A mechanism has been found that explains the distribution of products obtained in the isomerizations of long‐chain alkanes on ZSM‐22 and SAPO‐11 catalysts so well that it should now be possible to tailor reactions for the synthesis of branched hydrocarbons. The reactions occur at the external surface of the catalyst according to a lock‐and‐key model (shown on the right); thus, the classical concept of shape‐selective catalysis within micropores is substantially extended.

According to the decane catalytic test reaction, the pore architecture of zeolite MCM-22, with unknown topology, contains t w o micropore systems circumscribed by 10-and 12-rings; the 12-ring channel system is monodimensional and has n o connections with the 10-ring pores, where the strongest acid sites are located.

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Ein Mechanismus wurde gefunden, der die bei Isomerisierungen langkettiger Alkane an ZSM‐22‐ und SA‐PO‐11‐Katalysatoren erhaltenen Produktverteilungen so gut erklärt, daß nun maßgeschneiderte Reaktionen zur Synthese verzweigter Kohlenwasserstoffe leicht möglich sein sollten. Die Reaktionen laufen an der äußeren Katalysatoroberfläche nach dem Schlüssel‐Schloß‐Prinzip ab (Bild rechts), womit das klassische Konzept der formselektiven Katalyse im Inneren von Mikroporen wesentlich erweitert wird.

Slim through spatial constraints: A higher content of linear and monobranched propene trimers is obtained with ZSM‐22 as catalyst than with many other zeolite catalysts (see picture). This is explained by the constraints imposed by the diameter of the tubular pores of ZSM‐22. ZSM‐22 also brings an important environmental benefit compared with the presently used industrial catalyst silica‐supported phosphoric acid.