A Pt-doped molybdenum-based catalyst and its preparation method and application

Abstract

The present invention belongs to the field of catalyst technology, specifically a Pt-doped molybdenum-based catalyst and its preparation method and application. Melamine and ammonium molybdate tetrahydrate are placed in a container, H2PtCl6 solution and an appropriate amount of pure water are added, and magnetic stirring is performed at room temperature. The beaker is then placed in an oil bath pot and stirred and evaporated until it is dry, and then the residue is completely dried and ground to obtain a precursor; the obtained precursor is spread in a corundum crucible, and placed in a tubular furnace protected by an inert gas for two-step calcination. After the calcination is completed, it is cooled to room temperature to obtain the Pt-doped molybdenum-based catalyst. The present invention is simple to operate, and the solvent in the preparation process is only water, which is environmentally friendly and pollution-free; the prepared Pt-doped molybdenum-based catalyst achieves high activity and high selectivity in catalytic reduction of aromatic nitro compounds to aromatic amine compounds, and has good cycle stability and universality.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a Pt-doped molybdenum-based catalyst and a preparation method and application thereof. Background Art

[0002] The efficient and selective catalytic reduction of aromatic nitro compounds to organic amines is a very important reaction in the field of fine chemicals and bulk chemicals. The products of aromatic amines are important intermediates for the manufacture of fine chemicals in medicines, pesticides, dyes, polymers and various other industries. However, in this reaction, when catalytically reducing aromatic nitro compounds containing other reducible groups, such as -X (X=F, Cl, Br and I), -C=C, -C≡C, and -C≡N, it is a very big problem to achieve high activity and high selectivity in reducing nitro groups while remaining inert to other groups. At present, researchers have focused a lot of research on improving catalyst performance to solve this problem. Both precious metal catalysts (Pt, Pd, Au, etc.) and non-precious metal catalysts (Fe, Co, Ni, Mo, etc.) have been widely studied. In general, precious metal catalysts have the advantages of high activity and long life, but also have the disadvantages of high price and low selectivity. Although non-precious metal catalysts are low in cost, they often have low catalytic activity. Therefore, combining the advantages and disadvantages of precious metals and non-precious metals, using low-content precious metals and adjusting the structure of non-precious metal catalysts is a reliable method to prepare ideal catalysts.

[0003] Among various non-precious metal catalysts, molybdenum-based materials are very promising in traditional catalysis and electrochemistry due to their abundant earth reserves and unique physical and chemical properties. In particular, the performance of molybdenum oxide in the catalytic reduction of aromatic nitro compounds has attracted the attention of many researchers.

[0004] Although the molybdenum oxide catalysts prepared so far have shown good performance in some aspects, there are still some problems. For example, (1) the catalyst preparation process is complicated and the preparation conditions are harsh. In addition, organic solvents and HF aqueous solutions are often used to prepare and treat the catalysts, which can easily cause environmental pollution. (2) Some MoO2 catalysts have poor cyclic stability and require high-temperature calcination of the catalysts after several cycles to restore their performance, which increases the number of operating steps and economic burden. (3) Some molybdenum oxide catalysts have poor catalytic activity and selectivity, especially when catalytically reducing aromatic nitro compounds containing other unsaturated groups.

[0005] Therefore, it is very important to develop a molybdenum oxide catalyst with simple preparation process, greenness, high catalytic activity and selectivity, and good stability. Summary of the invention

[0006] The purpose of the present invention is to provide a Pt-doped molybdenum-based catalyst and a preparation method and application thereof, so as to solve the problems of the existing molybdenum-based catalyst preparation process being complicated and environmentally unfriendly, having low activity and selectivity and poor cycle stability when catalyzing the reduction of aromatic nitro compounds to generate aromatic amine compounds.

