镓掺杂SO_4^(2-)/ZrO_2的制备及其对正丁烷异构化反应的催化性能

Preparation of Gallium-Promoted SO_4^(2-)/ZrO_2 and Its Catalytic Performance for Isomerization of n-Butane

通过沉淀、回流和浸渍法制备了镓掺杂的纳米级固体超强酸SO2 -4/Ga2 O3 /ZrO2 ,并用X射线衍射、透射电镜、热重、吡啶吸附红外光谱、低温N2 BET及化学分析等技术对SO2 -4/Ga2 O3 /ZrO2 的结构、表面性质及其对正丁烷异构化反应的催化活性进行了研究 .结果表明 ,掺杂Ga2 O3 可以抑制制备过程中ZrO2 晶粒长大 ,有利于抑制高温下催化剂由四方相转变为单斜相 .与未掺杂的催化剂相比 ,Ga2 O3 的掺杂提高了催化剂表面SO2 -4的分解温度 ,有利于催化剂表面形成更多的酸中心 .SO2 -4/Ga2 O3 /ZrO2 对正丁烷异构化反应显示出优异的催化性能 .其中 ,含 3%Ga2 O3 的样品的活性最高 ,2 2 0℃下其初活性为5 9 1% ;反应 1h后 ,其活性基本保持稳定 ,稳态转化率大于 5 1% 。

The strong acidity of sulfated zirconia makes it a fascinating catalyst in hydroisomerization, hydrocracking, alkylation and oligomerization. Despite of capability of sulfated zirconia for catalyzing hydrocarbon isomerization, the fast deactivation is always occurred at high temperature. To enhance the stability and activity, a series of gallium promoted nanocrystalline sulfated zirconia (SO 2- 4/Ga 2O 3/ZrO 2) were prepared by wetness impregnation of zirconium hydroxide with an aqueous solution of Ga 2(SO 4) 3. The impregnation was carried out using precipitated Zr(OH) 4 previously digested at 100 ℃. The structure and the acidity of SO 2- 4/Ga 2O 3/ZrO 2 catalyst were characterized using XRD, TEM, TG DTG, pyridine adsorption IR, chemical analysis and N 2 adsorption desorption techniques. The gallium doped sulfated zirconia can prevent the grain growth and stabilize the tetragonal phase. The catalyst has a narrow size distribution and the average crystallite size is about 8 nm. The gallium oxide can retard the decomposition of sulfate groups so that it has a positive effect on retaining surface sulfate and increasing strong acid sites. The n butane isomerization on the catalyst was investigated in the presence of hydrogen. At the same time, the influence of calcination temperature and gallium content was also studied. Compared with other metal promoted catalysts, the catalytic activity and the stability of SO 2- 4/Ga 2O 3/ZrO 2 are greatly improved. The n butane conversion on the catalyst containing x (Ga 2O 3)=3% calcined at 700 ℃ is more than 51% which is closed to the equilibrium conversion of n butane.