Untersuchungen an dealuminierten Pentasil-Katalysatoren

Investigations of a ZSM-5 type zeolite (HS 30, manufactured by VEB CK Bitterfeld without using any template) show that by dealumination various ratios of Si/Alframework can be achieved within a rather broad scale without structural changes of the initial substance. In any case the number of strong acid Bronsted centres of the elementary unit corresponds to the number of Al atoms contained therein. Throughout all investigations the relative catalytic activity of the catalysts has been found to be in a linear relationship to the number of strong acid Bronsted centres (bridged OH groups). With the isomerisation of m-xylene the initial non-dealuminated sample already brings about a selectivity of ≈80% for the para-isomere. No influence of dealumination on p-selectivity could be observed. With the conversion of methanol reduced catalytic activity of dealuminated samples results in an increase of the selectivity of lower olefins at the expense of aromatics for both reaction temperatures. The values obtained at 580°C are in favour of an additional formation of lower olefins due to the cracking of higher olefins. Dealumination gives also rise to an essential growth of the stability (i.e. possible integral charge by CH3OH) of the catalyst. With growing dealumination of the catalyst the attainable time on stream increases and reaches a maximum falling of thereafter.