Effect of manganese on the thermostability and reducibility of cobalt nanomaterials
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Effect of manganese on the thermostability and reducibility of cobalt nanomaterials. Zofia Lendzion-Bieluń West Pomeranian University of Technology, Szczecin, Institute of Chemical and Environment Engineering, Pułaskiego 10, 70-322 Szczecin, Poland ABSTRACT Cobalt nanomaterials with promoters have been prepared by precipitation followed by calcination and impregnation method. The obtained materials are characterized by ICP, H2-TPR, BET and XRD. A small addition of manganese increases the specific surface area of cobalt nanomaterials and thermostability under reduction atmosphere. Bulk Co3O4 has been reduced in two steps (Co3+oCo2+oCo). A small addition of manganese to the cobalt oxide shifts the reduction peaks to high temperatures. INTRODUCTION Nanocrystalline cobalt oxides and cobalt have been important subject for studies. These materials are applied in various fields of modern technology, including catalysts for various processes [1,2]. Catalytic properties of these materials depend on many factors e.g. preparation methods, promoters, structure and morphology. Specific surface area is a key factor to determine the activity of cobalt catalysts. Metallic cobalt is an active form of cobalt catalyst in more important industrial processes e.g. Fischer-Tropsch synthesis and methane stream reforming. A small addition of structural promoters, e.g. Al2O3, CaO increases the specific surface area of the cobalt oxide but the reduction process of this material is slower than pure cobalt oxide [3,4]. Next, very important factor is thermostability of catalytic materials in reaction conditions. The temperature and reaction environment are the parameters that can change the properties of the catalysts. The catalyst deactivation processes are usually investigated by measurements of catalytic activity, specific surface area, the crystallite size or the dispersion of the active phase [5]. The aim of this work is to investigate cobalt nanomaterials doped with manganese, examination of the additives influence on the specific surface area and thermostability under reduction conditions.
EXPERIMENT The cobalt oxide Co3O4, is obtained by cobalt hydroxide precipitation followed by calcinations at 200oC during 2 h in air. Such obtained cobalt oxide, with specific surface area approximately 64 m2/g, is impregnated by promoters solutions. Precursors of promoters are solutions of calcium, aluminium and potassium nitrates and manganese acetate. Concentration of proper salt is calculated to reach established content of promoters in cobalt nanomaterials. Thereafter calcinations process for 4 h in the temperature at 200oC and for 2 h in the temperature at 500oC is conducted.
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Quantitative composition of elements in the materials is determined by atomic emission spectroscopy with inductively coupled plasma ICP-OES (spectrometer Optima 5300 DV, Perkin Elmer). Phase composition is determined by means of X-ray diffraction XRD (X’Pert PRO Philips diffractometer with CuKα radiation). The specific surface area (BET) of the cobalt nanomaterials is
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