Characteristics of the dehydration and thermal destruction of organic templates in microporous alumo-and silicaalumophosphates

Abstract

The characteristics of the dehydration, thermal desorption, and thermal destruction of organic templates in zeolite-like alumo-and silicaalumophosphates of different structural types has been elucidated. The influence of pore size and acid centers on the composition of the products of thermal destruction, including processes of secondary synthesis of normal, cyclic, and aromatic hydrocarbons, has been established. The possibility of dehydration, oligomerization, cyclization, cracking, aromatization and alkylation of hydrocarbons in zeolite-like phosphates has been shown.Zeolite-like alumo-and silicaalumophosphates (ZP) differ from aluminosilicate zeolites (ZT) in the wide size range of micropores (3-13 Å [1-3]) and acid properties. The stability of ZP as inclusion compounds and the strength of the organic template linked to the skeleton is determined by the nature and strength of the acid centers and also the dimensions of the micropores. Evidently detailed studies of the process of dehydration and the products of thermolysis of the organic templates in ZP with different structural types can give valuable information not only of the conditions for their activation as adsorbents and catalysts, but also on the chemical nature of the surfaces, adsorption and catalytic properties. Until recently only a single type of investigation has been carried out on the thermolysis of templates predominantly thermal analysis and IR spectroscopy on and by mass spectrometry (ions with m/z < 45) on , however systematic studies of ZT and ZP of different structural types have received practically no attention.The present work is connected with a comparative investigation of the dehydration and destruction of organic templates in ZP by thermogravimetric desorption with mass spectrometric control (ionization of the products by electron impact) (TPDM).For this investigation phosphates of different structural types, different chemical composition, and varying micropore size were synthesized: SAPO-34 of shabazite type (~3.8 Å, template tetraethylammonium hydroxide (TEAOH); AlPO 4 -5 and SAPO-5 (~7.3 Å, TEAOH [1]); SAPO-37 of faujasite type (~7.4 Å, tetramethylammonium hydroxide (TMAOH) and tetrapropylammonium hydroxide (TPAOH)) [2]; VPI-5 and SiVPI-5 (~13.0 Å, di-n-propylamine (DPA)) [3]. 2600040-5760/06/4204-0260