Supporting Information Nb 2 5 nh 2 as a heterogeneous catalyst with water-tolerant Lewis acid sites Kiyotaka Nakajima, Yusuke Baba, Ryouhei Noma, Masaaki Kitano, Junko N. Kondo, Shigenobu Hayashi, П,* and Michikazu Hara Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan, Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan П Kanagawa Academy of Science and Technology, 3-2-1 Sakado, Takatsu-ku, kawasaki 213-0012, Japan Content 1. Method 2. Schematic structure of Nb 2 5 nh 2. 3. Estimation of the amounts of Brønsted and Lewis acid sites for dehydrated Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2. 4. C adsorption experiment and estimation of the amounts of Brønsted and Lewis acid sites for hydrated Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2. 5. FT-IR spectra for pyridine-adsorbed original and Na + -exchanged Nb 2 5 nh 2. 6. Pyridine-adsorption experiment on Nb 2 5 nh 2 in saturated H 2 vapor. 7. Catalyst reuse experiment with Nb 2 5 nh 2 for 5 runs. 8. MALDI-TF-MASS for the reaction solution. 9. Catalyst reuse experiment with H 3 P 4 -treated Nb 2 5 nh 2 for 5 runs. 10. 31 P MAS NMR spectrum for H 3 P 4 -treated Nb 2 5 nh 2. 11. C adsorption experiment for hydrated and dehydrated H 3 P 4 /Nb 2 5 nh 2. S1
Figure legends in Supporting Information Figure S1 Schematic structure of Nb 2 5 nh 2 Figure S2 FT-IR spectra for Nb 2 5 nh 2 (a) after evacuation at room temperature for 24 h and (b) after heating the sample at 423 K for 1 h under vacuum Figure S3 FT-IR spectra for pyridine-adsorbed (a) original Nb 2 5 nh 2 and (b) its Na + -exchanged form. Figure S4 FT-IR spectra for Nb 2 5 nh 2. (a) hydrated Nb 2 5 nh 2 in saturated H 2 vapor, (b) pyridine and H 2 -adsorbed Nb 2 5 nh 2 in pyridine and H 2 vapor, and (c) pyridine and H 2 -adsorbed Nb 2 5 nh 2 obtained by evacuation (room temperature) for 60 min after (b). The marked square area in A is enlarged in B. Figure S5 Catalytic activity of reused Nb 2 5 nh 2 for HMF production from D-glucose at 393 K. Catalyst: 0.2 g; water: 2.0 ml; D-glucose: 0.02 g. Figure S6 MALDI-TF-MASS for the reaction solution. Nb 2 5 nh 2 : 0.05 g; D-glucose: 0.05 g; water: 5.0 ml; reaction temperature: 393 K; reaction time: 6 h; ion detection: positive; matrix: 2,5-dihydroxybenzoic acid-acetonitrile solution. Figure S7 Catalytic activity of reused H 3 P 4 /Nb 2 5 nh 2 for HMF production from D-glucose at 393 K. Catalyst: 0.2 g; water: 2.0 ml; D-glucose: 0.02 g. Figure S8 31 P MAS NMR spectrum for H 3 P 4 /Nb 2 5 nh 2. S2
Figure S9 Differential FT-IR spectra for a) dehydrated and b) hydrated H 3 P 4 /Nb 2 5 nh 2 at 90 K. (a) Prior to C adsorption, the sample was heated at 423 K for 1 h under vacuum. C pressure: (a) 6.4 10-3, (b) 1.2 10-2, (c) 2.0 10-2, (d) 3.9 10-2, (e) 6.7 10-2, and (f) 1.3 10-1 kpa. (b) Prior to C adsorption, the sample was dehydrated at room temperature for 24 h under vacuum. C pressure: (a) 1.7 10-2, (b) 3.0 10-2, (c) 4.3 10-2, (d) 5.3 10-2, (e) 6.8 10-3, (f) 1.1 10-1, and (g) 1.4 10-1 kpa. S3
1. Method Preparation of Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2 Nb 2 5 nh 2 was typically synthesized using a mixture of NbCl 5 (5 g) and distilled water (200 ml) stirred at room temperature for 3 h. The resulting white precipitate was repeatedly washed with distilled water (ca. 500 ml) until the filtrate became neutral. Nb 2 5 nh 2 powder was obtained by drying the precipitate overnight at 353 K. Na + /Nb 2 5 nh 2 was obtained by Na + -exchange of Nb 2 5 nh 2. 