Supported cerium oxide catalyst as well as preparation method and application thereof

Abstract

The invention relates to a catalyst preparation technology, and aims to provide a supported cerium oxide catalyst as well as a preparation method and application thereof. The catalyst is a cerium oxide catalyst taking modified aluminum oxide as a carrier and is recorded as iCeO2 / Al2O3-X, i represents the loading capacity, and X represents a modifier. The preparation method of the catalyst is simple, the catalyst is used for preparing cyclohexene and benzene through oxidative dehydrogenation of cyclohexane, a fixed bed reactor is adopted for reaction, the reaction is continuous, products and the catalyst do not need to be separated, and the whole reaction process is easy to operate; according to the present invention, the catalyst can achieve the cyclohexane conversion rate of 50.6%, the cyclohexene selectivity of 41.2% and the benzene selectivity of 22.8% at the mild reaction temperature, has excellent stability, and can be recycled;

Description

Technical Field

[0001] The present invention relates to the field of cyclohexane dehydrogenation, and particularly to a supported cerium oxide catalyst, a preparation method thereof and an application thereof. The supported cerium oxide catalyst can be applied to the oxidative dehydrogenation reaction of cyclohexane. Background Art

[0002] Cyclohexene is an important organic chemical raw material, which is widely used in the production of pharmaceuticals, foods, agrochemicals, feeds, polyesters and other fine chemical products. In addition, cyclohexene can also be used as a catalyst solvent, a petroleum extractant and a stabilizer for high-octane gasoline. The strong demand for cyclohexene in the downstream product chain is due to its numerous uses. Since the direct oxidation of cyclohexene to adipic acid was successful, cyclohexene has been considered as the best raw material for synthesizing cyclohexanone, cyclohexanol and adipic acid.

[0003] At present, among many cyclohexene preparation processes, the benzene selective hydrogenation process is a commonly used method for selectively hydrogenating cheap benzene to prepare cyclohexene. However, this process needs to be carried out under high-pressure conditions, the treatment process is complex, and inevitably about 20% of by-product cyclohexane is produced.

[0004] CN 103,214,336 A discloses a method for preparing cyclohexene by oxidative dehydrogenation of cyclohexane, with K, Mg, Mo as the main active components, V as the promoter, and alumina or titanium oxide as the carrier. The reaction is carried out with air under a pressure condition of 0 - 5 kPa, the reaction temperature is 400 - 600 °C, and the reaction time is 0.05 - 1 s. The conversion rate of cyclohexane is close to 20%, and the highest yield of cyclohexene can reach 10.6%. However, this method has a high reaction temperature, the catalyst is prone to coking and deactivation, and the components are relatively complex, and it is difficult to control the content of the supported metal oxide.

[0005] Therefore, if a more optimized catalyst can be selected for the gas-phase oxidative dehydrogenation to prepare cyclohexene, it can not only provide a new way for the preparation of cyclohexane, but also constitute a practical green process route for the recycling of benzene - cyclohexene - cyclohexane. This has important practical and economic significance for improving the raw material utilization rate and process economy. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a preparation method and an application of a supported cerium oxide catalyst.

[0007] To solve the technical problem, the technical solution of the present invention is realized as follows:

[0008] The present invention first provides a supported cerium oxide catalyst, which is a cerium oxide catalyst with modified alumina as the carrier, denoted as iCeO2 / Al2O3-X, where i represents the loading amount (mass ratio of cerium oxide to modified alumina × 100%), and the value range is between 5% and 30%, and X represents the modifier.

[0009] The present invention further provides a preparation method of the supported cerium oxide catalyst, comprising the following steps:

[0010] 1) Modify alumina: Mix the alumina carrier and the modifier, heat and stir under reflux, then centrifuge to separate the alumina, and perform vacuum freeze-drying; Transfer the dried alumina carrier to a quartz boat, load it into a tubular furnace, and calcine under the protection of an inert gas to remove residues; Place the calcined alumina carrier in an inert gas for standby;

[0011] 2) Weigh cerium salt and dissolve it in deionized water to obtain a cerium salt solution, slowly add a quantitative amount of the modified alumina carrier prepared in step 1) to the cerium salt solution and continuously stir to make it uniformly mixed to obtain a solid-liquid mixture;

[0012] 3) Prepare the supported cerium oxide catalyst from the solid-liquid mixture by an impregnation method or a hydrothermal method.

