An FTIR study of the adsorption of formic acid and formaldehyde on potassium-promoted Cu/SiO2 catalysts

FT-IR spectra are reported for formic acid and formaldehyde adsorbed on a reduced Cu/SiO2 catalyst with and without the addition of potassium promoter. Catalysts partially oxidised by treatment with nitrous oxide have also been studied. Formic acid on potassium-promoted Cu/SiO2 produced a formate species on "potassium" and bidentate copper formate. More of the former was generated in the presence of Cu than for a reduced potassium/ SiO2 catalyst without copper, suggesting that either the formate species formed initially on the copper surface subsequently spilled over onto potassium sites, or that the morphology of potassium oxide was influenced by the presence of copper. Adsorption of formaldehyde on a potassium/silica catalyst resulted in the formation of unidentate formate and physisorbed formaldehyde on potassium. Polymerised formaldehyde structures were also observed. Formaldehyde on a reduced potassium-promoted copper/silica catalyst gave not only bidentate formate species formed on copper but also a substantial increase in the quantity of unidentate formate species on potassium. This result suggested that new adsorption sites at interfaces between copper and potassium oxide were created, which facilitated formate production.