Molecular graphics image comparing the catalytic potential of two different forms of iron crystal surface in the synthesis of ammonia from nitrogen. A nitrogen molecule (blue) is shown on both surfaces. The iron (111) surface at right is known to be 500 times more catalytically active than the iron (110) surface. This is supported here by the close-packed appearance of iron (110) compared to the uneven iron (111), with its greater number of available sites for the adsorption of nitrogen molecules. Experiments have confirmed that the ability of nitrogen to stick to an iron surface is reflected in the reaction rate.