CN114054023B

CN114054023B - Preparation method and application of alloy monoatomic catalyst

Info

Publication number: CN114054023B
Application number: CN202010765906.8A
Authority: CN
Inventors: 庞纪峰; 郑明远; 李新生; 李显泉; 张涛
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2023-08-25
Anticipated expiration: 2040-07-31
Also published as: CN114054023A

Abstract

The invention provides an alloy single-atom catalyst, a preparation method and application thereof, wherein the alloy single-atom catalyst is prepared by a two-step method, a carrier is silicon dioxide, an active component is copper and second metal, the copper content is 1-30wt%, the second metal is at least one of transition metals of groups 8, 9 and 10, and the second metal content is 0.01-2wt%. The catalyst is used in the direct dehydrogenation reaction of ethanol, the reaction is carried out on a fixed bed, the reaction atmosphere is one or more than two of hydrogen, nitrogen, helium and argon, the reaction temperature is more than or equal to 120 ℃, the selectivity of acetaldehyde is more than 90%, and the catalyst runs stably for more than 500 hours. Compared with the existing acetaldehyde production technology, the raw material adopted by the invention is bioethanol, and has the advantages of rich reserves, environmental friendliness, greenness, no pollution and the like. Meanwhile, the acetaldehyde has high economy and wide utilization path. In addition, the catalyst has low price, high reaction selectivity, good stability and easy separation of products, and has important economic value and industrialization prospect.

Description

Preparation method and application of alloy monoatomic catalyst

Technical Field

The invention belongs to the technical field of bioenergy chemical industry, and particularly relates to an alloy monoatomic catalyst and a preparation method and application thereof.

Background

With exhaustion of fossil fuel, aggravation of environmental pollution and rapid development of fermentation technology, ethanol attracts wide attention as a novel energy chemical platform compound. By 2010, ethanol yields reach 600 gigaliters. Most of the ethanol is mainly used for adding oil products at present, so that the fuel oil is partially replaced. However, due to the limitations of safety and solvent compatibility, the addition amount of ethanol in oil products is limited and can only be less than 10%, which severely restricts the development and application of ethanol.

In recent years, the high-value utilization of ethanol has been developed sufficiently to form a variety of products such as butanol and 1, 3-butadiene, which has strongly promoted the development of the ethanol industry. Among them, ethanol dehydrogenation is a key step of ethanol catalytic conversion, and its intensive research has set up a bridge for ethanol to high-value chemicals. In addition, acetaldehyde is an important aliphatic compound, is a key raw material for manufacturing chemicals such as acetic acid, peracetic acid, pentaerythritol, pyridine and the like, and has high application value.

At present, acetaldehyde is mainly prepared by adopting an ethylene oxidation method, and has the defects of non-renewable raw materials and the like. Compared with the method, the method for converting ethanol into acetaldehyde through one-step catalysis has the advantages of high atom economy, simple process and the like.

In the research of ethanol catalytic dehydrogenation, the preparation method of the catalyst has substantial influence on the reactivity and stability of the catalyst, and most of the catalysts still have the problems of requiring toxic auxiliary agents, poor stability and the like. For example Tu et al [ reference 1: chem.tech.biotechnol,1994, 59:141-147; reference 2: mol. Catalyst, 1994, 89:179-190]Cu is used as an active component, and toxic Cr ₂ O ₃ Is an auxiliary agent, and is prepared by a coprecipitation method and used for ethanol dehydrogenation reaction performance. The acid-base property of the metal oxide auxiliary agent is found to seriously influence the activity of the catalyst on dehydrogenation reaction, and the activity of the catalyst is highest when the molar ratio of Cr/Cu is 4/40. Chang et al [ reference 3: appl.catalyst.a: general,2003, 246:253-264; reference 4: appl.catalyst.a: general,2005, 288:53-61]Cu is used as an active component, and a series of catalysts are prepared by adopting an impregnation method and an ion exchange method and are used for alcohol dehydrogenation reaction. The result shows that rice husk is better than commercial silica gel as a carrier, and the ion exchange method has higher catalyst stability and still has deactivation phenomenon. Lu et al [ reference 5: chemCatChem 2017,9 (3), 505-510; reference 6: chemCatChem 2019，11，481-487；]A series of carbon-supported copper catalysts are synthesized for alcohol dehydrogenation reaction, so that good alcohol conversion rate and acetaldehyde selectivity are obtained, but the stability of the catalyst is poor and is generally lower than 500 minutes. Liu Gong supra [ reference 7: CN 103127945B]Copper is loaded on SiO ₂ 、Al ₂ O ₃ 、ZrO ₂ And on the carrier, the catalytic dehydrogenation of ethanol is realized by adopting P modification, so that the selectivity of the acetaldehyde is 98%. However, the catalyst still has the defects of poor activity and the like, the ethanol conversion rate is lower under the same conditions, and the stability of the catalyst is poor.