1 g of Nb 2 5 nh 2 was stirred in 200 ml of 0.2 M NaCl solution maintained at ph = 5.5-5.8 by adding 0.05 M NaH solution. After 24 h, the collected sample was washed repeatedly with distilled water until Na + and Cl - ions were no longer detected and was then dried at 373 K for 12 h. H 3 P 4 /Nb 2 5 nh 2 was prepared by adsorbing H 3 P 4 on Nb 2 5 nh 2. 1 g of Nb 2 5 nh 2 was stirred in 200 ml of 1 M H 3 P 4 solution. After 48 h, the collected sample was washed repeatedly with distilled water until phosphate ions were no longer detected and was then dried at 373 K for 12 h. Allylation of benzaldehyde with tetraallyl tin The reaction was carried out in a Pyrex reaction vessel containing distilled water (15 ml), benzaldehyde (0.4 mmol), tetraallyl tin (0.2 mmol), catalyst (0.1 g) and sodium dodecyl sulfate (0.3 mmol). After 1 h at 298 K, the reaction solution was analyzed by gas chromatography-mass spectrometry (GC-MS). HMF formation from glucose Distilled water (2.0 ml) containing D-glucose (0.02 g) and catalyst (0.02 or 0.2 g) was typically heated in a sealed Pyrex tube at 393 K. The solutions after reaction were analyzed using HPLC and GC-MS. S4
2. Schematic structure of Nb 2 5 nh 2 Brønsted acid H δ+ δ Nb H H H Nb Brønsted acid δ δ+ H H Lewis acid Figure S1 Schematic structure of Nb 2 5 nh 2 S5
3. Estimation of the amounts of Brønsted and Lewis acid sites for dehydrated Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2. The amounts of Lewis and Brønsted acid sites on Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2 were estimated using FT-IR measurements for pyridine-adsorbed samples at 298 K. Nb 2 5 nh 2 samples were pressed into self-supporting disks (20 mm diameter, 25 mg) and placed in an IR cell attached to a closed glass-circulation system. Prior to pyridine adsorption, the sample was dehydrated by heating at 423 K for 1 h under vacuum. The intensities of the bands at 1450 cm -1 (pyridine coordinatively bonded to Lewis acid sites, molecular absorption coefficient: 3.15 µmol cm -1 ) and 1540 cm -1 (pyridinium ions formed by Brønsted acid sites, molecular absorption coefficient: 1.20 µmol cm -1 ) were plotted against the amounts of pyridine adsorbed on the Lewis and Brønsted acid sites of the samples, respectively. The intensities of both bands increased with the amount of chemisorbed pyridine, reaching plateaus with the appearance of the band due to physisorbed pyridine (1440 cm -1 ). While the band at 1440 cm -1 disappeared after evacuation at room temperature, there was no significant difference in intensity of the bands at 1450 and 1540 cm -1 before and after evacuation, which indicated that the maximum intensities of the bands at 1450 and 1540 cm -1 correspond to the amounts of Lewis and Brønsted acid sites available to chemisorb pyridine to saturation, respectively. The amounts of Brønsted and Lewis acid sites on Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2 were estimated from the maximum band intensities and molecular absorption coefficients at 1450 and 1540 cm -1. S6
4. C adsorption experiment and estimation of the amounts of Brønsted and Lewis acid sites for hydrated Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2. Experimental procedure FT-IR spectra were obtained at a resolution of 4 cm -1 using a spectrometer (FT/IR 6100, Jasco) equipped with an extended KBr beam splitting device and a mercury cadmium telluride (MCT) detector. A total of 64 scans were averaged for each spectrum. The samples were pressed into self-supporting disks (20 mm diameter, 20-30 mg) and placed in an IR cell attached to a closed glass-circulation system. The disk was