Catalysis

A catalyst is a compound that alters the rate of a reaction, but is chemically unchanged by the reaction.   A catalyst can either increase the rate of a reaction (called a positive catalyst) or decrease the rate of a reaction (called a negative catalyst, or an inhibitor).   The primary method through which a catalysts operates in by lowering the energy barrier to the products of the reaction, or in other words, a catalyst permits reactions or processes to take place more effectively by requiring less energy.   A catalyst can also change the temperature at which the reaction takes place, making the reaction more feasible than it would be otherwise.   Twenty percent of the modern industrial processes depend on catalysis.

Generic graph showing the effect of a catalyst in an hypothetical exothermic chemical reaction.  The presence of the catalyst opens a different reaction pathway (shown in red) with a lower activation energy.  The final result and the overall thermodynamics are the same. 

There are two types of catalysts: A homogeneous catalyst takes place in the same phase at a reaction mixture, while a heterogeneous catalyst is in a different phase (like a solid catalyst in solution).   The rate of a reaction depends in part on the surface area of the reactants.   By minimizing the size of a particle, the surface area can be maximized per gram.   Because the particles in nano-catalysts are so small, there are more of them in the same volume than a regular catalyst would have, which means that a gram of nanoparticles has a greater surface area than a gram of larger particles.   The greater the surface area of the catalyst, the faster the rate at which the reaction progresses and the greater the efficiency of the catalyst.

Many processes can and are currently benefiting from nanocatalysts.   Nanocatalysts can be used in fuel cells, to reduce the wear and tear on automobile engines, for better catalytic converters, and to reduce the time of industrial processes.   They can increase the fuel efficiency through using a catalyst that burns more of the fuel at the given temperature.   Certain nanocatalysts can also convert cellulose to ethanol for fuel.