A series of reactions including water, oxygen, hydrogen and nitric oxide dissociation and carbon monoxide or nitric oxide oxidations catalyzed by metallic surfaces have been investigated by means of periodic density functional calculations with the main aim of establishing the importance of spin polarization when the substrate is nonmagnetic. Numerical differences in the calculated total energies and bond lengths of the breaking/forming bonds corresponding to spin restricted or spin unrestricted formalisms are usually smaller than the inherent error of density functional theory based methods. Nevertheless, it is important to insist on the fact that the spin polarized solution exists and is lower in energy than the one corresponding to the spin restricted formalism, as one would expect, and from a practical point of view, results obtained without taking spin polarization into account lead to the same description of the potential energy surface.