Chinese Journal of Catalysis ›› 2019, Vol. 40 ›› Issue (6): 940-952.DOI: 10.1016/S1872-2067(19)63339-5

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A facile one-pot hydrothermal synthesis as an efficient method to modulate the potassium content of cryptomelane and its effects on the redox and catalytic properties

Huiyan Pana, Xiaowei Chena, Oihane Sanzb, Miguel A. Cauquia, Jose M. Rodríguez-Izquierdoa, Juan J. Delgadoa   

  1. a Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, Campus Río San Pedro, Puerto Real (Cádiz), E-11510, Spain;
    b Applied Chemistry Department, University of Basque Country (UPV-EHU), Apdo.1072, San Sebastian, 20080, Spain
  • Received:2019-01-21 Revised:2019-02-27 Online:2019-06-18 Published:2019-04-26
  • Contact: S1872-2067(19)63339-5
  • Supported by:

    This work has been supported by the Ministry of Science and Innovation of Spain/FEDER Program of the EU (MAT2013-50137-EXP, MAT 2013-40823-R and ENE2017-82451-C3-2-R). J. J. Delgado and X. Chen thank the "Ramón y Cajal" Program from MINECO/FEDER of Spain. H. Pan is grateful for the financial support from Chinese Scholarship Council to accomplish her PhD study.

Abstract:

Cryptomelane has been widely applied as catalyst in oxidation reactions due to its excellent redox properties and low cost. Here, a novel one-pot hydrothermal synthesis using a potassium permanganate aqueous solution as precursor and ethanol as reducing agent has successfully been developed to obtain cryptomelane nano-oxides. This synthetic route makes it possible to control the amount of potassium incorporated into the structure of the cryptomelane by selecting the appropriate synthesis temperature and ethanol initial concentration. Taking advantage of this approach, the effect of potassium concentration on the structural stability and reducibility of the cryptomelane, which are poorly discussed in the literature, has been studied. We have observed that samples with low content of potassium (~11%) show high conversions of CO to CO2 especially at low temperatures. The lower activity of the samples with high K contents (~16%) can be ascribed to the beneficial effect of K on the structural stability of cryptomelane in detriment of labile oxygen on cryptomelane surface.

Key words: Cryptomelane, Pyrolusite, Catalytic CO oxidation, Hydrothermal synthesis, Potassium content