Titanium dioxide nanotube confined catalysts for dry methane reforming, methods of making and using the same

Abstract

The application discloses a titania nanotube confined catalyst for dry reforming of methane and a preparation method and application thereof. The catalyst is a rare earth element modified titania nanotube confined transition metal element catalyst, and transition elements are used as an active phase. The content of the transition elements is 1-10% and preferably 1-5% based on the weight of the dry reforming catalyst of methane, and the content of the rare earth elements is 1-5%. The catalyst solves the problems of activity reduction and poor stability of the dry reforming catalyst of methane in the prior art due to easy carbon deposition.

Description

Technical fields:

[0001] This invention relates to the field of catalytic materials technology, specifically to a titanium dioxide nanotube confined catalyst for methane dry reforming, its preparation method, and its application. Background technology:

[0002] Among various carbon dioxide conversion and utilization schemes, dry reforming of methane (DRM) to syngas is one of the important methods. However, during the reaction, a large amount of carbon deposits are generated on the catalyst surface due to the coking reaction, which reduces the catalyst stability or causes deactivation. Furthermore, studies have shown that the main reactions in dry reforming can only occur under high-temperature conditions, and are only thermodynamically feasible at temperatures above 918 K. Therefore, high requirements are placed on the materials of the reaction equipment. Among non-precious metal catalysts, transition metals such as Ni and Co have exhibited catalytic performance comparable to precious metals and have therefore been widely studied, but their resistance to carbon deposition is relatively poor. Therefore, improving the resistance to carbon deposition of non-precious metal catalysts and reducing the reaction temperature have become the focus of research in thermocatalytic dry reforming of methane in recent years. Summary of the Invention:

[0003] The purpose of this invention is to provide a titanium dioxide nanotube confined catalyst for methane dry reforming, its preparation method and application, which solves the problems of reduced activity and poor stability of existing methane dry reforming catalysts due to easy carbon deposition.

[0004] This invention is achieved through the following technical solutions:

[0005] A titanium dioxide nanotube confined catalyst for methane dry reforming uses transition metal elements as the active phase, which are titanium dioxide nanotubes confined with rare earth metal elements. Based on the weight of the methane dry reforming catalyst, the content of transition metal elements is 1-10%, preferably 1-5%, and the content of rare earth elements is 1-5%.

[0006] The transition metal is any one or more of Ni, Fe, Co, Ru, or Cu; preferably, the transition metal is at least one of Ni and Co.

[0007] The rare earth metal includes any one or more of La, Ce, Y, Pr, and Nd; preferably, the rare earth metal is at least one of La and Ce.

[0008] The preparation method of the titanium dioxide nanotube confined catalyst for methane dry reforming includes the following steps:

[0009] (a) Dissolve transition metal precursors and rare earth metal precursors in a solvent to form a mixed solution, add titanium dioxide nanotube carrier, confine under vacuum of -0.01 to -0.5 MPa, and stir thoroughly until homogeneous.

[0010] (b) The mixture obtained in step (a) is dried and then reduced at 300-500°C under a reducing atmosphere to obtain an anti-sintering methane dry reforming catalyst.

[0011] In step (a), the transition metal precursor is at least one of the nitrate, sulfate, chloride or acetate of the transition metal; the rare earth metal precursor is at least one of the nitrate, sulfate, chloride or acetate of the rare earth metal; and the solvent includes any one or more of water, ethanol, acetone and isopropanol.

[0012] Step (b) The reducing atmosphere includes either H2 or CO, the gas flow rate is 10-100 mL / min, and the reduction time is 1-20 h.

[0013] This invention also protects the application of the titanium dioxide nanotube confined catalyst for methane dry reforming in the preparation of syngas from methane dry reforming, comprising the following steps: contacting methane and carbon dioxide with the catalyst, the reaction being carried out in a fixed-bed reactor at a reaction temperature of 600-700℃, a molar ratio of methane to carbon dioxide of 0.5-1.5:1, and a gas hourly space velocity of 3000-400000 mL·g. -1 ·h -1 .

[0014] The beneficial effects of this invention are as follows:

[0015] 1) The addition of rare earth elements and the confinement effect of titanium dioxide nanotubes make the distribution of transition metal nanoparticles more uniform. It has a unique synergistic effect of electron-deficient inside titanium dioxide nanotubes and electron-rich outside, providing more active sites for CO2 activation and carbon oxidation. At the same time, the reaction shows good stability and overcomes the disadvantages of low activity and easy carbon deposition of non-precious metal catalysts.

