Mutual Diffusivity of an n-Hexane-2,2-Dimethyl Butane Binary Mixture Confined to Zeolite Y.

A molecular dynamic study of a mixture of n-hexane and 2,2-dimethyl butane (22DMB) confined to zeolite NaY has been carried out to understand the distinct diffusivity and mutual diffusivity. Results have been compared with the bulk mixture. For each of these mixtures, eight different runs were employed to compute distinct and mutual diffusivity. From the velocity auto- and cross-correlation functions between n-hexane and n-hexane, n-hexane and 22DMB, 22DMB and 22DMB, the self- and distinct diffusivity of the mixture has been computed. The thermodynamic factor and mutual diffusivity have been calculated. The ratio of D11 to Ds is seen to be 1.11 and 0.75 for the confined mixture, while they are 1.21 and 0.79 for the bulk mixture at 200 and 300 K, respectively.

Shared hydrogen bonds: water in aluminated faujasite.

Water confined in faujasite, a zeolite, with aluminium content, exhibits properties different from those of bulk water as well as water confined in siliceous faujasite. The RDF between oxygen of water (OW) and oxygen of aluminium (OAl) shows a prominent first peak near to 2.9 Å similar to any oxygen-oxygen RDF seen in bulk water and unlike water confined in siliceous faujasite. Further, HW-OAl shows a peak near 1.9 Å suggesting hydrogen bonding between hydrogen of water and OAl. The water satisfies the hydrogen bond criteria with both O1Al and O2Al indicating that it is participating in a shared hydrogen bond. The hydrogen bond exchange between such a water forming a shared hydrogen bond to OAl and another water molecule H2Ob is investigated through the changes in the distances and appropriate angles. The O-Al-O angle of the zeolite increases by about 7 degrees on the formation of the shared hydrogen bond. The jump dynamics of the shared hydrogen bond when the two bonds break simultaneously has been obtained and this is reported. This jump reorientation dynamics is different compared to normal hydrogen bonding reported by Laage and Hynes: it has a short lifetime, around 50-100 fs computed from SHB(t). The intermittent and continuous hydrogen bond correlation functions are also reported.