Cobalt‐Doped K‐OMS‐2 Nanofibers: A Novel and Efficient Water‐Tolerant Catalyst for the Oxidation of Carbon Monoxide

Abstract

Cobalt-doped manganese octahedral molecular sieves with an ordered cryptomelanes tructure (OMS-2) were synthesized by ao ne-step hydrothermalm ethod. The cobalt precursor was directly added into the solution before crystallization to allow its incorporation into the mixed-valent framework of K-OMS-2. The structure, redox properties, and surface hydrophobicity of Co-doped K-OMS-2 were examined by X-ray diffraction, FTIR spectroscopy,R amans pectroscopy,S EM,T EM, N 2 sorption, temperature-programmed reduction by H 2 ,X -ray photoelectron spectroscopy,a nd water contact-angle system. The incorporation of Co induced am orphological change in K-OMS-2 from nanorods to nanofibers and an increase in the specific surfacea rea from 70.6 to 188.3 m 2 g À1 .C o-doped K-OMS-2 was shown to be able to completely convert CO at 100 8Ci nt he presenceo fa pproximately 3% water vapor.T he promotion effect of Co on the catalytic activity is believed to originate from the enhanced redox capacity and surfacea rea of K-OMS-2, whereas the improved surfaceh ydrophobicity may induce superiorw ater-tolerant performance.CatalyticC Oo xidation hasb een extensively investigated and has already been applied in the field of air purification,a utomotive exhaust cleaning, CO removal of cigarettes moke, and CO 2 lasers. [1] However,f or the above purposes, the presence of water vapor inevitably leads to catalystd eactivation through temporary poisoning of the exposed active sites. [2] Such strict operation conditions have thus stimulated an increase in the demandt od evelop highly efficient and water-tolerantc atalysts for CO oxidation. Noble-metal catalysts such as Pd, Pt, and Au have been widely recognized as preferred choices, but both high costs and finite resources limit their application. [3] Alternatively,aseries of cheap transition-metal oxides (i.e.,C uO,

Water Vapor Adsorption by Some Manganese Oxide Forms

“…Polymorphic forms of manganese dioxide are widely used as catalysts for such gaseous reactions as ozone decomposition [1][2][3], CO oxidation [4,5], NO reduction [6,7], and volatile organic compound oxidation [8,9]. The activity and stable action of such catalysts significantly depend on a relative humidity of gaseous mixtures.…”

“…In most cases, water vapor adsorption causes complete loss of catalytic activity of manganese oxides towards the above-mentioned reactions [2,3,6]. Therefore, besides nitrogen adsorption required for determination of textural properties of manganese oxides and used in many works [1][2][3][4][5][6][7][8][9], water vapor adsorption is also topical. Water vapor sorption isotherms are able to provide significant information about hydrophilic/hydrophobic behavior of these materials.…”

Structure-induced hollow Co3O4 nanoparticles with rich oxygen vacancies for efficient CO oxidation

“…6c, the XPS spectra of O 1s were fitted with three types of peaks, including the O latt at 530.00 eV, O ads at 531.40 eV, and O wat at 532.80 eV. The O ads /O latt molar ratios (Table 1) were calculated from their relative area to evaluate the quantity of initial oxygen vacancies on the catalyst surface [10]. As excepted, H-Co 3 O 4 @H-C owned the highest value of the O ads /O latt molar ratio among these three catalysts, which was 2.6 times higher than that of Co 3 O 4 @H-C.…”

“…It is generally accepted that the CO oxidation catalyzed by Co 3 O 4 proceeds via the Mars-van Krevelen mechanism, in which the oxygen vacancies on the surface of Co 3 O 4 can activate O 2 molecules to form actively adsorbed oxygen (O ads ) that would react with CO adsorbed on Co 3+ ions to produce CO 2 [5][6][7]. The initial oxygen vacancies determine the amount of O ads on the surface of Co 3 O 4 to affect the activity of CO oxidation [8][9][10]. In this regard, it is desirable to effectively enrich the oxygen vacancies on the surface of Co 3 O 4 .…”

Facile Fabrication of Macroscopic Self-Standing Ni or Co-doped MnO2 Architectures as Catalysts for Propane Oxidation

“…Amongst various transition metal oxides, manganese dioxide has been considered as one of the most potential low-temperature catalysts due to its environmental friendliness as well as its low cost [1]. In order to further improve the catalytic activity of MnO 2 , one of the most common strategies is doping with a different cation, such as Ni [2,3] and Co [4,5]. On the other hand, self-assembly of nanomaterials into macroscopic architectures provides the possibility for exploring the practical applications.…”