Complexity of ammonia interactions on activated carbons modified with V2O5

A micro/mesoporous wood-based activated carbon was modified with different loadings of vanadium pentoxide via incipient impregnation with ammonium vanadate solution followed by heating in nitrogen at 500 °C. The materials were used as adsorbents for ammonia. Both adsorption and desorption curves were recorded. The initial and exhausted samples were characterized by Fourier transform infrared spectroscopy (FTIR), potentiometric titration, thermal analysis and adsorption of nitrogen. An improvement in ammonia uptake compared to the virgin carbon was observed, and the adsorption capacity was found linearly dependent on the metal content. Water increases ammonia adsorption capacity via dissolution of the gas, but it also competes with ammonia because both of them are preferentially adsorbed on the same vanadium oxide sites (vanadyl oxygens). Even though an increase in the interactions strength between ammonia and the adsorbents' surface has been reached compared to previous studies, some weakly adsorbed ammonia was still released from the surface during air purging.

Vanadium pentoxide provides additional Brønsted sites for ammonia retention. Although water favors ammonia dissolution, it has also detrimental effect competing with ammonia for adsorption on the vanadyl oxygen.Figure optionsDownload as PowerPoint slide