[0007] The present invention is specifically implemented by the following technical scheme. According to a preparation method of a Pt-doped molybdenum-based catalyst proposed in the present invention, the method comprises the following steps:

[0008] (1) Melamine and ammonium molybdate tetrahydrate are placed in a container, H2PtCl6 solution and an appropriate amount of pure water are added to the container, and magnetic stirring is performed for 0.5 to 1 h at room temperature. The beaker is then placed in a 60 to 70 °C oil bath and stirred to evaporate until there is no water. The residue is then placed in a 50 to 60 °C oven and dried completely. The residue is ground into powder using an agate mortar to obtain a precursor.

[0009] (2) Spreading the obtained precursor in a corundum crucible, and then placing it in a tubular furnace protected by inert gas for two-step calcination, the first step calcination temperature is 400°C, and the second step calcination temperature is 700-900°C. After calcination, it is cooled to room temperature to obtain the Pt-doped molybdenum-based catalyst.

[0010] In the aforementioned method for preparing the Pt-doped molybdenum-based catalyst, in step (1), the mass ratio of melamine to ammonium molybdate tetrahydrate is 5:1, and the volume ratio of H2PtCl6 solution to pure water is 17:3.

[0011] In the aforementioned method for preparing a Pt-doped molybdenum-based catalyst, the concentration of the H2PtCl6 solution in step (1) is 0 to 4.7 mg / mL.

[0012] Preferably, in step (2), the first calcination time is 2 to 4 h, and the second calcination time is 2 to 4 h.

[0013] Preferably, the temperature of the second calcination in step (2) is 700°C, 800°C or 900°C.

[0014] More preferably, the catalytic performance of the Pt-doped molybdenum-based catalyst prepared when the second step calcination temperature is 700°C is better.

[0015] In the aforementioned preparation method of the Pt-doped molybdenum-based catalyst, when the two-step calcination is performed in step (2), the corundum crucible can be calcined with or without a lid. Preferably, the corundum crucible is calcined with a lid.

[0016] The present invention also provides a Pt-doped molybdenum-based catalyst prepared according to the above method and its application in catalytic reduction of aromatic nitro compounds to generate aromatic amine compounds. The conditions of the catalytic reaction are: after mixing the Pt-doped molybdenum-based catalyst, aromatic nitro compounds and isopropanol, hydrazine hydrate is added thereto, and the reaction is carried out under magnetic stirring at 100-120°C for 6-30 minutes, and the aromatic nitro compounds are converted into aromatic amine compounds; wherein the molar ratio of hydrazine hydrate to aromatic nitro compounds is 3:1, and the mass ratio of catalyst to aromatic nitro compounds is 1:9.3.

[0017] Furthermore, the aromatic nitro compound is at least one of 3-nitrostyrene, 3-nitrostyreneacetylene, 4-nitrochlorobenzene, 3-bromonitrobenzene and 3-nitrosobenzonitrile.

[0018] Compared with the prior art, the present invention has obvious advantages and beneficial effects. By means of the above technical solution, the present invention can achieve considerable technical progress and practicality, and has a wide range of utilization value, and has at least the following advantages:

[0019] (1) The present invention optimizes the key process of catalyst preparation (such as calcination temperature, whether the corundum crucible has a cover, and whether the precursor contains precious metal Pt) by a method of first impregnation and then calcination, so as to achieve a simple process, green and high-performance catalyst preparation. The entire preparation process is simple and easy to operate, and the solvent used is only water, without organic solvents and HF, etc., which is environmentally friendly and pollution-free, and solves the problems of the currently prepared molybdenum oxide catalyst having a complex preparation process, harsh preparation conditions, and the use of organic solvents and HF solutions that easily cause environmental pollution.

[0020] (2) The Pt-doped molybdenum-based catalyst prepared by the present invention is loaded with a low content of precious metal Pt. The Pt content is only 1.38 wt%, which is much lower than many Pt catalysts that have been publicly reported. Therefore, the cost of the catalyst is significantly reduced and the application range of the catalyst is expanded. The prepared Pt-doped molybdenum-based catalyst has good cycle stability when catalyzing the reduction of aromatic nitro compounds. After five cycles of catalysis, it can still maintain a high catalytic activity and selectivity. After use, the catalyst only needs to be washed with solvent isopropanol and centrifuged before it can be directly used in the next catalytic experiment. The operation process is simple, the performance is stable, and the economic burden is reduced.

