The surface species formed from the reaction of COCH2O and
COCO2 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 COCH2O
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 ºas(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!H2 CCO2) 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 O2. The formate species is further decomposed
with time to carbonate species |
