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Vapor-phase nitration of benzene over solid acid catalysts (1): Nitration with nitric oxide (NO2)
Applied Catalysis A: General 174 (1998) 77±81
Vapor-phase nitration of benzene over solid acid catalysts (1): Nitration with nitric oxide (NO2) H. Sato*, K. Hirose Technology and Research Management Of®ce, Sumitomo Chemical Co., Ltd. 27-1, Shinkawa 2-chome, Chuo-ku, Tokyo 104-8260, Japan Received 6 October 1997; received in revised form 24 April 1998; accepted 6 May 1998
Abstract Vapor-phase nitration of benzene over acidic catalysts is expected to be a clean process with no sulfuric acid waste. We investigated this process over acidic catalysts utilizing nitric oxide (NO2) as a nitrating agent, and found that several mixed metal oxides, such as silica±alumina, zinc-oxide±titania, and tungsten-oxides±molybdenum-oxide, exhibited a fairly good activity. Among them, WO3±MoO3 is the most active, but this catalyst alone deviated from the linear relationship between the activity and acidity. In order to explain this discrepancy several factors, such as acid amount, acid strength, and BET surface area, are examined in detail. # 1998 Elsevier Science B.V. All rights reserved.
1. Introduction Vapor-phase nitration of benzene to nitrobenzene over solid acid catalysts is expected to be a clean process without sulfuric acid waste, in contrast to the conventional liquid process which uses a mixed acid (concentrated nitric and sulfuric acids) as a nitrating agent and is accompanied with a large amount of diluted sulfuric acid waste (Eq. (1)). Many efforts devoted to developing a vapor phase process have been unsuccessful, because either the activity or life of catalysts is not satisfactory [1±3]. (1) Previously, we have reported in a piece of patent description [4] that mixed metal oxides, comprising WO3 and MO3, exhibited a fairly high and stable activity. *Corresponding author. Fax: +81355435909.
In this paper, we will report the results of our detailed study on the catalytic performance of various solid acid catalysts for benzene nitration with nitric oxide (NO2) as a nitration agent (Eq. (2)). (2) 2. Experimental Mixed metal oxides were prepared in three ways: a co-precipitation, a co-grinding, or an impregnation method. In particular, a WO3±MoO3 system was prepared by mixing and grinding the two oxides in a wet state. The mixed oxides were then calcined in air at 5008C for 3 h. Vapor-phase nitration was conducted in a ¯ow reactor made of quartz with a ®xed-catalyst bed at atmospheric pressure. A nitric oxide vapor was introduced into the ¯ow reactor from a container with a nitrogen carrier gas. The nitration products were
0926-860X/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S0926-860X(98)00161-6
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H. Sato, K. Hirose / Applied Catalysis A: General 174 (1998) 77±81
cold-trapped, analyzed, and identi®ed by gas chromatography. 3. Results and discussion 3.1. Investigation of active catalysts for nitration The results of benzene nitration with nitric oxide over various solid acid catalysts are summarized in Table 1. Among many catalysts examined, the mixed oxide catalyst comprising WO3(75 mol %)±MoO3(25 mol %) afforded a fairy good yield of nitrobenzene with almost no decay of activity for 5 h. The sulfuric acid catalyst supported on silica±alumina also exhibited a good yield with a slight decay of activity. Other solid acid catalysts, such as TiO2(90 mol %)± MoO3(10 mol %), silica±alumina, Na®on-H, silicotungstoic acid, 25 wt.%H3PO4/silica±alumina, 30 wt.%H2SO4/silica±alumina, 20 wt.%NiSO4/silicagel, 18.5 wt.%Al2(SO4)3/silicagel, 10 wt.%(WO3(80 and mol %)±MoO3(20 mol %))/silica±alumina, 10 wt.%WO3/silicagel exhibited either low yields or rapid decay of activity.
