Infrared spectroscopical investigations on the adsorption of CO2 on aluminas and silica aluminas at elevated temperatures

Investigation of the behaviour of a Pd/γ-Al2O3 catalyst during methane combustion reaction using in situ DRIFT spectroscopy

“…They account for species adsorbed on the alumina support, since they also appeared when CO 2 was fed to pure alumina, in another study [56]. Based on literature data, the peak at 1650 cm À1 accounts for either hydrogenocarbonates [64,67,70] or carbonates species [60,65,66,68,69], likely in the bidentate configuration [65,60,68]. In the same region, another band may also appear below 200 8C, even in absence of CO 2 , at 1640 cm À1 .…”

“…The assignment of the peak at 1460 cm À1 is as difficult as that of the band at 1590 cm À1 . However, based on literature data (Table 1), it can tentatively be ascribed to free carbonates ions on the alumina surface or to m-CO 3 2À species [60,[65][66][67][68][69]71,74,[76][77][78], without excluding the potential formation of hydrogenocarbonates [64,67] or surface methoxy groups [73]. The peak at 1460 cm À1 will therefore tentatively be assigned to carbonates species, likely in the monodentate conformation.…”

“…Very close (if not identical) wavenumber values are ascribed to different surface species, especially concerning the peak observed at 1590 cm À1 . If we consider the 1600-1575 cm À1 range, this band accounts either for formates [54,59,60,64,65,[68][69][70][71][72][73][74] or for carbonates species [67,[75][76][77]. Some authors do not even dare to definitely ascribe a peak of this region to a well-defined structure (see e.g.…”

“…In addition, this investigation was also motivated by the experimental observation that, in our conditions, the surface of a powdered Pd (2 wt.%)/g-Al 2 O 3 catalyst was always in www.elsevier.com/locate/apcata Applied Catalysis A: General 295 (2005) [59][60][61][62][63][64][65][66][67][68][69][70] oxidized form after a conventional micro-reactor test [29][30][31][32]. Moreover, this oxidized surface state after test was observed even after an in situ reducing pre-treatment [30], or after a test in presence of low amounts of H 2 in the CCM feed [31,32].…”

High-Temperature Adsorption of Carbon Dioxide on Mixed Oxides Derived from Hydrotalcite-Like Compounds

“…The vibrational frequencies and their assignments are summarized in Table 5S of the Supporting Information (23,24). These various forms of carbonates are mainly associated with Ca, as unveiled by the differential thermogravimetry (DTG) profile (see Figure 2S, Supporting Information).…”