Intercalated hydrotalcite-like confined nano-copper catalyst and preparation and application method thereof

Abstract

The present invention discloses a confined nano copper catalyst of intercalated hydrotalcite-like structure and its preparation and application method. The preparation method directly intercalates anionic copper complex into the metal compound interlayer of hydrotalcite-like structure by coprecipitation method, and further calcines to form a catalyst containing layered metal oxide carrier and nano copper active components all loaded in the metal oxide carrier interlayer. When the catalyst is used in the oxygen-free dehydrogenation reaction of ethanol, it has excellent activity, selectivity and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, in particular to the technical field of nano copper catalysts. Background Art

[0002] In the prior art, ethanol to acetaldehyde mainly includes two pathways: ethanol oxidative dehydrogenation (ODH) and ethanol oxygen-free dehydrogenation (NODH). Compared with the oxidative dehydrogenation pathway, the oxygen-free dehydrogenation pathway has the following advantages: (1) low product separation cost; (2) hydrogen can be produced during the reaction, which can be further used as a clean renewable energy source or directly used in the in-situ reduction of the catalyst; (3) excessive oxidation of the product to form acetic acid and carbon dioxide can be avoided.

[0003] In recent years, supported copper-based catalysts have become a research hotspot in the field of ethanol oxygen-free dehydrogenation due to their high reaction selectivity. Among them, the interaction between the support and the active component of non-metallic support-supported copper-based catalysts such as Si-based, C-based, and B-based supports depends largely on the preparation method, and the existing preparation methods such as ammonia distillation, ion exchange, sol-gel, and impregnation generally face the problem that the activity and stability of the obtained products cannot be achieved at the same time. Even if some existing technologies have been improved to address this problem, other problems that hinder product performance have been introduced in the improvement.

[0004] For example, Chinese patent application CN114054079A discloses a technical solution for enhancing the interaction between Si-based carrier and active component Cu by using ammonia evaporation and ion exchange to improve the activity of catalyst and solve the deactivation problem. However, this method sacrifices the turnover frequency (TOF) per unit active site. Cu ); Chinese patent application CN103127945A discloses a method for preparing a Cu-based catalyst on a SiO2 carrier by a sol-gel method. In this method, the abundant silanol (Si-OH) on the surface of the SiO2 carrier will catalyze the side reaction of the product acetaldehyde, resulting in a low acetaldehyde yield; Chinese patent application CN105148911A discloses a method for using a mesoporous carbon-supported Cu catalyst for ethanol dehydrogenation reaction. Although the acetaldehyde yield obtained under specific materials, pressure and temperature can reach 70.4%, the stability of the obtained catalyst is poor due to the weak interaction between the active component and the carrier; Chinese invention patent CN115106094B discloses a method for loading Cu on a B-containing compound by an impregnation method. The acetaldehyde yield obtained under a specific temperature can reach 93%, but the catalyst can only be maintained for 50 hours at 240°C.

[0005] On the other hand, in recent years, hydrotalcite-like carriers are considered to be promising catalysts for ethanol dehydrogenation because of their easy adjustment of surface acidity and alkalinity, high specific surface area, and favorable dispersion of nano Cu particles. For example, Chinese patent application CN110773174B discloses a method for preparing a catalyst for the dehydrogenation of 1,4-butanediol to prepare γ-butyrolactone. The method uses hydrotalcite-like carriers as precursors to prepare catalysts Mg (6-x-y) Cu x Zn y Al2O9 can increase the activity of the catalyst by adjusting the acidity and alkalinity, but the stability of the catalyst prepared by this method is still poor. Similarly, other reported preparation methods of Cu-based hydrotalcite catalysts are to co-precipitate Cu 2+ It is introduced into the layer structure of hydrotalcite-like materials, and then calcined, reduced and pretreated to form the corresponding supported nano Cu catalyst. 2+ Occupies the sites of divalent metal cations in the hydrotalcite-like lamellae, and increases the Cu 2+ The content will lead to a decrease in the dispersion of Cu species and the basicity of the catalyst support, which is not conducive to the activity of the catalyst and the selectivity of acetaldehyde. Therefore, the development of more efficient and stable Cu-based catalysts with hydrotalcite-like supports is of great significance for promoting the industrial application of ethanol dehydrogenation to acetaldehyde. Summary of the invention

[0006] In view of the defects of the prior art, the present invention aims to provide a novel Cu-based catalyst on a hydrotalcite-like carrier, which has a special structure in which a nano copper compound is directly intercalated between the hydrotalcite-like layers and confined therein, and has high activity, high selectivity and high stability. The present invention also aims to provide a method for preparing a nano Cu catalyst having the intercalated hydrotalcite-like confined structure and a method for using the catalyst in a gas-phase dehydrogenation reaction of ethanol.

