Balancing Sodium Impurities in Alumina for Improved Properties

Wijayaratne, Hasini; Hyland, Margaret; McIntosh, Grant J.; Perander, Linus; Metson, James B.

doi:10.1007/s11663-018-1310-z

Cited by 4 publications

(5 citation statements)

References 17 publications

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“…Alumina from refineries have a high content of Na2O, typically around 0.5%. Although co-precipitated with the gibbsite during the Bayer process, it was showed in [3] that Na2O emerges to the surface of the alumina grains during calcination. Na2O is thermodynamically unstable when exposed to moisture and air and will react to form NaOH or Na2CO3 in the presence of H2O or CO2.…”

Section: Na2o and Naohmentioning

confidence: 99%

Alumina Scale Composition and Growth Rate in Distribution Pipes

et al. 2019

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Scaling in distribution pipes for secondary alumina is a major issue in aluminium smelters. The scale is formed inside the distribution pipes, and gradually reduces the cross section that is available for alumina transport. The scale cannot be removed without dismantling the transport pipes and using chemical and/or mechanical treatments. This leads to interruptions in normal operation, requires additional labour, and a stock of additional pipe sections. To get a better understanding of the scale formation mechanisms, the rate of scale growth was monitored by acoustic measurements in a transport pipe section at an aluminium producing plant over a period of several months. Correlation between growth rate, and recorded parameters from the associated pots, fume treatment system and meteorological data were studied. In addition, samples from the actual scale were examined by SEM, TEM and AFM to investigate the microstructure and chemical composition.

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Section: Na2o and Naohmentioning

confidence: 99%

Alumina Scale Composition and Growth Rate in Distribution Pipes

et al. 2019

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“…Although most sodium‐containing synthetic alumina revealed an anticorrelation between the amount of Na and α‐Al 2 O 3 ,53 transition or amorphous alumina without sodium had been reported to transform completely to α‐Al 2 O 3 . 54 Recent studies have suggested that although sodium had a positive role in a product's attrition strength, it inhibited α‐Al 2 O 3 formation 55 . Saad et al 56 .…”

Section: Introductionmentioning

confidence: 99%

“…54 Recent studies have suggested that although sodium had a positive role in a product's attrition strength, it inhibited α-Al 2 O 3 formation. 55 Saad et al 56 and Srinivasan et al 57 claimed that Al vacancies were occupied by sodium in γ-Al 2 O 3 . They argued that Na decreased reactivity, which required an acidic site, manifested by a correlated decrease in surface acidity of γ-Al 2 O 3 .…”

Section: Introductionmentioning

confidence: 99%

Influence of sodium hydroxide on phase transformation of gamma alumina to alpha alumina

Farrokhnemoun,

Sajjadivand,

Parapari

et al. 2023

J Am Ceram Soc.

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Corundum and transition alumina powders are commonly produced through the Bayer process—that is, by digestion of bauxite in a sodium hydroxide solution, followed by gibbsite precipitation, which contains significant amounts of Na+ ions. During the de‐hydroxylation of gibbsite, Na+ is associated with retardation of the structural phase transformations between transition alumina and corundum (α‐Al2O3) phases, although the exact role of Na is unclear. The influence of Na+ ions on the phase transformation of γ‐Al2O3 to α‐alumina was investigated by varying the concentration of NaOH in aqueous γ‐Al2O3 suspensions. The phase transformation behavior of γ‐Al2O3 was monitored through thermal analysis, X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectrometer (XPS), and transmission electron microscope. As the Na concentration in γ‐alumina suspensions increased, the amount of α‐Al2O3 decreased in samples that were heat treated at 1200°C for 2 h. XPS analysis indicated that washing transition alumina powders with NH4OH solutions had decreased the surface concentration of Na+ and facilitated the phase transformation to α‐Al2O3.

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“…), whereas the support material is typically chosen either to be inert, to promote the desired catalytic reactivity, or to stabilize the active phase. However, many commonly used commercial supports contain trace impurities, [4–7] which can significantly impact the chemistry and stability of the catalyst surface despite their low concentration. Therefore, both the design of industrial catalysts and fundamental studies of catalyst structure‐property relationships must account for the potential role of impurities in altering the structure and chemistry of the catalyst surface.…”

Section: Introductionmentioning

confidence: 99%

“…Promoters can impact catalyst performance by blocking surface sites and by altering the electronic properties of the metal carbide. Alkali metals are also among the most abundant impurities in commonly used catalyst supports, [4,5] and many studies do not control for the potential effects of alkali impurities on catalytic properties. In this work, we investigate the role of the alkali metal sodium in promoting Co and Co 2 C catalysts during syngas conversion, with particular attention given to the effects of Na impurities inherent in the support and the impact of low concentration Na on the structure and performance of the catalyst.…”

Section: Introductionmentioning

confidence: 99%

Impurity Control in Catalyst Design: The Role of Sodium in Promoting and Stabilizing Co and Co₂C for Syngas Conversion

et al. 2021

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The design of supported heterogeneous catalysts requires a detailed understanding of the structure and chemistry of the active surface. Although the chemical components of the active phase, support material, and process feed are typically considered to be the most important factors governing catalyst structure and performance, many common commercial supports contain trace impurities, which can have profound effects on catalyst properties. In this work, we study silica‐supported cobalt‐based catalysts, which are widely used in syngas conversion to value‐added products. Supported metallic Co is a commercial Fischer‐Tropsch catalyst, whereas Co2C has shown promise for the direct conversion of syngas to higher oxygenates. This study examines the effects of Na, a commonly detected support impurity and a frequently used promoter, on the structure and reactivity of Co and Co2C. We show that trace Na impurities significantly decrease catalyst activity of supported metallic Co, and that high Na concentrations result in Co2C formation and a loss in Fischer‐Tropsch activity. However, in Co2C catalysts, Na plays an important role in stabilizing the Co2C phase, but excess Na decreases catalyst activity. We use in situ X‐ray absorption spectroscopy to study Co2C formation and decomposition in the Na‐free catalyst under carburization and reaction conditions. The work reveals the importance of carefully controlling alkali metal content, particularly at trace levels, in catalyst design.

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Balancing Sodium Impurities in Alumina for Improved Properties

Cited by 4 publications

References 17 publications

Alumina Scale Composition and Growth Rate in Distribution Pipes

Alumina Scale Composition and Growth Rate in Distribution Pipes

Influence of sodium hydroxide on phase transformation of gamma alumina to alpha alumina

Impurity Control in Catalyst Design: The Role of Sodium in Promoting and Stabilizing Co and Co₂C for Syngas Conversion

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Balancing Sodium Impurities in Alumina for Improved Properties

Cited by 4 publications

References 17 publications

Alumina Scale Composition and Growth Rate in Distribution Pipes

Alumina Scale Composition and Growth Rate in Distribution Pipes

Influence of sodium hydroxide on phase transformation of gamma alumina to alpha alumina

Impurity Control in Catalyst Design: The Role of Sodium in Promoting and Stabilizing Co and Co2C for Syngas Conversion

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Product

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Impurity Control in Catalyst Design: The Role of Sodium in Promoting and Stabilizing Co and Co₂C for Syngas Conversion