The systematic study of aluminium speciation in medium concentrated aqueous solutions

Perry, Carole C.; Shafran, Kirill L.

doi:10.1016/s0162-0134(01)00326-9

Cited by 71 publications

(79 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The typical general features of Al hydrolysis seem to be also present in our system, as is suggested by the similar shape of the titration curve shown in Figure 3 and the curves reported in literature [22,23]. ] ratio of 4.9 at pH 5, where a colorless X-ray amorphous solid was recovered.…”

Section: Resultssupporting

confidence: 88%

Understanding the complexity of a catalyst synthesis: Co-precipitation of mixed Cu,Zn,Al hydroxycarbonate precursors for Cu/ZnO/Al2O3 catalysts investigated by titration experiments

Behrens

Brennecke

Girgsdies

et al. 2011

Applied Catalysis A: General

View full text Add to dashboard Cite

Co-precipitation of CuZn(Al) precursor materials is the traditional way of synthesizing Cu/ZnO/(Al2O3) catalysts for industrial methanol synthesis. This process has been investigated by titration experiments of nitrate and formate solutions. It was found that the solidification of the single components proceeds sequentially in case of nitrates: Cu 2+ is precipitated at pH 3 and Zn 2+ (as well as Al 3+ ) near pH 5. This behavior prevents a homogeneous distribution of all metal species in the initial precipitate upon gradual increase of pH and requires application of the constant pH micro-droplet method. This effect is less pronounced if formate instead of nitrate is used as counter ion. This can be explained by the strong modification of the hydrolysis chemistry of the metal ions due to the presence of formate anions, which act as ligands and buffer. A formate-derived Cu/ZnO/Al2O3 catalyst was more active in methanol synthesis compared to a nitrate-derived sample although the same crystallographic phases were present in the precursor after co-precipitation and ageing. The effect of precipitation temperature was studied for the binary CuZn nitrate model system. Increasing the temperature of co-precipitation above 50 °C leads to down-shift of the precipitation pH of Zn 2+ by a full unit. Thus, in warm solutions more acidic conditions can be used for complete co-precipitation, while in cold solutions, some Zn 2+ may remain dissolved in the mother liquor at the same precipitation pH. The higher limit of temperature is given by the tendency of the initial Cu precipitate towards formation of CuO by oxolation. On the basis of these considerations, the empirically determined optimal pH and temperature conditions of the industrially applied synthesis can be rationalized.

show abstract

Section: Resultssupporting

confidence: 88%

Understanding the complexity of a catalyst synthesis: Co-precipitation of mixed Cu,Zn,Al hydroxycarbonate precursors for Cu/ZnO/Al2O3 catalysts investigated by titration experiments

Behrens

Brennecke

Girgsdies

et al. 2011

Applied Catalysis A: General

View full text Add to dashboard Cite

show abstract

“…Often, different reaction schemes can be used to simulate the experimental titration curves, and decision about correctness is very difficult. Here it may suffice that students become aware of the experimental problems (see, e.g., the references [12,13]). The goal of this text is that students understand the formal calculation of equilibria, so that they are prepared to handle such systems later in their professional career.…”

mentioning

confidence: 99%

The calculation of the solubility of metal hydroxides, oxide-hydroxides, and oxides, and their visualisation in logarithmic diagrams

Scholz

Kahlert

2015

ChemTexts

View full text Add to dashboard Cite

The aim of this text is to show how the solubility (S) of metal hydroxides, oxide-hydroxides, and oxides can be calculated as function of the equilibrium pH of the solutions, taking into account the formation of various cationic and anionic species of metal aqua ions; however excluding all foreign ligands. The plots of log S versus pH are constructed and their applications to treat separations by consecutive precipitation are discussed.