[0013] As a preferred embodiment, the modifier includes formic acid, acetic acid, propionic acid, citric acid, oxalic acid and their aqueous solutions.

[0014] As a preferred embodiment, the inert gas includes argon, nitrogen, and helium.

[0015] As a preferred embodiment, the alumina carrier is α-alumina, β-alumina, γ-alumina, θ-alumina or spherical alumina; Further preferably, the carrier is α-alumina. The molar ratio of the alumina carrier to the acid in the modifier is 1:1 to 1:30.

[0016] As a preferred embodiment, the temperature of heating and stirring under reflux is 80-120 °C, and the time is 0.5-3 h; The calcination temperature is 300-500 °C, and the calcination time is 1-10 h.

[0017] As a preferred embodiment, the modification of alumina can be specifically implemented by the following examples:

[0018] 1.1) Modify the alumina carrier with the modifier, pour a certain amount of alumina carrier and a certain concentration of modifier into a single-neck flask, place it in an oil bath and heat and stir under reflux, and the temperature is in the range of 80-120 °C;

[0019] 1.2) After 0.5-3 h of oil bath, take it out and cool, centrifuge to separate the alumina, and then perform vacuum freeze-drying;

[0020] 1.3) Transfer the dried alumina support to a quartz boat, load it into a tubular furnace, and calcine it for 1 - 10 h under the protection of an inert gas to remove residues, with the calcination temperature in the range of 300 - 500 °C;

[0021] 1.4) Store the calcined alumina support in an inert gas.

[0022] As a preferred embodiment, in step 2), the cerium salt is selected from one or more of the following: cerium nitrate or its hydrate, cerium chloride or its hydrate, cerium acetate or its hydrate, cerium carbonate or its hydrate; the amount of the cerium salt is weighed according to the mass ratio of the modified alumina support to cerium dioxide in the final catalyst being 1:0.05 - 1:0.3.

[0023] As a preferred embodiment, the impregnation method is as follows: transfer the solid-liquid mixture to an ultrasonic oscillator and ultrasonicate it at room temperature; then transfer the solid-liquid mixture to a quartz boat and dry it in an oven; take out the dried solid and calcine it in a muffle furnace to obtain the supported cerium oxide catalyst.

[0024] As a preferred embodiment, a certain amount of alkali solution is added to the solid-liquid mixture to make the pH equal to 10 and aged for 0.5 - 6 h, where the alkali solution is ammonia water, sodium hydroxide solution or sodium carbonate solution. Then, after sealing the autoclave, it is placed in an oven for crystallization, with the temperature range of 60 - 200 °C and the time of 2 - 24 h to obtain the supported cerium oxide catalyst.

[0025] The impregnation method can be the equal-volume impregnation method or the excess impregnation method. Preferably, it is the equal-volume impregnation method. When using the equal-volume impregnation method, the volume of water in the cerium salt solution prepared in step 2) is equal to the saturated water adsorption capacity of the modified alumina support. When using the excess impregnation method, the volume of water in the cerium salt solution prepared in step 2) is greater than the saturated water adsorption capacity of the modified alumina support. Preferably, in the excess impregnation method, before drying, the mixed solution should be heated and stirred in an 80 °C oil bath to volatilize water.

[0026] The catalyst of the present invention can be in the form of powder, granule, block, etc.

[0027] In the impregnation method, the calcination temperature is 300 - 600 °C, the calcination time is 1 - 8 h, and the heating rate before reaching the calcination temperature is 1 - 10 °C / min. Further preferably, the heating rate is 2 °C / min.

