Adsorption of Nitrogen, Oxygen, and Argon in Cobalt(II)-Exchanged Zeolite X

Abstract

Adsorption of nitrogen, oxygen, and argon on cobalt(II)-exchanged zeolite X at 288.2 and 303.0 K was studied. The nitrogen and oxygen adsorption capacities increase upon cobalt ion exchange up to 71%, beyond which it shows a decreasing trend because of the partial degradation of the zeolite structure during the cation exchange and high-temperature vacuum dehydration processes. The magnitude of the increase in the adsorption capacities for nitrogen is much higher than that of oxygen. The nitrogen/oxygen as well as nitrogen/argon selectivities in the low-pressure region increase with an increase in cobalt exchange. Marginal oxygen selectivity over argon is observed for zeolite samples with higher cobalt exchange. The heats of adsorption values for nitrogen and oxygen increase and that for argon remain unaffected by cobalt exchange in zeolite X. The very high nitrogen adsorption capacity, selectivity, and heat of adsorption in the low-pressure region for cobalt-exchanged zeolite X compared to the parent sodium form of the zeolite show stronger interaction between nitrogen molecules with the extraframework cobalt cations of the zeolite. This stronger interaction has been explained in terms of the pi-complexation between nitrogen molecules and cobalt cations of the zeolites, as confirmed by diffuse reflectance infrared Fourier transform spectroscopy, wherein the N[triple bond]N stretching frequency at 2099 cm(-1) is observed for N2 molecules adsorbed in NaCoX.

Study on adsorption of N2 and O2 by magnesium (II)-exchanged zeolite A

“…The results can be explained by the reduction of offset cations number in the framework, caused by replacement of two Na + cations by one Mg 2+ cation. In addition, Mg 2+ has a smaller radius than Na + and occupies less space in the cavity of zeolite, resulting in the increase of surface area as well [17].…”

“…Ca 2+ [10][11][12]) and transition metal cations (e.g. Ce 3+ [13], Mn 2+ [14], Ag + [15,16] and Co 2+ [17]). …”

Adsorptive properties of X zeolites modified by transition metal cation exchange

“…Transition metal complexes are reported to interact with N 2 through end-on coordination (M-N≡N) (Nakamoto 1997). The adsorption of nitrogen on the cobalt-exchanged zeolite X with different cobalt content was investigated (Sebastian et al 2005). The stronger interactions of the nitrogen molecules were explained in terms of the π -complexation between nitrogen molecules and extraframework cobalt cations of the zeolites.…”

Gas adsorption properties of ZSM-5 zeolites heated to extreme temperatures

“…The porous framework of ZSM-5 accounts for its high specific surface area and makes it an interesting material for gas adsorption [25]. Furthermore, compared to Y-type zeolites, ZSM-5 has an exceptionally high degree of thermal stability due to its high silicon/aluminum ratio and pore structure; it is therefore, potentially useful for processes involving elevated temperatures [20][21][22].…”