Disclosure of Invention

The invention aims to provide an alloy monoatomic catalyst, and a preparation method and application thereof. The method has the advantages of simple operation, low catalyst cost, economy, practicality, high acetaldehyde production efficiency, low energy consumption and the like.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

in one aspect, the present invention provides a method of preparing an alloy monoatomic catalyst comprising a support and an active component; the active component includes copper and a second metal; the alloy monoatomic catalyst is prepared in two steps; the first step: preparing a copper catalyst; and a second step of: loading a second metal on the copper catalyst to obtain the alloy monoatomic catalyst;

the first step adopts an ammonia distillation method; the ammonia distillation method comprises the following steps:

(1) Dissolving copper salt in water, and stirring to obtain copper salt solution;

(2) Adding ammonia water into the copper salt solution, and stirring to obtain a copper ammonia solution;

(3) Adding a carrier into the cuprammonium solution, stirring for 1-10h at 10-60 ℃, then raising the temperature to 70-100 ℃, and evaporating the ammoniacal solution until the pH of the solution is less than 8 to obtain a catalyst precursor 1;

(4) Filtering, washing and drying the catalyst precursor 1, roasting at 300-700 ℃, and reducing at 200-600 ℃ after roasting to obtain a copper catalyst;

the molar ratio of the ammonia water to the copper salt is 100:1-2:1;

the carrier is at least one of dealuminated molecular sieve, pure silicon molecular sieve and crystalline silicon dioxide;

the second metal is at least one of transition metals of groups 8, 9 and 10; the second metal is monoatomically dispersed in copper.

Based on the above scheme, preferably, the second step adopts a displacement method; the substitution method comprises the following steps:

(1) Dissolving the salt of the second metal in water, and stirring for 1-24h in the gas protection to obtain a solution 1;

(2) Adding 0.1-10M NaOH solution into the solution 1 until the pH value of the solution is 9-11 to obtain solution 2;

(3) Dispersing the copper catalyst in the solution 2, and stirring for 1-24 hours at 30-100 ℃ to obtain a catalyst precursor 2;

(4) Filtering, washing and drying the catalyst precursor 2, roasting at 300-700 ℃, and reducing at 200-600 ℃ after roasting to obtain the alloy monoatomic catalyst.

Based on the above, preferably, the aluminum content in the carrier is less than 1wt%; the content of copper in the active component is 1-30wt% and the content of the second metal is 0.01-2wt%; the second metal is at least one of Co, ni, pt, pd, ru, ir.

Based on the scheme, preferably, the dealuminated molecular sieve is obtained by treating a molecular sieve with a silicon-aluminum ratio of more than 20 for 2-100 hours at 20-100 ℃ by 10-66% nitric acid, wherein the molecular sieve with the silicon-aluminum ratio of more than 20 is one or more of ZSM-5, H beta, X-type and Y-type molecular sieves; the pure silicon molecular sieve is at least one of SBA-15, MCM-41, MCM-48 and Silicalite-1; the crystalline silica is silica having a crystallinity of greater than 60%; the copper salt is at least one of copper nitrate, copper chloride and copper acetate.

