Abstract
Highly pure sodium niobate nanotubes (NaNbNTs) were prepared by treating nonporous Nb2O5 powder with 1.0 M NaOH solution at 423 K. SEM revealed that these NaNbNTs formed nanotube-bundles with diameters of 50-250 nm and lengths of several microns. A TEM image of nanotubes indicated that they had outer diameters of 15-20 nm and inner pore diameters of 3-4 nm. BET surface area and pore volume of NaNbNTs were 65 m2 g-1 and 0.17 mL g-1, respectively. Treatment with diluted phosphoric or sulfuric solutions transformed NaNbNTs into phosphate- or sulfate-promoted protonated niobate nanotubes (PO4-3/HNbNTs and SO4-2/HNbNTs), which had a surface area of ∼80 m2 g-1, a pore volume ∼ 0.26 mL g-1 and a surface that was densely covered with acid sites (1.0-1.5 mmol g-1). Owing to the high density of its acid sites, SO4-2/HNbNTs outperformed a superacidic sulfated metal oxide like SO4-2/HfO2 in catalyzing the formation of cyclic acetals from carbonyl compounds and ethylene glycol. TPD/NH3 investigations indicated that the acid site density in PO4-3/HNbNTs was even higher than in SO4-2/HNbNTs, but its activity in catalyzing the formation of cyclic acetals was lower. These results reveal that acid sites in PO4-3/HNbNTs had a severe steric effect owing to the thick surface phosphate layer, permitting only the adsorption of small molecules. Large molecules, like heptanal, may not be easily adsorbed on a surface that is densely populated with PO4-3 groups, causing PO4-3/HNbNTs to have a lower activity than SO4-2/HNbNTs, which had a lower surface population of equally bulky SO4-2 groups.
| Original language | English |
|---|---|
| Pages (from-to) | 94-104 |
| Number of pages | 11 |
| Journal | Microporous and Mesoporous Materials |
| Volume | 223 |
| DOIs | |
| Publication status | Published - 2016 Mar 15 |
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All Science Journal Classification (ASJC) codes
- Chemistry(all)
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
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Sulfated and phosphated H-type niobate nanotubes as solid acid catalysts. / Huang, Y. M.; Lin, Chiu-Hsun.
In: Microporous and Mesoporous Materials, Vol. 223, 15.03.2016, p. 94-104.Research output: Contribution to journal › Article
TY - JOUR
T1 - Sulfated and phosphated H-type niobate nanotubes as solid acid catalysts
AU - Huang, Y. M.
AU - Lin, Chiu-Hsun
PY - 2016/3/15
Y1 - 2016/3/15
N2 - Highly pure sodium niobate nanotubes (NaNbNTs) were prepared by treating nonporous Nb2O5 powder with 1.0 M NaOH solution at 423 K. SEM revealed that these NaNbNTs formed nanotube-bundles with diameters of 50-250 nm and lengths of several microns. A TEM image of nanotubes indicated that they had outer diameters of 15-20 nm and inner pore diameters of 3-4 nm. BET surface area and pore volume of NaNbNTs were 65 m2 g-1 and 0.17 mL g-1, respectively. Treatment with diluted phosphoric or sulfuric solutions transformed NaNbNTs into phosphate- or sulfate-promoted protonated niobate nanotubes (PO4-3/HNbNTs and SO4-2/HNbNTs), which had a surface area of ∼80 m2 g-1, a pore volume ∼ 0.26 mL g-1 and a surface that was densely covered with acid sites (1.0-1.5 mmol g-1). Owing to the high density of its acid sites, SO4-2/HNbNTs outperformed a superacidic sulfated metal oxide like SO4-2/HfO2 in catalyzing the formation of cyclic acetals from carbonyl compounds and ethylene glycol. TPD/NH3 investigations indicated that the acid site density in PO4-3/HNbNTs was even higher than in SO4-2/HNbNTs, but its activity in catalyzing the formation of cyclic acetals was lower. These results reveal that acid sites in PO4-3/HNbNTs had a severe steric effect owing to the thick surface phosphate layer, permitting only the adsorption of small molecules. Large molecules, like heptanal, may not be easily adsorbed on a surface that is densely populated with PO4-3 groups, causing PO4-3/HNbNTs to have a lower activity than SO4-2/HNbNTs, which had a lower surface population of equally bulky SO4-2 groups.
AB - Highly pure sodium niobate nanotubes (NaNbNTs) were prepared by treating nonporous Nb2O5 powder with 1.0 M NaOH solution at 423 K. SEM revealed that these NaNbNTs formed nanotube-bundles with diameters of 50-250 nm and lengths of several microns. A TEM image of nanotubes indicated that they had outer diameters of 15-20 nm and inner pore diameters of 3-4 nm. BET surface area and pore volume of NaNbNTs were 65 m2 g-1 and 0.17 mL g-1, respectively. Treatment with diluted phosphoric or sulfuric solutions transformed NaNbNTs into phosphate- or sulfate-promoted protonated niobate nanotubes (PO4-3/HNbNTs and SO4-2/HNbNTs), which had a surface area of ∼80 m2 g-1, a pore volume ∼ 0.26 mL g-1 and a surface that was densely covered with acid sites (1.0-1.5 mmol g-1). Owing to the high density of its acid sites, SO4-2/HNbNTs outperformed a superacidic sulfated metal oxide like SO4-2/HfO2 in catalyzing the formation of cyclic acetals from carbonyl compounds and ethylene glycol. TPD/NH3 investigations indicated that the acid site density in PO4-3/HNbNTs was even higher than in SO4-2/HNbNTs, but its activity in catalyzing the formation of cyclic acetals was lower. These results reveal that acid sites in PO4-3/HNbNTs had a severe steric effect owing to the thick surface phosphate layer, permitting only the adsorption of small molecules. Large molecules, like heptanal, may not be easily adsorbed on a surface that is densely populated with PO4-3 groups, causing PO4-3/HNbNTs to have a lower activity than SO4-2/HNbNTs, which had a lower surface population of equally bulky SO4-2 groups.
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U2 - 10.1016/j.micromeso.2015.10.037
DO - 10.1016/j.micromeso.2015.10.037
M3 - Article
AN - SCOPUS:84947259126
VL - 223
SP - 94
EP - 104
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
SN - 1387-1811
ER -