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Direct hydrogenation of aliphatic carboxylic acids to corresponding aldehydes with cr2o3 catalyst
Science and Technology in Catalysis 1998 Copyright © 1999 by Kodansha Ltd.
76 Direct Hydrogenation of Aliphatic Carboxylic Acids to Corresponding Aldehydes with Cr203 Catalyst Naoko YAMAGATA, Naoko FUJITA, Toshiharu YOKOYAMA and Takao MAKI Research Center, Mitsubishi Chemical Corporation, 1000 Kamoshida-cho, Aoba-ku, Yokohama 227-8502, Japan
Abstract A new process for the production of aliphatic aldehydes was developed and conunercialized. Using highly pure Cr203 catalysts, we succeeded in hydrogenating aliphatic carboxylic acids directly to corresponding aldehydes in excellent yields. Noteworthy was that acids with a C=C double bond (e.g. 10-undecenoic acid [10-UDEA]) were selectively hydrogenated at the C=0 group without hydrogenation or migration of their C=C bond to give 10-undecenal [10-UDEH]. Examination of the surface of Cr203 indicated its neutral property, which was believed to be the reason for the high selectivity of this catalyst. 1. INTRODUCTION Although the direct hydrogenation of carboxylic acids has been regarded as a desirable way to produce aldehydes, it was not until recendy that a commercial process was developed. The first and only example so far has been our process for the production of aromatic aldehydes using Cr doped Z1O2 ^^ ^ catalyst. This catalyst, however, is not suitable when applied to the hydrogenation of aliphatic carboxylic acids because of its low selectivity. As we started our research to find a catalyst for the aliphatic aldehyde production, we chose 10-UDEA, an unsaturated aliphatic acid, as the target of hydrogenation. A compound with two a -hydrogens is liable to undergo ketonization, and its C=C double bond easily migrates or is hydrogenated, as was observed in the case when Cr/Zr02
Selective hydrogenation 10-UDEA
I
I
V^^^^=c isomerization ^
^CHO ,
^^^ ^""^^^^^^^"^''^^
^
10-UDEH 9-UDEH a-UDEH Undecanal
C = C hydrogenation
• "'"°"'"^'°"
•
V,
Scheme 1 Hydrogenation of 10-Undecenoic Acid 441
K.ton,
442 N. Yamagata et al. or other oxides were used as catalysts (Scheme 1). In this report the catalytic performances and characterization of Cr203 for the hydrogenation of 10-UDEA and other acids are discussed. 2. Experimental Section ^^2^3 ^ ^ prepared by the calcination of chromium hydroxide at 700 **C in an air stream. Cr/Zr02 (Cr/Zr=5/100 atomic ratio) and Zr02 were prepared by the method previously described [2]. Alumina was commercially obtained. Hydrogenation of carboxylic acids was carried out under an atmospheric pressure by a conventional flow system. The reaction products were analyzed by GLC. The IR spectra of the absorbed species on oxides were recorded by using a Fourier transform IR spectrometer (Nicolet, System 800). The samples for FT-IR analysis were prepared in the same method as described previously [2]. TPD data were obtained using ammonia and carbon dioxide as probe gases. A sample was first treated at 600^*0 in He flow, then pre-hydrogenated in a mixture of 5% hydrogen in Ar. Probe gas was fed pulse-wise at 100X. After the probe gas was fully absorbed by the sample, temperature was raised at a rate of lOT/min. until 600'^C. The desorbed gas was monitored with a TCD detector. 3. Results and discussion 3.1. Hydrogenation of 10-undecenoic acid over various oxide catalysts The hydrogenation of 10-UDEA was performed over various oxides ( Table 1 ). y -AI2O3 showed poor activity. When Zr02 was used as a catalyst, ketone was obtained as a major product. The Cr/Zr02 catalyst suitable for aromatic aldehyde production showed better selectivity towards UDEH formation, although migration of C=C double bond occurred. 9-UDEH and 8-UDEH were observed as migration products. The ratio of 10-UDEH among these isomers is shown in the table as "10-UDEH/Total-UDEH". On highly pure Cr203, 10-UDEA reacted to produce 10-UDEH in very high selectivity. The formation of ketone or migration isomers was very low. Several commercially available Cr203 were tested, but not all of them showed good selectivity. It was found that impurities in Cr203, especially alkaline metals and alkaline earth metals, had a bad influence on the catalytic performance. Even a small amount of impurities in Cr203 caused a
Table 1 Hydrogenation of lO-UDEA over Various Metal Oxide Catalysts (Reaction conditions: H2 GHSV=1250 h'^' 10-UDEA/H2-2/98 TOI-%, 1 atm.) Catalyst
Temperature
Cr203
rc) 370
Conversion ofacid(%) 74
CrjOj'
370
32
Selectivity (%) Total-UDEH Ketone 98 1 43
55
10-UDEH /Total-UDEH 0.96 0.87
0.38 16 330 87 83 Cr/Zr02 e 79 330 97 10 Z1O2 c 96 330 8 r.Al203 3 a) high purity Cr203, b) Cr203 including 1.4% of alkaline and alkaline earth metals as Impurities. c) not analyzed.
