ADSORPTION AND REACTION OF HCOOH ON DOPED CU(110) - COADSORPTION WITH CESIUM, OXYGEN, AND CSA+OA

The adsorption and reaction of formic acid on a clean Cu(110) surface and Cu(110) surfaces covered with oxygen, cesium, and oxygen + cesium have been studied with thermal desorption mass spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). Formic acid adsorbs molecularly on clean Cu(110) at 110 K, but largely decomposes on the surface to yield adsorbed formate (HCOOa) and Ha, at T ≤ 270 K (possibly as low as 200 K). The Ha desorbs as H2 at ~ 300 K. The HCOOa decomposes to yield H2 and CO2 at 475 K. Preadsorbed oxygen abstracts the acid hydrogen of HCOOH more efficiently than clean Cu, so formate production increases. At high θo, evidence is seen for formate disproportionation (2HCOOa→ HCOOH + CO2), probably via OHa. Adsorbed cesium also increases formate production. At low coverages, cesium accelerates HCOOa decomposition. Above 1 2 monolayer, a new formate decomposition peak at 530 K is attributed to a new, more stable formate which is directly bonded to Cs. At high θCs, surface carbonate (Cs · CO3,a) is formed from the decomposition products of HCOOa. This carbonate decomposes at ~ 650 K. When oxygen and cesium are coadsorbed, their effects on HCOOHa and HCOOa are largely a sum of their separate effects, although Cs-stabilized surface hydroxyl species are also produced with the combination. © 1990.