Studies on stability of nanocrystalline MFI zeolite synthesized by a novel method against OH− attack

Two samples of nanocrystalline MFI zeolite with silicon to aluminium (SAR) molar ratios of 75 and 125 were hydrothermally synthesized by our improved one step procedure in static conditions at 200 °C under autogeneous pressure. Another sample with SAR = 50 was also synthesized by the conventional hydrothermal synthesis method. The samples were subjected to alkali attack to study the effect of duration of alkali treatment, concentration of alkali and method of synthesis on the stability of zeolite structure. Loss of crystallinity and change in crystallite size were investigated using XRD and FTIR. Samples were also characterized by TGA, N2 adsorption and SEM analyses. The extent of removal of silicon by alkali treatment for creation of mesopores with preservation of the zeolite structure has also been investigated.

► MFI samples synthesized by our novel method have better resilience against OH− than those synthesized by conventional method.
► Mesoporosity formation due to OH− attack depends on the methods of synthesis.
► The adsorption isotherms of desilicated samples indicate the formation of micro-mesoporous materials.
► The rate of dissolution process overcomes the process of precipitation when the base treatment period extended to 60 min.