Synergistic Effect of Mixed Oxide on the Adsorption of Ammonia with Metal-Organic Frameworks

A hydrotalcite-derived MgAl oxide (MMO) was evaluated in combination with the metal-organic frameworks (MOFs) UiO-66 and UiO-66-NH2 for the adsorption of ammonia. Analysis of the materials textural properties after ammonia breakthrough adsorption revealed no change in the PXRD patterns or FTIR spectra; however, a slight decrease in surface area was observed, consistent with the hypothesized presence of strongly adsorbed species after adsorption. UiO-66:MMO and UiO-66-NH2:MMO composites maintained ammonia adsorption capacity under dry conditions. An almost 2-fold increase in humid ammonia capacity was observed for the UiO-66:MMO composite, far beyond that expected through a linear combination of the two materials capacities. The synergistic effect observed in humid conditions was further investigated with water adsorption experiments, which suggested the effect is the result of the high water affinity of MMO.