Adsorption and decomposition of formic acid on the NiO(111)-p(2x2) surface: TPD and steady state kinetics studies

The adsorption and decomposition of formic acid on NiO(111)-p(2 x 2) films grown on Ni(111) single crystal surface were studied by temperature-programmed desorption (TPD) spectroscopy. Exposure of formic acid at 163 K resulted in both molecular adsorption and dissociation to formate. The adsorbed formate underwent further dissociation to H-2, CO2 and CO. H-2 and CO2 desorbed at the same temperatures of 340, 390 and 520 K, while CO desorbed at 415 and 520 K. The desorption features varied with the formic acid exposure. Two reaction channels were identified for the decomposition of formate under equilibrium with gas-phase formic acid with a pressure of 2.5 x 10(-4) Pa, one preferentially producing H, and CO, with an activation energy of 22 +/- 2 kJ mol(-1) and the other preferentially producing CO and H2O with an activation energy of 16 +/- 2 kJ mol(-1). The order of both reaction paths was 0.5 with respect to the pressure of formic acid.