Fig. 1. Relation between the rate constant (k) of nitratin and the acid amount of the catalyst. Reaction conditions: NO2/benzene/ N20.2/1.0/0.7 (molar ratios), Temperature1508C, SV220 hÿ1. Catalysts (molar ratio): (a) WO 3 (95%)±MoO 3 (5%); (b) WO3(90%)±TiO2(10%); (c) WO3(10%)±TiO2(90%); (d) ZnO(7%)±TiO 2 (93%); (e) SiO 2 (92%)±Al 2 O 3 (8%); (f) SiO2(81%)±Al2O3(19%).
determined by the amine titration method by utilizing Hammett indicators. The results are shown in terms of the ®rst-order rate constant (k) for nitration (Figs. 1 and 2). These results show that the nitration activity was almost proportional to both, the acid amount (Fig. 1) and acid strength (Fig. 2) of the catalysts. This tendency is in accordance with the conventional nitration mechanism by a nitronium cation ÿ in (HNO3 2H2 SO4 ! NO 2 H3 O 2HSO4 ) the liquid phase. However, it is noteworthy that the
3.2. Relation between nitration activity and acidity of the catalysts In order to elucidate the properties of the active site for nitration, acidities of the mixed oxides were Table 1 Nitration of benzene with NO2 over solid acid catalysts Catalyst
Reaction conditions
WO3(75%)±MoO3(25%) TiO2(90%)±MoO3(10%) Silica±aluminac Nafion-H Silicontungustoic acidd 25%H3PO4/silica±aluminac 30%H2SO4/silica±aluminauc 20%NiSO4/silicagel 18.5%Al2(SO4)3/silicagel 10%(WO3(80%)±MoO3(20%))/silica±aluminac 10%WO3/silicagel
NO2/Bz.b 2.3 1.0 1.0 2.3 1.0 1.0 1.0 1.0 1.0 1.0 1.0
a
Nitrobenzene yield based on NO2. Molar ratio of NO2/benzene. c N631L; Al2O88%. b
SV (hÿ1) 13 5000 12 000 2600 19 500 2800 3600 3800 2000 3500 1300 2240
Yield % of nitrobenzenea temperature (8C) 200 150 150 200 150 150 150 200 150 150 160
after 1 h 24.5 0.8 18.3 23.6 15.4 3.6 17.6 3.8 1.3 5.6 2.3
after 5 h 25.8 ± 8.0 1.9 1.6 ± 15.4 1.7 0.7 6.8 1.3
H. Sato, K. Hirose / Applied Catalysis A: General 174 (1998) 77±81
Fig. 2. Relation between the rate constant (k) of nitration and the acid strenght of the catalyst. Reaction conditions: see caption in Fig. 1. Catalysts (molar ratios): (a) WO3(95%)±MoO3(5%); (b) WO 3 (90%)±TiO 2 (10%); (c) WO 3 (10%)±TiO 2 (90%); (d) ZnO(7%)±TiO 2 (93%); (e) SiO 2 (92%)±Al 2 O 3 (8%); (f) SiO2(81%)±Al2O3(19%).
most active mixed oxide, comprising WO3(95%)± MoO3(5%), exhibited the least amount of acid and the lowest acid strength. Therefore, the active site in the WO3±MoO3 system seems to differ from the ordinary acidic site. 3.3. Reaction kinetics of the nitration reaction over the WO3±MoO3 catalyst The time-on-stream of the nitration of benzene over the WO3(95%)±MoO3(5%) catalyst is shown in Fig. 3. A high yield of 93% (vs. nitric oxide) of
Fig. 3. Time-on-stream of nitration reaction. Reaction conditions: NO2/benzene/N2O.2/1.0/0.7 (molar ratios), Temperature1508C, SV100 hÿ1; Catalyst: WO3(95%)±MoO3(5%).