[0007] The present invention first provides the following technical solution:

[0008] A method for preparing an intercalated hydrotalcite-like confined nano-copper catalyst, comprising:

[0009] The copper metal salt and the anionic ligand are mixed and dissolved in water to carry out a complex reaction to obtain a Cu-anionic ligand solution;

[0010] Under an inert atmosphere, a mixed salt solution including a trivalent metal salt and a divalent metal salt and an alkali solution are added to the Cu-anion ligand solution, heated to perform an aging reaction, and the obtained solid is separated and dried to obtain a Cu-intercalated hydrotalcite precursor;

[0011] In an air atmosphere, calcining the intercalated hydrotalcite precursor at 300-700° C. to obtain the intercalated hydrotalcite confined nano-copper catalyst;

[0012] Wherein, the divalent metal salt is selected from one or two of Mg salt, Mn salt, Co salt, Ni salt or Zn salt; the trivalent metal salt is selected from Al salt and / or Fe salt; the molar ratio of the copper metal salt to the anionic ligand is 1:1-5.

[0013] In the above preparation method of the present invention, the obtained precursor material has a structure in which anionic copper complex is directly intercalated into the interlayer of hydrotalcite-like material, and the catalyst obtained by further calcination comprises a layered metal oxide support and nano Cu species active components supported between the metal oxide support layers, and all Cu species (such as Cu 2+ , Cu 1+ , Cu 0 ) has a content of 1 to 20 wt%, and is located between the layers of the carrier, with an obvious confinement phenomenon.

[0014] The preparation method of the present invention forms an intercalated hydrotalcite precursor by a coprecipitation method of simultaneously dropping an alkali solution and a mixed salt solution after complexing the copper salt with the ligand, and then calcining in an air atmosphere to obtain a mixed metal oxide. During the reaction, the in-situ reduced structure is reconstructed due to the dehydrogenation of ethanol, and finally a metal oxide-supported Cu-based catalyst is obtained.

[0015] The above preparation method of the present invention can further adjust the dispersion, loading and Cu content of the copper oxide in the catalyst by selecting the calcination temperature, ligand type and precursor solution concentration. 0 / Cu 1+ ratio to meet different requirements of ethanol gas-phase dehydrogenation reaction.

[0016] According to some preferred embodiments of the present invention, the temperature of the complexation reaction is 30-90°C.

[0017] According to some preferred embodiments of the present invention, the temperature of the aging reaction is 30-90°C.

[0018] According to some preferred embodiments of the present invention, the complexation reaction time is 0.5 to 2 hours.

[0019] According to some preferred embodiments of the present invention, the aging reaction time is 12 to 24 hours.

[0020] According to some preferred embodiments of the present invention, the calcination time is 3 to 7 hours.

[0021] According to some preferred embodiments of the present invention, the metal salt is selected from one or more of nitrates, acetates and acetylacetonates of the corresponding metals.

[0022] In the above preferred embodiments of the present invention, the metal salt may include any one of the aforementioned divalent metal salt, trivalent metal salt and copper metal salt.

[0023] According to some preferred embodiments of the present invention, the anionic ligand is selected from one or more of ethylenediaminetetraacetic acid, propylenediaminetetraacetic acid, and citric acid.

[0024] According to some preferred embodiments of the present invention, the alkaline solution is selected from aqueous solutions of alkali, and the alkali is selected from NaOH and / or KOH.

[0025] According to some preferred embodiments of the present invention, the preparation method further comprises: in the process of adding the mixed salt solution and the alkaline solution together to the Cu-anion ligand solution, controlling the pH of the obtained mixed system to be 9-11.

[0026] According to some preferred embodiments of the present invention, the molar ratio of the copper metal salt to the anionic ligand is 1:1-2.

[0027] According to some preferred embodiments of the present invention, in the mixed salt solution, the concentration ratio of the divalent metal salt to the trivalent metal salt is 2 to 3:1.

[0028] According to some preferred embodiments of the present invention, the ratio of the amount of copper metal salt in the mixed solution obtained by mixing and dissolving the copper metal salt and the anionic ligand in water to the total amount of metal salt in the mixed salt solution is 1:3-10.