443
1
•
•
77" (b) (c) (d) (•)
3 O
1
1 ZK), O/ZrO, • 0,0, C r , 0 , (alkali rfopad)
-e o O O O 200
300
400
100
300
40)
CO, - T P D Patterns
NH,-TPD Patterns Figure 1
200
Temperature ( C )
Temperature CC)
Acid and Base Properties of Metal OxJde Surfaces
drastic decrease in activity and selectivity [1]. The decrease in selectivity was mainly due to ketone formation. 3.2. NH3 and CO2 TPD on oxides The acid-base properties of the catalyst surfaces were characterized by NH3 and CO2TPD (Figure 1). Compared to other oxides, pure Cr203 had less amount of acidic sites and almost no basic sites. When alkali was doped on Cr203, the acidic sites vanished and basic sites appeared. 3.3. FT-IR spectra of adsorbed species on oxides The FT-IR spectra of the adsorbed species after the hydrogenation of 10-UDEA showed the existence of bidentate carboxylate species adsorbed on the metal oxide surfaces (Table 2, Figure 2). In our previous paper[2], we assumed the carboxylate species to be the intermediate in the hydrogenation of aromatic carboxylic acids on zirconia. Also on Cr203, carboxylate was regarded as an intermediate. Cr203 gave the lowest carboxylate stretching frequency among the oxides. The IR peak for ketone was observed on the surface of some catalysts which showed high ketone selectivity. 3.4. Hydrogenation of various carboxylic acids Cr203 catalyst exhibited high selectivity in the hydrogenation of other aliphatic carboxylic acids as well (Table 3). Saturated carboxylic acids showed better selectivities than 10-UDEA. 9-Octadecenoic acid was hydrogenated to 9octadecenal in an excellent yield.
Table 2 The FT-IR Spectroscopy of Adsorbed 10-UDEA on Oxides after Hydrogenation Stretching Flrequency(ciif *) Carboxylate Ketone Vas Vcs peak
.
CrjOj Cr203alkall Cr/Zr02 ZrOj y .AI2O3
'
1800
1530 1560 1540 1540 1570
+++ + ++
-
1700
1600
1500
1420 1440 1455 1455 1460
1400 1300 1200
WAVENUMBER Figure 2
FT-IR Spectra of the Absorbed Species on Metal Oxide Surfaces
Rsactant «nd Oxidat »n ai fonowr. (a) UDEA-Cr/ZrO,(b>U0EA-Cr,0, (o) LauHo Add - Cr,0» (d) UDEA - Cr,0,(anuili doped) (.) UDEA - ZrO, (0 UDEA - r -AI.O,
444 N. Yamagata et al.
Table 3 Hydrogenation of Various Cari>oxylic Acids over Cr^Oj Catalyst ^^ Cart)oxylic acids
Temp.
CC)
Decanoic acid 350 Dodecanoic acid 350 Octadecanoic acid 350 9-Octadecenoic acid 350 Cyclohexanecariioyylic acid 370 a)H2-GHSV=1250hr-l, acid/H2-2/98%.
