Polyphosphomolybdate heterogeneous catalyst for preparing nitrosobenzene through aniline oxidation under room-temperature darkroom condition as well as preparation method and application of polyphosphomolybdate heterogeneous catalyst

Abstract

The invention discloses a polyphosphomolybdate heterogeneous catalyst for preparing nitrosobenzene through aniline oxidation under the condition of a room temperature darkroom. The molecular formula of the catalyst is as follows: [Co (H2O) 6] 2 [(Mo2O4) 16Co36 (H2O) 42 (HPO4) 36 (PO4) 12]. The preparation method comprises the following steps: mixing CoCl2. 6H2O, Na2MoO4. 2H2O, L-tryptophan and phosphoric acid, adding water, stirring for 1.5 hours, adjusting the pH value to 2.65 by using a NaOH solution, reacting for 4 days at the temperature of 160 DEG C, and cooling to room temperature to obtain the polyphosphomolybdate catalyst. When the catalyst is used as a polyphosphomolybdate heterogeneous catalyst for preparing nitrosobenzene through aniline oxidation under the condition of a room-temperature darkroom, the catalyst shows excellent aniline conversion rate and high nitrosobenzene selectivity. Meanwhile, the catalyst has good stability and can be repeatedly used, so that the whole oxidation process can be efficiently and stably carried out under mild conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of heterogeneous catalyst based on polyphosphomolybdate and its preparation method and application, in particular to a kind of heterogeneous catalyst of polyphosphomolybdate for the oxidation of aniline to nitrosobenzene under room temperature darkroom condition and its preparation method and application, which can be catalyzed under room temperature darkroom condition High-efficiency oxidation of aniline to generate nitrosobenzene. BACKGROUND

[0002] Aniline as a stubborn water pollutant, has been proved to be carcinogenic, and its treatment has been a difficult point in environmental management. However, if it can be reasonably oxidized, it can be converted into high-value compounds, which has significant environmental benefits and economic value.

[0003] Nitrosobenzene (NSB) is an important target product prepared by catalytic oxidation of aniline, which is widely used in the fields of dyes, medicines, spices, etc. However, NSB itself has high reactivity, and is easy to overreact in the oxidation process, generating by-products such as nitrobenzene (NB), azobenzene (AB) and azoxybenzene (AOB), which brings challenges to selective synthesis.

[0004] Traditional nitrosobenzene production process often takes a long time, and needs to rely on harsh reagents and conditions. Therefore, it has become a key issue in modern catalytic research to develop a kind of heterogeneous catalyst for selective catalytic oxidation of aniline to prepare nitrosobenzene under high efficiency, environmental protection and room temperature or even darkroom conditions. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a kind of heterogeneous catalyst of polyphosphomolybdate for the oxidation of aniline to nitrosobenzene under room temperature darkroom condition and its preparation method and application, which can catalyze the oxidation reaction of aniline under normal temperature and pressure and darkroom condition, has excellent catalytic activity and high product selectivity to generate target product nitrosobenzene. At the same time, it has good stability and can be reused, so that the whole oxidation process can be carried out efficiently and stably under mild conditions.

[0006] The technical solution of the present application is:

[0007] A kind of heterogeneous catalyst of polyphosphomolybdate for the oxidation of aniline to nitrosobenzene under room temperature darkroom condition, the molecular formula of the catalyst is as follows:

[0008] [Co (H2O) 6]2[(Mo2O4) 16 Co 36 (H2O) 42 (HPO4) 36 (PO4) 12 ].

[0009] A preparation method of a polyphosphomolybdate heterogeneous catalyst for preparing nitrosobenzene from aniline under room temperature and dark conditions, and the specific steps are as follows:

[0010] CoCl2.6H2O, Na2MoO4.2H2O, L-tryptophan and phosphoric acid are mixed according to a molar ratio of 0.85:2.06:0.25:11.7, water is added, and stirring is performed for 1.5 h, a NaOH solution is used to adjust the pH to 2.65, and then the mixture is put into a reaction kettle and reacted at a temperature of 160 DEG C for 4 days; after being cooled to room temperature, a red-black rhombic crystal polyphosphomolybdate catalyst is obtained.

