Detemplation of DDR type zeolites by ozonication

Ozonication is a technique which can be used to remove the template from zeolites at much lower temperatures than conventional calcination. The template removal by ozonication has been investigated for small pore zeolites of the DDR topology. The pore size of the DDR type zeolites (4.4 x 3.6 angstrom) is smaller than the molecular diameter of ozone (4.6 angstrom). The detemplation of these zeolites confirms the assumption of ozone breaking down into radicals at the zeolite surface before diffusing through the pore system. All silica DDR (DD3R), all-silica ZSM-58 and aluminum containing NaZSM-58 (Si/Al = 170) have been synthesized. The crystal size distributions of the materials show the DD3R crystals have an average size of 2.7 mu m, while the ZSM-58 sample consists of 6.1 mu m hexagonal shaped crystals. The NaZSM-58 material consists of globular aggregates of 36 mu m, consisting of small 1 mu m primary particles. The ozonication was carried out at 473 K using 100 ml min(-1) of a mixture of 80 g Nm(-3) ozone in oxygen. DD3R was completely detemplated in 38 h of ozonication, showing porosity characteristics equal to that of a thermally calcined sample. The all-silica ZSM-58 and NaZSM-58 samples were detemplated for 75% in 38 h and 90% in 8 h, respectively, as compared to the thermally calcined samples. The incomplete detemplation is expected to be due to the larger size of the SDA for ZSM-58 (MTI) compared to the SDA for DD3R (1-ADA). The lower template removal of the all-silica ZSM-58 is attributed to the larger crystal size. (C) 2008 Elsevier Inc. All rights reserved.