Effects of isomorphous substitution of Si with Ti and Zr in mesoporous silicates with the MCM-41 structure Original Research Article

Mesoporous silica and mesoporous silicates can be easily synthesized from the hydrothermal transformation at 110°C, of hydrogels with composition, M:25.95SiO2:5.2(C2H5)4NOH:7.5(CH3(CH2)15N(CH3)3)2O:790H2O, where M=0, Zr(OC3H7)4 or Ti(OC4H9)4. These MCM-41 type crystals have Si/M molar ratio similar to the one in the parent hydrogel. After calcination at 600°C/12 h in air, the solids have surface area and pore volume in the 940–1740 m2/g range and 0.8–1.2 cm3/g range, respectively. The small mesopores have an average pore diameter (APD) of ∼2.8 nm and are separated by walls 1.30–1.65 nm thick. The isomorphous substitution of Si with Ti or Zr has little effects on pore size and on pore wall thickness. However, thermogravimetric analysis has indicated that charge compensating organic cations are located on different sorption sites and that site strength increases in the order: Si–OH