Mohamed Elanany

Computational methods for the design of zeolitic materials

Recently we developed an accelerated quantum chemical molecular dynamics program “colors”, which is approximately 5000 times faster than the first principle quantum chemical molecular dynamics calculation. In the present study we have applied our Colors program to the investigation of the structure and dynamics of big periodic models for crystobalite (96 atoms) and H-mordenite (145 atoms). Our results show clearly the proton migration in-between the two oxygen atoms named O16 and O18 in H-mordenite model which are more energetically preferable than other two oxygen atoms named O41 and O19 surrounding the A1 atom. The change of the proton charge during the simulation has been observed.

Influence of force fields on the selective diffusion of para-xylene over ortho-xylene in 10-ring zeolites

A molecular dynamics study of diffusion of p-xylene and o-xylene has been performed over three different pure silica 10-ring zeolites, MFI, SFG and TUN. The shape selective properties of the frameworks of these three materials have been tested using four different types of force fields commonly used based on united atom, rigid-ion and core-shell approximations. The performance of each force field is analysed in order to find which force fields can give sufficiently accurate estimations that allow to select appropriate zeolites for selective separation of para/ortho xylene. This performance was found to depend on the quality of the structural properties of the zeolite, in particular the size and shape of the 10 rings which act as bottlenecks for the diffusion. The computational results allow us to define some optimum characteristics for the selective diffusion of p-xylene.

On the role of organic amine templates in the synthesis of A1PO molecular sieves: An experimental and computational study

Abstract A combined experimental and theoretical study is carried out to show the effect of various organic amine templates on the synthesis of A1PO-5 from the same gel composition. It is shown that under mild conditions, TEAOH is the best template. However, after addition of HF to the synthesis gels, TPA/HF and TEAOH/HF give better A1PO-5 crystals than MCHA/HF or TEA/HF.

An accelerated quantum molecular dynamics study of NH3 interaction with the brønsted acid in periodic zeolite models

Abstract We report the adsorption characteristics of NH 3 on the periodic model of acidic mordenite (H-MOR), which is unique and different from the conventional bare- and embedded-cluster description of the zeolite active site, and that the calculated adsorption energy is very close to the experimental results. Moreover, for the first time, the dynamic behavior of ammonium ion interacting with the zeolites lattice is studied. Our main finding is that the protons are in continuous transfer in-between NH 4 + ion and the lattice oxygen atoms around the aluminum site.

Dynamics of water and methanol in h-mordenite

Abstract The dynamic behaviors of water and methanol in acidic mordenite are studied using a novel quantum chemical molecular dynamics program and density functional method. The calculated adsorption energies for methanol and water are -108.3 and -95.2 kJ/mol, respectively. Although cationic species viz., H 3 O + and CH 3 OH 2 + were found to be more stable than neutral species by DF method, molecular dynamics simulations at finite temperatures revealed that cationic species are only short-time living species. Increasing the loading ratio of methanol to two molecules per one acidic site decreases the adsorption energy to -87.6 kJ/mol.

Density functional investigations on the acidic properties of the novel ZOL molecular sieves

Density functional calculations on periodic models of various acidic microporous molecular sieves, viz., H-CHA, H-SAPO-34, H-ZOL-1C, and H-ZOL-2C, are conducted to characterize the acidic properties of the novel zeolites with organic lattices (ZOL) sieves and to compare them to the acidic properties of the largely-investigated zeolites and SAPOs. Adsorption energy of ammonia as a basic probe is considered to tackle this goal. Introducing methylene group into the inorganic zeolite framework is studied. Results show that ZOL have intermediate acid site strength between the zeolite and SAPO of the same structural topology.

Toward a better understanding of the templating effect in the formation of porous frameworks: AlPO4-5 a case of study

Abstract AlPO 4 -5 has been synthesized using four different organic templates, viz., methyldicyclohexylamine (MCHA), triethylamine (TEA), tripropylamine (TPA), and tetraethylammonium hydroxide (TEAOH). The effect of these templates on the produced AlPO 4 -5 samples is investigated using various experimental techniques: SEM, XRD, TG, and FT-Raman spectroscopy. Although AlPO 4 -5 structure is observed clearly with all organic templates under the synthesis condition, the crystals morphology is different.