Sol–gel polymer-template synthesis of mesoporous WO3/ZrO2

Melezhyk, O.V.; Prudius, S.V.; Brei, V. V.

doi:10.1016/s1387-1811(01)00397-3

Cited by 25 publications

(10 citation statements)

References 4 publications

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“…Tungstated zirconia (notation WZ) was prepared by coprecipitation of aqueous solutions of ZrOCl 2 ·8H 2 O (Merck) and ammonium metatungstate (Aldrich) with ammonia using polyvinyl alcohol (Aldrich) as a template according to a procedure described in detail in the literature [32]. The gel obtained was dried at 473 K for 24 h in air.…”

Section: Sample Preparationmentioning

confidence: 99%

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Routes of formation and composition of NOx complexes adsorbed on palladium-promoted tungstated zirconia

Kantcheva

Çayırtepe

2006

Journal of Molecular Catalysis A: Chemical

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Surface species obtained during the adsorption of NO and NO/O 2 coadsorption at room temperature on Pd-free (WZ) and Pd-promoted tungstated zirconia (Pd/WZ) are identified by means of in situ FT-IR spectroscopy. The WZ and Pd/WZ samples have a tetragonal structure and contain randomly distributed mesoporous phase. Dispersed palladium(II) species are present in two different environments: (i) Pd 2+ ions, which have only Zr 4+ ions in their second coordination sphere and (ii) Pd 2+ ions, which are linked to both zirconium and tungsten ions via oxygen bridges. On the Pd/WZ sample, NO undergoes oxidation to various NO x species depending on the temperature. The compounds formed at room-temperature oxidation are adsorbed N 2 O 3 and products of its self-ionization, NO + and NO 2 − . In this process W(VI) is involved, being reduced to W(IV). At high temperature N 2 O 3 decomposes, restoring the W O species. Under these conditions, NO undergoes oxidation to NO 2 by the Pd(II) ions, which are reduced to Pd(I). The nitrosyls of Pd(I) display high thermal stability and do not disappear upon evacuation at 623 K. During NO/O 2 coadsorption on the Pd/WZ catalyst at room temperature, the amounts of surface nitrates and NO 2 /N 2 O 4 formed in the gas phase are significantly lower than those observed under identical conditions in the presence of tungstated zirconia. It is concluded that promotion of tungstated zirconia with palladium(II) suppresses the oxidation of NO by molecular oxygen at room temperature due to the elimination of acidic protons involved in the process.

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Section: Sample Preparationmentioning

confidence: 99%

“…The zirconia was synthesized by the same method [32], without the addition of ammonium metatungstate solution. The final carbonization temperature was 873 K. After that the material was calcined at 773 K for 5 h.…”

Section: Sample Preparationmentioning

confidence: 99%

Routes of formation and composition of NOx complexes adsorbed on palladium-promoted tungstated zirconia

Kantcheva

Çayırtepe

2006

Journal of Molecular Catalysis A: Chemical

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“…The traditional procedure for the production of mesoporous oxides using organic templates is unsuitable for the production of mesoporous ZrO 2 since burning of the template at 500°C leads to destruction of its porous structure [40]. It was proposed to use polyvinyl alcohol as template for the production of mesoporous WO 3 /ZrO 2 [41]. Pyrolysis of the samples in an inert atmosphere at 500-700°C leads to the formation of a carbon film on the surface of the oxide, which prevents enlargement of the 168 Fig.…”

Section: Synthesis Of Superacidic Wo 3 /Zromentioning

confidence: 99%

Superacids Based on Zirconium Dioxide

Brei

2005

Theor Exp Chem

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“…Such catalysts have been prepared by sol-gel method and dried either in supercritical condition of solvents or in ordinary condition [4][5][6][7][8][9] since sol-gel route offers a better control of the homogeneity of the prepared solids as regards to other methods [10][11][12]. For zirconia based catalysts, the sol-gel method offered the opportunity to introduce in one step zirconium alkoxide, metal precursor and sulfate groups as dopant in order to assure the homogeneity and to control morphological and textural properties of the final materials [13,14].The obtained results showed that aerogels manifest developed textural properties as well as higher acidity.…”

Section: Introductionmentioning

confidence: 99%