dehydrated by heating at 423 K for 1 h under vacuum in order to remove physisorbed water. In the experiments for the hydrated samples, the self-supported disk was evacuated at room temperature for 24 h under vacuum in order to remove weakly adsorbed water. C, as a basic probe molecule, was adsorbed on the dehydrated and hydrated sample disks at 90 K in the IR cell using liquid N 2. Each IR spectrum was measured after adsorbed C and C in the gas phase reached an equilibrium. The IR spectra of the sample at 90 K before C adsorption were used as the backgrounds for the differential spectra obtained by subtracting the backgrounds from the spectra for C-adsorbed samples. Hydrated Nb 2 5 nh 2 sample for FT-IR experiments Figures S2a and S2b show FT-IR spectra for Nb 2 5 nh 2 after evacuation at room temperature for 24 h and 423 K for 1 h, respectively. Figure S2a has two distinctive signals at 3800-2600 and 1600 cm -1 that are assignable to the H stretching and bending modes of physisorbed H 2, respectively, which indicates that there is a considerable amount of physisorbed H 2 molecules on the sample evacuated at room temperature for 24 h. In contrast, the signals due to physisorbed H 2 disappeared after evacuation at 423 K for 1 h under S7
vacuum. The amount of physisorbed H 2 on the hydrated Nb 2 5 nh 2 sample was estimated to be 3.0 mmol g -1 by measuring the total amount of desorbed H 2 during heating the sample at 423 K under vacuum. Assuming that the adsorption cross section area of a H 2 molecule is 0.125 nm 2, then 1.3 layers of H 2 would be adsorbed on the hydrated Nb 2 5 nh 2 sample. Nb- str. absorbance 0.5 H str. H bend. a Nb-H str. b 4000 3000 2000 1000 Wavenumber / cm -1 Figure S2 FT-IR spectra for Nb 2 5 nh 2 (a) after evacuation at room temperature for 24 h and (b) after heating the sample at 423 K for 1 h under vacuum Estimation of the amounts of Brønsted and Lewis acid sites for hydrated Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2. The amounts of effective Brønsted and Lewis acid sites on hydrated Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2 were estimated from FT-IR measurements of C adsorbed samples. The correlation between the amount and band intensity of each C species adsorbed on the Brønsted and Lewis acid sites was obtained by FT-IR for C-adsorbed dehydrated Nb 2 5 nh 2 (Lewis acid sites: 0.15 mmol g -1, Brønsted acid sites 0.14 mmol g -1 ). First, C was adsorbed on the dehydrated sample at 90 K. The intensities of three bands at S8
2145, 2168 and 2188 cm -1, assignable to physisorbed C, C adsorbed on Brønsted and Lewis acid sites, respectively, increased with the amount of introduced C, and the band intensities due to acid sites reaches plateaus at Pco > 4.8 kpa. The correlation of the band intensity and amount of each C species adsorbed on the Brønsted and Lewis acid sites was estimated from each acid density obtained by pyridine-adsorption experiment and maximum band intensity. FT-IR spectra for C-adsorbed hydrated Nb 2 5 nh 2, Na + / Nb 2 5 nh 2 and H 3 P 4 /Nb 2 5 nh 2 were then measured at 90 K. The intensities of the bands due to C adsorbed on Brønsted and Lewis acid sites increased with the amount of introduced C, reaching plateaus at Pco > 4.8 kpa, as was the case for dehydrated Nb 2 5 nh 2. Each effective acid density on the hydrated samples, hydrated Nb 2 5 nh 2 (Brønsted acid; 0.14 mmol g -1, Lewis acid; 0.032 mmol g -1 ), Na + / Nb 2 5 nh 2 (Brønsted acid; below limitation of detection, Lewis acid; 0.034 mmol g -1 ) and hydrated H 3 P 4 /Nb 2 5 nh 2 (Brønsted acid; 0.043 mmol g -1, Lewis acid; 0.019 mmol g -1 ) was calculated from the band intensity-amount correlation. S9
