Performance and Deactivation of Ir–Pt and Rh–Pt/SiO 2 –Al 2 O 3 Catalysts for Selective Decalin Ring Opening

Abstract

Bifunctional catalysts of Pt, Rh, and Ir monometallic and bimetallic (Ir–Pt and Rh–Pt, atomic ratio = 1) with total metallic content 1 wt % supported on SiO2–Al2O3 were studied for selective ring opening of decalin at 300, 325, and 350 °C. The formation of Ir–Pt and Rh–Pt alloys was determined by temperature-programmed reduction, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). Small well-dispersed Ir–Pt and Rh–Pt alloy particles were obtained. The acidity and hydrogenolytic activity of the Rh–Pt catalyst were lower than those of the Ir–Pt catalyst. It was found that the decrease in the apparent activation energy of decalin on Pt due to the incorporation of Ir and Rh is more significant for the Rh–Pt catalyst. The selectivity of the formation of decalin ring-opening products at all three reaction temperatures exceeded 60%. At 300 and 325 °C, all catalysts formed low amounts of undesirable products of cracking and dehydrogenates; consequently, the deactivation was low. The bifunctional mechanism predominates in the formation of ring-opening products. At 350 °C, the highest yields of decalin opening products were obtained with the bimetallic catalysts, ∼60%, close to the monometallic iridium. As the reaction temperature increases, the amount of carbon deposited on the acid function of the catalysts increased. In addition, at 350 °C, the lowest carbon deposition was obtained with the bimetallic catalysts. The larger metal particle size of the Rh–Pt catalyst compared to the Ir–Pt catalyst resulted in a lower yield of dehydrogenated products, directly related to the coke formation of the bimetallic catalysts.