CN103071541B - A kind of preparation method of load type metal catalyst of highly disperse active center - Google Patents

Abstract

The invention discloses a preparation method of a supported metal catalyst with highly dispersed active centers, which adopts an improved impregnation method: after the conventional carrier of the catalyst is dried and pretreated, it is impregnated with a multifunctional compound containing more than two hydroxyl-friendly functional groups, and then dried Immersing in a metal salt solution; or directly immersing the carrier without surface modification in a metal salt solution of a multifunctional compound containing two or more hydroxyl-friendly functional groups; then drying and calcining to obtain a metal-loaded catalyst. Through the improved impregnation method, that is, the complex impregnation method, the function of the carrier and the active center can be improved, the amount of multifunctional compound is small and easy to control, the preparation process is simple and reliable, and it is a new way to prepare high-efficiency catalysts; prepared by the complex impregnation method The catalyst, the metal active component is evenly distributed on the surface of the catalyst, the dispersion degree increases, and the particle size of the active component can be controlled within 10nm, and the particle size distribution can be adjusted.

Description

A kind of preparation method of the supported metal catalyst of highly dispersed active center

Technical field:

The invention belongs to the technical field of catalysts, and in particular relates to a preparation method of a loaded metal catalyst with highly dispersed active centers.

Background technique:

Supported catalysts are commonly used catalysts in the chemical industry, and the metal active components can be uniformly dispersed on the surface of the catalyst. Supported catalysts generally use less metal, and the preparation process is simple and easy to control. Common methods for preparing supported catalysts include impregnation, ion exchange, sol-gel and co-precipitation. In order to prepare catalysts with higher dispersion and higher activity, new preparation methods are constantly emerging. For example: use cold/hot plasma to prepare ultra-fine particle catalysts, and plasma sputtering to assist the deposition of catalyst active components to prepare highly dispersed and highly active catalysts. However, special plasma devices are required in the preparation process, and there are high voltages in the process. The vacuum system, the scale of catalyst preparation is limited (Catalysis Today Volume 72 (2002), 173-184). Use ion exchangers as carriers, introduce active components in the form of counter ions, and prepare highly dispersed, large specific surface supported metal catalysts; carriers are commonly used as various molecular sieves; catalysts prepared by ion exchange method have less metal loading and require Multiple exchanges can achieve a higher exchange degree and loading capacity. At the same time, the cations in the catalyst carrier are always difficult to be completely replaced, which has an adverse effect on some reactions. In addition, this method is limited by the type of carrier (Catalysis Today Volume77( 2003), 299-314 and Chemical Engineering Journal209(2012), 652-660); sol-gel method refers to the solidification of metal-organic or inorganic compounds through solutions, sols and gels, and then heat treatment to form oxides or other compounds solid method. The prepared catalyst has high uniformity, the reaction process is simple and easy to control, the catalyst has high dispersion, high specific surface area and good pore size, the reaction temperature is low during the preparation process, and the crystal form and particle size of nanoparticles are controllable; however, it is widely used in practical applications Metal-organic compounds or organic gels, catalyst production costs are higher (Angewandte Chemie Volume35(1996), 1420-1436 and Catalysis Today Volume137(2008), 132-143); Philippe Serp et al. (Chemical Reviews Volume102(2002), 3085 -3128) reviewed the preparation of supported catalysts by chemical vapor deposition (i.e., gas phase impregnation-decomposition method). The metal active precursor was vaporized and then deposited on the carrier, and finally heated and roasted to decompose. Compared with the conventional impregnation method, the metal active component The distribution is more uniform, and the activity is much improved, but the metal prerequisite requires easy vaporization and decomposition. The metal precursors commonly used in the actual process are metal carbonyl compounds. Due to their high toxicity, anhydrous and oxygen-free preparation conditions are required, which is not conducive to large-scale application.

Invention content:

The purpose of the present invention is to provide a method for preparing a loaded metal catalyst with a highly dispersed active center by a complex impregnation method.

