Preparation and application of metal oxide nanotube catalyst with limited field effect

Abstract

The application relates to a preparation method of a metal oxide nanotube catalyst with a limited field effect and application thereof, and belongs to the field of catalyst preparation. The nanotube is prepared by a hydrothermal method, and a noble metal is loaded into the inside and outside of the nanotube by an impregnation method; the nanotube has an outer diameter of 20-300 nm, a wall thickness of 10-150 nm and a length of 30-500 nm; the catalyst is composed of an active component and a carrier, wherein the active component is a noble metal, the carrier is the nanotube, the nanotube is one of CeO2 nanotubes and TiO2 nanotubes, and the noble metal is one of Pd, Ir, Rh and Ru; the content of the active component accounts for 0.1%-10% of the total mass of the catalyst, and the content of the carrier accounts for 90%-99.9% of the total mass of the catalyst; the obtained catalyst is used for preparing methanol by CO2 hydrogenation; and due to the limited field effect of the nanotube, the catalyst with the noble metal loaded in the inside is superior to the catalyst with the noble metal loaded in the outside in performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of metal oxide nanotube catalyst with confinement effect and application thereof, and belongs to the technical field of catalyst preparation. BACKGROUND

[0002] Confinement effect is a concept first proposed in the field of catalysis and surface science, and is widely used in the field of catalyst preparation. In the process of catalyst preparation, confinement effect can affect the number and distribution of active centers, and also provide a chemical microenvironment for the nucleation and growth of crystals to obtain unique physical and chemical properties. Therefore, confinement effect has been widely used in materials for hydrogen storage, sensing, catalysis, drug release and separation.

[0003] Confinement effect mainly includes interface confinement and channel confinement. The internal loading of active centers in carbon nanotubes, core-shell structure catalysts and metal oxide nanotubes is beneficial to the sintering resistance and reaction stability of the catalyst. Carbon nanotubes and core-shell structure catalysts have been widely studied, while the confinement effect of metal oxide nanotubes with hollow structure remains to be studied. Therefore, it is of great significance to explore the confinement effect of metal oxide nanotubes.

[0004] In the catalytic system, the catalyst with noble metal as active center has the advantages of high activity and good stability. If the activity of the catalyst can be improved and the loading amount of noble metal can be reduced, the cost of the catalyst will be greatly reduced, and the application prospect of noble metal catalyst will be improved. By combining noble metal with metal oxide nanotubes with confinement effect, and using a specific preparation method to load noble metal into the inside and outside of metal oxide nanotubes, the inner diameter of metal oxide nanotubes limits the growth of active metal in the tube, which can maximize the dispersion of active metal, and also hinders the aggregation of active center particles during the reaction, thereby improving the performance and sintering resistance of the catalyst. When applied to the preparation of methanol from CO2 hydrogenation, the confinement effect of metal oxide nanotubes makes the performance of the catalyst with noble metal loaded inside the tube better than that of the catalyst with noble metal loaded outside the tube, thereby optimizing the performance. SUMMARY

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary purpose of the present application is to provide a preparation method of metal oxide nanotube catalyst with confinement effect.

[0006] Another purpose of the present application is to provide the application of the above-mentioned metal oxide nanotube catalyst with confinement effect in the preparation of methanol from CO2 hydrogenation.

[0007] The application provides a metal oxide nanotube catalyst with a confinement effect, and a preparation method and application thereof, and is characterized in that the nanotube has a hollow tubular structure, the outer diameter of the nanotube is 20-300 nm, the wall thickness of the nanotube is 10-150 nm, the length of the nanotube is 30-500 nm, and the nanotube is composed of an active component and a carrier, wherein the active component is a noble metal, and the carrier is a metal oxide nanotube; the active component is located in the tube or outside the tube; the metal oxide nanotube has a confinement effect on the loaded active component; the content of the active component accounts for 0.1%-10% of the total mass of the catalyst, and the carrier accounts for 90%-99.9% of the total mass of the catalyst; the catalyst is applied to the preparation of methanol by CO2 hydrogenation; by changing the location of the active component on the carrier and using the confinement effect of the metal oxide nanotube, the performance of the catalyst is optimized, and the performance of the catalyst with the noble metal loaded in the tube is better than that of the catalyst with the noble metal loaded outside the tube; the metal oxide nanotube is one of CeO2 nanotube, TiO2 nanotube, Fe2O3 nanotube, MnO2 nanotube and Al2O3 nanotube, and the noble metal is one of Pd, Ir, Rh and Ru.