[0029] According to some preferred embodiments of the present invention, the concentration of the copper metal salt in the mixed solution obtained by mixing and dissolving the copper metal salt and the anionic ligand in water is 0.01 to 1 mol / L.

[0030] According to some preferred embodiments of the present invention, the preparation method further comprises: dispersing the powder of the intercalated hydrotalcite-like confined nano-copper catalyst in a gel solution to obtain a gel mixture, wherein the gel solution comprises water, ethylene glycol and citric acid;

[0031] The porous carrier is immersed in the gel mixture until the gel mixture is completely absorbed, and then the porous carrier is dried and calcined at 500-700° C. to obtain a supported intercalated hydrotalcite-like confined nano-copper catalyst.

[0032] According to some preferred embodiments of the present invention, the porous support is selected from honeycomb ceramic materials.

[0033] The present invention further provides an intercalated hydrotalcite-like confined nano-copper catalyst or a supported intercalated hydrotalcite-like confined nano-copper catalyst prepared according to the above preparation method.

[0034] The intercalated hydrotalcite catalyst comprises a layered metal oxide support and a nano Cu active component loaded between the metal oxide support layers, wherein the Cu species (such as Cu 2+ , Cu 1+ , Cu 0 ) is basically fixed between the layers of the carrier.

[0035] According to some preferred embodiments of the present invention, the intercalated hydrotalcite-like catalyst comprises 85-99 wt % of a layered metal oxide support and 1-15 wt % of a nano copper species.

[0036] According to some preferred embodiments of the present invention, the layered metal oxide support is ABO x A multi-component mixed oxide carrier, wherein A is a divalent metal salt, wherein the divalent metal is selected from one or two of Mg, Mn, Co, Ni or Zn; and B is a trivalent metal salt, wherein the trivalent metal is selected from Al and / or Fe. The catalyst has excellent stability, catalytic activity and acetaldehyde selectivity.

[0037] The present invention further provides the use of the above intercalated hydrotalcite-like confined nano-copper catalyst or the supported intercalated hydrotalcite-like confined nano-copper catalyst in ethanol dehydrogenation reaction.

[0038] According to some preferred embodiments of the present invention, the ethanol dehydrogenation reaction is an ethanol dehydrogenation reaction to produce ethanol.

[0039] According to some preferred embodiments of the present invention, the ethanol dehydrogenation reaction is carried out in a fixed bed reactor loaded with the catalyst, and in the reaction, the feed space velocity of the raw material anhydrous ethanol or 70-95% aqueous bioethanol ethanol is 0.1-5 mL / g cat / h, fixed bed gas hourly space velocity is 500~20000mL / g cat / h, the carrier gas is nitrogen, and the reaction temperature is 180-320℃.

[0040] According to the above preferred application method of the present invention, the activity and selectivity of the catalyst can be stable for at least 80 hours.

[0041] In the above application method of the present invention, the catalyst can directly catalyze the ethanol dehydrogenation reaction without reduction pretreatment, and the catalytic effect is similar to that of the catalyst subjected to reduction pretreatment, the catalytic activity and selectivity are high, and long-term stability can be maintained.

[0042] In some specific embodiments, the catalyst may be subjected to reduction pretreatment before being subjected to the ethanol dehydrogenation reaction, wherein the pretreatment comprises: subjecting the catalyst to a reduction reaction with a reducing gas containing hydrogen at 260 to 270° C. for 60 to 90 minutes.

[0043] The preparation method of the invention is simple, stable and has good reproducibility; the raw materials are economical and readily available, and it is conducive to industrial scale-up synthesis.

[0044] The preparation method of the present invention can obtain a precursor in which metal elements are dispersed and intercalated in a hydrotalcite-like structure at the atomic level by introducing active sites between layers, and correspondingly obtain a catalyst in which Cu species are uniformly dispersed and confined between layers.

[0045] The preparation method of the present invention can improve the catalyst basicity, Cu species dispersion and loading amount by regulating parameters such as ligand type and calcination temperature, and further improve the activity, selectivity and anti-carbon deposition and anti-sintering capabilities of the catalyst.

[0046] The catalyst of the present invention is applied to the reaction of ethanol dehydrogenation to acetaldehyde, and has a fast reaction speed, high yield, and can be applied to large-scale production. When applied, the catalyst precursor can be directly put into use after calcination, and the pre-treatment link of the catalyst is omitted, which can greatly improve the production efficiency and reduce the production cost, and has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the XRD comparison of the precursors of catalysts 1, 8, 11, and A in Example 5.

