CN116393136B - Preparation method and application of a reverse-loaded cobalt-based catalyst for synthesizing higher alcohols from carbon dioxide hydrogenation - Google Patents

Abstract

The invention discloses a catalyst for preparing higher alcohols by converting carbon dioxide, and its preparation method and application, which belong to the technical field of carbon dioxide resource utilization. The preparation method is: lanthanum oxide is loaded on metal cobalt nanoparticles by a reverse impregnation method, and a catalyst product is obtained after calcination and hydrogen/carbon monoxide/nitrogen/helium/argon heat treatment. The invention provides a method for preparing a catalyst for converting carbon dioxide to prepare higher alcohols, using nano metal cobalt and lanthanum salt as raw materials, loading lanthanum oxide on the surface of nano metal cobalt by a reverse impregnation method, forming Co ⁰ ‑Co ^x+ dual catalytic sites at the interface of nano metal cobalt and lanthanum oxide, these dual sites can catalyze the generation of alcohols and the growth of carbon chains, greatly promoting the selectivity of higher alcohols, and the selectivity of higher alcohols is higher than 85%; lanthanum oxide forms a protective layer on the surface of metal cobalt to avoid dissolution and agglomeration of metal cobalt, and significantly improves the stability of the catalyst; the preparation method has the characteristics of less waste liquid, low cost and simple process, and has good application prospects.

Description

A preparation method and application of a reverse-loaded cobalt-based catalyst for synthesizing higher alcohols from carbon dioxide hydrogenation

Technical Field

The technical field of carbon dioxide resource utilization, specifically, relates to a preparation method and application of a catalyst for synthesizing higher alcohols by hydrogenating carbon dioxide.

Background Art

In recent years, with the rapid development of society and economy, fossil fuels have been over-consumed, resulting in a large amount of carbon dioxide ( _CO2 ) emissions, leading to serious environmental problems. Therefore, reducing the concentration of _CO2 in the atmosphere to slow down global warming is of great significance to the development of human society. Among the various _CO2 emission reduction strategies, catalytic _CO2 hydrogenation into high value-added products is an important means to reduce _CO2 emissions and reduce the concentration of _CO2 in the atmosphere. Ethanol is an important fuel and chemical with a wide market demand. However, the current selectivity of _CO2 hydrogenation to synthesize ethanol is low, which hinders its further industrial application. The key to solving this problem is to develop a catalyst with high activity, high selectivity and high stability by optimizing the composition and preparation method of the catalyst.

CN111763731A discloses a multifunctional step-by-step catalyst for _CO2 hydrogenation to ethanol, which consists of five parts: the first part is a Pd-based catalyst for _CO2 hydrogenation to CO; the second part is a Cu-based catalyst for CO hydrogenation to methanol; the third part is a γ _{- Al2O3} catalyst for methanol dehydration to dimethyl ether; the fourth part is an H-MOR or H-FER catalyst for dimethyl ether carbonylation to methyl acetate; and the fifth part is a Cu-based catalyst for methyl acetate hydrogenation to ethanol. The above five catalysts are loaded in five layers from top to bottom in a catalytic reactor. The catalyst is applied to _CO2 hydrogenation to ethanol, with a _CO2 conversion rate of 12%, an ethanol selectivity of 30%, and a methanol selectivity of about 35%. The method involves the combined use of multiple catalysts, the method is complicated, and the use of precious metals is expensive, which is not conducive to industrial application.

CN109569712A discloses a catalyst for embedding Cu metal in molecular sieve crystals for producing ethanol by _CO2 hydrogenation and a preparation method thereof, comprising the following steps: adding a molecular sieve to an alkaline solution, treating for a period of time, filtering, washing and drying to obtain a molecular sieve containing mesopores. Then, a soluble Cu metal salt is loaded onto the molecular sieve by an impregnation method, and the loaded molecular sieve is obtained after drying and calcining. An aluminum source, a silicon source, and tetraethylammonium hydroxide are mixed with the loaded molecular sieve to form a gel, and then aged, calcined and reduced to obtain a molecular sieve catalyst. In the _CO2 hydrogenation reaction, although the catalyst has a high selectivity for ethanol, the carbon dioxide conversion rate is only 12.5%, and there is room for further improvement.