79
Fig. 4. First-order plot between residual NO2 (unconverted % in logarithm) and V/F. Reaction conditions: NO2/benzene/N20.2/ 1.0/0.7 (molar ratios), Temperature1508C; Catalyst: WO3(95%)± MoO3(5%).
nitrobenzene was obtained for more than 12 h timeon-stream. Fig. 4 shows the ®rst-order plot of the nitration reaction over WO3(95%)±MoO3(5%), and a rough linearity between the logarithms of unreacted nitric oxide and V/F (ml cat h/mmol) values can be recognized. Fig. 5 shows a linear increase of the nitrobenzene yield with an increase of the molar ratio of nitric oxide to benzene. This indicates that the reaction is of the ®rst order with the nitric oxide
Fig. 5. Influence of NO2/Benzene molar ratios on the nitration acitivity. Reaction conditions: Temperature1508C, SV1033 hÿ1; Catalyst: WO3(95%)±MoO3(5%).
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H. Sato, K. Hirose / Applied Catalysis A: General 174 (1998) 77±81
Fig. 6. Influence of nitration temperature on the nitrobenzene yield. Reaction conditions; NO2/benzene/N20.2/1.0/0.2 (molar raios), Temperature1508C, SV485 hÿ1; Catalyst: WO3(95%)± MoO3(5%).
Fig. 7. Influence of MoO3/WO3 molar ratios on the STY of nitrobenzene. Catalyst: WO3±MoO3. Reaction conditions: NO2/ benzene/N21.0/1.0/3.0 (molar ratios), Temperature1508C, SV2000 hÿ1.
concentration. Therefore, considering the safety requirement to avoid an explosive composition, we settled the nitric oxide molar ratio to benzene as 0.2, and intended to attain a quantitative conversion of nitric oxide. The in¯uence of the reaction temperature on the nitrobenzene yield is illustrated in Fig. 6; a maximum yield is obtained ca. 1208C. This result coincides with the phenomenon regarding the onset of the degradation of nitric oxide to nitrous oxide and oxygen at tempertures >1508C [5]. From the linear part in Fig. 6, between 858 and 1208C, one can calculate the activation energy of the nitration reaction at 7.22 kcal/mol, which is very small as compared to the typical value (15.3 kcal/mol) for the conventional liquid-phase nitration. 3.4. Factors influencing the catalytic activity of the WO3±MoO3 system The nitration activity increases with the content of MoO3 in the WO3±MoO3 system, reaching a maximum at 5 mol % of MoO3 (Fig. 7). However, no proportionality was observed between the content of MoO3 and the acidity of the WO3±MoO3 system. The rate constant of the nitration reaction was plotted against the BET values of the WO3(95%)± MoO3(5%) catalysts prepared in various conditions (Fig. 8), and an almost linear relationship was
Fig. 8. Dependence of the rate constant (k) on the BET surface area of the catalyst. Catalyst: WO3(95%)±MoO3(5%). Reaction conditions: NO 2 /benzene/N 2 0.2/1.0/0.7 (molar ratios), Temperature1508C, SV680 hÿ1.
obtained between them. Therefore, factors other than acidity must be taken into consideration. 3.5. Nitration by nitric oxide in the presence of oxygen over the WO3(95%)±MoO3(5%) catalyst In the vapor-phase nitration by nitric oxide, onethird of the nitric oxide is consumed as nitrous oxide
H. Sato, K. Hirose / Applied Catalysis A: General 174 (1998) 77±81
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not so ef®cient as to attain a high theoretical yield of nitrobenzene. Therefore, the complete utilization of nitric oxide is not possible within a reasonable contact time over this catalyst. Some co-catalyst for in situ oxidation of NO into NO2 may improve the overall reaction rate. 4. Conclusion
Fig. 9. Comparison of the first-order plots in the absence, and presence of oxygen for in-situ oxidation of NO to NO2. Reaction conditions: NO2/benzene/N20.2/1.0/0.17±0.7 (molar ratios), NO2/benzene/O20.2/1.0/0.17±0.7 (molar ratios), Temperature 1508C; Catalyst: WO3(95%)±MoO3(5%).