The present invention is achieved through the following technical solutions:

Using the improved dipping method, the specific steps are as follows:

After the conventional carrier of the catalyst is dried and pretreated, it is impregnated with a multifunctional compound containing two or more hydroxyl-friendly functional groups (such as hydroxyl, carboxyl, amino, aldehyde, etc.) for 6~24h, and dried at 50~150℃ for 6~24 hours to obtain The surface-modified carrier, and then immersing the surface-modified carrier in a metal salt solution for 6-24 hours;

Alternatively, a multifunctional compound containing two or more hydroxyl-friendly functional groups is directly added to the metal salt solution, and the carrier that has not been surface-modified but only dried and pretreated is directly impregnated with the metal salt solution of a multi-functional compound containing two or more hydroxyl-friendly functional groups 6~24h;

The above-mentioned catalyst impregnated with the metal salt aqueous solution is spin-dried at 50-100°C for 10-24 hours, dried at 100-200°C for 10-24 hours, then calcined at 300-800°C for 2-4 hours, and the heating rate is controlled at 1~10℃/min to obtain metal-supported catalyst;

The molar ratio of the metal in the metal salt aqueous solution to the multifunctional compound containing two or more hydroxyl-friendly functional groups is between 1:0.5 and 1:10; the metal loading wt% (the mass of the active component metal and the conventional support percentage) is 1 to 40%, preferably 1 to 25%.

The conventional catalyst supports include metal oxide supports (such as Al ₂ O ₃ ), non-metal oxide supports (such as SiO ₂ ) or molecular sieves (such as MCM-41).

The catalyst carrier drying pretreatment means that the metal oxide carrier or non-metal oxide carrier is dried at 100-200° C. for 6-24 hours; the molecular sieve carrier is burned at 550° C. for 2-6 hours to remove the template agent.

The polyfunctional compound containing two or more hydroxyl-friendly functional groups is preferably ethylenediamine, or citric acid, lactic acid, ethylene glycol, sorbitol, glucose, glycerol, and 1,4-butanediol.

The metal salt in the metal salt aqueous solution, as an active component of the metal-supported catalyst, includes Co(NO ₃ ) ₂ ·6H ₂ O, Cu(NO ₃ ) ₂ ·3H ₂ O or Ni(NO ₃ ) ₂ · 6H ₂ O and other metal salts.

The present invention has the following beneficial effects:

1) Through the improved impregnation method, that is, the complex impregnation method, using the hydrophilic properties of the carrier, using the interaction between the multifunctional compound containing the hydroxyl group and the carrier, and the metal ions, the catalyst carrier is first impregnated or impregnated during the catalyst preparation process. Adding multifunctional compounds containing more than two hydroxyl-friendly functional groups (hydroxyl, carboxyl, amino, aldehyde) directly into the metal salt solution, the amount of multifunctional compounds is small and easy to control, the preparation process is simple and reliable, and it is simple and practical to prepare high-efficiency catalysts new way.

2) The catalyst prepared by the complex impregnation method can improve the function of the carrier and the active center, the metal active components are evenly distributed on the surface of the catalyst, the dispersion degree increases, and the particle size of the active component of the highly dispersed metal-supported catalyst is controllable Within 10nm, and the particle size distribution can be adjusted.

Description of drawings:

Fig. 1 is the XRD spectrogram of the catalyst of different metal loads;

Fig. 2 is the XRD spectrogram of the catalyst that different sintering temperatures obtain;

Fig. 3 is the XRD spectrogram of the catalyst that different ethylene glycol consumptions obtain;

Fig. 4 and Fig. 5 are the XRD spectrograms of the catalyst that different alcohols obtain;

Fig. 6 is the XRD spectrogram of the catalyst that different polyphilic hydroxyl compounds obtain;

Fig. 7, Fig. 8, Fig. 9 and Fig. 10 are the XRD spectrograms of the catalyst obtained by different metals and supports;

Among them, 2θ represents the diffraction angle of XRD

Detailed ways:

The following is a further description of the present invention, rather than a limitation of the present invention. The conventional carrier of the catalyst, the polyfunctional compound of the hydroxyl-philic functional group or the metal salt in the metal salt solution is exemplified by the following examples without limitation thereto.

