Dehydration of 1,5-pentanediol over rare earth oxides

Dehydration of 1,5-pentanediol over rare earth oxides

Applied Catalysis A: General 419–420 (2012) 41–48 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General journal homepage: ...

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Applied Catalysis A: General 419–420 (2012) 41–48

Contents lists available at SciVerse ScienceDirect

Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata

Dehydration of 1,5-pentanediol over rare earth oxides Fumiya Sato, Hiro Okazaki, Satoshi Sato ∗ Graduate School of Engineering, Chiba University, Yayoi, Inage, Chiba 263-8522, Japan

a r t i c l e

i n f o

Article history: Received 18 November 2011 Received in revised form 27 December 2011 Accepted 5 January 2012 Available online 14 January 2012 Keywords: Dehydration 1,5-Pentanediol 4-Penten-1-ol Rare earth oxides Bixbyite Reactivity

a b s t r a c t Vapor-phase catalytic dehydration of 1,5-pentanediol was investigated over rare earth oxides (REOs) at 325–450 ◦ C. The conversion of 1,5-pentanediol over REOs calcined at 700 and 800 ◦ C was higher than that calcined at 500 ◦ C. Sc2 O3 , Yb2 O3 , and Lu2 O3 with cubic bixbyite structure showed the selectivity to 4-penten-1-ol with higher than 74 mol%, while REOs with hexagonal and monoclinic structures showed the selectivity with less than 50 mol%. Especially, Yb2 O3 and Lu2 O3 calcined at 1000 ◦ C showed high formation rate of 4-penten-1-ol per specific surface area over 1 mmol h−1 m−2 at 400 ◦ C. In the Yb2 O3 catalyst calcined at 800 ◦ C, the conversion of 1,5-pentanediol was increased up to 74.4 mol% with increasing contact time, together with stable selectivity to 4-penten-1-ol of 71.8 mol%. In comparing the reactivity of alkanediols to form the corresponding unsaturated alcohols over Yb2 O3 , we found the reactivity of alkanediols into the corresponding unsaturated alcohols was the following order: 1,4-butanediol > 1,3diols  1,5-pentanediol  1,6-hexanediol. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Unsaturated alcohols are raw materials for important chemicals such as medicine, agricultural chemicals, and polymers. We have recently reported that unsaturated alcohols are produced in the vapor-phase dehydration of 1,3-butanediol to produce 3buten-2-ol and trans-2-buten-1-ol [1–3], in the dehydration of 1,4-butanediol into 3-buten-1-ol [4–7], and in the dehydration of 1,5-pentanediol [8] and other diols with long chain carbons [9] into the corresponding unsaturated alcohols. In these reactions, rare earth oxides (REOs) show high catalytic activities. In a pioneering work, it is known that REOs catalyze the dehydration of mono alcohols, Hoffman elimination, to produce ␣-olefin [10]. In the dehydration of alkanediols, the catalytic activity depends upon the surface structure of REOs [2,3,5–7]: heavy REOs with cubic bixbyite structure and fluorite CeO2 are selective for the formation of unsaturated alcohols. In particular, 1,4-butanediol is dehydrated into 3-buten-1-ol with the selectivity higher than 85 mol% over Tb4 O7 , Er2 O3 , Tm2 O3 , and Yb2 O3 that calcined at high temperature of 800 ◦ C [7]. Other than REOs, In2 O3 with the same bixbyite structure also has the catalytic activity in the dehydration of diols [11]. In the previous report, we have investigated vapor-phase dehydration of 1,5-pentanediol into 4-penten-1-ol over various catalysts such as SiO2 -Al2 O3 , ZrO2 , and Yb2 O3 [8]. Over acidic

∗ Corresponding author. Tel.: +81 43 290 3376; fax: +81 43 290 3401. E-mail address: [email protected] (S. Sato). 0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2012.01.005

catalysts such as SiO2 -Al2 O3 , Al2 O3 , and TiO2 , tetrahydropyran (THP) that is cyclodehydration product is the main product. The selectivity to THP is higher than 65 mol%, while 4-penten-1-ol is rarely detected. In contrast, Yb2 O3 preferentially catalyzes the formation of 4-penten-1-ol in the dehydration of 1,5-pentanediol. At temperatures of 375 and 400 ◦ C, the selectivity to 4-penten-1-ol shows the highest value close to 70 mol%. Yb2 O3 is one of heavy REOs, so that Dy2 O3 , Ho2 O3 , Er2 O3 , Tm2 O3 , and Lu2 O3 have similar physical properties, such as crystal structure and valence of metal, to that of Yb2 O3 . Therefore, we expect that a specific REO other than Yb2 O3 has high catalytic activities in the dehydration of 1,5pentanediol into 4-penten-1-ol.

