The effect of framework organic moieties on the acidity of zeolites: A DFT study

Elanany, Mohamed; Su, Bao‐Lian; Vercauteren, Daniel P.

doi:10.1016/j.molcata.2006.08.062

Cited by 20 publications

(19 citation statements)

References 38 publications

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“…The acidity increase order correlates with the Al−O(H) bond length increase, except for the O4 site. Our result for E DEP at O2 is different from that of Elanany et al because of the different integration grid size and exchange-correlation functional …”

Section: Modeling Methodscontrasting

confidence: 99%

Theoretical Modeling of Zeolite Nanoparticle Surface Acidity for Heavy Oil Upgrading

et al. 2008

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We performed periodic density functional theory (DFT) and quantum-mechanics/molecular mechanics (QM/MM) investigations of the surface acidity of zeolite nanoparticles derived from natural minerals that can be used for bitumen upgrading; in particular, in the process combining bitumen precracking with impurities removal that we recently reported. Bitumen molecules are large and cannot enter zeolite pores. These mainly adsorb on the outer surface of zeolite nanoparticles, which can be optimized for efficient bitumen upgrading and impurities removal. Two chabazite slab models obtained by (003) and (003̄) cuts that have four and two surface OH groups per unit cell, respectively, are used for the periodic DFT modeling of nanoparticle surfaces. The first model is also treated by using the QM/MM method. Bitumen molecules are represented by probing bases such as ammonia, pyridine, and 2,6-dimethylpyridine that are commonly used for experimental acidity characterization. Analysis of the model acidity characteristics, such as deprotonation energies, aluminum substitution energies, OH stretching frequencies. and Fukui functions produces very good correlations. For the deprotonated chabazite, the electrophilic Fukui functions predict the most stable Brønsted site. Our results suggest that the most reactive chabazite sites are O1 and O3. The three bases investigated become fully protonated upon adsorption to the chabazite Brønsted sites. The molecular orbital spatial distributions obtained by using the periodic and QM/MM methods are very similar, which indicates good correlations between the two modeling methods. The results of our zeolite acidity calculations are in good agreement with experimental data and other computational studies available. Our findings can be useful for the further modeling and rational design of catalytic zeolite nanoparticles for heavy oil upgrading.

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Section: Modeling Methodscontrasting

confidence: 99%

Theoretical Modeling of Zeolite Nanoparticle Surface Acidity for Heavy Oil Upgrading

et al. 2008

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“…As indicated in Table , most of the zeolites have not been synthesized at the pure end compositional ranges, and an evaluation of the GeOGe and SiOSi angles can only be approached by using computational techniques. A reasonable estimation of the resulting TOT angles can only be achieved by using periodic boundary conditions which take into account properly the topological restraints specific to each structure. − Although a quantum-chemistry approach would be desirable, the large number of structures to be considered and the large size of some unit cells would result into a very expensive approach in terms of computational resources. Further, such a quantum-chemistry approach would need to optimize not only the atomic coordinates but also the unit cell parameters of both silica and germania cases, which will result in a very high demanding computational task even for large parallel computers.…”

Section: Methodology and Modelsmentioning

confidence: 99%

Predicting Structural Feasibility of Silica and Germania Zeolites

Sastre

Corma

2010

J. Phys. Chem. C

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High throughput experimental techniques for zeolite synthesis, combined with the introduction of germanium in the synthesis gel, have allowed an increase in the number of new zeolites, especially of those containing large and extralarge pores. Zeolite phases containing Si/Ge as tetrahedral atoms stabilize certain unique topologies. One particular feature of Ge-containing zeolites is the stabilization of small TOT (T ) Si, Ge) angles compared to their silica counterparts. This study employs computational chemistry techniques to calculate and rationalize the relative stability of zeolite phases as silicates and germanates. Atomistic force fields are used to simulate the structural properties of experimentally synthesized Si/Ge-containing zeolites, and an ab initio Hartree-Fock methodology is used to estimate the energetics of TOT angles. It is shown that each particular topology is only compatible with certain ranges of TOT angles, and, depending on the chemical composition, this induces stability or strain. A calculation of the energetic penalty associated with TOT angles for the different chemical compositions at each topology allows an estimate of their feasibility. The results are in agreement with experiments and allow one to make predictions about feasibility of new SiO 2 or GeO 2 zeolite structures.

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“…(Elanany et al, 2007). Double numerical basis set with polarization functions (DNP) has been used in all calculations carried out in this study.…”

Section: Computational Modeling Of Polymer Surrogates Interactions Wimentioning

confidence: 99%

Evaluating polymeric inhibitors of ethane clathrate hydrates

Hould

Elanany

Aleisa

et al. 2015

Journal of Natural Gas Science and Engineering

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The effect of framework organic moieties on the acidity of zeolites: A DFT study

Cited by 20 publications

References 38 publications

Theoretical Modeling of Zeolite Nanoparticle Surface Acidity for Heavy Oil Upgrading

Theoretical Modeling of Zeolite Nanoparticle Surface Acidity for Heavy Oil Upgrading

Predicting Structural Feasibility of Silica and Germania Zeolites

Evaluating polymeric inhibitors of ethane clathrate hydrates

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