Infrared study of the adsorption of carbon monoxide, carbon dioxide, acetic acid and acetic anhydride on the surface of anhydrous vanadyl pyrophosphate

Abstract

Acetic acid and acetic anhydride are dissociatively adsorbed to give acetate anions on the surface of vanadyl pyrophosphate. Undissociated acetic acid molecules ligated to Lewis-acidic surface sites are partially displaced as the surface concentration of acetate anions increased. The products of adsorption of carbon dioxide and carbon monoxide are probably carbonate or bicarbonate species resulting from reaction with surface oxide ions. Adsorbed acetate and carbonate ions are predominantly in the bidentate configuration.An infrared study1 of the adsorption of water and pyridine has established that Brarnsted-acidic hydroxy groups and Lewis-acidic sites exist on the surface of anydrous vanadyl pyrophosphate (VO),P,O,, which is an important component of vanadiumphosphorus mixed-oxide catalysts for the oxidation of hydrocarbons to maleic anhydride.,? The mechanism of the oxidative reaction involves surface oxide ions as reactive intermediate specie^.^-^ The reactivity of surface oxide ions is here monitored by infrared studies of the adsorption on (VO),P,O, of the probe molecules carbon monoxide, carbon dioxide and acetic acid. Carbon monoxide and acetic acid were chosen also because of their ability to ligate to coordinatively unsaturated exposed cations in the surface of solids. It was hoped that comparison of adsorption data for water, pyridine,l carbon monoxide and acetic acid might facilitate the further characterisation of Lewis-acidic surface sites. Acetic anhydride was chosen as a model adsorbate to probe the interactions between a simple acid anhydride and the surface of (VO),P,O, because it was expected that at least some of the resulting adsorbed species would resemble species produced by the adsorption of acetic acid.

Accessibility and Dispersion of Vanadyl Sites of Vanadium Silicate-1 Nanoparticles Deposited in SBA-15

“…57 Carbonate species have been reported to be formed by reaction of CO 2 with surface oxide ions in vanadyl compounds. 58 Case (b) in Scheme 1 represents a CO 2 addition reaction toward one of the equatorial oxygens. In this case, the isotropic 13 C hyperfine will be small because the carbon nucleus will be out of the equatorial plane.…”

“…Different binding modes involving framework oxygen and a cation were reported for oxides . Carbonate species have been reported to be formed by reaction of CO 2 with surface oxide ions in vanadyl compounds . Case (b) in Scheme represents a CO 2 addition reaction toward one of the equatorial oxygens.…”

Room-temperature-adsorption behavior of acetic anhydride on a TiO2(110) surface

“…The HREELS and LEED patterns indicated dissociative adsorption of Ac 2 O on the TiO 2 (1 1 0) [44] and a zeolite [45].…”

Direct Conversion of Cellulose into Ethyl Lactate in Supercritical Ethanol–Water Solutions

“…Over three consecutive runs at 260 8C, the yield of EL from cellulose steadily decreased with the re-used catalystw ithout regeneration( Figure S7), which implied that the re-polymerizedh umins might inhibit the catalysta ctivity.T he yields of furfural and HMF increased with increasing catalyst cycles. [25][26][27] Therefore, carboxylic acid groupsw ere identified on the spent catalysts urface, which enhanced the Brønsted acidity and led to the higher yields of HMF and furfural. As shown in Figure 4b, the attenuated total reflectance (ATR)-FTIR spectra of the spent Zr-SBA-15c atalyste xhibit ab road peak at~3380 cm À1 that is attributed to the stretching ÀOH band;t he peaks at 2960 to 2840 cm À1 are the stretching vibration signal of the CH band in ÀCH 2 À or ÀCH 3 groups;t he peaks located at 1730 cm À1 are probably the stretching vibrations of C=Ob ands in carboxylic acids and the bands at 1460 and 1360cm À1 belongt ot he ÀCH 2 À and ÀCH 3 deformation vibrations.…”

“…As shown in Figure 4b, the attenuated total reflectance (ATR)-FTIR spectra of the spent Zr-SBA-15c atalyste xhibit ab road peak at~3380 cm À1 that is attributed to the stretching ÀOH band;t he peaks at 2960 to 2840 cm À1 are the stretching vibration signal of the CH band in ÀCH 2 À or ÀCH 3 groups;t he peaks located at 1730 cm À1 are probably the stretching vibrations of C=Ob ands in carboxylic acids and the bands at 1460 and 1360cm À1 belongt ot he ÀCH 2 À and ÀCH 3 deformation vibrations. [25][26][27] Therefore, carboxylic acid groupsw ere identified on the spent catalysts urface, which enhanced the Brønsted acidity and led to the higher yields of HMF and furfural. The organic S.R.s on the spent catalysts can be easily removedb yc alcination in air flow.A ccording to the FTIR characterization, the regenerated catalysts howed similar spectra to the fresh catalyst.…”