[0048] Figure 2 This is a comparison chart of XRD of catalysts 1, 8, 11, and A in Example 5.

[0049] Figure 3 The H2-TPR comparison results of catalysts 1, 8, 11, and A in Example 5 are shown.

[0050] Figure 4 TEM comparison of catalyst 1 before and after reaction (a, b) and catalyst A after reaction (c) in Example 8.

[0051] Figure 5 This is an XPS comparison chart of catalyst 1 and catalyst A after reaction in Example 8.

[0052] Figure 6 The stability test results of catalyst 1 in Example 11 are shown in FIG.

[0053] Figure 7 The activity test results of catalyst 21 in Example 12 are shown in FIG. DETAILED DESCRIPTION

[0054] The present invention is described in detail below in conjunction with the embodiments and drawings, but it should be understood that the embodiments and drawings are only used to exemplify the present invention and do not constitute any limitation on the protection scope of the present invention. All reasonable changes and combinations within the scope of the inventive concept of the present invention fall within the protection scope of the present invention.

[0055] Example 1

[0056] The Mg3Al-CuEDTA-600 catalyst was prepared by the following process:

[0057] 0.01 mol Cu(NO3)2·3H2O, 0.01 mol C 10 H 20 N2O 10 and 100 ml of deionized water were placed in a 500 ml three-necked flask, stirred for 40 min in a 50°C water bath to obtain a Cu-anion ligand solution;

[0058] Dissolve 0.03 mol Mg(NO3)2·6H2O and 0.01 mol Al(NO3)3·6H2O in 100 ml deionized water to obtain a metal precursor mixed solution, which is poured into a 100 ml constant pressure funnel as a salt funnel;

[0059] Take 0.15 mol NaOH and dissolve it in 100 ml deionized water, then pour it into a 100 ml constant pressure funnel as an alkaline funnel;

[0060] Open the salt funnel and the base funnel and drip the solution contained therein into the three-necked flask for preparing the Cu-anion ligand solution, control the dripping speed, and use a pH meter to control the pH = 10 ± 0.5;

[0061] After the addition was completed, the mixture was aged in a water bath at 50°C for 24 hours, the solid was filtered and washed with deionized water until it was neutral, and then dried in an oven at 80°C overnight to obtain a Mg3Al-CuEDTA catalyst precursor;

[0062] The Mg3Al-CuEDTA catalyst precursor was calcined in air at 600°C for 5 h to obtain a Mg3Al-CuEDTA catalyst corresponding to a calcination temperature of 600°C, namely, Mg3Al-CuEDTA-600 catalyst, which was recorded as catalyst 1.

[0063] Example 2

[0064] According to the steps of Example 1, the parameters such as the trivalent metal salt, the divalent metal salt, the anionic ligand, the calcination temperature, etc. are changed (the specific changes are shown in Table 1, wherein PDTA is propylenediaminetetraacetic acid and CA is citric acid), to obtain A xB-CuY-T catalyst, wherein A is a divalent metal salt selected from one or two of Mg, Mn, Co, Ni or Zn salts; B is a trivalent metal salt selected from one or two of Al and Fe salts, T represents the calcination temperature, x is determined by the molar ratio of the divalent metal salt A to the trivalent metal salt B, and Y represents an anion complexing agent, which are recorded as catalysts 2 to 20.

[0065] Example 3

[0066] The supported XMg3Al-CuEDTA-600 / CD catalyst was prepared by the following process:

[0067] 6 g of the Mg3Al-CuEDTA-600 powder prepared in Example 1 was dispersed in 40-50 ml of a gel composed of water, ethylene glycol and citric acid at room temperature to obtain a gel mixture, and cordierite ceramic (CD) was impregnated into the gel mixture until the mixture was exhausted. The obtained CD containing the impregnation material was dried at 80°C overnight, and then calcined at 600°C in air for 5 h to obtain a CD-loaded Mg3Al-CuEDTA-600 catalyst, i.e., XMg3Al-CuEDTA-600 / CD catalyst, recorded as catalyst 21, wherein X is the loading amount, which can be determined by the mass change of the carrier before and after loading.