Example 1: Effect of Metal Loading

Weigh 2.5g of granular 40-60 mesh commercial carrier SiO ₂ and dry it at 120°C for 12 hours for later use. At room temperature, ethylene glycol (glycol, abbreviated as EG) was added to impregnate the SiO ₂ support for 6 h, and then dried at 50 °C for 24 h to obtain a surface-modified support. At room temperature, impregnate an aqueous solution containing 2.4692g Co(NO ₃ ) ₂ ·6H ₂ O on the surface-modified carrier for 12 hours, spin dry at 90°C for 12 hours, and dry at 120°C for 12 hours. Calcined in a Furnace at 400°C for 2 hours, with a heating rate of 2°C/min, to obtain a 10% loaded Co/SiO ₂ catalyst, changing the amount of Co(NO ₃ ) ₂ ·6H ₂ O, repeating the above process, and the obtained catalyst was recorded as 1 %Co-SiO ₂ , 10% Co-SiO ₂ , 20% Co-SiO ₂ , 25% Co-SiO ₂ , 30% Co-SiO ₂ , 40% Co-SiO ₂ . The corresponding XRD spectrum is shown in Figure 1. It can be concluded from the figure that when the metal loading is below 25wt%, the metal active centers are very uniformly loaded on the carrier _SiO2 , and the dispersion is very high; the particle size is so small that the XRD spectrum The peaks on the figure completely disappear or are very dispersed. When the metal loading is 25wt%, the particle size is calculated to be 3.7nm; when the metal loading is 30wt% and 40wt%, the particle size is calculated to be 12.8nm and 15.2nm; Alcohol surface-modified carrier, the diffraction peak of Co ₃ O ₄ is obvious (see (d) XRD diffraction peak in Figure 4), and the calculated particle size is 16.3nm.

Embodiment 2: the influence of sintering temperature

The implementation steps and conditions are the same as in Example 1, and the commercial carrier SiO ₂ is dried at 100° C. for 24 hours, taking a 10% loaded Co/SiO ₂ catalyst as an example. At room temperature, ethylene glycol (EG) was added to impregnate the _SiO2 support for 24 h, and then dried at 150 °C for 6 h to obtain a surface-modified support. The surface-modified ethylene glycol carrier was impregnated with Co(NO ₃ ) ₂ ·6H ₂ O, then impregnated for 20 hours, spin-dried at 50°C for 24 hours, and dried at 200°C for 10 hours. After drying, the sample was placed in a muffle furnace at 300°C, 400°C , 500°C, 600°C, 700°C, 800°C for 2 hours, and the heating rate is 2°C/min. The corresponding XRD spectrum is shown in Figure 2. The active centers of the samples calcined below 600°C are very uniformly loaded on the carrier SiO ₂ , the dispersion is very high, and the XRD diffraction peaks completely disappear; the calcined above 600°C, very diffuse XRD diffraction appears Peak, particle size calculated to be 4.9-5.2 nm.

Embodiment 3: the influence of ethylene glycol dosage

Weigh 2.5g of granular 40-60 mesh commercial carrier SiO ₂ and dry it at 200°C for 6 hours for later use. At room temperature, impregnate an aqueous solution of ethylene glycol containing 2.4692g Co(NO ₃ ) ₂ ·6H ₂ O on the carrier for 6 hours, spin dry at 60°C for 20h, and dry at 100°C for 24 hours; after drying, the sample is placed in Calcined at 400°C for 2 hours in a muffle furnace with a heating rate of 2°C/min to obtain a 10% supported Co/SiO ₂ catalyst; the molar ratios of metal and ethylene glycol in the metal salt were: 1:0.5, 1:1 , 1:2, 1:4, 1:6, 1:10. The corresponding XRD spectrum is shown in Figure 3, and it can be drawn from the figure that when the molar ratio of metal and ethylene glycol in the metal salt solution is less than 1:1, the metal active center is very uniformly loaded on the carrier SiO ₂ and the dispersion is very high. The XRD diffraction peak completely disappeared; when the ratio was 1:1, a very diffuse XRD diffraction peak appeared, and the particle size was calculated to be 4.7nm; when the ratio was 1:0.5, a clear and sharp XRD diffraction peak appeared, and the particle size was calculated to be 15.2nm.

