Palladium nano-catalyst, preparation method thereof and application of palladium nano-catalyst in spontaneous synthesis of solid aromatic amine from solid reactant driven by solar energy

Abstract

The invention relates to the technical field of organic synthesis, and particularly discloses a palladium nano-catalyst, a preparation method thereof and application of the palladium nano-catalyst in spontaneous synthesis of solid aromatic amine from a solid reactant driven by solar energy. The preparation method of the palladium nano-catalyst comprises the following steps: preparing 4-dodecyl aniline diazonium salt from 4-dodecyl aniline, tetrafluoroboric acid and sodium nitrite; the palladium nano-catalyst is prepared from palladium acetate, 4-dodecyl aniline diazonium salt and sodium borohydride. And carrying out sunlight static irradiation on a solid nitro compound at room temperature in an H2 atmosphere by taking the palladium nano-material as a catalyst, and carrying out solid synthesis to obtain the solid aromatic amine compound. According to the invention, the solar-driven spontaneous solid reaction is utilized to produce the aromatic amine, the reaction can be smoothly and spontaneously carried out, mechanochemistry does not need to be introduced, and only static irradiation with sunlight is needed at room temperature within a short time. The method has wide substrate applicability, and can be used for preparing products with potential significance from the perspective of medicines.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a palladium nanocatalyst and a preparation method thereof, and application thereof in spontaneous synthesis of solid aromatic amines by solid reactants driven by solar energy. Background Art

[0002] Fresh grapes can produce wine through fermentation, but raisins cannot. Milk spoils easily, but powdered milk can remain unchanged. Similarly, dried meat can be stored for a long time, while broth will quickly rot when left alone. By observing these phenomena, it can be seen that the transformation of one material into another occurs in the liquid state, not in the solid state. Aristotle, one of the most famous ancient Greek philosophers, summarized these observations and concluded that "No Coopora nisi Fluida", which means "No reaction occurs without a solvent". These philosophies have had a major impact on the development of modern science in Europe, which provides a historical reason that most organic reactions are carried out in solutions (Springer, Berlin Heidelberg, 2004, 115-245; Chem. Rev. 2000, 100, 1025-1074). The current pharmaceutical industry and fine chemical industry strongly rely on solvent-based organic synthesis, which leads to a serious problem of solvent waste, because organic solvents usually account for 80-90% of the total mass used in any organic reaction (Science 2002, 297, 799-803.). Although solvent recovery is a very effective way to reduce solvent waste, organic chemists should focus on (re)designing organic synthesis to reduce or eliminate the use of solvents. In this context, solid-state organic transformations have attracted considerable attention as cleaner and more sustainable synthetic alternatives (Nature 1997, 387, 583-586; J. Am. Chem. Soc. 2023, 145 (12), 6823-6837; Chem. Sci. 2024, 15, 14798-14805).

[0003] In solid synthesis, the reactant molecules are in a restricted state, and the molecular conformation is relatively stable, which greatly limits their ability to participate in reactions in the solid state. Combined with the theory of topological chemistry, solid-state synthesis reactions can usually be divided into four links for implementation: first, crystal defects, deformation, and molecular loosening are generated in a single or several nucleation sites. The second is that the old chemical bonds break and generate new bonds under a given environment. The third is that a few products will quickly form solids / solutions in the original crystals. The fourth is product crystallization and separation; among them, the rate-limiting step in solid-state reactions is the diffusion of atoms or ions through the crystalline phases of reactants, intermediates, and products. This process is very slow, takes days or even weeks, and even requires high-temperature treatment, and consumes a lot of energy (Chem.Soc.Rev.2011,40,2317-2329). Solid-state grinding, ultrasonic radiation, mechanical vibration or stirring, spark plasma sintering and high-temperature melting are effective means to accelerate this process (J.Am.Chem.Soc.2023,145(28),15118-15127; Angew.Chem.Int.Ed.2022,61,e202212694). Among them, solid-state grinding occupies half of the current solid-state synthesis field and has been widely used in drug eutectic synthesis, material development, electroplating and other aspects. Mechanical grinding can increase the free energy of the solid surface, integrate the shear force, friction force and elastic tension generated by extrusion, generate instantaneous microheat, and then activate the reaction system and accelerate the reaction. However, it inevitably requires the use of external force, which people usually call mechanochemistry. However, in the context of energy crisis, green chemistry and sustainable development, the field of solid-state organic synthesis faces new opportunities and challenges: 1. Spontaneous solid-state organic synthesis is difficult to achieve under mild conditions; 2. Most solid-state synthesis strategies are often only suitable for individual special cases, and their activity and selectivity often cannot be universally controlled; 3. Conventional catalysts often show high activity on the contact surface when catalyzing solid-state reactions, and the uncontacted parts are usually difficult to react or have a long reaction time, which makes it difficult to simultaneously achieve spatial integration of conversion rate and selectivity control.

