B2O3/ZrO2催化剂的11B MAS NMR表征

 用11B MAS NMR技术研究了B2O3/ZrO2催化剂中B2O3活性组分的存在形式及作用状态. 结果表明,B2O3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B2O3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.

Characterization of B2O3/ZrO2 Catalyst by 11B MAS NMR

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.