CN113000044A

CN113000044A - Carbon dioxide oxidation ethane dehydrogenation catalyst and preparation method thereof

Info

Publication number: CN113000044A
Application number: CN202110276410.9A
Authority: CN
Inventors: 李映春; 敬方梨; 罗仕忠
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2021-03-15
Filing date: 2021-03-15
Publication date: 2021-06-22
Anticipated expiration: 2041-03-15
Also published as: CN113000044B

Abstract

The invention relates to a dehydrogenation catalyst for oxidizing ethane by carbon dioxide and a preparation method thereof, belonging to the technical field of catalysts. The invention aims to provide a preparation method of a dehydrogenation catalyst for oxidizing ethane by carbon dioxide. The method comprises the following steps: and (2) uniformly mixing cerium salt, ethyl orthosilicate and a solvent, dropwise adding ammonia water under stirring until the pH value is 8.5-9.5, continuously stirring for 0.5-2 h, then aging for 20-30 h, carrying out solid-liquid separation, drying the solid, and roasting in an oxygen-containing atmosphere to obtain the carbon dioxide ethane oxide dehydrogenation catalyst. The method is simple and low in cost, and the catalyst obtained by the methodCatalyst with good catalytic activity and selectivity and suitable for CO₂In the ODHE reaction, the selectivity of ethylene is improved while the time required for the reaction to achieve stable performance is reduced.

Description

Carbon dioxide oxidation ethane dehydrogenation catalyst and preparation method thereof

Technical Field

The invention relates to a dehydrogenation catalyst for oxidizing ethane by carbon dioxide and a preparation method thereof, belonging to the technical field of catalysts.

Background

Oxidative dehydrogenation of ethane (CO) by carbon dioxide₂-ODHE) is a new process for the preparation of ethylene starting from ethane, using the greenhouse gas CO₂As an oxidant with milder activity, the catalyst can improve the selectivity of ethylene by effectively inhibiting the deep oxidation of reaction intermediate products, and simultaneously, CO is used₂As a carbon source, the carbon source can also relieve the adverse effect of greenhouse gases on the environment. However, limited by current catalyst productivity, CO₂The large-scale industrial production of the-ODHE is not realized.

At present, for CO₂The most common metal oxide catalysts for the-ODHE reaction are Cr, V, Ga, In and Co, respectively. The Cr-based catalyst has multiple valence ions of Cr, and oxidation-reduction circulation is easily formed between high valence ions and low valence ions to CO₂The ODHE has very good catalytic performance and is the most studied transition metal oxide catalyst at present. Cr-based catalysts tend to exhibit higher ethane conversion in a short time, but have a shorter lifetime due to their CO-to-CO ratio₂The conversion rate is low, and the catalyst is easy to deposit carbon. The Cr oxide is loaded on SiO₂When the catalyst is carried on carriers such as MCM-41, H-ZSM-5 and the like, the activity of the catalyst is greatly improved, and although Cr can be well dispersed in mesopores and can expose more active sites, more Cr exists in the form of low-activity polychromate. Increase Cr content⁶⁺/Cr³⁺The ratio of (3) is a main method for improving the activity of the Cr-based catalyst, Li and the like realize the regulation and control of the ratio of Cr6+/Cr3+ of the Cr-based catalyst by introducing different auxiliaries, and further improve the activity of the catalyst. Despite these advances, chromium catalysts have short lifetimes, and Cr³⁺The high toxicity of (a) has to be careful in preparing, using and disposing of the material, and thus its wide application is limited. Because V ions can be switched between trivalent, tetravalent, and pentavalent, there has been much research on V-based catalysts. The research on the V-based catalyst has focused more on the catalyst on which it is supportedThe activity of the support, since vanadium oxide is the same as chromium, depends on the influence of the support on the reducibility, the acidity-basicity and the dispersibility. While V-based catalysts hold great promise for Oxidative Dehydrogenation (ODH) reactions, it remains a challenge to control the acidic sites that promote olefin cleavage, and there is also information about V₂O₅Dust health problems. Ga-based catalyst for activating CO by virtue of good adsorption₂Ability to be applied to CO₂-ODH. Unloaded Ga₂O₃Has better olefin selectivity, but the catalyst is quickly deactivated because of serious carbon deposition. And Ga after loading₂O₃Make alkane and CO₂Competitive adsorption occurs, resulting in lower conversion of alkanes.