(NO) according to the stoichiometry of Eq. (2) (this stoichiometry has been con®rmed by quantitative analysis of NO by gas chromatography). Therefore, in order to re-use nitrous oxide by in-situ oxidation, nitration in the presence of oxygen was examined (Eq. (3)). (3) The result is illustrated in Fig. 9 in comparison with the result in the absence of oxygen. In the presence of oxygen and at a contact time as much as 40±45 s (V/F0.27 ml cat h/mmol), the yield of nitrobenzene based on benzene increased from 11.5 to 15.8%. However, theoretical yields based on nitric oxide correspond to 86.6 and 79.0%, respectively. Therefore, the theoretical yield based on nitric oxide rather decreased in the presence of oxygen. This means that, in-situ oxidation of nitrous oxide into nitric oxide is
We investigated the vapor-phase nitration of benzene by nitric oxide over various solid acid catalysts, and found that the mixed metal oxides comprising WO3±MoO3 affords the highest catalytic activity. This high activity cannot be explained simply by the solid acidity (acid strength and acid amount) of the catalyst. The complete utilization of nitric oxide by in situ oxidation of by-produced nitrous oxide (see the following reaction sequences) within a reasonable contact time could not be attained.
Therefore, in order to improve the overall reaction rate, some co-catalyst for in situ oxidation of NO into NO2 must be investigated. Acknowledgements The authors wish to express their sincere thanks to Ms. A. Sakamoto for her contribution in characterization of catalysts and to Mr. H. Tojima for his help with his reaction techniques. References [1] [2] [3] [4]
S. Suzuki, K. Tohmori, Y. Ono, Chem. Lett., 1986, 747. U.S. Patent No. 4660702 (1986) (to Monsanto Co.). E. Suzuki, K. Tohmori, Y. Ono, Chem. Lett., 1987, 2273. H. Sato, K. Hirose, S. Nakamura, U.S. Patent No. 4551568 (1985). [5] GMELINE Stickstoffdioxyd; N-749, p. 781.
Vapor-phase nitration of benzene over solid acid catalysts (1): Nitration with nitric oxide (NO2) H. Sato*, K. Hirose Technology and Research Management Of®ce, Sumitomo Chemical Co., Ltd. 27-1, Shinkawa 2-chome, Chuo-ku, Tokyo 104-8260, Japan Received 6 October 1997; received in revised form 24 April 1998; accepted 6 May 1998
Abstract Vapor-phase nitration of benzene over acidic catalysts is expected to be a clean process with no sulfuric acid waste. We investigated this process over acidic catalysts utilizing nitric oxide (NO2) as a nitrating agent, and found that several mixed metal oxides, such as silica±alumina, zinc-oxide±titania, and tungsten-oxides±molybdenum-oxide, exhibited a fairly good activity. Among them, WO3±MoO3 is the most active, but this catalyst alone deviated from the linear relationship between the activity and acidity. In order to explain this discrepancy several factors, such as acid amount, acid strength, and BET surface area, are examined in detail. # 1998 Elsevier Science B.V. All rights reserved.
1. Introduction Vapor-phase nitration of benzene to nitrobenzene over solid acid catalysts is expected to be a clean process without sulfuric acid waste, in contrast to the conventional liquid process which uses a mixed acid (concentrated nitric and sulfuric acids) as a nitrating agent and is accompanied with a large amount of diluted sulfuric acid waste (Eq. (1)). Many efforts devoted to developing a vapor phase process have been unsuccessful, because either the activity or life of catalysts is not satisfactory [1±3]. (1) Previously, we have reported in a piece of patent description [4] that mixed metal oxides, comprising WO3 and MO3, exhibited a fairly high and stable activity. *Corresponding author. Fax: +81355435909.