[0011] Further, the molar volume ratio of L-tryptophan to water is 1:20 mol / L.

[0012] Further, the phosphoric acid is analytical pure, and the mass fraction is 85%.

[0013] Further, the concentration of the NaOH solution is 1 mol / L. -1 .

[0014] The application of the polyphosphomolybdate catalyst in the preparation of nitrosobenzene from aniline under room temperature and dark conditions as a polyphosphomolybdate heterogeneous catalyst for preparing nitrosobenzene from aniline shows excellent aniline conversion rate and high nitrosobenzene selectivity.

[0015] Further, under the conditions of room temperature and dark, polyphosphomolybdate catalyst powder [Co(H2O)6]2[(Mo2O4) 16 Co 36 (H2O) 42 (HPO4) 36 (PO4) 12 ], a substrate aniline and 30% mass fraction hydrogen peroxide are added into a reaction container, a solvent is added, and after being fully mixed, the catalytic reaction is performed for 12 h under normal temperature and light-free conditions to obtain nitrosobenzene.

[0016] Further, the molar ratio of the polyphosphomolybdate catalyst (0.05 mmol%) to aniline (93 μL, 1 mmol) and hydrogen peroxide (3.4 mmol) is 5.0 x 10 -4 :1:3.4.

[0017] Further, a cocatalyst (NH4)2S2O8 is also added during the catalytic reaction, and the molar ratio of the polyphosphomolybdate catalyst to the cocatalyst is 5.0 x 10 -4 :1.

[0018] Further, the solvent is cyclohexane, and 6 L of cyclohexane is added per mole of aniline.

[0019] The beneficial effects of the present application are:

[0020] (1) Optimized reaction conditions: The oxidation reaction of aniline is efficiently carried out at room temperature and in a dark room. This not only greatly reduces energy consumption and production cost, but also significantly improves the safety of operation.

[0021] (2) Innovative catalyst system: A new catalyst system is provided for the preparation of nitrosobenzene, which can efficiently catalyze the oxidation reaction of aniline at room temperature and in the dark, with aniline conversion rate of 98.3% and nitrosobenzene selectivity of 93.3%.

[0022] (3) Reduce environmental pollution: By using recyclable polyphosphomolybdate-based catalyst and mild reaction conditions, not only the traditional process of noble metal catalyst and high temperature conditions are effectively replaced, the impact on the environment is reduced, and the efficient recycling of the catalyst is realized. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of the synthesis process of embodiment 1 of the present application;

[0024] Figure 2 is the powder X-ray diffraction pattern of embodiment 1 of the present application;

[0025] Figure 3 is the coordination environment diagram and one-dimensional chain structure diagram of embodiment 1 of the present application;

[0026] Figure 4 is the infrared spectrum of embodiment 1 of the present application;

[0027] Figure 5 is the thermogravimetric curve diagram of embodiment 1 of the present application;

[0028] Figure 6 is the X-ray photoelectron energy spectrum of embodiment 1 of the present application;

[0029] Figure 7 is the thermal filtration experiment result diagram of embodiment 1 of the present application;

[0030] Figure 8 is the kinetic study diagram of embodiment 1 of the present application;

[0031] Figure 9 is the cycle stability column chart of embodiment 1 of the present application;

[0032] Figure 10 is the infrared spectrum before and after the cycle of embodiment 1 of the present application;

[0033] Figure 11 is the PXRD spectrum before and after the cycle of embodiment 1 of the present application;

[0034] Figure 12is the X-ray photoelectron spectrogram of before and after the cycle of the embodiment 1 of the present application;

[0035] Figure 13 is the SEM spectrogram of before and after the cycle of the embodiment 1 of the present application;

[0036] Figure 14 is the Raman spectrogram of before and after the catalytic reaction of the embodiment 1 of the present application. DETAILED DESCRIPTION

[0037] Example 1 Synthesis of [Co(H2O)6]2[(Mo2O4) 16 Co 36 (H2O) 42 (HPO4) 36 (PO4) 12 ]