show abstract

“…2) show all major inflexions characteristic of the analogous systems at room temperature: [11] (1) h < 0.2 ± hydrolysis of Al monomers; (2) 0.2 < h < 2.6 ± formation of Al polycations including Al dimers/trimers, Al 13 -mers and Al 30 -mers; (3) 2.6 < h < 3.0 ± collapse of Al polycations and formation of the metastable colloidal phase of Al hydroxide; (4) h~3.0 ± bulk precipitation of Al hydroxide; (5) h > 3.0 ± gradual dissolution of Al hydroxide with the formation of Al(OH) 4 ± . At prolonged hydrolysis times the early hydrolysis stages (inflexion 1) did not change profoundly.…”

mentioning

confidence: 99%

High‐Temperature Speciation Studies of Al‐Ion Hydrolysis

Shafran

Deschaume²,

Perry

2004

Adv Eng Mater

View full text Add to dashboard Cite

Preparation of industrially important aluminium oxide, aluminium hydroxide and aluminium salt materials is often based on the hydrolysis of aluminium-ion solutions. [1] One of the frequently employed processes is neutralisation of Al-ion solutions with alkali or acid. [2] A number of reaction conditions affect the structure and properties of the resulting Alcontaining materials, such as pH, temperature, ionic strength, type of anion, etc. [1,2] Better control of materials synthesis through aqueous routes can be obtained by known speciation of Al-ions. The key problem of Al aqueous speciation in solutions with noncomplexing anions (chloride, nitrate, etc.) is the presence of large Al polycations of the Keggin type ± Al 13 -mer (I) and Al 30 -mer (II). [3,4] These polycations are used in a number of material science applications including clay pillaring, [5] preparation of Al 2 O 3 nanoparticles, [6] antiperspirant actives, [7] catalysts, [8] composite materials, [9] etc. The Al 13 -mer has been studied for decades, [10] whereas the structure of the Al 30 -mer has been identified recently. [3,4] Thermodynamic and kinetic data on the Al 30 -mer are not available in the literature.Aim: Preliminary results of a multi-technique study for Al-speciation are presented for model aqueous systems at high temperature and medium Al concentrations for the formation of large aluminium polycations. Information on the reaction pathway may aid in the development of routes to solutions containing single species that can be used in model studies to investigate the effects of aluminium in the environment as well as in the generation of materials from molecular scale precursors.Results and Discussion: The pH-metric titration curves reconstructed from multi-batch measurements (Fig. 2) show all major inflexions characteristic of the analogous systems at room temperature: [11] (1) h < 0.2 ± hydrolysis of Al monomers; (2) 0.2 < h < 2.6 ± formation of Al polycations including Al dimers/trimers, Al 13 -mers and Al 30 -mers; (3) 2.6 < h < 3.0 ± collapse of Al polycations and formation of the metastable colloidal phase of Al hydroxide; (4) h~3.0 ± bulk precipitation of Al hydroxide; (5) h > 3.0 ± gradual dissolution of Al hydroxide with the formation of Al(OH) 4 ± . At prolonged hydrolysis times the early hydrolysis stages (inflexion 1) did not change profoundly. The greatest time-dependent change was observed at stages (3), (4) and (5) in Figure 2. The major inflexion (4) moves to slightly higher hydrolysis ratios (from h~2.8 at 0 h to h~3.0 at 48 h). Other inflexions retained their position during 48 h of experiment. 27 Al solution NMR spectroscopy revealed a number of Al species present in the sample batches. Assignment of the NMR signals and corresponding Al species is given in Table 1. 27 Al solution NMR spectra of the sample solutions of hydrolysed Al-ions (Fig. 3) indicate all species listed in COMMUNICATIONS 836

show abstract

The systematic study of aluminium speciation in medium concentrated aqueous solutions

Cited by 71 publications

References 14 publications

Understanding the complexity of a catalyst synthesis: Co-precipitation of mixed Cu,Zn,Al hydroxycarbonate precursors for Cu/ZnO/Al2O3 catalysts investigated by titration experiments

Understanding the complexity of a catalyst synthesis: Co-precipitation of mixed Cu,Zn,Al hydroxycarbonate precursors for Cu/ZnO/Al2O3 catalysts investigated by titration experiments

The calculation of the solubility of metal hydroxides, oxide-hydroxides, and oxides, and their visualisation in logarithmic diagrams

High‐Temperature Speciation Studies of Al‐Ion Hydrolysis

Contact Info

Product

Resources

About