Interaction of HCOOH with a rhodium surface, studied by Auger electron, electron energy loss, and thermal desorption spectroscopy

Abstract

The interaction of HCOOH with Rh foil has been investigated by various techniques at low and high temperatures with the primary motivation to determine the stability of formate species on unsupported Rh. The electron energy loss spectrum of Rh foil in the electronic range exhibited losses at 4.1,5.4, 19.6, and 29.5 eV. Adsorption of HCOOH on Rh at 95 K produced new losses at 8.2, 11.3, and 14.2 eV. The intensities of these losses decreased with rise of sample temperature, and new losses developed at 9.5 (O(.,) and 13.2 eV (CO&. On the basis of the behaviour of the above losses, as well as that of the observed decomposition/desorption products of adsorbed HCOOH, it is concluded that (i) HCOOH is adsorbed dissociatively on Rh even at -100 K, producing adsorbed H and formate species, (ii) the surface formate starts to decompose slightly below 200 K yielding HZ, C02, chemisorbed CO, and 0, (iii) the decomposition goes to completion around 300 K, and (iv) the primary products of decomposition of formate species strongly interact with the Rh surface.

Adsorption of HCOOH on Rh(111) and its reaction with preadsorbed oxygen

“…The EEL spectrum of adsorbed HCOOH at 100 K agreed well with those observed for Rh foil [15]. The origin of these losses has been discussed earlier in detail [15], but no comparison with UPS was made.…”

“…It is very likely that the much larger amount of CO formed on Rh foil in the surface decomposition of HCOOH is mostly due to the effect of this boron impurity [16]. This view is supported by the EELS spectra, where an intense loss feature was produced at 9.5 eV during heating of the HCOOH-covered Rh foil to above 300 K [15].…”

“…It was purified in the manner reported earlier [15]. Extended vacuum evaporation removed CH 30H and CH 3COOH.…”

“…The origin of these losses has been discussed earlier in detail [15], but no comparison with UPS was made. Taking into account the energy levels of adsorbed HCOOH on the Rh(IlI) surface determined by UPS we assign the observed losses at 7.9, 11.3 and 14.8 eV to the intramolecular electron transitions from the lOa, 2b, the 9a, l b, and the 8a, 7a orbitals to the unfilled 3b or lla orbitals of RCOOH, respectively, which are situated at around 1.6-2.0 eV above the Fermi level.…”

“…We earlier investigated the adsorption of HCOOH on polycrystalline Rh [15]. In the present work the interaction of HCOOH with an ordered surface structure of Rh, i.e.…”