[0038] As shown in Figure 1 , CoCl2·6H2O (0.20 g, 0.85 mmol), Na2MoO4·2H2O (0.5 g, 2.06 mmol), L-tryptophan (0.05 g, 0.25 mmol) and H2O (5.0 mL) were mixed and stirred at room temperature for 1.5 h, H3PO4 (analytically pure, mass fraction 85%) (1.35 g, 11.7 mmol) was added, and the pH was adjusted to 2.65 with 1 mol·L -1 NaOH, and then placed in a 25 mL polytetrafluoroethylene-lined stainless steel autoclave, and then heated at 160°C for four days, cooled to room temperature, and red-brown crystals were obtained, which were washed with deionized water and dried at room temperature to obtain red-black rhombic crystal molybdophosphate catalyst [Co(H2O)6]2[(Mo2O4) 16 Co 36 (H2O) 42 (HPO4) 36 (PO4) 12 ]; the yield was 36%, the powder X-ray diffraction spectrogram (PXRD) thereof is shown in Figure 2 , and the coordination environment diagram thereof is shown in Figure 3 . In Comparative Example 1, L-tryptophan was not added in Example 1, and the others were the same as in Example 1.

[0039] CoCl2·6H2O (0.20 g, 0.85 mmol), Na2MoO4·2H2O (0.5 g, 2.06 mmol) and H2O (5.0 mL) were mixed and stirred at room temperature for 1.5 h, H3PO4 (analytically pure, 85%) (1.35 g, 11.7 mmol) was added, and the pH was adjusted to 2.65 with 1 mol·L -1NaOH was added to adjust the pH to 2.65, and then the mixture was placed in a 25 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 160°C for four days. After cooling to room temperature, a red precipitate was obtained. L-tryptophan promoted the formation of clusters during the reaction, and without L-tryptophan, only a red precipitate was obtained, and red-brown crystals could not be formed.

[0040] I. Characterization of the polyphosphomolybdate catalyst based on Example 1 of the present application

[0041] (1) Powder X-ray diffraction for characterization of phase purity

[0042] The prepared sample catalyst was characterized by a powder X-ray diffractometer of Rigaku Ultima IV. The radiation source was Cu-Ka, the scanning range was 2theta = 5-50°, the scanning speed was 2° / min, and the structure and crystal phase composition of the analyzed substance were analyzed. As shown in Figure 2 The PXRD spectrum of Example 1 showed a high consistency between the experimental value and the simulated value, indicating that Example 1 had a high phase purity.

[0043] (2) Infrared spectroscopy for characterization of phase composition

[0044] The prepared sample catalyst was characterized by a Vari Nmeline 640 FT-IR Fourier infrared spectrometer. The wavelength range was 400-4000 cm -1 , and the sample and potassium bromide were uniformly mixed with a mass ratio of 1:100. As shown in Figure 4 , the characteristic peaks in the range of 761-767 cm -1 were attributed to the stretching vibration of v(Mo-O-Mo); the characteristic peaks at 955-957 cm -1 were attributed to the stretching vibration of v(Mo=O). In addition, the characteristic peaks near 1061-1069 cm -1 were attributed to v(P-O). The characteristic peaks at 3416-3439 cm -1 and 1636-1640 cm -1 were respectively attributed to the stretching vibration of water molecules. The wide absorption peak at 520-526 cm -1 was due to the stretching vibration of v(Co-O). Further confirmed the structural composition of Example 1.

[0045] (3) Thermogravimetric analysis for characterization of the stability of the polyphosphomolybdate catalyst of Example 1

[0046] Thermogravimetric analysis (TGA) was performed using a Hitachi TG / DTA7200 analyzer in a N2 atmosphere, at a temperature of 30-970°C, and a heating rate of 10°C / min. As shown in Figure 5 , the TGA curve showed that the polyphosphomolybdate catalyst of Example 1 underwent a three-step weight loss process.

