Ammonia Vapor Removal by Cu3(BTC)2and 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 Cu3(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 Cu3(BTC)2framework. Indeed, 1H MAS NMR reveals that a major disruption of the relatively simple spectrum of Cu3(BTC)2occurs to generate a composite spectrum consistent with Cu(OH)2and (NH4)3BTC 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 Cu3(BTC)2structure retained. Cu(II)-induced paramagnetic shifts exhibited by various species in 1H and 13C MAS NMR spectra are consistent with model compounds and previous literature. Although results show extensive ammonia capacity of Cu3(BTC)2, much of the capacity is due to reaction with the structure itself, causing a permanent loss in porosity and structural integrity.