CN115837278A - Preparation and application of high-defect molybdenum oxysulfide bifunctional catalyst - Google Patents

Abstract

The invention discloses preparation and application of a high-defect molybdenum oxysulfide bifunctional catalyst, and relates to a constructed molybdenum oxysulfide bifunctional catalyst. Dissolving ammonium molybdate and thiourea in water, performing crystallization treatment in a hydrothermal reaction kettle, and then filtering, washing and drying to obtain molybdenum sulfide nanosheets; roasting the molybdenum sulfide nanosheets in a muffle furnace to obtain a molybdenum oxysulfide composite catalyst; warp H ₂ After reduction, the high defect molybdenum oxysulfide bifunctional catalyst is prepared. The catalyst can be used inPreparing aromatic hydrocarbon by atmospheric pressure gas-solid phase hydrodeoxygenation of lignin derived phenolic compounds at the reaction temperature of 300-400 ℃ and H ₂ The pressure was 1atm. The catalyst of the invention has low price, shows excellent activity and deoxidation selectivity in the hydrogenation deoxidation reaction of phenols, and has good industrial application prospect.

Description

Preparation and Application of a Highly Defective Molybdenum Sulfur Oxide Bifunctional Catalyst

technical field

The invention relates to the technical field of catalysts, in particular to the preparation and application of a high-defect molybdenum sulfur oxide bifunctional catalyst.

Background technique

Lignin biomass is the second largest biomass resource after cellulose in the plant kingdom. Due to its stable structure, the development and utilization of lignin biomass is still in its infancy. Usually, the utilization of lignin includes two stages. Firstly, bio-crude oil is obtained by rapid pyrolysis at a temperature of 500-600°C, the main components of which are phenolic compounds. Bio-crude oil has high oxygen content, high viscosity, low calorific value, and instability, so it needs to be further upgraded by catalytic hydrodeoxygenation. However, due to the extremely strong C-O bond of the phenolic hydroxyl group, it is difficult to break the C-O bond, which leads to serious side reactions such as benzene ring hydrogenation or C-C hydrogenolysis, which makes the selectivity of the target product aromatics low. Therefore, the focus and difficulty of research lies in the design of efficient catalysts. Selective deoxygenation of phenols to aromatics. In addition, due to the complexity of bio-crude oil components, using model molecules, such as m-cresol, anisole, guaiacol and other bio-oil components with representative oxygen-containing functional groups, to screen catalysts and explore the reaction mechanism is the current research It also provides a good theoretical basis for the direct hydrodeoxygenation and upgrading of bio-crude oil. In past explorations, commonly used catalysts for phenolic hydrodeoxygenation include traditional CoMoS catalysts, noble metal catalysts, oxides, and sulfides. Among them, the low-cost molybdenum oxide catalyst has attracted the attention and exploration of many researchers due to its high selective deoxidation performance.

The active center of the molybdenum oxide catalyst is oxygen vacancies, which can effectively activate the phenolic hydroxyl groups to achieve selective deoxygenation. However, the content of oxygen vacancies on the surface of traditional molybdenum oxide is less, and the ability of molybdenum oxide itself to activate hydrogen is relatively weak, resulting in the low activity of molybdenum oxide catalysts reported in the literature. The method currently used by researchers to modify molybdenum oxide catalysts is mainly to introduce noble metals or transition metals into the molybdenum oxide substrate to enhance the ability to activate hydrogen. Deoxygenation and subsequent hydrogenation of phenols. However, due to the presence of metal components, the benzene rings in phenols tend to interact with metals, making the hydrogenation reaction of benzene rings and C–C hydrogenolysis side reactions easy to proceed, thereby reducing the selectivity of the target deoxygenation products. Therefore, how to make full use of the characteristics of oxygen vacancies in molybdenum oxide to activate phenolic hydroxyl groups without adding metals, and to construct efficient catalysts based on this is the key problem that needs to be broken through.

Contents of the invention

Aiming at the disadvantages of molybdenum oxide having few oxygen vacancies and weak ability to activate hydrogen in the prior art, the invention provides a preparation method of a high-defect molybdenum sulfur oxide bifunctional catalyst.