CN113559934B discloses a method for preparing a catalyst for _CO2 hydrogenation to ethanol, comprising the following steps: first, tetraporphyrin, N, N-dimethylformamide and cupric chloride are added to a container to generate a precipitate, centrifuged, washed, and dried to obtain a precursor. Then, the precursor is added to N, N-dimethylformamide and completely dissolved, dried after adding zirconium chloride and benzoic acid ultrasonic treatment, cooled to room temperature, filtered after adding N, N-dimethylformamide, filtered after adding tetrahydrofuran, and filtered after adding dichloromethane to obtain the catalyst. The catalyst is applied to _CO2 hydrogenation to ethanol, and the ethanol selectivity reaches 85%, but the preparation process is complicated, produces organic waste liquid, and is not conducive to large-scale application.

In summary, the current production of ethanol from carbon dioxide hydrogenation has the disadvantages of low carbon dioxide conversion rate, low selectivity, complex preparation process and high cost.

Summary of the invention

Based on the characteristics of current _CO2 hydrogenation catalysts to produce higher alcohols and the deficiencies in their applications, the purpose of the present invention is to provide a method for preparing and applying a catalyst to solve the problems of high cost, complex preparation process, low _CO2 conversion rate, and low selectivity for higher alcohols in the prior art.

In order to achieve the above object, the present invention adopts the following technical solution:

A catalyst for converting _CO2 to produce higher alcohols, characterized in that lanthanum oxide is loaded on metal cobalt nanoparticles by an impregnation method, and the obtained catalyst is used after heat treatment.

As a further preferred embodiment of the technical solution of the present invention, in the above-mentioned catalyst for converting _CO2 into higher alcohols, the weight content of metal cobalt is 5-95%, and the weight content of lanthanum oxide is 5-95%.

As a further preferred embodiment of the technical solution of the present invention, the lanthanum precursor used in the above-mentioned catalyst is one or a mixture of lanthanum nitrate, lanthanum chloride, lanthanum acetate and lanthanum sulfate.

As a further preferred embodiment of the technical solution of the present invention, the solvent used in the impregnation process in the above catalyst preparation method is deionized water, methanol, ethanol or a mixture of several thereof.

As a further preferred embodiment of the technical solution of the present invention, the heat treatment atmosphere in the above-mentioned catalyst preparation method is one or a mixture of hydrogen, nitrogen, carbon monoxide, helium or argon, the heat treatment temperature is 300 to 800 degrees Celsius, and the heat treatment time is 2 to 48 hours.

At the same time, the present invention also claims protection for the catalyst prepared by the above method.

At the same time, the present invention also claims the use of the above catalyst in the catalytic preparation of low-carbon alcohols by carbon dioxide hydrogenation. Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention uses nano-metal cobalt and lanthanum salt as raw materials, and loads lanthanum oxide on the surface of nano-metal cobalt by a reverse loading method, forming a ^Co0 - ^Cox+ dual catalytic site at the interface between the nano-metal cobalt and lanthanum oxide to catalyze alcohol generation and carbon chain growth, thereby greatly promoting the synthesis of higher alcohols.

(2) The present invention loads lanthanum oxide on the surface of nano-metal cobalt by a reverse impregnation method, forming a lanthanum oxide film on the surface of the cobalt oxide, which weakens the hydrogenation activity of the metal cobalt, thereby effectively reducing the generation of hydrocarbons.

(3) The present invention loads lanthanum oxide on the surface of nano-metal cobalt by a reverse impregnation method, forming a lanthanum oxide film on the surface of cobalt oxide, thereby preventing the agglomeration of cobalt nanoparticles during the reaction process, thereby effectively improving the stability of the catalyst.