[0068] The specific conditions of the above catalysts 1 to 21 are shown in Table 1 below:

[0069] Table 1

[0070]

[0071]

[0072] Example 4

[0073] Comparative catalysts A to D were prepared by the following existing preparation method:

[0074] Place 0.02 mol Na2CO3 and 100 ml deionized water in a 500 ml three-necked flask and stir in a 50°C water bath;

[0075] Dissolve 0.05 mol Mg(NO3)2·6H2O, 0.01 mol Cu(NO3)2·3H2O, and 0.02 mol Al2(NO3)3·6H2O in 100 ml of deionized water, and then pour into a 100 ml constant pressure funnel as a salt funnel;

[0076] Take 0.16 mol NaOH and dissolve it in 100 ml deionized water, then pour it into a 100 ml constant pressure funnel as an alkaline funnel;

[0077] Open the salt funnel and the alkali funnel and add the solution to the three-necked flask, control the dropping speed, and use a pH meter to control the pH to 10±0.5. The obtained mixed solution is aged in a water bath at 50°C for 24 hours. The obtained solid is filtered and washed with deionized water until it is neutral, and then placed in an oven at 80°C for drying overnight to obtain Mg5CuAl2-CO3 precursor, whose structural formula is: Mg5CuAl2(OH) 16 (CO3)·4H2O

[0078] The Mg5CuAl2-CO3 precursor was calcined in air at 600°C for 5 hours to obtain Mg5CuAl2-CO3 corresponding to the calcination temperature of 600°C, namely, catalyst Mg5CuAl2-CO3-600, which was recorded as catalyst A.

[0079] Further, according to the above preparation steps, the Cu content parameters were adjusted to obtain comparative catalysts B to D, as shown in Table 2 below:

[0080] Table 2

[0081]

[0082] Example 5

[0083] XRD characterization was performed on the typical catalysts 1, 8, 11 and their precursors obtained in Examples 1-2 and the comparative catalyst A with a typical existing hydrotalcite-like structure obtained in Example 4 and its precursor. The characterization results are compared as follows: Figure 2 , Figure 1 shown.

[0084] from Figure 1 It can be seen that compared with the precursor of the typical hydrotalcite-like structure catalyst A, in the precursor of the Cu-intercalated hydrotalcite-like structure catalyst obtained by the preparation method of the present invention, the d value of the (003) crystal plane has increased to varying degrees (0.33-0.65 nm), indicating that the Cu-containing intercalated structure increases the interlayer spacing of the hydrotalcite; at the same time, the precursor structures of the catalysts 1, 8, and 11 have certain irregularities, indicating that the actual loaded Cu content in the catalyst precursors 1, 8, and 11 is different due to the difference in the complexing ability of the ligand.

[0085] from Figure 2 It can be seen that compared with catalysts 1, 8, and 11, characteristic diffraction peaks of CuO can be observed in the existing catalyst A, proving that the dispersion of the catalyst obtained in the present invention is better than that of the typical Cu embedded hydrotalcite layer catalyst.

[0086] Furthermore, catalysts 1, 8, and 11 were characterized by H2-TPR, such as Figure 3As shown, the results show that compared with catalysts 1, 8, and 11, catalyst A, a typical Cu embedded in hydrotalcite laminae, has a lower initial reduction temperature due to the agglomeration of Cu species, which is consistent with the XRD results.

[0087] Example 6

[0088] Ethanol and air were introduced into a fixed bed reactor loaded with 0.2 g of the catalysts 1 to 20 prepared in Examples 1 and 2 to carry out gas phase dehydrogenation of ethanol at a reaction temperature of 180 to 320° C., an ethanol feed flow rate of 0.6 to 1.2 ml / h, and a gas hourly space velocity (GHSV) of 15000 h -1 Under the conditions of (specific conditions are shown in Table 3), multiple groups of reactions are set up, and the generated product is acetaldehyde (AC), and the by-products include butanol (BA), ethyl acetate (ET), ethylene (EL), acetone (AO) and the like.

[0089] In the above reactions, after the reaction was stable at each temperature, the ethanol conversion rate and product selectivity were analyzed online by gas chromatography. The reaction results are shown in Table 3.

[0090] Table 3

[0091]

[0092]

[0093]

[0094] It can be seen that the activity and selectivity of the catalyst can be regulated by regulating the composition of the catalyst, the preparation conditions of the catalyst and the reaction conditions (including reaction temperature, feed flow rate and gas hourly space velocity), as shown in the following examples:

[0095] For catalyst 1 (Mg3Al-CuEDTA-600), under the condition of lower gas hourly space velocity, the ethanol injection flow rate was changed, and the acetaldehyde selectivity was relatively high (93-99%) in the reaction temperature range of 220-300°C; and when the ethanol injection flow rate was 2.4 ml / h and the reaction temperature was 320°C, the catalyst could still obtain 87% ethanol conversion rate, 95% acetaldehyde selectivity, and the space-time yield was 4.67 g / min. cat -1 h -1 , TOF Cu =49.3mol ethanol mol Cu -1 h -1 .

