Effect of post-synthesis salt solution treatment on Ti-MCM-41 acid-basic properties.Influence on their activity and selectivity in catalytic liquid-phase epoxidation of cyclohexene.

摘要

Ti-MCM-41 mesoporous molecular sieves with Si/Ti = 20 were synthesized and modified by treatment with alkaline and ammonium salt aqueous solution,and characterized by XRD,N_2 physisorption,DRIFT,~(29)Si MAS NMR,Raman and UV-Vis-DRS analysis.Titanosilicates MCM-41 treated with alkaline salts exhibited mainly basic properties,whereas ammonium salt treatment maintained acid properties of Ti-MCM-41 materials.The resulting acidic Ti-MCM-41 materials were active and selective catalysts for epoxidation of cyclohexene with TBHP.Ti-MCM-41 catalysts with basic properties showed lower activities and selectivities.Moreover,post-synthesis salt treatment did not change the hydrophilic nature of Ti-MCM-41.As a result,the catalysts were rapidly deactivated by water which made them unsuitable for cyclohexene epoxidation with hydrogen peroxide.