KINETIC-STUDY OF THE THERMAL COLLAPSE OF MAZZITE SAMPLES OF DIFFERENTMORPHOLOGIES

The kinetics of thermal decomposition of zeolite omega in air has been followed between 850 and 920-degrees-C for prismatic single crystals (sample A) and between 660 and 800-degrees-C for spheroidal particles (sample B). The order in function of time is one for sample A at 875 a nd 900-degrees-C and the activation energy 92 kcal/mole. X-ray diffrac tion and infrared spectra show that the collapse of the structure occu rs with dealumination of the lattice, which affects selectively S4R si tes. In the case of sample B, the kinetics appear to be limited by dif fusion (activation energy 6.8 kcal/mole) at low temperature, but not a t high temperature (activation energy 60 kcal/mole). The lattice colla pse of sample B occurs with much less dealumination. The different sta bilities of the two samples can be attributed to different partitionin g of aluminum between the two T sites: Dealumination of S6R sites more populated in sample B leads to lattice collapse.