[0096] Furthermore, it can be seen that for catalysts 1 to 12, the actual Cu loading of the catalysts obtained by different anionic ligands is different. On the other hand, with the increase of calcination temperature, the conversion rate of ethanol increases, and the selectivity of acetaldehyde decreases relatively. In particular, the Mg3Al-CuEDTA-T catalyst with EDTA ligand shows almost no catalytic activity when calcined at 300°C due to incomplete decarburization and dehydroxylation between hydrotalcite layers; when calcined at 600°C, the ethanol conversion rate can reach 54% and the acetaldehyde selectivity can reach 99% at 220°C; when calcined at 700°C, the Cu species localized between the carrier layers are more dispersed, and the ethanol conversion rate at 220°C is increased to 53%, and the selectivity of acetaldehyde decreases to 93%.

[0097] It can be seen that for catalysts 13 to 20 with different layered metal oxides confined with Cu, the ethanol conversion rates are quite different, and the selectivity of the dehydration product is improved, especially Zn3Al-CuEDTA-600, which can obtain 99% ethanol conversion rate and 99% ethylene selectivity at 300°C. This shows that in the scheme of the present invention, the presence of solid base has a great influence on the high selectivity of acetaldehyde. In addition, it can be observed that the selectivity of ethyl acetate (ET) is improved, which is caused by the migration of the product acetaldehyde to the interface formed by Cu and the transition metal oxide to further undergo condensation reaction with ethanol species.

[0098] Example 7

[0099] Catalysts A to D prepared in Example 4 were used to carry out the same ethanol gas phase dehydrogenation reaction and test as in Example 6, with an ethanol flow rate of 1.2 ml / h and GHSV=15000 h -1 The results are shown in Table 4 below:

[0100] Table 4

[0101]

[0102] It can be seen from Table 4 that when different contents of Cu are introduced into the catalyst obtained by the hydrotalcite layer structure, when the Cu content is high, the increase in Cu content causes the Mg content in the catalyst precursor to decrease, the MgO content after calcination to decrease, and the basicity of the catalyst to decrease, which is not conducive to the selectivity of acetaldehyde. As shown in catalysts A to C, their selectivity for acetaldehyde at high temperatures is low (80% to 82%).

[0103] Example 8

[0104] The catalyst 1 before and after the ethanol gas phase dehydrogenation reaction in Example 6 and the catalyst A after the ethanol gas phase dehydrogenation reaction in Example 7 were characterized by TEM. Figure 4As shown, the catalyst 1 after the ethanol gas phase dehydrogenation reaction and the catalyst A after the reaction were characterized by XPS, as shown in the attached Figure 5 shown.

[0105] from Figure 4 It can be seen that in the catalyst 1 before the reaction, the CuO formed by the calcination of the precursor of the catalyst 1 is evenly distributed on the surface of the metal oxide. The average diameter of the nano Cu formed after the ethanol gas phase dehydrogenation reaction is ~3.1nm, which is highly dispersed between the layered metal oxide layers, and there is no scattered nano copper. This proves that the catalyst obtained by the present invention can confine and disperse the copper species before and after the reaction, and the reconstruction process of in-situ reduction is conducive to the dispersion of the Cu species. The average diameter of the nano Cu of the catalyst A after the reaction is

[0106] ~3.9nm, slightly larger than catalyst 1, and has nano Cu particles scattered outside the carrier (such as Figure 4 The area in the middle frame) proves that the interaction between the nano-Cu in the layer and the carrier is weak and has no confinement effect.

[0107] from Figure 5 It can be seen that in the catalyst 1 after the reaction, in Cup 3 / 2 The octahedral Cu was observed in the spectrum. 2+ and Cu + / Cu 0 They appear at ~935eV, ~934eV, ~933eV, and ~932eV, respectively, and are accompanied by Cu 2+ The vibration satellite peaks (938-946 eV) of the catalyst A after the reaction prove the existence of the in-situ reduction process. 2+ The proportion of (52%) is greater than that of the catalyst 1 after the reaction (37%), indicating that the nano-Cu species in the layer area are not fully exposed, and the active sites (Cu 0 / Cu + ) is less, thus only a lower acetaldehyde selectivity can be obtained, and when the Cu content is further reduced, its active sites will be further reduced, resulting in a significant decrease in the conversion rate of ethanol (as shown in Table 4).