[0021] (3) The Pt-doped molybdenum-based catalyst prepared by the present invention has good universality and can achieve both high activity and high selectivity in the catalytic reduction of aromatic nitro compounds. It not only has excellent catalytic performance for catalyzing the conversion of 3-nitrostyrene into 3-aminostyrene, but also has extremely high conversion rate and selectivity. It can also show extremely high catalytic activity and selectivity for other aromatic nitro compounds containing unsaturated groups (such as -Cl, -Br, -C=C, -C≡C, -C≡N), with conversion rate and selectivity both reaching more than 99%, achieving nearly complete conversion and good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the X-ray diffraction (XRD) pattern of the catalyst prepared in Examples 1 to 5 of the present invention.

[0023] Figure 2 This is the full X-ray photoelectron spectroscopy (XPS) spectrum of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1 of the present invention.

[0024] Figure 3 This is a performance diagram of the cyclic use of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1 of the present invention.

[0025] Figure 4 The figure is a comparison of the performance of the catalysts prepared in Examples 1 to 5 of the present invention in catalytic reduction of 3-nitrostyrene.

[0026] Figure 5 It is the conversion rate and selectivity of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1 of the present invention when catalyzing different reaction substrates. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The present invention is described in detail with specific examples below. If no specific conditions are specified in the following examples, they are all carried out according to conventional conditions or conditions recommended by the manufacturer. The raw materials and reagents used without specifying the manufacturer are all conventional products that can be purchased from the market. Example 1

[0029] (1) 2.0 g of melamine and 0.4 g of ammonium molybdate tetrahydrate were placed in a 100 mL beaker, and 17 mL of 4.7 mg / mL H2PtCl6 solution and 3 mL of pure water were added thereto. The mixture was magnetically stirred at room temperature for 0.5 h. The beaker was then placed in a 60°C oil bath and stirred to evaporate until anhydrous. The residue was then dried completely in a 60°C oven and ground into powder using an agate mortar to obtain a precursor for calcination.

[0030] (2) The precursor obtained in step (1) was spread flat in a corundum crucible with a lid, and then placed in an argon-protected tube furnace for calcination in two steps. The first step of calcination was heated at a rate of 5°C / min and kept at 400°C for 2 h. The second step of calcination was then carried out. The second step of calcination was heated at a rate of 5°C / min and kept at 700°C for 2 h. After calcination, it was cooled to room temperature. The obtained Pt-doped molybdenum-based catalyst was a Pt-doped MoO2 / MoC catalyst, denoted as Pt-MoO2 / MoC-7. The weight of the catalyst Pt-MoO2 / MoC-7 was weighed, and the Pt content in the catalyst was calculated to be 1.38 wt.%, which is much lower than many Pt catalysts that have been publicly reported.

[0031] The X-ray diffraction (XRD) pattern of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1 is as follows: Figure 1 As shown, compared with the XRD standard peaks of MoO2 and MoC, it can be observed that MoO2 and MoC exist in the Pt-MoO2 / MoC-7 catalyst.

[0032] The full X-ray photoelectron spectroscopy (XPS) spectrum of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1 is as follows: Figure 2 As shown, it can be observed that Pt, Mo, C, N, and O elements exist in the Pt-MoO2 / MoC-7 catalyst. Figure 1 , proving the formation of Pt-MoO2 / MoC-7 catalyst, in which nitrogen and carbon formed nitrogen-doped carbon during the calcination process, which promoted the stabilization of the catalyst and the increase of the contact area between the reactants.

