Mildly acidic aluminosilicate catalysts for stable performance in ethanol dehydration

Ethanol dehydration is effectively catalyzed by strongly acidic zeolites which, however, exhibit poor time-on-stream stability. For example, HZSM-5 features strong acid sites, catalyzes ethylene oligomerization, and is prone to coking. Alumina and silica-alumina on the other hand have lower acidity, are relatively stable, but reach only low activity. Here, a series of mesoporous aluminosilicate catalysts was prepared by non-hydrolytic sol-gel (NHSG) and are shown to feature an intermediate level of acidity (both in strength and nature), resulting in intermediate catalytic performance. Importantly, the best NHSG-made samples were very stable with time on stream, did not produce any traces of ethylene oligomers, did not show any trace of coke formation, and their texture was unaffected. Characterization (ICP-OES, N₂-physisorption, TEM, XPS, IR-pyridine, Raman and solid state NMR spectroscopies) revealed that this behavior must be correlated with the remarkable degree of homogeneity in the NHSG-made aluminosilicate (only tetrahedrally coordinated Al species).