[0108] Example 9

[0109] Bioethanol aqueous solutions with water content of 95% and 70% by mass were prepared using commercially available 95% bioethanol as a raw material. Catalysts 1 to 4 were used to carry out gas-phase oxidative dehydrogenation of ethanol, respectively. The reaction conditions were the same as those in Example 7. The results are shown in Table 5.

[0110] Table 5

[0111]

[0112] The data in Table 5 show that as the water content in ethanol increases, the selectivity of acetic acid (AA) increases significantly (5% to 11%). The selectivity of acetaldehyde can reach 88% or more. The boiling points of acetaldehyde (AC), acetone (AO) and acetic acid (AA) are ~21°C, 57°C and 118°C, respectively. The significant difference is conducive to product separation. Using cheaper water-containing bioethanol as a reaction raw material can significantly reduce the cost of industrial production.

[0113] Example 10

[0114] The catalyst 1 obtained in the example was pretreated, and the pretreatment process was: the catalyst 1 was reduced using a nitrogen-hydrogen mixed gas with a H2 content of 10 vol% at 265° C. for 75 minutes.

[0115] The pretreated catalyst 1 was subjected to the same ethanol gas phase dehydrogenation reaction and detection as in Example 6, with an ethanol flow rate of 0.6 ml / h and GHSV=15000 h -1 The comparison of the results with the reaction results of Catalyst 1 which was not pretreated is shown in Table 6:

[0116] Table 6

[0117]

[0118] It can be seen from Table 6 that at the initial reaction temperature of 180°C, the pretreated catalyst showed a higher selectivity for acetaldehyde than the unpretreated catalyst (99%>87%). This indicates that at this temperature, the unpretreated catalyst is still in the process of in-situ reduction and structural reconstruction, and some active species are still in the form of Cu 2+ in the form of, resulting in the production of a certain amount of butanol (BA) as a by-product during the in-situ reduction process; at 260°C or 300°C, the catalytic activity and product selectivity of the pretreated and unpretreated catalysts are similar, indicating that the unpretreated catalyst can achieve the catalytic performance of the pretreated catalyst through the in-situ reduction process. Under this condition, the catalyst of the present invention can be in-situ reduced using the H2 generated in the reaction system, without the need for additional introduction of H2 and pre-reduction treatment, thereby reducing production costs and improving production efficiency.

[0119] Embodiment 11

[0120] Catalyst 1 (Mg3Al-CuEDTA-600) obtained in Example 1 was tested for the stability of ethanol gas phase dehydrogenation. The reaction was carried out in a fixed bed reactor under normal pressure, including loading 0.2 g of catalyst (150-180 μm) into a quartz tube with an inner diameter of 8 mm, and the carrier gas was an inert gas, with GHSV = 15000 mL / g. cat / h, ethanol feed flow rate 1.2ml / h, temperature 260℃, FuliGC 9070II gas chromatograph was used to analyze the reaction products online. According to the reaction products, the catalyst conversion rate of raw material ethanol (EA) and the selectivity of product acetaldehyde (AC) were recorded at different reaction times. Before the test, the catalyst was first reduced in situ at 180℃ and 200℃ by hydrogen generated by itself for 1h, and then heated to 260℃ for the above stability test. The test results are shown in the attached Figure 6 shown.

[0121] By attaching Figure 6 It can be seen that the catalyst showed no obvious deactivation within 80 hours of use, and could still maintain high activity after 80 hours, with acetaldehyde selectivity reaching over 94%.

[0122] Example 12

[0123] The catalyst 21 supported by cordierite ceramic (CD) obtained in Example 3 was tested for ethanol gas phase dehydrogenation activity. The reaction was carried out in a fixed bed reactor under normal pressure, including loading 10 g of the catalyst into a quartz tube with an inner diameter of 20 mm, using an inert gas as the carrier gas, and GHSV = 600 mL / g. cat / h, ethanol feed flow rate was 1.5 or 2.1 mL / h, temperature was 200-320°C, and the reaction products were analyzed online using FuliGC 9070II Plus gas chromatograph. According to the reaction products, the conversion rate of the catalyst to the raw material ethanol (EA) and the selectivity of the product acetaldehyde (AC) were recorded at different reaction temperatures and ethanol feed flow rates. The results are shown in the attached figure. Figure 7 shown.

