| The catalytic oxidative activity on acetone solution of transition metal oxides supported on Nano-zirconia was studied in this paper. Modern experimental techniques were used to study its surface structure characters.ZrO2 carrier was prepared by sol-gel method. Zirconium oxychloride was the raw material, using concentrated ammonia to titrate the Zr(OH)4 gel controlling pH about 9. And then it was treated by aging,washing, alcoholized, filtration, drying and calcination. This method solved the reduction of the catalysts surface area during the heating process from Zr(OH)4 to ZrO2. Use different transition metal nitrate solutions as raw materials with impregnation method to prepare the supported nano-composite oxidative catalysts.TEM, SEM, BET, XRD, TG-DSC, UV-Raman and IR were used to characterize the catalysts. From TEM and SEM results, it was found that: homogeneous catalyst particles, about the size of 20nm, honeycomb surface of the porous structure. It was indicated that the structure of carrier was stable in the preparation process, without the effects of impregnation, calcination and other processes. BET results show that specific surface area was affected by the loading of manganese. With manganese's loading increasing, the specific surface area declined. The specific surface area varied from 44.2m2/g to 32.9m2/g. The reason might be the reunite of active component, covering and the porous of carrier's plugging. Calcination temperature and time on the specific surface area are of no effect. XRD results show that there's no Mn2O3 characteristic diffraction peak at 450℃calcination, but it appears after 550℃. And with the increasing of temperature, the intensity of diffraction peak grows. The TG-DSC spectra of Mn(NO3)2/ZrO2 show that there is a major endothermic peak without quality loss during 520°C～720℃. Combined with the XRD result, it was obtained that the peak is from the change of amorphous to crystal Mn2O3. The UV-Raman results discovered that when manganese nitrate load on the zirconium oxide, the temperature of manganese nitrate decomposed into Mn2O3 species dropped. IR results showed that after loading of manganese, the stretching vibration absorption frequencies of Zr-O bond moved to high wave number, from 504.20cm-1 to 507.32 cm-1 . Bending and stretching vibration of–OH also has migration, the former from 1630.09 cm-1 moved to 1636.04 cm-1, and the latter from 3424.59 cm-1 to 3423.08 cm-1. It illustrates that there is interaction between manganese and carrier. The IR result explains the UV-Raman phenomenon further.The oxidation of acetone aqueous was taken as the probe reaction to evaluate catalytic activity of catalysts. A variety of transition metal oxide (Mn, Ni, Cu, Fe, Co,Cr) catalysts were stedied for the initial screening,. From the reaction results, it was found that the catalyst for the oxidation of acetone showed well catalytic activity. On this basis, we draw the conclusion that Mn2O3/ZrO2 had the better catalytic activity than others. The preparation conditions such as contents,calcination temperature and time on the activity of catalyst were inspected. According to the experimental results, we got the best conditions: 6% manganese loading, calcination temperature of 450°C, 6 hours of baking, the conversion of acetone reached 77%. The experiment also studied the reaction temperature,reservation time and using times to the effect of catalytic oxidation of acetone. With the reaction temperature increasing acetone's conversion improved. The conversion was 43%, 46%, 60%, 77% and 78% respectively at 20℃, 30℃, 40℃, 50℃, 60℃. From 30℃to 50℃the reaction temperature affected the conversion obviously. From 50℃to 60℃the conversion only increased by 1%.The conversion of acetone dropped from 77% to 67%, when the catalyst was reserved 6 months. The activity of catalyst dropped by 15% compared the second times to the first times. It was 62% and 56% at the second and the third times. The activity declined obviously at the forth times.The catalysts prepared in this paper has many advantages such as homogeneous particle, steady configuration and high catalytic activity. Amorphous species Mn2O3 was the activity center of catalyst. There is interaction between manganese and carrier.
|
PDF Full Text Request