Molecular Basis for the High CO₂ Adsorption Capacity of Chabazite Zeolites

Abstract

CO2 adsorption in Li-, Na-, K-CHA (Si/Al=6,=12), and silica chabazite zeolites was investigated by powder diffraction. Two CO2 adsorption sites were found in all chabazites with CO2 locating in the 8-membered ring (8MR) pore opening being the dominant site. Electric quadrupole-electric field gradient and dispersion interactions drive CO2 adsorption at the middle of the 8 MRs, while CO2 polarization due to interaction with cation sites controls the secondary CO2 site. In Si-CHA, adsorption is dominated by dispersion interactions with CO2 observed on the pore walls and in 8 MRs. CO2 adsorption complexes on dual cation sites were observed on K-CHA, important for K-CHA-6 samples due to a higher probability of two K(+) cations bridging CO2. Trends in isosteric heats of CO2 adsorption based on cation type and concentration can be correlated with adsorption sites and CO2 quantity. A decrease in the hardness of metal cations results in a decrease in the direct interaction of these cations with CO2.

Rational Synthesis of Chabazite (CHA) Zeolites with Controlled Si/Al Ratio and Their CO2/CH4/N2 Adsorptive Separation Performances

“…[32,34,35] Chabazite (CHA) is ar epresentative small-pore zeolite and its analogs (SSZ-13 and SAPO-34) have been introduced as catalysts for methanol-to-olefins (MTO) processes and for selective catalytic reduction (SCR) of NO x .I na ddition, the remarkable separation performances of CHA zeolite in regard to small gas molecules have been verified. [36][37][38] CHA zeolite is generally synthesized by using N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as an organic structure-directinga gent (OSDA). [39,40] The consumption of the expensive TMAdaOH contributesg reatlyt ot he overall costs of CHA zeolite.…”

Tuning Zeolite Properties towards CO2 Methanation: An Overview

“…The interaction of CO 2 molecules with the zeolite samples is also modified by the Al content, since catalysts with higher Si/Al ratios (↓Al) present less negative charges in the structure (↓basicity). As a result, the type/nature of interaction between the zeolite adsorption sites and the reactant molecules will be affected ,,. Zeolites with lower Si/Al ratios can adsorb a greater number of carbon dioxide molecules since, as already referred, CO 2 interacts with basic framework oxygens and/or compensating cations, whose number will increase directly with the Al content in the structure ,.…”

“…As a result, the type/nature of interaction between the zeolite adsorption sites and the reactant molecules will be affected. [21,25,[114][115][116][117][118][119] Zeolites with lower Si/Al ratios can adsorb a greater number of carbon dioxide molecules since, as already referred, CO 2 interacts with basic framework oxygens and/or compensating cations, whose number will increase directly with the Al content in the structure. [117,118] Additionally, the strength of the interactions established between zeolites and CO 2 , typically as carbonate-like species, could be also affected by the Si/Al ratio.…”

“…[21,25,[114][115][116][117][118][119] Zeolites with lower Si/Al ratios can adsorb a greater number of carbon dioxide molecules since, as already referred, CO 2 interacts with basic framework oxygens and/or compensating cations, whose number will increase directly with the Al content in the structure. [117,118] Additionally, the strength of the interactions established between zeolites and CO 2 , typically as carbonate-like species, could be also affected by the Si/Al ratio. [119] Indeed, systematic studies performed in the literature for evaluating the influence of this parameter [37] confirmed that the affinity and interactions of zeolite samples to CO 2 is favoured for lower Si/Al ratios, even though the observed catalytic activity decreases.…”

Determination of zeolite-group mineral compositions by electron probe microanalysis

“…Carbonate sorption on synthetic zeolite surfaces is discussed in Harjula et al (1993), who demonstrate how the reactive interplay of NaOH -, HCO 3 -and CO 3 2-solutes affects the Si-Al framework. For low-Si zeolites, there has been recent interest in the chabazite structure and its affinity for CO 2 , in relation to carbon-capture studies using synthetics (Kim et al, 2014;Pham et al, 2014). Thus, while it is difficult to analyse for low concentrations of C routinely by EPMA, its potential presence should be borne in mind in interpretation of compositional data, and its determination by other analytical techniques should be considered (e.g.…”