A biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst, a preparation method and application thereof

Abstract

The application discloses a biomass-based nitrogen-doped carbon-carbide molybdenum composite catalyst and a preparation method and application thereof, and is characterized in that: a widely-sourced biomass, especially agricultural biomass waste, is used as a carbon and nitrogen source, ammonium molybdate is used as a molybdenum source, and a nitrogen-doped carbon-carbide molybdenum composite catalyst is prepared through one-step pyrolysis under an ammonia atmosphere; the catalyst is mesoporous nitrogen-doped carbon loaded with pure beta-phase carbide molybdenum, has the characteristics of a large pore size, high dispersion of beta-phase carbide molybdenum and the like, and has good thermal stability; the catalyst can efficiently denitrogenate quinoline and directively convert the quinoline, and high-selectivity aromatic hydrocarbon products can be obtained; the conversion rate is not less than 99%, the denitrogenation rate is not less than 99%, the selectivity of aromatic compounds is not less than 86%, and the catalyst has the characteristics of low hydrogen consumption due to the avoidance of hydrogen saturation reaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation and catalytic application, and in particular to a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst, and a preparation method and application thereof. Background Art

[0002] Molybdenum carbide has good thermal stability, mechanical properties and high conductivity, and is widely used in catalysis, energy storage, environmental treatment and electronic devices. Molybdenum carbide has three typical crystal structures, including face-centered cubic (fcc), hexagonal close-packed (hcp) and simple hexagonal (hex) structures, of which the most common ones are represented by α-MoC 1-x , β-Mo2C and MoC. Pure phase molybdenum carbide can be prepared by temperature-programmed reduction (TPR), often using a methane / hydrogen mixed gas as a carbon source. For example, the literature [M.Lewandowskia et al, Applied Catalysis B: Environmental, 2020, 261, 118239] uses the TPR method. However, the molybdenum carbide particles prepared by this method are usually densely stacked, with a small specific surface area and lack of mesopores. Combining molybdenum carbide nanoparticles with nitrogen-doped carbon is an effective strategy to overcome the above-mentioned shortcomings of pure phase bulk molybdenum carbide. Compared with pure carbon supports, nitrogen-doped carbon has richer defect sites and more unique surface properties due to the introduction of nitrogen atoms, which can produce stronger interactions with molybdenum carbide particles and change the morphology and electronic properties of molybdenum carbide particles. Nitrogen-doped carbon-supported molybdenum carbide can be prepared using pure compounds such as dicyandiamide or glucose as carbon and nitrogen sources. Expanding the use of biomass, especially agricultural biomass waste (such as straw), as a carbon and nitrogen source to prepare molybdenum carbide-nitrogen-doped carbon composites is an important improvement direction. However, in the process of preparing molybdenum carbide composites using biomass as a carbon source, the crystal phase of molybdenum carbide is difficult to control, especially the controllable acquisition of pure phase molybdenum carbide is a major challenge.

[0003] Quinoline, as a nitrogen-containing heterocyclic compound, is widely present in petroleum, coal and biomass. Its hydrodenitrogenation reaction is a typical catalytic reaction process and has been widely studied, such as the content published in the article "Z. Qiu, Molecular Catalysis, 2021, 516: 1-11". However, most of the aromatic rings are destroyed during the hydrodenitrogenation of quinoline, and saturated compounds are mainly generated after denitrogenation. Pure phase molybdenum carbide can be used for the hydrodenitrogenation reaction of quinoline, but the damage to the aromatic ring is also large. The selectivity of aromatic hydrocarbon compounds is usually less than 48.5%, and it also causes higher hydrogen consumption. Therefore, how to generate aromatic ring compounds while hydrodenitrogenating while keeping the aromatic ring of quinoline intact remains a challenge.

