Synthesis and Properties of Manganese Oxides Obtained via Combustion Reactions with Glycine and Citric Acid
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HESIS AND PROPERTIES OF INORGANIC COMPOUNDS
Synthesis and Properties of Manganese Oxides Obtained via Combustion Reactions with Glycine and Citric Acid V. D. Zhuravleva, *, **, Sh. M. Khaliullina, L. V. Ermakovaa, and V. G. Bamburova aInstitute
of Solid State Chemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620990 Russia *e-mail: [email protected] **e-mail: [email protected] Received April 4, 2020; revised May 28, 2020; accepted May 30, 2020
Abstract—Manganese oxides were synthesized via combustion reactions with glycine and citric acid. When the synthesis used reaction solutions containing predominant amounts of citric acid Σ(ϕcit + ϕgl) = 1.8–2.1 at ϕgl = 0.5, the reactions proceeded with moderate intensity at a maximum temperature not higher than 315°C. The resulting nanopowders (16–33 nm) were dominated by tetragonal Mn3O4. The primary crystallites were assembled into laced “crumpled paper” aggregates with numerous holes and through pores and had specific surface area of 22–27 m2/g. The variations of the maximum combustion temperature as a function of the reactor area, the mass of the obtained oxide, and the water content in the xerogel were calculated. Keywords: manganese oxide, combustion synthesis, calculation of the maximum temperatures of SCS reactions DOI: 10.1134/S003602362010023X
INTRODUCTION Manganese oxides, together with vanadium, cerium, chromium, copper, and cobalt oxides, are considered as promising catalysts for general oxidation of volatile organic compounds (VOCs) and are more stable than noble metal-based catalysts [1–5]. Most efficient among them is Mn3O4 [6]. High activity of manganese oxide-based catalysts was detected in the neutralization of NOx in the 120–350°C range both in the presence and in the absence of SO2 [7]. The catalyst regeneration after sulfur-induced deactivation completely restored the initial catalytic activity. The mixed CeO2/MnOx oxides were used in the selective catalytic reduction of nitrogen oxides using ammonia [8]. The presence of Mn3O4 with a low degree of crystallinity in the resulting material is apparently the key factor responsible for high activity of these catalysts. Manganese oxide Mn3O4 is regarded as an efficient anode material for lithium ion batteries [9–11] and electrodes for supercapacitors [12–15]. It is under study in the search of methods for the treatment of cancer [16]. For all of the above-mentioned applications, the main requirements to manganese oxides, in particular Mn3O4, include high specific surface area and high degree of dispersion. Therefore, they are obtained, most often, by hydrothermal methods [9, 10, 12, 14] or by the solution combustion synthesis (SCS) [1, 5, 7, 8]. For example, a solution of manganese (cobalt)
nitrate with glyoxylic (C2H2O3) or ketoglutaric (C5H6O5) acid has been used [5]. The results reported in [5] indicate that the synthesis was performed with excess reducing agent and at an acid to manganese nitrate ratio favorable for complexation. In the former case, this ratio was 2 : 1, while in the l
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