In this work, we investigated dehydration of 1,5-pentanediol into 4-penten-1-ol over REOs to find suitable catalyst and reaction conditions. We found that Sc2 O3 , Yb2 O3 , Lu2 O3 which had cubic bixbyite structure showed high catalytic activities for the dehydration of 1,5-pentanediol. We also discussed the reactivity of 1,5-pentanediol, comparing with 1,3-propanediol, 1,3-butanediol, and 1,4-butanediol in order to clarify the influence of the length of carbon chains and the position of hydroxyl groups of diols. 2. Experimental Alkanediols such as 1,5-pentanediol, 1,3-propanediol, 1,3butanediol, and 1,4-butanediol were purchased from Wako Pure Chemical Industries, Japan. REO samples were supplied by Kanto

F. Sato et al. / Applied Catalysis A: General 419–420 (2012) 41–48

3. Results 3.1. Effect of calcination temperature of REOs on the catalytic activity in the dehydration of 1,5-pentanediol We have reported stable catalytic activities of CeO2 and ZrO2 in the dehydration of butanediols [2,8]. In the dehydration of 1,5pentanediol over REOs, we also observed stable catalytic activity. Then, the conversion of 1,5-pentanediol and the selectivity to each product were averaged in the initial 5 h to evaluate the catalytic activity. Fig. 1 shows the conversion of 1,5-pentanediol and selectivity to 4-penten-1-ol in the dehydration of 1,5-pentanediol over Sc2 O3 , Yb2 O3 , and Lu2 O3 calcined at different temperatures. As shown in Fig. 1A, the conversion over Sc2 O3 increased moderately with increasing calcination temperature below 800 ◦ C whereas the conversion of Sc2 O3 calcined at 1000 ◦ C was lower than 800 ◦ C. The selectivity to 4-penten-1-ol was virtually maintained constant regardless of calcination temperature below 800 ◦ C. As shown in Fig. 1B, the conversion over Yb2 O3 showed a maximum value at calcination temperature of 700 ◦ C. At calcination temperatures higher than 700 ◦ C, the conversion gradually decreased with increasing calcination temperature whereas the selectivity to 4-penten-1-ol was increased from 66.8 to 81.3 mol%. As shown in Fig. 1 C, the conversion over Lu2 O3 shows a maximum at the calcination temperature of 700 ◦ C in a similar way to Fig. 1B. The selectivity to 4-penten-1-ol was slightly increased with increasing calcination temperature. In short, the catalysts calcined at 700 and 800 ◦ C showed high values in the conversion and selectivity. Thereafter, we used catalysts calcined at 800 ◦ C in the following sections. 3.2. Dehydration of 1,5-pentanediol over various rare earth oxides Table 1 summarizes catalytic activities of various REOs in the dehydration of 1,5-pentanediol at 400 ◦ C. REOs have different crystal structures depending on the elements [14,15]. Over the catalysts with A-type hexagonal phase such as La2 O3 and Nd2 O3 , the conversion level was as low as 16%, and the selectivity to 4-penten-1-ol was lower than those to tetrahydropyran and ı-valerolactone. Over REOs with B-type monoclinic phase such as Sm2 O3 , Eu2 O3 , and Gd2 O3 , the selectivity into 4-penten1-ol was higher than that over A-type REOs, although the conversion level was also low (18.0–23.1%). Monoclinic Dy2 O3 and Ho2 O3 , on the other hand, the selectivity was as high as 60%. Although REOs with C-type cubic phase of bixbyite structure such as Sc2 O3 , Yb2 O3 , Lu2 O3 showed

A

100

Conversion & selectivity / %

Sc2O3 80

(b) 60

(81.8)

(66.2)(51.5)

40

(a)

20

(30.9)

0 500

600

700

800

900

1000

Calcination temperature / °C

B

100

Yb2O3 Conversion & selectivity / %

Kagaku Co. Ltd., Japan. The REOs were calcined at 500, 700, 800, and 1000 ◦ C. Physical properties of REOs are reported in the previous paper [12]. The dehydration of alkanediols, such as 1,5-pentanediol, 1,3propanediol, 1,3-butanediol, and 1,4-butanediol, was carried out in a fixed-bed down-flow reactor under the atmospheric pressure of nitrogen gas at the flow rate of 30 cm3 min−1 . In each test, 0.3 g of catalyst was loaded into the reactor. After the catalyst bed had been heated in nitrogen flow at 500 ◦ C, the catalytic reaction was performed at 300–450 ◦ C. An alkanediol was fed into the reactor at a liquid flow rate of 1.8 cm3 min−1 (17 mmol h−1 for 1,5-pentanediol, W/F = 18 gcat. h mol−1 where W and F are catalyst weight and 1,5pentanediol feed rate, respectively), LHSV = 6.0 h−1 . A reaction effluent recovered every hour was analyzed by gas chromatography (GC-8A, Shimadzu, Japan) with a 30 m capillary column (InertCap WAX-HT, GL Science, Japan). A gas chromatography mass spectrometer (GCMS-QP5050A, Shimadzu, Japan) equipped with a 30 m capillary column (DB-WAX, Agilent Technologies, USA) was used for identification of compounds in the effluent.

(b)

80

60

(a)

(35.9) (28.8)

40

(15.7)

(37.8) 20

0

500

600

700

800

900

1000

Calcination temperature / °C

C

100

Lu2O3 Conversion & selectivity / %

42

80

(b) 60

(38.2) 40

(44.2)

(a)

(27.8)

(14.1) 20

0

500

600

700

800

900

1000

Calcination temperature / °C Fig. 1. Calcination temperature dependence of (a) 1,5-pentanediol conversion and (b) selectivity into 4-penten-1-ol over (A) Sc2 O3 , (B) Yb2 O3 , and (C) Lu2 O3 at 400 ◦ C. W/F = 17.5 gcat h mol−1 . The figures in parentheses indicate specific surface area (m2 g−1 ) of catalysts cited Ref. [12].

