Ni-molybdenum oxide / Nb2O5 nano composite catalyst as well as preparation method and application thereof

Abstract

The invention provides a Ni-molybdenum oxide / Nb2O5 nano composite catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The catalyst precursor is prepared by adopting an excessive impregnation method, then the Ni-molybdenum oxide / Nb2O5 nano-composite catalyst is prepared by adopting a hydrogen reduction treatment method, active components in the catalyst are uniformly loaded, and the catalyst has excellent self-hydrogen hydrothermal catalytic performance. The Ni-molybdenum oxide / Nb2O5 nano composite catalyst prepared by the invention can minimize the dissociation energy of a C-O bond, promote the breakage of the C-O bond, enable the reaction to be carried out in a forward direction, and realize high-value conversion of guaiacol to catechol under mild reaction conditions without exogenous hydrogen.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst and a preparation method and application thereof. Background Art

[0002] As the only sustainable source of aromatics, lignin has good prospects for industrial application. However, its stable and complex structure reduces the potential and reaction controllability of upgrading lignin to viable and valuable products. Therefore, in order to further achieve efficient utilization of lignin, it is usually converted into platform compounds such as guaiacol and then directed into downstream products. Guaiacol, as a typical phenolic compound, can be upgraded through chemical synthesis and catalytic conversion to obtain high-value products such as ethers and phenols. Catechol, as one of the high-value products of guaiacol catalytic conversion, can be used as an important chemical / chemical intermediate for the synthesis of fine chemicals such as vanillin, antioxidants and pesticides. It can also be used as a precursor of epoxy resin curing agent or polyamide monomer for the preparation of high-temperature resistant materials, showing great economic potential.

[0003] O-demethylation (ODM) is a key reaction in the conversion of guaiacol to catechol. Traditional inorganic acid-catalyzed processes for this reaction are relatively mature. However, aqueous inorganic acids are often highly corrosive, resulting in relatively harsh reaction conditions and irreversible damage to the reactor. Consequently, heterogeneously mediated liquid-phase ODM systems for the conversion of guaiacol have attracted considerable attention. The core of these systems lies in the catalyst and high H₂ pressure. While noble metal-based catalysts have demonstrated excellent catalytic performance, their scarcity and high cost have hindered their commercialization. Furthermore, the safety and affordability of external hydrogen sources during production, storage, and transportation have limited the development of this process. Therefore, leveraging the potential hydrogen source (-OCH₃) within the lignin structure and hydrogen supplied by green solvents, designing highly efficient catalysts with non-noble metals as catalytically active centers and excellent CO bond cleavage ability is of great significance for the self-hydrogen transfer catalysis of lignin and its model compounds to catechol. Summary of the Invention

[0004] The present invention aims to provide a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst and its preparation method and application, which can realize high-value conversion of guaiacol to catechol under mild reaction conditions without exogenous hydrogen.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, comprising the following steps:

[0007] mixing a nickel source and a molybdenum source with water to obtain a nickel-molybdenum bimetallic salt solution;

[0008] mixing niobium pentoxide with the nickel-molybdenum bimetallic salt solution, and sequentially heating, drying, and calcining the resulting composite suspension to obtain a catalyst precursor;

[0009] The catalyst precursor is reduced under a reducing atmosphere to obtain a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst.

[0010] Preferably, the nickel source includes nickel nitrate or nickel chloride; and the molybdenum source includes ammonium molybdate or sodium molybdate.

[0011] Preferably, the molar ratio of the nickel source, molybdenum source and water is 0-0.05:0-0.004:3.33, and the molar numbers of the nickel source and the molybdenum source are not 0.

[0012] Preferably, the molar ratio of niobium pentoxide to nickel source and molybdenum source is 0.0376:0-0.05:0-0.04, and the molar numbers of the nickel source and the molybdenum source are not 0;

[0013] The heating treatment temperature is 60-80°C and the time is 4-6 hours; the heating treatment is carried out under stirring conditions, the stirring speed is 200-400 rpm, and the time is 4-6 hours;

[0014] The drying temperature is 90-120°C and the drying time is 12-24 hours;

[0015] The calcination temperature is 400-600° C. and the calcination time is 3-5 hours.

[0016] Preferably, the reducing atmosphere is a hydrogen atmosphere, and the flow rate of the hydrogen is 80 to 100 mL / min;

[0017] The reduction reaction temperature is 500-600° C., and the time is 1-3 hours.

[0018] The present invention provides a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst prepared by the preparation method described in the above technical solution.

