Synthesis of Highly Active Nanozeolites Using Methods of Mechanical Milling, Recrystallization, and Dealumination (A Review)

Abstract

Methods for preparing zeolites with the particle size of 50–200 nm using mechanical milling on bead mills (top-down approach) are analyzed. The milling can be described by a first-order rate equation, but mathematical models allowing prediction of the particle size and degree of crystallinity of zeolite after milling, based on the process parameters, are still lacking. The milling is accompanied by degradation of the zeolite lattice, leading to a decrease in the zeolite crystallinity and activity in catalytic reactions. Recrystallization and dealumination may be promising ways to restore the zeolite structure after milling; in this case, the choice of the conditions for such posttreatment is of crucial importance. Evolution of textural and acid properties of zeolites in the course of milling is considered, and the effect of milling conditions on the catalytic activity of zeolites in various reactions is discussed. The main outcome from a decrease in the size of zeolite catalysts is an increase in their activity and a decrease in the deactivation rate.