F. Sato et al. / Applied Catalysis A: General 419–420 (2012) 41–48

43

Table 1 Dehydration of 1,5-butanediol over REOs calcined at 800 ◦ Ca . Catalyst

Sc2 O3 Y2 O3 La2 O3 CeO2 Pr6 O11 Nd2 O3 Sm2 O3 Eu2 O3 Gd2 O3 Tb4 O7 Dy2 O3 Ho2 O3 Er2 O3 Tm2 O3 Yb2 O3 Lu2 O3 a b c d e f

SBET c (m2 g−1 )

Ionic radiusb (nm)

0.0745 0.0900 0.1032 0.0970 0.0990 0.0983 0.0958 0.0947 0.0938 0.0923 0.0912 0.0901 0.0890 0.0880 0.0868 0.0861

51.5 29.3 18.0 53.7 22.7 18.2 20.3 19.8 20.6 17.7 19.1 23.7 21.5 27.0 28.8 27.8

CPc , d

C M+C H CF CF H M M M CF M M M+C C C C

Conversion (%)

63.3 30.4 13.5 22.4 9.8 16.8 18.0 18.8 18.9 23.2 22.7 23.1 39.3 44.9 50.9 55.3

Selectivity (mol%)e

Formation rate of 4P1OL (mmol h−1 m−2 )

4P1OL

THP

DVL

13PDE

Othersf

75.5 60.0 11.6 25.8 16.5 27.2 42.2 44.4 41.0 68.0 59.6 72.0 60.0 64.0 74.0 77.8

7.5 17.4 26.8 3.9 21.2 23.6 13.8 11.7 15.1 8.5 12.8 6.2 17.4 10.7 8.3 7.5

1.6 7.9 21.5 21.0 18.3 16.4 15.6 11.5 15.3 6.2 7.7 2.7 7.9 6.4 2.8 1.6

0.4 0 0 0 0 0 0 0 0 0 0 0.6 0 0 0 0.9

14.9 18.9 40.1 33.6 44.0 32.8 28.5 32.4 28.6 17.3 19.9 14.7 18.9 13.9 18.5 14.8

0.530 0.356 0.050 0.062 0.041 0.143 0.214 0.241 0.215 0.509 0.405 0.401 0.627 0.608 0.747 0.884

Reaction temperature: 400 ◦ C. W/F = 18 gcat h mol−1 . Conversion and selectivity were averaged in the initial 5 h. Ionic radius of trivalent rare earth cation with coordination number 6, except Ce4+ with coordination number 8, the data from Ref. [13]. Cited from Ref. [12]. CP: Crystal phase. H: A-type hexagonal, M: B-type monoclinic, C: C-type cubic bixbyite, and CF : cubic fluorite. 4P1OL: 4-penten-1-ol, THP: tetrahydropyran, DVL: ␦-valerolactone, and 13PDE: 1,3-pentadiene. Include 1-pentanol, cis- and trans-3-penten-1-ol, 3,4-dihydropyran, and pentanal.

high selectivity into 4-penten-1-ol (higher than 70%) at relatively high conversion (44.9–63.3%). In contrast, CeO2 and Pr6 O11 with cubic fluorite phase had low selectivity at most 25.8%. Fluorite Tb4 O7 , however, showed high selectivity of 68.0%. This will be discussed in the Section 4.2. Fig. 2 indicates effect of contact time (W/F) on the conversion of 1,5-pentanediol and the selectivity to 4-penten-1-ol at 400 ◦ C over Yb2 O3 calcined at 800 ◦ C. The conversion of 1,5-pentanediol was increased from 31.4 to 74.4% with increasing W/F, whereas the selectivity to 4-penten-1-ol was slightly changed around 72%. This result indicates that the excessive reaction, such as decomposition of 4-penten-1-ol, rarely proceeds even under high W/F conditions. 3.3. Dehydration of several alkanediols over Yb2 O3 at different reaction temperatures We compared reactivity of 1,5-pentanediol with other alkanediols such as 1,3-propanediol, 1,3-butanediol, and 1,4-butanediol

Conversion & selectivity / %

100

(b)

80

60

40

(a)

over Yb2 O3 calcined at 800 ◦ C, which has cubic bixbyite structure [12]. Table 2 exhibits the catalytic activity of Yb2 O3 calcined at 800 ◦ C in the dehydration of 1,5-butanediol at different reaction temperatures. The conversion of 1,5-pentanediol was gradually increased with increasing reaction temperature from 350 to 425 ◦ C. Below 425 ◦ C, 4-penten-1-ol was the main product, while the selectivity to 4-penten-1-ol was considerably decreased over 425 ◦ C. We have previously reported that the reaction-temperature dependence of uncalcined Yb2 O3 in the dehydration of 1,5-pentanediol (Table 2 in Ref. [13]): the trend is similar to Table 5 in this work. In addition, it is important that the calcination temperature significantly affects the crystal structure of REOs [5]. Table 3 shows the conversion and selectivity in the dehydration of 1,3-propanediol into 2-propen-1-ol at different temperatures. The conversion was monotonically increased from 6.2% to 73.1% with increasing reaction temperature. The selectivity to 2-propen1-ol showed the highest value (84.2%) at 375 ◦ C. At temperatures lower than 350 ◦ C, however, decomposition into methanol proceeded to a large extent. Table 4 shows changes in the conversion and selectivity in the dehydration of 1,3-butanediol into 3-buten-2-ol, 2-buten-1ol, and 3-buten-1-ol with reaction temperature. The conversion of 1,3-butanediol was drastically increased from 16.5 to 76.9% with increasing reaction temperature from 300 to 350 ◦ C, while there was little change in total selectivity to unsaturated alcohols including 3-buten-2-ol, 2-buten-1-ol, and 3-buten-1-ol. Table 5 shows the conversion and selectivity in the dehydration of 1,4-butanediol at different reaction temperatures. The conversion was increased with increasing reaction temperature below 350 ◦ C. The selectivity to 3-buten-1-ol was slightly decreased from 88.0 to 74.1% with increasing temperature, while those to 2-buten1-ol and tetrahydrofuran were increased.