[0004] The invention with patent application number CN202310947598.4 discloses a low-temperature plasma-synergized Mn / nitrogen-doped porous carbon catalyst. The catalyst uses zinc acetate dihydrate, polyvinyl pyrrolidone and methanol as raw materials, and the raw material cost is relatively high. Summary of the Invention

[0005] To overcome the shortcomings of the aforementioned prior art, the present invention provides a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst, its preparation method, and application. Using biomass as a carbon and nitrogen source and ammonium molybdate as a molybdenum source, the nitrogen-doped carbon-molybdenum carbide composite catalyst is prepared by single-step pyrolysis in an ammonia atmosphere. The catalyst is a nanosized catalyst with a porous structure, high crystallinity, and highly dispersed pure β-phase molybdenum carbide. Under the catalytic action of the catalyst, quinoline hydrogenation can achieve high denitrogenation rates while yielding highly selective aromatic hydrocarbon products.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst with a porous nanostructure and pure β-phase molybdenum carbide supported by mesoporous nitrogen-doped carbon with a specific surface area of ​​80 m 2 / g~110m 2 / g, pore volume 0.3cm 3 / g~0.5cm 3 / g, an average pore diameter of 20nm~25nm, a Mo content of 61wt%~75wt%, a C content of 21wt%~31wt%, a N content of 2wt%~4wt%, and an O content of 1wt%~5wt%.

[0008] A method for preparing a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst comprises the following steps:

[0009] (1) Grind the biomass into 80-100 mesh powder and dry it in an oven at 100-105°C for 8-10 hours;

[0010] (2) The biomass powder prepared in step (1) was mixed and dissolved in distilled water with ammonium molybdate in a mass ratio of (0.8-1):1, and the mass ratio of ammonium molybdate to distilled water was 1:(1-1.5). After mechanical stirring for 8 h to 10 h and ultrasonic mixing for 1 h to 2 h, the mixture was transferred to a vacuum oven and dried at 80 ° C to 90 ° C for 10 h to 12 h to obtain a precursor;

[0011] (3) Grind the precursor obtained in step (2) into 100-120 mesh powder, transfer it to a tubular heating furnace, and raise the temperature to 650-750°C at a rate of 4-6°C / min and maintain it for 1-3 hours in an ammonia atmosphere with a flow rate of 100 mL / min-150 mL / min, and then cool it to room temperature to obtain a nitrogen-doped carbon-β-phase molybdenum carbide composite material.

[0012] The biomass includes soybean straw, sorghum straw or cotton straw.

[0013] The invention discloses an application of a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst, which specifically comprises the following steps: loading the prepared nitrogen-doped carbon-β-phase molybdenum carbide composite material into a fixed-bed hydrogenation reactor, and performing a hydrogenation catalytic reaction on quinoline. The reaction conditions are controlled as follows: the H2 pressure is 4.0MPa to 6.0MPa, and the liquid hourly volume space velocity is 10 to 18h -1 , the hydrogen / oil volume ratio is 400 / 1 to 600 / 1, and the temperature is 360 to 390°C; finally, quinoline is denitrogenated to obtain aromatic compounds.

[0014] The beneficial effects of the present invention are:

[0015] 1. In the present invention, biomass (agricultural waste such as soybean straw, sorghum straw and cotton straw) is used as a carbon and nitrogen source for one-step pyrolysis to prepare nitrogen-doped carbon-molybdenum carbide composite materials. This type of biomass has the advantages of wide availability and low cost, and can promote resource reuse.

[0016] 2. The present invention overcomes the shortcomings of conventional methods in the difficult-to-direct preparation of specific crystalline molybdenum carbide under an ammonia atmosphere and preparation steps, and prepares a pure β-phase molybdenum carbide catalyst supported by mesoporous nitrogen-doped carbon. The solid-phase reaction of carbonaceous compounds in biomass and molybdenum salts in an ammonia atmosphere produces a large number of mesopores, and the in-situ generated β-phase molybdenum carbide particles are embedded in the nitrogen-doped carbon, suppressing the tendency of particles to aggregate and grow, thereby achieving a high dispersion of β-phase molybdenum carbide. The β-phase molybdenum carbide is surrounded by nitrogen-doped carbon, making it difficult to agglomerate at high temperatures. In addition, the porous and loose nitrogen-doped carbon has good thermal conductivity, so the prepared catalyst has good thermal stability.

