ADSORPTION AND REACTIONS OF FORMIC-ACID ON (2X2)-NIO(111) NI(111) SURFACE .1. TPD AND IRAS STUDIES UNDER ULTRAHIGH-VACUUM CONDITIONS/

The adsorption and decomposition of formic acid on (2x2)-NiO(111) surf ace have been studied using temperature-programmed desorption (TPD) an d infrared reflection absorption spectroscopy (IRAS) under ultrahigh v acuum (UHV) condition. Formic acid dissociated to surface formate at 1 63 K for low exposure and molecular adsorption occurred at higher expo sure of formic acid. Absorption bands observed at 2858, 1570, 1360, an d 778 cm(-1) on the IRA spectra were assigned to the C-H stretching, O -C-O asymmetric stretching, O-C-O symmetric stretching, and O-C-O defo rmation modes of adsorbed formate, respectively. Cumulative considerat ion of vibrational frequencies, assignment of the bands, and the selec tion rule of IRAS revealed that the formate is in bidentate configurat ion but is tilted sideways to the surface. The adsorbed formate decomp osed through two reaction pathways on raising the temperature; dehydro genation producing H-2 and CO2 occurred at 340, 390, and 520 K and deh ydration producing CO occurred at 415 and 520 K. The temperature-depen dent IRA spectra reflected the thermal desorption behavior of adsorbed formate.