Synthesis, characterization and applications of Ir-containing mesoporous Y-Al2O3 catalysts for ammonia decomposition

OSCAR A. ANUNZIATA; MARCOS B. GÓMEZ COSTA; JULIANA M. JUÁREZ; ANDREA R. BELTRAMONE

Current Topics in Catalysis

Research Trends

Año: 2009 vol. 8 p. 57 - 72

0972-4508

Ir/Y-alumina catalysts for decomposition of ammonia were prepared by Iridium ion exchange procedure, onto mesoporous Y-alumina synthesized by sol-gel method. In order to determine the physical and chemical properties we used X ray diffraction (XRD) analysis, Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR-MAS). The samples displayed the characteristic band at 1620 cm-1 corresponds to N-H ammonia bending adsorbed on electron-acceptor sites, and pyridine adsorption and desorption determined the presence of Lewis acid sites, with absence of Bronsted sites, showing higher acid strength than commercial sample used as reference. The analysis of particle size and morphology reveal uniformity, with tendency to a spheroid aspect and smaller to 3 micrometers of diameter. The 27Al NMR-MAS test, allowed determining the tetrahedral and octahedral aluminium presence in both samples, where the higher proportion of octahedral Al in Y-alumina synthesized by us. The designed method was effective for Ir/Y-alumina catalysts synthesis. XRD analyses show the absence of maximums at 28º and 34.7º 2Tita corresponding to iridium oxide, indicating a high efficiency of the reduction treatment, increasing the active sites for ammonia decomposition. The distribution of the Ir crystallites determined by XRD and TEM indicated that, the samples Prepared by ion exchange method produced smaller Iridium clusters with higher surface area and greater anchorage sites. According to preliminary catalytic tests, the Ir/Y-alumina catalysts prepared by a novel method showed higher activity to ammonia decomposition to N2 and H2.