The catalytic decomposition of formic acid and methyl formate on cation-exchanged 13X molecular sieves

Abstract

The kinetics of the catalytic decomposition of formic acid to carbon monoxide and water and of methyl formate to carbon monoxide and methanol on 13X-type molecular sieves containing uni-, bi-, or ter-valent cations have been investigated in the temperature range 110–180°. A flow system with hydrogen as carrier gas was used, reactant partial pressures being 10–50 mm. Hg. In the formic acid reaction, activation energies and relative rates increased with increase in cation charge; for cerium and lanthanum sieves after pretreatment for 1 hr. in hydrogen at 360° the activation energy was ca. 84 kJ mole^–1 compared with ca. 125 in the absence of pretreatment. In the methyl formate reaction, while relative rates increased with increase in cation charge, activation energies correspondingly decreased, and the effect of pretreatment in hydrogen at 360° for cerium, lanthanum, and magnesium sieves was to raise the activation energy by ca. 25 kJ mole^–1. Mechanisms for the two reactions, and reasons for the changes in activation energy after the pretreatment are discussed. Experiments with formic acid and sieves partially exchanged with nickel, magnesium, or lanthanum ions, together with diffuse reflectance spectra for 20% and 60% exchanged nickel sieves, indicated that nickel ions preferentially occupy S_II or S_III sites on the supercages, while magnesium and lanthanum ions prefer S_I sites in the hexagonal prisms.