A low-load, high-activity short-chain alkane catalytic combustion catalyst and its preparation method

Abstract

The present invention belongs to the field of environmentally friendly catalytic materials, specifically relating to a low-load, high-activity catalyst for the catalytic combustion of short-chain alkanes and its preparation method. The catalyst preparation process of the present invention includes four steps: first, ammonium cerium nitrate is prepared into cerium oxide gel using a gel preparation technique; second, the cerium oxide gel is prepared into nano-cerium oxide using a hydrothermal method; third, the nano-cerium oxide doped with precious metal salts is prepared into CeO2@Pd(Pt) gel using a gel preparation technique; and finally, the CeO2@Pd(Pt) gel is dissolved in aluminum sol using a ball milling method, coated on a cordierite surface, and then dried and calcined to obtain a CeO2@Pd(Pt) / Al2O3+cordierite catalyst. The catalyst prepared by the present invention exhibits higher catalytic activity and stability in the catalytic combustion reaction of short-chain alkanes, reflecting the characteristics of low load and high activity.

Description

Technical Field

[0001] The present invention belongs to the field of environmentally friendly catalytic materials, and in particular relates to a low-load, high-activity short-chain alkane catalytic combustion catalyst and a preparation method thereof. Background Art

[0002] Catalytic combustion technology is considered to be one of the most flexible and efficient technologies for the treatment of low-concentration short-chain alkanes due to its advantages such as small equipment footprint, low operating costs, flameless combustion, low reaction temperature, high treatment efficiency, large treatment volume, and no secondary pollution. Precious metal catalysts have the advantages of high activity, low resistance and low pressure drop, making them the preferred catalysts for the catalytic combustion of short-chain alkanes. However, the disadvantages of small reserves, high prices, volatility and easy sintering of precious metals have limited the widespread use of precious metal catalysts. Therefore, the development of low-loading, high-activity precious metal catalysts remains the focus of catalytic combustion catalyst research.

[0003] Currently, precious metal catalytic combustion catalysts are generally prepared by loading precious metals such as Pt or Pd onto a composite oxide coating supported on cordierite. Invention patent CN202210404645.6 discloses a catalyst for the catalytic combustion of VOCs, its preparation method, and its application. The catalyst uses a composite oxide of sodium phosphite-modified aluminum oxide and cerium oxide as a carrier, on which 1% precious metal Pt is loaded, resulting in a catalytic combustion catalyst with excellent catalytic activity. Invention patent CN201410368084.4 discloses a monolithic catalyst for the catalytic combustion of methane and its preparation method. The catalyst comprises a coating of aluminum oxide, cerium oxide, and yttrium oxide on cordierite, on which precious metal Pd is loaded. The Pd loading is 0.05-0.2% of the cordierite. The resulting methane catalytic combustion catalyst exhibits excellent catalytic activity. While these catalysts exhibit excellent catalytic activity, the actual amount of precious metal used is relatively large, making industrial production unsuitable.

[0004] This invention provides a highly efficient precious metal catalyst for the catalytic combustion of short-chain alkanes and its preparation method. First, nano-CeO2 with secondary oxygen vacancies and precious metal clusters are prepared using a gel method. The nano-CeO2 and precious metal clusters are then coated onto a cordierite surface along with dissolved aluminum to produce the final catalyst. The prepared catalyst exhibits enhanced catalytic efficiency for the catalytic combustion of short-chain alkanes. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-load, high-activity catalyst for the catalytic combustion of short-chain alkanes and a preparation method thereof. The obtained CeO2@Pt(Pd) / Al2O3+cordierite catalyst has a good catalytic synergistic effect and exhibits good catalytic efficiency for the catalytic combustion reaction of short-chain alkanes. The specific technical scheme is as follows:

[0006] The method for preparing the low-load, high-activity short-chain alkane catalytic combustion catalyst comprises the following steps:

[0007] (1) Preparation of cerium oxide gel: Dissolve ammonium cerium nitrate in a certain amount of deionized water, add 0.5-3g urea and 2-6g starch, and stir at a constant temperature of 120-160°C to prepare cerium oxide gel.

[0008] (2) Preparation of Nano-cerium Oxide: The cerium oxide gel is placed in a hydrothermal reactor and hydroheated at 160-200°C for 18-36 hours to completely hydrolyze the starch and obtain nano-cerium oxide.

[0009] (3) Preparation of nano-CeO2@Pt(Pd) active metal precursor: A certain amount of Pd or Pt metal salt is dissolved in nano-CeO2, and then 2-6g of starch is added and stirred at a constant temperature of 120-160℃ to prepare CeO2@Pd(Pt) gel.

