Rational design and in situ fabrication of MnO2@NiCo2O4 nanowire arrays on Ni foam as high-performance monolith de-NOx catalysts

Abstract

In this work, we have rationally designed and originally developed a novel monolith de-NO_x catalyst with nickel foam as the carrier and three dimensional hierarchical MnO₂@NiCo₂O₄ core–shell nanowire arrays in situ grown on the surface via a two-step hydrothermal process with a post calcination treatment. The catalysts were systematically examined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, elemental mapping, ion sputtering thinning, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectroscopy, H₂ temperature-programmed reduction, NH₃/NO + O₂ temperature-programmed desorption measurements and catalytic performance tests. The results indicate that the nanowire is composed of hollow NiCo₂O₄ spinel as the core and MnO₂ nanoparticles as the shell layer. By ingeniously making the hierarchical Ni–Co oxide nanowires as the support for manganese oxides, the MnO₂@NiCo₂O₄@Ni foam catalyst not only takes advantage of the high surface area of Ni–Co nanowires to achieve high loading amounts as well as high dispersion of manganese oxides, but also makes use of the synergistic catalytic effect between Ni, Co and Mn multiple oxides, and exhibits excellent low-temperature catalytic performance in the end. In addition, with the structure and morphology well maintained under long term steady isothermal operation, the catalyst is able to sustain high NO conversion and exhibits superior catalytic cycle stability and good H₂O resistance. Considering all these favorable properties, the MnO₂@NiCo₂O₄@Ni foam catalyst could serve as a promising candidate for the monolith de-NO_x catalyst at low temperatures and the rational design of in situ synthesis of 3D hierarchical monolith catalysts also puts forward a new way for the development of environmental-friendly and highly active monolith de-NO_x catalysts.