Acidic Characterization of Copper Oxide and Niobium Pentoxide Supported on Silica–Alumina

Garcia, Fillipe A.C.; Braga, Vítor; Silva, Júnia C. M.; Dias, José A.; Dias, Sílvia C.L.; Davo, Jorge L. B.

doi:10.1007/s10562-007-9204-8

Cited by 15 publications

(5 citation statements)

References 23 publications

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“…This band is related to water adsorbed on H 3 PW, as observed for the pure heteropolyacid [24]. The presence of Brønsted sites is in agreement with pure H 3 PW and niobia (calcined at low temperatures) having only this type of sites on their surfaces [24,35,40].…”

Section: Acidity Analysis Of the X% H 3 Pw/nb 2 O 5 Materialssupporting

confidence: 81%

“…The spectra indicated that there are two kinds of chemical environments for PW 12 O 3À 40 : the first consists of bulky partially hydrated H 3 PW crystals deposited on the Nb 2 O 5 surface with weaker interactions (d $ À13.5 ppm), and the second is the anhydrous Keggin anion strongly and directly interacting with the most basic hydroxyl sites on the Nb 2 O 5 surface (d $ À11.5 ppm), which may be forming species such as ½BNbOH 2 þ n ½H 3Àn PW 12 O 40 nÀ3 . For the H 3 PW samples within 20-25 wt%, the second kind was predominant, leading to a broad signal in the 31 P MAS NMR spectra.…”

Section: Analysis By Solid State 31 P Nmr Spectroscopymentioning

confidence: 99%

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Preparation and characterization of H3PW12O40 supported on niobia

Caliman

Dias

et al. 2010

Microporous and Mesoporous Materials

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Section: Acidity Analysis Of the X% H 3 Pw/nb 2 O 5 Materialssupporting

confidence: 81%

Section: Analysis By Solid State 31 P Nmr Spectroscopymentioning

confidence: 99%

Preparation and characterization of H3PW12O40 supported on niobia

Caliman

Dias

et al. 2010

Microporous and Mesoporous Materials

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“…The curves corresponding to the calculated enthalpy difference (ΔH) versus the number of mmoles of Py added was plotted in Figure 6 . The curves indicated that pyridine initially reacted preferentially with the stronger Brønsted acid sites (site 1), due to the most negative free energy associated with these sites [ 40 ]. In the middle of the titration, there was a simultaneous interaction of the base with either Brønsted sites or Lewis sites.…”

Section: Resultsmentioning

confidence: 99%

“…In the middle of the titration, there was a simultaneous interaction of the base with either Brønsted sites or Lewis sites. At the end of the titration, the probe molecule interacted mainly with Lewis sites and weaker hydrogen bonding sites, which may contribute to lower the average strength of site 2 [ 40 ]. It can be observed that HB has stronger acid sites than the other catalysts, and many more sites were accessible to pyridine.…”

Section: Resultsmentioning

confidence: 99%

Niobium on BEA Dealuminated Zeolite for High Selectivity Dehydration Reactions of Ethanol and Xylose into Diethyl Ether and Furfural

et al. 2020

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In this work, we investigated the role of solid-state dealumination by (NH4)2SiF6 (25% Al removal and 13% Si insertion), the impregnation of niobium (10, 18, and 25 wt. %) on dealuminated *BEA (DB) zeolite and their catalytic properties in ethanol and xylose transformations. Among all the studied catalysts, 18%Nb-DB showed increased mesoporosity and external areas. A leveling effect in the number and strength of the proposed two sites (Brønsted and Lewis) present in the catalyst (n1 = 0.24 mmol g−1, −ΔH1 = 49 kJ mol−1, and n2 = 0.20 mmol g−1, –ΔH2 = 42 kJ mol−1) in the catalyst 18%Nb-DB, might be responsible for its good activity. This catalyst presented the highest selectivity for diethyl ether, DEE (97%) with 61% conversion after 50 ethanol pulses at 230 °C (turnover number, TON DEE = 1.15). These features allowed catalytically fruitful bonding of the ethanol molecules to the neighboring sites on the channels, facilitating bimolecular ether formation through a possible SN2 mechanism. The same catalyst was active and selective for transformation of xylose at 180 °C, showing 64% conversion and 51% selectivity for furfural (TON Furfural = 24.7) using water as a green solvent.

