The catalytic activity and stability of the catalyst sample for formaldehyde oxidation were studied by atmospheric fixed bed experiments.The results show that under the reaction conditions of 25℃,initial HCHO concentration of 60 ppm,space velocity of 73000 h^-1 and 75%RH,the HCHO conversion rate is85%.Fe-N-C catalyst has the ability to catalyze the oxidation of HCHO at room temperature,and the humidity has no obvious effect on the catalytic activity.The activity of Fe-N-C catalyst decreases gradually with the passage of reaction time,which may be caused by the occupation of active sites by some intermediate products produced in the reaction process.