Catalysis of Organic..

150CO Oxidation0.02(a)21802110(b)2180212220462004Time(Min.)4.003.002.00Absorbance1.000.00216720001833224521051965Wavenumber (cm -1 )Figure 3. (a) IR spectra of adsorbed CO on HAuCl 4 Catalyst at 298 K, (b) IRspectra of adsorbed CO on AuCl 3 Catalyst at 298 K during switch of the flow(35cm 3 /min) from CO/He (90/10 Vol%) to He (100 Vol%).The presence of various types of Au sites and carbonate/carboxylate species as wellas variation in the OH intensity of TiO 2 (not shown here) during the reactionsuggests that CO oxidation over AuCl 3 catalyst could follow the carboxylatemechanism which involves the reaction of adsorbed CO with OH to produce acarbonate/carboxylate species on Au cations and the decomposition of carboxylate toCO 2 .(3, 10) Transient infrared study needs to be employed to further verify the roleof carbonate/carboxylate species in the reaction pathway. (13)CO and CH 3 CH 2 OH Pulses with and without H 2 O 2Hydrogen peroxide (H 2 O 2 ) is used as an oxidizing agent to produce adsorbed oxygenspecies to gain a better understanding of the mechanisms of CO 2 formation.Addition of H 2 O 2 promoted CO oxidation. H 2 O 2 addition also enhanced ethanoloxidation as indicated by the increase in IR intensity of CO 2 at 2351 cm -1 , as shownin Fig. 4(b). Fig. 4 also shows pulsing ethanol into He/H 2 O 2 /O 2 causes (i)emergence of the ethanol’s C-H stretching bands at 3973, 2923, and 2893 cm -1 , (ii)the formation of acetate and carboxylate in 1290 - 1570 cm -1 (14, 15) (iii) anddisplacement of H 2 O as indicated by the decrease in H 2 O intensity at 1633 cm -1 andthe increase H-bonding intensity of ethanol in the 3380 cm -1 region. The variation ofacetate and carboxylate intensity with the change in CO 2 intensity suggests thatacetate and carboxylate species may be a reaction intermediate.