The present invention also provides the application of the high-defect molybdenum sulfur oxide bifunctional catalyst prepared by the above preparation method.

To achieve the above object, the technical scheme adopted in the present invention is as follows:

On the one hand, the present invention provides a kind of preparation method of high-defect molybdenum sulfur oxide bifunctional catalyst, comprising the following steps:

(1) placing molybdenum sulfide nanosheets in a muffle furnace for roasting to obtain molybdenum oxysulfide composite materials;

(2) Reducing the molybdenum oxysulfide composite material in a fixed bed to obtain a molybdenum oxysulfide bifunctional catalyst.

Preferably, the molybdenum sulfide nanosheets described in step (1) are prepared through the following steps:

(1.1) Ammonium molybdate and thiourea are dissolved in water and crystallized in a hydrothermal reaction kettle;

(1.2) The crystallized product was filtered, washed, and dried to obtain molybdenum sulfide nanosheets.

Preferably, the mass ratio of ammonium molybdate and thiourea in step (1.1) is 1.16:1.

Preferably, the crystallization temperature in step (1.1) is 220° C., and the crystallization time is 18 hours.

Preferably, the calcination temperature in step (1) is 80-550°C, the calcination time is 0.5-10h, and the heating rate is 2-10°C/min.

Preferably, the reduction temperature in step (2) is 300-500°C, the reduction time is 0.5-4h, and the heating rate is 2-10°C/min.

On the other hand, the present invention also provides the application of the above-mentioned highly defective molybdenum sulfur oxide bifunctional catalyst in the hydrodeoxygenation of lignin-derived phenolic compounds.

m-cresol was used as the model reactant, in which phenolic hydroxyl group is a kind of main oxygen-containing functional group of lignin-derived bio-oil. The reaction is carried out in a gas-solid phase reactor at atmospheric pressure, the reaction temperature is 300-400° C., the reaction hydrogen pressure is 1 atm, a quantitative syringe is used to inject samples, and the reaction products are identified by online gas chromatography analysis.

Compared with the prior art, the present invention provides a method for preparing a molybdenum oxysulfide bifunctional catalyst with abundant oxygen vacancies, and applies the prepared catalyst to catalytic hydrodeoxygenation of lignin-derived phenolic compounds to prepare aromatics. The catalyst combines the properties of molybdenum sulfide to activate hydrogen and the properties of oxygen vacancies in molybdenum oxide to efficiently activate oxygen-containing functional groups, and exhibits excellent catalytic activity and aromatics selectivity in the hydrodeoxygenation reaction of phenols.

Description of drawings

Fig. 1 is the XRD spectrogram of the catalyst prepared in Example 1 and Comparative Example 1-2.

Fig. 2 is the NH ₃ -TPD diagram of the catalysts prepared in Example 1 and Comparative Examples 1-2.

Fig. 3 is the H ₂ -D ₂ -TPSR spectra of the catalysts prepared in Example 1 and Comparative Example 1-2.

Fig. 4 shows the conversion rate and toluene selectivity of the catalysts prepared in Example 1 and Comparative Examples 1-2 to catalyze m-cresol conversion.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

The molybdenum sulfide nanosheets described in the present invention can be commercially available or self-made by methods known in the art.

Comparative example 1

Preparation of molybdenum sulfide nanosheets

Dissolve 3.53g of ammonium molybdate tetrahydrate and 3.04g of thiourea in 100mL of water, place the solution in a 150mL hydrothermal kettle, and put it into an oven for crystallization at 220°C for 18h. After being taken out from the oven and cooled to room temperature, the molybdenum sulfide nanosheets were obtained by filtering, washing and drying. The XRD spectrum of the catalyst after reduction at 400°C is shown in Figure 1, and its diffraction peaks correspond to the 2H-type molybdenum sulfide nanosheet structure. The situation of its unsaturated coordination sites is analyzed by NH ₃ -TPD characterization, as shown in Figure 2, the quantitative analysis of the desorbed NH ₃ (m/z=16) gives the number of unsaturated coordination sites of the catalyst About 32.3μmol/g _cat .

