Journal ArticleDOI
Isopropanol oxidation by pure metal oxide catalysts: number of active surface sites and turnover frequencies
Deepak Kulkarni,Israel E. Wachs +1 more
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In this paper, the number of active surface sites and their nature, redox or acidic, for bulk metal oxide catalysts using isopropanol as a chemical probe molecule was determined.Abstract:
The objective of the present study was to determine the number of active surface sites and their nature, redox or acidic, for bulk metal oxide catalysts using isopropanol as a chemical probe molecule. Isopropanol oxidation activity on the following metal oxides was investigated: MgO, CaO, SrO, BaO, Y 2 O 3 , La 2 O 3 , CeO 2 , TiO 2 , ZrO 2 , HfO 2 , V 2 O 5 , Nb 2 O 5 , Ta 2 O 5 , Cr 2 O 3 , MoO 3 , WO 3 , Mn 2 O 3 , Fe 2 O 3 , Co 3 O 4 , Rh 2 O 3 , NiO, PdO, PtO, CuO, Ag 2 O, Au 2 O 3 , ZnO, Al 2 O 3 , Ga 2 O 3 , In 2 O 3 , SiO 2 , SnO 2 and Bi 2 O 3 . On average, the number of active surface sites for isopropanol dissociative adsorption on these catalysts was ∼2–4 μmol/m 2 . The number of active surface sites enabled quantification of the turnover frequency (TOF) for these catalysts. The TOF values for the various pure metal oxides were normalized at 200 °C. The TOFs of catalysts showing redox activity vary by six-orders of magnitude (10 2 to 10 −4 s −1 ). For catalyst showing acidic activity, the TOFs varied by over eight-orders of magnitude (10 1 to 10 −7 s −1 ). The reaction products from isopropanol oxidation at low conversions reflected the nature of the active surface sites, redox or acidic, on these catalysts. Redox surface sites yield acetone and acidic surface sites yield propylene. Small amounts of isopropyl ether formation are sometimes also observed via bimolecular recombination of surface isopropoxide species on acidic surface sites. All catalysts with the exception of Fe 2 O 3 and TiO 2 , exhibited extremely high selectivity to either redox or acidic products. Except for the sharp decrease in TOFs towards redox products with increasing bulk M–O heats of formation at low −Δ H f , no correlations were found between the TOFs and bulk metal oxide properties (TPR–H 2 and −Δ H f ). However, an inverse relation was found between the TOFs (redox) and the surface isopropoxide intermediate decomposition temperature at low decomposition temperatures. At moderate and high decomposition temperatures, the TOFs (redox) were almost independent of the surface isopropoxide decomposition temperature. The selectivity of the metal oxide catalysts was found to be independent of the TOFs.read more
Citations
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Shape-dependent catalytic properties of Pt nanoparticles.
S. Mostafa,Farzad Behafarid,Jason R. Croy,Luis K. Ono,Long Li,Judith C. Yang,Anatoly I. Frenkel,Beatriz Roldan Cuenya +7 more
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References
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Book
CRC Handbook of Chemistry and Physics
TL;DR: CRC handbook of chemistry and physics, CRC Handbook of Chemistry and Physics, CRC handbook as discussed by the authors, CRC Handbook for Chemistry and Physiology, CRC Handbook for Physics,
Journal ArticleDOI
Methanol oxidation as a catalytic surface probe
TL;DR: In this article, the selectivity pattern and the formation rates of the reaction products are used to characterize both structural (dispersion) as well as chemical properties (acid base and redox) on supported oxide catalysts, especially for molybdenum-based systems supported on silica and vanadia on titanium oxide.
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Journal ArticleDOI
Acidity and basicity of metal oxide surfaces. II, Determination by catalytic decomposition of isopropanol
Antonella Gervasini,Aline Auroux +1 more
TL;DR: In this paper, the acid-base catalytic properties of a series of metal oxides were investigated and a relationship between the strength of the acid sites microcalorimetrically evaluated and the activation energy of the dehydration reaction was found.
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