Ammonia Vapor Removal by Cu3(BTC)2 and Its Characterization by MAS NMR

Adsorption equilibria and NMR experiments were performed to study the adsorption and interactions of ammonia with metal-organic framework HKUST-1, or Cu-3(BTC)(2) (BTC = 1,3,5-benzenetricarboxylate). Ammonia capacities determined from chemical breakthrough measurements show significantly higher uptake capacities than from adsorption alone, suggesting a stronger interaction involving a potential reaction with the Cu-3(BTC)(2) framework. Indeed, H-1 MAS NMR reveals that a major disruption of the relatively simple spectrum Of Cu-3(BTC)(2) occurs to generate a composite spectrum consistent with Cu(OH)(2) and (NH4)(3)BTC species under humid conditions-the anticipated products of a copper(II) carboxylate reacted with limited ammonia. These species are not detected under dry conditions; however, reaction stoichiometry combined with XRD results suggests the partial formation of an indeterminate diammine copper(II) complex with some residual Cu-3(BTC)(2) structure retained. Cu(II)-induced paramagnetic shifts exhibited by various species in H-1 and C-13 MAS NMR spectra are consistent with model compounds and previous literature. Although results show extensive ammonia capacity Of Cu-3(BTC)(2), much of the capacity is due to reaction with the structure itself, causing a permanent loss in porosity and structural integrity.