[0019] Preferably, in the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, the theoretical loading amount of Ni element is 8-20 wt%, and the theoretical loading amount of molybdenum oxide is 8-20 wt%.

[0020] The present invention provides the use of the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst described in the above technical solution in catalyzing the hydrothermal conversion of guaiacol to prepare catechol.

[0021] Preferably, the application method comprises: mixing a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, guaiacol and water, and performing a hydrothermal reaction to obtain catechol.

[0022] Preferably, the usage ratio of the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, guaiacol and water is 0.3-0.7 g:5 mL:50 mL; the conditions of the hydrothermal reaction include: reaction temperature of 280-320°C, reaction time of 1-3 h, and reactor speed of 300-400 rpm.

[0023] The present invention provides a preparation method of a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, wherein Ni and Mo elements are jointly loaded on a Nb2O5 carrier, wherein Ni has high catalytic activity in hydrogenation reactions; Mo has good CO bond breaking ability and hydrogenation assisting ability; niobium pentoxide is used as a catalyst carrier, and its abundant oxygen vacancies on the surface can effectively reduce the dissociation energy barrier of water molecules and significantly promote the hydrogen evolution process; the present invention simultaneously loads transition metal nickel and molybdenum oxide on the surface of the Nb2O5 carrier, which can form a strong metal-carrier electronic interaction (SMSI effect), improve sintering resistance and catalytic activity, and show significant advantages in a hydrothermal catalytic system.

[0024] The preparation method of the present invention is simple and has low raw material cost. The catalyst precursor is first prepared by an excess impregnation method, and then the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst is prepared by a hydrogen reduction treatment method. The active components in the catalyst are evenly loaded and have excellent self-hydrogen hydrothermal catalytic performance.

[0025] The Ni-molybdenum oxide / Nb2O5 supported catalyst prepared by the present invention can activate the O-demethylation reaction (ODM), Ni promotes the hydrogenation process of guaiacol, and molybdenum oxide (MoO x ) provides oxygen absorption and assists in situ hydrogenation. The Nb2O5 support surface also possesses both B and L acid sites, minimizing the dissociation energy of the CO bond, promoting its cleavage and enabling the forward reaction. This allows for high-value conversion of guaiacol to catechol under mild reaction conditions without exogenous hydrogen. Therefore, this invention provides a novel Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst for the one-pot preparation of catechol from guaiacol in a hydrogen environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 5Ni-5MoO prepared in Example 1 x / Nb2O5 nanocomposite catalyst and 10Ni / Nb2O5 in comparative example 1 and 10Mo / Nb2O5 in comparative example 2. (a) is the scanning electron microscope characterization image of Ni / Nb2O5 in comparative example 1 at a scale of 200nm; (b) is the scanning electron microscope characterization image of 5Ni-5MoO in example 1. x (c) is a scanning electron microscope characterization image of 10Mo / Nb2O5 at a scale of 200nm; (d) is a scanning electron microscope characterization image of 10Mo / Nb2O5 at a scale of 200nm in Comparative Example 2;

[0027] Figure 2 The 10Ni / Nb2O5 in Comparative Example 1, the 10Mo / Nb2O5 in Comparative Example 2, and the 5Ni-5MoO x Schematic diagram of the temperature-programmed reduction test results of / Nb2O5 (Temperature-temperature, Intensity-intensity);

[0028] Figure 3 The 10Ni / Nb2O5 metal nanocatalyst in Comparative Example 1 and the 5Ni-5MoO x XRD characterization analysis diagram of 10Mo / Nb2O5 nanocomposite catalyst and 10Mo / Nb2O5 metal nanocatalyst and niobium pentoxide raw material in Comparative Example 2;

[0029] Figure 4 This is a graph showing the results of preparing catechol by hydrothermal conversion of guaiacol using different catalysts in Application Example 1 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0030] In the present invention, unless otherwise specified, the required raw materials or reagents are commercially available products well known to those skilled in the art.

[0031] The present invention provides a method for preparing a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, comprising the following steps:

[0032] mixing a nickel source and a molybdenum source with water to obtain a nickel-molybdenum bimetallic salt solution;

[0033] mixing niobium pentoxide with the nickel-molybdenum bimetallic salt solution, and sequentially heating, drying, and calcining the resulting composite suspension to obtain a catalyst precursor;

[0034] The catalyst precursor is reduced under a reducing atmosphere to obtain a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst.

