Structure and Surface Chemistry of Two-Dimensional Phosphate Catalysts

在减压下用磷酸溶液除去磷酸锆凝胶中的杂质水，使磷酸锆结晶。对于给定的磷酸浓度，根据温度和处理时间，通过该过程获得几种形式的微晶。合成的ZrP_2O_2和ε-Zr（HPO_4）_2催化剂，在约100 ℃抽真空，在约100 ℃下进行催化剂的活性评价。800 K时，对烯烃异构化反应的催化活性高于其它形式的磷酸锆或其它常规固体酸催化剂。为了解释这些高催化活性，我们用~ 1 <31>P魔角自旋核磁共振（~ 1 <31>P MASNMR）研究了不同温度下真空处理后的磷酸锆，发现<31>随着层间距的减小，~ 1 P化学位移向高磁场方向移动。表现出较高活性的催化剂在H_3PO_4的-38ppm左右表现出较高的化学位移。这些结果表明，在800 K左右抽空后剩余的磷酸盐基团可以增强质子特性，因为电子的积累从表面上的磷酸盐基团移动到位于Zr原子平面之间的磷原子。

Zirconium phoshate are crystallized during the removal of hybration water in the zirconium phosphate gel with phosphoric acid slution under reduced pressure. Several forms of crystallites are obtained by this procedure, depending on the temperature and process time, for a given concenttration of phosphoric acid. Synthetic ZrP_2O_2 and epsilon-Zr(HPO_4)_2 catalysts, which were evacuated at ca. 800 K, showed higher catalytic activities for catalytic isomerization of alkenes than other forms of zirconium phosphates or other conventional solid acid catalysts. In order to elucidate those higher catalytic activities, ^<31>P magic angle spinning nmr (^<31>P-MASNMR) has been employed to study zirconium phosphates after evacuation at different temperatures.The ^<31>P chemical shifts move towards higher magnetic fields as the layer separations became amaller. The catalysts which showed higher activities showed higher chemical shifts at around -38 ppm from H_3PO_4. These results suggest that phosphate froups remaining after evacuation at around 800 K may enhance the protonic characteristics, since the accumulation of electrons moves from the phosphate groups on the surface to phosphorus atoms which are located between Zr atom planes.