Preparation And Characterization Of Manganese-based Catalysts For Removing Of Formaldehyde

According to the development and shortcoming of removing formaldehyde with manganese base catalysts at home and abroad,in this paper,the M/MnO₂?M=Cr,Cu,Zn?,Ag/Cr/MnO₂ and Ce/Cr/MnO₂ catalysts were prepared by hydrothermal co-precipitation method.The effects of the technologic factors of the chromium to manganese molar ratio,hydrothermal temperature,hydrothermal time,calcination temperature and time on the formaldehyde removal rate of Cr/MnO₂ catalyst at room temperature were investigated by single-factor experimental method,and the preparation process of Ag/Cr/MnO₂ and Ce/Cr/MnO₂ catalysts were optimized by response surface experiment.The structure,microstructure,surface functional groups and thermal stability properties of the manganese base catalysts were investigated by using the X-ray diffractometer?XRD?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,Raman spectrometer?Raman?,Fourier transform infrared Spectrometer?FT-IR?and thermogravimetric analyzer?TG-DTA?,and the oxidation mechanism of the manganese base catalysts for for removing formaldehyde at room temperature was also discussed this paper.The results were showed as the following:?1?The formaldehyde removal rate at room temperature of the Cr/MnO₂ sample would increase and then decrease with increasing in the addition of ammonia water,Cr/Mn molar ratio,the hydrothermal temperature,the calcination temperature,or with prolonging in the hydrothermal time and calcination time.?2?The maximum formaldehyde removal rate at room temperature of the Cr/MnO₂ sample is 71.5%when the preparation prceoss is 5mL of 0.1mol/L sodium oxalate,the Cr/Mn molar ratio is 1:1,the ammonia water addition amount is 0.5mL,the hydrothermal temperature is 90?,the hydrothermal time is 6h,the calcination temperature is 400?and the calcination time is 3h.?3?The best optimization process of the Ag/Cr/MnO₂ sample is:5mmol of potassium permanganate,4.1mmol of Cr,0.445mmol of Ag,and precipitant 0.1mol/L sodium oxalate 5mL,5mol/L of ammonia 0.5mL,hydrothermal temperature 85.99?,hydrothermal time 6h,calcination temperature 224.82?,calcination time 3h,and the range of formaldehyde removal rate at room temperature of the Ag/Cr/MnO₂ catalyst is 92.35%-94.78%,and the average deviation from the predicted value?94.65%?is1.31%,which indicates that the predicted value of the model is more reliable.?4?The best optimization process of Ce/Cr/MnO₂ catalyst is:5mmol of potassium permanganate,0.50mmol of Cr,0.75mmol of Ce,and 0.1mol/L sodium oxalate 5mL,5mol/L ammonia water 0.5mL,hydrothermal temperature 90?,hydrothermal time 3.59h,calcination temperature 400?,calcination time 3.75h,and the range of room temperature formaldehyde removal rate of the prepared Ag/Cr/MnO₂ catalyst is 93.57%-95.68%,which the average deviation from the predicted value?95.13%?is 0.75%.The prediction results of this model is more accurate and reliable.?5?The formaldehyde removal rate at room temperature of the Ag/Cr/MnO₂ and Ce/Cr/MnO₂ samples would gradually decreased with the increase of the number of cycles,and after 6 cycles,the formaldehyde removal rate of the specimen from 94.78%and 95.31%to 89.10%and 91.12%,which decrease by 5.68%and 4.19%,respectively,which have better stability of removing formaldehyde at room temperature,and the stability of Ce/Cr/MnO₂ catalyst is better.?6?Ag/Cr/MnO₂ sample is composed of amorphous phase and MnO₂ crystal phase,and the weight loss rates of sample are 9%,1.73%,and 5.79%within the room temperature to 120?,120-500?,and 500-780?,respectively.Ce/Cr/MnO₂ sample is composed of amorphous phase,and the weight loss rates of sample are 5.85%,2.79%,and 4.54%within the room temperature to ?140?,140-480?,and480-780?,respectively.Ag/Cr/MnO₂ and Ce/Cr/MnO₂ specimen were all spherical,and which have intermolecular hydrogen bonding O-H stretching vibration,C-H stretching vibration,C=O stretching vibration and C-H bending vibration at3342.41cm^-1,2925.21cm^-1,1633.05cm^-1 and 140.03 cm^-1,respectively.