[0008] The method comprises the following steps:

[0009] (1) Preparation of metal oxide nanotube; a metal-containing precursor, a ligand and deionized water are mixed according to a mass ratio of (1-50):(1-100):(40-200), and then a hydrothermal reaction is carried out at 120-220 DEG C for 10-48 h; after the reaction, solid-liquid separation is carried out, the solid is collected, washed and dried, and then calcination is carried out at 300-750 DEG C for 2-6 h to obtain the metal oxide nanotube.

[0010] (2) Impregnation method for loading noble metal in the tube and outside the tube of the metal oxide nanotube: the noble metal precursor is loaded in the nanotube by vacuum-assisted stirring, and the noble metal precursor is loaded outside the nanotube by ordinary stirring impregnation method, and then dried and calcined at 300-700 DEG C for 2-6 h.

[0011] In one embodiment of the application, in step (1), the metal precursor is one of Ce(OH)CO3, titanium dioxide P25, FeCl3, KMnO4 and Al(NO3)3·9H2O, and the ligand solution is one or more of NaOH, NH4H2PO4, HCl, cetyltrimethylammonium bromide and urea.

[0012] In one embodiment of the present application, in step (2), the noble metal precursor is a salt or acid of noble metal Ir, Rh, Pd, Ru; and can be selected from any one or more of H2PdCl4, H2IrCl6, K3RhCl6, (NH4)RuCl6, Na2IrCl6; the noble metal accounts for 0.1% to 10% of the total mass of the catalyst, and the metal oxide nanotube accounts for 90% to 99.9% of the total mass of the catalyst.

[0013] The present application also provides the use of the metal oxide nanotube catalyst with a confinement effect according to any one of the preceding items in catalyzing the hydrogenation of carbon dioxide to produce methanol.

[0014] In one embodiment of the present application, the catalyst does not need to be reduced, and can be directly heated in the raw gas to start the reaction.

[0015] In one embodiment of the present application, the reaction conditions for the catalytic hydrogenation of carbon dioxide to produce methanol are as follows: CO2 / H2=1:1 to 5, specifically 1:3; the space velocity is 3 to 20 L / g cat / h, specifically 3 L / g cat / h; the reaction temperature is 100 to 500°C, specifically 240°C; and the reaction pressure is 0 to 5 MPa, specifically 3 MPa.

[0016] Compared with the disadvantages and deficiencies of the prior art, the present application has the following beneficial effects:

[0017] The present application can prepare the metal oxide nanotube with a confinement effect through a simple hydrothermal method, and then load the noble metal into the nanotube and outside the nanotube through an impregnation method. The present application combines the noble metal with the metal oxide nanotube with a confinement effect, and uses a specific preparation method to load the noble metal into the nanotube and outside the nanotube. The inner diameter of the metal oxide nanotube limits the growth of the active metal in the nanotube, which can maximize the dispersion. In the reaction process, the metal oxide nanotube can also hinder the aggregation of the active center particles, and improve the performance and sintering resistance of the catalyst. When applied to the hydrogenation of CO2 to produce methanol, the metal oxide nanotube with a confinement effect makes the performance of the catalyst with the noble metal loaded in the nanotube better than the performance of the catalyst with the noble metal loaded outside the nanotube, thereby optimizing the performance. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 a is one of the transmission electron microscope images of the catalyst prepared in Example 1. Figure 1 b is the second transmission electron microscope image of the catalyst prepared in Example 1.

[0019] Figure 2 a is one of the transmission electron microscope images of the catalyst prepared in Example 2. Figure 2b is the second transmission electron micrograph of the catalyst prepared in Example 2. DETAILED DESCRIPTION

[0020] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0021] Catalyst performance evaluation: the carbon dioxide hydrogenation reactions in the following examples were carried out in a stainless steel fixed bed reactor, and the specific catalyst performance test method is as follows:

[0022] (1) 0.2 g of metal oxide nanotube catalyst was mixed with 0.4 g of quartz sand and placed in the reactor.

