磷酸铝铬介孔材料的紫外-可见光谱及其甘油脱水性能

采用固相合成法制备了介孔磷酸铝铬催化材料,并对材料进行了XRD、UV-Vis、XPS和N2吸附-脱附表征。研究了铝盐配阴离子与十六烷基三甲基溴化铵(CTAB)的用量对磷酸铝铬紫外-可见光谱与甘油脱水性能的影响。结果表明,Cr(Ⅲ)离子在660nm附近的d-d电子自旋允许跃迁〔4A2g(F)→4T2g(F)〕与其在690nm附近所产生的d-d电子禁戒跃迁〔4A2g(F)→2T1g(G)〕的相对强度对甘油的转化率及产物选择性具有一定的调控作用;CTAB的用量和铝盐配阴离子的种类通过对催化剂物相织构的调控间接影响这种跃迁。催化剂中的Cr(Ⅲ)离子是甘油脱水反应的活性位点,较高温度下,磷酸铝铬中的Cr(Ⅵ)与Cr(Ⅲ)的相互转变直接影响羟基丙酮和丙烯醛的选择性。

Ultraviolet-visible Spectroscopy and Dehydration Activity of Glycerol on the Chromium Aluminophosphate Mesoporous Catalytic Materials

Mesoporous chromium aluminophosphate catalysts were prepared by a solid state reaction route and characterized by X-ray diffraction(XRD),ultraviolet visible light spectroscopy(UV-Vis)and N2 adsorption-desorption.The effect of the anionic coordination in aluminum chlorohydrate and the consumption of cetyltrimethylammonium bromide on the ultraviolet-visible spectroscopy of mesoporous chromium aluminophosphate catalyst and the dehydration activity of glycerol were investigated.The results shown that the relative intensity between the absorption peak at near 660 nm,which is ascribed to the spin-allowed d-d electron transition [4A2g(F)→4T2g(F)]of Cr(Ⅲ)ion,and that at near 690 nm,which is ascribed to the spin-forbidden transition [4A2g(F)→2T1g(G)] of Cr(Ⅲ)ion in chromium aluminophosphate,and directly controlls the total conversion of glycerol and the selectivity of products.Moreover,the consumption of CTAB and the variety of anionic coordination indirectly influenced the electron transitions mentioned above.It is confirmed that Cr(Ⅲ)ion is the active site of dehydration reaction of glycerol.Under the high temperature,the interchange of Cr(Ⅵ)and Cr(Ⅲ)in chromium aluminophosphate catalyst can affect the product selectivity of acrolein and hydroxyacetone.