Effect of ammonium salts on the synthesis and catalytic properties of TS-1

Effects of ammonium salts on the synthesis and characteristics of TS-1 were studied by adding different ammonium salts (NH4F, NH4Cl, NH4Br, NH4I, CH3COONH4, NH4NO3, (NH4)2CO3, (NH4)2SO4 and (NH4)3PO4) to the synthesis gel. It was shown that the fine structure and crystal morphology of the synthesized materials depended on the type of ammonium salts. Except for NH4F, the ammonium salts, and particularly (NH4)2SO4 and (NH4)3PO4 significantly decreased the crystallization rate as a result of remarkably reducing the pH value of the crystallization mixture. Nevertheless, all of these ammonium salts were favorable for the incorporation of Ti in the framework, and the beneficial effect was dependent on the type of ammonium salts. In addition, the ammonium salt also has a strong influence on the catalytic properties of the prepared catalyst. It is worth noting that the catalytic performance of TS-1 was closely related to the substrate molecules. TS-1 catalyst prepared in the presence of (NH4)2SO4 gave the highest conversion in the epoxidation of 1-hexene, whereas that prepared with (NH4)2CO3 was suitable for the oxidation of phenol.