Conversion (%) 91 97 98 96 92
Selectivity to aldehydes (%) 97 96 93 97 98
3.5. Discussion Results from TPD indicate that the surface of highly pure Cr203 has very small amount of acidic sites and no basic sites. Basic sites on the surface seem to mediate ketonization, which is suggested by the TPD data of aklaline-doped Cr203. The carboxylate on the alkaline-doped Cr203 seems to be adsorbed near the alkaline metal, since the positions of its carboxylate stretch modes are similar to those found by infrared spectrum for sodium 10-undecenoate. The alkaline or alkaline earth metals are thought to deactivate the acidic sites and cause new basic sites to appear, which become active sites for ketone formation. The interpretation of the FT-IR data has to wait for further examination, but since the carboxylate ion paired to sodium cation shows higher wavenumber, and the carboxylate on y AI2O3, generally regarded to be an acidic oxide, also gave the highest frequency among the oxides tested, it seems that the lowest shift of Cr203 is due to the smallness of charge or weakness of its Lewis acidic sites. Other factors like ionicity of carboxylate-metal bonds may be also relevant. The mechanism for the migration of C=C double bond is not yet clear. The interaction of C=C double bond with the surface of the oxide seems to be suppressed on Cr203 by some reason, probably because of the character of its Lewis acidic sites. The unique surface property of pure Cr203 can easily be destroyed by impurities, and this is why the commercially available Cr203 generally shows poor selectivity. The uniformity of the acid sites on the surface of highly pure Cr203 seems to be an important factor. Moreover our recent research shows that the uniformity of the crystal structure of Cr203 is also important for the catalytic performances. This will be discussed elsewhere. 4. Conclusion Highly pure Cr203 was found to give an excellent selectivity in hydrogenating unsaturated aliphatic carboxylic acids without ketonization or C=C double bond migration. The neutrality of the surface of Cr203 plays a critical role in its high selectivity. This new process, compared to the conventional methods, gives not only a higher yield and selectivity, but is environmentally friendly because it produces no waste. The process was further refined and has been successfully commercialized since last year for the production of aldehydes such as 10-UDEH and dodecanal. References [1] T. Yokoyama, N. Fujita andT. Maki, Stud. Surf. Sci. Catal., 92, (1994), 33L [2] T. Yokoyama, T. Setoyama, N. Fujita, T. Maki and K. Fujii, Appl. Catal., 88 (1992), 149.
76 Direct Hydrogenation of Aliphatic Carboxylic Acids to Corresponding Aldehydes with Cr203 Catalyst Naoko YAMAGATA, Naoko FUJITA, Toshiharu YOKOYAMA and Takao MAKI Research Center, Mitsubishi Chemical Corporation, 1000 Kamoshida-cho, Aoba-ku, Yokohama 227-8502, Japan
Abstract A new process for the production of aliphatic aldehydes was developed and conunercialized. Using highly pure Cr203 catalysts, we succeeded in hydrogenating aliphatic carboxylic acids directly to corresponding aldehydes in excellent yields. Noteworthy was that acids with a C=C double bond (e.g. 10-undecenoic acid [10-UDEA]) were selectively hydrogenated at the C=0 group without hydrogenation or migration of their C=C bond to give 10-undecenal [10-UDEH]. Examination of the surface of Cr203 indicated its neutral property, which was believed to be the reason for the high selectivity of this catalyst. 1. INTRODUCTION Although the direct hydrogenation of carboxylic acids has been regarded as a desirable way to produce aldehydes, it was not until recendy that a commercial process was developed. The first and only example so far has been our process for the production of aromatic aldehydes using Cr doped Z1O2 ^^ ^ catalyst. This catalyst, however, is not suitable when applied to the hydrogenation of aliphatic carboxylic acids because of its low selectivity. As we started our research to find a catalyst for the aliphatic aldehyde production, we chose 10-UDEA, an unsaturated aliphatic acid, as the target of hydrogenation. A compound with two a -hydrogens is liable to undergo ketonization, and its C=C double bond easily migrates or is hydrogenated, as was observed in the case when Cr/Zr02
Selective hydrogenation 10-UDEA
I
I
V^^^^=c isomerization ^
^CHO ,
^^^ ^""^^^^^^^"^''^^
^
