A study on the synthesis, characterization and catalytic activity of ruthenium-substituted MFI (Mobil Five) zeolite

Hydrothermal synthesis was adapted to prepare a series of ruthenium (Ru)-incorporated Mobil Five (MFI) zeolite materials with silicon (Si) to aluminium (Al) ratio of 100 and with Al to Ru ratios 1:1, 2:1 and 3:1. An X-ray diffractometer (XRD) and FT-IR were employed to identify the formation of the zeolite phase. A favourable environment was maintained in the gel to overcome the difficulties of isomorphous substitution of ruthenium into the MFI framework. The unit cell volume change and the shift in XRD reflection positions showed a positive correlation with increased ruthenium content in the samples. UV–Vis (DRS) spectra confirmed the position of ruthenium in the T-site in the MFI structure. Thermogravimetric analysis was carried out for studying water and template removal patterns and also for studying the thermal stability of the synthesized samples. Formation of uniform rectangle- and twinned-rectangle-shaped MFI particles with particle size approaching $27\mu \text{m}$ was confirmed by scanning electron microscopy. Energy-dispersive X-ray analysis was carried out for quantification of Si, Al and Ru. The catalytic activities of the synthesized samples for the hydroxylation of phenol was investigated, the major products being catechol and hydroquinone.