20 4. Discussion

0

10

20

30

40

50

60

W/F / gcat. h mol-1 Fig. 2. Contact time dependence of (a) 1,5-pentanediol conversion and (b) selectivity into 4-penten-1ol over Yb2 O3 at 400 ◦ C. Calcination temperature: 800 ◦ C.

4.1. Dehydration of 1,5-pentanediol over Sc2 O3 , Yb2 O3 , and Lu2 O3 Specific surface area of Sc2 O3 , Yb2 O3 , and Lu2 O3 , shown as the number in parenthesis of Fig. 1, was decreased with increasing

44

F. Sato et al. / Applied Catalysis A: General 419–420 (2012) 41–48

Table 2 Dehydration of 1,5-pentanediol over Yb2 O3 calcined at 800 ◦ Ca . Reaction temperature (◦ C)

325 350 375 400 425 450 a b c

Selectivity (mol%)b

Conversion (%)

7.6 17.6 30.3 50.9 83.1 97.8

4P1OL

THP

49.1 57.1 67.0 74.0 68.9 33.3

1.1 1.5 5.1 8.3 5.1 5.3

DVL 10.2 11.2 5.3 2.8 1.5 0

13PDE

Othersc

0 0 0 0.6 2.0 8.9

39.6 30.2 22.6 18.5 22.5 52.5

Catalyst weight: 0.3 g. W/F = 18 gcat h mol−1 . Conversion and selectivity were averaged in the initial 5 h. 4P1OL: 4-penten-1-ol, THP: tetrahydropyran, DVL: ␦-valerolactone, and 13PDE: 1,3-pentadiene. Include 1-pentanol, cis- and trans-3-penten-1-ol, 3,4-dihydropyran, and pentanal.

Table 3 Dehydration of 1,3-propanediol over Yb2 O3 calcined at 800 ◦ Ca . Reaction temperature (◦ C)

300 325 350 375 a b c

Conversion (%)

9.0 56.2 81.4 86.8

Selectivity (mol%)b 2P1OL

MeOH

EtOH

1-PrOH

2-PrOH

Othersc

68.5 40.8 62.4 84.2

18.9 36.9 20.6 7.9

4.9 9.3 5.5 2.0

5.1 4.1 2.7 2.2

0.9 3.7 3.5 1.4

1.7 5.3 5.3 2.3

Catalyst weight: 0.3 g. W/F = 12 gcat h mol−1 . Conversion and selectivity were averaged in the initial 5 h. 2P1OL: 2-propen-1-ol, MeOH: methanol, EtOH: ethanol, 1-PrOH: 1-propanol, and 2-PrOH: 2-propanol. Include acetaldehyde and propanal.

Table 4 Dehydration of 1,3-butanediol over Yb2 O3 calcined at 800 ◦ Ca . Reaction temperature (◦ C)

300 325 350 375 a b c d

Conversion (%)

16.5 38.4 76.9 97.9

Selectivity (mol%)b 3B2OL

2B1OL

3B1OL

C4 ketonesc

Othersd

43.9 44.2 47.4 46.6

33.8 31.1 35.0 26.9

0.5 1.0 1.4 1.9

5.2 11.2 7.8 10.2

16.5 12.6 8.4 14.4

Catalyst weight: 0.3 g. W/F = 15 gcat h mol−1 . Conversion and selectivity were averaged in the initial 5 h. 3B2OL: 3-buten-2-ol, 2B1OL: 2-buten-1-ol, and 3B1OL: 3-buten-1-ol. C4 kentones include 2-butanone and 3-buten-2-one. Others include 1,3-butadiene, acetaldehyde, acetone, methanol, ethanol, 2-butanol, and 1-butanol.

calcination temperature. Irregardless of values of specific surface area, the catalysts calcined at 700 and 800 ◦ C were more active than those calcined at 500 ◦ C: maximum conversion was observed in the samples at high calcination temperature; Sc2 O3 calcined at 800 ◦ C, Yb2 O3 and Lu2 O3 calcined at 700 ◦ C. Fig. 3 illustrates changes in formation rate of 4-penten-1-ol per unit surface area, which is calculated from the value shown in Table 1 and Fig. 1. Over Sc2 O3 , Yb2 O3 , and Lu2 O3 , the formation rate per unit surface area is increased with decreasing specific surface area while there is an exception of Sc2 O3 calcined at 1000 ◦ C. The formation rate per unit surface area means the intrinsic catalytic activity of the REOs. This tendency indicates that active sites are increased with increasing calcination temperature of Sc2 O3 , Yb2 O3 , and Lu2 O3 .

