Location and valence state of strontium cations on the framework of a carbon dioxide selective porous silicoaluminophosphate

Dealuminated Beta Zeolite Modified by Alkaline Earth Metals

“…For Mg 2.0 DeAlBeta, Sr 2.0 DeAlBeta, and Ca 2.0 DeAlBeta, the broad band are seen at 267, 279, and 263 nm, respectively, related to isolated mononuclear Mg (II), Sr(II), and Ca(II) species well dispersed in the beta structure. e band at around of 267-279 nm could be attributed to pseudotetrahedral Mg(II), Sr(II), and Ca(II) species formed as a results of reaction of magnesium, strontium, and calcium ions with silanol groups of vacant T-atom sites of mesoporous DeAlBeta zeolite, in line with earlier reports on Sr-SAPO-34 [41] and MgAPSO-34 [42]. In the case of the Mg 2.0 DeAlBeta sample, the very small and broad band at about 300 nm is seen.…”

New Insight into the Doping Effect of Transition Metals (Fe, Ti, Mn, and Ce) on the Structure and Catalytic Performance of Cu-SSZ-13 Zeolite Catalysts for the NH3-SCR Reaction

“…It should be noted that multiple reduction peaks can be observed on the Cu 3.25 -SSZ-13 catalyst. According to the literature and previous studies, there are four ion sites in the CHA structure of the zeolite (Figure ), and the reduction peaks (α, β, and γ) in the H 2 -TPR spectrum correspond to the reduction of isolated Cu 2+ species at three of them: peak α (196 °C) is attributed to the reduction of isolated Cu 2+ species (Cu1) close to the eight-membered ring window (site IV); peak β (266 °C) is assigned to the reduction of isolated Cu 2+ species (Cu2) located in the supercage deviating from the double hexatomic ring (site I); and peak γ (367 °C) reflects the reduction of isolated Cu 2+ (Cu3), which is centered in the hexagonal prism (sites III); moreover, peak ζ (>800 °C) represents the reduction of ionic Cu + to metallic Cu 0 . ,− By doping transition metals, we can see that only peak β and peak γ can be observed below 500 °C. H 2 -consumption of peak α decreases from 67 μmol·g –1 to almost disappearing, which indicates the dopant ions are likely to exchange with Cu1 species located near the octatomic ring window.…”

Carbon Dioxide Removal from Humid Atmosphere by a Porous Hierarchical Silicoaluminophosphate/Carbon Composite Adsorbent

“…As shown in Figure 1, the distinctive reflections from the chabazite (CHA) like phase (i.e., are present in the patterns of CSAPO-34. 13 However, the decrease in peak intensities observed for Na + -CSAPO-34 compared with those reported for sole SAPO-34 could be due to the presence of the amorphous AC. In the case of the strontium ion-exchange composite (i.e., Sr 2+ -CSAPO-34), a decrease in peak intensities was also observed when compared with Na + -CSAPO-34; this is probably as a result of the ion exchange.…”

“…13,14 It was also determined that the Sr 2+ active sites were located in exposed locations within the framework main cage (see Scheme 1), occupying unique preferential positions (near sites II' and III) that are connected to the enhancement in adsorption capacity at low CO 2 concentrations. 13 Sr 2+ -SAPO-34 adsorbents can also be easily regenerated using a vacuum swing with or without a thermal intervention, which helps to minimize or plausibly eliminate any significant energy expenditure. 15 Nevertheless, although the Sr 2+ -SAPO-34 framework is tolerant to water, its adsorptive capacity is limited due to the competitive adsorption of water since a CO 2 roll-up behavior was observed during fixed-bed adsorption tests.…”

“…Among zeolitic adsorbents, silicoaluminophosphates (SAPOs), particularly Sr 2+ -SAPO-34, have shown efficacy in the removal of CO 2 at very low concentrations due to physisorption enhancement from overlapping surface electrostatic potential fields generated in combination with the extra-framework Sr 2+ and their interaction with the adsorbate; this is possible in part due to the relative sizes of the adsorbate (kinetic diameter, σ = 3.30 Å), the adsorbent pore (∼ 4–5 Å), and the actual distances between the active Sr 2+ adsorption sites within the SAPO structure. , It was also determined that the Sr 2+ active sites were located in exposed locations within the framework main cage (see Scheme ), occupying unique preferential positions (near sites II’ and III) that are connected to the enhancement in adsorption capacity at low CO 2 concentrations . Sr 2+ -SAPO-34 adsorbents can also be easily regenerated using a vacuum swing with or without a thermal intervention, which helps to minimize or plausibly eliminate any significant energy expenditure .…”