Computational evaluation of the capability of transition metal exchanged zeolites for complete purification of hydrogen for fuel cell applications: the cheapest performs the best

Abstract

The study reports an estimation of the capability of zeolites exchanged with different monovalent transition metal cations to be used for the deep purification of hydrogen for PEMFC applications from CO, ammonia and hydrogen sulfide impurities. The estimation is based on thermodynamic data derived by computational modeling using the periodic DFT approach, and allows determination of the minimal impurity gas concentration in the H₂ feed that could be achieved with the specific adsorbent. The results suggest that zeolites exchanged with Co⁺, Ni⁺, Cu⁺, Rh⁺ or Ir⁺ cations can purify hydrogen under standard conditions to CO concentrations of 10⁻¹²–10⁻¹⁶, depending on the metal. A theoretically recommended material for hydrogen purification is Cu exchanged zeolite, since it is able to reduce CO concentrations down to 10⁻¹¹ and has weaker binding of CO compared to the other modeled cations, which facilitates the regeneration of the adsorbent. In addition, this zeolite can capture NH₃ and H₂S impurities and reduce their concentration in the H₂ feed to 10⁻¹⁰, while the other modeled cation exchanged zeolites show a higher permeability of these impurities and are less appropriate. Thus, the modeled adsorbents, in particular Cu exchanged zeolite, are good candidates for H₂purification due to their low cost and predicted high efficiency, and could be considered as an appropriate alternative to the other currently applied approaches.