[0023] (2) The reaction gas (H2 / CO2=3 / 1) was flowed through the catalyst bed at a flow rate of 10 mL / min, the reaction pressure was gradually increased to 3 MPa set pressure, and the reaction temperature was gradually increased to the set temperature of 240℃ to start the reaction.

[0024] (3) The products were directly introduced into the gas chromatograph for detection and analysis. The gas chromatograph is equipped with TCD and FID detectors, the TCD detector uses high-purity argon as the carrier gas, and uses a sieve 5A stainless steel chromatographic column to separate H2, N2, CO2, CO, CH4 and other permanent gases. The FID detector uses high-purity N2 as the carrier gas, and uses two FID capillary columns of HP-Innowax and HP-AL / S, HP-AL / S is used to separate C1-C5 hydrocarbons; HP-Innowax is used to separate C 6+ alkanes, aromatic hydrocarbons and oxygen-containing carbon compounds.

[0025] CO2 conversion rate = (moles of inlet CO2 - moles of outlet CO2) / moles of inlet CO2 x 100%;

[0026] Product selectivity = (moles of outlet product x number of carbon atoms in product molecule) / (moles of inlet CO2 - moles of outlet CO2) x 100%.

[0027] The loading amount involved in the present application refers to the mass fraction of the content of the active component metal in the total mass of the catalyst.

[0028] Example 1

[0029] (1) 4.8 g of sodium hydroxide was dissolved in 80 ml of deionized water, 0.1 g of Ce(OH)CO3 precursor was added, and after uniform mixing, it was placed in a 200 ml polytetrafluoroethylene lined stainless steel reaction kettle for hydrothermal reaction at 120℃ for 24 h, cooled, washed and dried, and calcined at 450℃ for 4 h to obtain CeO2 nanotubes.

[0030] (2) The Pd was loaded in the CeO2 nanotube by vacuum assisted impregnation method. 1 g of CeO2 nanotube was placed in a three-necked flask, 0.0168 g of H2PdCl4 was dissolved in 10 ml of water and placed in a separatory funnel, the whole device was vacuumed for 30 min, the separatory funnel was opened, the solution and the CeO2 nanotube were mixed, stirred for 2 h, dried, and calcined at 550 °C for 5 h. Figure 1 a and Figure 1 b are transmission electron micrographs of the catalyst prepared in this example, from Figure 1 a, it can be seen that the support ceria is a hollow nanotube structure, the outer diameter of the tube is 48 nm, and the inner diameter of the tube is 16 nm. From Figure 1 b, it can be seen that the Pd particles are loaded in the tube of the CeO2 nanotube.

[0031] Activity test: The catalytic activity of the prepared catalyst was evaluated in a fixed bed reactor according to the aforementioned "Catalyst performance evaluation", and the activity test results are shown in Table 1.

[0032] Example 2

[0033] (1) The same as Example 1;

[0034] (2) The Pd was loaded on the outside of the CeO2 nanotube by impregnation method. 0.0168 g of H2PdCl4 was dissolved in 10 ml of water, 1 g of CeO2 nanotube was added and stirred for 2 h, dried, and calcined at 550 °C for 5 h. Figure 2 a and Figure 2 b are transmission electron micrographs of the catalyst prepared in this example, from Figure 2 a, it can be seen that the support ceria is a hollow nanotube structure, the outer diameter of the tube is 48 nm, and the inner diameter of the tube is 16 nm. From Figure 2 b, it can be seen that the Pd particles are loaded on the outside of the CeO2 nanotube.

[0035] Activity test: The catalytic activity of the prepared catalyst was evaluated in a fixed bed reactor according to the aforementioned "Catalyst performance evaluation", and the activity test results are shown in Table 1.

[0036] Example 3

[0037] (1) 48 g of NaOH was dissolved in 120 ml of water, 1 g of titanium dioxide P 25 was added and stirred for 30 min, the mixed solution was transferred to a 200 ml polytetrafluoroethylene lined stainless steel reaction kettle, and then subjected to hydrothermal treatment at 180 °C for 48 h, cooled, washed, dried, and calcined at 600 °C for 2 h to obtain TiO2 nanotubes;

[0038] (2) Pd was loaded on the outer surface of TiO2 nanotubes by impregnation method, 0.0168 g H2PdCl4 was dissolved in 10 ml water and added into 1 g TiO2 nanotubes, stirred for 2 h, dried and calcined at 550 °C for 5 h.