Comparative example 2

Preparation of molybdenum oxide

The molybdenum sulfide nanosheets in Comparative Example 1 were calcined in a muffle furnace at a calcination temperature of 600°C, a calcination time of 3 hours, and a heating rate of 2°C/min to obtain a sulfur-free molybdenum oxide catalyst. The XRD spectrum of the catalyst after reduction at 400°C is shown in Figure 1, and its diffraction peaks include the diffraction signals of MoO ₃ and MoO ₂ . The situation of its unsaturated coordination sites is analyzed by NH ₃ -TPD characterization, as shown in Figure 2, the quantitative analysis of the desorbed NH ₃ (m/z=16) gives the number of unsaturated coordination sites of the catalyst It is about 33.8μmol/g _cat , indicating that the molybdenum oxide material itself has very little unsaturated coordination sites, which is also one of the main reasons for its poor activity.

Example 1

Preparation of molybdenum oxysulfide

The molybdenum sulfide nanosheets in Comparative Example 1 were calcined in a muffle furnace at a calcination temperature of 300° C., a calcination time of 3 h, and a heating rate of 2° C./min to obtain a molybdenum oxysulfide catalyst. The XRD spectrum of the catalyst after reduction at 400°C is shown in Figure 1, and its diffraction peaks include the diffraction signals of 2H-type molybdenum sulfide and MoO ₂ . The situation of its unsaturated coordination sites is analyzed by NH ₃ -TPD characterization, as shown in Figure 2, the quantitative analysis of the desorbed NH ₃ (m/z=16) gives the number of unsaturated coordination sites of the catalyst It is about 273.4 μmol/g _cat , which is greatly improved compared with Comparative Examples 1 and 2, reflecting the outstanding advantages of molybdenum oxysulfide material.

Example 2

Probe Reaction for Hydrogen Activation Ability

The H ₂ -D ₂ temperature-programmed surface reaction was used to detect the ability of the three catalysts of Comparative Example 1, Comparative Example 2 and Example 1 to activate hydrogen respectively. The probe reaction is carried out in a gas-phase fixed-bed reactor at normal pressure, and the product is analyzed by an online mass spectrometer. Firstly, a certain amount of catalyst was weighed and reduced in situ at 400° C. under H ₂ (30 mL/min) atmosphere for 1 h. After the reactor was lowered to room temperature, _H2 was switched to 30mL/min 50% _H2 +50% _D2 mixed gas, at this time, _H2 was monitored in real time by mass spectrometer (m/z=2), _D2 ( m/z=4), HD (m/z=3) signal evolution. After the signal was stabilized, the reactor was programmed to heat up to 400°C at a rate of 5°C/min. The evolution curves of the H ₂ -D ₂ temperature-programmed surface reactions of the catalysts obtained in Comparative Example 1, Comparative Example 2 and Example 1 as a function of temperature are shown in FIG. 3 . The generation of HD means that H _{and D} are dissociated and activated on the catalyst surface. Obviously, the initial generation temperature of HD satisfies the following rule: Comparative Example 1<Example 1<Comparative Example 2, indicating that Comparative Example 1 has the strongest _H Activation ability is second to Example 1, and Comparative Example 2 has the weakest ability to activate hydrogen.

Comparative example 3

Catalyst catalyzed m-cresol hydrodeoxygenation reaction prepared in comparative example 1

The m-cresol hydrodeoxygenation reaction was carried out in a gas-solid phase reactor at atmospheric pressure. The catalyst was first reduced in situ at 400 °C and 1 atm of H ₂ atmosphere for 1 h and then adjusted to a reaction temperature of 300 °C. Inject m-cresol into the reaction tube through a quantitative syringe, and heat to 220°C at the injection port to vaporize m-cresol. The flow rate of m-cresol is 0.03mL/h, passing through the catalyst bed, and the product is analyzed by online gas chromatography. During the reaction, the molar ratio of H ₂ /m-cresol was controlled to be 90, and W/F=3h. The reaction results are shown in Figure 4. Under the current reaction conditions, the conversion rate of m-cresol on the catalyst of Comparative Example 1 was 5%, and the selectivity of toluene was 94%.