[0047] (4) X-ray photoelectron spectroscopy characterization of the polyphosphoromolybdate catalyst in Example 1

[0048] The tests were performed using an Al-Kα excited X-ray photoelectron spectroscopy (XPS) instrument at a power of 150 W. Figure 6 As shown, in the XPS spectrum of the polyphosphoromolybdate catalyst of Example 1, two peaks at 781.9 eV and 797.9 eV were clearly detected and attributed to Co 2p. 3 / 2 and Co 2p 1 / 2 This confirms Co 2+ The presence of [a specific element] indicates that Mo 3d exhibits two peaks at 232.0 eV and 235.0 eV, corresponding to [specific values] of Mo 3d. 5 / 2 and Mo 3d 3 / 2 The elemental composition and chemical oxidation state of Example 1 were determined by XPS spectroscopy. This further confirmed the presence of Co. 2+ and Mo 5+ The presence of [something] helps to improve catalytic activity.

[0049] II. Crystal Structure Determination

[0050] Single-crystal X-ray diffraction (SCXRD) data were collected using a Bruker SMART APEXIICCD diffractometer (λ = 0.71073 Å) with Mo Kα radiation. These data were analyzed and precisely corrected using Olex 2 software to determine the crystal structure of Example 1. Specific crystallographic parameters are shown in Table 1.

[0051] Table 1 Crystallographic data

[0052]

[0053] III. In Example 1, hydrogen peroxide with a mass concentration of 30% was used as the oxidant and a certain amount of polyphosphoromolybdate catalyst to achieve the oxidation reaction of aniline.

[0054] Firstly, the polyphosphomolybdate salt catalyst of Example 1 was accurately weighed into a reaction tube and 6 mL of solvent was added. Subsequently, aniline was added to the reaction tube, and hydrogen peroxide with a mass concentration of 30% was introduced as the oxidant. Under the action of the acidic polyphosphomolybdate salt catalyst cluster at room temperature and in the dark, the basic aniline can be easily adsorbed to the surface of the cluster by electrostatic interaction. In the process of catalytic oxidation, the Mo(V) and Co(II) ions in the polyphosphomolybdate salt catalyst form a metal-peroxide complex under the action of H2O2, and then the N-H bond of aniline is attacked by the generated peroxy bond and further reacts to form the intermediate N-phenylhydroxylamine. Finally, the intermediate N-phenylhydroxylamine is oxidized to the final product nitrosobenzene (NSB), thus successfully realizing the multi-step oxidative conversion process.

[0055] (I) The catalytic effect of Example 1 in the selective oxidation of aniline was explored by adjusting the type of different single solvents.

[0056] With 3.4 mmol of hydrogen peroxide with a mass concentration of 30% as the oxidant, 0.05 mmol% of the polyphosphomolybdate salt catalyst of Example 1 was mixed with 3 mL of solvent, and then 1 mmol of aniline was added. The catalytic reaction was carried out at room temperature and in the dark for 12 hours to study the effect of different solvents on the oxidation of aniline (Table 2). The results showed that when cyclohexane was used as the solvent, the conversion rate of aniline reached 64.7%, and the selectivity of the product nitrosobenzene was 83.5%. For the aniline oxidation reactions carried out in other solvents (Table 2, Nos. 2, 3, 4, 5 and 6), ethanol, methanol and acetonitrile could not effectively promote the efficient conversion of aniline, and the selectivity of the target product nitrosobenzene was low; further examination of p-toluene and 1,4-dioxane as solvents showed that the conversion rate increased, but both were lower than 55%. Therefore, cyclohexane was the preferred solvent.

[0057] Table 2 Screening of aniline oxidation solvents [a]

[0058]

[0059] [a] During the reaction, the following steps were followed: firstly, 0.05 mmol% of the polyphosphomolybdate salt catalyst of Example 1 was mixed with 3 mL of different types of solvents, then 1 mmol of aniline was added, and then 3.4 mmol of hydrogen peroxide with a mass fraction of 30% was added. The reaction system was reacted at room temperature and in the dark for 12 hours to explore the effect of different solvents on the oxidation of aniline.

