Analysis of NMR Adsorption Isotherms of Zeolite ZSM-5: Adsorption Profiles Derived from the Pressure and Temperature Dependences of 129Xe NMR Chemical Shift and Signal Intensity

Abstract

Xe NMR spectroscopy of nanomaterials, such as zeolites, can provide valuable information on the nanostructure and physicochemical properties of adsorption. In the present study the pressure and temperature dependences of the 129 Xe NMR chemical shift and the signal intensity were investigated in detail with a zeolite ZSM-5. The pressure dependence of the signal intensity at constant temperature was analyzed based on the Langmuir and Dubinin-Radushkevich (D-R) models, from which the thermodynamic parameters and energetic profiles of adsorption were obtained together with information concerning the nanospace size. From this isotherm analysis the coverage, θ, was calculated and used for isotherm analysis of the chemical shift. The θ dependence of the chemical shift was successfully fitted by an exponential function, and the results were discussed in relation to the chemical shift at zero coverage, that at full coverage and the curvature of the exponential function. The chemical shift data reported with the zeolites NaA and KA, where separated signals were observed for the different number of encapsulated Xe atoms in the α cage, were analyzed and discussed collectively.

Unravelling the structure of CO2 in silica adsorbents: an NMR and computational perspective

“…Owing to the sensitivity to probe adsorbate-adsorbate and adsorbate-adsorbent interactions, NMR relaxation methods have been used to quantify adsorbed gases on solids enabling to register adsorption isotherms. [109][110][111][112][113][114][115][116][117][118] In general, this approach covered a wide range of materials including zeolites, mesoporous silica, activated carbons and MOFs which were probed for the adsorption of CO 2 , CH 4 , C 2 H 6 , C 3 H 8 and also vapours of MeOH, PrOH and H 2 O for gas capture/separation and other emerging applications. In most cases, these experiments were limited to the use of low-field magnets and carried out ex situ.…”

“…In most cases, these experiments were limited to the use of low-field magnets and carried out ex situ. [109][110][111][112]114 In contrast, in situ tests were less common mainly due to the difficulties in designing and building the experimental setup. One alternative was found by integrating NMR with either a sorption analyser or a homemade gas dosing system.…”

Assessing CO2 Capture in Porous Sorbents via Solid-State NMR-Assisted Adsorption Techniques

“…Due to their sensitivity to probe adsorbate–adsorbate and adsorbate–adsorbent interactions, NMR relaxation methods have been used to quantify adsorbed gases and vapors into solid porous sorbents, mainly employing ex situ NMR measurements and limited to low-field magnets. − Recent studies showcased in situ measurements of adsorption isotherms by integrating NMR with either a sorption analyzer or a homemade gas dosing system. , Nevertheless, previous methodologies are only able to follow the physisorbed fraction of the adsorbate, where the majority of these methods are restricted to monitoring 1 H signals in the adsorbed molecule due to sensitivity reasons.…”