5. FT-IR spectra for pyridine-adsorbed original and Na + -exchanged Nb 2 5 nh 2 Abs. 0.5 1445 cm -1 1540 cm -1 a b 1600 1400 Wavenumber / cm -1 Figure S3 FT-IR spectra for pyridine-adsorbed (a) original Nb 2 5 nh 2 and (b) its Na + -exchanged form. The Brønsted acid sites of Na + / Nb 2 5 nh 2 was examined by FT-IR measurement. We did not adopt C but pyridine as a basic molecular probe on this purpose because the signal for bridged Na + C Na + species (2158 cm -1 ) formed on Na + exchanged solid acid obscures the band for adsorbed C on Brønsted acid site (2165 cm -1 ). 1 Figure S3 shows FT-IR spectra for pyridine-adsorbed Nb 2 5 nh 2 and Na + / Nb 2 5 nh 2. The band at 1445 cm -1 assignable to adsorbed pyridine on Lewis acid site is observed in both spectra. n the other hand, the band for pyridinium ion formed on Brønsted acid sites (1540 cm -1 ) is not observed in Na + / Nb 2 5 nh 2 (Figure S3 (b)). This indicates that the Brønsted acid sites on Na + / Nb 2 5 nh 2 are blocked with Na +. Ref. 1) tero Areán, C.; Nachtigallová, D.; Nachtigall, P.; Garrone, E.; Rodriguez Delgado, M. Phys. Chem. Chem. Phys., 2007, 9, 1421. S10
6. Pyridine-adsorption experiment on Nb 2 5 nh 2 in saturated H 2 vapor A B Abs. 0.5 H str. Abs. 0.5 H bend. (a) (b) (c) (a) (b) (c) 4000 3000 2000 1000 1800 1600 1400 1200 Wavenymber / cm -1 Wavenymber / cm -1 Figure S4 FT-IR spectra for Nb 2 5 nh 2. (a) hydrated Nb 2 5 nh 2 in saturated H 2 vapor, (b) pyridine and H 2 -adsorbed Nb 2 5 nh 2 in pyridine and H 2 vapor, and (c) pyridine and H 2 -adsorbed Nb 2 5 nh 2 obtained by evacuation (room temperature) for 60 min after (b). The marked square area in A is enlarged in B. Pyridine adsorption on Nb 2 5 nh 2 in saturated H 2 vapor was examined by FT-IR to study the Lewis acid sites on Nb 2 5 nh 2. Figure S4 shows FT-IR spectra for (a) hydrated Nb 2 5 nh 2 in saturated H 2 vapor, (b) pyridine and H 2 -adsorbed Nb 2 5 nh 2 in pyridine and H 2 vapor, and (c) pyridine and H 2 -adsorbed Nb 2 5 nh 2 obtained by room temperature evacuation for 60 min after (b). Nb 2 5 nh 2 was pressed into a self-supporting disk (20 mm diameter, 20-30 mg) and placed in an IR cell attached to a closed glass-circulation system. After the disk was exposed to saturated H 2 vapor (20~25 Torr) at room temperature for 60 min (Figure S4(a)), small amount of pyridine vapor (ca. 0.08 mmol) was further added to the reaction system (391.6 cm 3 ). Figure S4(b) was measured after 60 min in the presence of H 2 and pyridine vapor. The sample was evacuated at room temperature S11
for 60 min to remove the physisorbed H 2 and pyridine molecules on the surface (Figure S4 (c)). Figure S4(a) clearly exhibits two signals at 3700~2500 cm -1 and 1700~1500 cm -1 assignable to H stretching and bending mode of H 2 molecule, respectively. There are several peaks in Figure S4(b) after introduction of small amount of pyridine. A broad and weak peak at 1540 cm -1 is due to pyridine on Brønsted acid sites (cationic pyridinium ion). Two sharp peaks at 1487 and 1445 cm -1 are assignable to both of pyridine on Brønsted and Lewis acid sites and pyridine on Lewis acid sites (coordinated pyridine), respectively. These peaks due to pyridine adsorbed on acid sites remain even after evacuation (Figure S4(c)), thus indicating that the Lewis acid sites can interact with pyridine molecules even on Nb 2 5 nh 2 in saturated H 2 vapor, multilayer adsorption of water. S12
