Density Functional Theory Study on the Adsorption of H₂S and Other Claus Process Tail Gas Components on Copper- and Silver-Exchanged Y Zeolites

The potential use of Cu- and Ag-exchanged Y zeolites as selective adsorbents for hydrogen sulfide (H₂S) from Claus process tail gas was investigated with density functional theory (DFT). The adsorption energies of H₂S and other Claus tail gas components (CO, H₂O, N₂, and CO₂) were computed for these zeolites as well as for Li–Y, Na–Y, and K–Y on a cluster model. Comparison of adsorption energies for H₂S versus the other components indicated that Ag–Y has potential for selective adsorption of H₂S, whereas Cu–Y is subject to strong adsorption of CO, and alkali metal-exchanged Y zeolites are subject to H₂O adsorption. Comparison with alkali metal-exchanged Y zeolites was performed to clarify the role of d electrons, while the influence of the zeolite framework was assessed by comparing adsorption energies on the cluster model with those on bare cations. Absolutely localized molecular orbital energy decomposition analysis (ALMO EDA) revealed that for Cu- and Ag-containing systems, transfer of electrons between the cation and the adsorbate, i.e., the donation of d electrons and the acceptance of electrons in the unoccupied orbitals of the cation, plays an important role in determining the adsorption energy. On the other hand, for alkali metals-containing systems, charge transfer is negligible and adsorption energies are dominated by interactions due to electrostatics, polarization, and structural distortions

Coating of Open Cell Foams

The interior surfaces of three-dimensional open cell foams were coated by a combination of dip coating and spin coating. Glycerol/water solutions were used as model Newtonian liquids, and the coating processes were studied on open cell carbon foams with 10 or 30 pores per inch (PPI). The amount of liquid retained in the foam structures after dip coating increased with withdrawal speed and coating viscosity, as expected from the conventional understanding of dip coating onto nonporous substrates such as flat plates and rods. However, the liquid retention and hence average coating thickness increased with surface tension, a result counter to the observation with coating onto nonporous substrates. Pockets of liquid were observed after dip coating and results with coatings of alumina suspension showed that after drying, the trapped liquid can block pore windows. Spinning the foams after dip coating resulted in uniform liquid distribution and uniform coatings. Foams were placed in a special apparatus and rotated using a commercial spin coater. The liquid layer thickness decreased with spinning time and rotational speed, and increased with the liquid viscosity, results consistent with spin coating theory. The coating thickness after spinning was not affected by the initial dip coating procedure. The dip and spin process was also used to create γ-alumina and zeolite coatings, which are of interest for catalysis applications