In this paper, we will report the results of our detailed study on the catalytic performance of various solid acid catalysts for benzene nitration with nitric oxide (NO2) as a nitration agent (Eq. (2)). (2) 2. Experimental Mixed metal oxides were prepared in three ways: a co-precipitation, a co-grinding, or an impregnation method. In particular, a WO3±MoO3 system was prepared by mixing and grinding the two oxides in a wet state. The mixed oxides were then calcined in air at 5008C for 3 h. Vapor-phase nitration was conducted in a ¯ow reactor made of quartz with a ®xed-catalyst bed at atmospheric pressure. A nitric oxide vapor was introduced into the ¯ow reactor from a container with a nitrogen carrier gas. The nitration products were
0926-860X/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved. PII: S0926-860X(98)00161-6
78
H. Sato, K. Hirose / Applied Catalysis A: General 174 (1998) 77±81
cold-trapped, analyzed, and identi®ed by gas chromatography. 3. Results and discussion 3.1. Investigation of active catalysts for nitration The results of benzene nitration with nitric oxide over various solid acid catalysts are summarized in Table 1. Among many catalysts examined, the mixed oxide catalyst comprising WO3(75 mol %)±MoO3(25 mol %) afforded a fairy good yield of nitrobenzene with almost no decay of activity for 5 h. The sulfuric acid catalyst supported on silica±alumina also exhibited a good yield with a slight decay of activity. Other solid acid catalysts, such as TiO2(90 mol %)± MoO3(10 mol %), silica±alumina, Na®on-H, silicotungstoic acid, 25 wt.%H3PO4/silica±alumina, 30 wt.%H2SO4/silica±alumina, 20 wt.%NiSO4/silicagel, 18.5 wt.%Al2(SO4)3/silicagel, 10 wt.%(WO3(80 and mol %)±MoO3(20 mol %))/silica±alumina, 10 wt.%WO3/silicagel exhibited either low yields or rapid decay of activity.
Fig. 1. Relation between the rate constant (k) of nitratin and the acid amount of the catalyst. Reaction conditions: NO2/benzene/ N20.2/1.0/0.7 (molar ratios), Temperature1508C, SV220 hÿ1. Catalysts (molar ratio): (a) WO 3 (95%)±MoO 3 (5%); (b) WO3(90%)±TiO2(10%); (c) WO3(10%)±TiO2(90%); (d) ZnO(7%)±TiO 2 (93%); (e) SiO 2 (92%)±Al 2 O 3 (8%); (f) SiO2(81%)±Al2O3(19%).
determined by the amine titration method by utilizing Hammett indicators. The results are shown in terms of the ®rst-order rate constant (k) for nitration (Figs. 1 and 2). These results show that the nitration activity was almost proportional to both, the acid amount (Fig. 1) and acid strength (Fig. 2) of the catalysts. This tendency is in accordance with the conventional nitration mechanism by a nitronium cation ÿ in (HNO3 2H2 SO4 ! NO 2 H3 O 2HSO4 ) the liquid phase. However, it is noteworthy that the
3.2. Relation between nitration activity and acidity of the catalysts In order to elucidate the properties of the active site for nitration, acidities of the mixed oxides were Table 1 Nitration of benzene with NO2 over solid acid catalysts Catalyst
Reaction conditions
WO3(75%)±MoO3(25%) TiO2(90%)±MoO3(10%) Silica±aluminac Nafion-H Silicontungustoic acidd 25%H3PO4/silica±aluminac 30%H2SO4/silica±aluminauc 20%NiSO4/silicagel 18.5%Al2(SO4)3/silicagel 10%(WO3(80%)±MoO3(20%))/silica±aluminac 10%WO3/silicagel
NO2/Bz.b 2.3 1.0 1.0 2.3 1.0 1.0 1.0 1.0 1.0 1.0 1.0
a
Nitrobenzene yield based on NO2. Molar ratio of NO2/benzene. c N631L; Al2O88%. b
SV (hÿ1) 13 5000 12 000 2600 19 500 2800 3600 3800 2000 3500 1300 2240
Yield % of nitrobenzenea temperature (8C) 200 150 150 200 150 150 150 200 150 150 160
after 1 h 24.5 0.8 18.3 23.6 15.4 3.6 17.6 3.8 1.3 5.6 2.3
after 5 h 25.8 ± 8.0 1.9 1.6 ± 15.4 1.7 0.7 6.8 1.3
H. Sato, K. Hirose / Applied Catalysis A: General 174 (1998) 77±81
Fig. 2. Relation between the rate constant (k) of nitration and the acid strenght of the catalyst. Reaction conditions: see caption in Fig. 1. Catalysts (molar ratios): (a) WO3(95%)±MoO3(5%); (b) WO 3 (90%)±TiO 2 (10%); (c) WO 3 (10%)±TiO 2 (90%); (d) ZnO(7%)±TiO 2 (93%); (e) SiO 2 (92%)±Al 2 O 3 (8%); (f) SiO2(81%)±Al2O3(19%).