[0060] The addition of reaction promoters can significantly improve the reaction process, increase the dispersion of the catalyst, and reduce the reaction energy barrier. Considering that when cyclohexane is used as the solvent, the main product of aniline conversion is nitrosobenzene, and the selectivity can reach 83.5%, respectively. As shown in Table 3, a series of additives (such as Na2S2O8 and Na2SO3, etc.) were added to cyclohexane as the solvent to explore the effect on the reaction of aniline oxidation to nitrosobenzene. Among them, when the co-catalyst (NH4)2S2O8 is used, the conversion rate of catalytic oxidation of aniline to nitrosobenzene is 99.0%, and the selectivity reaches 78.2%.

[0061] Table 3 Screening of aniline oxidation catalyst additives in cyclohexane solvent [a]

[0062]

[0063]

[0064] [a] Process conditions: First, 0.05 mmol% of the polyphosphomolybdate catalyst of Example 1 was mixed with 1 mmol of different co-catalysts, then 3 mL of cyclohexane was added as the solvent, and then 1 mmol of aniline and 3.4 mmol of 30% mass fraction hydrogen peroxide were added. The above mixture was subjected to co-catalytic reaction at room temperature and in the dark, and the reaction time was 12 hours, in order to study the effect of different co-catalysts on the oxidation of aniline in cyclohexane solvent.

[0065] Further, with 30% mass concentration hydrogen peroxide as the oxidant, the effect of oxidant dosage on the catalytic oxidation of aniline was explored. The results showed that in cyclohexane solvent, when the amount of hydrogen peroxide reached 3.4 mmol, the conversion rate of aniline reached 99.0% (Table 4).

[0066] Table 4 Screening of oxidant dosage for catalytic oxidation of aniline in cyclohexane solvent [a]

[0067]

[0068] [a] Process: First, 0.05 mmol% of the polyphosphomolybdate catalyst of Example 1, 3 mL of cyclohexane solvent, 1.0 mmol of (NH4)2S2O8 and 1.0 mmol of aniline were weighed and mixed. Then, different amounts of 30% mass fraction hydrogen peroxide were introduced, and the reaction was carried out at room temperature and in the dark for 12 hours. After the reaction, naphthalene was used as the internal standard, and gas chromatography was used to determine the products to analyze the conversion rate of aniline and the selectivity of the products, so as to screen the optimal catalytic effect of hydrogen peroxide dosage on the reaction performance.

[0069] Further, under the above optimal conditions, when 0.05 mmol% of Example 1 was added as a catalyst, the substrate conversion rate reached 99.0% after 12 h of catalytic oxidation of aniline at room temperature and in a dark room. With the increase of the amount of catalyst, the over-oxidation of nitrosobenzene can lead to a decrease in selectivity (Table 5). It is shown that the ideal amount of polyphosphomolybdate catalyst is 0.05 mmol%.

[0070] Table 5 Catalyst dosage for catalytic oxidation of aniline in cyclohexane solvent [a]

[0071]

[0072]

[0073] [a] Process conditions: First, the polyphosphomolybdate catalyst of Example 1 in different amounts in the above table was added to the reactor, followed by the addition of 3 mL of cyclohexane solvent, then 1.0 mmol of (NH4)2S2O8 and 1.0 mmol of aniline and 3.4 mmol of 30% mass fraction of hydrogen peroxide. The mixture was subjected to catalytic reaction at room temperature and in a dark room for 12 hours to promote the conversion of aniline and the formation of target products. Finally, the products were determined and analyzed by gas chromatography.

[0074] In cyclohexane solvent, the effect of (NH4)2S2O8 co-catalyst dosage on the catalytic oxidation of aniline was explored. When the amount of (NH4)2S2O8 added was increased to 1.0 mmol, the conversion rate reached 99%, and the selectivity was 78.2%. However, with the increase of the amount of additive, the selectivity tended to decrease. Therefore, 1.0 mmol of (NH4)2S2O8 was determined as the optimal amount of additive for the reaction.