[0017] 3. The catalyst obtained by the present invention can efficiently denitrogenate quinoline and achieve targeted conversion, with a conversion rate of not less than 99%, a denitrogenation rate of not less than 99%, and an aromatic compound selectivity of not less than 86%. In addition, the catalyst has the characteristic of low hydrogen consumption due to the avoidance of hydrogenation saturation reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a transmission electron microscope image of the nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst (Cat-1) prepared in Example 1.

[0019] Figure 2This is a transmission electron microscope image of the nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst (Cat-2) prepared in Example 2.

[0020] Figure 3 This is a transmission electron microscope image of the nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst (Cat-3) prepared in Example 3.

[0021] Figure 4 1 is the X-ray diffraction pattern of the nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst prepared in Examples 1, 2 and 3. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0023] Example 1

[0024] The present embodiment provides a method for preparing a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst, comprising the following steps:

[0025] (1) See Table 1. Grind soybean straw into powder (80 mesh) and dry in an oven at 100°C for 10 h.

[0026] (2) The biomass powder obtained in step (1) was mixed with ammonium molybdate in a mass ratio of 0.8:1 and dissolved in distilled water, with the mass ratio of ammonium molybdate to distilled water being 1:1. After 8 h of mechanical stirring and 2 h of ultrasonic mixing, the mixture was transferred to a vacuum oven and dried at 80 °C for 12 h to obtain a precursor.

[0027] (3) The precursor prepared in step (2) was ground into a 120-mesh powder, transferred to a porcelain boat and placed in a tubular heating furnace. In an ammonia atmosphere (flow rate of 150 mL / min), the temperature was raised to 700°C at a rate of 4°C / min and maintained for 2 h, and then cooled to room temperature to obtain a nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst, which was labeled Cat-1.

[0028] The obtained product Cat-1 is a catalyst, the components of which are shown in Table 2. It is a pure β-phase molybdenum carbide supported by mesoporous nitrogen-doped carbon ( Figure 4 as shown); Figure 1 As shown, the specific surface area is 110m 2 / g, pore volume 0.5cm 3 / g, an average pore diameter of 20 nm, a Mo content of 75 wt%, a C content of 21 wt%, a N content of 3 wt%, and an O content of 1 wt%.

[0029] Application of this embodiment:

[0030] The prepared nitrogen-doped carbon-β phase molybdenum carbide composite material Cat-1 was loaded into a fixed bed hydrogenation reactor, and the reaction conditions were controlled as follows: H2 pressure of 4.0 MPa, liquid hourly volume space velocity of 18 h -1 The hydrogen / oil volume ratio is 600 / 1, the temperature is 380°C, and quinoline is catalyzed to react, which can efficiently denitrogenate quinoline and convert it in a targeted manner to obtain highly selective aromatic compounds. In addition, it has the characteristic of low hydrogen consumption due to avoiding the occurrence of hydrogenation saturation reaction.

[0031] The quinoline conversion rate was 99.5%, the denitrification rate was 99.2%, and the total selectivity of aromatic products was 91.7%, including benzene (8.6%), toluene (31.6%), ethylbenzene (16.9%), and n-propylbenzene (34.6%).

[0032] Example 2

[0033] The present embodiment provides a method for preparing a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst, comprising the following steps:

[0034] (1) As shown in Table 1, the cotton straw was ground into powder (90 mesh) and dried in an oven at 102 °C for 9 h;

[0035] (2) The biomass powder obtained in step (1) was mixed with ammonium molybdate in a mass ratio of 1:1 and dissolved in distilled water, with the mass ratio of ammonium molybdate to distilled water being 1:1.5. After 9 h of mechanical stirring and 1.5 h of ultrasonic mixing, the mixture was transferred to a vacuum oven and dried at 90 °C for 12 h to obtain a precursor.