Example 4: Effect of other alcohols

The implementation steps and conditions are the same as in Example 3, taking 10% loaded Co/SiO ₂ catalyst as an example, add monohydroxy compound ethanol (ethanol) in the impregnated solution, and the content in water is 20% (the molar ratio of metal and alcohol is less than 1: 1), spin dry at 60°C for 24 hours, and dry at 120°C for 10 hours; in addition, other polyols such as sorbitol, glucose, glycerol, 1,4-butanediol (1 , 4-butanediol), the water content is 10% (the molar ratio of metal and alcohol is less than 1:1), spin-dry at 80°C for 12 hours, and dry at 150°C for 12 hours; see Example 3 for other steps. The corresponding XRD spectra are shown in Figures 4 and 5. It can be concluded from the figures that although the ethanol content in water is 20%, the hydroxyl content is equivalent to 10% ethylene glycol, but due to monodentate coordination, there are no redundant hydroxyl and The carrier is combined, there is no interaction between the metal ion and the carrier, and the particle size of the metal active center is relatively large, and the particle size is calculated to be 15.8nm. When polyols such as sorbitol, glucose, glycerin, and 1,4-butanediol are used as additives, due to the multidentate coordination, the remaining hydroxyl groups are bound to the carrier, and the interaction between the metal ion and the carrier occurs, and the metal active center It can be well dispersed on the surface of the carrier, the XRD diffraction peaks completely disappear or are very dispersed, and the calculated particle size is below 3nm.

Example 5: Effect of Other Polyphilic Hydroxyl Compounds

The implementation steps and conditions are the same as in Example 3, taking 10% loaded Co/ _SiO2 catalyst as an example, adding a multifunctional group compound containing more than two hydroxyl-friendly functional groups in the impregnated solution: ethylenediamine (ethylenediamine), citric acid ( citric acid), lactic acid, urea, the content in water is 10% (the molar ratio of metal and alcohol is less than 1:1), spin dry at 70°C for 16 hours, and dry at 120°C for 10 hours; others Step see embodiment 3. The corresponding XRD spectrum is shown in Figure 6. It can be concluded from the figure that other multifunctional group compounds containing more than two hydroxyl-friendly functional groups also play the role of polyhydroxyl compounds, and the metal active centers can be well dispersed on the surface of the carrier. The XRD diffraction peaks completely disappear or are very diffuse, and the calculated particle size is below 4.9nm. However, the addition of inorganic urea may be due to the low decomposition temperature of urea, which cannot well control the interaction between the metal ion and the carrier, resulting in a weak interaction, and the particle size of the metal active center is large. The particle size is calculated as 9.7nm.

Example 6: Effect of other metals and supports

Weigh 8g of granular 40-60 mesh commercial carrier SiO ₂ and dry it at 120°C for 12 hours for later use. At room temperature, impregnate an aqueous solution containing 4.5621g Cu(NO ₃ ) ₂ ·3H ₂ O and 1.1721g ethylene glycol on the carrier for 24 hours, spin dry at 100°C for 10h, and dry at 200°C for 10 hours; Calcined in a muffle furnace at 400 °C for 4 hours with a heating rate of 1 °C/min to obtain a catalyst with a loading capacity of 15% Cu/SiO ₂ . The corresponding XRD spectrum is shown in Figure 7. It can be concluded from the figure that the metal active center is loaded very uniformly on the carrier SiO ₂ , the dispersion is very high, the XRD diffraction peak is very diffuse, and the particle size is calculated to be 6.8nm without improvement. The particle size of the catalyst prepared by impregnation method is 39.7nm.

