B_2O_3/ZrO_2催化剂的^(11)BMASNMR表征

Characterization of B_2O_3/ZrO_2 Catalyst by ^(11)B MAS NMR

用11BMASNMR技术研究了B2 O3 /ZrO2 催化剂中B2 O3 活性组分的存在形式及作用状态 .结果表明 ,B2 O3 在ZrO2 表面以三配位BO3 与四配位BO4结构单元存在 .ZrO2 载体的预焙烧温度和硼含量对B2 O3 的作用状态具有重要的影响 ,并改变BO3 与BO4结构单元之间的比例 .催化剂表面吸附水的存在对BO4与BO3 之间的分布有很大的影响 ,催化剂焙烧脱水至少可使部分BO4转化为BO3 .BO4结构形式容易在无定形的微孔大比表面积的ZrO2 表面形成 ;BO3 结构形式却倾向于在结晶形的中孔小比表面积的ZrO2 上存在 .

The structure and the interaction state of B 2O 3 in B 2O 3/ZrO 2 catalyst were studied by 11B MAS NMR technique. The results showed that the tetrahedral BO 4 and the trigonal BO 3 were detected as the basic units in B 2O 3/ZrO 2 catalyst. The precalcination temperature of ZrO 2 support and the load level of boron oxide played an important role in the interaction state of B 2O 3, and changed the ratio of BO 4 to BO 3. The water adsorbed on the catalyst surface greatly influenced the BO 4/BO 3 ratio; BO 4 units could be partly transformed into BO 3 units through removing water from the catalyst by calcination. The BO 4 units were easy to be formed on the micro-porous surface of ZrO 2 with larger surface area, but the BO 3 units were inclined to be formed on the mesoporous surface of ZrO 2 with smaller surface area.