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The effect of zirconia polymorphs on the structure and catalytic properties of V2O5/ZrO2 catalysts

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Abstract.
The effect of zirconia polymorphs on the activity and selectivity of V2O5/ZrO2 for the alkylation of phenol
with methanol has been investigated. Relatively pure monoclinic zirconia (m-ZrO2) and tetragonal
zirconia (t-ZrO2) were prepared. A series of vanadium oxide supported on m- and t-ZrO2 with varying
vanadium oxide content from 2.5 to 15 wt% were prepared by wet impregnation method. The catalysts
were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (UV-DRS),
temperature-programmed reduction of H2 (TPR), temperature-programmed desorption (TPD) of NH3,
specific surface area and pore size distribution measurements. The XRD results suggest that highly
dispersed or amorphous state of vanadium oxide is present at lower loadings. X-ray diffraction patterns
also indicate the presence of crystalline V2O5 phase from 7.5 wt% of V2O5 on m-ZrO2 support and there is
no indication for the formation of V2O5 crystalline phase up to 15 wt% of V2O5 on t-ZrO2 support. The UV–
vis diffuse reflectance spectra indicate the existence of isolated and clusterized tetrahedral (Td) V5+
species at lower loadings in all catalysts. The temperature-programmed reduction of H2 shows a single
reduction peak corresponding to V5+ to V3+ in all the samples. TPD of ammonia suggests that surface acid
density of m-ZrO2 phase is found to be more than t-ZrO2 phase. Acidity of the supported catalysts is
increased with increase in V2O5 loading up to monolayer formation and decreased with the appearance of
crystalline phase of V2O5. At monolayer coverage, V2O5/m-ZrO2 is fourfold more active than V2O5/t-ZrO2
for alkylation of phenol at 673 K. Selectively C-alkylated products were formed on all the catalysts. A
linear correlation is observed between catalytic activity and surface acidity of catalysts.

Keywords:
Vanadia
Monoclinic zirconia
Tetragonal zirconia
Alkylation
Phenol

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Informasi Detail

Judul Seri

Catalysis Today

No. Panggil

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Penerbit

London : Elsevier B.V.., 2009

Deskripsi Fisik

Catalysis Today 141 (2009) 187–194

Bahasa

English

ISBN/ISSN

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Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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