Microcalorimetric studies of the iridium catalyst for hydrazine decomposition reaction

Abstract

Microcalorimetric studies of H 2, NH 3 and O 2 adsorption, as well as the NH 3 decomposition activities evaluation were used to characterize the iridium catalysts for hydrazine decomposition with different supports (Al 2O 3, SiO 2) and iridium contents (1.8, 10.8 and 22.1%). The higher H 2 chemisorption amounts on Ir/Al 2O 3 catalysts than those on the corresponding Ir/SiO 2 counterparts revealed that the strong interaction of iridium and Al 2O 3 led to higher dispersion of iridium on Ir/Al 2O 3 catalysts than on Ir/SiO 2 catalysts. The larger increase in strong H 2 adsorption sites on highly loaded Ir/Al 2O 3 than the corresponding Ir/SiO 2 ones could be attributed to the interaction not only between iridium atoms but also between iridium and Al 2O 3. The microcalorimetric results for NH 3 adsorption showed that no apparent chemisorption of NH 3 existed on Ir/SiO 2 catalysts while NH 3 chemisorption amounts increased on Ir/Al 2O 3 catalysts with iridium loadings, which arose from the interaction of the catalysts support of Al 2O 3 with chloride anion. Both highly dispersed iridium active sites and chloride anion on Ir/Al 2O 3 catalysts could be beneficial to the intermediate NH 3 decomposition in N 2H 4 decomposition. The similar O 2 plots of differential heat versus normalized coverage on Ir/Al 2O 3 and Ir/SiO 2 catalysts could not be due to the metal–support interaction, but to the formation of strong Ir O bond.