[0016] 2) The catalyst preparation method described in this application has the advantages of simple process, easy operation and low cost. Attached image description:

[0017] Figure 1 These are the activity evaluation results of the catalysts used in the dry reforming of methane in Examples 1-3 and Comparative Examples 1-3.

[0018] Figure 2 These are the stability evaluation results of the catalysts used in Example 1 and Comparative Example 1 for the dry reforming of methane. Detailed implementation method:

[0019] The following is a further description of the invention, but not a limitation thereof.

[0020] Example 1: A method for preparing a titanium dioxide nanotube confined catalyst for methane dry reforming

[0021] The specific steps are as follows:

[0022] 0.14 g of nickel nitrate and 0.27 g of cerium nitrate were added to 10 mL of deionized water and stirred for 30 min. Then, 1 g of titanium dioxide nanotubes were added to the mixture and kept under a vacuum of -0.1 MPa for 2 h. After that, the mixture was placed in an oven at 120 °C for 6 h and then reduced at 400 °C under H2 atmosphere for 8 h to obtain Ce-modified titanium dioxide nanotube confined Ni material F1.

[0023] The above catalyst is applied to the dry reforming of methane, and the specific application method is as follows:

[0024] The reaction was evaluated using a laboratory-scale fixed-bed catalytic oxidation reactor. 1 g of material F1 was used as the catalyst. The gas mixture consisted of CH4:CO2:Ar at a ratio of 1:1:18, with a flow rate of 20 ml / min. At 650 °C and atmospheric pressure, a conversion rate of 93.3% was achieved. After 100 h, the reaction exhibited good stability. (See [reference needed]). Figure 2 This overcomes the shortcomings of non-precious metal catalysts, such as low activity and easy carbon deposition.

[0025] Example 2: A method for preparing a nanotube-confined catalyst for methane dry reforming

[0026] The specific steps are as follows:

[0027] 0.12 g of nickel chloride and 0.19 g of lanthanum chloride were added to 10 mL of anhydrous ethanol and stirred for 30 min. Then, 1 g of titanium dioxide nanotubes were added to the mixture and kept under a vacuum of -0.1 MPa for 2 h. After that, the mixture was placed in an oven at 120 °C for 6 h and then reduced at 500 °C under a CO atmosphere for 8 h to obtain the La-modified titanium dioxide nanotube confined Ni material F2.

[0028] The above catalyst is applied to the dry reforming of methane, and the specific application method is as follows:

[0029] The reaction was evaluated using a laboratory-scale catalytic oxidation fixed-bed reactor. 1g of material F2 was used as the catalyst. The gas ratio of CH4:CO2:Ar was 1:1:18, and the gas flow rate was 20ml / min. Under normal pressure and temperature conditions of 650℃, a conversion rate of 89.7% was achieved. After 100h of reaction, the reaction showed good stability.

[0030] Example 3: A method for preparing a nanotube-confined catalyst for methane dry reforming

[0031] The specific steps are as follows:

[0032] 0.14 g of cobalt chloride and 0.23 g of cerium chloride were added to 10 mL of anhydrous ethanol and stirred for 30 min. Then, 1 g of titanium dioxide nanotubes were added to the mixture and kept under a vacuum of -0.1 MPa for 2 h. After that, the mixture was placed in an oven at 120 °C for 6 h and then reduced at 500 °C under a CO atmosphere for 8 h to obtain the Ce-modified titanium dioxide nanotube confined Co material F3.

[0033] The above catalyst is applied to the dry reforming of methane, and the specific application method is as follows:

[0034] The reaction was evaluated using a laboratory-scale catalytic oxidation fixed-bed reactor. 1 g of material F3 was used as the catalyst. The gas ratio of CH4:CO2:Ar was 1:1:18, and the gas flow rate was 20 ml / min. Under normal pressure and temperature conditions of 650 °C, a conversion rate of 73.8% was achieved. After 100 h of reaction, the reaction showed good stability.

[0035] Comparative Example 1:

[0036] The specific steps are as follows: 0.14 g of nickel chloride is added to 10 mL of anhydrous ethanol and stirred for 30 min. Then, 1 g of titanium dioxide nanotubes is added to the mixture, and the mixture is kept under a vacuum of -0.1 MPa for 2 h. After that, it is placed in an oven at 120 °C for 6 h and then reduced at 500 °C under a CO atmosphere for 8 h to obtain Ni-confined material F4. The specific steps are as follows:

[0037] The above catalyst is applied to the dry reforming of methane, and the specific application method is as follows:

[0038] The experiment was evaluated using a laboratory-scale catalytic oxidation fixed-bed reactor. 1g of material F3 was used as the catalyst. The gas ratio of CH4:CO2:Ar was 1:1:18, and the gas flow rate was 20ml / min. Under normal pressure and temperature conditions of 650℃, a conversion rate of 31.2% was achieved. However, the reaction stability was poor after 100h.

