Improved catalytic activity upon Ge incorporation into ZSM-5 zeolites

The catalytic stability of ZSM-5 can be greatly improved by the isomorphous substitution of some Si atoms by Ge. The catalytic properties of Ge-ZSM-5 zeolites have been compared to ZSM-5 in a series of acid-catalysed test reactions (the dehydration of 2-propanol and 2-butanol, the isomerisation of isobutyraldehyde to 2-butanone, and the Friedel–Crafts acylation of anisole). The propene yield in the 2-propanol dehydration reaction at 180 °C is as high as 98% for Ge-ZSM-5 and only 40% for ZSM-5. For the other investigated reactions similar differences are observed. The presence of a considerable amount of mesopores in Ge-ZSM-5 (compared to ZSM-5) is proposed to be the main explanation for the difference. These mesopores are formed upon synthesis and reduce the effect of pore blocking by coke residues that are formed at high reaction temperatures.