Ultrafine α-Fe2O3 particles were prepared from l.0 mol/L Fe（OH）3 gel by dispelling oven hydrothermal method and characterized by measurement of SEM and XRD.The results showed that the reactions could be finished at...Ultrafine α-Fe2O3 particles were prepared from l.0 mol/L Fe（OH）3 gel by dispelling oven hydrothermal method and characterized by measurement of SEM and XRD.The results showed that the reactions could be finished at 148℃ in 30～90 minutes,anions of iron（Ⅲ）salts and original pH values in suspension had remarkable effects on the morphology and size of α-Fe2O3 particles.Using FeCl3 as starting raw material,the pesudocubic particles with the mean size of 350 nm were obtained at pH 2.5 and the spherical particles with the mean size less than 170 nm were produced above pH 6.0.At the same time,using FeSO43 and Fe(NO3)3 as starting raw materials at pH 2.5,the resulting products were ellipsoidal particles with the mean size of 100 nm and spherical particles with the mean size of 120 nm,respectively.展开更多
To facilitate the recovery of Pb/SiO_(2) catalyst,magnetic Pb/Fe_(3)O_(4)/SiO_(2) samples were prepared separately by emulsification,sol-gel and incipient impregnation methods.The catalyst samples were characterized b...To facilitate the recovery of Pb/SiO_(2) catalyst,magnetic Pb/Fe_(3)O_(4)/SiO_(2) samples were prepared separately by emulsification,sol-gel and incipient impregnation methods.The catalyst samples were characterized by means of X-ray diffraction and N_(2) adsorption-desorption,and their catalytic activity was investigated in the reaction for synthesizing propylene carbonate from urea and 1,2-propylene glycol.When the gelatin was applied in the preparation of Fe_(3)O_(4) at 60℃ and the pH value was controlled at 4 in the preparation of Fe_(3)O_(4)/SiO_(2),the Pb/Fe_(3)O_(4)/SiO_(2) sample shows good catalytic activity and magnetism.Under the reaction conditions of a reaction temperature of 180℃,reaction time of 2h,catalyst percentage of 1.7 wt-% and a molar ratio of urea to PG of 1∶4,the yield of propylene carbonate attained was 87.7%.展开更多
In this study,we prepared Fe_(2)O_(3)-Nb_(2)O_(5)binary mixed oxide catalysts using co-precipitation(CP),sol-gel(SG),and solid process(SR)methods and tested their performance.All the catalysts exhibited over 75%NO_(x)...In this study,we prepared Fe_(2)O_(3)-Nb_(2)O_(5)binary mixed oxide catalysts using co-precipitation(CP),sol-gel(SG),and solid process(SR)methods and tested their performance.All the catalysts exhibited over 75%NO_(x)removal efficiency between 250℃and 400℃.Compared with the samples prepared by the SR method,catalyst synthesized using CP and SG methods possessed a larger specific surface area,which could compensate for the lower surface area-normalized reaction rate originat-ing from the insufficient reactive surface oxygen species,hence exhibiting a relatively high low-temperature apparent deNO_(x)activity.However,at a high-temperature region,limited amount of reactive surface oxygen species,together with abundant strong acid sites,facilitated the proceeding of NH_(3)reduction of NO_(x),which well explained the higher apparent activity of the catalyst prepared by SG method than the other two samples.It seemed that specific surface area had an important role to play in the low-temperature apparent performance of the catalysts,while chemical properties mainly decided the activity at an elevated temperature.展开更多
文摘Ultrafine α-Fe2O3 particles were prepared from l.0 mol/L Fe（OH）3 gel by dispelling oven hydrothermal method and characterized by measurement of SEM and XRD.The results showed that the reactions could be finished at 148℃ in 30～90 minutes,anions of iron（Ⅲ）salts and original pH values in suspension had remarkable effects on the morphology and size of α-Fe2O3 particles.Using FeCl3 as starting raw material,the pesudocubic particles with the mean size of 350 nm were obtained at pH 2.5 and the spherical particles with the mean size less than 170 nm were produced above pH 6.0.At the same time,using FeSO43 and Fe(NO3)3 as starting raw materials at pH 2.5,the resulting products were ellipsoidal particles with the mean size of 100 nm and spherical particles with the mean size of 120 nm,respectively.
基金This work has been supported by the National Natural Science Foundation of China(Grant No.20576025)the Hebei Provincial Fund for Natural Science(B2007000010).
文摘To facilitate the recovery of Pb/SiO_(2) catalyst,magnetic Pb/Fe_(3)O_(4)/SiO_(2) samples were prepared separately by emulsification,sol-gel and incipient impregnation methods.The catalyst samples were characterized by means of X-ray diffraction and N_(2) adsorption-desorption,and their catalytic activity was investigated in the reaction for synthesizing propylene carbonate from urea and 1,2-propylene glycol.When the gelatin was applied in the preparation of Fe_(3)O_(4) at 60℃ and the pH value was controlled at 4 in the preparation of Fe_(3)O_(4)/SiO_(2),the Pb/Fe_(3)O_(4)/SiO_(2) sample shows good catalytic activity and magnetism.Under the reaction conditions of a reaction temperature of 180℃,reaction time of 2h,catalyst percentage of 1.7 wt-% and a molar ratio of urea to PG of 1∶4,the yield of propylene carbonate attained was 87.7%.
文摘In this study,we prepared Fe_(2)O_(3)-Nb_(2)O_(5)binary mixed oxide catalysts using co-precipitation(CP),sol-gel(SG),and solid process(SR)methods and tested their performance.All the catalysts exhibited over 75%NO_(x)removal efficiency between 250℃and 400℃.Compared with the samples prepared by the SR method,catalyst synthesized using CP and SG methods possessed a larger specific surface area,which could compensate for the lower surface area-normalized reaction rate originat-ing from the insufficient reactive surface oxygen species,hence exhibiting a relatively high low-temperature apparent deNO_(x)activity.However,at a high-temperature region,limited amount of reactive surface oxygen species,together with abundant strong acid sites,facilitated the proceeding of NH_(3)reduction of NO_(x),which well explained the higher apparent activity of the catalyst prepared by SG method than the other two samples.It seemed that specific surface area had an important role to play in the low-temperature apparent performance of the catalysts,while chemical properties mainly decided the activity at an elevated temperature.