[0004] Solar-driven photothermal synergistic catalysis may provide an interesting approach for spontaneous, efficient, and highly selective solid-state synthesis under mild conditions (Chinese J. Catal. 2024, 60, 128-157; Science 2011, 333, 712-717). Using solar thermal effect to drive organic synthesis is expected to replace traditional thermal catalytic technology, thereby achieving low-energy chemical production. In fact, the photothermal effect has been widely studied in the fields of energy utilization, biomedicine, catalytic conversion, smart devices, etc., and has been applied in photothermal solar evaporation, photothermal therapy, photothermal catalysis, agricultural heaters, photothermal energy storage, photothermal-induced self-healing materials, photothermal-driven robots, photothermal functional materials, etc. (Chem. Rev. 2022, 473, 214794). In view of the current energy crisis, energy consumption demand is one of the important factors restricting the development of modern chemical industry. Using solar energy to drive organic synthesis and converting and storing solar energy into chemical energy provides a new idea for alleviating the current energy dilemma. Metal nanostructures have unique plasmon optical properties, which provide opportunities for realizing this technical approach (Chem. Rev. 2018, 118, 3054-3099). However, in response to the requirement of making full use of solar energy in solid-state synthetic conversion chemical production, the industry faces two key scientific and technological problems: how to capture solar energy broadly and how to effectively introduce the captured solar photon energy into solid-state chemical reactions. Metal palladium is an efficient catalyst for many organic reactions, but the localized surface plasmon properties of metal palladium nanostructures are always inferior to those of common gold and silver. The absorption cross section is small and the response spectrum range is limited to the ultraviolet band, which brings great difficulties to the capture and utilization of solar energy. How to regulate and optimize these two processes according to the needs of organic synthesis is the key to solving the problems in this field at present. Among them, loading photosensitive metals or semiconductor materials is an effective method to enable them to absorb light in a wide range of visible light. The photothermal effect after absorption produces local high temperatures sufficient to provide heat sources for organic reactions, realizing the combination of solar energy utilization and catalytic activity in spatial distribution. Reducing structural symmetry is another effective way to enhance visible light absorption (ACS Catal. 2018, 8(10), 9280-9286). It is worth noting that these two strategies are not a problem in organic reactions in liquid state, but due to the reduced penetration of light in solid-state reactions and the confinement problem of solid-state molecules, solar thermal catalysis is difficult to occur under solid-state conditions, especially under spontaneous conditions without external forces. In fact, at present, solar thermal catalysis technology is only limited to liquid phase, sometimes assisted by stirring. In comparison, the huge application potential of solid-state thermal catalytic reactions in the fields of energy and environment should be regarded as a powerful weapon for green chemistry, but it is more challenging. Therefore, the development of visible light thermal catalytic materials is the ultimate goal of studying solar-driven spontaneous solid-state synthesis. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problem that the prior art cannot realize the selective synthesis of solid aromatic amines under solid conditions without external force, and to provide a palladium nanocatalyst and a preparation method thereof and an application in the spontaneous synthesis of solid aromatic amines by solid reactants driven by solar energy.

[0006] In order to solve the above-mentioned technical problems, the technical solution adopted by the present invention is:

[0007] A preparation method of palladium nanocatalyst:

[0008] 4-dodecylaniline diazonium salt is prepared by using 4-dodecylaniline, tetrafluoroboric acid and sodium nitrite;

[0009] Palladium nanocluster catalyst was prepared by using palladium acetate, 4-dodecylaniline diazonium salt and sodium borohydride.