10-UDEH 9-UDEH a-UDEH Undecanal
C = C hydrogenation
• "'"°"'"^'°"
•
V,
Scheme 1 Hydrogenation of 10-Undecenoic Acid 441
K.ton,
442 N. Yamagata et al. or other oxides were used as catalysts (Scheme 1). In this report the catalytic performances and characterization of Cr203 for the hydrogenation of 10-UDEA and other acids are discussed. 2. Experimental Section ^^2^3 ^ ^ prepared by the calcination of chromium hydroxide at 700 **C in an air stream. Cr/Zr02 (Cr/Zr=5/100 atomic ratio) and Zr02 were prepared by the method previously described [2]. Alumina was commercially obtained. Hydrogenation of carboxylic acids was carried out under an atmospheric pressure by a conventional flow system. The reaction products were analyzed by GLC. The IR spectra of the absorbed species on oxides were recorded by using a Fourier transform IR spectrometer (Nicolet, System 800). The samples for FT-IR analysis were prepared in the same method as described previously [2]. TPD data were obtained using ammonia and carbon dioxide as probe gases. A sample was first treated at 600^*0 in He flow, then pre-hydrogenated in a mixture of 5% hydrogen in Ar. Probe gas was fed pulse-wise at 100X. After the probe gas was fully absorbed by the sample, temperature was raised at a rate of lOT/min. until 600'^C. The desorbed gas was monitored with a TCD detector. 3. Results and discussion 3.1. Hydrogenation of 10-undecenoic acid over various oxide catalysts The hydrogenation of 10-UDEA was performed over various oxides ( Table 1 ). y -AI2O3 showed poor activity. When Zr02 was used as a catalyst, ketone was obtained as a major product. The Cr/Zr02 catalyst suitable for aromatic aldehyde production showed better selectivity towards UDEH formation, although migration of C=C double bond occurred. 9-UDEH and 8-UDEH were observed as migration products. The ratio of 10-UDEH among these isomers is shown in the table as "10-UDEH/Total-UDEH". On highly pure Cr203, 10-UDEA reacted to produce 10-UDEH in very high selectivity. The formation of ketone or migration isomers was very low. Several commercially available Cr203 were tested, but not all of them showed good selectivity. It was found that impurities in Cr203, especially alkaline metals and alkaline earth metals, had a bad influence on the catalytic performance. Even a small amount of impurities in Cr203 caused a
Table 1 Hydrogenation of lO-UDEA over Various Metal Oxide Catalysts (Reaction conditions: H2 GHSV=1250 h'^' 10-UDEA/H2-2/98 TOI-%, 1 atm.) Catalyst
Temperature
Cr203
rc) 370
Conversion ofacid(%) 74
CrjOj'
370
32
Selectivity (%) Total-UDEH Ketone 98 1 43
55
10-UDEH /Total-UDEH 0.96 0.87
0.38 16 330 87 83 Cr/Zr02 e 79 330 97 10 Z1O2 c 96 330 8 r.Al203 3 a) high purity Cr203, b) Cr203 including 1.4% of alkaline and alkaline earth metals as Impurities. c) not analyzed.
443
1
•
•
77" (b) (c) (d) (•)
3 O
1
1 ZK), O/ZrO, • 0,0, C r , 0 , (alkali rfopad)
-e o O O O 200
300
400
100
300
40)
CO, - T P D Patterns
NH,-TPD Patterns Figure 1
200
Temperature ( C )
Temperature CC)
Acid and Base Properties of Metal OxJde Surfaces
drastic decrease in activity and selectivity [1]. The decrease in selectivity was mainly due to ketone formation. 3.2. NH3 and CO2 TPD on oxides The acid-base properties of the catalyst surfaces were characterized by NH3 and CO2TPD (Figure 1). Compared to other oxides, pure Cr203 had less amount of acidic sites and almost no basic sites. When alkali was doped on Cr203, the acidic sites vanished and basic sites appeared. 3.3. FT-IR spectra of adsorbed species on oxides The FT-IR spectra of the adsorbed species after the hydrogenation of 10-UDEA showed the existence of bidentate carboxylate species adsorbed on the metal oxide surfaces (Table 2, Figure 2). In our previous paper[2], we assumed the carboxylate species to be the intermediate in the hydrogenation of aromatic carboxylic acids on zirconia. Also on Cr203, carboxylate was regarded as an intermediate. Cr203 gave the lowest carboxylate stretching frequency among the oxides. The IR peak for ketone was observed on the surface of some catalysts which showed high ketone selectivity. 3.4. Hydrogenation of various carboxylic acids Cr203 catalyst exhibited high selectivity in the hydrogenation of other aliphatic carboxylic acids as well (Table 3). Saturated carboxylic acids showed better selectivities than 10-UDEA. 9-Octadecenoic acid was hydrogenated to 9octadecenal in an excellent yield.
