Rodiansono
ab,
Syahrul
Khairi
a,
Takayoshi
Hara
a,
Nobuyuki
Ichikuni
a and
Shogo
Shimazu
*a
aGraduate School of Engineering, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan. E-mail: shimazu@faculty.chiba-u.jp; Fax: +81 43 290 3379; Tel: +81 43 290 3379
bDepartment of Chemistry, Lambung Mangkurat University, Jl. A. Yani Km 36 Banjarbaru, Indonesia 70714
First published on 13th June 2012
Inexpensive Ni–Sn-based alloy catalysts, both bulk and supported, exhibited high selectivity in the hydrogenation of a wide range of unsaturated carbonyl compounds and produced unsaturated alcohols almost exclusively. For the bulk Ni–Sn alloy catalysts, a relatively high reaction temperature of 453 K was required to achieve an efficient hydrogenation of CO rather than C
C. The catalyst that consisted of the Ni–Sn alloy dispersed on TiO2 allowed a remarkable reduction of the reaction temperature to 383 K. Both the Ni3Sn2 and Ni3Sn alloy phases were found to be responsible for the enhancement of the chemoselectivity. The Ni–Sn alloy catalysts were reusable without any significant loss of selectivity.
Catalysts based on Ni, which is also a Pt-group metal, would be good candidates because of the similarity of their catalytic behaviour to that of Pt, and such catalysts have been widely used for numerous chemical reactions both in the laboratory and in industry.10 A few reports have shown that tin alloyed with Ni exhibited a unique catalytic performance for the hydrogenation of alkyne,11 the dehydrogenation of cyclohexane,12 reforming,13 oxidation,14 and carbonylation.15 Unlike tin alloyed with Pt, the utilisation of Ni–Sn alloy-based catalysts for the selective hydrogenation of unsaturated carbonyl compounds has been rarely investigated thus far.16
Recently, we reported the synthesis of Ni–Sn alloy catalysts supported on aluminium hydroxide (Ni–Sn/AlOH) by the hydrothermal treatment of a mixture of RANEY®nickel supported on aluminium hydroxide (R-Ni/AlOH) and SnCl2·2H2O solution. We subsequently applied the catalysts to the chemoselective hydrogenation of various unsaturated carbonyl compounds.17 We found that the chemoselectivity of Ni could be controlled precisely by changing the Ni/Sn ratio to form a Ni–Sn alloy that might play a key role in the enhancement of the chemoselectivity.
In the present report, we have extended our study to the preparation of Ni–Sn alloy catalysts supported on various inorganic compounds such as Al2O3, aluminium hydroxide (AlOH), active carbon (AC), SiO2, and TiO2. Both bulk and supported Ni–Sn alloy catalysts were prepared via the hydrothermal treatment of a solution that contained Ni and Sn species at 423 K for 24 h followed by H2 treatment at 573–873 K for 90 min. The effects of the Ni/Sn ratio and the supports on the activity and the selectivity in the hydrogenation of furfural (FFald) and various unsaturated carbonyl compounds were studied.
