用离子交换方法将单取代型Keggin结构杂多阴离子PW_(11)O_(39)Cr(H_2O)^(4-),PW_(11)TiO_(40)^(5-)及PW_(11)VO_(40)^(4-)嵌入Zn-Al型阴离子粘土层间,获得了底面间距(d_(001))为(1.48±0.02)nm的新型层柱状微孔材料ZnAl-PW_(11)Cr,ZnAl-PW_(11)Ti及ZnAl-PW_(11)V。根据^(27)Al,^(31)P MAS NMR测试结果,提出了PW_(11)VO_(40)^(4-)以其C_2对称轴垂直于层板方向取向定位的立体层柱结构模型。发现它们对乙酸与正丁醇的酯化反应,比H型分子筛具有更高的酯化催化活性。
Ainonic clays pillared by heteropolyoxometalate Zn2Al-PW11Z (Z= Cr3+ , Ti4+ and V5+) were synthesized via ion exchange reaction. The IR spectra and XRD patterns showed that the layered anions remained the integrity of Keggin structure, and the gallery heights of the layered compounds were 1.01± 0.01 nm. The MAS NMR spectra of 27Al and 31P indicated the layered ahion had little effect on the Al of the octahedra center of the hydroalde, but the layer and octallydron VO6 had great effect on the P of the layered PW11V. The peak of 31P MAS NMR split to the two peaks of -11.867 ppm and -14.031 ppm whose corresponding area ratio is 2:1. All these results showed that the C2 axia of the heteropolyoxometalate in the layer was perpondicular to the brucite layer. Further experiments found that these compounds had high selectivity and activity for the esterification of acetic acid with n-butyl alcohol.
