Two series of Zn-ZSM-5 catalysts were prepared by ion exchanging two commercial zeolites with different Si/Al ratios (40 and 15) with increasing Zn loadings. The nature of the Zn sites in the zeolite was studied by spectroscopy using laboratory and synchrotron techniques. All the evidences suggest that catalytic activity is associated with [Zn(H2O)n(OH)] + species located in the exchange positions of the materials with little or no contribution of ZnO or metallic Zn. The effect of Zn/Al ratio on their catalytic performance in methanol conversion to aromatics has been investigated. In all cases, higher Zn content causes an increase in the yield of aromatics while keeping the production of alkanes low. For similar Zn contents, high densities of Al sites favour the hydrogen transfer reactions and alkane formation whereas in samples with low Al contents, and thus higher Zn/Al ratio, the dehydrogenation reactions in which molecular hydrogen is released are favoured.

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Three small-pore silicoaluminophosphates containing relatively large cavities in their structure (LEV, LTA and SAV) have been hydrothermally synthesized with various silicon concentrations. The effect of the silicon content and distribution on both the physicochemical and the catalytic properties of the SAPO molecular sieves was studied. Remarkable differences in the Si incorporation were found, showing that the topological features and the structure directing agent employed in each case play an important role, controlling not just the Si location in the framework, but also the amount of Si incorporated. In all the cases, the formation of Si islands, associated to stronger acid sites, was favoured by the use of higher concentrations of the Si source in the synthesis gel. However, it has been found that framework topology can have greater influence than acidity on the catalytic behaviour of SAPO materials in the MTO transformation.