[0010] As a further optimization of the preparation method of a palladium nanocatalyst of the present invention, the preparation method specifically comprises the following steps:

[0011] S1: 4-dodecylaniline and tetrafluoroboric acid are mixed at 0-5°C and a sodium nitrite aqueous solution is slowly added, and after stirring, the mixture is filtered and washed to obtain 4-dodecylaniline diazonium salt, which is then dried and stored at 0-5°C;

[0012] S2: Mix the methanol solution of palladium acetate and the tetrahydrofuran solution of 4-dodecylaniline diazonium salt at 0-5°C and slowly add the methanol solution of sodium borohydride. Stir vigorously at 0-5°C to react. After the reaction is completed, remove the methanol and tetrahydrofuran and dissolve in dichloromethane. 2 SO 4 、NaHCO 3 Aqueous solution and deionized H 2 After washing with O, it was dried over anhydrous sodium sulfate and finally filtered to remove the solvent.

[0013] As a further optimization of the preparation method of a palladium nanocatalyst of the present invention, the preparation method also includes step S3: dispersing the product after filtration and removal of the solvent in anhydrous ethanol, discarding the supernatant after centrifugation, and drying the obtained solid to obtain a palladium nanomaterial catalyst.

[0014] In the step S1, the molar ratio of the added amounts of 4-dodecylaniline diazonium salt, sodium nitrite and tetrafluoroboric acid is 1:4.5:21.

[0015] In the step S2, the molar ratio of palladium acetate, 4-dodecylaniline diazonium salt and sodium borohydride added is 1:1:5.

[0016] The invention also provides a palladium nanocatalyst, which is prepared by the method.

[0017] The present invention also provides the use of the palladium nanocatalyst in spontaneously synthesizing solid aromatic amines from solid reactants driven by solar energy.

[0018] As a further optimization of the application of the palladium nanocatalyst of the present invention in the spontaneous synthesis of solid aromatic amines by solid reactants driven by solar energy: 2 In the atmosphere, the above palladium nanomaterial is used as a catalyst, and the solid nitro compound is statically irradiated with sunlight to synthesize solid aromatic amine compounds in the solid state.

[0019] As a further optimization of the application of the palladium nanocatalyst of the present invention in the spontaneous synthesis of solid aromatic amines by solid reactants driven by solar energy: the molar ratio of the added amount of the solid nitro compound to the palladium nanomaterial is 1:0.0001-0.1, preferably, the molar ratio of the added amount of the solid nitro compound to the palladium nanomaterial is 1:0.01.

[0020] As a further optimization of the application of the palladium nanocatalyst of the present invention in the spontaneous synthesis of solid aromatic amines from solid reactants driven by solar energy: the reaction is detected to be complete by HPLC, and then the solid aromatic amine compounds are purified by recrystallization or column chromatography.

[0021] The present invention has the following beneficial effects: the present invention utilizes a spontaneous solid-state reaction driven by solar energy to produce aniline, and the reaction can proceed smoothly and spontaneously without the introduction of mechanochemistry, and only requires static irradiation with sunlight for a short period of time at ambient temperature (25°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the solid-state catalytic performance diagram under different light intensities;

[0023] Figure 2 Schematic diagram of monitoring the reaction process by optical microscopy;

[0024] Figure 3 For 12R Pd-NCs, Pd(OAc) 2 and TOF values ​​of Pd / C catalysts;

[0025] Figure 4 This is the experimental diagram of 12R-Pd-NCs solid-state catalytic cycle;

[0026] Figure 5 Transmission electron microscopy image of 12R-Pd-NCs;

[0027] Figure 6 This is an infrared thermal image of the solid-state reaction of the template substrate;

[0028] Figure 7 The NMR of the target product Ⅱ-01 1 H NMR spectrum;

[0029] Figure 8 The NMR of the target product Ⅱ-01 13 C NMR spectrum;

[0030] Fig. 9 Schematic diagram of the mechanism of spontaneous synthesis of solid aromatic amines from solid reactants driven by solar energy. DETAILED DESCRIPTION

[0031] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0032] <Pd-Catalyst 12R-Pd-NCs>

[0033] The preparation method of palladium nanocatalyst 12R-Pd-NCs is as follows:

[0034] 4-Dodecylaniline (261.45 mg, 1.0 mmol) and 50% tetrafluoroboric acid (5 mL) were added to a 25 mL flask at 0°C. A pre-prepared aqueous solution of sodium nitrite (0.3 g, 4.5 mmol, 1.0 mL H 2 O) Slowly add to the stirred 4-dodecylaniline and HBF 4 The solution was stirred for 30 minutes, and then a yellow solid was obtained, which was filtered with a Buchner funnel and washed with H 2 O (2×2.5 mL). 4-Dodecylaniline diazonium salt was dried in a vacuum desiccator and stored at 0°C.

