Synthesis of hierarchically porous ZSM-5 zeolites by steam-assisted crystallization of dry gels silanized with short-chain organosilanes

Abstract

Three short-chain organosilanes, i.e., 3-aminopropyltrimethoxy-silane (APTMS), [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEAPTMS) and phenylaminopropyltrimethoxysilane (PHAPTMS), were used for the synthesis of hierarchically micro-/mesoporous ZSM-5 zeolites by steam-assisted crystallization of silanized dry gels. Corresponding to the different moieties of organosilanes, the obtained hierarchically porous ZSM-5 zeolites have different degrees of mesoporosity and exhibit spherical morphology composed of small nanounits. Among the three organosilanes, PHAPTMS with a bulky cross-section is the most excellent mesopore directing agent. Tracking the structural evolution of PHAPTMS-ZSM-5 during crystallization shows that a large number of mesopores are produced in the initial steaming, but it is confirmed that it does not occur due to the presence of PHAPTMS. This initial mesoporosity is mostly preserved by the PHAPTMS molecules which inhibit the growth of the crystalline phase and suppress the high mobility of aluminosilicate species under the steam atmosphere.