Based on the above scheme, preferably, the second metal salt is at least one of nitrate, acetate and ammoniated salt; the shielding gas is at least one of nitrogen, argon and helium.

Based on the above scheme, preferably, the reducing atmosphere is hydrogen, methane or a mixed gas, and the mixed gas refers to a mixture of one of hydrogen and methane and at least one of nitrogen, argon and helium.

In another aspect, the present invention provides an alloy monoatomic catalyst prepared by the method described above; the alloy monoatomic catalyst at least has a mesoporous structure.

Preferably, the alloy monoatomic catalyst has a microporous, mesoporous, multi-stage pore structure.

In yet another aspect, the present invention uses the alloy monoatomic catalyst described above for catalyzing the reaction of ethanol dehydrogenation to produce acetaldehyde.

Based on the above scheme, preferably, a fixed bed is adopted as a reactor for the reaction, and the reaction steps are as follows:

(1) Filling the alloy monoatomic catalyst in the middle of a fixed bed, and reducing the alloy monoatomic catalyst under hydrogen, methane or mixed gas at the reduction temperature of 200-400 ℃;

(2) Reducing, cooling to the reaction temperature, introducing carrier gas, pumping ethanol solution, and reacting;

in the reaction process, the reaction pressure is 0.1-1MPa; the reaction temperature is 120-350 ℃; the mass space velocity of the catalytic reaction is 0.1 to 20 hours ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The carrier gas is at least one of nitrogen, helium and argon; the flow rate ratio of the carrier gas ethanol is 1000:1-1:1; the mixed gas refers to the mixture of one of hydrogen and methane and at least one of nitrogen, argon and helium. .

Based on the above scheme, preferably, the acetaldehyde selectivity of the reaction exceeds 90%.

The invention has the following advantages:

1. the invention provides a preparation method of an alloy monoatomic catalyst, which is used for alcohol dehydrogenation reaction, the catalyst prepared by the method can obviously improve the yield of acetaldehyde, reduce the generation of byproducts in the reaction process, and obviously improve the stability and service life of the catalyst.

2. The method uses the ethanol as the reactant to prepare the acetaldehyde, has large ethanol yield and sufficient source, and the acetaldehyde generated by the ethanol dehydrogenation reaction has wide application in the fields of fuel, chemicals and the like.

3. The alloy monoatomic catalyst prepared by the invention has the following three structural advantages: a) The ammonia treatment method can enable copper particles and the carrier silicon oxide to have stronger acting force; b) The carrier of the catalyst is a high-crystallinity molecular sieve or crystalline silica, which can stabilize different types of copper active species; c) The catalyst synthesized by the ammonia distillation method has a microporous and mesoporous multi-level pore structure, and can promote the diffusion, adsorption and desorption of molecular reactants, so that the catalyst has higher stability and reactivity.

4. In the catalyst, the introduction of the second metal can stabilize the original metal; in addition, the alloy monoatoms can obviously improve the activation temperature of the ethanol reactant, and have higher reactivity (lower reaction temperature).

5. The alloy monoatomic catalyst provided by the invention is easy to prepare, low in cost and good in stability, and when being used for alcohol dehydrogenation reaction, the product is easy to separate and use, the whole process has good economical efficiency and practicability, meets the requirement of sustainable development, and has wide application prospects in biomass conversion.

Drawings

FIG. 1 shows a high resolution electron micrograph of the monoatomic catalyst prepared in example 1.

Detailed Description

The present invention will be described in detail with reference to the following examples, which are not intended to limit the scope of the invention. The examples give several typical catalyst preparation methods, but the specific process conditions are not limited to the parameters given in the examples.