Entry | Catalysta | Compositionb/mol% | Major alloy phasec | H2d/μmol g−1 | S BET e/m2 g−1 | D f/nm |
---|---|---|---|---|---|---|
a The value in the parentheses is Ni/Sn ratio. b Determined by ICP-AES. c Based on the crystallographic databases,18 and mol% of alloy component was calculated by the Multi-Rietveld Analysis Program LH-Riet 7.00 method on the Rietica software.19 d H2 uptake at 273 K (noted after corrected for physical and chemical adsorption). e BET specific surface areas, determined by N2 physisorption at 77 K. f The average Ni–Sn crystallite sizes derived from the Scherrer's equation. g Ni3Sn(201). h Ni3Sn2(101). i Ni3Sn4(112). j Ni(111). | ||||||
1 | Ni–Sn(3.0) | Ni74.9Sn25.1 | Ni3Sn (66%) | 12.0 | 5 | 13g |
2 | Ni–Sn(1.5) | Ni59.9Sn40.1 | Ni3Sn2 (91%) | 8.6 | 12 | 17h |
3 | Ni–Sn(0.75) | Ni42.7Sn57.3 | Ni3Sn4 (87%) | 4.7 | 57 | 23i |
4 | Ni–Sn(1.5)/Al2O3 | Ni60.2Sn39.8 | Ni3Sn2 | 9.1 | 94 | 16h |
5 | Ni–Sn(1.5)/AlOH | Ni60.0Sn40.0 | Ni3Sn2 | 9.0 | 120 | 15h |
6 | Ni–Sn(1.5)/AC | Ni61.2Sn38.8 | Ni3Sn2 | 13.0 | 676 | 17h |
7 | Ni–Sn(1.5)/SiO2 | Ni58.7Sn41.3 | Ni3Sn2 | 13.5 | 234 | 10h |
8 | Ni–Sn(1.5)/TiO2 | Ni60.4Sn39.6 | Ni3Sn2 | 13.0 | 52 | 6h |
9 | R–Ni/AlOH | Ni47.6Sn52.4 | — | 104 | 151 | 11j |
Based on the ICP-AES analyses, the compositions of the bulk and supported Ni–Sn alloys were approximately equivalent to the feeding ratios of each precursor and were reflected in the composition of each Ni–Sn alloy phase (Table 1, entries 1–3). In the case of Ni–Sn(3.0), the major alloy phase was Ni3Sn (Fig. 1a), whereas Ni–Sn(1.5) and Ni–Sn(0.75) gave Ni3Sn2 and Ni3Sn4 as the major alloys formed, respectively (Fig. 1b and c).18 The simulated calculation using the multi-Rietveld analysis program LH-Riet in the Reitica software package19 for each of the XRD patterns of the synthesised bulk Ni–Sn alloy catalysts was performed to estimate the proportions of the different Ni–Sn alloy phases formed; the profiles are shown in Fig. S1–S3, ESI.†
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Fig. 1 XRD patterns of the synthesised bulk Ni–Sn alloy catalysts after H2 treatment at 673 K with Ni/Sn ratios of (a) 3.0, (b) 1.5, and (c) 0.75.(★) Ni3Sn. (⊗) Ni3Sn2. (●) Ni3Sn4. |
The major alloy components were approximately 66% Ni3Sn for Ni–Sn(3.0), 91% Ni3Sn2 for Ni–Sn(1.5), and 87% Ni3Sn4 for Ni–Sn(0.75) after the treatment with H2 at 673 K. Komatsu et al. reported the formation of bulk Ni3Sn2 from the arc melting of Ni/Sn mixtures at 1433 K,11a whereas Masai et al. have reported the formation of a mixture of Ni3Sn, Ni3Sn2 and Ni3Sn4 alloys by H2 treatment at 773 K.12d In general, a Ni3Sn2 alloy is formed at temperatures greater than 1730 K because the melting points of Ni and Sn are 1730 K and 505 K, respectively.11a Ni3Sn, Ni3Sn2, and Ni3Sn4 alloy phases were successfully synthesised at relatively lower temperature using our simple method.
The H2 uptake, the BET surface area, and the average Ni–Sn crystallite sizes are also summarised in Table 1. With increasing Sn content (decreasing Ni/Sn ratio), the H2 uptake decreased, whereas the BET surface area and the average Ni–Sn crystallite sizes increased (Table 1, entries 1–3). The average Ni–Sn crystallite sizes of Ni3Sn, Ni3Sn2, and Ni3Sn4 were 13, 17, and 27 nm, respectively, which were comparable to the previous report.12b The H2 uptakes of bulk Ni3Sn, Ni3Sn2, and Ni3Sn4 were 12.0 μmol g−1, 8.6 μmol g−1, and 4.7 μmol g−1, respectively. Our results are consistent with the previous reports of Komatsu et al. that Ni3Sn exhibited a H2 uptake greater than that of Ni3Sn2 or Ni3Sn4.12c