[0010] (4) Catalyst preparation. CeO2@Pd(Pt) gel was mixed with commercial aluminum sol (Shandong Xinzhuoyuan Chemical Co., Ltd., solid content 24%, pH 2.8), ball milled at 30-60 Hz for 30-90 min, and then coated on the cordierite surface. The mixture was dried at 120°C for 4 h and calcined for 4 h to obtain CeO2@Pd(Pt) / Al2O3+cordierite catalyst.

[0011] Furthermore, the starch in step (1) is one or more of sweet potato starch, potato starch, wheat starch, corn starch, and pea starch.

[0012] Furthermore, the precious metal salt Pd (Pt) added in step (3) is one or more of PdCl2, H2PtCl6 solution; the precious metal content in Pd (Pt) is 150, 200g precious metal / m 3 Iolite.

[0013] Furthermore, the calcination temperature in step (4) is any one of 800, 1000, and 1200°C.

[0014] Advantages of the catalyst prepared by the method described in the present invention:

[0015] On the one hand, it has the advantage of nano-cerium oxide auxiliary oxygen vacancies, and on the other hand, there is a catalytic synergistic effect between Pt (Pd) and CeO2, and the prepared catalyst surface has a higher catalytic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 N2 adsorption-desorption isotherms of the catalysts obtained in Examples 1-7 and Comparative Example;

[0017] Figure 2 The pore size distribution diagram of the catalysts obtained in Examples 1-7 and the comparative example;

[0018] Figure 3 The XRD spectra of the catalysts obtained in Examples 1-7 and Comparative Example are shown.

[0019] Figure 4 This is the SEM image of the catalyst obtained in Example. DETAILED DESCRIPTION

[0020] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0021] A low-load, high-activity short-chain alkane catalytic combustion catalyst, the preparation method of which comprises the following steps:

[0022] (1) Dissolve 17.88 g of ammonium cerium nitrate in 40 g of deionized water, add 2 g of urea and 4 g of starch, and stir in an oil bath at 150°C for 15 min to prepare cerium oxide gel;

[0023] (2) placing the cerium oxide gel in a hydrothermal reactor and hydroheating at 180° C. for 24 h to completely hydrolyze the starch to obtain nano-cerium oxide;

[0024] (3) A certain amount of Pd or Pt metal salt was dissolved in nano-CeO2, and then 4 g of starch was added and stirred at 150 °C for 15 min to prepare CeO2@Pd(Pt) gel;

[0025] (4) CeO2@Pd(Pt) gel was mixed with 80 g of commercial aluminum sol (Shandong Xinzhuoyuan Chemical Co., Ltd., solid content of 24%, pH of 2.8), ball milled at a frequency of 30 Hz for 60 min in a ball mill, and coated on the surface of cordierite after thorough ball milling. The mixture was dried at 120 °C for 4 h and calcined at a certain temperature for 4 h to obtain CeO2@Pd(Pt) / Al2O3+cordierite catalyst.

[0026] 2.0 g of the catalyst prepared above was loaded into the reaction tube of a fixed bed reactor, and a reaction gas composed of 0.53% n-butane and 99.47% air was introduced at a reaction space velocity (GHSV) of 22620 mL g -1 h -1 The reaction temperature is 200-500°C, the heating rate is 2°C / min, the reaction pressure is normal pressure, and the VOCs gas concentration at the inlet and outlet is continuously detected using a gas chromatograph equipped with an FID detector.

[0027] Example 1

[0028] (1) Dissolve 17.88 g of ammonium cerium nitrate in 40 g of deionized water, slowly add 2 g of urea and 4 g of wheat starch under magnetic stirring, and then place in a 150°C oil bath and stir at constant temperature for 15 min to prepare cerium oxide gel;

[0029] (2) placing the cerium oxide gel in a hydrothermal reactor and hydroheating it at 180° C. for 24 h to completely hydrolyze the wheat starch to obtain nano-cerium oxide;

[0030] (3) The precious metal content is 2.64×10 -3 The PdCl2 solution of gPd was added to nano-CeO2, and then 4g starch was added and stirred at 150℃ for 15min to prepare CeO2@Pd(Pt) gel;

[0031] (4) CeO2@Pd(Pt) gel was mixed with 80 g of commercial aluminum sol (Shandong Xinzhuoyuan Chemical Co., Ltd., solid content 24%, pH 2.8) and ball milled in a ball mill at 30 Hz for 60 min. After thorough ball milling, the gel was coated onto a spherical plate with a length, width, and height of 50, 22, and 12 mm (volume 13.2 × 10 -6 m 3 ) on the cordierite surface, dried at 120℃ for 4h and calcined at 800℃ for 4h to obtain CeO2@Pd(Pt) / Al2O3+cordierite catalyst, named Pd-1.

