Dissolution of amorphous aluminosilicate zeolite precursors in alkaline solutions. Part 2.—Mechanism of the dissolution

Antonić, Tatjana; Čižmek, Ankica; Subotić, Boris

doi:10.1039/ft9949001973

Cited by 30 publications

(16 citation statements)

References 16 publications

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“…XRD patterns show that the rate of crystallization of MTW-30-t is obviously slower than that of MTW-10-t. Its induction period is prolonged to ∼54 h (Figure S4D), because the lower concentrations of nutriments and alkalinity in the reaction system could decelerate its crystallization. 58 Details of the crystallization of MTW-30-t are further illuminated by other characterizations. As shown in Figure S5B, the sol becomes more and more turbid from 0 to 48 h but no solid phase can be separated by LSC.…”

Section: Resultsmentioning

confidence: 99%

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Tailoring the Morphology of MTW Zeolite Mesocrystals: Intertwined Classical/Nonclassical Crystallization

et al. 2017

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The morphology and porosity of zeolite play a significant role in the activity and selectivity of catalytic reactions. It is a dream to optionally modulate zeolite morphology by regulating the crystallization process on the basis of comprehensively understanding the mechanisms. Herein, a series of MTW zeolite mesocrystals can be consciously fabricated with morphologies from a dense structure to a loose one of an oriented nanocrystallite aggregate by changing the H 2 O/SiO 2 ratio. Their intertwined classical/nonclassical crystallization processes are investigated comprehensively. The results indicate that the crystallization of MTW zeolite takes place by a chain of events, including the formation of wormlike particles (WLPs), their aggregation, and crystallization of aggregates. MTW with a loose structure mainly crystallizes by an internal reorganization after a fast aggregation of WLPs in a concentrated system. On the other hand, the dense structure of MTW is realized via the co-occurrence of a coalescence of the participating WLPs during its crystal growth with a slower rate in a dilute system. Moreover, the advantages of MTW with a loose structure are confirmed through cumene cracking and 1,2,4trimethylbenzene transformation. This method could pave the way for the synthesis of other zeolites with diverse morphologies and/or mesoporosities via subtle regulation of the crystallization pathway.

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Section: Resultsmentioning

confidence: 99%

Section: Results and Discussionmentioning

confidence: 99%

Tailoring the Morphology of MTW Zeolite Mesocrystals: Intertwined Classical/Nonclassical Crystallization

et al. 2017

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“…The phase transformation, particle size, and morphology evolution of sodium aluminosilicate has been the subject of many studies, which are summarized in Table . Most of this research concerns the kinetics of precipitation and dissolution and identification of the phases formed from synthetic alkaline solution or from gels. − In the seminal work, Barrer and co-workers investigated the formation of various types of zeolites at different temperatures with different anion salts. , As summarized by Zhdanov, sodium aluminosilicate crystallization generally follows a sequence of phase transformations from an amorphous solid phase to zeolite A and finally to sodalite. Peng et al also considered this desilication sequence in the context of known chemical thermodynamic driving forces and explained the observed crystallization pathway by the Ostwald successive transformation step rule …”

Section: Introductionmentioning

confidence: 99%

Role of the Amorphous Phase during Sodium Aluminosilicate Precipitation

Peng

Seneviratne

Vaughan

2018

Ind. Eng. Chem. Res.

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In the Bayer process, reactive silica associated with bauxite dissolves into alkaline solution and subsequently precipitates as a sodium aluminosilicate “desilication product” (DSP). Multiple DSP phases can be formed, which include an amorphous solid as well as crystalline zeolite A, sodalite, and cancrinite. Even though the ability to control DSP particle size would be of great practical benefit, there remains limited fundamental understanding of the precipitation process, especially during the early stages of the reaction. In this study, DSP was precipitated from synthetic NaOH–NaAl(OH)4–Na2SiO3–H2O solution at 75 and 90 °C. Four distinct reaction stages were observed: (1) precipitation of the amorphous solid, (2) dissolution of the amorphous solid, (3) growth of crystalline phases, and (4) maturation of the crystalline phases. In addition to the amorphous phase, the nucleation of both particles and two-dimensional crystal planes occurs in the early stages of the reaction. Subsequently, the amorphous phase dissolves, which feeds the early growth of the crystalline DSP phases. After the amorphous phase disappears, the crystal phases continue to grow with reactants from the bulk solution until equilibrium is approached. In the maturation stage, the solution silicate concentration decreases only slightly; however, during this time the sizes of individual crystals decrease slightly while the overall particle size increases via crystal agglomeration, which is promoted at higher temperature.

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“…The dissolution process of zeolites has been studied only in the bulk. C ˇizˇmek et al 37 found that the rate of dissolution of aluminosilicate zeolite precursors is directly proportional to the external surface area. C ˇizˇmek 5 and coworkers also conducted a study on the dissolution of zeolite A under a solution of sodium hydroxide at 80 1C.…”

Section: Understanding the Rates Of Dissolutionmentioning

confidence: 99%

In situ atomic force microscopy of zeolite A dissolution

Meza

Anderson

Slater

et al. 2008

Phys. Chem. Chem. Phys.

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In the present study, the {100} surface of zeolite A was exposed to a range of solutions and the response was monitored in real-time by means of atomic force microscopy (AFM). The zeolite dissolves by a well-defined layer process that is characterised by uncorrelated dissolution of units that are structurally unconnected and terrace retreat when building units are inter-connected. This process was observed to be coupled with the formation of nano-squares that are stabilized at the zeolite surface for a period before complete dissolution. Theoretical work suggests that three terminating structures are central to understanding the dissolution mechanism. Stripping the surface of the secondary building unit, the single 4-ring, is predicted to be a rate-determining step in dissolution, but this process occurs by removing monomeric rather than oligomeric units.

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Dissolution of amorphous aluminosilicate zeolite precursors in alkaline solutions. Part 2.—Mechanism of the dissolution

Cited by 30 publications

References 16 publications

Tailoring the Morphology of MTW Zeolite Mesocrystals: Intertwined Classical/Nonclassical Crystallization

Tailoring the Morphology of MTW Zeolite Mesocrystals: Intertwined Classical/Nonclassical Crystallization

Role of the Amorphous Phase during Sodium Aluminosilicate Precipitation

In situ atomic force microscopy of zeolite A dissolution

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