most active mixed oxide, comprising WO3(95%)± MoO3(5%), exhibited the least amount of acid and the lowest acid strength. Therefore, the active site in the WO3±MoO3 system seems to differ from the ordinary acidic site. 3.3. Reaction kinetics of the nitration reaction over the WO3±MoO3 catalyst The time-on-stream of the nitration of benzene over the WO3(95%)±MoO3(5%) catalyst is shown in Fig. 3. A high yield of 93% (vs. nitric oxide) of
Fig. 3. Time-on-stream of nitration reaction. Reaction conditions: NO2/benzene/N2O.2/1.0/0.7 (molar ratios), Temperature1508C, SV100 hÿ1; Catalyst: WO3(95%)±MoO3(5%).
79
Fig. 4. First-order plot between residual NO2 (unconverted % in logarithm) and V/F. Reaction conditions: NO2/benzene/N20.2/ 1.0/0.7 (molar ratios), Temperature1508C; Catalyst: WO3(95%)± MoO3(5%).
nitrobenzene was obtained for more than 12 h timeon-stream. Fig. 4 shows the ®rst-order plot of the nitration reaction over WO3(95%)±MoO3(5%), and a rough linearity between the logarithms of unreacted nitric oxide and V/F (ml cat h/mmol) values can be recognized. Fig. 5 shows a linear increase of the nitrobenzene yield with an increase of the molar ratio of nitric oxide to benzene. This indicates that the reaction is of the ®rst order with the nitric oxide
Fig. 5. Influence of NO2/Benzene molar ratios on the nitration acitivity. Reaction conditions: Temperature1508C, SV1033 hÿ1; Catalyst: WO3(95%)±MoO3(5%).
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H. Sato, K. Hirose / Applied Catalysis A: General 174 (1998) 77±81
Fig. 6. Influence of nitration temperature on the nitrobenzene yield. Reaction conditions; NO2/benzene/N20.2/1.0/0.2 (molar raios), Temperature1508C, SV485 hÿ1; Catalyst: WO3(95%)± MoO3(5%).
Fig. 7. Influence of MoO3/WO3 molar ratios on the STY of nitrobenzene. Catalyst: WO3±MoO3. Reaction conditions: NO2/ benzene/N21.0/1.0/3.0 (molar ratios), Temperature1508C, SV2000 hÿ1.