Five types of supports (Al2O3, AlOH, AC, SiO2, and TiO2) were employed for the preparation of the supported Ni–Sn(1.5) alloy catalysts using a procedure similar to that used for the synthesis of the bulk phases. The physicochemical properties of the supported Ni–Sn(1.5) alloy catalysts are also summarised in Table 1 (entries 4–8), and the XRD patterns are shown in Fig. 2. The total loading amount of Ni–Sn was 2.3∼2.4 mmol g−1 (based on the ICP-AES results) for all of the supported Ni–Sn(1.5) samples (the composition (mol%) of Ni and Sn are listed in Table 1). The H2 uptake and the average Ni3Sn2 alloy crystallite sizes for Ni–Sn(1.5)/Al2O3 and Ni–Sn(1.5)/AlOH were almost equal to that of the bulk alloy (Table 1, entries 4–5), while the H2 uptakes for Ni–Sn(1.5)/AC, Ni–Sn(1.5)/SiO2, and Ni–Sn(1.5)/TiO2 were 13.0, 13.5, and 13.0 μmol g−1, respectively (entries 6–8). The XRD patterns also revealed that Ni3Sn2, a major alloy phase, was formed on the Al2O3, AlOH, and AC supports (Fig. 2a–c). In contrast, the XRD patterns Ni–Sn(1.5)/SiO2 and Ni–Sn(1.5)/TiO2 exhibited broadened peaks at 2θ = 30.8°, 42.5°, and 44.2°, which correspond to the Ni3Sn2(101), Ni3Sn2(102), and Ni3Sn2(110) diffraction peaks, respectively.18 These results suggest that the higher dispersions of the Ni–Sn alloy on the SiO2 and TiO2 were formed as roughly depicted in the average Ni3Sn2(101) crystallite sizes, which were 10 nm and 6 nm, respectively (Table 1, entries 7 and 8). In conclusion, the XRD analysis and H2 measurement results confirm that Ni–Sn alloy phases were also formed on the supports and that their characteristics were consistent with the results observed for the bulk material.
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Fig. 2 XRD patterns of Ni–Sn(1.5) on various supports of (a)Al2O3, (b) AlOH, (c) AC, (d) SiO2, and (e) TiO2. |
Entry | Catalyst | Conversion/% | Yielda/% | Selectivityb/% |
---|---|---|---|---|
Reaction conditions: FFald, 1.1 mmol; (FFald/Ni ratio = 15); iso-PrOH, 3 mL; H2, 3.0 MPa, 383 K, 75 min.a Yield of FFalc, determined by GC using an internal standard technique.b Selectivity to FFalc. The value in the parantheses is the selectivity to THFalc.c At 433 K.d At 403 K. | ||||
1 | Ni–Sn(3.0) | 72 | 70 | 97(3) |
2c | Ni–Sn(1.5) | 67 | 67 | 100(0) |
3c | Ni–Sn(0.75) | 16 | 12 | 75(25) |
4 | Ni–Sn(1.5)/Al2O3 | 85 | 84 | 99(1) |
5 | Ni–Sn(1.5)/AlOHd | 67 | 67 | 100(0) |
6 | Ni–Sn(1.5)/AC | 72 | 72 | 100(0) |
7 | Ni–Sn(1.5)/SiO2 | 32 | 62 | 99(1) |
8 | Ni–Sn(1.5)/TiO2 | >99 | >99 | 100(0) |
9d | R–Ni/AlOH | >99 | >99 | 0(100) |
10 | Sn/AlOH | 0 | 0 | 0 |
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Scheme 1 Reaction pathways of FFald hydrogenation by Ni–Sn alloy catalysts. |
On the Ni–Sn(3.0) alloy catalyst, FFald conversion was 72% with a furfuryl alcohol (FFalc) yield of 70% (Table 2 entry 1), whereas, on the Ni–Sn(1.5) alloy, a 67% yield of FFalc was obtained without tetrahydrofurfuryl alcohol (THFalc) formation (entry 2). In contrast, the Ni–Sn(0.75) alloy gave only a 12% yield of FFalc (75% selectivity) (entry 3). These results suggest that the presence of Ni3Sn and Ni3Sn2 alloy catalysts played an important role in the selective hydrogenation of CO rather than C
C groups in the unsaturated carbonyl compounds.17
Screening tests using supports other than the five types in Table 2 were also performed and resulted in insufficient results.20 For catalysts supported on AlOH, Al2O3, SiO2, and AC, relatively high FFald conversions and yields of FFalc were obtained (Table 2, entries 4–7). For the Ni–Sn(1.5)/Al2O3 catalyst, FFald conversion was 85% with a FFalc yield of 84% (Table 2, entry 4), whereas the Ni–Sn(1.5)/AlOH, Ni–Sn(1.5)/AC, and Ni–Sn(1.5)/SiO2 catalysts produced FFalc yields of 67%, 72%, and 62%, respectively (Table 2, entries 5–7). A remarkably high FFald conversion (>99%) and FFalc selectivity (100%) were obtained when Ni–Sn(1.5)/TiO2 was used under the same conditions (Table 