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“…44,45 The spectra showed three bands at 1545, 1490 and 1445 cm -1 , which are associated to Brønsted sites, a combination of Brønsted/ Lewis sites and Lewis sites respectively. [46][47][48] The acidity of cerium materials has been widely discussed, but there is no consensus about the types of acid sites present on their surfaces. 49,50 Gu et al 49 reported the presence of Brønsted and Lewis sites in CeO 2 by ammonia adsorption studies.…”

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confidence: 99%

Effect of cerium loading on structure and morphology of modified Ce-USY zeolites

Garcia¹,

Araújo²,

Silva³

et al. 2011

J. Braz. Chem. Soc.

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Este trabalho descreve detalhadamente o efeito da quantidade de cério na estrutura e morfologia da zeólita NH 4 USY. Ce-USY (2-25% m/m de CeO 2 ) foi obtido por impregnação úmida de CeCl 3 seguida de calcinação a 550 ºC por 8 h. Em quantidades baixas (2-10%), foi observado que as espécies de cério encontram-se nas posições de troca iônica na rede, enquanto em maiores teores (15-25%) pequenos agregados formaram-se na superfície da HUSY. Difratometria de raios X (XRD) mostrou apenas reflexões relacionadas à HUSY, confirmando a alta dispersão das espécies de cério, porém as análises por espectroscopia Raman com transformada de Fourier (FT-Raman) detectaram CeO x para os materiais acima de 10%. A reação do CeCl 3 com NH 4 USY produziu NH 4 Cl, o qual se decompõe em HCl, ocasionando a desaluminização da rede. Os materiais apresentaram um aumento da razão Lewis/Brønsted com o aumento da quantidade de cério, devido a interação do excesso de cério com os grupos OH da USY e consequente formação de espécies CeO x . This work describes comprehensibly the effect of cerium loading on the structure and morphology of NH 4 USY zeolite. The Ce-USY (2-25 wt.% of CeO 2 ) was obtained by wet impregnation of CeCl 3 followed by calcination at 550 ºC for 8 h. At low loadings (2-10%), cerium species are mainly located at ion exchange positions in the framework, whereas at higher loadings (15-25%), small aggregates were formed on the HUSY surface. X-ray diffractograms (XRD) exhibited only the reflections related to HUSY, demonstrating the high dispersion of cerium species, but Fourier transform Raman spectroscopy (FT-Raman) detected CeO x for the materials above 10%. Reaction of CeCl 3 with NH 4 USY produced NH 4 Cl, which decomposed to form HCl, leading to framework dealumination. The materials showed an increased Lewis/Brønsted ratio with increasing cerium loadings due to the interaction between the excess cerium and the OH groups of USY, and the consequent formation of CeO x species.Keywords: cerium USY zeolite, cerium oxide, ultra stable Y zeolite, solid-state ion exchange, 27 Al and 29 Si MAS NMR spectroscopy IntroductionFaujasite-type zeolites (X and Y) are largely applied in fluid catalytic cracking (FCC) of crude oil distillates and in hydrodesulfurization of fossil diesel oil and gasoline. 1 Y zeolites, either in their sodium or ammonium form, can be exchanged for rare earth ions to achieve the following main goals: (i) to prevent aluminum loss from the zeolite structure, which results in enhanced structural resistance to the severe hydrothermal conditions of the regeneration step of FCC, 2 and (ii) to increase the activity, because the introduction of rare earth species modifies the number of acidic protons through either hydrolysis or enhancement of ionic fields inside the zeolite structure. 3 Because rare earth cations modify the acidic properties of zeolites, their insertion has an effect on both thermal and mechanical stability, which are important for zeolite application to industrial processes such as pyrolysis, 4 oxidat...

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Acidic Characterization of Copper Oxide and Niobium Pentoxide Supported on Silica–Alumina

Cited by 15 publications

References 23 publications

Preparation and characterization of H3PW12O40 supported on niobia

Preparation and characterization of H3PW12O40 supported on niobia

Niobium on BEA Dealuminated Zeolite for High Selectivity Dehydration Reactions of Ethanol and Xylose into Diethyl Ether and Furfural

Effect of cerium loading on structure and morphology of modified Ce-USY zeolites

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