具有良好热稳定性的Al_2O_3改性Fe_2O_3基金催化剂

Al_2O_3-Modified Fe_2O_3 Based Gold Catalysts with Good Thermal Stability

通过共沉淀法和沉积-沉淀法制备出了具有良好热稳定性的Al2O3改性Fe2O3基金催化剂,并通过透射电镜(TEM)、X射线衍射(XRD)、N2吸附-脱附及热重和差示扫描量热(TG-DSC)分析等表征手段对催化剂的结构与表面形貌进行了研究分析.TEM测试结果表明:500℃焙烧后,未掺杂Al2O3的催化剂中金颗粒粒径分布较宽,平均粒径约为7.0nm,载体颗粒尺寸在50-100nm范围内;而掺杂Al2O3的催化剂中金颗粒粒径分布变窄,平均粒径约为5.0nm,且载体颗粒大小也明显小于未掺杂Al2O3的催化剂,保持在30-50nm的范围内.N2吸附-脱附测试结果表明,Al2O3的掺杂有利于保持催化剂的介孔结构和比表面积,从而提高了载体的热稳定性.XRD和TG-DSC测试结果表明,Al2O3的掺杂可以有效地抑制Fe2O3的结晶,进而抑制了高温焙烧过程中金颗粒的长大.选用CO低温氧化反应对催化剂的活性进行了评价,即使在500℃高温下焙烧12h,掺杂了Al2O3的催化剂仍然可在26.7℃将CO完全转化,而未掺杂Al2O3的催化剂CO最低完全转化温度(T100)高达61.6℃.Al2O3的掺杂显著提高了催化剂的热稳定性能.

Al2O3-modified Fe2O3 based gold catalysts with good thermal stability were prepared by co-precipitation and deposition-precipitation method.Characterization techniques,such as transmission electron microscope（TEM）,X-ray diffraction（XRD）,N2 adsorption-desorption,and thermogravimetry-differential scanning calorimetry（TG-DSC）,were used to investigate the structures,and surface morphologies of the catalysts.TEM results showed that after calcination at 500 ℃ the size distribution of the gold particles in the catalyst without Al2O3 doping was wide,the average diameter of the gold particles was about 7.0 nm and the size of the support particles ranged from 50 to 100 nm.However,the size distribution of the gold particles in the Al2O3-doped catalysts was narrow and the average diameter of the gold particles was around 5.0 nm.The Al2O3-doped Fe2O3 based Au particle size remained in a range of 30-50 nm,which is smaller than that of the Fe2O3 grains that were not doped with Al2O3.N2 adsorption-desorption measurements showed that Al2O3 doping resulted in a stable mesoporous structure for the catalysts and remained a higher specific surface area,which promoted the thermal stability of the support.XRD and TG-DSC results indicated that Al2O3 doping retarded the crystallization of the support and consequently inhibited the growth of gold particles during high-temperature calcination.Low temperature CO oxidation was used as a probe reaction to evaluate the catalytic activity.Even when calcined at 500 ℃ for 12 h,the catalyst with Al2O3 doping achieved complete CO conversion at 26.7 ℃ while the lowest temperature of the complete CO conversion（T100） of the catalyst without Al2O3 doping was as high as 61.6 ℃.Apparently,thermal stability is enhanced considerably by Al2O3 doping.