[0032] (5) Pd-1 catalyst was ground into 20-40 mesh size, 2 g of the catalyst was loaded into the constant temperature section of the fixed bed reactor, and air was introduced under normal pressure at 500°C for activation for 30 min. After cooling to 200°C, a reaction gas composed of 0.53% n-butane and 99.47% air was introduced at a reaction space velocity of 22620 mL·g -1 ·h -1 The temperature was raised to 500°C at a heating rate of 0.5°C / min, and the n-butane concentration at the inlet and outlet was continuously detected using a gas chromatograph equipped with an FID detector, and the n-butane conversion rate was calculated based on the chromatographic peak area.

[0033] Example 2

[0034] The starch in step (1) was replaced with pea starch, and the other operations were the same as in Example 1. The obtained material was named Pd-2.

[0035] Example 3

[0036] The calcination temperature in step (4) was adjusted to 1000° C., and the other operations were the same as in Example 1. The obtained material was named Pd-3.

[0037] Example 4

[0038] The coating and baking temperature in step (4) was adjusted to 1200° C., and the other operations were the same as in Example 1. The obtained material was named Pd-4.

[0039] Example 5

[0040] The Pd content in step (3) was adjusted to 150 gPd / m 3 Cordierite, and the calcination temperature in step (4) was adjusted to 1000°C. Other operations were the same as in Example 1. The obtained material was named Pd-5.

[0041] Example 6

[0042] Replace PdCl2 in step (3) with H2PtCl6, with a precious metal content of 200gPt / m 3 Cordierite, and the calcination temperature in step (4) was adjusted to 1000°C. Other operations were the same as in Example 1. The obtained material was named Pt-1.

[0043] Example 7

[0044] Replace PdCl2 in step (3) with H2PtCl6 and adjust the precious metal content to 150gPt / m 3 Cordierite, and the calcination temperature in step (4) was adjusted to 1000°C. Other operations were the same as in Example 1. The obtained material was named Pt-2.

[0045] Comparative Example 1

[0046] The Pt / (Al2O3+CeO2) / cordierite produced by Shandong Xinjing Environmental Technology Co., Ltd. was used as a comparison sample. The actual loading of precious metals was 200gPt / m 3 Cordierite, named Pt-0.

[0047] The physical properties of the prepared catalysts are shown in Figure 1-4 And Table 1.

[0048] Table 1 Catalyst physical properties

[0049]

[0050] Note: The grain size is calculated by the Scherrer formula based on the characteristic diffraction peak corresponding to the (200) crystal plane of CeO2 cubic fluorite structure.

[0051] The reaction activity of the catalyst was evaluated using n-butane. The activity evaluation results of the catalyst are shown in Table 2.

[0052] Table 2 Catalyst activity parameters

[0053] Catalysts <![CDATA[T 10％ (℃)]]> <![CDATA[T 99％ (℃)]]> Pd-1 350 458 Pd-2 356 470 Pd-3 290 368 Pd-4 362 65％ Pd-5 314 404 Pt-1 278 386 Pt-2 308 416 Pt-0 344 464

[0054] Note: T 10％ : Reaction temperature when n-butane conversion rate is 10%

[0055] T 99％ : Reaction temperature when n-butane conversion rate is 99%

[0056] Depend on Figure 1 The nitrogen adsorption-desorption curves of the catalysts show that the catalysts prepared in all examples and comparative examples are typical mesoporous materials. Pd-1, Pd-2, and Pt-0 exhibit H1-type hysteresis loops, while Pd-3, Pd-4, Pd-5, Pt-1, and Pt-2 exhibit typical H3-type hysteresis loops. Figure 2 The pore size distribution diagram of the catalyst shows that the pore size distribution of Pd-1, Pd-2, and Pt-0 is relatively concentrated, while Pd-3, Pd-4, Pd-5, Pt-1, and Pt-2 begin to have a multi-level pore structure; Figure 3 The XRD patterns of the catalysts show that the XRD diffraction peak intensities of Pd-1, Pd-2, and Pt-0 are relatively low, while those of Pd-3, Pd-4, Pd-5, Pt-1, and Pt-2 increase significantly, and Pd-4 undergoes a transformation into an alumina crystal phase. Figure 4 The SEM images of the catalysts show that when the calcination temperature in step (4) is 1000°C, the catalyst begins to undergo a transformation into an alumina crystal phase. At 1200°C, the alumina in the (Pd-4) catalyst is completely transformed into α-Al2O3. As shown in Table 1, the specific surface areas of Pd-1, Pd-2, and Pt-0 are relatively high, while the specific surface areas of Pd-3, Pd-4, Pd-5, Pt-1, and Pt-2 show a significant loss. This indicates that changing the calcination temperature in step (4) significantly affects the catalyst's texture, which in turn changes the interaction between the precious metal and the support, thereby affecting the catalytic activity.