[0028] The present invention further provides the application of the supported cerium oxide catalyst in the catalytic oxidative dehydrogenation of cyclohexane, including the following steps:

[0029] 1) Weigh the supported cerium oxide catalyst and load it into a reaction tube;

[0030] 2) Install the reaction tube in a fixed-bed reactor. Using air or an oxygen-containing inert gas as the oxidant, introduce the oxidant and cyclohexane into the fixed-bed reactor; prepare cyclohexene and benzene by catalytic oxidative dehydrogenation of cyclohexane; during the reaction process, control the reaction temperature to be constant, and the reaction pressure to be atmospheric pressure.

[0031] As a preferred embodiment, the oxidant is any one of the following: air, an oxygen-helium mixture in any proportion, or an oxygen-nitrogen mixture in any proportion.

[0032] More preferably, the oxidant is an oxygen-helium mixture with a volume fraction of 10%.

[0033] More preferably, the flow rate of the oxidant is 50 - 300 mL·min -1 。

[0034] As a preferred embodiment, the cyclohexane is pumped into the reaction system by a peristaltic pump, and the mass space velocity is 1 - 20 h -1 。

[0035] As a preferred embodiment, the reaction temperature is 300 - 600 °C.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1) The catalyst preparation method provided by the present invention is simple and reproducible;

[0038] 2) The catalyst provided by the present invention is used for the dehydrogenation of cyclohexane to prepare cyclohexene and benzene. The reaction is carried out in a fixed-bed reactor, and the reaction is continuous. There is no need to separate the products and the catalyst, and the overall reaction process is simple to operate;

[0039] 3) The catalyst provided by the present invention can achieve a cyclohexane conversion rate of 50.6%, a cyclohexene selectivity of 41.2%, and a benzene selectivity of 22.8% at a relatively mild reaction temperature;

[0040] 4) The catalyst provided by the present invention has excellent stability, can be continuously used for more than 100 h without deactivation, and is easy to regenerate. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a graph showing the experimental results of the catalytic stability of the 30% CeO2 / γAl2O3 catalyst in Example 7 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] The following further illustrates the present invention in conjunction with examples.

[0043] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The test reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0044] Example 1

[0045] Preparation of 10% CeO2 / γAl2O3: Using the equal-volume impregnation method, dissolve 0.2523 g of cerium nitrate hexahydrate in 2 mL of deionized water. Take 1 g of γAl2O3 support and slowly add it to the solution, and continuously stir to make it evenly mixed to obtain a solid-liquid mixture. Transfer it to an ultrasonic oscillator and ultrasonically treat it at room temperature for 2 h, then transfer it to a quartz boat and place it in an oven at 60 °C to dry for 12 h. Then take out the dried solid and calcine it in a muffle furnace at 2 °C / min through 500 °C for 4 h to obtain the catalyst.

[0046] Evaluation of the catalyst: Place 0.3 g of the prepared catalyst in a fixed-bed reactor. Cyclohexane is pumped into the vaporization chamber through a feed pump, the vaporization temperature is 180 °C, and the mass space velocity is 7 h -1 . The vaporized cyclohexane is mixed with a 10 vol.% O2 / He gas mixture and then passes through the catalyst bed. The gas flow rate is 200 mL / min, and the reaction is carried out at 400 °C and atmospheric pressure. Samples are taken regularly during the reaction process, and the composition of the products is analyzed using a gas chromatograph.

