An in situ infrared cell capable of studying reactions over heterogeneous catalysts in the temperature range 77 to 773 K has been designed. In particular, the adsorption of formic acid on a model Cu/SiO2 methanol synthesis catalyst was investigated. Exposure of a reduced copper surface to formic acid at 300 K resulted in the formation of both formic acid molecules, which were ligated to the copper catalyst, and chemisorbed bidentate copper formate species. Under temperature-programming conditions, the bidentate species displayed a maximum rate of desorption at 433 K, which correlates to a desorption activation energy of 120 kJ mol-1. In contrast, on the reoxidized catalyst, unidentate formate species were preferentially formed. These exhibited a maximum rate of desorption at a temperature of 408 K, and a desorption activation energy of 113 kJ mol-1. A mechanism was postulated to explain this behavior, and evidence was presented to show that useful kinetic data can be obtained for desorption from a catalyst in the form of a pressed disk.
Graeme J. Millar, David Newton, Graham A. Bowmaker, and Ralph P. Cooney, "In Situ FT-IR Investigation of Formic Acid Adsorption on Reduced and Reoxidized Copper Catalysts," Appl. Spectrosc. 48, 827-832 (1994)