Effect of the Preparation of Pt-Modified Zeolite Beta-Bentonite Extrudates on Their Catalytic Behavior in n-Hexane Hydroisomerization

Four different types of shaped catalysts with controlled deposition of platinum and the same composition were prepared by extrusion of beta zeolite agglomerated with bentonite as an aluminosilicate clay binder. The catalysts were characterized using mechanical strength tests; scanning electron microscopy for morphology; transmission electron microscopy for porosity and periodicity; nitrogen physisorption for surface area, pore volume, and pore size distribution; and Fourier transform infrared spectroscopy using pyridine as a probe molecule to elucidate the presence, strength, and amount of Bronsted and Lewis acid sites. Elemental analysis was carried out using energy-dispersive X-ray microanalysis. Activity and selectivity of catalysts in the isomerization of n-hexane were evaluated using a fixed bed reactor at 200-350 degrees C. At low temperature, the performance of metal/acid bifunctional shaped catalysis was strongly affected by the metal-to-acid site ratio. This ratio and the total acidity were strongly influenced by the preparation method of the shaped catalysts, while the textural properties were comparable. The highest conversion of n-hexane and selectivity to C-6 isomers (comprising all branched isomers, such as methyl pentane and dimethylbutane) was obtained with extrudates prepared via in situ synthesis with platinum located on the zeolite. The extrudates prepared in this way have the highest metal-to-acid site ratio and their closest proximity, albeit the lowest mechanical strength.