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Combination of supported bimetallic rhodium – molybdenum catalyst and cerium oxide for hydrogenation of amide

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ABSTRACT

Hydrogenation of cyclohexanecarboxamide to aminomethylcyclohexane was conducted with silica-supported bimetallic catalysts composed of noble metal and group 6–7 elements. The combination of rhodium and molybdenum with molar ratio of 1:1 showed the highest activity. The effect of addition of various metal oxides was investigated on the catalysis of Rh–MoOx/SiO2, and the addition of CeO2 much increased the activity and selectivity. Higher hydrogen pressure and higher reaction temperature in the tested range of 2–8 MPa and 393–433 K, respectively, were favorable in view of both activity and selectivity. The highest yield of aminomethylcyclohexane obtained over Rh–MoOx/SiO2 + CeO2 was 63%. The effect of CeO2 addition was highest when CeO2 was not calcined, and CeO2 calcined at >773 K showed a smaller effect. The use of CeO2 as a support rather decreased the activity in comparison with Rh–MoOx/SiO2. The weakly-basic nature of CeO2 additive can affect the surface structure of Rh–MoOx/SiO2, i.e. reducing the ratio of Mo–OH/Mo–O− sites.

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Hydrogenation of cyclohexanecarboxamide (CyCONH2) over Rh–MoOx/SiO2 + calcined CeO2. Reaction conditions: Rh–MoOx/SiO2 (Rh 4 wt%, Mo/Rh = 1) 100 mg, CeO2 100 mg, 1,2-dimethoxyethane 20 g, H2 8 MPa, 413 K, 4 h. Cy = cyclohexyl. ‘Others’ comprise unknown solid products leading to loss of carbon balance during catalysis. ‘r.t.’ stands for room temperature.
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Figure 3: Hydrogenation of cyclohexanecarboxamide (CyCONH2) over Rh–MoOx/SiO2 + calcined CeO2. Reaction conditions: Rh–MoOx/SiO2 (Rh 4 wt%, Mo/Rh = 1) 100 mg, CeO2 100 mg, 1,2-dimethoxyethane 20 g, H2 8 MPa, 413 K, 4 h. Cy = cyclohexyl. ‘Others’ comprise unknown solid products leading to loss of carbon balance during catalysis. ‘r.t.’ stands for room temperature.

Mentions: While we used commercial CeO2 without calcination pretreatment, it is well known that the crystallinity and the surface area of CeO2 can be changed by calcination pretreatment [35, 36]. The surface area is reduced by calcination at higher temperature, and the surface of CeO2 samples without calcination or calcined at lower temperature (<873 K) is partly amorphous [37]. Indeed, we have used CeO2 catalysts after calcination at different temperatures for various CO2 utilization reactions such as carbonate synthesis, and we have found that CeO2 after 873 K calcination shows the highest activity probably because crystalline CeO2 surface is the active site [37–40]. Figure 3 shows the results of hydrogenation of CyCONH2 over Rh–MoOx/SiO2 and CeO2 calcined at various temperatures. The addition effect of CeO2 was highest when CeO2 was not calcined or calcined at <773 K, and the effect became smaller when CeO2 was calcined at higher temperature. This behavior shows that the addition effect was mostly determined by the surface area.


Combination of supported bimetallic rhodium – molybdenum catalyst and cerium oxide for hydrogenation of amide
Hydrogenation of cyclohexanecarboxamide (CyCONH2) over Rh–MoOx/SiO2 + calcined CeO2. Reaction conditions: Rh–MoOx/SiO2 (Rh 4 wt%, Mo/Rh = 1) 100 mg, CeO2 100 mg, 1,2-dimethoxyethane 20 g, H2 8 MPa, 413 K, 4 h. Cy = cyclohexyl. ‘Others’ comprise unknown solid products leading to loss of carbon balance during catalysis. ‘r.t.’ stands for room temperature.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036504&req=5

Figure 3: Hydrogenation of cyclohexanecarboxamide (CyCONH2) over Rh–MoOx/SiO2 + calcined CeO2. Reaction conditions: Rh–MoOx/SiO2 (Rh 4 wt%, Mo/Rh = 1) 100 mg, CeO2 100 mg, 1,2-dimethoxyethane 20 g, H2 8 MPa, 413 K, 4 h. Cy = cyclohexyl. ‘Others’ comprise unknown solid products leading to loss of carbon balance during catalysis. ‘r.t.’ stands for room temperature.
Mentions: While we used commercial CeO2 without calcination pretreatment, it is well known that the crystallinity and the surface area of CeO2 can be changed by calcination pretreatment [35, 36]. The surface area is reduced by calcination at higher temperature, and the surface of CeO2 samples without calcination or calcined at lower temperature (<873 K) is partly amorphous [37]. Indeed, we have used CeO2 catalysts after calcination at different temperatures for various CO2 utilization reactions such as carbonate synthesis, and we have found that CeO2 after 873 K calcination shows the highest activity probably because crystalline CeO2 surface is the active site [37–40]. Figure 3 shows the results of hydrogenation of CyCONH2 over Rh–MoOx/SiO2 and CeO2 calcined at various temperatures. The addition effect of CeO2 was highest when CeO2 was not calcined or calcined at <773 K, and the effect became smaller when CeO2 was calcined at higher temperature. This behavior shows that the addition effect was mostly determined by the surface area.

View Article: PubMed Central - PubMed

ABSTRACT

Hydrogenation of cyclohexanecarboxamide to aminomethylcyclohexane was conducted with silica-supported bimetallic catalysts composed of noble metal and group 6&ndash;7 elements. The combination of rhodium and molybdenum with molar ratio of 1:1 showed the highest activity. The effect of addition of various metal oxides was investigated on the catalysis of Rh&ndash;MoOx/SiO2, and the addition of CeO2 much increased the activity and selectivity. Higher hydrogen pressure and higher reaction temperature in the tested range of 2&ndash;8 MPa and 393&ndash;433 K, respectively, were favorable in view of both activity and selectivity. The highest yield of aminomethylcyclohexane obtained over Rh&ndash;MoOx/SiO2 + CeO2 was 63%. The effect of CeO2 addition was highest when CeO2 was not calcined, and CeO2 calcined at &gt;773 K showed a smaller effect. The use of CeO2 as a support rather decreased the activity in comparison with Rh&ndash;MoOx/SiO2. The weakly-basic nature of CeO2 additive can affect the surface structure of Rh&ndash;MoOx/SiO2, i.e. reducing the ratio of Mo&ndash;OH/Mo&ndash;O&minus; sites.

No MeSH data available.


Related in: MedlinePlus