[0036] (3) The precursor prepared in step (2) was ground into a 100-mesh powder, transferred to a porcelain boat and placed in a tubular heating furnace. In an ammonia atmosphere (flow rate of 100 mL / min), the temperature was raised to 650°C at a rate of 5°C / min and maintained for 3 h, and then cooled to room temperature to obtain a nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst, which was labeled Cat-2.

[0037] The obtained product Cat-2 is a catalyst, the components of which are shown in Table 2. It is a pure β-phase molybdenum carbide supported by mesoporous nitrogen-doped carbon ( Figure 4 as shown); Figure 2 As shown, the specific surface area is 100m 2 / g, pore volume 0.4cm 3 / g, the average pore diameter is 22nm, the Mo content is 61wt%, the C content is 31wt%, the N content is 4wt%, and the O content is 4wt%.

[0038] Application of this embodiment:

[0039] The prepared nitrogen-doped carbon-β phase molybdenum carbide composite material Cat-2 was loaded into a fixed bed hydrogenation reactor, and the reaction conditions were controlled as follows: H2 pressure of 6.0 MPa, liquid hourly volume space velocity of 15 h -1 The catalytic reaction of quinoline at a hydrogen / oil volume ratio of 500 / 1 and a temperature of 390°C can efficiently denitrogenate quinoline and directionally convert it to obtain highly selective aromatic compounds. In addition, the process has the characteristic of low hydrogen consumption due to the avoidance of hydrogenation saturation reaction.

[0040] The quinoline conversion rate was 99.1%, the denitrification rate was 99.0%, and the total selectivity of aromatic products was 85.2%, including benzene (5.6%), toluene (28.1%), ethylbenzene (18.7%), and n-propylbenzene (87.1%).

[0041] Example 3

[0042] The present embodiment provides a method for preparing a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst, comprising the following steps:

[0043] (1) As shown in Table 1, sorghum straw was ground into powder (100 mesh) and dried in an oven at 105 °C for 8 h;

[0044] (2) The biomass powder obtained in step (1) was mixed with ammonium molybdate in a mass ratio of 0.9:1 and dissolved in distilled water, and the mass ratio of ammonium molybdate to distilled water was 1:1.2. After 10 h of mechanical stirring and 1 h of ultrasonic mixing, the mixture was transferred to a vacuum oven and dried at 85 ° C for 11 h to obtain a precursor.

[0045] (3) The precursor prepared in step (2) was ground into a 110 mesh powder, transferred to a porcelain boat and placed in a tubular heating furnace. In an ammonia atmosphere (flow rate of 120 mL / min), the temperature was raised to 750°C at a rate of 6°C / min and maintained for 1 h, and then cooled to room temperature to obtain a nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst, which was labeled Cat-3.

[0046] The obtained product Cat-3 is a catalyst, the components of which are shown in Table 2. It is a pure β-phase molybdenum carbide supported by mesoporous nitrogen-doped carbon ( Figure 4 as shown); Figure 3 As shown, the specific surface area is 80m 2 / g, pore volume 0.3cm 3 / g, an average pore diameter of 25 nm, a Mo content of 68 wt%, a C content of 25 wt%, a N content of 2 wt%, and an O content of 5 wt%.

[0047] Application of this embodiment:

[0048] The prepared nitrogen-doped carbon-β phase molybdenum carbide composite material Cat-3 was filled in a fixed bed hydrogenation reactor, and the reaction conditions were controlled as follows: H2 pressure of 5.0 MPa, liquid hourly volume space velocity of 17 h -1 The hydrogen / oil volume ratio is 400 / 1, the temperature is 360°C, and quinoline is catalyzed to react, which can efficiently denitrogenate quinoline and convert it in a targeted manner to obtain highly selective aromatic compounds. In addition, it has the characteristic of low hydrogen consumption due to avoiding the occurrence of hydrogenation saturation reaction.