DETAILED DESCRIPTION

The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Unless otherwise specified, all commodities or reagents in the present invention were purchased through market channels.

Example 1

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) Add 1.0 g of nano-metal cobalt and 0.05 g of lanthanum nitrate to 20 mL of water to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in nitrogen and heat treated at 800° C. for 2 h to obtain a catalyst.

The catalyst performance was tested in a slurry bed reactor.

Example 2

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) 0.05 g of nano-metal cobalt and 0.95 g of lanthanum chloride were added to 50 mL of water and 20 mL of ethanol to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in argon gas and heat treated at 300° C. for 48 h to obtain a catalyst.

The catalyst performance was tested in a fixed bed reactor.

Example 3

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) 0.6 g of nano-metal cobalt and 0.6 g of lanthanum acetate were added to 10 mL of water and 10 mL of methanol to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in hydrogen and heat treated at 400° C. for 5 h to obtain a catalyst.

The catalyst performance was tested in a slurry bed reactor.

Example 4

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) 0.8 g of nano-metal cobalt and 0.2 g of lanthanum sulfate were added to 10 mL of water, 5 mL of methanol and 5 mL of ethanol to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in carbon monoxide and heat treated at 600° C. for 2 h to obtain a catalyst.

The catalyst performance was tested in a fixed bed reactor.

Example 5

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) 0.9 g of nano-metal cobalt, 0.1 g of lanthanum acetate and 0.5 g of lanthanum nitrate were added to 20 mL of water to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in nitrogen and heat treated at 400° C. for 10 h to obtain a catalyst.

The catalyst performance was tested in a fixed bed reactor.

Example 6

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) Add 0.8 g of nano-metal cobalt and 0.2 g of lanthanum nitrate to 20 mL of water to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in nitrogen and heat treated at 700° C. for 6 h to obtain a catalyst.

The catalyst performance was tested in a slurry bed reactor.

Example 7

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) 0.8 g of nano-metal cobalt, 0.2 g of lanthanum chloride and 0.3 g of lanthanum sulfate were added to 20 mL of water to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in hydrogen and heat treated at 600° C. for 5 h to obtain a catalyst.

The catalyst performance was tested in a fixed bed reactor.

Example 8

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) 1.5 g of nano-metal cobalt, 0.2 g of lanthanum nitrate and 0.2 g of lanthanum sulfate were added to 20 mL of water to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in nitrogen and heat treated at 600° C. for 5 h to obtain a catalyst.

The catalyst performance was tested in a fixed bed reactor.

Comparative Example 1

A method for preparing a catalyst for preparing higher alcohols by hydrogenating carbon dioxide, comprising the following steps:

(1) 1.0 g of lanthanum oxide and 0.3 g of cobalt nitrate were added to 10 mL of water, 5 mL of methanol and 5 mL of ethanol to obtain a mixed solution.

(2) After stirring the mixed solution for 30 minutes, it was dried at 80°C until the liquid was completely evaporated.

(3) The dried mixture obtained in step (2) is placed in hydrogen and heat treated at 600° C. for 5 h to obtain a catalyst.

The catalyst performance was tested in a fixed bed reactor.

Test Case

Fixed bed reactor: 0.3 g of the prepared catalyst was mixed with 2 g of SiC and placed in a reactor. The raw gas (a mixture of 20 v% carbon dioxide, 70 v% hydrogen, and 10 v% nitrogen) flowed through the catalyst bed at a certain flow rate. The space velocity adopted was 2 liters/gram catalyst/hour. The reaction pressure was gradually increased to 5 MPa, and the reaction temperature was gradually increased to 250°C to start the reaction. A performance test lasting 100 hours was carried out. The product at the reactor outlet was kept warm at 150°C and passed into the chromatograph for online analysis.