From this, the mainstream catalysts studied in many cases today have the following problems: the catalyst is affected by carbon deposition and is inactivated quickly. ② Cr and V metals have toxicity, which is not beneficial to industrial application. ③ partial catalyst activates CO₂The capacity is not strong, and the oxidation-reduction cycle is slowed down.

Cerium (Ce) is one of the most abundant and cheapest rare earth elements, and has good anti-carbon deposition capability because of its own good oxygen storage and release properties, which makes it have industrial application prospects.

Zhang Xiu Ling in "load type CeO₂CO on catalyst₂Research on reaction for preparing ethylene from ethane oxide in Yi Wen (Zhang Xiu Ling et al, load type CeO)₂CO on catalyst₂Study of reaction for preparing ethylene from Oxirane [ J]University of university, 2006 (12): 25-34) and preparing supported CeO by adopting an impregnation method₂Catalysts and investigation thereof in CO₂The catalytic performance of the reaction for preparing ethylene by oxidizing ethane is found to be CeO₂/γ-Al₃O₂Catalyst pair CO₂The reaction for preparing ethylene by oxidizing ethane has better catalytic activity, but only CeO is used₂As an active center for catalyzing the reaction, both selectivity and stability are required to be further improved.

Disclosure of Invention

Aiming at the defects, the technical problem solved by the invention is to provide a preparation method of a dehydrogenation catalyst for oxidizing ethane by carbon dioxide, and the catalyst prepared by the method has good selectivity and stability.

The preparation method of the dehydrogenation catalyst for oxidizing ethane by carbon dioxide comprises the following steps:

and (2) uniformly mixing cerium salt, ethyl orthosilicate and a solvent, dropwise adding ammonia water under stirring until the pH value is 8.5-9.5, continuously stirring for 0.5-2 h, then aging for 20-30 h, carrying out solid-liquid separation, drying the solid, and roasting in an oxygen-containing atmosphere to obtain the carbon dioxide ethane oxide dehydrogenation catalyst.

In one embodiment of the invention, the cerium salt is Ce (NO)₃)₃·6H₂O。

In one embodiment of the present invention, the molar ratio of silicon in the ethyl orthosilicate to cerium in the cerium salt is 0.1 to 1: 1.

In one embodiment, the solvent is ethanol.

In a preferred embodiment of the invention, ammonia is added to adjust the pH to 9.

In one embodiment of the present invention, the temperature of the calcination is 550 to 700 ℃. In one embodiment of the invention, the temperature of calcination is 600 ℃.

In one embodiment of the present invention, the oxygen-containing atmosphere is an air atmosphere.

The invention also provides the carbon dioxide ethylene oxide dehydrogenation catalyst prepared by the preparation method of the carbon dioxide ethylene oxide dehydrogenation catalyst.

The invention relates to a dehydrogenation catalyst for oxidizing ethane by carbon dioxide, which uses CeO₂As active sites for catalyzing this reaction, in CeO₂The surface is covered with SiO with a certain thickness₂The selectivity of the catalyst can be improved and the time required for the reaction to reach stable performance can be reduced.

Compared with the prior art, the method is simple, the cost is low, and the catalyst obtained by the method has good catalytic activity and selectivity, and can be suitable for CO₂In the reaction of-ODHE, the selectivity of ethylene is improved, and simultaneouslyReducing the time required for the reaction to reach stable performance.

Drawings

FIG. 1 shows Si as a sample in example 1_0.1-CeO₂On He⁺、Ne⁺LEIS plot after alternate sputtering.

FIG. 2 shows Si as a sample in example 2_0.3-CeO₂On He⁺、Ne⁺LEIS plot after alternate sputtering.

FIG. 3 is a graph of the rate of consumption of reactants in a catalytic reaction experiment.

Figure 4 is a graph of the rate of ethylene production.

Detailed Description

The method adopts a coprecipitation method to prepare the carbon dioxide ethylene oxide dehydrogenation catalyst. By adding in CeO₂The surface is covered with SiO with a certain thickness₂The product distribution of the reaction can be regulated and controlled, and the selectivity and the stability of the catalyst are improved. In addition, the method has the advantages of wide raw material source, low price, simple preparation process and capability of reducing the cost of the catalyst.