7. Catalyst reuse experiment with Nb 2 5 nh 2 for 5 runs 100 : Glucose conversion : HMF yield Conversion, yield (%) 80 60 40 20 0 1 st 2 nd 3 rd 4 th 5 th Figure S5 Catalytic activity of reused Nb 2 5 nh 2 for HMF production from D-glucose at 393 K. Catalyst: 0.2 g; water: 2.0 ml; D-glucose: 0.02 g. The result for reuse experiment on Nb 2 5 nh 2 is shown in Figure S5. The glucose conversion and HMF yield were measured after 3 h of reaction. The collected catalyst was repeatedly rinsed with distilled water and was then reused for the subsequent reaction. No significant decrease in glucose conversion and HMF yield was observed even after 5 reuses of the catalyst, thus indicating that Nb 2 5 nh 2 can function as a stable acid catalyst for the reaction. S13
8. MALDI-TF-MASS for the reaction solution. Mass intensity / a.u. 60 50 40 30 20 10 Glucose+Na 203.13 149.18 277.19 *: Matrix-derived signal 427.28 467.29 575.36 617.38 629.41 743.46 893.54 0 100 280 460 640 820 1000 m / z Figure S6 MALDI-TF-MASS for the reaction solution. Nb 2 5 nh 2 : 0.05 g; D-glucose: 0.05 g; water: 5. 0 ml; reaction temperature: 393 K; reaction time: 6 h; ion detection: positive; matrix: 2,5-dihydroxybenzoic acid-acetonitrile solution. S14
9. Catalyst reuse experiment with H 3 P 4 -treated Nb 2 5 nh 2 for 5 runs. 100 : Glucose conversion : HMF yield Conversion, yield (%) 80 60 40 20 0 1 st 2 nd 3 rd 4 th 5 th Figure S7 Catalytic activity of reused H 3 P 4 /Nb 2 5 nh 2 for HMF production from D-glucose at 393 K. Catalyst: 0.2 g; water: 2.0 ml; D-glucose: 0.02 g. The result for reuse experiment on H 3 P 4 /Nb 2 5 nh 2 is shown in Figure S7. The glucose conversion and HMF yield were measured after 3 h of reaction. The collected catalyst was repeatedly rinsed with distilled water and was then reused for the subsequent reaction. The glucose conversion and HMF yield of the catalyst retained unchanged even after 5 reuses for the reaction. Therefore, H 3 P 4 /Nb 2 5 nh 2 could be used repeatedly as solid acid catalyst without loss of original activity. S15
10. 31 P MAS NMR spectrum for H 3 P 4 -treated Nb 2 5 nh 2 100 50 0-50 -100 Chemical shift / ppm Figure S8 31 P MAS NMR spectrum for H 3 P 4 /Nb 2 5 nh 2 The 31 P MAS NMR spectrum for the sample was measured at room temperature and at a Larmor frequency of 162.0 MHz using a single-pulse sequence with high-power proton decoupling. A Bruker MAS probehead was used with a 4 mm zirconia rotor. The spinning rate of the sample was 8 khz. The 31 P chemical shift was referenced to 85% H 3 P 4 at 0.0 ppm. (NH 4 ) 2 HP 4 was used as a second experimental reference material with the signal set at 1.33 ppm. The amount of phosphorous species on H 3 P 4 /Nb 2 5 nh 2 was estimated to be ca. 1.0 mmol g -1 by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). S16
11. C adsorption experiment for hydrated and dehydrated H 3 P 4 /Nb 2 5 nh 2 absorbance a) A Bb) a) 0.05 C Nb δ+ δ δ+ - H C δ physisorbed physisorbed C C absorbance b) Nb 0.03 g e f f e d d c a bc b a 2200 2150 2100 2200 2150 2100 C H H Wavenumber / cm -1 Wavenumber / cm -1 Figure S9 Differential FT-IR spectra for a) dehydrated and b) hydrated H 3 P 4 /Nb 2 5 nh 2 at 90 K. a) Prior to C adsorption, the sample was heated at 423 K for 1 h under vacuum. C pressure: (a) 6.4 10-3, (b) 1.2 10-2, (c) 2.0 10-2, (d) 3.9 10-2, (e) 6.7 10-2, and (f) 1.3 10-1 kpa. b) Prior to C adsorption, the sample was dehydrated at room temperature for 24 h under vacuum. C pressure: (a) 1.7 10-2, (b) 3.0 10-2, (c) 4.3 10-2, (d) 5.3 10-2, (e) 6.8 10-3, (f) 1.1 10-1, and (g) 1.4 10-1 kpa. S17