2, entry 8). The high conversion of FFald and the high selectivity of FFalc over Ni–Sn(1.5)/TiO2 can be attributed to the relatively high dispersion of the Ni–Sn alloy on TiO2 giving rise to active sites with a significantly higher catalytic activity. Alternatively, the high conversion and selectivity may be a result of the strong interactions between the active metals and TiO2 generating significant interactions between CO groups and Ni–TiOx sites and leading to high selectivity to unsaturated alcohols.6a Kijenski et al. have reported that Pt catalysts supported on TiO2 gave higher selectivity to FFalc in the hydrogenation of FFald than did Pt supported on SiO2, ZrO2 or MgO.6f Recently, Corma et al. studied the chemoselectivity of Ni supported on TiO2 in the hydrogenation of substituted nitroaromatics.6f Moreover, the monometallic R-Ni/AlOH catalyst converted FFald to give >99% THFalc, which indicates that R-Ni/AlOH hydrogenated both C
C and C
O of FFald (entry 9), whereas Sn/AlOH was not active for the hydrogenation of FFald under the same conditions (entry 10). These results suggest that the addition of tin to form a Ni–Sn alloy retards the C
C hydrogenation activity of nickel. Swift et al. have reported that the formation of a Ni–Sn alloy by the addition of tin to a Ni/SiO2 catalyst remarkably changed the reactivity of Ni/SiO2 because of the change in the electron density of nickel metal.12f Delbecq et al. indicated that the C
O hydrogenation selectivity in the hydrogenation of α,β-unsaturated aldehydes could be enhanced by the formation of a Pt–Sn alloy because of the higher affinity of the alloy towards C
O rather than towards C
C bonds, as noted previously.9 Resasco et al. have reported that the selective hydrogenation of C
O versus C
C in α,β-unsaturated aldehydes by a Pd–Cu alloy supported on silica was caused by the preferential η2-coordination of C
O to Pd.21
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Fig. 3 Effect of reaction temperature on the FFalc yield over the bulk and supported Ni–Sn(1.5) alloy catalysts. Reaction conditions: catalyst, 0.05 g; FFald, 1.1 mmol; iso-PrOH, 3 mL; H2, 3.0 MPa, 75 min. |
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Fig. 4 Effect of initial H2 pressure on the conversion and selectivity in the hydrogenation of FFald over Ni–Sn(1.5)/TiO2 alloy catalyst. Reaction conditions: catalyst, 0.05 g; FFald, 1.1 mmol; iso-PrOH, 3 mL; 383 K, 75 min. |
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Fig. 5 Time profile of the hydrogenation of FFald over the bulk and the supported Ni–Sn(1.5) alloy catalysts. Reaction conditions: catalyst, 0.05 g; FFald, 1.1 mmol; iso-PrOH, 3 mL; H2, 3.0 MPa, 383 K. |
Run | 1 | 2 | 3 | 4 | 5 | 6a |
---|---|---|---|---|---|---|
Reaction conditions: FFald, 1.1 mmol; (FFald/Ni ratio = 15); iso-PrOH (3 mL); H2, 3.0 MPa, 383 K, 75 min.a The used catalyst was treated by H2 at 673 K for 1 h before reaction.b Selectivity to FFalc, determined by GC using an internal standard technique. | ||||||
Conversion (%) | >99 | 62 | 51 | 46 | 43 | >99 |
Selectivityb (%) | 100 | 96 | 97 | 99 | 99 | 99 |
The used Ni–Sn(1.5)/TiO2 catalyst was easily separated by either simple centrifugation or filtration after the reaction. The activity of the catalyst decreased while the high selectivity was maintained for at least five consecutive runs. The amount of Ni and Sn that leached into the reaction solution was 0.58% and 1.3% after four runs, respectively. Treatment of the used Ni–Sn(1.5)/TiO2 catalyst (after five runs) with H2 at 673 K for 1 h restored the catalyst's original activity and selectivity.24
Entry | Substrate | Product | Temp./K | Bulk Ni–Sn(1.5) | Ni–Sn(1.5)/TiO2 | ||
---|---|---|---|---|---|---|---|
Conv.a (%) | Select.a (%) | Conv.a (%) | Select. a(%) | ||||