[0035] Palladium acetate methanol solution (112.3 mg, 0.5 mmol) and dodecylaniline diazonium tetrahydrofuran solution (173 mg, 0.5 mmol) were mixed at 0°C and stirred for 30 minutes. Then sodium borohydride methanol solution (2.5 mmol sodium borohydride dissolved in 2.0 mL methanol) was slowly added and vigorously stirred (300-500 r / min) at 0°C for 2 hours. After the reaction was completed, methanol and tetrahydrofuran were removed by rotary evaporator, dissolved in dichloromethane, and heated with 0.5 MH 2 SO 4 (3 × 20 mL), 0.5 M NaHCO 3 (3 × 20 mL) and H 2 O (3 × 20mL), dried with anhydrous sodium sulfate, and spun dry. 12R-Pd-NCs were dispersed in anhydrous ethanol. After centrifugation, obvious stratification could be seen. The supernatant solvent was discarded, and the solid was dried to obtain 12R-Pd-NCs. Figure 5 Shown is a high-resolution transmission electron microscopy photograph of the prepared palladium nanoclusters.

[0036] Sometimes, interesting discoveries come from a powerful and unconstrained style. In fact, as McQueen said, "...most material discoveries in the field of solid-state chemistry in history have been discovered by chance rather than by carefully designed reactions..." (Acc.Chem.Res.2018,51,2918-2925). The applicant "accidentally" designed a class of simple nanopalladium, with 3nm palladium clusters as the main body, solar energy as the driving force, and solid reactants as prey. The extreme asymmetry exhibited by the defective structure of the cluster can greatly enhance the absorption of visible light and provide a steady stream of power for it. The flexible alkyl chain will then exhibit perfect capture and driving characteristics. This pre-designed catalyst can spontaneously, efficiently and selectively synthesize solid aromatic amines in the solid state at room temperature, requiring only a steady supply of energy from the sun. It is worth mentioning that the catalyst has a wide range of substrate applicability, can achieve gram-scale reactions up to 15g, and maintain a yield of 98% and a chemical selectivity of >99%, requiring only a very small amount of catalyst. This is a new discovery in the field of solid-state photocatalysis. The development of this strategy will provide opportunities and unlimited possibilities for the large-scale application of solid-state green synthesis driven by solar energy.

[0037] <Solar-energy-driven spontaneous synthesis of solid aromatic amines from solid reactants>

[0038] In 12R-Pd-NCs and H 2 Under the condition of the presence of 0.1 MPa, the solid nitro compound is statically irradiated under sunlight for 4 hours, and the reaction is complete when detected by HPLC. The solid aromatic amine compound is obtained by recrystallization or column chromatography purification, and the reaction formula is as follows:

[0039]

[0040] Wherein, R represents methoxy, methyl or phenyl substitution; X represents a C atom or a N atom.

[0041] This invention introduces solar energy into spontaneous solid-state organic reactions for the first time. Under static sunlight, solid nitro reactants can be converted to solid aromatic amines with near-perfect conversion rates and chemical selectivity in a short period of time. In addition, this method has a wide range of substrate versatility, and the gram-scale reaction can reach 15g. The TOF value is as high as 139169h -1 ( Figure 3 ) is an order of magnitude higher than the optimal value previously reported for nitrobenzene hydrogenation. It was also found that the "temperature gradient driven" effect is above the "local motion inhibition" threshold, which is a necessary condition for an effective response ( Figure 1In addition, the physical form of the reaction mixture changes dramatically during the reaction from a highly aggregated crystalline structure to a foamy appearance ( Figure 2 ). 1 H-NMR and 13 C-NMR spectroscopy was able to elucidate the structure of the product ( Figure 7 and Figure 8 ), infrared thermal imaging data such as Figure 6 shown. Figure 4 This is the cycling experiment diagram of 12R-Pd-NCs.