In the resent works, it is suggested that dehydration of 1,3and 1,4-butanediols proceed over {1 1 1} or {2 2 2} facets of REOs [2,6,14–16]. Yoshida et al. reported similar surface-structure sensitivity was observed in the direct synthesis of dimethylcarbonate from methanol and carbon dioxide over CeO2 [17]. Stubenrauch et al. also reported that the ketonization of carboxylic acid over CeO2 was surface-structure sensitive reaction: the ketonization proceeds only over {1 1 1} facets of CeO2 [18]. We have reported {2 2 2} facets of cubic bixbyite phase were grown at high temperatures because {2 2 2} facets were most stable [11]. In the dehydration of 1,5-pentanediol over REOs, the reaction probably proceeds over {2 2 2} facets of REOs in a similar way to the dehydration of 1,3- and 1,4-butanediols. Because {2 2 2} facets is well grown at high temperatures, REOs calcined at high temperatures could be

Table 5 Dehydration of 1,4-butanediol over Yb2 O3 calcined at 800 ◦ Ca . Reaction temperature (◦ C)

300 325 350 375 a b c

Conversion (%)

19.0 41.7 74.5 76.3

Selectivity (mol%)b 3B1OL

2B1OL

THF

GBL

13BDE

Othersc

88.0 87.3 80.9 74.1

5.0 7.3 12.7 14.9

3.1 3.0 4.6 6.4

1.9 1.0 0.6 0.6

0 0 0.2 0.5

2.0 1.3 1.2 4.0

Catalyst weight: 0.3 g. W/F = 15 gcat h mol−1 . Conversion and selectivity were averaged in the initial 5 h. 3B1OL: 3-buten-1-ol, 2B1OL: 2-buten-1-ol, THF: tetrahydrofuran, GBL: ␥-butyrolactone, and 13BDE: 1,3-butadiene. Include 1-butanol.

F. Sato et al. / Applied Catalysis A: General 419–420 (2012) 41–48

1

Crystal phase Cubic bixbyite Cubic fluorite Cubic+Monoclinic Monoclinc Hexagonal

Lu Yb 1.0

Tb Eu Y Sm, Gd Nd La Pr

0

20

40

Sc

Ce 60

Formation rate of 4P1OL / mmol h-1 m-2

Formation rate of 4P1OL / mmol h-1 m-2

1.5

0.5

45

Lu 0.8

0.6

Surface area / m2 g-1 Fig. 3. Changes in the formation rate of 4-penten-1-ol (4P1OL) from 1,5-pentanediol at 400 ◦ C with specific surface area of the catalyst. Calcination temperature: 800 ◦ C (except Sc2 O3 , Yb2 O3 , and Lu2 O3 ); 500, 700, 800, and 1000 ◦ C (Sc2 O3 , Yb2 O3 , and Lu2 O3 ). (Closed circle) C-type cubic bixbyite, (double circle) Cubic fluorite, (closed diamond) coexistence of cubic bixbyite and B-type monoclinic, (open triangle) monoclinic, and (open square) A-type hexagonal.

high selective to 4-penten-1-ol. Catalytic activity and selectivity could depend on crystal facets, so that we will confirm this speculation with theoretical calculation in the near future. The formation rate of 4-penten-1-ol over Sc2 O3 , Yb2 O3 , and Lu2 O3 calcined at 800 ◦ C was higher than those of other REOs (Fig. 3). The reason for this tendency is discussed in the following Section 4.2. 4.2. Dehydration of 1,5-pentanediol over rare earth oxides The catalytic activity is affected by crystal phase of rare earth oxides (Fig. 3). Heavy REOs such as Lu2 O3 , Yb2 O3 , and Tm2 O3 which have cubic bixbyite phase [19,20] show high formation rate of 4penten-1-ol per unit surface area. In contrast, light REOs such as La2 O3 , Sm2 O3 , and Ho2 O3 which have hexagonal and monoclinic phase [19,20] show formation rate lower than heavy REOs. In the B-type monoclinic REOs, Dy2 O3 and Ho2 O3 are more selective than Sm2 O3 , Eu2 O3 , and Gd2 O3 . Even in the fluorite REOs, Tb4 O7 is more selective than CeO2 and Pr6 O11 . This could be explained by the intrinsic catalytic activity of REOs governed with ionic radius of rare earth cation not by only the crystal phase (Table 1). Fig. 4 summarizes the intrinsic catalytic activity of REOs with ionic radius of rare earth cation. Except Sc2 O3 , the formation rate of 4-penten-1-ol per unit surface area over REOs was increased with decreasing ionic radius of rare earth cation. These results indicate that the dehydration process of alkanediol is affected by crystal phase of catalyst and ionic radius of rare earth cation. These tendencies are similar to those of the dehydration of 1,3-butanediol and 1,4-butanediol [3,7]. In the dehydration of 1,3-butanediol, fluorite CeO2 is catalytically active [6]. However, in the dehydration of 1,5-pentanediol, oxides with bixbyite structure such as Sc2 O3 , Yb2 O3 , Lu2 O3 (Table 1), and In2 O3 [11] are active and selective. In addition, In2 O3 has a similar crystal phase to REOs and has catalytic activity higher than those of REOs (formation rate of 4penten-1-ol over In2 O3 = 2.93 mmol h−1 m−2 at 375 ◦ C, calculated from the data presented in Table 4 of Ref. [11]). Thus, the maximum formation rate of 4-penten-1-ol appears at 0.0800 nm, the position of 6-coordicate In3+ , while the rate of In2 O3 is too high to show in Fig. 4. In the dehydration of 1,3- and 1,4-butanediols, activities of In2 O3 and CeO2 are much higher than REOs except

Er

Tm

Sc

0.4

Ho

Tb Dy

Y

Eu Gd

0.2

0 0.07

80

Yb

0.08

Sm Nd Pr La Ce

0.09

0.1

0.11

Ionic radius / nm Fig. 4. Formation rate of 4-penten-1-ol at 400 ◦ C with different ionic radii of rare earth cations of the catalysts. Calcination temperature: 800 ◦ C. Symbols are the same as those in Fig. 3.