Example 1

Carrier treatment:

taking H beta molecular sieve with silicon-aluminum ratio of 25 as an example: 10g H beta molecular sieve is weighed into 100mL66% nitric acid solution and treated at 80 ℃ for 24 hours. Then filtering, washing, roasting for 3 hours at 550 ℃ to obtain the dealuminated H beta molecular sieve, wherein the aluminum content of the sample after dealumination is lower than 1wt% through XRF measurement.

Preparation of copper-based catalyst: preparation of Cu-H beta-des-Al catalyst by ammonia distillation method

The process of preparing catalyst by ammonia distillation method with copper acetate as precursor is as follows: 3.1g of copper acetate is weighed and added into a three-neck flask containing 70mL of distilled water, after stirring until the copper acetate is completely dissolved, 16mL of ammonia water with the mass fraction of 25% is slowly added dropwise, at the moment, the pH value of the solution is 11-12, and the solution is vigorously stirred in a sealed manner for 90min. Then 9g of H beta-deAl molecular sieve powder is weighed and added into a three-necked flask, 30mL of distilled water is added, and the mixture is vigorously stirred for 8 hours at 20-25 ℃. And heating to 80 ℃ by adopting a super constant-temperature water bath, placing the three-neck flask in an open way, and stopping stirring until ammonia in the system is distilled out until the slurry is neutral. Naturally cooling to room temperature, filtering, washing with deionized water, and washing with absolute ethanol. Taking out the filter cake, putting the filter cake into a vacuum drying oven, drying the filter cake for 8 hours at 80 ℃, roasting the filter cake for 2 hours at 400 ℃, and reducing the filter cake for 1 hour at 300 ℃ in a hydrogen atmosphere to obtain 15wt% Cu-H beta-de Al catalyst prepared by an ammonia distillation method.

Preparation of alloy monoatomic catalyst: preparation of Ni-Cu H beta-de Al catalyst by displacement method

0.0158g of nickel nitrate is weighed, dissolved in water and stirred for 12h under the protection of nitrogen. Then, 1M NaOH solution was added to adjust the pH to 10.8. 1g of 15wt% Cu H.beta. -deAl catalyst reduced by ammonia distillation was dispersed in the above solution and stirred at 60℃for 12 hours. The solid product is filtered, washed and dried, then baked for 3 hours at 400 ℃, and reduced for 2 hours at 300 ℃ to obtain the 0.3% Ni-Cu H beta-des-Al catalyst, wherein the second metal is in a monoatomic state after the catalyst is reduced and is tightly chelated on copper particles, and the specific view is shown in figure 1.

Examples 2 to 6

Example 2 differs from example 1 only in that the second metal is Fe;

example 3 differs from example 1 only in that the second metal is Co;

example 4 differs from example 1 only in that the second metal is Pt;

example 5 differs from example 1 only in that the second metal is Pd;

example 6 differs from example 1 only in that the second metal is Rh.

Comparative example 1

The only difference from example 1 is that no second metal was added during the catalyst preparation.

Reaction example 1

The catalytic conversion experiments were carried out in a fixed bed reactor under the following specific conditions: the catalysts prepared in examples 1 to 6 and comparative example 1 were used for alcohol dehydrogenation reaction, respectively, the catalyst was used in an amount of 0.2g, the catalyst was added into a fixed bed reactor, on-line hydrogen reduction was performed at a gas flow rate of 60mL/min, a reduction temperature was 300℃and a reduction time was 2 hours. Reducing, cooling to reaction temperature, introducing nitrogen at a gas flow rate of 40mL/min, pumping raw materials, and analyzing gas phase product by online gas chromatography. The results of the catalytic dehydrogenation of ethanol over different alloy monoatomic catalysts are shown in table 1:

TABLE 1 results of catalytic dehydrogenation of monoatomic ethanol for different alloys (ethanol concentration 98wt%, reaction temperature 230 ℃ C., reaction mass space velocity of 0.98 h) ^-1 After 24 hours of reaction, the second metal content was 0.3 wt.%)

Table 1 compares M-Cu-H.beta. -deAl catalysts prepared with different metal additions. From the reaction data, it can be seen that the conversion and selectivity of ethanol generally increased after the second metal was introduced by the exchange process. In particular, on the Pt-Cu-H beta-de Al catalyst, the ethanol conversion rate reaches 95.6%, the acetaldehyde selectivity reaches 96.8%, and the reaction activity is obviously superior to that of a catalyst without pure copper. In addition, the introduction of Fe leads to a reduction in the conversion of ethanol, possibly due to the limited ability of the monoatomic alloy Fe catalyst to activate ethanol.