[0035] In the present invention, a nickel source and a molybdenum source are dissolved in deionized water to obtain a nickel-molybdenum bimetallic salt solution.

[0036] In the present invention, the nickel source preferably includes nickel nitrate or nickel chloride, more preferably nickel nitrate hexahydrate; the molybdenum source preferably includes ammonium molybdate or sodium molybdate, more preferably ammonium molybdate.

[0037] In the present invention, the molar ratio of the nickel source, molybdenum source and water is preferably 0-0.05:0-0.004:3.33, and the molar numbers of the nickel source and the molybdenum source are both not 0, more preferably 0-0.04259:0-0.00372:3.33, and more preferably 0.01067:0.00231:3.33.

[0038] The present invention preferably adds a niobium pentoxide carrier to a nickel-molybdenum bimetallic salt solution to obtain a composite suspension; the composite suspension is sequentially subjected to heat treatment, drying and calcination to obtain a NiO-molybdenum oxide-loaded Nb2O5 catalyst precursor.

[0039] In the present invention, the molar ratio of niobium pentoxide to nickel source and molybdenum source is preferably 0.0376:0-0.05:0-0.04, and the molar numbers of the nickel source and the molybdenum source are both not 0, more preferably 0.0376:0-0.0426:0-0.02606, and more preferably 0.0376:0.01617:0.00231.

[0040] In the present invention, the temperature of the heat treatment is preferably 60 to 80°C, more preferably 65 to 75°C, and more preferably 70°C; the time is preferably 4 to 6 hours, more preferably 4.5 to 5.5 hours, and more preferably 5 hours; the heat treatment is preferably carried out in a water bath with stirring, the stirring speed is preferably 200 to 400 rpm, more preferably 250 to 350 rpm, and more preferably 300 rpm; the time is preferably 4 to 6 hours, more preferably 4.5 to 5.5 hours, and more preferably 5 hours. The present invention improves the solubility of the metal salt by heating and stirring.

[0041] In the present invention, the drying temperature is preferably 90-120° C., more preferably 100-110° C., and more preferably 105° C.; the drying time is preferably 12-24 h, more preferably 14-18 h, and more preferably 16 h.

[0042] In the present invention, the calcination temperature is preferably 400-600° C., more preferably 450-550° C., and more preferably 500° C.; the calcination time is preferably 3-5 h, more preferably 3.5-4.5 h, and more preferably 4 h.

[0043] In the present invention, the reducing atmosphere is preferably a hydrogen atmosphere, and the flow rate of the hydrogen is preferably 80 to 100 mL / min, more preferably 85 to 95 mL / min, and even more preferably 90 mL / min.

[0044] In the present invention, the temperature of the reduction reaction is preferably 500-600° C., more preferably 530-570° C., and more preferably 544° C.; the time is preferably 1-3 h, more preferably 1.5-2.5 h, and more preferably 2 h.

[0045] The present invention provides a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst prepared by the preparation method described in the above technical solution.

[0046] In the present invention, in the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, the theoretical loading amount of Ni element is preferably 8-20 wt%, and the theoretical loading amount of molybdenum oxide is preferably 8-20 wt%.

[0047] The present invention provides the use of the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst described in the above technical solution in catalyzing the hydrothermal conversion of guaiacol to prepare catechol.

[0048] In the present invention, the application method preferably comprises: mixing Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, guaiacol and water, and performing a hydrothermal reaction to obtain catechol.

[0049] In the present invention, the usage ratio of the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, guaiacol and water is preferably 0.3-0.7 g:5 mL:50 mL, more preferably 0.45-0.55 g:5 mL:50 mL, and more preferably 0.5 g:5 mL:50 mL.

[0050] In the present invention, the conditions of the hydrothermal reaction preferably include: a reaction temperature of 280 to 320°C, more preferably 290 to 310°C, more preferably 300°C; a reaction time of 1 to 3 hours, more preferably 1.5 to 2.5 hours, more preferably 2 hours; and a reactor speed of 300 to 400 rpm, more preferably 330 to 370 rpm, more preferably 350 rpm.

[0051] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0052] The following experimental methods and detection methods, unless otherwise specified, are conventional methods; the following reagents and raw materials, unless otherwise specified, are commercially available.