[0075] Table 6 Screening of additive dosage for catalytic oxidation of aniline in cyclohexane solvent [a]

[0076]

[0077] [a] Process flow: First, 0.05 mmol% of the polyphosphomolybdate catalyst of Example 1, 3 mL of cyclohexane solvent, 3.4 mmol of 30% mass fraction of hydrogen peroxide and 1.0 mmol of aniline were mixed. Subsequently, catalytic reaction was carried out at room temperature and in a dark room for 12 hours. By controlling the amount of different co-catalysts (NH4)2S2O8, the conversion rate of aniline and the selectivity of products were explored. After the completion of the catalytic reaction, the conversion rate and selectivity of the reaction were determined by gas chromatography.

[0078] After exploring the types of solvent, adjuvant, oxidant, catalyst and adjuvant, the selectivity of aniline oxidation to NSB was further improved by adjusting the amount of solvent. As shown in Table 7, with the increase of the amount of solvent, the selectivity gradually increased. It may be that the increase of the amount of solvent prevents the further oxidation of NSB, thereby improving the selectivity of NSB. With the increase of the amount of solvent, the conversion rate of catalytic oxidation of aniline decreased. Therefore, 6 ml was determined as the best.

[0079] Table 7 Amount of cyclohexane solvent in catalytic oxidation of aniline [a]

[0080]

[0081]

[0082] [a] Process flow: First, 0.05 mmol% of the polyphosphomolybdate salt catalyst of Example 1, 1.0 mmol of (NH4)2S2O8, 3.4 mmol of 30% mass fraction hydrogen peroxide and 1.0 mmol of aniline were mixed. Subsequently, the catalytic reaction was carried out at room temperature and in a dark room for 12 hours. By controlling the amount of different cyclohexane solvents, the conversion rate of aniline and the selectivity of the product were explored. After the completion of the catalytic reaction, the conversion rate and selectivity of the reaction were determined by gas chromatography.

[0083] In the investigation of the factors affecting the catalytic oxidation of aniline, under the optimal conditions, Co 38 Mo 32 P 48 , Na2MoO4, CoCl2 and their physical mixture were used as catalysts for comparative experiments. As shown in Table 8, in the absence of catalyst, the conversion rate of aniline was only 43.4%. Compared with Co 38 Mo 32 P 48 , Na2MoO4, CoCl2 and their physical mixture had unsatisfactory effect. The results showed that the catalyst obtained by simply physical mixing could not effectively promote the oxidation reaction of aniline, Co 38 Mo 32 P 48 had a good catalytic effect on the oxidation reaction of aniline, and the catalytic effect was the synergistic effect of Co and Mo.

[0084] Table 8 Selective oxidation of aniline by different catalysts [a]

[0085]

[0086] [a] Process: First, 6 mL of cyclohexane solvent, 1.0 mmol of (NH4)2S2O8, 3.4 mmol of 30% mass fraction of hydrogen peroxide, 1.0 mmol of aniline and different catalysts were mixed. Then, the catalytic reaction was carried out at room temperature and in a dark room for 12 hours. By controlling the type of catalyst, the conversion rate of aniline and the product selectivity were explored. After the completion of the catalytic reaction, the conversion rate and selectivity of the reaction were determined by gas chromatography.

[0087] (II) The heterogeneous catalytic performance of the polyphosphomolybdate salt catalyst of Example 1 was explored by a hot filtration experiment.

[0088] The heterogeneous catalytic performance of Co 38 Mo 32 P 48 was verified by a hot filtration experiment. As shown in Figure 7 , the conversion rate of aniline reached 42.3% within 1 h, and the conversion rate of aniline was basically unchanged after the catalyst was removed, which proved the heterogeneous nature of Co 38 Mo 32 P 48 . In order to further explore the kinetics of Co 38 Mo 32 P 48 in the reaction, as shown in Figure 8 , ln(C0 / Ct) and reaction time t are linearly related (C0: initial substrate concentration; C t : substrate concentration at time t), which is consistent with the pseudo-first-order kinetic model. It can be seen that the kinetic constant k of the pseudo-first-order reaction is 0.3251 h -1 .