[0039] Activity test: The prepared catalyst was evaluated for catalytic activity in a fixed bed reactor according to the aforementioned "Catalyst performance evaluation", and the activity test results are shown in Table 1.

[0040] Example 4

[0041] (1) The same as Example 3;

[0042] (2) Pd was loaded on the outer surface of TiO2 nanotubes by impregnation method, 0.0168 g H2PdCl4 was dissolved in 10 ml water and added into 1 g TiO2 nanotubes, stirred for 2 h, dried and calcined at 550 °C for 5 h.

[0043] Activity test: The prepared catalyst was evaluated for catalytic activity in a fixed bed reactor according to the aforementioned "Catalyst performance evaluation", and the activity test results are shown in Table 1.

[0044] Example 5

[0045] (1) 5.1 g FeCl3, 1.3 g NH4H2PO4 and 80 ml ultrapure water were mixed uniformly and placed in a 200 ml polytetrafluoroethylene-lined stainless steel reaction kettle, then hydrothermally treated at 220 °C for 48 h, cooled, washed, dried and calcined at 550 °C for 5 h to obtain Fe2O3 nanotubes.

[0046] (2) Pd was loaded on the outer surface of TiO2 nanotubes by impregnation method, 0.0168 g H2PdCl4 was dissolved in 10 ml water and added into 1 g TiO2 nanotubes, stirred for 2 h, dried and calcined at 550 °C for 5 h.

[0047] Activity test: The prepared catalyst was evaluated for catalytic activity in a fixed bed reactor according to the aforementioned "Catalyst performance evaluation", and the activity test results are shown in Table 1.

[0048] Example 6

[0049] (1) The same as Example 5;

[0050] (2) Impregnation method was used to load Pd on the outer surface of Fe2O3 nanotubes. 0.0168 g of H2PdCl4 was dissolved in 10 ml of water, and then added to 1 g of Fe2O3 nanotubes and stirred for 2 h. After drying, the mixture was calcined at 550 °C for 5 h.

[0051] Activity test: The prepared catalyst was evaluated for catalytic activity in a fixed bed reactor according to the aforementioned "Catalyst performance evaluation", and the activity test results are shown in Table 1.

[0052] Example 7

[0053] (1) 1.32 g of KMnO4, 1.77 g of concentrated HCl and 150 ml of ultrapure water were mixed and stirred uniformly, and then placed in a 200 ml polytetrafluoroethylene-lined stainless steel reaction kettle. Hydrothermal treatment was then carried out at 150 °C for 10 h, and then the mixture was cooled, washed and dried. The mixture was then calcined at 550 °C for 5 h to obtain MnO2 nanotubes.

[0054] (2) Vacuum-assisted stirring impregnation method was used to load Pd on the inner surface of MnO2 nanotubes. 1 g of MnO2 nanotubes was placed in a three-necked flask, 0.0168 g of H2PdCl4 was dissolved in 10 ml of water and placed in a separatory funnel, the whole device was vacuumed for 30 min, the separatory funnel was opened, the solution and MnO2 nanotubes were mixed, stirred for 2 h, dried, and calcined at 550 °C for 5 h.

[0055] Activity test: The prepared catalyst was evaluated for catalytic activity in a fixed bed reactor according to the aforementioned "Catalyst performance evaluation", and the activity test results are shown in Table 1.

[0056] Example 8

[0057] (1) The same as Example 7;

[0058] (2) Impregnation method was used to load Pd on the outer surface of MnO2 nanotubes. 0.0168 g of H2PdCl4 was dissolved in 10 ml of water, and then added to 1 g of MnO2 nanotubes and stirred for 2 h. After drying, the mixture was calcined at 550 °C for 5 h.

[0059] Activity test: The prepared catalyst was evaluated for catalytic activity in a fixed bed reactor according to the aforementioned "Catalyst performance evaluation", and the activity test results are shown in Table 1.

[0060] Example 9

[0061] (1) 7.504 g of Al (NO3) 3·9H2O, 7.288 g of hexadecyl trimethyl ammonium bromide, 6.004 g of CO (NH2) 2 and 144 ml of ultrapure water were mixed and stirred uniformly, and then placed in a 200 ml polytetrafluoroethylene-lined stainless steel reaction kettle. Hydrothermal treatment was then carried out at 125 °C for 15 h, and then the mixture was cooled, washed and dried. The mixture was then calcined at 550 °C for 5 h to obtain Al2O3 nanotubes.

