Outstanding synergistic effect of Au–Ir/Al2O3 catalysts on the total oxidation of propane

Abstract

Bimetallic Au–Ir catalysts supported on ɣ-Al2O3 were synthesized by a sequential deposition-precipitation with urea (DPU) method. These materials displayed outstanding synergistic performance in the propane oxidation reaction at low reaction temperatures. A T50 of 150 °C was obtained for a bimetallic Au–Ir catalyst (Au loading of 3 wt % and Ir loading of 5 wt %), while for their gold and iridium monometallic counterparts it was of 370 and 190 °C, respectively. The synthesized materials were characterized by XRD, HRTEM-HAADF, H2-TPR, O2-TPD, UV–vis, and pyridine thermo-desorption, followed by FTIR and XPS, showing distinct characteristics that were correlated with their catalytic activity. Outcomes revealed a strong interaction among the gold and iridium particles when the catalysts were activated in H2 and that the thermal treatment atmosphere (hydrogen or air) modified the active sites; likewise, gold-iridium and monometallic iridium catalysts supported on ɣ-Al2O3 showed considerable endurance to activity loss because they hardly presented metal sintering at high reaction temperatures. Moreover, XPS results revealed electron transfer between Au–Ir (Au0 and Ir2+ species). Only the bimetallic system presented Lewis and Brønsted acidity (2.95 and 0.25 μ-mol m−2, respectively), which may have been responsible for enhancing the total oxidation of C3H8 at a low temperature. Likewise, the 3Au–5Ir/Al2O3 catalyst exhibited high stability and reusability during five reaction cycles and using a GHSV of 41,000 h−1.