CeO2 [3,7,11]. Redox property of In2 O3 is reported by using temperature-programmed-reduction analysis [21,22]. A number of groups reported that CeO2 had redox property with oxygen defects generation and disappearance [23–28]. In the dehydration of 1,5pentanediol, redox property of CeO2 probably has small effect on the intrinsic catalytic activity, and it is different from the dehydration of 1,3-butanediol, in which possible reaction mechanism via redox cycle is proposed previously [3,29]. It is possible that redox property of catalyst affects the dehydration ability. Pr6 O11 and Tb4 O7 have the reducible nature [20,30,31]. Except CeO2 , Pr6 O11 and Tb4 O7 , other REOs have little redox property [20,31], and they have acid-base property [12]. In the dehydration of 1,5-pentanediol over REOs, the intrinsic catalytic activity of REOs seems to be affected by ionic radius of rare earth cation. In our previous work, the strength of basic sites on the REO surface was increased with increasing ionic radius of REO cation (Fig. 7 in Ref. [12]). However, the intrinsic catalytic activity of REOs is inversely proportional to the strength of basic sites. These results indicate that the dehydration of 1,5-pentanediol is not a simple base-catalyzed reaction. On the acidity, however, it is not explained by NH3 adsorption [12]. Therefore, it is speculated that the dehydration of 1,5-pentanediol over REOs proceeds via acidbase concerted reaction. The selectivity to 4-penten-1-ol is almost constant irrespective of contact time, W/F (Fig. 2). The excessive reaction, such as decomposition of 4-penten-1-ol, rarely proceeds over Yb2 O3 . In other words, the product 4-penten-1-ol is stable over the selective catalysts under the reaction conditions. Fig. 5 summarizes the conversion and selectivity to 4-penten-1-ol over REOs with ionic radius of rare earth cation. The conversion decreases with increasing ionic radius. The selectivity shows plateau at radius below ca. 0.09 nm, and it decreases with increasing ionic radius at radius above 0.09 nm. Ionic radius of In3+ (0.0800 nm [13]) is located between Sc and Lu. The selectivity over In2 O3 is ca. 70% [11], which is fitted on the plateau line in Fig. 5. The radius of rare earth cation is correlated with the lattice parameter of REO crystal phase. Fig. 5 also indicates that the selectivity is affected by the surface geometry concerned with not only crystal phase but also lattice parameter of the crystal phase. Lattice parameter of REOs with cubic bixbyite phase [20] depends on ionic radius of rare earth cation. We have also speculated a three-hold adsorption structure as an active center in the dehydration of diols [7,9]. Distance between the adsorption sites depending on the lattice parameter

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F. Sato et al. / Applied Catalysis A: General 419–420 (2012) 41–48

La3+ cations is calculated to be 0.394 nm, which is longer than the distance between other rare earth cations: Sc3+ , 0.348 nm; Lu3+ , 0.367 nm; Yb3+ , 0.369 nm; Tm3+ , 0.371 nm. REOs with hexagonal phase would have low intrinsic catalytic activity because the distance between rare earth cations is too long. In monoclinic Sm2 O3 [33], distance between Sm3+ cations is 0.363 nm, which is as long as that of Lu3+ cations in cubic bixbyite Lu2 O3 with high activity. Thus, catalytic activity of REOs with monoclinic phase could be affected on another factor rather than distance between cations. We speculate that the factor is the distance between metal cation and oxygen anion. However, surface structure of REOs with monoclinic phase is insufficiently analyzed. Then, it is too early to conclude why intrinsic catalytic activity of REOs with monoclinic phase was lower than that of REOs with cubic bixbyite phase.

Conversion ( ) and selectivity ( ) / %

100

Sc

Lu Tm Y Dy Gd Sm Nd La Yb Er Ho Tb Eu Ce Pr

80

60

40

20

0 0.07

4.3. Reaction scheme of dehydration of 1,5-pentanediol

0.08

0.09

0.1

0.11

Ionic radius / nm Fig. 5. Conversion and selectivity to 4-penten-1-ol with different ionic radii of rare earth cations of the catalysts. Calcination temperature: 800 ◦ C. The data are the same as those in Table 1.

could affect the catalytic nature of REOs. Actually, intrinsic catalytic activity of REOs with cubic bixbyite phase was increased with decreasing distance between the nearest neighboring rare earth cations. As described previously, REOs with hexagonal and monoclinic phases show lower activity than those with cubic bixbyite phase. Based on structure of hexagonal La2 O3 [32], a distance between

In the dehydration of 1,5-pentanediol to 4-penten-1-ol, we observed several side-reaction products such as tetrahydropyran, ı-valerolactone, and 1,3-pentadiene (Table 1). Fig. 6 illustrates a probable reaction route of the reaction of 1,5-pentanediol. 1,5-Pentanediol is mainly dehydrated to 4-penten-1-ol. A few 4penten-1-ol is further dehydrated to 1,4-pentadiene, which is also isomerized to 1,3-pentadiene because of conjugated stabilization. 1,5-Pentanediol is also dehydrated to tetrahydropyran without further reaction due to the stability of cyclic ether. Additionally, 1,5-pentanediol is dehydrogenated to unstable 5-hydroxypentanal, which can be immediately cyclized to tetrahydropyran-2-ol followed by the dehydrogenation to produce ı-valerolactone. In the dehydration of 1,4-butanediol (Table 5), cyclic ether and lactone

Fig. 6. Several side reactions in the dehydration of 1,5-pentanediol.

