In order to understand why nanocrystal catalysts are so promising, one first needs to understand some basic principles of Chemistry. For any chemical reaction to occur, two reactive species must come in contact with each other. The term reactive does not imply unstable; wood is relatively inert unless it is heated. However, if it is warmed to approximately 451o Fahrenheit, the hydrogen and carbon composition of the wood reacts with oxygen in the air to form carbon dioxide and water. While this paper will not address how or why this reaction occurs, it is important to understand that it will cease if the reactive species are not in close proximity to each other. Fire will never originate in the core of burning logs because oxygen is not able to penetrate far beyond the surface. Anyone who has built a campfire knows that the fire only burns on the woods exterior.
Another key concept to understanding nanocrystal catalysis involves the ratio of surface area and volume. As an object gets larger, its surface area increases less in relation to its volume. A good way to visualize this is to imagine a cube (Figure 1). Volume is measured by multiplying the cubes length, width, and height. Surface area is determined by finding the area of one face of the cube (length x height) and multiplying it by the number of faces: in this case, six.