Microenvironment of mesopores of MCM-41 supported CuO catalyst: An investigation using positronium probe

Investigation of microenvironment of mesopores in CuO loaded mesoporous materials is vital to predict its catalytic performance. Mesoporous MCM-41 supported CuO catalyst was prepared by a conventional solid state grinding method and characterized by different techniques to understand the microenvironment of mesopores. The samples were characterized using X-ray diffraction (XRD), small angle X-ray scattering (SAXS), Transmission electron microscopy (TEM) and N-2 gas adsorption techniques. XRD and TEM measurements have shown the formation of CuO nanocrystallites larger than mesopores size of MCM-41. SAXS and TEM also provide evidence of fine dispersion of CuO on mesopores' inner walls of MCM-41 along with the formation of large size crystallites outside the mesopores. With the loading of CuO, N-2 adsorption measurements show a negligible change in pore size along with a continuous reduction in pore volume and surface area of MCM-41. Ortho-positronium (o-Ps) probe was used to investigate the atomic level dispersion of catalyst in MCM-41 pores. A complete absence of positronium formation in the mesopores of CuO loaded samples has been observed which has been unequivocally ascribed to the inhibition of positronium formation on the pores' surfaces. The results indicate that CuO is finely dispersed at atomic level on mesopores' inner walls leading to its layer by layer growth.