[0039] Comparative Example 2:

[0040] The specific steps are as follows:

[0041] 0.14 g of cobalt chloride and 0.23 g of cerium chloride were added to 10 mL of anhydrous ethanol and stirred for 30 min. Then, 1 g of titanium dioxide nanotube support was added and stirred at 80 °C for 12 h. After that, the mixture was placed in an oven at 120 °C for 6 h and then reduced at 500 °C under H2 atmosphere for 8 h to obtain the Ce-modified titanium dioxide nanotube Co-supported material F5.

[0042] The above catalyst is applied to the dry reforming of methane, and the specific application method is as follows:

[0043] The experiment was evaluated using a laboratory-scale catalytic oxidation fixed-bed reactor. 1g of material F3 was used as the catalyst. The gas ratio of CH4:CO2:Ar was 1:1:18, and the gas flow rate was 20ml / min. Under normal pressure and temperature conditions of 650℃, a conversion rate of 16.6% was achieved. However, the reaction stability was poor after 100h.

[0044] Comparative Example 3:

[0045] 0.27 g of cerium nitrate was added to 10 mL of deionized water and stirred for 30 min. Then, 1 g of titanium dioxide nanotubes were added to the substrate and kept under a vacuum of -0.1 MPa for 2 h. After that, the substrate was placed in an oven at 120 °C for 6 h and then reduced at 400 °C under H2 atmosphere for 8 h to obtain Ce-modified titanium dioxide nanotube confinement material F6.

[0046] The above catalyst is applied to the dry reforming of methane, and the specific application method is as follows:

[0047] The experiment was evaluated using a laboratory-scale catalytic oxidation fixed-bed reactor. 1g of material F6 was used as the catalyst. The gas ratio of CH4:CO2:Ar was 1:1:18, and the gas flow rate was 20ml / min. Under normal pressure and temperature conditions of 650℃, a conversion rate of 0.43% was achieved. However, the reaction stability was poor after 100h.

Claims

1. A titanium dioxide nanotube confined catalyst for dry reforming of methane, characterized in that, Using transition metal elements as the active phase, the titanium dioxide nanotubes are modified with rare earth metal elements to confine the transition metal elements. Based on the weight of the methane dry reforming catalyst, the content of the transition metal elements is 1-10%, and the content of rare earth metal elements is 1-5%. The transition metal elements are any one or more of Ni, Fe, Co, Ru, or Cu. The rare earth metal elements include any one or more of La, Ce, Y, Pr, and Nd. The preparation method of the methane dry reforming titanium dioxide nanotube confined catalyst includes the following steps: (a) Dissolve transition metal precursors and rare earth metal precursors in a solvent to form a mixed solution, add titanium dioxide nanotube carrier, confine under vacuum of -0.01 to -0.5 MPa, and stir thoroughly until homogeneous. (b) The mixture obtained in step (a) is dried and then reduced at 300-500°C under a reducing atmosphere to obtain an anti-sintering methane dry reforming catalyst.

2. The titanium dioxide nanotube confined catalyst according to claim 1, characterized in that, The content of transition metal elements is 1-5%.

3. The titanium dioxide nanotube confined catalyst according to claim 1, characterized in that, In step (a), the transition metal precursor is at least one of the nitrate, sulfate, chloride or acetate of the transition metal element; the rare earth metal precursor is at least one of the nitrate, sulfate, chloride or acetate of the rare earth metal element; and the solvent includes any one or more of water, ethanol, acetone and isopropanol.

4. The titanium dioxide nanotube confined catalyst according to claim 1, characterized in that, Step (b) The reducing atmosphere includes either H2 or CO, the gas flow rate is 10~100 mL / min, and the reduction time is 1~20 h.

5. The application of the titanium dioxide nanotube confined catalyst for methane dry reforming according to claim 1 in the preparation of syngas from methane dry reforming, characterized in that, The reaction includes the following steps: contacting methane and carbon dioxide with the catalyst in a fixed-bed reactor at a temperature of 600-700°C, a molar ratio of methane to carbon dioxide of 0.5-1.5:1, and a gas hourly space velocity of 3000-400000 mL·g. -1 ·h -1 .

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