Preparation,characterization and catalytic activity of Co-Zn-based manganites obtained from carbonate precursors

摘要

Cobalt—zinc manganites at rather low Co content (x Co/(Co ± Zn) 0, 0.01, 0.05, 0.10) were prepared by thermal decomposition of carbonate precursors obtained by coprecipitation at constant pH. Precursors were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA-DTA) and magnetic suscepti-bxXixy measurements. For aiX samples, a single rhoaochrose-Yske p’ttase, CO5 LUy3Afl(~—x—y~2O3, was torme~, as etecte~X’OxJ XRD. Magnetic analysis confirmed that cobalt and manganese were present as Co2± and Mn2+ in the rhodochrosite crystal lattice. The carbonate monophasic precursors were decomposed at 723 and 973 K in air and Co—Zn—Mn based spinel-like solid solutions were obtained at both temperatures. The DRS and magnetic susceptibility data suggested that after calcination cobalt was mainly present as Co3± ions in the octahedral sites of the spinel together with Mn3 ions, The catalyst reducibilit) in H2 was studied by temperature-programmed reduction (TPR). The cobalt containing catalx st-. reduced almost as the pure ZnMn2O4 suggesting that cobalt does not show a detectable influence on the spinel reduJbilit~. Preliminarx results of the catalytic activity for the reduction of NO by hydrocarbons in absence of C Sen are presented.