Reaction conditions: Substrate/Ni = 15; iso-PrOH, 3 mL; H2, 3MPa; time, 75 min.a Conversion and selectivity were determined by GC using an internal standard technique. | |||||||
1 |
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383 | 29 | 90 | 98 | 94 |
2 |
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403 | 32 | 73 | 93 | 96 |
3 |
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403 | 34 | 89 | >99 | 90 |
4 |
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403 | 28 | 80 | >99 | 91 |
5 |
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403 | 45 | 74 | 70 | 88 |
6 |
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383 | 13 | 100 | 41 | 100 |
7 |
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403 | 78 | 97 | 65 | 100 |
8 |
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383 | 52 | 89 | 88 | 96 |
9 |
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383 | 78 | 89 | 91 | 73 |
10 |
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383 | 49 | 100 | 89 | 100 |
The catalytic activity of supported Ni–Sn(1.5)/TiO2 in the hydrogenation of various α,β-unsaturated aliphatic aldehydes, including citronellal, 2-ethyl-2-hexenal, trans-2-octenenaldehyde, trans-2-hexenaldehyde, and crotonaldehyde, was approximately 1.5–3.5 times higher than that of the bulk Ni–Sn(1.5) (Table 4, entries 1–5). For example, the hydrogenation of citronellal over bulk Ni–Sn(1.5) gave 29% conversion (90% selectivity), whereas the same reaction over supported Ni–Sn(1.5)/TiO2 gave 98% conversion (94% selectivity) at 383 K (Table 4, entry 1). The hydrogenation of cinnamaldehyde over bulk Ni–Sn(1.5) and supported Ni–Sn(1.5)/TiO2 catalysts gave notable conversions of 13% and 41%, respectively, at 383 K with 100% selectivity to cinnamyl alcohol (entry 6). In addition, the hydrogenation of 3-cyclohexencarboxaldehyde over the bulk Ni–Sn(1.5) alloy gave 78% conversion (97% selectivity), and the same reaction over supported Ni–Sn(1.5)/TiO2 gave 65% conversion (100% selectivity) at 403 K (entry 7).
In the case of the hydrogenation of the α,β-unsaturated ketone 2-nonene-2-one over bulk Ni–Sn(1.5) and supported Ni–Sn(1.5)/TiO2 catalysts, 52% and 88% conversions were achieved, respectively, and the desired product of 2-nonene-2-ol was produced with selectivities of 89% and 96%, respectively (entry 8). In the hydrogenation of 2-cyclohexen-1-one, relatively high conversions of 78% (89% selectivity) and 91% (73% selectivity) were achieved for the bulk and supported catalysts, respectively. Notable selectivities towards cyclohexanone of 21% and 27% over the bulk and supported Ni–Sn(1.5)/TiO2 catalysts, respectively, were obtained at 383 K (entry 9). In addition, hydrogenation of the aromatic ketone acetophenone over both the bulk and supported Ni–Sn(1.5)/TiO2 alloy catalysts at 383 K gave a high selectivity to 1-phenylethanol (100%) at conversion rates of 78% and 89%, respectively (entry 10). Based on these results, Ni–Sn alloy catalysts can be concluded to be promising catalysts for the selective hydrogenation of a wide range of α,β-unsaturated aldehydes and ketones into the corresponding unsaturated alcohols.
All organic chemical compounds were purified using standard procedures prior to use.
The H2 uptake was determined through irreversible H2 chemisorption. After the catalyst was heated at 393 K under vacuum for 30 min, it was treated at 673 K under H2 for 30 min. The catalysts were subsequently cooled to room temperature under vacuum for 30 min. The H2 measurement was conducted at 273 K, and H2 uptake was calculated according to the method described in the literature.26
Footnote |
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c2cy20216f |
This journal is © The Royal Society of Chemistry 2012 |