Catalytic activity of Ti- and Al-pillared montmorillonite and beidellite for cumene cracking and hydrocracking

Titanium- and aluminum-pillared beidellite and montmorillonite clays were prepared from Mg-beidellite synthesized hydrothermally, and Mg-montmorillonite obtained by Mg2+ ion exchange of a natural montmorillonite (STx-1, Source Clay Minerals Repository). The pillaring solutions were prepared by hydrolysis of aluminium chloride and titanium tetraethoxide solutions, to produce the tridecameric ''Al-13'' polyoxocation, AlO4Al12(OH)(24)(H2O)(12)(7+), and ''Ti-x'' poly oxocations (structure not known), respectively. X-ray diffraction analysis of the basal spacing (d(001)) of the samples showed that the Ti-pillared beidellite is thermally more stable than analogous montmorillonite. The order of the overall activity for cumene conversion of the clay samples is found to be: Mg-montmorillonite < Al-13-montmorillonite = Ti-x-montmorillonite < Mg-beidellite < Ti-x-beidellite < Al-13-beidellite. While the conversions were very different, the selectivity of beidellite based catalysts for cracking (measured by benzene produced) was consistently in the range of 86-93% and was not influenced by the presence of aluminium or titanium oxide pillars. However this was not the case for montmorillonite. Mg-STx-1 had a relatively lower benzene selectivity (36%), and both Al2O3 and TiO2 pillars increased this significantly. The difference probably arises because the beidellite surface is more acidic due to its tetrahedral layer charge, hence making the effect of pillars less critical.