Why are manganese compounds powerful catalysts?
Let’s start with the definition of a catalyst. A catalyst is a substance that accelerates a reaction without undergoing net chemical change. Another common way of looking at a catalyst is that it provides an alternative reaction route with a lower activation energy than the original. A good example of a catalyzed reaction is the decomposition of hydrogen peroxide catalyzed by manganese oxide. Each molecule of hydrogen peroxide is broken down into one equivalent of water and half an equivalent of oxygen.
What happens at the surface of the manganese oxide in relation to the hydrogen peroxide is very interesting. But it’s beyond the scope of this video. But the first principle is that the catalyst serves to bring together the reactants in high concentration, and then weakens the internal bonds of the reactants by forming other bonds. This allows other reactions to occur, additions, substitutions, et cetera, and considerably speeds up the rates of these reactions.
Manganese has the electronic structure with an argon core of 4s²3d⁵. This means that there are 4s and 3d electrons available to donate into reactants to form extra bonds. In manganese compounds, you’ll have charged manganese species. These may have electron configurations with empty 4s and 3d orbitals for accepting electrons. These two factors combine together to significantly weaken the reactant bonds, making manganese compounds powerful catalysts.
Now, we need to write all this in full sentences. Why are manganese compounds powerful catalysts? Because manganese has 4s and 3d electrons and empty orbitals which can be used in the formation of bonds between manganese and reacting molecules. Firstly, this leads to an increase in the concentration of these molecules on the surface of the catalyst. And, secondly, a weakening of the bonds of the reactant molecules and a reduction in the activation energy of the reaction.