Synthesis,Properties And Characterization Of Cobalt-based Catalysts For Removal Of Formaldehyde At Room Temperature

According to the research progress and problems of cobalt-based catalysts at home and abroad,the Co₃O₄ prepared catalyst by hydrothermal method in this paper.Starting from the process factors affecting the formaldehyde removal performance of Co₃O₄catalyst,the Co₃O₄ catalyst was modified by doping transition metal element?Fe,Cr,Zn?,and the best doped element Zn was selected.Optimization by adopting the method of orthogonal test,the response surface optimization Zn/Co₃O₄ catalyst preparation technology conditions.Investigating the influence of Zn/Co₃O₄ catalyst performance mechanism combined with X-ray diffraction?XRD?,Fourier infrared spectrometer?FT-IR?,Raman spectroscopy?Raman?,N₂-adsorption/desorption,scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray energy spectrometer?XPS?,thermo-gravimetric?TG-DTA?and other characterization.Response surface optimization method was used to optimize the preparation process of Cr/Zn/Co₃O₄ catalyst,and its catalytic mechanism was discussed by combining XRD,FT-IR,Raman and other methods.The main conclusions are as follows:?1?When other preparation processes remain constant,the formaldehyde removal rate of Co₃O₄ catalyst shows a change rule of first increasing and then decreasing with the increase of hydrothermal temperature,hydrothermal time,calcination temperature,calcination time,urea and polyvinylpyrrolidone.When cobalt nitrate was 0.04mol,hydrothermal temperature was 105?,hydrothermal time was 12h,calcination temperature was 300?,calcination time was 8h,urea was 1.5g,polyvinylpyrrolidone was 0.75g,the Co₃O₄ catalyst formaldehyde removal rate was 52.75%.?2?With the increase of the doping amount of iron nitrate,chromium nitrate and zinc nitrate,the removal rate of formaldehyde in M/Co₃O₄?M=Fe,Zn,Cr?catalyst showed a change rule of increasing first and then decreasing.When the doping amount of iron nitrate,chromium nitrate and zinc nitrate was 3×10^-3mol,6×10^-3mol and6×10^-3mol respectively,the removal rate of formaldehyde in the sample reached its maximum value of 54.3%,74%and 81.3%,respectively.Zn/Co₃O₄ and Cr/Co₃O₄samples were composed of pure Co₃O₄ phase,while Fe/Co₃O₄ sample was composed of Co₃O₄ and Fe₂O₃ phase.?3?Orthogonal test was carried out to obtain the order of strength of formaldehyde removal rate of Zn/Co₃O₄ samples by process factors:doping amount of zinc nitrate>calcination temperature>calcination time>hydrothermal temperature>hydrothermal time.The best preparation technology was obtained:cobalt nitrate was 0.04mol,nitric acid zinc doping quantity was 6×10^-3mol,hydrothermal temperature was 115?,hydrothermal time was 8h,calcination temperature was 300?,calcination time was 12h,urea was 1.5g,polyvinylpyrrolidone was 0.75g,the formaldehyde removal rate of Zn/Co₃O₄ catalyst was 86.94%at room temperature.?4?The regression equation of formaldehyde removal rate of Zn/Co₃O₄ samples obtained by response surface method is Y=88.09-0.025A-2.04B-0.23C+2.82AB+1.33AC-0.75BC-10.37A²-10.19B²-5.54C²?R²=0.9467,P<0.0001?.The optimized process conditions as follows:Cobalt nitrate was 0.04mol,zinc nitrate was 5.96×10^-3mol,hydrothermal temperature was 115?,hydrothermal time was 8h,calcination temperature was 294.8?,calcination time was 11.98h,urea was 1.5g,polyvinylpyrroli-done was 0.75g.The mean value of formaldehyde removal rate at room temperature was88.09%,the maximum deviation from the predicted value?88.20%?was 1.51%,and the average deviation was 0.10%,indicating that the prediction result of this model was accurate and reliable.When Zn was doped in Co₃O₄ sample,the surface oxygen vacancy concentration increased from 13.6%to 43.7%,and the specific surface area increased from 43.78m²/g to 60.4m²/g.?5?The regression equation for the removal rate of formaldehyde in Cr/Zn/Co₃O₄sample obtained by response surface methodology was Y=94.76-2.39A+9.31B-2.4C+7.27AB-1.22AC+1.07BC-12A²-14.9B²-5.66C²?R²=0.9778,P<0.0001?.The optimal process condition was obtained:Chromium cobalt nitrate was 0.04mol,nitric acid doping amount was 5.82×10^-3mol,urea content was 0.8g,polyvinylpyrrolidone was1.28g,zinc nitrate doping amount was 6×10^-3mol,hydrothermal temperature was 115?,hydrothermal time was 8h,calcination temperature was 300?,calcination time was 12h.The mean value of formaldehyde removal rate at room temperature was 94.76%,and the maximum deviation from the predicted value of this model?95.82%?was 2.22%,with an average deviation of 1.06%.The predicted results of this model were accurate and reliable.?6?Doping with Zn and Cr could increase the specific surface area of Co₃O₄catalyst from 52.57m²/g to 177.53m²/g,reduce the average pore diameter from 14.64nm to 3.57nm and increase the oxygen vacancy/lattice oxygen?molar ratio?from 0.28 to0.76.The Cr⁶⁺/Cr³⁺molar ratio on the sample surface was 0.09.The formaldehyde removal rate of samples decreased slowly with the increase of test time.After 23h test,the formaldehyde removal rate of samples decreased from 96.6%to 82.9%,which was12h longer than that of Zn/Co₃O₄ samples.