Study of physisorbed carbon dioxide on zeolites modified by addition of oxides or acetate impregnation

Macroporous Niobium Phosphate-Supported Magnesia Catalysts for Isomerization of Glucose-to-Fructose

“…Figure typically shows the FT-IR spectra of MgO, 40%MgO/NbP-500, and 40%MgO/NbP-700 after adsorption of CO 2 at 25 °C and sequential desorption at 100, 200, and 300 °C to illustrate the structure of CO 2 chemisorbed on the catalyst surfaces. Cosimo, Iglesia, and Belin et al demonstrated that CO 2 was adsorbed on the surface of MgO mainly through bicarbonate, bidentate, and unidentate carbonates species, which refer to the low-, medium-, and high-strength basic sites, respectively. − The formation of bicarbonates requires the presence of hydroxyl groups on the MgO surface, which exhibit a C–OH bending mode at ∼1220 cm –1 , as well as asymmetric and symmetric O–C–O stretching modes at ∼1650 and 1480 cm –1 , respectively. Formation of bidentate and unidentate carbonates were both attributed to the presence of surface basic oxygen atoms (low-coordinated oxygen anions).…”

Probing zeolites by vibrational spectroscopies

“…Besides, although framework oxygen atoms have been by far the most frequently investigated in the literature, other basic centers can be encountered in zeolites for instance hydroxy groups resulting from the dissociation of water in hydrated extraframework cations, 567 basic oxygen atoms or hydroxy groups in oxide clusters, 568 or basic NH groups obtained by nitridation. In other words, the lower the electronegativities of the cations, the lower is the intermediate electronegativity, and more negative are the oxygen framework atoms.…”

“…On the basis of DFT calculations carried out on linear ion-CO 2 complexes, however, Pirngruber et al discussed the formation of such species by noting that on basic zeolites, such as K-Y or Cs-Y zeolites, the carbon atom of CO 2 adsorbed in 12-ring windows (supercages) does interact with zeolite framework oxygen atoms, leading to a slight bending of the OQCQO angle (o31), and can be considered as a precursor of bridged carbonate species (Fig. 568,603 For completeness, it should be noted that boric acid trimethyl ester (B(OCH 3 ) 3 ) was proposed as a Lewis acid probe molecule by Li et al for the characterization of the basic properties of metal oxides 546 and zeolites. 602 The impossibility of forming carbonate species on light alkali-exchanged zeolites, such as Li-or Na-Y, is explained within this qualitative model by (i) the lower basicity of framework oxygen atoms and (ii) the position of the small cations, which are close to a hexagonal window, leading to short M + Á Á ÁOCO distances (Fig.…”

Glucose isomerisation into fructose over magnesium-impregnated NaY zeolite catalysts

“…The basic sites density of the pure NaY zeolite is increased through Mg addition [48]. However, it can be seen that no further benefit is achieved by overloading the sample with magnesium, since Moreover, Belin et al [50] showed that bicarbonate species appear to be the dominant CO 2 adsorbed species on Mg-impregnated NaX zeolites. In addition, the calcination temperature is reported to influence the proportion of the various basic sites, weaker basic sites prevailing with an increase of the temperature due to a reduction of the MgO surface defects [51].…”