Synthesis, characterization of FAU/EMT intergrowths and its catalytic performance in n-pentane hydroisomerization reaction

Zeolites FAU, EMT and their intergrowths were synthesized using 15-crown-5, 18-crown-6 and their equimolar mixture, respectively. The synthesized products were characterized by XRD, SEM-EDX, N2 adsorption and TPD-NH3. The solids obtained were all highly crystalline. The FAU samples were formed by octahedral submicrometric crystallites, EMT samples had hexagonal plate morphology of 2–5 μm. The intergrowth crystals were micrometric hexagonal plates through whose hexagonal faces, the octahedral FAU crystallites intergrow. The intergrowth proportion was evaluated by means of DIFFaX, resulting in different intergrowth proportions, depending on the molar ratio of template/Al2O3 and on the relative template proportion used in the synthesis gel. For a template/Al2O3 ratio of 0.70, a 50%FAU/50%EMT intergrowth proportion was obtained, with cluster-type stacking and for template/Al2O3 of 0.30 the intergrowth proportion was 12%FAU/88%EMT with two stacking arrangements: clusters and random. Platinum was incorporated to these zeolites and their intergrowths by solid ion exchange; the metal dispersion was evaluated by TEM. For most catalysts the platinum particles were between 4 and 10 nm. All the catalysts were active for n-pentane conversion. The activity was found to be a function of acidity. The intergrowth catalysts were the most active materials. The iso-pentane selectivity, at 350 °C and carrier gas composition of H2:N2 = 2:1, was 82% independent of time on stream, acidity, Pt/Al ratio and Pt dispersion. The selectivity increased with decreasing temperature and as carrier gas composition became richer in H2. The catalytic remaining activity (at 10 min) decreased in the following order: FAU > EMT > intergrowth.

At 350 °C and with a carrier gas flow composition of H2:N2 = 2:1, the iso-pentane yield appeared to be a direct function of conversion, as shown in figure, for whatever structure (i.e. FAU, EMT or FAU/EMT) and at different times on stream. The slope of this curve is the selectivity; therefore, it appears to be independent of structure, time on stream, acidity, Pt/H+ ratio and metal dispersion, for this series of catalysts under these conditions (given temperature and carrier gas composition). From the slope is obtained a value of 82% selectivity.Figure optionsDownload as PowerPoint slide