[0053] Example 1

[0054] Dissolve 0.01067 mol of nickel nitrate hexahydrate and 0.00231 mol of ammonium molybdate in 3.33 mol of deionized water to obtain a nickel-molybdenum bimetallic salt solution;

[0055] 10 g of niobium pentoxide carrier was added to the nickel-molybdenum bimetallic salt solution to obtain a composite suspension. The composite suspension was magnetically stirred in a water bath at 70 ° C for 5 h at a speed of 300 rpm, then dried in an oven at 105 ° C for 16 h, and finally calcined in a muffle furnace at 500 ° C for 4 h to obtain the loaded NiO-MoO x Nb2O5 catalyst precursor;

[0056] The obtained catalyst precursor was subjected to a reduction reaction under a hydrogen atmosphere. The hydrogen flow rate was set to 90 mL / min, the reduction temperature was set to 544 °C, and the time was set to 2 h to obtain a nanocomposite catalyst, which was recorded as 5Ni-5MoO x / Nb2O5.

[0057] Comparative Example 1

[0058] The other conditions in Example 1 were kept unchanged, and the molar amounts of nickel nitrate hexahydrate, ammonium molybdate, and deionized water were modified to 0.04259 mol, 0 mol, and 3.33 mol, respectively. The temperature of the reduction reaction was 434° C. to obtain 10Ni / Nb2O5 metal nanoparticles.

[0059] Comparative Example 2

[0060] The other conditions in Example 1 were kept unchanged, and the molar amounts of nickel nitrate hexahydrate, ammonium molybdate, and deionized water were modified to 0 mol, 0.00372 mol, and 3.33 mol, respectively. The temperature of the reduction reaction was set to 653° C. to obtain 10Mo / Nb2O5 metal nanoparticles.

[0061] Comparative Example 3

[0062] The other conditions in Example 1 were kept unchanged, and the temperature of the reduction reaction was changed to 748° C. to obtain 5Ni-5Mo / Nb 2 O 5 metal nanoparticles.

[0063] Characterization and performance testing

[0064] 1) 5Ni-5MoO prepared in Example 1 x The / Nb2O5 nanocomposite catalyst and the 10Ni / Nb2O5 in comparative example 1 and the 10Mo / Nb2O5 in comparative example 2 were characterized by scanning electron microscopy. Figure 1 As shown; Figure 1 In the figure, (a) is the scanning electron microscope characterization image of Ni / Nb2O5 in comparative example 1 at a scale of 200nm; (b) is the scanning electron microscope characterization image of 5Ni-5MoO in example 1. x / Nb2O5 scanning electron microscope characterization image at 200nm scale; (c) is the scanning electron microscope characterization image of 10Mo / Nb2O5 in comparative example 2 at 200nm scale; Figure 1 It can be seen that Ni metal is dispersed in granular form, Mo metal is arranged in a non-uniform mosaic in a blocky manner, and the 5Ni-5MoO containing bimetallic components is x / Nb2O5 nanocomposite catalyst showed the characteristics of reduced granular fragments and reduced block particle size, and the overall loading was more uniform.

[0065] 2) 10Ni / Nb2O5 in Comparative Example 1, 10Mo / Nb2O5 in Comparative Example 2, 5Ni-5MoO x / Nb2O5 were subjected to temperature programmed reduction tests respectively, and the temperature programmed reduction test results of different materials were obtained, as shown in the figure. Figure 2 As shown. Figure 2 It can be seen that the reduction peak of NiO appears at 350-440℃ for 10Ni / Nb2O5 metal nanocatalyst, and the reduction peak of MoO appears at about 640-670℃ for 10Mo / Nb2O5 metal nanocatalyst. x Reduction peak of 5Ni-5MoO x The surface redox peaks of the 10Ni / Nb2O5 nanocomposite catalyst at 470-550℃ are similar to those of the 10Ni / Nb2O5 metal nanocatalyst, and the surface redox peaks of the 10Mo / Nb2O5 metal nanocatalyst at 725-775℃ are similar to those of the 10Mo / Nb2O5 metal nanocatalyst. Therefore, in order to retain the oxidation state of the Mo element, 544℃ was selected for reduction to obtain 5Ni-5MoO x / Nb2O5 nanocomposite catalyst.

