Adsorption and Activation of CO₂ by Amine-Modified Nanoporous Materials Studied by Solid-State NMR and ¹³CO₂ Adsorption

Abstract

The interaction of gaseous CO 2 with the surface of amine-modified nanoporous clays has been studied. CO 2 adsorption and adsorption microcalorimetry revealed high adsorption capacity and strong interaction with the surface at low pressures, due to the presence of amine groups. Considerable surface heterogeneity and high initial adsorption heat (125 kJ mol -1 ) have been observed, although the adsorption was reversible with hysteresis at low pressures and very slow desorption kinetics. Interaction between 13 CO 2 and the surface of the nanoporous clay materials has been investigated by 13 C and 15 N magic-angle spinning (MAS) NMR. 13 C NMR resonances at ca. 164 and 160 ppm have been assigned to, respectively, carbamate and carbamic acid, and the stability of these species have been studied. Peak areas and the amount of 13 CO 2 adsorbed allowed the determination of the concentration of carbamate and carbamic acid. To the best of our knowledge, this is the first time that solid-state NMR is used to clearly establish the formation of amine-CO 2 bonding at the surface of amine-modified nanoporous materials and to identify the nature of the species formed. The results presented here shed light on the mechanism of CO 2 activation, since the CO 2 adsorption on the surface of such materials is the activation step that allows further reactions to occur. The instability of the carbamate and carbamic acid species formed on the surface is important in explaining the reactivity of these intermediates and supports the possible application of these materials in CO 2 activation.

Designed amyloid fibers as materials for selective carbon dioxide capture

“…2B). As expected, no signal is detected around 125 ppm (28). Therefore, the NMR peak at 163.9 ppm arises from the carbon which is Solid data points represent gas adsorption and open points are gas desorption after a maximum pressure of ∼800 Torr.…”

“…covalently bound to the fiber (28). Indeed, this peak should arise from the formation of carbamate through the reaction of carbon dioxide with the primary amino groups of lysine residues similar to that observed in the amine solutions (4).…”

Simple synthesis of porous melamine-formaldehyde resins by low temperature solvothermal method and its CO2 adsorption properties

“…CO 2 molecule can not combine with tertiary amino group in the absence of water [41]. Thus the theoretical maximum amino utilization efficiency of the branched PEI is about 35% [42][43][44]. The results in this study showed Yin et al -eXPRESS Polymer Letters Vol.11, No.11 (2017) 873-884 Figure 7.…”

“…The influence of temperature on the CO 2 adsorption of PMFR-PEI-30% (30% PEI loading) was investigated ( Figure 8). It is obvious that the PMFR-PEI-30% adsorbent showed a maximum adsorption capacity of 2.89 mmol/g at 30°C, implying the balance between CO 2 diffusion into inner layer of PEI and the desorption of CO 2 from PEI [43,45]. The adsorption process at a lower temperature was diffusion controlled, elevation of temperature would accelerate the diffusion of CO 2 inside of the thick layer of the PEI, and be beneficial for the full extension of the PEI's chain and hence provide more adsorption sites, leading to more sufficient contact with CO 2 .…”

CO2adsorption on different organo-modified SBA-15 silicas: a multidisciplinary study on the effects of basic surface groups

“…(Figure 9). Moreover, an additional resonance at 164 ppm was clearly visible in all the samples and was attributed to the presence of carbamate groups 54 . Moore et.al has studied CO 2 adsorption on hyperbranched amine polymers grown from the mesoporous silica SBA--15 which exhibited mixture of chemisorption products, including carbamate, carbamic acid and bicarbonate moieties [55] .…”