[0047] Example 2

[0048] Preparation and evaluation of 10% CeO2 / γAl2O3-FA (formic acid):

[0049] Modify γAl2O3: Mix the γAl2O3 support and formic acid solution (the molar ratio of formic acid in the γAl2O3 support to formic acid solution is 1:10), heat and stir under reflux at 100 °C, then centrifuge to obtain γAl2O3-FA, and carry out vacuum freeze-drying; transfer the dried γAl2O3-FA support to a quartz boat, load it into a tube furnace, and calcine it under nitrogen protection to remove residues; place the calcined γAl2O3-FA support in an inert gas for standby; using the equal-volume impregnation method, dissolve 0.2523 g of cerium nitrate hexahydrate in 2 mL of deionized water. Take 1 g of γAl2O3-FA support and slowly add it to the solution, and continuously stir to make it evenly mixed to obtain a solid-liquid mixture. Transfer it to an ultrasonic oscillator and ultrasonically treat it at room temperature for 2 h, then transfer it to a quartz boat and place it in an oven at 60 °C to dry for 12 h. Then take out the dried solid and calcine it in a muffle furnace at 2 °C / min through 500 °C for 4 h to obtain the catalyst. The evaluation conditions of the catalyst are as in Example 1.

[0050] Example 3

[0051] Preparation and evaluation of 10% CeO2 / γAl2O3-HAc (acetic acid): The modification conditions of γAl2O3 are the same as in Example 2, where the modifier formic acid is replaced by acetic acid; the equal-volume impregnation method is adopted. Dissolve 0.2523 g of cerium nitrate hexahydrate in 2 mL of deionized water. Take 1 g of the γAl2O3-HAc support and slowly add it to the solution, and continuously stir to make it evenly mixed to obtain a solid-liquid mixture. Transfer it to an ultrasonic oscillator and ultrasonicate at room temperature for 2 h. Then transfer it to a quartz boat and place it in an oven at 60 °C to dry for 12 h. Then take out the dried solid and calcine it in a muffle furnace at 2 °C / min through 500 °C for 4 h to obtain the catalyst. The evaluation conditions of the catalyst are the same as in Example 1.

[0052] Example 4

[0053] Preparation and evaluation of 10% CeO2 / γAl2O3-CA (citric acid): The modification conditions of γAl2O3 are the same as in Example 2, where the modifier formic acid is replaced by citric acid; the equal-volume impregnation method is adopted. Dissolve 0.2523 g of cerium nitrate hexahydrate in 2 mL of deionized water. Take 1 g of the γAl2O3-CA support and slowly add it to the solution, and continuously stir to make it evenly mixed to obtain a solid-liquid mixture. Transfer it to an ultrasonic oscillator and ultrasonicate at room temperature for 2 h. Then transfer it to a quartz boat and place it in an oven at 60 °C to dry for 12 h. Then take out the dried solid and calcine it in a muffle furnace at 2 °C / min through 500 °C for 4 h to obtain the catalyst. The evaluation conditions of the catalyst are the same as in Example 1.

[0054] Example 5

[0055] Preparation and evaluation of 10% CeO2 / γAl2O3-OA (oxalic acid): The modification conditions of γAl2O3 are the same as in Example 2, where the modifier formic acid is replaced by oxalic acid; the equal-volume impregnation method is adopted. Dissolve 0.2523 g of cerium nitrate hexahydrate in 2 mL of deionized water. Take 1 g of the γAl2O3-OA support and slowly add it to the solution, and continuously stir to make it evenly mixed to obtain a solid-liquid mixture. Transfer it to an ultrasonic oscillator and ultrasonicate at room temperature for 2 h. Then transfer it to a quartz boat and place it in an oven at 60 °C to dry for 12 h. Then take out the dried solid and calcine it in a muffle furnace at 2 °C / min through 500 °C for 4 h to obtain the catalyst. The evaluation conditions of the catalyst are the same as in Example 1.

[0056] Example 6

[0057] Preparation and evaluation of 10% CeO2 / γAl2O3 - OA (oxalic acid): The modification conditions of γAl2O3 are the same as in Example 2, where the modifier formic acid is replaced by oxalic acid; using the hydrothermal method, dissolve 0.2523 g of cerium nitrate hexahydrate in 30 mL of deionized water, slowly add 1 g of γAl2O3 - OA support to the solution and continuously stir to make it evenly mixed to obtain a solid - liquid mixture. Add a certain amount of ammonia water solution to the solid - liquid mixture to make the pH equal to 10 and age for 0.5 h. Seal the autoclave and put it into the oven for crystallization at a temperature of 120 °C for 6 h. Take it out, cool and centrifuge to separate, put it into the oven at 60 °C for drying for 12 h, and then take out the dried solid and calcine it in a muffle furnace at 2 °C / min through 500 °C for 4 h to obtain the catalyst. The evaluation conditions of the catalyst are the same as in Example 1. Example 7