Examples 7 to 10

Example 7 differs from example 4 only in that the carrier is silicate-1;

example 8 differs from example 4 only in that the carrier is SBA-15;

example 9 differs from example 7 only in that the second metal is Ni;

example 10 differs from example 9 only in that the support is a Y-type molecular sieve.

Reaction example 2

Specific reaction conditions the same as in reaction example 1, and the results of catalytic dehydrogenation of ethanol on different supports are shown in table 2:

TABLE 2 comparison of results of catalytic dehydrogenation conversions of ethanol on different supports (98 wt% ethanol concentration, 230 ℃ C. Reaction temperature, 0.98h reaction mass space velocity) ^-1 The reaction is carried out for 24 hours, and then the result is obtained; the second metal content was 0.3 wt%)

As can be seen from the reaction data in Table 2, the selectivity of acetaldehyde over dealuminated molecular sieves and pure silicon molecular sieves was above 90%.

Reaction example 3

The reaction conditions were the same as in reaction example 1 except for the reaction conditions specifically described in Table 3, and the results of catalytic dehydrogenation of ethanol under different reaction conditions are shown in Table 3.

TABLE 3 catalytic dehydrogenation of ethanol under different reaction conditions (ethanol concentration 98wt% and reaction after 24 h; example 7 catalyst: pt-Cu-silicate-1)

It was found (Table 3) that the ethanol conversion was gradually increased with increasing reaction temperature by changing the reaction conditions, and 94.2% ethanol conversion and 92.7% acetaldehyde selectivity were achieved at 230 ℃. However, too high a temperature causes side reactions such as dehydration and decomposition, and the selectivity is lowered. Increasing the reaction space velocity to 3h ^-1 At this point, the ethanol conversion was reduced, but still reached 88.7%。

Reaction example 4

The reaction conditions were the same as in reaction example 1 except for the reaction conditions specifically described in Table 3, and the comparison of the reactivity of the second metal at different levels was shown in Table 4.

TABLE 4 comparison of ethanol dehydrogenation reaction results at different Pt contents (ethanol concentration 98wt%, reaction temperature 230 ℃ C., reaction mass space velocity of 0.98 h) ^-1 Results after 24h of reaction

Catalyst	Conversion/%	Acetaldehyde selectivity/%
			0.3％Pt-Cu-silicate-1	94.2	92.7
0.03％Pt-Cu-silicate-1	93.4	94.2
			1％Pt-Cu-silicate-1	94.6	93.7
3％Pt-Cu-silicate-1	90.2	87.5

As shown in Table 4, the metal content of Pt has a great effect on the reaction. At metal levels less than 2%, both ethanol conversion and acetaldehyde selectivity are over 90%. However, the selectivity for acetaldehyde was significantly reduced at a Pt content of 3%, only 87.5%, and the ethanol conversion was also reduced.

Reaction example 5

Stability comparison of catalysts:

stability experiments were performed using the Pt-Cu-H.beta. -des catalyst of example 4 and the Pt-Cu-silicate-1 catalyst of example 7, with a reaction time of 500 hours, and other reaction conditions were the same as in reaction example 1.

The experimental results of the present invention are compared with the results of the prior art.