[0033] The Pt-MoO2 / MoC-7 catalyst prepared in this example is used to catalytically reduce 3-nitrostyrene to 3-aminostyrene. The specific steps include: using Pt-MoO2 / MoC-7 as a catalyst, 3-nitrostyrene as a reaction substrate, and isopropanol as a solvent, 8 mg of Pt-MoO2 / MoC-7 catalyst, 0.5 mmol of 3-nitrostyrene, and 2 mL of isopropanol are placed in a sealed tube, and then 1.5 mmol of hydrazine hydrate is added to the sealed tube. Thereafter, the catalytic reaction is carried out at 110°C with magnetic stirring, and a certain amount of the reaction solution is taken every 1 to 2 minutes for analysis by high performance liquid chromatography, and the conversion rate and selectivity of the reaction are calculated. When the conversion rate of 3-nitrostyrene to 3-aminostyrene is greater than 99%, it is considered to be almost completely converted. The reaction time at this time is the time for the catalytic reaction to be completely carried out. The results are shown in FIG. Figure 4 As shown, it can be seen that the Pt-MoO2 / MoC-7 catalyst prepared in this embodiment can achieve nearly complete conversion of 3-nitrostyrene to 3-aminostyrene in only 6 minutes. Therefore, the Pt-MoO2 / MoC-7 catalyst prepared in the present invention has excellent conversion rate and selectivity, and exhibits outstanding catalytic activity. Example 2

[0034] (1) Place 2.0 g of melamine and 0.4 g of ammonium molybdate tetrahydrate in a 100 mL beaker, add 20 mL of pure water, and stir magnetically at room temperature for 0.5 h. Then place the beaker in a 60°C oil bath and stir to evaporate until there is no water. Then, dry the residue completely in a 60°C oven and grind it into powder with an agate mortar to obtain a precursor for calcination.

[0035] (2) The same method as in Example 1 was used to obtain a coexisting catalyst of MoO2 and MoC, which was recorded as MoO2 / MoC-7.

[0036] The X-ray diffraction (XRD) pattern of the MoO2 / MoC-7 catalyst prepared in Example 2 is as follows: Figure 1 As shown, compared with the XRD standard peaks of MoO2 and MoC, it can be observed that MoO2 and MoC exist in the catalyst.

[0037] According to the method of Example 1, the MoO2 / MoC-7 catalyst prepared in this example was used to catalytically reduce 3-nitrostyrene to produce 3-aminostyrene. The results are as follows: Figure 4 As shown, it can be seen that it takes 13 min to achieve nearly complete conversion and selectivity, indicating that the activity of the MoO2 / MoC-7 catalyst is much lower than that of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1, proving the importance of the presence of Pt. Example 3

[0038] The only difference between this embodiment and embodiment 1 is that the obtained precursor for calcination is spread flat in an uncovered corundum crucible, and the other conditions and steps are the same as those in embodiment 1. The obtained Pt-doped MoO2 / MoC catalyst is recorded as Pt-MoO2 / MoC-7-no.

[0039] The X-ray diffraction (XRD) pattern of the "Pt-MoO2 / MoC-7-no" catalyst prepared in this example is as follows: Figure 1 As shown, compared with the XRD standard peaks of MoO2 and MoC, it can be observed that MoO2 and MoC exist in the catalyst.

[0040] According to the method of Example 1, the Pt-MoO2 / MoC-7-no catalyst prepared in this example was used to catalytically reduce 3-nitrostyrene to produce 3-aminostyrene. The results are as follows: Figure 4 As shown, it can be seen that 8 min is required to achieve nearly complete conversion and selectivity, indicating that the activity of the Pt-MoO2 / MoC-7-no catalyst is slightly lower than that of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1, indicating that a corundum crucible with a lid is preferably used for calcination. Example 4

[0041] The only difference between this embodiment and embodiment 1 is that in step (2), the second step calcination temperature is replaced with 800°C, and the other conditions and steps are the same as those in embodiment 1. The obtained Pt-doped MoO2 / MoC catalyst is recorded as Pt-MoO2 / MoC-8.

[0042] The X-ray diffraction (XRD) pattern of the Pt-MoO2 / MoC-8 catalyst prepared in this example is as follows: Figure 1 As shown, compared with the XRD standard peaks of MoO2 and MoC, it can be observed that MoO2 and MoC exist in the catalyst.

