A square lattice topology coordination network that exhibits highly selective C₂H₂/CO₂ separation performance

Abstract

C 2 H 2 /CO 2 separation is an industrially important process that remains challenging because of the similar physicochemical properties of C 2 H 2 and CO 2. We herein report that the new square lattice (sql) coordination network [Cu (bipy-xylene) 2 (NO 3) 2 ] n , sql-16-Cu-NO 3 , 16 = bipy-xylene = 4,4′-(2,5-dimethyl-1,4-phenylene)dipyridine, exists in at least three forms, as-synthesised (α), activated (α′) and hydrated (β). The activated phase, sql-16-Cu-NO 3-α′, is an ultramicroporous material that exhibits high selectivity towards C 2 H 2 over CO 2 as revealed by dynamic gas breakthrough experiments (1:1, C 2 H 2 /CO 2) that afforded 99.87% pure CO 2 in the effluent stream. The separation selectivity at 298 K and 1 bar, 78, is the third best value yet reported for C 2 H 2 selective physisorbents whereas the mid-loading performance sets a new benchmark. The performance of sql-16-Cu-NO 3-α′ is attributed to a new type of C 2 H 2 binding site in which CH•••ONO 2 interactions enable moderately strong sorbent-sorbate binding (Q st (C 2 H 2) = 38.6 kJ/mol) at low loading. Conversely, weak CO 2 binding (Q st (CO 2) = 25.6 kJ/mol) at low loading means that (ΔQ st) AC [Q st (C 2 H 2)-Q st (CO 2)] is 13 kJ/mol at low coverage and 11.4 kJ/mol at mid-loading. Analysis of in situ powder X-ray diffraction and modelling experiments provide insight into the sorption properties and high C 2 H 2 /CO 2 separation performance of sql-16-Cu-NO 3-α′.

Breaking the trade-off between selectivity and adsorption capacity for gas separation

“…Therefore, comparing (Δ Q st ) AC at low coverage does not always translate well to a prediction of relative binding affinity and is why we consider (Δ Q st ) AC at half loading to be a suitable metric to estimate relative binding for an equimolar mixture. 42 Figure 4 B reveals that NbOFFIVE-3-Cu and SIFSIX-21-Ni set new benchmarks of (Δ Q st ) AC values at half loading, 15.2 and 14.9 kJmol −1 , respectively. This result is consistent with their DCB separation performances especially higher α AC relative to those of TIFSIX-4-Ni , SIFSIX-21-Cu , TIFSIX-4-Cu , and NbOFFIVE-3-Ni .…”

“…26 To the best of our knowledge, only a few (20) 41 and sql-16-Cu-NO 3 -a'. 42 Whereas these results are promising, they do not fully address the spectrum of performance parameters needed before a material can be considered for commercialization. 43 In particular, in addition to selectivity, working capacity and recyclability (including the kinetics and energy of regeneration) are also key performance parameters.…”

“…Our review of the literature reveals that C 2 H 2 /CO 2 separation selectivity ( α AC ) values for equimolar (v/v) mixtures have been experimentally measured for only 16 sorbents, most of which are classified as MOFs: SIFSIX-Cu-TPA , 29 TCuI , 30 TCuBr , 30 TCuCl , 30 JCM-1 , 31 NKMOF-1-Ni , 32 FJU-22a , 33 FJU-89a , 34 HOF-3 , 35 FJU-6-TATB , 36 SSNU-45 , 37 JXNU-5 , 38 FJU-36a , 39 FeNiM′MOF , 40 UTSA-74a , 41 and sql-16-Cu-NO 3 -α' . 42 Whereas these results are promising, they do not fully address the spectrum of performance parameters needed before a material can be considered for commercialization. 43 In particular, in addition to selectivity, working capacity and recyclability (including the kinetics and energy of regeneration) are also key performance parameters.…”

“…In our experience, for most C 2 H 2 selective sorbents, particularly those with high surface areas, Q st (C 2 H 2 ) at half and full coverage decline from their zero loading values because of weak multilayer adsorption. Therefore, comparing (DQ st ) AC at low coverage does not always translate well to a prediction of relative binding affinity and is why we consider (DQ st ) AC at half loading to be a suitable metric to estimate relative binding for an equimolar mixture 42. Figure4Breveals that NbOFFIVE-3-Cu and SIF-SIX-21-Ni set new benchmarks of (DQ st ) AC values at half loading, 15.2 and 14.9 kJmol À1 , respectively.…”

Nanostructure@metal-organic frameworks (MOFs) for catalytic carbon dioxide (CO2) conversion in photocatalysis, electrocatalysis, and thermal catalysis

“…As for electrocatalytic CO 2 reduction reaction (CO 2 RR), metal-organic frameworks (MOFs) have been extensively studied as brilliant electrocatalysts. Their highly tunable structure/active site/pore size and remarkable specific surface area are beneficial to CO 2 molecule enrichment for promoting CO 2 RR activity [17][18][19][20]. And the well-defined catalytic environments in MOFs were also considered to be a suitable system for catalytic mechanism explanation.…”