Evaluation of metal oxide phase assembling mode inside the nanotubular pores of mesostructured silica

The assembling mode of transition metal oxides and metallic guest phases (GP) embedded in nanotubular pores of ordered mesostructured silicas (OMS) hosts was evaluated based on N₂ adsorption-desorption data. The corresponding isotherms were measured for sample sets of composite materials MoO₃/Al-MCM-41, WO₃/SBA-15, TiO₂/SBA-15, ZrO₂/SBA-15, NiO/SBA-15 and Ni°/SBA-15 with GP loadings in the range of 20-80 wt%. The materials were also characterized by XRD, HRTEM and local/total EDS. It was shown that a combination of composite surface area values normalized per gram of OMS with pore size distribution (PSD) derived from the adsorption or desorption branch of the isotherm distinguishes the ensemble of small nanoparticles with a size of less than an OMS mesopore diameter and single nanoparticles of a size comparable with OMS mesopore diameter. It also discerns amorphous layer at the surface of OMS pore walls from the ensemble of amorphous nanoparticles. At high GP loadings the PSD derived from the adsorption branch of the N₂-adsorption isotherm more reliably reflects the filling of OMS mesopores with crystalline or amorphous guest nanoparticles.