[0124] By attaching Figure 7 It can be seen that at two different ethanol feed flow rates, the selectivity of acetaldehyde is greater than 90%, among which the acetaldehyde selectivity obtained at a flow rate of 2.1 mL / h is slightly higher than the ethanol selectivity obtained at a flow rate of 1.5 mL / h, but the overall ethanol conversion rate obtained at a flow rate of 1.5 mL / h is slightly higher than the ethanol conversion rate obtained at a flow rate of 2.1 mL / h. On the other hand, as the reaction temperature increases, the ethanol conversion rate increases, while the selectivity of acetaldehyde always maintains a similar high level. The above results show that the industrialized shaped catalyst obtained by loading the catalyst powder on cordierite ceramics (CD) has high activity and high acetaldehyde selectivity.

[0125] The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a confined nano-copper catalyst of an intercalated hydrotalcite-like substance, characterized in that: It includes: The copper metal salt and the anionic ligand are mixed and dissolved in water to carry out a complex reaction to obtain a Cu-anionic ligand solution; Under an inert atmosphere, a mixed salt solution including a trivalent metal salt and a divalent metal salt and an alkaline solution are added dropwise to the Cu-anion ligand solution, during which the pH of the obtained mixed system is controlled to be 9-11, and then heated to perform an aging reaction, and the obtained solid is separated and dried to obtain a Cu-intercalated hydrotalcite precursor; In an air atmosphere, calcining the intercalated hydrotalcite precursor at 400-700° C. to obtain the intercalated hydrotalcite confined nano-copper catalyst; Wherein, the divalent metal in the divalent metal salt is selected from one or two of Mg, Mn, Co, and Ni; the trivalent metal in the trivalent metal salt is selected from Al and / or Fe; the molar ratio of the copper metal salt to the anionic ligand is 1:1-5; The temperature of the complex reaction is 30-90°C; the temperature of the aging reaction is 30-90°C; the metal salt is selected from one or more of nitrates, acetates, and acetylacetonates; the anionic ligand is selected from one or more of ethylenediaminetetraacetic acid, propylenediaminetetraacetic acid, and citric acid; in the mixed salt solution, the concentration ratio of the divalent metal salt to the trivalent metal salt is 2-3:1; the ratio of the amount of copper metal salt in the mixed solution obtained by mixing and dissolving the copper metal salt and the anionic ligand in water to the amount of total metal salt in the mixed salt solution is 1:3-10.

2. The preparation method according to claim 1, characterized in that: in, The complexing reaction time is 0.5 to 2 hours; and / or, the aging reaction time is 12 to 24 hours; and / or, the calcination time is 3 to 7 hours.

3. The preparation method according to claim 1, characterized in that: in, The alkaline solution is selected from aqueous solutions of alkalis, and the alkali is selected from NaOH and / or KOH.

4. The preparation method according to claim 1, characterized in that: It also includes: Dispersing the powder of the intercalated hydrotalcite-like confined nano-copper catalyst in a gel solution to obtain a gel mixture, wherein the gel solution comprises water, ethylene glycol and citric acid; The porous carrier is immersed in the gel mixture until the gel mixture is completely absorbed, and then the porous carrier is dried and calcined at 600-700° C. to obtain a supported intercalated hydrotalcite-like confined nano-copper catalyst.

5. The preparation method according to claim 4, characterized in that: The porous support is selected from honeycomb ceramic materials.

6. The intercalated hydrotalcite-like confined nano-copper catalyst prepared by the preparation method according to any one of claims 1 to 3 or the supported intercalated hydrotalcite-like confined nano-copper catalyst prepared by the preparation method according to claim 4 or 5.

7. Use of the intercalated hydrotalcite-like confined nano-copper catalyst prepared by the preparation method according to any one of claims 1 to 3 or the supported intercalated hydrotalcite-like confined nano-copper catalyst prepared by the preparation method according to claim 4 or 5 in the reaction of ethanol dehydrogenation to acetaldehyde.

8. The use according to claim 7, characterized in that: The ethanol dehydrogenation to acetaldehyde reaction is carried out in a fixed bed reactor loaded with the catalyst. During the reaction, the feed space velocity of anhydrous ethanol or aqueous bioethanol with an ethanol content of 70-95% is 0.1-5 mL / g. cat / h, fixed bed gas hourly space velocity is 500~20000mL / g cat / h, the carrier gas is nitrogen, and the reaction temperature is 180~320℃.

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