用程序升温氨脱附研究SO_4^(2-)/ZrO_2超强酸催化剂的酸性质

Study on the Acidic Properties ofSO_4^(2-) /ZrO_2 Superacid Catalyst by NH3TPD

用程序升温氨脱附研究了Ｈ２ＳＯ４的浓度、焙烧温度、氨水的浓度和锆前体的晶型等制备参数对ＳＯ４２－／ＺｒＯ２催化剂的酸性质的影响。结果表明，当Ｈ２ＳＯ４的物质的量浓度不大于１．０ｍｏｌ／Ｌ时催化剂表面主要为一种强酸中心。随着Ｈ２ＳＯ４浓度的增大，表面酸性质发生了明显改变，不仅酸强度减弱，而且总的酸量减少。当Ｈ２ＳＯ４的物质的量浓度增至２．０ｍｏｌ／Ｌ时表面主要为一种弱酸中心。焙烧温度不高于７７３Ｋ时，表面主要为一种强酸中心，且酸量大。随着温度的升高，逐渐向多种强度的酸中心并存转化，且强酸中心数量减少。用浓氨水制得的催化剂存在多种强度的酸中心，且酸量大。用稀氨水时催化剂表面主要为一种强酸中心。用Ｈ２ＳＯ４处理晶型ＺｒＯ２时得不到超强酸。

he effects of preparation conditions on the acidic property of SO_4^(2-)/ZrO_2 superacid catalysts have been studied by NH_3TPD technique.It is found that:(1)The acidic sites on catalytic surface are mainly strong ones when the concentration of H2SO4(CH2SO4) is not higher than 1.0 mol/L.With CH2SO4 increasing,the acidic strength becomes weaker and the total amount of acid decreases;when CH2SO4 increases to 2.0 mol/L,there are mainly weaker acidic sites on the surface.(2)When calcination temperature is not higher than 773K the acidic sites on the catalyst surface are mainly strong ones and the acid quantity also increases.With calcination temperature increasing,there are more than one type of acid sites on the surface.(3)Both strong and weak acid sites exist with large amount of acid when the catalyst is prepared from concentrated ammonia liquor,while there are only strong acid sites on the catalyst prepared from dilute ammonia liquor.(4)The SO_4^(2-)/ZrO_2 catalyst has no superacid properies when it is prepared by modifying crystalline ZrO_ with H_2SO_4.