Mechanism of catalytic decomposition of formic acid on a nickel surface

Abstract

The decomposition of formic acid on a nickel surface was studied by volumetric measurement of the adsorption during the reaction and also by the infra-red technique. The chemisorbed species during the decomposition of formic acid were only formate ion and proton. The rate of the decomposition was proportional to the formic acid pressure and decreased markedly by the increasing amounts of formate ion on the surface. Accordingly, the decomposition proceeded on the surface not covered by the formate ion. The rate of the decomposition of the formate surface layers was expressed by the Zeldovich-Roginsky equation as a function of coverage. A part of the overall reaction proceeded via the formate ion, and the rest between the formic acid molecule and the surface not covered by the formate ion. The overall reaction rate was given by rate =kP_HCOOHf(1–θ)+k′ exp [a(x–x_o)]

where (1–θ) is the fractional surface not covered by formate ion; the second term gave the rate via the formate ion in the surface. The exchange reaction of formate ion and proton in the surface with those in formic acid molecules in the ambient gas is a process independent of the decomposition reaction.