A HREELS STUDY OF THE ADSORPTION OF FORMIC-ACID ON SLIGHTLY OXIDIZED NB(110) SURFACE

An investigation has been made on the adsorption and decomposition of formic acid on slightly oxidized Nb(110) surface (O/Nb atom ratio = 0. 2) using high resolution electron energy loss spectroscopy (HREELS), a nd a corresponding surface reaction mode is given. At 140 K, formic ac id of low exposure on such an Nb(110) surface decomposed to formate, w hich bonded on Nb in monodentate configuration, simultaneously some fo rmate decomposed to CO, which adsorbed on the surface. Formic acid mul tilayers formed when the exposure was high. While the temperature was increased to above 190 K, multilayer formic acid desorbed, and the sur face was covered with monodentate-bonded formate and CO. In the temper ature range of 250-300 K, chemisorbed formate changed from monodentate configuration into bridging configuration and CO molecules disappeare d. The decomposition of formate at higher temperatures led to the oxid ation of Nb. The formate formed in the high exposure case was so stabl e that it did not decompose even the temperature was as high as 540 K.