(412e) Investigations of CO, NO and Water Adsorption on Nickel Faujasites X and Y- - DFT Calculations, Synthesis and Thermodynamic Studies

This article evaluates the adsorption capacity of NO, CO and water on faujasites zeolite X and Y exchanged with the nickel cation. This work is in keeping with the occupational health and more specifically the treatment of diesel exhaust gas in confined work environments. Indeed, many investigations have been performed for NO and CO treatments issue exhaust gas diesel. Catalysis is one of technic the most common used like selective catalytic reduction (SCR). However, catalysis processes have proven to be particularly efficient only at high temperature (<300°C). Thus, the resulting technological solutions are not well adapted for non-road vehicles that run discontinuously during the day leading to low exhaust gas temperature. Therefore, remove these pollutants requires to find a selective material which can adsorb of NO and CO in the presence of water. The trap would be placed upstream the catalytic reactor.

Nickel transition metal has been chosen thanks to molecular modelling: DFT calculations used PBE GGA with D2 dispersion correction scheme method. A screening has been performed on several divalent cations and Si/Al ratio. Interaction energy of each gas has been reach. Ni cation behaves more efficiently, since each faujasites, NiX and NiY, show a greater affinity for NO and CO than water.

The cation-exchange was then performed by treating faujasites NaY and NaX with nickel salt solution. ICP OES and XRD analysis, carried out on the solid phase, allowed to observe an over-exchange. The manometry (Belsorp max II apparatus - BEL company), was used to provide adsorption isotherms of CO, NO and water with sodium and nickel exchanged faujasites. Experiments carried out at least three temperatures (5, 25 and 35°C) to obtain the isosteric heat of all gas by the isoster method. The textural properties were obtained by nitrogen adsorption/desorption experiments carried out at 77 K. These investigations allowed showing that the crystal structure has not been damaged by the multiple exchanges carried out.

This work allowed validating DFT calculations, to determine equilibrium constant and to assess the adsorbed amount maximum of gas. The cationic exchange has not a significant influence on the water adsorption. Its adsorption capacity keeps the same order of magnitude after comparison between NaY/NiY and NaX/NiX but it remained very high for X-faujasite: X-faujasites were moderately selectivity for water. Hence, the zeolite studied indicated that the NiY zeolite is the most appropriate faujasite to trap the NO and CO molecules in the presence of water.

Figure 1: Isosteric heat of NO, CO and water for NiY faujasite (Si/Al: 2.55) versus the amount of gas adsorbed. Isoster method has been used. Color cross characterizes DFT calculation at zero coverage for NiY and NaY.