Any cerium salt commonly used in the art may be suitable for use in the present invention, for example, cerium nitrate, cerium chloride, etc. In one embodiment of the invention, the cerium salt is Ce (NO)₃)₃·6H₂O。

The amount of ethyl orthosilicate can be adjusted to SiO₂In one embodiment of the present invention, the molar ratio of silicon in the ethyl orthosilicate to cerium in the cerium salt is 0.1 to 1: 1.

Solvents commonly used in the art to dissolve cerium salts and ethyl orthosilicate are suitable for use in the present invention. In one embodiment, the solvent is ethanol.

The calcination may be performed in an oxygen-containing atmosphere, and it is preferable that the oxygen-containing atmosphere is an air atmosphere for cost saving.

The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.

Example 1

Si was prepared as follows_0.1-CeO₂Catalyst:

to 60ml of ethanol was added 4.34g of Ce (NO)₃)₃·6H₂Adding a certain amount of Tetraethoxysilane (TEOS) according to the atomic ratio of Si to Ce of 0.1:1, stirring for 1h at room temperature to fully mix the materials, dripping a certain amount of ammonia water at a constant speed within 30min until the pH value of the solution is 9, and then stirring the solution for 1 h. The mixture was then aged at room temperature for 24h, subsequently filtered with suction and the solid obtained was dried at 100 ℃ for 12 h. Finally, the catalyst is obtained by roasting in the air at 600 ℃. Sample was named Si_0.1-CeO₂。

Example 2

Si was prepared as follows_0.3-CeO₂Catalyst:

to 60ml of ethanol was added 4.34g of Ce (NO)₃)₃·6H₂O, then adding a certain amount of Si and Ce according to the atomic ratio of 0.3:1Tetraethoxysilane (TEOS), stirred at room temperature for 1h, mixed thoroughly, a certain amount of ammonia was added dropwise at a constant rate over 30min until the solution pH became 9, and then the above solution was stirred for 1 h. The mixture was then aged at room temperature for 24h, subsequently filtered with suction and the solid obtained was dried at 100 ℃ for 12 h. Finally, the catalyst is obtained by roasting in the air at 600 ℃. Sample was named Si_0.3-CeO₂。

Example 3

Si was prepared as follows_0.6-CeO₂Catalyst:

to 60ml of ethanol was added 4.34g of Ce (NO)₃)₃·6H₂Adding a certain amount of Tetraethoxysilane (TEOS) according to the atomic ratio of Si to Ce of 0.6:1, stirring for 1h at room temperature to fully mix the materials, dripping a certain amount of ammonia water at a constant speed within 30min until the pH value of the solution is 9, and then stirring the solution for 1 h. The mixture was then aged at room temperature for 24h, subsequently filtered with suction and the solid obtained was dried at 100 ℃ for 12 h. Finally, the catalyst is obtained by roasting in the air at 600 ℃. Sample was named Si_0.6-CeO₂。

Example 4

Si was prepared as follows_1.0-CeO₂Catalyst:

to 60ml of ethanol was added 4.34g of Ce (NO)₃)₃·6H₂And O, adding a certain amount of Tetraethoxysilane (TEOS) according to the atomic ratio of Si to Ce of 1:1, stirring for 1 hour at room temperature to fully mix the materials, dripping a certain amount of ammonia water at a constant speed within 30min until the pH value of the solution is 9, and then stirring the solution for 1 hour. The mixture was then aged at room temperature for 24h, subsequently filtered with suction and the solid obtained was dried at 100 ℃ for 12 h. Finally, the catalyst is obtained by roasting in the air at 600 ℃. Sample was named Si_1.0-CeO₂。

Comparative example 1

CeO was prepared by the following method₂Catalyst:

to 60ml of ethanol was added 4.34g of Ce (NO)₃)₃·6H₂O, stirring at room temperature for 1h, dropping a certain amount of ammonia water at constant speed within 30min until the solution pH becomes 9, and then stirring the above solution for 1 h. Then at room temperatureAging for 24h, suction filtration, and drying the solid at 100 deg.C for 12 h. Finally, the catalyst is obtained by roasting in the air at 600 ℃. The sample was named CeO₂。

