Spectroscopic and kinetic studies of the reaction of CO+H2O and CO+O-2 and decomposition of HCOOH on Au/H-mordenite catalysts

摘要

The surface species formed from the reaction of CO + H2O and CO + O-2 and decomposition of HCOOH on Au incorporated into H-mordenite zeolite have been studied by means of in situ FTIR spectroscopy. On H-mordenite, a bidentate formate species (2912, 1536, and 1390 cm(-1)) is produced upon exposure to the CO + H2O gas mixture at 323 K, as well as different carbonate-like species (1956, 1852, 1705, and 1360 cm(-1)). The latter species was extensively formed in a short time and was responsible for hindering the CO2 adsorbed species. However, Au/H-mordenite presented different vibration modes of formate species with a high emphasis on the monodentate ones (2950, 2916, 2896, 1690, and 1340 cm(-1)). The HCOOH adsorption on Au/H-mordenite showed two bands at 1622 and 1590 cm(-1) of the v(as)(OCO) species, suggesting the formation of two types of formate species. The decomposition rate of the formate species formed on Au moieties was faster than that formed on H-mordenite. This was consistent with the calculated activation energies of CO2 formation that showed a lower value (40.1 kJ/mol) on the former sample than on the latter one (63.3 kJ/mol). A dehydrogenation mechanism is proposed (HCOOH --> H-2 + CO2) for the decomposition of HCOOH on the Au/H-mordenite catalyst. On the other hand, the Au/H-mordenite catalyst activated the CO oxidation reaction. This reaction proceeded mainly through the formation of carboxylate species at first, which tended to obviate with time, preferring the formate species. The latter species resulted from the interaction of CO with OH stretching of the zeolite assisted by the presence of gas phase O-2. The formate species is further decomposed with time to carbonate species, (C) 2000 Academic Press. [References: 26]