Catalytic removal of NO

Metal nanoparticles have attracted much attention over the last decade owing to their unique properties as compared to their bulk metal equivalents, including a large surface-to-volume ratio and tunable shapes. To control the properties of nanoparticles with particular respect to shape, size and dispersity is imperative, as these will determine the activity in the desired application. Supported metal nanoparticles are widely employed in catalysis. Recent advances in controlling the shape and size of nanoparticles have opened the possibility to optimise the particle geometry for enhanced catalytic activity, providing the optimum size and surface properties for specific applications. This Review describes the state of the art with respect to the preparation and use of supported metal nanoparticles in catalysis. The main groups of such nanoparticles (noble and transition metal nanoparticles) are highlighted and future prospects are discussed.

Sustainable Preparation of Supported Metal Nanoparticles and Their Applications in Catalysis

Copper-based catalysts are active in a wide range reactions of transformation of nitrogen oxides and represent an useful model system to better understand the fundamental aspects of the chemistry and mechanism of reaction of catalytic transformation of these pollutants. After an introduction on the reactivity of copper-based catalysts (supported and unsupported copper oxide, Cu-zeolites, cuprates and other copper compounds) in various reactions of conversion of nitrogen oxides, four main sub-topics are discussed in detail: (i) nature of copper species, (ii) chemisorption and surface transformations of NO, (iii) relationship between copper species and activity in the conversion of nitrogen oxides and (iv) mechanism of reduction of nitrogen oxides to N 2 . Five reactions of transformation of nitrogen oxides are discussed in detail: (i) decomposition of NO, (ii) reduction of NO with ammonia in the presence or not of oxygen, (iii) reduction of NO with hydrocarbons in the presence of oxygen, (iv) reduction of NO with CO and (v) decomposition of N 2 O. The mechanism of reduction of nitrite and N 2 O by copper enzymes is also discussed, with a view to provide some useful insights on the chemistry of transformation. In this review particular attention is directed towards controversial points in the literature, underestimated questions, and hypothesis and theories which do not allow interpretation of all sets of experimental data. Discussion is also focused on the presence of multiple and competitive pathways of transformation, the relative roles of which depend on reaction conditions.

Mordecai Shelef

Papers

Ammonia Formation in Catalytic Reduction of Nitric Oxide by Molecular Hydrogen. II. Noble Metal Catalysts

Ammonia Formation in Catalytic Reduction of Nitric Oxide by Molecular Hydrogen. I. Base Metal Oxide Catalysts