An improved route for the synthesis of Al₁₃-pillared montmorillonite catalysts

Abstract

The distribution of Al₁₃ pillars and the process of intercalation in montmorillonite can be enhanced through the application of an ultrasonic treatment. This paper describes the results of ultrasonic treatment in the preparation of Al-pillared montmorillonite with and without prior exchange with Na⁺. The resulting materials have been characterised by X-ray diffraction (XRD), N₂ adsorption/desorption, Scanning Electron Microscopy and Atomic Force Microscopy (AFM). The catalytic activity was tested with the n-heptane hydroconversion test. Optimum results were obtained after ultrasonic treatment up to 20 min without prior Na-exchange before the Al₁₃ intercalation. Longer ultrasonic treatment resulted in partial destruction of the pillared structure. The pore size diameter also increased with increasing ultrasonic treatment up to 20 min with values in the range of 4 nm. This behaviour can be explained by the loss of the typical house of cards structure after prolonged ultrasonic treatment. AFM showed that the pillars in the interlayer of the montmorillonite resulted in a distortion of the tetrahedral sheets of the clay. At atomic scale resolution it was clear that the pillar distribution is not homogenous, confirming earlier results using high resolution TEM. The effects of ultrasonic treatment on the catalytic activity is rather limited, although the pillared clays prepared with short ultrasonic treatments of 5 and 10 min performed slightly better.