Analysis of Mackinawite-like Iron Sulfides as Catalysts and Mediators of Nitrite Reduction- Effects of Structure, Dopants, Protons and Selectivity of Reduction Products

What is it about? The reduction reaction is a kind of chemical reaction in which a reactant (A) gives electrons to another reactant (B) to produce a product (P). To explain the reduction reaction, two different mechanisms has been proposed. In one case, the flow of the electrons goes directly from A to B to produce P in a reaction called “direct reduction reaction”. In the second case, the flow of the electrons goes from an extra reactant (C) to B to produce P, in which A is present but does not directly interfere with the reaction. This latter reaction is called “catalytic reduction reaction”. This thesis explores the differences between these two chemical reactions by using the nitrite (NO2-) reduction to produce ammonia (NH3). These reactions are mediated by a set of iron sulfides materials which interestingly are founded in different sceneries such as in the active site of enzymes and in the structure of natural chimney in the bottom of the ocean where the life is believed begun. Why is it important? We show that the relationship between direct and catalytic reduction reactions is important to understand because the two reactions compete with each other in any practical application of a catalysts were a reduction reaction is involved. All iron sulfides tested could act as both catalysts and as direct reductants of NO2- to ammonia, and the pH, concentration of reactants and disorder level of the materials are the determinate factors in the selectivity by one or other process. It is an important consideration in catalyst design and in directing product selectivity. Perspectives: “Understanding the differences between of direct, and catalytic reduction reactions offers a theoretical framework for the development of efficient and economic new generation of catalyst”