Slurry bed reactor: 3 g of the prepared catalyst was mixed with 100 mL of high boiling point wax oil at room temperature, and then the mixture was transferred to a 1 L continuous stirring reactor. The feed gas (a mixture of 20 v% carbon dioxide, 70 v% hydrogen, and 10 v% nitrogen) was introduced into the reactor at a certain flow rate, and the space velocity adopted was 2 liters/gram catalyst/hour. The reaction pressure was gradually increased to 5.0 MPa, and the reaction temperature was gradually increased to 230°C to start the reaction. The product at the reactor outlet was kept at 150°C and introduced into a chromatogram for online analysis.

The carbon dioxide conversion rate and product selectivity were calculated according to the following formula:

Carbon dioxide conversion rate = (imported carbon dioxide moles - exported carbon dioxide moles) / imported carbon dioxide moles * 100%;

Product selectivity = number of moles of outlet product * number of carbon atoms in product / (number of moles of inlet carbon dioxide - number of moles of outlet carbon dioxide) * 100%.

The test results are shown in Table 1.

Test Case

Fixed bed reactor: 0.3 g of the prepared catalyst was mixed with 2 g of SiC and placed in a reactor. The raw gas (a mixture of 20 v% carbon dioxide, 70 v% hydrogen, and 10 v% nitrogen) flowed through the catalyst bed at a certain flow rate. The space velocity adopted was 2 liters/gram catalyst/hour. The reaction pressure was gradually increased to 5 MPa, and the reaction temperature was gradually increased to 250°C to start the reaction. A performance test lasting 100 hours was carried out. The product at the reactor outlet was kept warm at 150°C and passed into a chromatograph for online analysis.

Slurry bed reactor: 3 g of the prepared catalyst was mixed with 100 mL of high boiling point wax oil at room temperature, and then the mixture was transferred to a 1 L continuous stirring reactor. The feed gas (a mixture of 20 v% carbon dioxide, 70 v% hydrogen, and 10 v% nitrogen) was introduced into the reactor at a certain flow rate, and the space velocity adopted was 2 liters/gram catalyst/hour. The reaction pressure was gradually increased to 5.0 MPa, and the reaction temperature was gradually increased to 230°C to start the reaction. The product at the reactor outlet was kept at 150°C and introduced into a chromatogram for online analysis.

The carbon dioxide conversion rate and product selectivity were calculated according to the following formula:

Carbon dioxide conversion rate = (imported carbon dioxide moles - exported carbon dioxide moles) / imported carbon dioxide moles * 100%;

Product selectivity = number of moles of outlet product * number of carbon atoms in product / (number of moles of inlet carbon dioxide - number of moles of outlet carbon dioxide) * 100%.

The test results are shown in Table 1.

Table 1 Catalytic performance test results of catalysts

It can be seen from Table 1 that the catalyst prepared by the present invention can well achieve the technical effect of preparing low-carbon alcohols by hydrogenating carbon dioxide. Taking Example 1 as an example, the conversion rate of carbon dioxide is 30%, the total alcohol selectivity is as high as 94%, the ethanol selectivity is as high as 82%, and the catalyst operates stably for more than 300 hours.

The present invention illustrates the technical concept of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of individual raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims (1)

1. The application of the catalyst in preparing higher alcohol by carbon dioxide hydrogenation catalysis is characterized in that lanthanum oxide is loaded on metal cobalt nano particles by an impregnation method, and the obtained catalyst is used after heat treatment;

the weight content of the metallic cobalt in the catalyst is 5-95%, and the weight content of the lanthanum oxide is 5-95%;

the lanthanum precursor of lanthanum oxide is selected from one or a mixture of a plurality of lanthanum nitrate, lanthanum chloride, lanthanum acetate and lanthanum sulfate;

the solvent used in the dipping process is one or a mixture of more of deionized water, methanol and ethanol;

the heat treatment atmosphere is one or a mixture of more of hydrogen, nitrogen, carbon monoxide, helium or argon, the heat treatment temperature is 300-800 ℃, and the heat treatment time is 2-48 hours.