[0066] 3) The 10Ni / Nb2O5 metal nanocatalyst in Comparative Example 1 and the 5Ni-5MoO x The / Nb2O5 nanocomposite catalyst and the 10Mo / Nb2O5 metal nanocatalyst and niobium pentoxide raw material in comparative example 2 were characterized by XRD to obtain an XRD characterization analysis diagram, as shown in FIG. Figure 3 As shown; Figure 3 The standard card shows that the diffraction peaks of the Nb2O5 carrier can be observed to have two oxide crystal phases, namely Nb2O5 (2θ=22.6°, 28.3°) and NbO2 (2θ=23.8°), indicating that Nb 5+ Can be partially reduced to Nb during the reduction process 4+ Therefore, the catalyst carrier exists in the form of NbO x , which can provide some oxygen vacancies, and the position and strength are basically stable and consistent, which shows that 5Ni-5MoO xThe basic structure of the niobium pentoxide support was not destroyed during the preparation of the / Nb2O5 nanocomposite catalyst, and it was very stable. The significant diffraction peaks at 36.6° and 40.5° correspond to MoO2 and Mo4O, respectively. 11 The reflective crystal plane of the phase indicates that Mo remains in the oxide state during the preparation process, resulting in a better catalytic effect; and the existence of Ni2Mo3O8 (2θ=25.5°, 36.5°) and NiMoO4 (2θ=25.5°, 36.5°) phases indicates that there is a certain interaction between the bimetallic species during the preparation process.

[0067] 4) The 5Ni-5MoO prepared in Example 1 x The 10Ni / Nb2O5 and 10Mo / Nb2O5 nanocomposite catalysts prepared in Examples 1 and 2 were characterized by ICP-OES, and the property parameters of different nanocomposite catalysts were obtained, as shown in Table 1.

[0068] Table 1 Property parameters of different nanocomposite catalysts

[0069] Case Ni (wt%) <![CDATA[MoO x (wt%)]]> Example 1 8.91 8.27 Comparative Example 1 19.15 - Comparative Example 2 - 13.816

[0070] It can be seen from Table 1 that 5Ni-5MoO x / Nb2O5 nanocomposite catalyst has a good loading effect during the preparation process, and the actual loading amount (Ni and MoO x The ratio of the total loading amount (17.18 wt%) to the theoretical loading amount (20 wt%) is 85.9%, indicating that the Ni and Mo metals did not significantly lose or volatilize during the loading process, and the loading efficiency was high, providing a basis for the catalytic performance.

[0071] Application Example 1

[0072] In a hydrothermal reactor, 0.5 g of 5Ni-5MoO prepared in Example 1 was added. x / Nb2O5 nanocomposite catalyst, 5 mL of guaiacol and 50 mL of water were mixed and hydrothermally reacted at a temperature of 300°C and a reactor speed of 350 rpm for 120 min. The content and selectivity of catechol in the product were tested.

[0073] Comparative Application Example 1

[0074] The other conditions in the control application example 1 remain unchanged, and the 5Ni-5MoO prepared in the example 1 is not added. x / Nb2O5 nanocomposite catalyst, and the content of catechol in the product was tested.

[0075] Application Comparative Example 2

[0076] The other conditions in Example 1 remain unchanged, and the 5Ni-5MoO prepared in Example 1 is x The 10Ni / Nb2O5 nanocomposite catalyst was replaced by the 10Ni / Nb2O5 metal nanocatalyst in Comparative Example 1, and the content of catechol in the product was tested.

[0077] Application Comparative Example 3

[0078] The other conditions in Example 1 remain unchanged, and the 5Ni-5MoO prepared in Example 1 is x The Mo / Nb2O5 nanocomposite catalyst was replaced by 10Mo / Nb2O5 in Comparative Example 2, and the content of catechol in the product was tested.

[0079] Comparative Application Example 4

[0080] The other conditions in Example 1 remain unchanged, and the 5Ni-5MoO prepared in Example 1 is x The 5Ni-5Mo / Nb2O5 nanocomposite catalyst was replaced by the 5Ni-5Mo / Nb2O5 in Comparative Example 3, and the selectivity of catechol in the product was semi-quantitatively tested by GC-MS peak separation method.

[0081] The test results of quantitative detection of catechol content by GC-MS internal standard method for the products of Application Example 1 and Comparative Examples 1 to 3 are recorded in Table 2. The specific numerical comparison is shown in Table 2. Figure 4 .

[0082] Table 2 Test results of catechol content in the products of Application Example 1 and Comparative Examples 1 to 3

[0083] Application Cases Catechol content (mg / g) Application Example 1 26.628 Comparative Application Example 1 8.439 Application Comparative Example 2 10.946 Application Comparative Example 3 23.961

[0084] It can be seen from Table 2 that at a temperature of 300°C, 5Ni-5MoO x / Nb2O5 nanocomposite catalyst enables the content of catechol prepared by self-hydrogenation hydrothermal conversion of guaiacol to reach 26.628 mg / g, which is 18.189 mg / g higher than that under the condition of no catalyst; compared with the conditions of 10Ni / Nb2O5 metal nanocatalyst and 10Mo / Nb2O5 metal nanocatalyst, the content is increased by 15.682 mg / g and 2.667 mg / g respectively, indicating that 5Ni-5MoO x / Nb2O5 nanocomposite catalyst has good hydrothermal catalytic effect.

