Unexpected methanol-to-olefin conversion activity of low-silica aluminophosphate molecular sieves

Low-silica AlPO-18, AlPO-34, and AlPO-41 with Bronsted site densities of 0.006 to 0.014 mmol/g have been applied as methanol-to-olefin (MTO) conversion catalysts. At 673 K, AlPO-18 and AlPO-34 are active, while AlPO-41 did not exhibit obvious MTO activity. In situ UV/Vis spectroscopy of working AlPO-18 and AlPO-34 shows bands of aromatic compounds, but no formation of these species was found for AlPO-41 with one-dimensional 10-ring pores. This study indicates that the MTO reaction over aluminophosphates requires a minimum Bronsted site density and a suitable framework topology with cages like in AlPO-18 and AlPO-34 allowing the formation and stabilization of aromatics. (C) 2011 Elsevier B.V. All rights reserved.