Isolation and characterization of formates on CeOx–CuyO/Cu(1 1 1)

• Formate species are characterized on ceria-copper oxides model catalysts.
• Three types of formates are stabilized in copper oxides.
• Reverse spillover of formates is observed from nanoparticles of ceria to copper.

Formate species have been proposed to be either critical intermediates or spectators in the water–gas shift (WGS) and methanol synthesis processes. CeOx–CuyO/Cu(1 1 1) has been shown to be a very active inverse catalyst for the WGS reaction. We present here the study of formate species obtained from the deprotonation of formic acid (HCOOH) on the inverse catalysts. Exposure of CeOx–CuyO/Cu(1 1 1) to HCOOH at 300 K leads to the formation of formates on both ceria and Cu sites. The formates isolated on CeOx–CuyO/Cu(1 1 1) systems cannot be hydrogenated even at a pressure of 200 Torr H2 at 300–350 K. The formate species localized on ceria sites are thermally more stable than those on Cu sites, and the thermal decomposition of all of the formates occurs by dehydrogenation releasing CO2 and H2. Evidence of reverse spillover of formates from the oxide to the metal was observed on CeO2−x/Cu(1 1 1) inverse catalysts.

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