Table 2 The FT-IR Spectroscopy of Adsorbed 10-UDEA on Oxides after Hydrogenation Stretching Flrequency(ciif *) Carboxylate Ketone Vas Vcs peak
.
CrjOj Cr203alkall Cr/Zr02 ZrOj y .AI2O3
'
1800
1530 1560 1540 1540 1570
+++ + ++
-
1700
1600
1500
1420 1440 1455 1455 1460
1400 1300 1200
WAVENUMBER Figure 2
FT-IR Spectra of the Absorbed Species on Metal Oxide Surfaces
Rsactant «nd Oxidat »n ai fonowr. (a) UDEA-Cr/ZrO,(b>U0EA-Cr,0, (o) LauHo Add - Cr,0» (d) UDEA - Cr,0,(anuili doped) (.) UDEA - ZrO, (0 UDEA - r -AI.O,
444 N. Yamagata et al.
Table 3 Hydrogenation of Various Cari>oxylic Acids over Cr^Oj Catalyst ^^ Cart)oxylic acids
Temp.
CC)
Decanoic acid 350 Dodecanoic acid 350 Octadecanoic acid 350 9-Octadecenoic acid 350 Cyclohexanecariioyylic acid 370 a)H2-GHSV=1250hr-l, acid/H2-2/98%.
Conversion (%) 91 97 98 96 92
Selectivity to aldehydes (%) 97 96 93 97 98
3.5. Discussion Results from TPD indicate that the surface of highly pure Cr203 has very small amount of acidic sites and no basic sites. Basic sites on the surface seem to mediate ketonization, which is suggested by the TPD data of aklaline-doped Cr203. The carboxylate on the alkaline-doped Cr203 seems to be adsorbed near the alkaline metal, since the positions of its carboxylate stretch modes are similar to those found by infrared spectrum for sodium 10-undecenoate. The alkaline or alkaline earth metals are thought to deactivate the acidic sites and cause new basic sites to appear, which become active sites for ketone formation. The interpretation of the FT-IR data has to wait for further examination, but since the carboxylate ion paired to sodium cation shows higher wavenumber, and the carboxylate on y AI2O3, generally regarded to be an acidic oxide, also gave the highest frequency among the oxides tested, it seems that the lowest shift of Cr203 is due to the smallness of charge or weakness of its Lewis acidic sites. Other factors like ionicity of carboxylate-metal bonds may be also relevant. The mechanism for the migration of C=C double bond is not yet clear. The interaction of C=C double bond with the surface of the oxide seems to be suppressed on Cr203 by some reason, probably because of the character of its Lewis acidic sites. The unique surface property of pure Cr203 can easily be destroyed by impurities, and this is why the commercially available Cr203 generally shows poor selectivity. The uniformity of the acid sites on the surface of highly pure Cr203 seems to be an important factor. Moreover our recent research shows that the uniformity of the crystal structure of Cr203 is also important for the catalytic performances. This will be discussed elsewhere. 4. Conclusion Highly pure Cr203 was found to give an excellent selectivity in hydrogenating unsaturated aliphatic carboxylic acids without ketonization or C=C double bond migration. The neutrality of the surface of Cr203 plays a critical role in its high selectivity. This new process, compared to the conventional methods, gives not only a higher yield and selectivity, but is environmentally friendly because it produces no waste. The process was further refined and has been successfully commercialized since last year for the production of aldehydes such as 10-UDEH and dodecanal. References [1] T. Yokoyama, N. Fujita andT. Maki, Stud. Surf. Sci. Catal., 92, (1994), 33L [2] T. Yokoyama, T. Setoyama, N. Fujita, T. Maki and K. Fujii, Appl. Catal., 88 (1992), 149.