[0085] The test results of semi-quantitative detection of catechol selectivity by GC-MS peak separation method for the products of Application Example 1 and Comparative Example 4 are recorded in Table 3.

[0086] Table 3 Test results of catechol selectivity in the products of Application Example 1 and Comparative Example 4

[0087] Application Cases Catechol selectivity (%) Application Example 1 86.78 Comparative Application Example 4 44.09

[0088] As shown in Table 3, under the condition of 300℃, the 5Ni-5MoO x The / Nb2O5 nanocomposite catalyst enables the selectivity of guaiacol to be converted into catechol by self-hydrogenation hydrothermal conversion to reach 86.78%, which is 42.69% higher than that of the 5Ni-5Mo / Nb2O5 used in Comparative Example 4. This shows that among the bimetallic nanocomposite catalysts, the selective catalytic effect of retaining the oxidation state of the Mo element is better than that of the Mo element.

[0089] From the above examples, it can be seen that under the condition of temperature of 300°C, the 5Ni-5MoO x / Nb2O5 nanocomposite catalyst can activate O-demethylation reaction (ODM) through a "one-pot method", Ni promotes the hydrogenation process of guaiacol, and MoO x It provides oxygen absorption capacity and assists in-situ hydrogenation. At the same time, the surface of the Nb2O5 carrier has both B acid and L acid sites, which can minimize the dissociation energy of the CO bond, promote the breakage of the CO bond, and make the reaction proceed in the forward direction, thus achieving high-value conversion of guaiacol to catechol under mild reaction conditions without exogenous hydrogen.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, characterized in that: The following steps are involved: mixing a nickel source and a molybdenum source with water to obtain a nickel-molybdenum bimetallic salt solution; mixing niobium pentoxide with the nickel-molybdenum bimetallic salt solution, and sequentially heating, drying, and calcining the resulting composite suspension to obtain a catalyst precursor; The catalyst precursor is reduced under a reducing atmosphere to obtain a Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst.

2. The preparation method according to claim 1, characterized in that The nickel source includes nickel nitrate or nickel chloride; the molybdenum source includes ammonium molybdate or sodium molybdate.

3. The preparation method according to claim 2, characterized in that The molar ratio of the nickel source, the molybdenum source and water is 0-0.05:0-0.004:3.33, and the molar numbers of the nickel source and the molybdenum source are not 0.

4. The preparation method according to claim 1 or 3, characterized in that The molar ratio of the niobium pentoxide to the nickel source and the molybdenum source is 0.0376:0-0.05:0-0.04, and the molar numbers of the nickel source and the molybdenum source are not 0; The heating treatment temperature is 60-80°C and the time is 4-6 hours; the heating treatment is carried out under stirring conditions, the stirring speed is 200-400 rpm, and the time is 4-6 hours; The drying temperature is 90-120°C and the drying time is 12-24 hours; The calcination temperature is 400-600° C. and the calcination time is 3-5 hours.

5. The preparation method according to claim 4, characterized in that The reducing atmosphere is a hydrogen atmosphere, and the flow rate of the hydrogen is 80-100 mL / min; The reduction reaction temperature is 500-600° C., and the time is 1-3 hours.

6. The Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. The Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst according to claim 6, characterized in that: In the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, the theoretical loading amount of Ni element is 8-20 wt%, and the theoretical loading amount of molybdenum oxide is 8-20 wt%.

8. Use of the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst according to claim 6 or 7 in catalyzing the hydrothermal conversion of guaiacol to produce catechol.

9. The use according to claim 8, characterized in that The application method comprises: mixing a Ni-molybdenum oxide / Nb2O5 nano composite catalyst, guaiacol and water, and performing a hydrothermal reaction to obtain catechol.

10. The use according to claim 9, characterized in that The amount ratio of the Ni-molybdenum oxide / Nb2O5 nanocomposite catalyst, guaiacol and water is 0.3-0.7 g:5 mL:50 mL; the conditions of the hydrothermal reaction include: reaction temperature of 280-320° C., reaction time of 1-3 h, and reactor speed of 300-400 rpm.

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