F. Sato et al. / Applied Catalysis A: General 419–420 (2012) 41–48

Formation rate / mmol h-1 m-2

2.5

(a)

2.0

(b) (c)

1.5

(d) 1.0

0.5

(e) 0 300

350

400

450

Reaction temperature / °C Fig. 7. Changes in the dehydration ability of Yb2 O3 calcined at 800 ◦ C in the dehydration of alkanediols into corresponding unsaturated alcohols with reaction temperature. (a) 1,3-propanediol, formation rate of 2-propen-1-ol; (b) 1,3-butanediol, total formation rate of 3-buten-2-ol and 2-buten-1-ol; (c) 1,4-butanediol, total formation rate of 3-buten-1-ol and 2-buten-1-ol; (d) 1,5-pentanediol, formation rate of 4penten-1-ol over Yb2 O3 in this work; (e) 1,6-hexanediol over Sc2 O3 , formation rate of 5-hexen-1-ol which is calculated from the data of Sc2 O3 calcined at 800 ◦ C in Ref. [9].

are generated. However, due to instability of three- and fourmembered ring, cycloetherification and cycloesterification did not proceed in the dehydration of 1,3-propanediol (Table 3) and 1,3butanediol (Table 4). 4.4. Reactivity of alkanediols into corresponding unsaturated alcohols over Yb2 O3 As shown in Tables 2–4, Yb2 O3 catalyzes the selective formation of unsaturated alcohols from alkanediols. In the dehydration of 1,5pentanediol, 1,3-propanediol, 1,3-butanediol, and 1,4-butanediol, the conversion of alkanediols was generally increasing with increasing reaction temperature irrespective of the kind of reactant. Fig. 7 illustrates reactivity of the alkanediols dehydrated into the corresponding unsaturated alcohols over Yb2 O3 calcined at 800 ◦ C at different reaction temperatures. The formation rate of unsaturated alcohols in these reactions was increased with increasing reaction temperature. However, the temperatures where the conversion was considerably increased were different: the reactivity of alkanediol over Yb2 O3 is in the order, 1,5-pentanediol  1,3propanediol < 1,3-butanediol < 1,4-butanediol at <350 ◦ C. At 375 ◦ C, it is difficult to discuss reactivity of alkanediol expect 1,5pentanediol due to decomposition of generated unsaturated alcohols. It is noticed that CeO2 showed low catalytic activity in the dehydration of 1,5-pentanediol (Figs. 3 and 4) regardless of the ability of redox, whereas it showed the highest activity in the dehydration of 1,3-butanediol among the REOs [3], as discussed in the above section. We have also investigated the dehydration of 1,6-hexanediol into 5-hexen-1-ol [9]: Sc2 O3 calcined at 800 ◦ C is preferable in the reaction. The formation rate of 5-hexen-1-ol is calculated from the data in Fig. 2 of Ref. [9], and is plotted as a reference in Fig. 7. The formation rate of 5-hexen-1-ol at 400 ◦ C is at most 0.066 mmol h−1 m−2 , which is much smaller than that of 4-penten-1-ol. The formation rate of 5-hexen-1-ol over Yb2 O3 is about a half of Sc2 O3 [9]. It is reasonable that the reactivity of each alkanediol is different because the length of

