Preparation and characterization of zinc containing MCM-41 spheres

A series of pure siliceous and Zn-modified MCM-41 spheres were synthesized at room temperature, atmospheric pressure and at short reaction times. Mesoporous molecular sieves were characterized by a number of techniques: XRD, N2 adsorption, TEM, XPS and NH3–TPD. Pure siliceous MCM-41 exhibits the typical hexagonal array of well-defined pores with a mean pore diameter of 3.0 nm. Addition of a small percentage of Zn (Zn/Si ratio 0.02) into the synthesis gel produces a material with increased lattice parameter (ao), pore diameter and total adsorption capacity. These results suggest the incorporation of zinc, with a larger ionic radius, into the silica framework. Unfortunately, higher zinc contents (Zn/Si ratio 0.04) produce a deterioration of the long-range order of the material, together with a decrease in the surface area and total pore volume. In this sample, the presence of small ZnO nanoparticles embedded into the silica matrix can be envisaged. From a catalytic point of view, these Zn-modified MCM-41 mesoporous molecular sieves appear as quite interesting materials to be used as a catalyst by themselves or as a support for noble metal catalysts.