To catalyst Si_0.1-CeO₂And Si_0.3-CeO₂Using He⁺And Ne⁺Alternately sputtering/analyzing the catalyst, performing Low Energy Ion Scattering (LEIS) test after each sputtering, arranging corresponding test spectral lines in sequence, and He⁺、Ne⁺The LEIS figures after the alternate sputtering are shown in fig. 1 and fig. 2. In the figure, Kinetic Energy is expressed in eV. In Si_0.1-CeO₂In the catalyst, the signals of Si and Ce are weak in the initial stage of detection, and the signal of Ce is gradually increased with the increase of the sputtering times, while the signal of Si is weakened to disappear, which shows that in the sample, the trace amount of SiO is in the sample₂Only in a few atomic layers on the outer surface of the catalyst and partially covered with CeO₂. In Si_0.3-CeO₂In the catalyst, it can be seen that, from the beginning to the end of the experiment, the signal of Si is not changed, and the signal of Ce is also changed from weak to strong, which indicates that SiO₂Uniformly present in several atomic layers on the surface, and with increasing depth, CeO₂The content of (c) increases. It was found that the surface of the catalyst was SiO₂Is partially covered, and this layer is covered with SiO₂The thickness of the layer is positively correlated with the amount of Si source added during preparation, while SiO of suitable thickness₂The selectivity of the layer to the catalyst is greatly improved.

The catalytic activity of the catalysts of examples 1 to 4 and comparative example 1 was measured. The Conversion (Conversion) and Conversion frequency (TOF) and the distribution of the products after the catalyst reaction are shown in Table 1. The reaction conditions are as follows: the dosage of the catalyst is 300mg, the atmospheric pressure and the temperature are 700 ℃, the flow rate of reactants is 30mL/min, and the composition of the reactants is as follows: c₂H₆:CO₂:N₂Ar is 20:20:4: 56. The product distribution at 8h on stream is shown in Table 1.

The consumption rates of the reactants consumed in the catalytic reaction experiments are shown in FIG. 3, and the rates of ethylene production are shown in FIG. 43 and 4, a: CeO (CeO)₂，b：Si_0.1-CeO₂。

TABLE 1

^aTOF is based on total CeO₂And (4) calculating.

It can be seen that the selectivity with respect to ethylene is greatly improved for the catalyst of the invention, in particular for Si, at the same TOF_0.6-CeO₂Compared with CeO₂，Si_0.6-CeO₂The selectivity of ethylene is improved by 57.7 percent on the original basis (24 percent).

In terms of stability, the catalyst of the invention only needs 20 hours to achieve stable performance, and the time is reduced by 10 hours on the basis of the unmodified catalyst.

Claims

1. The preparation method of the dehydrogenation catalyst for oxidizing ethane by carbon dioxide is characterized by comprising the following steps of:

2. The method of preparing a catalyst for the dehydrogenation of carbon dioxide by oxidation of ethane according to claim 1, characterized in that: the cerium salt is Ce (NO)₃)₃·6H₂O。

3. The method for producing a catalyst for the oxidative dehydrogenation of ethane with carbon dioxide according to claim 1 or 2, characterized in that: the molar ratio of silicon in the ethyl orthosilicate to cerium in the cerium salt is 0.1-1: 1.

4. The method for producing a catalyst for the oxidative dehydrogenation of ethane with carbon dioxide according to claim 1 or 2, characterized in that: the solvent is ethanol.

5. The method for producing a catalyst for the oxidative dehydrogenation of ethane with carbon dioxide according to claim 1 or 2, characterized in that: the pH was 9.

6. The method for producing a catalyst for the oxidative dehydrogenation of ethane with carbon dioxide according to claim 1 or 2, characterized in that: the roasting temperature is 550-700 ℃; the preferred firing temperature is 600 ℃.

7. The method for producing a catalyst for the oxidative dehydrogenation of ethane with carbon dioxide according to claim 1 or 2, characterized in that: the oxygen-containing atmosphere is air.

8. The catalyst for the dehydrogenation of carbon dioxide by oxidation of ethane, which is produced by the method for the dehydrogenation of carbon dioxide by oxidation of ethane, according to any one of claims 1 to 7.