Propane Dehydrogenation over Alumina-Supported Iron/Phosphorus Catalysts: Structural Evolution of Iron Species Leading to High Activity and Propylene Selectivity

Abstract

A series of alumina-supported Fe-based catalysts is prepared via a dry impregnation method in the presence of a phosphorus source (phosphate salt) and then used for the catalytic dehydrogenation of propane. Specifically, supported catalysts with Fe:P molar ratios of 1:1, 2:1, and 3:1 are prepared and their chemical composition, textural properties, and redox properties are characterized with an array of techniques. In the nonoxidative dehydrogenation (PDH) of propane at 600 °C and atmospheric pressure, the most active catalyst (Fe:P ratio of 3:1) exhibits 15% propane conversion and >80% C3H6 selectivity. The calculated activity is 9.9 mmol/(h gFe) (mass basis) or 13 μmol/(h m2) (surface area basis), with a corresponding TOF of 19 h-1. During the initial stages of reaction under PDH conditions, the precatalyst is reduced and Fe(0) species are generated, eventually giving way to iron carbide species. During this induction period, significant carbon is incorporated into the catalyst and propylene selectivity is low. Only after the iron carbide phase appears do the reactivity and selectivity achieve steady-state conditions with high propylene selectivity and good activity. The addition of the phosphorus source in the precatalyst is found to be important in obtaining a catalyst with superior performance.