[0062] (2) Vacuum assisted impregnation method was used to load Pd into the Al2O3 nanotubes, 1 g of Al2O3 nanotubes was placed in a three-necked flask, 0.0168 g of H2PdCl4 was dissolved in 10 ml of water and placed in a separatory funnel, the whole device was vacuumed for 30 min, the separatory funnel was opened, the solution and the Al2O3 nanotubes were mixed, stirred for 2 h, dried, and calcined at 550 °C for 5 h.

[0063] Activity test: the prepared catalysts were evaluated for catalytic activity in a fixed bed reactor according to the aforementioned "catalyst performance evaluation", and the activity test results are shown in Table 1.

[0064] Example 10

[0065] (1) The same as Example 9;

[0066] (2) Impregnation method was used to load Pd outside the Al2O3 nanotubes, 0.0168 g of H2PdCl4 was dissolved in 10 ml of water, 1 g of Al2O3 nanotubes was added and stirred for 2 h, dried, and calcined at 550 °C for 5 h.

[0067] Activity test: the prepared catalysts were evaluated for catalytic activity in a fixed bed reactor according to the aforementioned "catalyst performance evaluation", and the activity test results are shown in Table 1.

[0068] The results of the catalytic reaction are shown in Table 1, which shows that in the reaction of CO2 hydrogenation to methanol, for the same type of metal oxide nanotubes, whether it is the conversion of CO2 or the selectivity of methanol, the performance of the catalyst with Pd loaded inside the tube is higher than that of the catalyst with Pd loaded outside the tube, indicating that the metal oxide nanotube has a confinement effect on the noble metal loaded inside the tube, and the confinement effect affects the metal-support interaction. The inner diameter of the metal oxide nanotube limits the growth of the active metal inside the tube, which can maximize the dispersion, and also hinders the aggregation of active center particles during the reaction, thereby improving the performance and sintering resistance of the catalyst.

[0069] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0070] Table 1 Reaction performance of different catalysts in examples

[0071]

Claims

1. The application of a metal oxide nanotube catalyst with confinement effect in the catalytic hydrogenation of carbon dioxide to methanol, characterized in that, The reaction conditions for the catalytic hydrogenation of carbon dioxide to methanol are: a volume ratio of CO2 / H2 of 1:1 to 5, and a space velocity of 3 to 20 L / g. cat / h, reaction temperature is 100~500℃, reaction pressure is 0~5MPa; The catalyst has a hollow nanotube structure with an outer diameter of 20–300 nm, a wall thickness of 10–150 nm, and a length of 30–500 nm. It consists of an active component and a support, wherein the active component is a noble metal, and the support is a metal oxide nanotube. The active component is located inside the nanotube on the support. The active component accounts for 0.1%–10% of the total mass of the catalyst, and the support accounts for 90%–99.9% of the total mass of the catalyst. The nanotube is either MnO2 nanotube or Al2O3 nanotube, and the noble metal is either Pd, Ir, Rh, or Ru. The catalyst preparation method includes the following steps: (1) Preparation of metal oxide nanotubes: The metal precursor, ligand and deionized water were mixed in a mass ratio of (1-50):(1-100):(40-200) and subjected to hydrothermal reaction at 125-150℃ for 10-15 h. After the reaction, the solid and liquid were separated, the solid was collected, washed and dried, and calcined at 300-750℃ for 2-6 h to obtain metal oxide nanotubes. When the metal precursor was KMnO4, the ligand was concentrated HCl. When the metal precursor was Al(NO3)3·9H2O, the ligands were hexadecyltrimethylammonium bromide and urea. (2) The noble metal precursor was loaded into the nanotube by vacuum-assisted stirring, then dried and calcined at 300-700℃ for 2-6 hours. Precious metal precursors are salts or acids of precious metals Ir, Rh, Pd, and Ru.

2. The application according to claim 1, characterized in that: The noble metal precursor is selected from any one or more of the following: H2PdCl4, H2IrCl6, K3RhCl6, (NH4)RuCl6, Na2IrCl6.

Images