Elucidation of phosphorus interaction in dual component zeolite/matrix catalysts: Selectivity control in olefin oligomerization with MTW/Al2O3

Abstract

Treatment of alumina bound MTW zeolite extrudates with H3PO4 causes conversion of the binding matrix from Al2O3 to tridymite AlPO4 and we show the crystalline AlPO4 coats the surface of the MTW zeolite crystals. In this transformation, the surface area and pore volume of the catalyst decrease precipitously, but the MTW crystallinity remains largely intact. Similar, but less specific behavior was observed when using NH4H2PO4 as the phosphorus source. After phosphate treatment, the interaction of P with zeolite framework Al is a major effect reducing acidity of the zeolite. These two effects allow for selectivity control during oligomerization of propylene and butenes. Increasing the phosphorus content of the catalyst from 0 to 10wt% causes a decrease in the amount of liquid product heavier than gasoline from 15wt% to 3wt%. Concomitantly, the selectivity to triisobutylenes increases to almost 50%. Thus we attain catalytic performance similar to traditional solid phosphoric acid catalyst, but with a significant yield of triisobutylenes.