TABLE 5 comparison of the invention with ethanol dehydrogenation catalysts from different documents (ethanol concentration 98wt%, temperature 230 ℃ C., space velocity 0.8 h) ^-1 )

By comparing with the literature (Table 5), the experimental result of the invention has outstanding substantial progress, the catalyst of the invention is easy to prepare, the reaction condition is milder, the catalyst has ultrahigh stability and higher practicability.

The foregoing is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and the present invention is not limited by the sequence of the embodiments, and any person skilled in the art can easily make changes or substitutions within the technical scope of the present invention. Therefore, the protection scope of the present invention should be limited by the claims.

Claims

1. A preparation method of an alloy monoatomic catalyst is characterized by comprising the following steps:

the alloy monoatomic catalyst comprises a carrier and an active component, wherein the active component comprises copper and a second metal;

the alloy monoatomic catalyst is prepared in two steps; the first step: preparing a copper catalyst; and a second step of: loading a second metal on the copper catalyst to obtain the alloy monoatomic catalyst;

the molar ratio of the ammonia water to the copper salt is 100:1-2:1;

the second metal is at least one of Co, ni, pt, pd, ru, ir, and the second metal is dispersed in copper in a monoatomic manner;

the second step adopts a displacement method; the substitution method comprises the following steps:

(2) Adding 0.1-10 of M NaOH solution into the solution 1 until the pH value of the solution is between 9 and 11 to obtain a solution 2;

(3) Dispersing the copper catalyst in the solution 2, and stirring at 30-100 ℃ for 1-24h to obtain a catalyst precursor 2;

(4) Filtering, washing, drying the catalyst precursor 2, and then at 300-700 ^o Roasting under CReducing at 200-600 ℃ after firing to obtain the alloy monoatomic catalyst;

the aluminum content in the carrier is lower than 1wt%; the content of copper in the active component is 1wt% -30wt%, and the content of the second metal is 0.01wt% -2wt%.

2. The method for preparing the alloy monoatomic catalyst according to claim 1, wherein: the dealuminated molecular sieve is obtained by treating a molecular sieve with a silicon-aluminum ratio of more than 20 with 10-66% nitric acid at 20-100 ℃ for 2-100H, wherein the molecular sieve with the silicon-aluminum ratio of more than 20 is one or more of ZSM-5, H beta, X-type and Y-type molecular sieves; the pure silicon molecular sieve is at least one of SBA-15, MCM-41, MCM-48 and Silicalite-1; the crystalline silica is silica having a crystallinity of greater than 60%; the copper salt is at least one of copper nitrate, copper chloride and copper acetate.

3. The method for preparing an alloy monoatomic catalyst according to claim 1, wherein the salt of the second metal is at least one of nitrate, acetate and ammoniated salt; the shielding gas is at least one of nitrogen, argon and helium.

4. The method for preparing an alloy monoatomic catalyst according to claim 1, wherein the reducing atmosphere is hydrogen, methane or a mixed gas, and the mixed gas is a mixture of one of hydrogen and methane and at least one of nitrogen, argon and helium.

5. An alloy monoatomic catalyst, characterized in that it is prepared by the process of any one of claims 1 to 3.

6. The alloy monoatomic catalyst according to claim 5, characterized in that it has at least a mesoporous structure.

7. Use of the alloy monoatomic catalyst according to claim 5, for catalyzing the reaction of alcohol dehydrogenation to acetaldehyde.

8. The use according to claim 7, characterized in that: the reaction adopts a fixed bed as a reactor, and the reaction steps are as follows:

(2) Reducing, cooling to the reaction temperature, introducing carrier gas, pumping ethanol solution, and reacting to obtain acetaldehyde;

in the reaction process, the reaction pressure is 0.1-1MPa; the reaction temperature is 120-350 ℃; the mass space velocity of the catalytic reaction is 0.1-20h ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The carrier gas is at least one of nitrogen, helium and argon; the flow rate ratio of the carrier gas to the ethanol is 1000:1-1:1; the mixed gas refers to the mixture of one of hydrogen and methane and at least one of nitrogen, argon and helium.