[0043] According to the method of Example 1, the Pt-MoO2 / MoC-8 catalyst prepared in this example was used to catalytically reduce 3-nitrostyrene to produce 3-aminostyrene. The results are as follows: Figure 4 As shown, it can be seen that it takes 8 min to achieve nearly complete conversion and selectivity, indicating that the activity of the Pt-MoO2 / MoC-8 catalyst is slightly lower than that of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1. Example 5

[0044] The only difference between this embodiment and embodiment 1 is that in step (2), the second step calcination temperature is replaced with 900°C, and the other conditions and steps are the same as those in embodiment 1. The obtained Pt-doped MoO2 / MoC catalyst is recorded as Pt-MoO2 / MoC-9.

[0045] The X-ray diffraction (XRD) pattern of the Pt-MoO2 / MoC-9 catalyst prepared in this example is as follows: Figure 1 As shown, compared with the XRD standard peaks of MoO2 and MoC, it can be observed that MoO2 and MoC exist in the catalyst.

[0046] According to the method of Example 1, the Pt-MoO2 / MoC-9 catalyst prepared in this example was used to catalytically reduce 3-nitrostyrene to produce 3-aminostyrene. The results are as follows: Figure 4 As shown, it can be seen that it takes 10 min to achieve nearly complete conversion and selectivity, indicating that the activity of the Pt-MoO2 / MoC-9 catalyst is lower than that of the Pt-MoO2 / MoC-7 catalyst prepared in Example 1.

[0047] 1. Investigation of catalyst activity:

[0048] The catalysts prepared in Examples 1 to 5 were used to catalytically reduce 3-nitrostyrene to 3-aminostyrene. The reaction time t, conversion rate and selectivity were as follows: Figure 4 As shown. Figure 4 It can be observed that the catalysts prepared in Examples 1 to 5 can all achieve a conversion rate and selectivity of more than 99%, but the Pt-MoO2 / MoC-7 catalyst prepared in Example 1 has a shorter reaction time for almost complete conversion of 3-nitrostyrene into 3-aminostyrene, showing more excellent catalytic activity.

[0049] (II) Investigation of catalyst stability:

[0050] The Pt-MoO2 / MoC-7 catalyst prepared in Example 1 was subjected to a cyclic catalytic experiment. The specific experimental process was as follows: 8 mg of Pt-MoO2 / MoC-7 catalyst, 0.5 mmol of 3-nitrostyrene, and 2 mL of isopropanol were placed in a sealed tube, and then 1.5 mmol of hydrazine hydrate was added to the sealed tube, and then magnetically stirred at 110°C for 6 min. The reaction solution after the reaction was analyzed by high performance liquid chromatography, and the conversion rate and selectivity of the reaction were calculated. After the reaction was completed, the used catalyst was washed with isopropanol and centrifuged, and then directly used in the next cyclic catalytic experiment. The cyclic experiments were performed 5 times in total, and a new reaction system was used for each catalytic experiment. The new reaction system refers to a reaction system composed of 0.5 mmol of 3-nitrostyrene, 2 mL of isopropanol, and 1.5 mmol of hydrazine hydrate. The catalytic experiment was magnetically stirred at 110°C for 6 min, and the conversion rate and selectivity of each catalytic experiment were calculated. The results are as follows: Figure 3 shown. Figure 3It shows that the Pt-MoO2 / MoC-7 catalyst prepared in Example 1 can still maintain excellent catalytic activity and selectivity after catalyzing the reduction of 3-nitrostyrene to 3-aminostyrene for 5 cycles, which reflects the stability and durability of the catalyst in the catalytic reduction of 3-nitrostyrene to 3-aminostyrene.