concentration. Therefore, considering the safety requirement to avoid an explosive composition, we settled the nitric oxide molar ratio to benzene as 0.2, and intended to attain a quantitative conversion of nitric oxide. The in¯uence of the reaction temperature on the nitrobenzene yield is illustrated in Fig. 6; a maximum yield is obtained ca. 1208C. This result coincides with the phenomenon regarding the onset of the degradation of nitric oxide to nitrous oxide and oxygen at tempertures >1508C [5]. From the linear part in Fig. 6, between 858 and 1208C, one can calculate the activation energy of the nitration reaction at 7.22 kcal/mol, which is very small as compared to the typical value (15.3 kcal/mol) for the conventional liquid-phase nitration. 3.4. Factors influencing the catalytic activity of the WO3±MoO3 system The nitration activity increases with the content of MoO3 in the WO3±MoO3 system, reaching a maximum at 5 mol % of MoO3 (Fig. 7). However, no proportionality was observed between the content of MoO3 and the acidity of the WO3±MoO3 system. The rate constant of the nitration reaction was plotted against the BET values of the WO3(95%)± MoO3(5%) catalysts prepared in various conditions (Fig. 8), and an almost linear relationship was
Fig. 8. Dependence of the rate constant (k) on the BET surface area of the catalyst. Catalyst: WO3(95%)±MoO3(5%). Reaction conditions: NO 2 /benzene/N 2 0.2/1.0/0.7 (molar ratios), Temperature1508C, SV680 hÿ1.
obtained between them. Therefore, factors other than acidity must be taken into consideration. 3.5. Nitration by nitric oxide in the presence of oxygen over the WO3(95%)±MoO3(5%) catalyst In the vapor-phase nitration by nitric oxide, onethird of the nitric oxide is consumed as nitrous oxide
H. Sato, K. Hirose / Applied Catalysis A: General 174 (1998) 77±81
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not so ef®cient as to attain a high theoretical yield of nitrobenzene. Therefore, the complete utilization of nitric oxide is not possible within a reasonable contact time over this catalyst. Some co-catalyst for in situ oxidation of NO into NO2 may improve the overall reaction rate. 4. Conclusion
Fig. 9. Comparison of the first-order plots in the absence, and presence of oxygen for in-situ oxidation of NO to NO2. Reaction conditions: NO2/benzene/N20.2/1.0/0.17±0.7 (molar ratios), NO2/benzene/O20.2/1.0/0.17±0.7 (molar ratios), Temperature 1508C; Catalyst: WO3(95%)±MoO3(5%).
(NO) according to the stoichiometry of Eq. (2) (this stoichiometry has been con®rmed by quantitative analysis of NO by gas chromatography). Therefore, in order to re-use nitrous oxide by in-situ oxidation, nitration in the presence of oxygen was examined (Eq. (3)). (3) The result is illustrated in Fig. 9 in comparison with the result in the absence of oxygen. In the presence of oxygen and at a contact time as much as 40±45 s (V/F0.27 ml cat h/mmol), the yield of nitrobenzene based on benzene increased from 11.5 to 15.8%. However, theoretical yields based on nitric oxide correspond to 86.6 and 79.0%, respectively. Therefore, the theoretical yield based on nitric oxide rather decreased in the presence of oxygen. This means that, in-situ oxidation of nitrous oxide into nitric oxide is
We investigated the vapor-phase nitration of benzene by nitric oxide over various solid acid catalysts, and found that the mixed metal oxides comprising WO3±MoO3 affords the highest catalytic activity. This high activity cannot be explained simply by the solid acidity (acid strength and acid amount) of the catalyst. The complete utilization of nitric oxide by in situ oxidation of by-produced nitrous oxide (see the following reaction sequences) within a reasonable contact time could not be attained.
Therefore, in order to improve the overall reaction rate, some co-catalyst for in situ oxidation of NO into NO2 must be investigated. Acknowledgements The authors wish to express their sincere thanks to Ms. A. Sakamoto for her contribution in characterization of catalysts and to Mr. H. Tojima for his help with his reaction techniques. References [1] [2] [3] [4]
S. Suzuki, K. Tohmori, Y. Ono, Chem. Lett., 1986, 747. U.S. Patent No. 4660702 (1986) (to Monsanto Co.). E. Suzuki, K. Tohmori, Y. Ono, Chem. Lett., 1987, 2273. H. Sato, K. Hirose, S. Nakamura, U.S. Patent No. 4551568 (1985). [5] GMELINE Stickstoffdioxyd; N-749, p. 781.