Supported iridium catalysts for the total oxidation of short chain alkanes and their mixtures: Influence of the support

Abstract

• Titania and silica efficient supports for iridium in total oxidation reactions. • Highly stable catalysts if heat-treated at temperatures over 450 °C. • High Ir-support interaction leads to poor performance as in Ir/Al 2 O 3. • Reactivity per exposed iridium active site depends on the support. • No general size-activity relationship. Catalytic total oxidation of noxious volatile organic compounds (VOCs) is an important process to remove these compounds from the atmosphere. This is the first systematic study of the influence of the support on the activity of iridium oxide supported catalysts for the total oxidation of VOCs. Iridium catalysts supported on titania, γ-alumina, silica and zeolites have been prepared using different calcination temperatures. The activity for the total oxidation of short chain alkanes and their mixtures has been evaluated and the physicochemical properties characterized by N 2 adsorption, XRD, (HR)TEM, EDX, CO-Chemisorption, TPR, XPS and Raman spectroscopy. Both the calcination temperature and the nature of the support of iridium catalysts play an important role for the catalytic performance. Silica, ZSM-5 zeolites and titania are suitable supports for IrOx, in contrast with γ-alumina. A strong influence of the Lewis acidity of the support on the turnover frequency of the iridium oxide is found. Additionally, for a given support, the calcination temperature has an effect on the catalytic activity. A possible size effect is discussed. However, the major controlling factor is the nature of the support. Therefore, our results provide a guideline towards a rational design of more active IrOx catalysts for the total oxidation of VOCs.