[0089] Fourth, the reuse stability of the polyphosphomolybdate salt catalyst of Example 1 of the application

[0090] In order to measure the stability of the catalyst, after the first catalytic reaction was completed, the catalyst was washed with cyclohexane solvent for 3 to 4 times, and after the washing was completed, the polyphosphomolybdate salt catalyst was placed in a vacuum oven and dried at 60°C overnight; after the catalyst was completely dried, it was added to the reaction tube, and 1.0 mmol of (NH4)2S2O8, 6 mL of cyclohexane solvent, 3.4 mmol of 30% mass fraction of hydrogen peroxide and 1.0 mmol of aniline were sequentially added, and a new round of catalytic oxidation reaction of aniline was carried out under room temperature and dark room conditions. As shown in Figure 9 , after 4 cycles, the conversion rate of aniline decreased from 98.3% to 95.2%, which may be due to the recovery and post-processing of Co 38 Mo 32 P 48The conversion and selectivity of the reaction catalyzed by the polyphosphomolybdate salt catalyst in Example 1 did not obviously decrease after multiple cycles, which proved the good stability of the catalyst.

[0091] As shown in Figure 10 , Figure 11 and Figure 12 , the catalyst powder after the cycle experiment was characterized by FT-IR, PXRD and X-ray photoelectron spectroscopy, and the characterization results had no obvious difference, which further proved the stability of the polyphosphomolybdate salt catalyst in Example 1 before and after the cycle reaction.

[0092] Transmission electron microscopy SEM images showed (as shown in Figure 13 a and Figure 13 b) that the particle size had only a slight change before and after the cycle, and the morphology remained basically unchanged. EDS analysis before and after the cycle showed that the distribution of elements had no obvious difference (as shown in Figure 13 c- Figure 13 j), which further proved the sustainability and repeatability of the catalyst.

[0093] V. Substrate scope of the aniline oxidation system catalyzed by the polyphosphomolybdate salt catalyst in Example 1

[0094] Based on the stability of Co 38 Mo 32 P 48 and its potential to catalyze the oxidation of aniline at room temperature and in the dark, the substrate scope of the aniline oxidation system catalyzed by the catalyst under the optimal conditions was further explored. As shown in Table 9, all aniline derivatives can be successfully converted into the corresponding nitrosobenzene products. The catalyst has high activity for compounds with electron-donating groups (n-Bu, i-Pr, -Et, -Me) and electron-withdrawing substituents (-Cl, -Br), which proves that the electronic effect has little effect on the catalytic reaction. In addition, the research results show that steric hindrance has a significant effect on the catalytic reaction. The electron-donating substituent is affected by the steric effect; the higher the steric hindrance of the substrate, the lower the catalytic activity, and when the -OMe substituent is located at the para position, the catalytic activity is higher than that when it is located at the ortho and meta positions.

[0095] Table 9 Effect of polyphosphomolybdate salt catalyst on aniline derivatives in cyclohexane solvent

[0096]

[0097]

[0098]

[0099] [a] Process: First, 0.05 mmol% of the polyphosphomolybdate catalyst of Example 1, 1.0 mmol of (NH4)2S2O8, 6 mL of cyclohexane solvent, 3.4 mmol of 30% mass fraction of hydrogen peroxide and different kinds of aniline derivatives were mixed. Subsequently, the catalytic reaction was carried out at room temperature in the dark for 12 hours, and the conversion rate and product selectivity of different kinds of aniline derivatives were explored. After the completion of the catalytic reaction, the conversion rate and selectivity of the reaction were determined by gas chromatography.

[0100] Six, Mechanism of the polyphosphomolybdate catalyst of Example 1 catalyzing aniline oxidation

[0101] In order to clarify the mechanism of the polyphosphomolybdate catalyst of Example 1 catalyzing aniline oxidation to prepare nitrosobenzene at room temperature and in the dark, a free radical capture experiment was carried out. Under the optimal catalytic conditions, the free radical scavenger 2,6-di-tert-butyl-4-methylphenol (BHT) was introduced into the reaction system, and the reaction was not obviously inhibited (Table 10). The results show that the reaction is mediated by an intermediate mechanism rather than a free radical mechanism. As shown in Figure 14 the Raman spectrum analysis of the catalyst before and after the reaction found that the characteristic peak shifted, which was attributed to the ν(O-O) stretching vibration peak, indicating that a peroxide intermediate was formed during the reaction.