47

carbon chains and the positions of hydroxyl groups are different. Thus, the reactivity of alkanediols into corresponding unsaturated alcohols over Yb2 O3 calcined at 800 ◦ C was the following order: 1,6-hexanediol  1,5-pentanediol  1,3-propanediol < 1,3butanediol < 1,4-butanediol at <350 ◦ C (Fig. 7). In the previous work, we speculated reaction mechanism and intermediate adsorption model that one molecular of alkanediol adsorbed on three sites of catalyst, where two acidic sites and one basic site of bixbyite REO surface [7,9]. It is highly probable that acidic sites are rare earth cations and basic sites are oxygen anions. Thus, it is necessary that the conformation of alkanediol is changed to stabilize adsorption energy, and structure distortion of alkanediol is generated. Furthermore, carbon chain length and a length between hydroxyl groups are different among alkanediols. Totally, the strain magnitude of adsorption structure is affected by carbon chain length and length between hydroxyl groups of alkanediol. Considering the molecular model, it is estimated that the strain magnitude of 1,5-pentanediol adsorption structure is larger than those of other diols when the alkanediols are adsorbed on REOs because carbon chain is too long in 1,5-pentanediol. Thus, we speculate that adsorption energy of 1,5-pentanediol on REOs {2 2 2} is lower than those of 1,3-propanediol, 1,3-butanediol, and 1,4butanediol. There still remain questions, so that we need further study to confirm the above-mentioned speculation by theoretical calculation. 5. Conclusions Vapor-phase dehydration of 1,5-pentanediol was investigated over REOs at 325–450 ◦ C. The conversion of 1,5-pentanediol over REOs calcined at 700 and 800 ◦ C was higher than those calcined at 500 and 1000 ◦ C. Sc2 O3 , Yb2 O3 , and Lu2 O3 with cubic bixbyite structure showed selectivity to 4-penten-1-ol higher than 74 mol%, while REOs with hexagonal structure showed lower than 30 mol% and those with monoclinic structure did lower than 50 mol%. Especially, Yb2 O3 and Lu2 O3 calcined at 1000 ◦ C showed high formation rate of 4-penten-1-ol per unit surface area over 1 mmol h−1 m−2 at 400 ◦ C. As increasing weight of Yb2 O3 catalyst used, the conversion of 1,5-pentanediol was increased up to 74.4% with retaining the selectivity to 4-penten-1-ol close to 70 mol%. Reactivity of alkanediols into the corresponding unsaturated alcohols over Yb2 O3 calcined at 800 ◦ C was the following order: 1,4-butanediol > 1,3-butanediol > 1,3-propanediol  1,5pentanediol  1,6-hexanediol at temperatures below 350 ◦ C. The results suggest that the dehydration of alkanediol is affected by crystal structure of REOs, ionic radius of rare earth cations, and carbon chain length of alkanediols. References [1] S. Sato, R. Takahashi, T. Sodesawa, N. Honda, H. Shimizu, Catal. Commun. 4 (2003) 77–81. [2] A. Igarashi, N. Ichikawa, S. Sato, R. Takahashi, T. Sodesawa, Appl. Catal. A: Gen. 300 (2006) 50–57. [3] H. Gotoh, Y. Yamada, S. Sato, Appl. Catal. A: Gen. 377 (2010) 92–98. [4] S. Sato, R. Takahashi, T. Sodesawa, N. Yamamoto, Catal. Commun. 5 (2004) 397–400. [5] A. Igarashi, S. Sato, R. Takahashi, T. Sodesawa, M. Kobune, Catal. Commun. 8 (2007) 807–810. [6] M. Kobune, S. Sato, R. Takahashi, J. Mol. Catal. A: Chem. 279 (2008) 10–19. [7] S. Sato, R. Takahashi, M. Kobune, H. Inoue, Y. Izawa, H. Ohno, K. Takahashi, Appl. Catal. A: Gen. 356 (2009) 64–71. [8] S. Sato, R. Takahashi, N. Yamamoto, E. Kaneko, H. Inoue, Appl. Catal. A: Gen. 334 (2008) 84–91. [9] K. Abe, Y. Ohishi, T. Okada, Y. Yamada, S. Sato, Catal. Today 164 (2011) 419–424. [10] A.J. Lundeen, R.V. Hoozer, J. Org. Chem. 32 (1967) 3386–3389. [11] M. Segawa, S. Sato, M. Kobune, T. Sodesawa, T. Kojima, S. Nishiyama, N. Ishizawa, J. Mol. Catal. A: Chem. 310 (2009) 166–173. [12] S. Sato, R. Takahashi, M. Kobune, H. Gotoh, Appl. Catal. A: Gen. 356 (2009) 57–63. [13] R.D. Shanon, Acta Cryst. A 32 (1976) 751–767.

48

F. Sato et al. / Applied Catalysis A: General 419–420 (2012) 41–48

[14] N. Ichikawa, S. Sato, R. Takahashi, T. Sodesawa, J. Mol. Catal. A: Chem. 231 (2005) 181–189. [15] N. Ichikawa, S. Sato, R. Takahashi, T. Sodesawa, H. Fujita, T. Atoguchi, A. Shiga, J. Catal. 239 (2006) 13–22. [16] Y. He, Q. Li, Y. Wang, Y. Zhao, Chin. J. Catal. 31 (2010) 619–622. [17] Y. Yoshida, Y. Arai, S. Kado, K. Kunimori, K. Tomishige, Catal. Today 115 (2006) 95–101. [18] J. Stubenrauch, E. Brosha, J.M. Vohs, Catal. Today 28 (1996) 431–441. [19] R. McPherson, J. Mater. Sci. 18 (1983) 1341–1345. [20] G. Adachi, N. Imanaka, Chem. Rev. 98 (1998) 1479–1514. [21] J.A. Perdigon-Melon, A. Gervasini, A. Auroux, J. Catal. 234 (2005) 421–430. [22] R. Takahashi, I. Yamada, A. Iwata, N. Kurahashi, S. Yoshida, S. Sato, Appl. Catal. A: Gen. 383 (2010) 134–140. [23] A. Trovarelli, Catalysis by Ceria and Related Materials, Imperial College Press, London, 2002.

[24] [25] [26] [27] [28] [29] [30] [31] [32] [33]

H. Nörenberg, G.A.D. Briggs, Surf. Sci. (1999) L352–L355. F. Giordano, A. Trovarelli, C. Leitenburg, M. Giona, J. Catal. 193 (2000) 273–282. K. Fukui, Y. Namai, Y. Iwasawa, Appl. Surf. Sci. 188 (2002) 252–256. Y. Namai, K. Fukui, Y. Iwasawa, Catal. Today 85 (2003) 79–91. F. Esch, S. Fabris, L. Zhou, T. Montini, C. Africh, P. Fornasiero, G. Comelli, R. Rosei, Science 305 (2005) 752–755. S. Sato, R. Takahashi, T. Sodesawa, N. Honda, J. Mol. Catal. A: Chem. 221 (2004) 177–183. S. Bernal, G. Blanco, J.J. Calvino, J.A. Perez Omil, J.M. Pintado, J. Alloys Compd. 408–412 (2006) 496–502. K. Sato, K. Nagaoka, H. Nishiguchi, Y. Takita, J. Jpn. Petrol. Inst. 52 (2009) 295–296. P. Aldebert, J.P. Traverse, Mater. Res. Bull. 14 (1979) 303–323. T. Schleid, G. Meyer, J. Less Common Metals 149 (1989) 73–80.