[0049] The quinoline conversion rate was 99.7%, the denitrification rate was 99.5%, and the total selectivity of aromatic products was 87.1%, including benzene (11.2%), toluene (25.3%), ethylbenzene (21.9%), and n-propylbenzene (28.7%).

[0050] Table 1 Elemental composition of soybean straw, sorghum straw and cotton straw

[0051]

[0052] Table 2 Elemental composition of nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst

[0053]

[0054] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst, characterized in that: It has a porous nano-sized structure and is a pure β-phase molybdenum carbide supported by mesoporous nitrogen-doped carbon with a specific surface area of ​​80m 2 / g~110m 2 / g, pore volume 0.3cm 3 / g~0.5cm 3 / g, an average pore diameter of 20nm-25nm, a Mo content of 61wt%-75wt%, a C content of 21wt%-31wt%, a N content of 2wt%-4wt%, and an O content of 1wt%-5wt%; The preparation method of the composite catalyst comprises the following steps: (1) Grind the biomass into 80-100 mesh powder and dry it in an oven at 100-105°C for 8-10 hours; (2) The biomass powder prepared in step (1) was mixed and dissolved in distilled water with ammonium molybdate in a mass ratio of (0.8-1):1, and the mass ratio of ammonium molybdate to distilled water was 1:(1-1.5). After mechanical stirring for 8 h to 10 h and ultrasonic mixing for 1 h to 2 h, the mixture was transferred to a vacuum oven and dried at 80 ° C to 90 ° C for 10 h to 12 h to obtain a precursor; (3) Grinding the precursor obtained in step (2) into 100-120 mesh powder, transferring it to a tubular heating furnace, heating it to 650-750°C at a rate of 4-6°C / min and maintaining it for 1-3 hours in an ammonia atmosphere with a flow rate of 100 mL / min-150 mL / min, and then cooling it to room temperature to obtain a nitrogen-doped carbon-β-phase molybdenum carbide composite material; The biomass includes soybean straw, sorghum straw and cotton straw.

2. The method for preparing a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst according to claim 1, characterized in that: The following steps are involved: (1) Grind sorghum straw into 100-mesh powder and dry it in an oven at 105°C for 8 h; (2) The biomass powder prepared in step (1) was mixed with ammonium molybdate in a mass ratio of 0.9:1 and dissolved in distilled water, with the mass ratio of ammonium molybdate to distilled water being 1:1.

2. After mechanical stirring for 10 h and ultrasonic mixing for 1 h, the mixture was transferred to a vacuum oven and dried at 85 ° C for 11 h to obtain a precursor; (3) The precursor obtained in step (2) was ground into a 110 mesh powder, transferred to a porcelain boat and placed in a tubular heating furnace. In an ammonia atmosphere, the flow rate was 120 mL / min, the temperature was increased to 750°C at a rate of 6°C / min and maintained for 1 h, and then cooled to room temperature to obtain a nitrogen-doped carbon-β-phase molybdenum carbide composite catalyst.

3. The use of a biomass-based nitrogen-doped carbon-molybdenum carbide composite catalyst according to claim 1, characterized in that: The specific steps are as follows: the prepared nitrogen-doped carbon-β phase molybdenum carbide composite material is loaded into a fixed bed hydrogenation reactor, and quinoline is subjected to a hydrogenation catalytic reaction. The reaction conditions are controlled as follows: the H2 pressure is 4.0 MPa to 6.0 MPa, and the liquid hourly volume space velocity is 10 to 18 h -1 , the hydrogen / oil volume ratio is 400 / 1 to 600 / 1, and the temperature is 360 to 390°C; finally, quinoline is denitrogenated to obtain aromatic compounds.

Images