General scheme of adsorption,electroreduction and catalytic hydrogenation of nitro-compounds of platinum—I. Kinetics and mechanism of adsorption

The kinetics and mechanism of adsorption of nitro-compounds (nitro-methane, nitro-ethane and nitro-benzene) on platinum and platinum group metals have been investigated by complex potentiodynamic pulses' and charging curves' techniques. The adsorption of nitro-compounds on platinum in the potential range from 0 to 1 V has been shown to proceed mainly with the formation of two types of chemisorbed particles. For potentials more positive than 0.35 V nitro-compounds are adsorbed due to a nitro-group with the formation of NPt and OPt bonds. In this region of potentials the adsorption of nitro-compounds is not accompanied with the flow of considerable amounts of electricity through the electrode—solution interface. These adsorbed particles react very rapidly with adsorbed hydrogen with the formation of semi-reduced chemisorbed particles, whose formation can be observed at 0 < E_r < 0.35 V, that is in the range of hydrogen desorption on platinum. Two hydrogen atoms are spent on the formation of a semi-reduced chemisorbed particle from a nitro-compound molecule, and the particle formed occupies 4 adsorption centres on the surface.The dependence of steady-state coverage of the platinum electrode surface with chemisorbed particles in nitro-compounds solutions is described by the Temkin isotherm and the adsorption kinetics by the Roginsky—Zel'dovich equation.