The temperature and coverage dependences of adsorbed formic acid and its conversion to formate on Pt(111)

Journal Article · Wed Feb 12 04:00:00 EST 1992 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00030a017· OSTI ID:232077

Columbia, M R; Crabtree, A M; Thiel, P A ^[1]

---

1. Iowa State Univ., Ames, IA (United States)

The authors have studied the absorption of HCOOH on Pt(111) at 80-100 K and it conversion to formate with increasing surface temperature. The techniques employed are thermal desorption spectroscopy. At very low exposures (<0.2 langmuir), the authors posit that HCOOH exists molecularly as monomers or discrete dimer pairs. As exposure increases, there is evidence for hydrogen-bonded chains with the molecular plane of HCOOH nearly parallel to the surface. At an exposure of 0.2 L, these chains resemble the solid-phase {beta}-polymorph as indicated by the vibrational frequencies of the OH out-of-plane bending vibration. Heating this surface causes the chains to break apart into discrete dimer pairs, followed by deprotonation to a bridging formate adspecies. The formate decomposes between 210 K and 280 K, causing CO{sub 2} desorption and leaving hydrogen adatoms. Increasing the exposure above 0.6 L causes the chains to adopt a structure similiar to the denser {alpha}-polymorph. Heating this surface causes molecular desorption in two states. One is centered at 160 K and is dominated by gaseous HCOOH dimers. Desorption in this state leaves bridging formate and {beta}-polymorphic HCOOH coexistent on the surface. The other is centered at 200 K and is primarily gaseous monomers. Desorption in this state leaves only the formate adspecies. Its decomposition then proceeds as on the surface exposed to 0.2 L HCOOH. 38 refs., 10 fig., 2 tab.

• OSTI ID: 232077
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 4 Vol. 114; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
DESORPTION
FORMIC ACID
PLATINUM
SORPTION
SORPTIVE PROPERTIES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K