Comparative example 4

The catalyst prepared in comparative example 2 catalyzes m-cresol hydrodeoxygenation reaction

The reaction evaluation operation is the same as that of Comparative Example 3. The reaction result is shown in Figure 4. Under the current reaction conditions, the conversion rate of m-cresol on the catalyst of Comparative Example 2 is only 3%, and the selectivity of toluene is 97%. This shows that the activity of pure molybdenum oxide itself is poor, combined with the characterization of NH ₃ -TPD (Figure 2) and H ₂ -D ₂ -TPSR (Figure 3), it is not difficult to see that the content of unsaturated coordination sites (oxygen vacancies) on the catalyst surface Less, and the ability to activate hydrogen is weak, which is the main reason for its low activity.

Example 3

Catalyst catalysis m-cresol hydrodeoxygenation reaction that embodiment 1 makes

The reaction evaluation operation is the same as that of Comparative Example 3. The reaction results are shown in Figure 4. Under the current reaction conditions, the conversion rate of m-cresol on the catalyst of Example 1 reached 20%, and the selectivity of toluene was 97%. Compared with Example 1, the activity has been improved by about 4 times. Combining NH ₃ -TPD (Fig. 2) and H ₂ -D ₂ -TPSR (Fig. 3), it can be speculated that the catalyst has both the ability of MoS ₂ to efficiently activate hydrogen and the advantages of abundant oxygen vacancies, thus achieving efficient deoxygenation.

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Anyone familiar with the technical field within the technical scope disclosed in the present invention, whoever is within the spirit and principles of the present invention Any modifications, equivalent replacements and improvements made within shall fall within the protection scope of the present invention.

Claims (8)

1. A preparation method for a high-defect molybdenum sulfur oxide bifunctional catalyst, is characterized in that, comprises the following steps: (1) placing molybdenum sulfide nanosheets in a muffle furnace for roasting to obtain molybdenum oxysulfide composite materials; (2) Reducing the molybdenum oxysulfide composite material in a fixed bed to obtain a molybdenum oxysulfide bifunctional catalyst. 2. the preparation method of a kind of high-defect molybdenum sulfur oxide bifunctional catalyst according to claim 1, is characterized in that, the molybdenum sulfide nanosheet described in step (1) is prepared by the following steps: (1.1) Ammonium molybdate and thiourea are dissolved in water and crystallized in a hydrothermal reaction kettle; (1.2) The crystallized product was filtered, washed, and dried to obtain molybdenum sulfide nanosheets. 3. The preparation method of a high-defect molybdenum sulfur oxide bifunctional catalyst according to claim 2, characterized in that the mass ratio of ammonium molybdate and thiourea in step (1.1) is 1.16:1. 4. The method for preparing a high-defect molybdenum sulfur oxide bifunctional catalyst according to claim 2, characterized in that the crystallization temperature in step (1.1) is 220° C., and the crystallization time is 18 hours. 5. The preparation method of a high-defect molybdenum sulfur oxide bifunctional catalyst according to claim 1, characterized in that the calcination temperature in step (1) is 80-550°C, the calcination time is 0.5-10h, and the temperature rises The rate is 2-10°C/min. 6. The preparation method of a high-defect molybdenum sulfur oxide bifunctional catalyst according to claim 1, characterized in that the reduction temperature in step (2) is 300-500°C, the reduction time is 0.5-4h, and the temperature rises The rate is 2-10°C/min. 7. The application of the highly defective molybdenum sulfur oxide bifunctional catalyst prepared by the preparation method described in any one of claims 1 to 6 in the hydrodeoxygenation of lignin-derived phenolic compounds. 8. The application according to claim 7, characterized in that the hydrodeoxygenation reaction is carried out in a gas-solid phase reactor at atmospheric pressure, the reaction temperature is 300-400° C., and the reaction hydrogen pressure is 1 atm.

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