CO Adsorption on Ag Nanoclusters Supported on Carbon Nanotube: A Molecular Dynamics Study

Abstract

Molecular dynamics simulations are used to study CO adsorption on Ag nanoclusters ranging from 38 to 500 Ag atoms, supported on carbon nanotube. Each nanocluster was simulated under various pressures of CO gas at different temperatures. The absolute value of enthalpy of adsorption was calculated for all of the nanoclusters in constant coverage which is increased sharply by decreasing cluster size. This increasing trend with coverage reaches a maximum around 0.75 ML for Ag 108 . Also, the structural changes are irreversible in such a way that by gradually decreasing the pressure to zero, the nanocluster geometry is not reversed to its initial structure in vacuum conditions. It was found that structural irreversibility increases with the size. Also, the difference between diffusivity of Ag nanoclusters in vacuum and CO atmosphere increases with the size.

H2adsorption on Ag-nanocluster/single-walled carbon nanotube composites: A molecular dynamics study on the effects of nanocluster size, diameter, and chirality of nanotube

“…This result is expectable, due to the fact that H 2 molecules are physisorbed on the Ag nanoclusters and at higher temperatures molecules gain more kinetic energy which can overcome to the adsorption potential. Therefore, at higher temperatures, more H 2 pressure is needed to reach saturation state, as reported earlier by Zhang et al Also this result is consistent with the fact that increasing of temperature decreases the coverage due to the more ability of adsorbates to be desorbed from the surface at higher temperatures . Moreover, these adsorption isotherms are according to those of the Langmuir type‐I …”

“…The similar graphs are obtained for other sizes of Ag nanoclusters deposited on other nanotubes with mentioned diameters and chiralities. The effect of nanocluster size on the H 2 adsorption is the same as that of our previous work, in such a way that composites with smaller nanocluster size reach to saturation state faster . As it is obvious from Figure , the saturation pressure increases by temperature.…”

“…This is also a reasonable result due to the operation of two phenomena: On one hand, N surf is lower for smaller nanoclusters, and On the other hand, smaller nanoclusters have lower cohesive energy and stability for which surface atoms have more tendencies to the adsorbates to increase the cohesive energy and stability of the cluster. This phenomenon can be explained by Wolf construction in which the cohesive energy of a N ‐atom nanocluster is given as: where E C ( N ) and E b0 are cohesive energies of N ‐atom cluster and complete macroscopic crystal, respectively. B a is the actual bond number on the cluster surface and B t is the bond number in the perfect macroscopic crystal.…”

“…Moreover, the enthalpy of adsorption, Δ H ads , for H 2 on Ag N /( m,n ) composites were obtained by Clausius–Clapeyron equation …”

Investigation of Thermodynamic, Dynamic, and Structural Properties of H2 Adsorption on a Ag–Au Nanoalloy with a Carbon Nanotube Support

“…Cheng et al34 performed MD simulations for H 2 adsorption on SWCNTs in order to study the effect of the diameter of nanotube and its chirality. More recently, Shamkhali and Akbarzadeh13 studied the adsorption of H 2 on a bundle of single‐walled carbon nanotubes (SWCNTs) and an Ag–Cu bimetallic nanocluster located on the groove site of the bundle by MD simulation. Their simulations were performed in order to study the effect of the Ag mole fraction and the diameter of the nanotube on the H 2 adsorption.…”