[0058] Preparation and evaluation of 30% CeO2 / γAl2O3 - OA (oxalic acid): The preparation method is the same as in Example 6, where the mass of cerium nitrate hexahydrate is 0.7569 g. The evaluation conditions of the catalyst are the same as in Example 1. Figure 1 It is the experimental result diagram of the catalytic stability of the 30% CeO2 / γAl2O3 - OA catalyst in Example 7. From Figure 1 It can be seen that the catalyst has excellent stability, and no obvious deactivation is observed after 100 h of reaction.

[0059] Description of the setting of the comparative examples:

[0060] The purpose of setting the following comparative examples is to illustrate that cyclohexane hardly undergoes conversion during the reaction process without a catalyst and with only an alumina support, and the activity of the supported catalyst is better than that of the pure cerium oxide catalyst.

[0061] Comparative Example 1

[0062] The evaluation conditions of the catalyst are the same as in Example 1, except that in Comparative Example 1, no catalyst is loaded. Cyclohexane is pumped into the vaporization chamber through a feed pump, the vaporization temperature is 180 °C, the vaporized cyclohexane is mixed with a 10 vol.% O2 / He mixture gas and then passes through the catalyst bed, the gas flow rate is 200 mL / min, and the reaction is carried out at 400 °C and under atmospheric pressure. Samples are taken regularly during the reaction process, and the composition of the products is analyzed by a gas chromatograph.

[0063] Comparative Example 2

[0064] The evaluation conditions of the catalyst are the same as in Example 1, except that in Comparative Example 2, only the γAl2O3 support is loaded. Cyclohexane is pumped into the vaporization chamber through a feed pump, the vaporization temperature is 180 °C, and the mass space velocity is 7 h -1The vaporized cyclohexane is mixed with a 10 vol.% O2 / He mixture gas and then passed through the catalyst bed. The gas flow rate is 200 mL / min, and the reaction is carried out at 400 °C and under atmospheric pressure. Samples are taken regularly during the reaction process, and a gas chromatograph is used to analyze the composition of the products.

[0065] Comparative Example 3

[0066] The evaluation conditions of the catalyst are the same as those in Example 1, except that in Comparative Example 3, only CeO2 is loaded. Cyclohexane is pumped into the vaporization chamber through a feed pump, the vaporization temperature is 180 °C, and the mass space velocity is 7 h -1 The vaporized cyclohexane is mixed with a 10 vol.% O2 / He mixture gas and then passed through the catalyst bed. The gas flow rate is 200 mL / min, and the reaction is carried out at 400 °C and under atmospheric pressure. Samples are taken regularly during the reaction process, and a gas chromatograph is used to analyze the composition of the products.

[0067] Table 1 Evaluation results of catalysts in each example and comparative example

[0068]

[0069]

[0070] As can be seen from Table 1, the supported cerium oxide catalyst described in the present invention has good catalytic effects on the oxidative dehydrogenation of cyclohexane to cyclohexene and benzene. When 30% CeO2 / γAl2O3 - OA (oxalic acid) is used as the catalyst and the reaction temperature is 400 °C, a cyclohexane conversion rate of 50.6%, a cyclohexene selectivity of 41.2%, and a benzene selectivity of 22.8% can be achieved. Moreover, the supported cerium oxide catalyst described in the present invention can achieve excellent catalytic performance under relatively mild reaction conditions, and the catalyst preparation and evaluation processes are simple to operate. The catalyst has good stability, can be recycled, and saves production costs.

[0071] The above has described the embodiments of the present invention. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments.

