Computational modelling of zeolite N ion exchange properties

Zeolites are porous alumino-silicate materials with properties that result in a wide range of industrial applications. Predictions of zeolite properties can enhance higher performance and economic value for many industries. In this research, the structure and ion exchange behaviour of synthetic zeolite N is modelled using computational chemistry techniques. Modelled outcomes are compared with experimental data that are also obtained on natural zeolites from two Australian deposits. This research shows that a precise understanding and prediction of zeolite chemical and physical properties can be achieved by correlated atomic-scale modelling and high-quality experimental techniques

The exchange mechanism of alkaline and alkaline-earth ions in zeolite N

Zeolite N is a synthetic zeolite of the EDI framework family from the more than 200 known zeolite types. Previous experimental laboratory and field data show that zeolite N has a high capacity for exchange of ions. Computational modelling and simulation techniques are effective tools that help explain the atomic-scale behaviour of zeolites under different processing conditions and allow comparison with experiment. In this study, the ion exchange behaviour of synthetic zeolite N in an aqueous environment is investigated by molecular dynamics simulations. The exchange mechanism of K+ extra-framework cations with alkaline and alkaline-earth cations NH4+, Li+, Na+, Rb+, Cs+, Mg2+ and Ca2+ is explored in different crystallographic directions inside the zeolite N structure. Moreover, the effect of different framework partial charges on MD simulation results obtained from different DFT calculations are examined. The results show that the diffusion and exchange of cations in zeolite N are affected by shape and size of channels controlling the ion exchange flow as well as the nature of cation, ionic size and charge density

Evaluation of DFT methods to calculate structure and partial atomic charges for zeolite N

Zeolite N is a synthetic zeolite of the EDI framework type with chemical formula K12Al10Si10O40Cl2·8H2O Experimental and computational investigations verify the valuable ion-exchange capability of zeolite N. In this study, we assess the effects of Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) DFT models on zeolite structural parameters and on partial atomic charges of framework atoms. We applied these functionals with different quality of convergence and SCF tolerances, numerical basis sets and dispersion correction schemes. Optimized zeolite N structures are evaluated by comparing the atom positions and framework TO bond lengths with experimental data. The obtained SiO and AlO bond lengths of optimized structures in this study are in agreement with previous experimental and computational studies on zeolite N and other zeolites. The values of Mulliken partial atomic charges are sensitive to the choice of numerical basis sets. Results show that the GGA-PBE functional with DNP-4.4 basis set and TS dispersion correction scheme is a reliable DFT model in order to optimize and establish the structural parameters of zeolite N for further MD simulations

Comprehensive mineralogical study of Australian zeolites.

Industrial applications of natural zeolites depend on their mineralogical, physical and chemical characteristics. Over the last 20 years, Australian natural zeolites have been investigated for use in various industrial applications. However, there are few, if any, mineral characterisation studies on Australian natural zeolites since the early 1990s that use modern techniques. In this study, a detailed mineralogical analysis was conducted on zeolite specimens from Avoca and Werris Creek deposits, located in Queensland and New-South-Wales, respectively, in Australia. Their physical properties, thermal behaviour and porosity, as well as mineral compositions were determined by conventional methods, including thermogravimetry, N2 adsorption/desorption, optical microscopy, XRF, in situ XRD, SEM/EDS and EPMA/WDS. High-precision, high-accuracy measurements of the chemical compositions of fine-grained zeolites (<20 μm) were performed in situ in thin section using accepted EPMA protocols and data reduction methods. The Australian zeolites were identified as magnesium heulandite/clinoptilolite-Ca which corrects interpretations from earlier studies.</p

Enhancement of the catalytic performance of H-clinoptilolite in propane-SCR-NOx process through controlled dealumination

We report for the first time the effect of clinoptilolite dealumination on the propane–SCR–NOx process. This has been accomplished using a mild acid like oxalic acid to avoid excess catalyst crystallinity deterioration. It had been shown that dealumination may result in a significant enhancement of NOx conversion to N2 when an optimum acid concentration of 0.050 M is used for a treatment period of 2 h. Dealumination substantially affects the distribution of the concentration of acid sites of different strength. The effect of dealumination on the HC-SCR activity of the zeolite samples is discussed in terms of Si/Al ratio, crystallinity, distribution of acid site strength, extra framework species concentration and textural characteristics of the samples