[0102] Table 10 Effect of adding scavengers on the catalytic aniline oxidation reaction of the catalyst [a]

[0103]

[0104] [a] Process: First, 0.05 mmol% of the polyphosphomolybdate catalyst of Example 1, 1.0 mmol of (NH4)2S2O8, 3.4 mmol of 30% mass fraction of hydrogen peroxide and 1.0 mmol of aniline were mixed. Subsequently, the catalytic reaction was carried out at room temperature and in the dark for 12 hours. The conversion rate and product selectivity of aniline were explored by controlling whether a scavenger was added. After the completion of the catalytic reaction, the conversion rate and selectivity of the reaction were determined by gas chromatography.

[0105] The above only describes specific embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A heterogeneous catalyst for the oxidation of aniline to nitrosobenzene under room temperature and dark conditions, characterized in that: The molecular formula of the catalyst is as follows: [Co(H2O)6]2[(Mo2O4) 16 What 36 (H2O) 42 (HPO4) 36 (PO4) 12 ]。 2. A method for preparing a polyphosphoromolybdate heterogeneous catalyst for the oxidation of aniline to nitrosamine under room temperature dark conditions as described in claim 1, characterized in that: Specific steps as follows: CoCl2·6H2O, Na2MoO4·2H2O, L-tryptophan and phosphoric acid were mixed in a molar ratio of 0.85:2.06:0.25:11.7, and water was added. The mixture was stirred for 1.5 h, and the pH was adjusted to 2.65 with NaOH solution. The mixture was then placed in a reaction vessel and reacted at 160 °C for 4 days. After cooling to room temperature, the polyphosphoromolybdate catalyst was obtained.

3. The method for preparing the polyphosphoromolybdate heterogeneous catalyst for the oxidation of aniline to nitrosamine under room temperature dark conditions according to claim 2, characterized in that: The molar volume ratio of L-tryptophan to water is 1:20 mol / L.

4. The method for preparing the polyphosphoromolybdate heterogeneous catalyst for the oxidation of aniline to nitrosamine under room temperature dark conditions according to claim 2, characterized in that: The phosphoric acid was of analytical grade and had a mass fraction of 85%.

5. The method for preparing the polyphosphoromolybdate heterogeneous catalyst for the oxidation of aniline to nitrosobenzene under room temperature dark conditions according to claim 2, characterized in that: The concentration of the NaOH solution is 1 mol·L⁻¹ –1 .

6. The use of the polyphosphoromolybdate heterogeneous catalyst as described in claim 1 as a polyphosphoromolybdate heterogeneous catalyst for the oxidation of aniline to nitrosobenzene under room temperature dark chamber conditions.

7. The application according to claim 6, characterized in that: in Under room temperature and dark conditions, the polyphosphoromolybdate catalyst powder [Co(H2O)6]2[(Mo2O4)] was prepared. 16 Co 36 (H2O) 42 (HPO4) 36 (PO4) 12 The substrate aniline and 30% hydrogen peroxide were added to the reaction vessel, along with a solvent. After thorough mixing, the mixture was catalytically reacted at room temperature and in the absence of light for 12 hours to obtain nitrosobenzene.

8. The application according to claim 6, characterized in that: The molar ratio of the polyphosphoromolybdate catalyst to aniline and hydrogen peroxide is 5.0 × 10⁻⁶. -4 :1:3.

4.

9. The application according to claim 6, characterized in that: During the catalytic reaction, a co-catalyst (NH4)2S2O8 was also added, and the molar ratio of the polyphosphoromolybdate catalyst to the co-catalyst was 5.0 × 10⁻⁶. -4 :

1.

10. The application according to claim 6, characterized in that: The solvent is cyclohexane, and 6L of cyclohexane is added to the solvent for every mole of aniline.

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