Claims

1. A preparation method of a supported cerium oxide catalyst, characterized in that, The supported cerium oxide catalyst is a cerium oxide catalyst supported on modified alumina, and the preparation method includes the following steps: 1) Mix the alumina support and the modifier, heat and stir under reflux, then centrifuge to separate the alumina, and perform vacuum freeze-drying; transfer the dried alumina support to a quartz boat, load it into a tube furnace, and calcine under the protection of an inert gas to remove residues; put the calcined alumina support into an inert gas for standby; 2) Weigh the cerium salt and dissolve it in deionized water to obtain a cerium salt solution, slowly add the quantitatively prepared modified alumina support in step 1) to the cerium salt solution, and continuously stir to make it evenly mixed to obtain a solid-liquid mixture; 3) Prepare the supported cerium oxide catalyst from the solid-liquid mixture by the impregnation method or the hydrothermal method.

2. The method according to claim 1, wherein The modifier used is formic acid, acetic acid, propionic acid, citric acid, oxalic acid or an aqueous solution of the above acids, and the alumina support is α-alumina, β-alumina, γ-alumina, θ-alumina or spherical alumina; the molar ratio of the alumina support to the acid in the modifier is 1:1 to 1:

30.

3. The method according to claim 1, wherein In step 1), the temperature of heating and stirring under reflux is 80-120 °C, and the time is 0.5-3 h; the calcination temperature is 300-500 °C, and the calcination time is 1-10 h.

4. The method according to claim 1, characterized in that, In step 2), the cerium salt is selected from one or more of the following: cerium nitrate or its hydrate, cerium chloride or its hydrate, cerium acetate or its hydrate, cerium carbonate or its hydrate; the amount of the cerium salt is weighed according to the mass ratio of the modified alumina support to cerium dioxide in the final catalyst of 1:0.05 to 1:0.

3.

5. The method according to claim 1, characterized in that, The impregnation method is as follows: transfer the solid-liquid mixture to an ultrasonic oscillator and ultrasonically vibrate at room temperature; then transfer the solid-liquid mixture to a quartz boat and dry it in an oven; take out the dried solid and calcine it in a muffle furnace to obtain the supported cerium oxide catalyst.

6. The method according to claim 2, characterized in that, The hydrothermal method is as follows: add a certain amount of alkali solution to the solid-liquid mixture to make the pH equal to 10 and age for 0.5-6 h, where the alkali solution is ammonia water, sodium hydroxide solution or sodium carbonate solution, and then seal the autoclave and put it into an oven for crystallization, the temperature range is 60-200 °C, and the time is 2-24 h to obtain the supported cerium oxide catalyst.

7. The method according to claim 5, wherein The impregnation method is preferably the equal-volume impregnation method. When using the equal-volume impregnation method, the volume of water in the cerium salt solution prepared in step 2) is equal to the saturated water adsorption capacity of the modified alumina support.

8. The method according to claim 5, wherein In the impregnation method, the calcination temperature is 300-600 °C, the calcination time is 1-8 h, and the heating rate before reaching the calcination temperature is 1-10 °C / min.

9. Use of the supported cerium oxide catalyst prepared by the method according to any one of claims 1-8 in catalytic oxidative dehydrogenation of cyclohexane, characterized in that, It includes the following steps: 1) Weigh the supported cerium oxide catalyst and load it into a reaction tube; 2) Install the reaction tube in a fixed-bed reactor, use air or an oxygen-containing inert gas as the oxidant, and introduce the oxidant and cyclohexane into the fixed-bed reactor; prepare cyclohexene and benzene by catalytic oxidative dehydrogenation of cyclohexane; during the reaction, control the reaction temperature to be constant, and the reaction pressure is normal pressure.

10. The application according to claim 9, wherein The flow rate of the oxidant is 50 - 300 mL·min -1 The mass hourly space velocity of the cyclohexane is 1 - 20 h -1 , and the oxidant is a mixture of oxygen and helium with a volume fraction of 10%; the reaction temperature is 300 - 600 °C.

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