[0057] As can be seen from the activity evaluation of the catalysts in Table 2, the catalytic activities of the examples and comparative examples are ranked as follows: Pd-3 > Pt-1 > Pd-5 > Pt-2 > Pd-1 > Pt-0 > Pd-2 > Pd-4. When the calcination temperature in step (4) is 1000°C, the catalysts Pd-3 and Pt-1 prepared exhibit excellent catalytic activity in the catalytic combustion of n-butane. In addition, the catalytic activities of the catalysts Pd-5 and Pt-2 prepared by reducing the precious metal loading by 1 / 4 are superior to those of Pd-1, Pt-0, Pd-2, and Pd-4, demonstrating the advantages of low loading and high activity.

[0058] The main reasons why Pd-3 and Pt-1 have excellent catalytic activity and Pd-5 and Pt-2 have low loading and high activity are: when the calcination temperature of step (4) is 1000℃, the noble metal in the catalyst and the carrier produce a suitable interaction, and the utilization rate of the noble metal atoms is greatly improved. When the calcination temperature of step (4) is 1000℃, the porous structure in the catalysts Pd-3, Pd-5, Pt-1, and Pt-2 is conducive to mass transfer; the high cerium oxide diffraction peak intensity and large grain size in Pd-3, Pd-5, Pt-1, and Pt-2 correspond to high lattice oxygen storage and good oxygen transport capacity, which is conducive to the active components in the catalyst to maintain the active oxidation state; Pd-3, Pd-5, Pt-1, and Pt-2 are in the critical state of alumina crystal phase transformation, and the unsaturated five-coordinated Al in the carrier is conducive to the active oxidation state of the catalyst. 3+ The sites are reduced, so that the interaction force between the noble metal and the carrier is between strong and weak, the noble metal oxide is easy to reduce, the noble metal particles are not easy to agglomerate, and the reduced noble metal can be quickly oxidized, realizing the PdO-Pd-PdO (PtO x -Pt-PtO x )’s rapid transformation.

[0059] The above description is only a preferred embodiment, and all equivalent changes and modifications made according to the scope of the patent application of the present invention are covered by the scope of the present invention.

Claims

1. A method for preparing a low-load, high-activity short-chain alkane catalytic combustion catalyst, characterized in that: The following steps are involved: (1) Preparation of cerium oxide gel Dissolve ammonium cerium nitrate in deionized water, add 0.5-3 g of urea and 2-6 g of starch, and stir at a constant temperature of 120-160 °C to prepare cerium oxide gel; (2) Preparation of nano-cerium oxide The cerium oxide gel is placed in a hydrothermal reactor for hydrothermal reaction, so that the starch is completely hydrolyzed to obtain nano-cerium oxide; (3) Preparation of nano-CeO2@Pt(Pd) active metal precursor Dissolve Pd or Pt metal salt into nano-CeO2, then add 2-6 g of starch and stir at a constant temperature of 120-160 °C to prepare CeO2@Pd(Pt) gel; (4) Preparation of catalyst CeO2@Pd(Pt) gel was mixed with commercial aluminum sol and ball-milled in a ball mill at a frequency of 30-60 Hz for 30-90 min. After thorough ball milling, it was coated on the surface of cordierite, dried at 120 °C for 4 h, and calcined for 4 h to obtain CeO2@Pd(Pt) / Al2O3+cordierite catalyst.

2. The method for preparing a low-load, high-activity short-chain alkane catalytic combustion catalyst according to claim 1, characterized in that: The starch added in step (1) is one or more of sweet potato starch, potato starch, wheat starch, corn starch, and pea starch.

3. The method for preparing a low-load, high-activity short-chain alkane catalytic combustion catalyst according to claim 1, characterized in that: In step (2), the hydrothermal treatment is carried out at 160-200 °C for 18-36 h.

4. The method for preparing a low-load, high-activity short-chain alkane catalytic combustion catalyst according to claim 1, characterized in that: In step (3), the Pd metal salt is PdCl2, and the Pt metal salt is H2PtCl6 solution.

5. The method for preparing a low-load, high-activity short-chain alkane catalytic combustion catalyst according to claim 1, characterized in that: The precious metal content of the Pd or Pt metal salt added in step (3) is 150, 200 g precious metal / m 3 Iolite.

6. The method for preparing a low-load, high-activity short-chain alkane catalytic combustion catalyst according to claim 1, characterized in that: The calcination temperature in step (4) is any one of 800, 1000, and 1200°C.

7. The method for preparing a low-load, high-activity short-chain alkane catalytic combustion catalyst according to claim 1, characterized in that: The drying in step (4) is specifically performed at 120°C for 4 hours.

8. A low-load, high-activity short-chain alkane catalytic combustion catalyst prepared by the method of claim 1.

9. Use of the catalyst as claimed in claim 8 in the catalysis of short-chain alkanes.

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