Mixed oxide

About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.

Comparative study of Nickel-based perovskite-like mixed oxide catalysts for direct decomposition of NO

Abstract: The mixed oxides LaNiO3, La0.1Sr0.9NiO3, La2NiO4 and LaSrNiO4 were prepared and used as catalysts for the direct decomposition of NO. The catalysts were characterized by means of XRD, XPS, O-2-TPD, NO-TPD and chemical analysis. By comparing the physico-chemical properties and catalytic activity for NO decomposition, a conclusion could be drawn as follows. The direct decomposition of NO over perovskite and related mixed oxide catalysts follows a redox mechanism. The lower valent metal ions Ni2+ and disordered oxygen vacancies seem to be the active sites in the redox process. The oxygen vacancy plays an important role favorable for the adsorption and activation of NO molecules on one hand and on the other hand for increasing the mobility of lattice oxygen which is beneficial to the reproduction of active sites. The presence of oxygen vacancies is one of the indispensable factors to give the mixed oxides a steady activity for NO decomposition.

Spinel structured CoaMnbOx mixed oxide catalyst for the selective catalytic reduction of NOx with NH3

Abstract: A highly efficient catalyst of a Co a Mn b O x mixed oxide prepared by the co-precipitation method was developed for the selective catalytic reduction (SCR) of NO x with ammonia. With an increase in the Mn content, the catalytic activity of the Co a Mn b O x mixed oxide exhibited a volcano-type tendency, and when Co/Mn molar ratio reached 7:3 (Co 7 Mn 3 O x ), the operation temperature for achieving >80% NO x conversion was 170 °C (116–285 °C window). The formation of spinel structured MnCo 2 O 4 is highly important, and the presence of the spinel structure in Co 7 Mn 3 O x contributes to the increase in active sites and thermal stability and promotes SO 2 and/or H 2 O resistance. In comparison with MnO x or CoO x alone, the Co a Mn b O x catalysts possess improved redox properties and more surface acid sites due to synergistic effects between the Co and Mn species. Among the Co a Mn b O x catalysts with different Co/Mn molar ratios, a higher NH 3 and NO + O 2 adsorption ability was found for the Co 7 Mn 3 O x catalyst, originating from its MnCo 2 O 4.5 phase and higher surface area, which leads to the higher activity of the Co 7 Mn 3 O x catalyst. In situ DRIFTs indicated that bridging nitrate and bidentate nitrate are the intermediate species in the NH 3 -SCR reaction, and the high NO adsorption ability and improved redox properties of the Co 7 Mn 3 O x catalyst are beneficial for the formation of nitrate species on the catalyst surface. Furthermore, NH 3 species adsorbed at Lewis acid sites taken part in SCR reaction, while the reactivity of NH 3 species adsorbed at Bronsted acid was not definitized.

Chemisorption sites on porous silica glass and on mixed-oxide catalysts

Abstract: It has been shown previously that two types of adsorption sites exist on the surface of porous silica glass (Corning code no. 7930) for the adsorption of polar molecules, such as ammonia. One site ...

Investigation of Acid−Base Properties of Catalysts Obtained from Layered Double Hydroxides

Abstract: Well-crystallized layered double hydroxides (LDH) containing Mg2+ or Ni2+ as divalent cations and Al3+ as trivalent cations were obtained either by coprecipitation (cp) or with the sol−gel (sg) method. After calcination, mixed oxide structures were achieved, as shown by XRD. Their acid−base properties were investigated through CO2 and NH3 TPD experiments and FT-IR spectroscopy, using CO2 and NH3 as probe molecules. Basic and acidic sites of medium-high strength were simultaneously revealed: the basic sites were mainly O2- atoms and Mn+−O2- pairs, while the Lewis acid sites were provided mainly by Al3+ in Mg-containing materials and by Al3+ and Ni2+ in Ni-containing materials. Several parameters, such as the nature of cations and anions involved in the LDH structure, the M2+/M3+ ratio, the synthesis method, and the activation conditions, influenced the acid−base properties of the mixed oxides. In particular, (i) Mg-containing samples showed higher basicity than Ni-containing samples, (ii) sg materials wer...