Surface acidic properties of alumina-supported niobia prepared by chemical vapour deposition and hydrolysis of niobium pentachloride

Silva, Carmem Lúcia Tavares da; Camorim, Vera Lúcia L.; Zotin, José Luiz; Pereira, Maria Luiza Rocco Duarte; Faro, Arnaldo C.

doi:10.1016/s0920-5861(99)00328-4

Cited by 38 publications

(7 citation statements)

References 13 publications

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“…Some authors have reported the existence of Brönsted acid sites in niobium-containing samples when they are exposed to water, [41] but they were not observed in our samples; the FT-IR spectra recorded after adsorption of py on samples previously exposed in situ to water vapour are similar to that recorded for the unwetted samples.…”

Section: Pyridine Adsorptionsupporting

confidence: 56%

Thermal Evolution of a MgAl Hydrotalcite‐Like Material Intercalated with Hexaniobate

2006

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A MgAl hydrotalcite-like material intercalated with hexaniobate has been prepared by the anion exchange method from the corresponding nitrate precursor; the sample and the oxides obtained upon its calcination were characterized by element chemical analysis, powder X-ray diffraction, thermal analyses (thermogravimetric and differential), nitrogen adsorption-desorption isotherms at -196°C, transmission electron microscopy, and FT-IR and UV/Vis spectroscopy. The results show the formation of a microporous hydrotalcite-type solid with a gallery height of 7.2 Å where the H 3 Nb 6 O 19 5-anions are oriented with their C 3 axes perpendicular to the layers. This material preserves its layered structure upon cal-

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Section: Pyridine Adsorptionsupporting

confidence: 56%

Thermal Evolution of a MgAl Hydrotalcite‐Like Material Intercalated with Hexaniobate

2006

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“…The peaks at around 1540 and 1448 cm −1 are due to Brønsted and Lewis acid sites, respectively. Similar findings have been reported by Morais et al [29] and da Silva et al [30] for niobic acid. It has been reported also that the acidity of niobic acid also depends on the calcination temperature [31].…”

Section: CMsupporting

confidence: 91%

Characterization and Catalytic Performance of Niobic Acid Dispersed over Titanium Silicalite

Prasetyoko

Ramli

Endud

et al. 2008

Advances in Materials Science and Engineering

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Niobic acid, Nb 2 O 5 ·nH 2 O, has been supported on the titanium silicalite by impregnation method. The obtained materials were characterized by X-ray diffraction, infrared, and ultra-violet-visible diffuse reflectance spectroscopy, temperature programmed reduction, pyridine adsorption, and field emission scanning electron microscopy techniques. It was demonstrated that the tetrahedral titanium species still retained after impregnation of niobic acid. The results revealed that niobium species interacted with hydroxyl groups on the surface of TS-1. The niobium species in the catalysts are predominantly polymerized niobium oxides species or bulk niobium oxide with the octahedral structure. All catalysts showed both Brønsted and Lewis acid sites. The catalysts have been tested for epoxidation of 1-octene with aqueous hydrogen peroxide. It was found that the presence of niobic acid in the catalysts enhanced the rate of the formation of epoxide at the initial reaction time. Diol as a side product was also observed due to the acidic properties of the catalysts.

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“…Only an extra peak at 2θ = 21.6° was observed, probably related to the formation of superficial aluminum phosphate 11 . 12 , while the band at 1581 cm -1 can be attributed to pyridine adsorbed on Brønsted acid sites 13 . The infrared spectra showed practically no change after the incorporation of phosphoric acid in the supports.…”

Section: Porous Propertiesmentioning

confidence: 99%

H3PO4/Al2O3 catalysts: characterization and catalytic evaluation of oleic acid conversion to biofuels and biolubricant

et al. 2006

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catalysts were investigated in the conversion of oleic acid to biofuels and biolubricant at 1 atm and at 623 K. The catalytic tests were performed in a fixed bed and continuous flow reactor, using an oleic acid-catalyst ratio of 4 and N 2 as the carrier gas. The reaction products were analyzed by gas chromatography and acidity measurements. N 2 adsorption-desorption, X ray diffraction, 31 P nuclear magnetic resonance and FT-IR spectroscopy were also employed to evaluate the textural, structural and acidic properties of the catalysts. The results showed that phosphoric acid impregnation improved the alumina decarboxylation activities, generating hydrocarbons in the range of gasoline, diesel oil and lubricant oil. The best catalytic performance was achieved with the highest surface area alumina impregnated with H 3 PO 4 , which was the solid that allied high total acidity with a large quantity of mesopores.

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Surface acidic properties of alumina-supported niobia prepared by chemical vapour deposition and hydrolysis of niobium pentachloride

Cited by 38 publications

References 13 publications

Thermal Evolution of a MgAl Hydrotalcite‐Like Material Intercalated with Hexaniobate

Thermal Evolution of a MgAl Hydrotalcite‐Like Material Intercalated with Hexaniobate

Characterization and Catalytic Performance of Niobic Acid Dispersed over Titanium Silicalite

H3PO4/Al2O3 catalysts: characterization and catalytic evaluation of oleic acid conversion to biofuels and biolubricant

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