[0042] Applicants have discovered that the rate-limiting step in solid-state reactions involves the diffusion of atoms, molecules or ions through crystalline phases of reactants, intermediates and products. This process is slow, typically requiring days or even weeks of continuous or intermittent oscillations, while consuming a lot of energy. Microwaves, ball milling, grinding, ultrasonic treatment, spark plasma sintering and high-temperature melting are effective methods to accelerate this process. However, achieving spontaneous solid-state synthesis without external forces faces major challenges. The present invention proposes a solar-driven spontaneous solid-state reaction to produce aromatic amines. The reaction can proceed smoothly and spontaneously without the introduction of mechanochemistry. It only requires the addition of trace amounts of pre-designed novel nanoclusters and static exposure to sunlight for a short period of time at ambient temperature. The "temperature gradient driven" effect above the "local motion inhibition" threshold is a necessary condition for an effective response. The yield and chemical structure of the reaction product can be combined with high-performance liquid chromatography and nuclear magnetic resonance. 1 HNMR, 13 CNMR. In addition, 12R-Pd-NCs can be recycled at least 5 times without significant loss of activity ( Figure 4 ), and catalytic cycle experiments proved that the stability of the catalyst far exceeds that of homogeneous palladium complexes.

[0043] <Example 1>

[0044] 0.5 mmol of compound I-01 and 2 mg of the 12R-Pd-NCs nanoparticles prepared above were added to a 10 mL reaction bottle, and then 0.1 MPa H 2 The raw material was subjected to static irradiation reaction under room temperature with sunlight (the illumination intensity of sunlight was equivalent to that of a 150W xenon lamp), and the reaction progress was detected by HPLC. After 4 hours, the reaction yield was >99%. The target compound II-01 was then purified by recrystallization or column chromatography to obtain a yellow solid.

[0045] The structural formulas of compound Ⅰ-01 and hydrogen are as follows:

[0046]

[0047] The structural formula of compound II-01 is as follows:

[0048]

[0049] The obtained product was analyzed, and the analysis data was: A yellow solid, >99% yield. 1 H NMR (500 MHz, CDCl 3 )δ6.76(d,J=10.0Hz,2H),6.65(d,J=10.0Hz,2H),3.75(s,3H),3.44(s,2H). 13 C NMR (126 MHz, CDCl 3 )δ153.04,140.29,116.70,115.08,56.02.

[0050] <Example 2>

[0051] 0.5 mmol of compound I-02 and 2 mg of the 12R-Pd-NCs nanoparticles prepared above were added to a 10 mL reaction bottle, and then 0.1 MPa H 2 The raw material was subjected to static irradiation reaction under room temperature with sunlight (the illumination intensity of sunlight was equivalent to that of a 200W xenon lamp), and the reaction progress was detected by HPLC. After 4 hours, the reaction yield was 99%. The target compound II-02 was then purified by recrystallization or column chromatography to obtain a yellow solid.

[0052] Among them, compound Ⅰ-02 and H 2 The structural formula is as follows:

[0053]

[0054] The structural formula of compound II-02 is as follows:

[0055]

[0056] The obtained product was analyzed, and the analytical data were: A yellow solid, >99% yield. 1 HNMR(500MHz,DMSO)δ7.28–7.14(m,2H),6.98–6.88(m,2H),5.21(s,2H),2.48(s,3H). 13 C NMR (126MHz, DMSO) δ135.76,120.67,118.92,107.19,10.78.

[0057] <Example 3>

[0058] 0.5 mmol of compound I-03 and 2 mg of the 12R-Pd-NCs nanoparticles prepared above were added to a 10 mL reaction bottle, and then 0.1 MPa H 2 The raw material was subjected to static irradiation reaction under room temperature with sunlight (the illumination intensity of sunlight was equivalent to that of a 250W xenon lamp), and the reaction progress was detected by HPLC. After 4 hours, the reaction yield was 99%. The target compound II-03 was then purified by recrystallization or column chromatography to obtain a yellow solid.

[0059] