Abstract
The complex configuration, H2 adsorption binding energy, magnetic, and optical properties of FAU zeolites with Ag cations loaded by ion exchange in the vacant dielectric cavities were investigated by employing the first-principles calculations with all-electron-relativistic numerical atom-orbitals scheme and the Metropolis Monte Carlo molecular simulations. The visible absorption spectrum peaked at distinct wavelengths arranging from red or green to blue colors when changing the net charge load, due to the produced various redox states of Ag cations exchanging at multiple Li+-substituted sites. The spin population analyses indicate the ferrimagnetic coupling between Al–O–Si framework and Ag cations originates from the major ferromagnetic spin polarization in Ag cation cluster coordinating with sodalite cages, with the net spins appreciably depending on the Ag content and exchange site. The H2 adsorption capacities and binding energies represent significant dependence on the content, location, and electronic property of Ag cations introduced into the FAU zeolites. The evident decrease of H2 adsorption binding energy with increased loading concentration demonstrates repulsive interaction between H2 molecules and heterogeneous adsorption configuration on Ag cations. The adsorption sites of H2 sorted by the binding energy with different adsorption configurations were correlated with exchange sites of Ag cations under different Ag loading to comprehend the H2 adsorption mechanism.
Highlights
The transition metal (TM) cations introduced by exchanging Si or Al covalent atoms with lower valence state atoms of III or II main group in zeolite framework at specific porous locations can present specific physical-chemistry environment due to the characteristic metal-framework interaction and dominate the adsorption and heterogeneous catalysis performance [1]
The essential mechanism of silver cations formation in the porous zeolite structures has not been well comprehended and precisely pictured, which play pixel role in understanding and improvement of gas storage and electrochromism especially when the silver cluster migrate between different locations at variable environment such as temperature and applied electric field. It has been suggested from experimental investigations that considerable magnetism and electrochromism could be introduced into lithium-exchanged low-silica X-type (Li-LSX) zeolites by doping TM [9], no ab initio theoretical study has been reported for TM-exchange Li-LSX zeolites to calculate the spin-polarized electronic structure, based on which the magnetic and optical properties will be predicted and the underlying physics can be revealed
Ag cations to model Ag-exchange Li-LSX (Agx Li1−x -LSX) zeolites, which will be as the initial structure for further geometry optimization of first-principles total energy calculations
Summary
The transition metal (TM) cations introduced by exchanging Si or Al covalent atoms with lower valence state atoms of III or II main group in zeolite framework at specific porous locations can present specific physical-chemistry environment due to the characteristic metal-framework interaction and dominate the adsorption and heterogeneous catalysis performance [1]. Ag-exchange linde type-A (LTA) or faujasite (FAU) zeolites are capable of emitting different fluorescent after celcination, resulting from the formation of multiple clusters such as Ag3 n+ and Ag6 n+ etc. In the Ag+ reduction process that the silver ions loaded in porous zeolites are being reduced to form charged silver clusters by dehydration, the electrons transfer primarily from the oxygen atoms in the framework or hydration water which will be oxidized to oxygen molecules. The essential mechanism of silver cations formation in the porous zeolite structures has not been well comprehended and precisely pictured, which play pixel role in understanding and improvement of gas storage and electrochromism especially when the silver cluster migrate between different locations at variable environment such as temperature and applied electric field. It has been suggested from experimental investigations that considerable magnetism and electrochromism could be introduced into lithium-exchanged low-silica X-type (Li-LSX) zeolites by doping TM [9], no ab initio theoretical study has been reported for TM-exchange Li-LSX zeolites to calculate the spin-polarized electronic structure, based on which the magnetic and optical properties will be predicted and the underlying physics can be revealed
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