Weigh 5g of granular 40-60 mesh commercial carrier Al ₂ O ₃ or 100-200 mesh molecular sieve MCM-41, and dry at 200°C and 550°C for 10 and 6 hours, respectively. At room temperature, impregnate an aqueous solution containing 4.9546g Ni(NO ₃ ) ₂ 6H ₂ O and 1.0575g ethylene glycol on the carrier for 10 hours, spin dry at 70°C for 24h, and dry at 120°C for 12 hours; after drying, the sample Place it in a muffle furnace and bake at 400°C for 4 hours with a heating rate of 10°C/min to obtain a catalyst with a loading capacity of 20%. The corresponding XRD spectra are shown in Figures 8 and 9. It can be concluded from the figures that the metal active centers are very uniformly loaded on the carrier Al ₂ O ₃ and the molecular sieve MCM-41, the dispersion is very high, the XRD diffraction peaks are very dispersed, and the particle size The calculated particle sizes are 5.0nm and 3.2nm, while the particle sizes of catalysts prepared without the improved impregnation method are 14.3nm and 48nm. Reduce the amount of ethylene glycol added so that the molar ratio of Ni:EG is 1:0.5. The XRD spectrum of the prepared 20%Ni-MCM-41 catalyst is shown in Figure 10. After hydrogen reduction at 450 °C, the diffraction peak of metal Ni appears, and the corresponding XRD diffraction peak It is still relatively dispersed; the amount of ethylene glycol is reduced, the interaction between the complex solution and the carrier is weakened, the peak intensity is obviously improved, and the calculated particle size is 3.9nm.

Claims (6)

1. a preparation method of a loaded metal catalyst with highly dispersed active centers, characterized in that the following steps are adopted: a. After the conventional carrier of the catalyst is dried and pretreated, it is impregnated with a multifunctional compound containing two or more hydroxyl-friendly functional groups for 6-24 hours, and dried at 50-150°C for 6-24 hours to obtain a surface-modified carrier, and then the surface-modified The carrier is immersed in a metal salt solution for 6-24 hours; the multifunctional compound containing more than two hydroxyl-friendly functional groups is selected from ethylene glycol, sorbitol, glucose, glycerin, and 1,4-butanediol; Alternatively, a multifunctional compound containing two or more hydroxyl-friendly functional groups is directly added to the metal salt solution, and the carrier that has not been surface-modified but only dried and pretreated is directly impregnated with the metal salt solution of a multi-functional compound containing two or more hydroxyl-friendly functional groups 6～24h; b. Spin-dry the catalyst impregnated with the metal salt aqueous solution at 50-100°C for 10-24 hours, dry at 100-200°C for 10-24 hours, and then calcinate at 300-800°C for 2-4 hours. Control at 1-10°C/min to obtain a metal-supported catalyst; The molar ratio of the metal in the metal salt aqueous solution to the multifunctional compound containing two or more hydroxyl-friendly functional groups is between 1:0.5-1:10; the weight % of the metal loading is 1-40%. 2. The preparation method of the loaded metal catalyst with highly dispersed active centers according to claim 1, characterized in that the conventional carrier of the catalyst is selected from a metal oxide carrier, a non-metallic oxide carrier or a molecular sieve. 3. the preparation method of the supported metal catalyst of highly dispersed active center according to claim 2, it is characterized in that described metal oxide carrier is Al ₂ O ₃ , non-metallic oxide carrier is SiO ₂ , molecular sieve carrier is MCM -41. 4. The preparation method of the loaded metal catalyst with highly dispersed active centers according to claim 1, characterized in that the metal salt in the metal salt aqueous solution is selected from Co(NO ₃ ) ₂ 6H ₂ O, Cu( NO ₃ ) ₂ ·3H ₂ O or Ni(NO ₃ ) ₂ ·6H ₂ O. 5. the preparation method of the supported metal catalyst of highly dispersed active center according to claim 1, it is characterized in that described metal loading wt% is 1～25%. 6. The method for preparing a supported metal catalyst with highly dispersed active centers according to claim 1, characterized in that the particle size of the active component of the metal-supported catalyst is within 10 nm, and the particle size distribution can be adjusted.