The adsorption of metal oxyanions on alumina

Mulcahy, Francis M.; Fay, Martin J.; Proctor, Andrew; Houalla, Marwan; Hercules, David M.

doi:10.1016/0021-9517(90)90118-4

Cited by 52 publications

(10 citation statements)

References 14 publications

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“…Moreover, it has been reported that tungstate has a broad adsorption envelope across a wide pH range with maximum adsorption below pH 5.1, more than 50% of WO 4 2− adsorption at neutral pH, and only 10% above pH 10 on the goethite surface (Xu et al, 2006). Mulcahy et al (1990) concluded that tungstate adsorbs on two types of surface sites producing loosely and tightly bound surface species. According to Mulcahy et al's (1990) study of adsorption of tungstate on alumina surfaces on the basis of EXAFS measurements and ratios of adsorbed tungstate, both loosely and tightly bound species were formed by the adsorption of polymeric tungstate anions when the pH of the impregnating solution is low enough to form these polymeric anions.…”

Section: Introductionmentioning

confidence: 98%

Evaluation of the Adsorption of Mono- and Polytungstates onto Different Types of Clay Minerals and Pahokee Peat

Tuna

Braida

2014

Soil and Sediment Contamination: An International Journal

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Detailed knowledge about the fate and transport of tungsten in soils is critical to understanding and effectively addressing tungsten behavior in the environment. Recent studies have shown that tungsten anions may polymerize (depending upon concentration, pH, and aquatic geochemistry) in aquatic and soil systems. However, to date, of all soluble tungstate species only monotungstates have been scrutinized to a fair extent in adsorption studies. There is a lack of information evaluating adsorption mechanisms of mono-and polytungstates onto clay minerals. The objective of this work is to investigate the adsorption behavior of monotungstates (sodium tungstate, Na 2 WO 4 ) and polytungstates (sodium metatungstate, 3Na 2 WO 4 ·9WO 3 ) onto different types of clay minerals (montmorillonite, kaolinite, illite) and an organic adsorbent (Pahokee peat). Batch equilibrium experiments as a function of concentration (adsorption isotherms) and pH (adsorption envelopes) were performed to provide information about mono-and polytungstate adsorption onto clays and Pahokee peat. Adsorption equilibrium data for mono-and polytungstates onto different types of clay mineralsand Pahokee peat were modeled with Freundlich and Langmuir isotherms. The adsorption affinity of clays and Pahokee peat for monotungstates follows the order: Pahokee peat>kaolinite>montmorillonite>illite; for polytungstates, the order is as follows: kaolinite>Pahokee peat>montmorillonite>illite. Results of this study suggest that the charges of the clay mineral surface, tungsten species, and solution pH are the main factors controlling tungsten adsorption. Moreover, polymeric tungsten species (i.e., metatungstate) appear to be more mobile in the environment than monomeric tungstate.

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Section: Introductionmentioning

confidence: 98%

Evaluation of the Adsorption of Mono- and Polytungstates onto Different Types of Clay Minerals and Pahokee Peat

Tuna

Braida

2014

Soil and Sediment Contamination: An International Journal

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“…For modeling, inner-sphere molybdate and tungstate surface complexes on goethite and ferrihydrite were used. ,, This was verified by numerous experimental work (on lepidocrocite and goethite using in situ ATR-IR, , on goethite by pressure-jump relaxation and EXAFS). The adsorption of POM (usually heptamer) is rarely assumed; however, it has been evoked for molybdenum on catalyst supports, both as outer-sphere or inner-sphere surface complexes. The last possibility was the formation of a surface polymer, which had been found to be consistent with EXAFS measurement of Mo on goethite and W on boehmite …”

Section: Introductionmentioning

confidence: 99%

Surface Polymerization of Mo(VI) and W(VI) Anions on Hematite Revealed by in Situ Infrared Spectroscopy and DFT+U Theoretical Study

et al. 2016

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The study of the interactions between dissolved Mo(VI) or W(VI) species and the surfaces of metal (hydr)oxides is relevant for two main areas: the optimization of the preparation of catalytic supports and the understanding of the environmental fate of these elements. For the latter, iron (hydr)oxides are the most important sinks for pollutants, and recently, their surface reactivity was the focus of many research works. In this work, we develop a joint approach, using in situ infrared spectroscopy and DFT simulations, to characterize the Mo(VI) and W(VI) species adsorbed on hematite (α-Fe 2 O 3 ). Surface sorbed polymers of tungstate and molybdate on hematite were identified for low pH and at high concentration of these elements, which is similar to the formation of polyoxometalates in solution phase. However, the surface speciation is different from the adsorption of polymolybdate or polytungstate already formed in solution and should be consistent with the growth of a surface polymer. For low concentrations/high pH conditions, the spectra are consistent with a monodentate surface complexation.

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“…23,24 In an effort to optimize the immobilization conditions, we immobilized the POM clusters under various pH conditions ranging from 6 to 1 (Figure 1) The W=O and W-O stretching and bending vibrations of the P2W15 generally occur below 1000 cm -1 thus it is difficult to detect them by Fourier transform-infrared (FT-IR) due to the strong IR absorption of the γ-Al2O3 supports in this region ( Figure S2). 13,27 The XRD pattern of the , respectively, which can be assigned to the W=O stretch bands and W-O-W stretch modes of the immobilized cluster.…”

Section: Resultsmentioning

confidence: 99%

Covalent Immobilization of Polyoxotungstate on Alumina and Its Catalytic Generation of Sulfoxides

Hong

Win

Zhang

et al. 2016

Chemistry A European J

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Structural and chemical stability of the immobilized polyoxometalates (POMs)-containing catalysts is one crucial factor for their industrial application. In this work, we discuss the preparation of a novel P2W15@Al2O3 catalyst using a facile condensation reaction between the tri-lacunary POM of Na12[α-P2W15O56]·24H2O (P2W15) and the hydroxyl groups on the surface of the spherical γ-Al2O3 under acidic conditions. The heterogeneous catalyst was characterized by the 31 P NMR, FT-IR, XRD, XPS, TG, Raman, HR-TEM and BET. The P2W15@Al2O3 catalyst showed excellent stability, highly efficient reactivity and selectivity for the oxygenation of thioethers to sulfoxides which are a very useful intermediate in organic synthesis and industrial preparation of drugs. The catalyst could be recycled and reused at least ten times without any observable loss of its catalytic efficiency, mainly due to the covalently grafted {P2W15} cluster and high dispersion onto the γ-Al2O3 surface.Polyoxometalates (POMs) are a class of discrete anionic metal-oxides of V, Mo, W and Nb etc.

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The adsorption of metal oxyanions on alumina

Cited by 52 publications

References 14 publications

Evaluation of the Adsorption of Mono- and Polytungstates onto Different Types of Clay Minerals and Pahokee Peat

Evaluation of the Adsorption of Mono- and Polytungstates onto Different Types of Clay Minerals and Pahokee Peat

Surface Polymerization of Mo(VI) and W(VI) Anions on Hematite Revealed by in Situ Infrared Spectroscopy and DFT+U Theoretical Study

Covalent Immobilization of Polyoxotungstate on Alumina and Its Catalytic Generation of Sulfoxides

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