[0051] (III) Investigation of the universality of catalysts:

[0052] The Pt-MoO2 / MoC-7 catalyst prepared in Example 1 was subjected to a substrate expansion experiment. The specific experimental process was as follows: 8 mg of Pt-MoO2 / MoC-7 catalyst, 0.5 mmol of different aromatic nitro compounds (the different aromatic nitro compounds were at least one of 3-nitrostyrene, 3-nitrostyreneacetylene, 4-nitrochlorobenzene, 3-bromonitrobenzene, and 3-nitrobenzenenitrile), and 2 mL of isopropanol were placed in a sealed tube, 1.5 mmol of hydrazine hydrate was added to the sealed tube, and the mixture was stirred magnetically at 110°C for 6 min. The reaction solution was analyzed by high performance liquid chromatography, and the conversion rate and selectivity of the reaction were calculated to determine the conversion rate and selectivity of the Pt-MoO2 / MoC-7 catalyst when catalyzing different reaction substrates. The results are shown in FIG. Figure 5 As shown. Figure 5 It can be seen that the Pt-doped molybdenum-based catalyst prepared by the present invention exhibits excellent catalytic activity and selectivity in the process of catalytic reduction of aromatic nitro compounds containing various unsaturated groups (-Cl, -Br, -C=C, -C≡C, -C≡N) to generate corresponding aromatic amine compounds, indicating that the Pt-doped molybdenum-based catalyst prepared by the present invention has excellent universality.

[0053] The above is only an embodiment of the present invention, and does not limit the present invention in any form. The present invention can also have other forms of embodiments according to the above structures and functions, which are not listed one by one. Therefore, any simple modification, equivalent change and modification made by any technician familiar with the profession to the above embodiment according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A Pt-doped molybdenum-based catalyst for catalytic reduction of aromatic nitro compounds to generate aromatic amine compounds, characterized in that The Pt-doped molybdenum-based catalyst contains Pt, MoO2 and MoC, and is used for catalytic reduction of aromatic nitro compounds 3-nitrostyrene, 3-nitrostyrene acetylene, 4-nitrochlorobenzene, 3-bromonitrobenzene and 3-nitrosobenzonitrile to convert them into aromatic amine compounds 3-aminostyrene, 3-aminophenylacetylene, 4-chloroaniline, 3-bromoaniline and 3-aminobenzonitrile, respectively. The Pt-doped molybdenum-based catalyst is prepared according to the following method: (1) Melamine and ammonium molybdate tetrahydrate were placed in a container at a mass ratio of 5:1, and a 4.7 mg / mL H2PtCl6 solution and an appropriate amount of pure water were added to the container. The volume ratio of H2PtCl6 solution to pure water was 17:

3. The mixture was stirred magnetically at room temperature for 0.5 to 1 h. The beaker was then placed in an oil bath at 60 to 70 °C and stirred to evaporate until anhydrous. The residue was then placed in an oven at 50 to 60 °C and dried completely. The residue was ground into powder using an agate mortar to obtain a precursor. (2) Spreading the obtained precursor in a corundum crucible, and then placing it in a tubular furnace protected by inert gas for two-step calcination, the first step of calcination temperature is 400 ° C, the time is 2 to 4 h, the second step of calcination temperature is 700 to 900 ° C, the time is 2 to 4 h, after calcination is completed, cooling to room temperature, to obtain the Pt-doped molybdenum-based catalyst for catalytic reduction of aromatic nitro compounds to generate aromatic amine compounds.

2. The Pt-doped molybdenum-based catalyst for catalytic reduction of aromatic nitro compounds to generate aromatic amine compounds as claimed in claim 1, characterized in that When used for catalytic reduction of aromatic nitro compounds to generate aromatic amine compounds, a Pt-doped molybdenum-based catalyst, an aromatic nitro compound, and isopropanol are mixed, hydrazine hydrate is added thereto, and the mixture is reacted at 100-120° C. with magnetic stirring for 6 minutes, so that the aromatic nitro compound is converted into an aromatic amine compound; wherein the molar ratio of hydrazine hydrate to the aromatic nitro compound is 3:1, and the mass ratio of the catalyst to the aromatic nitro compound is 1:9.3.

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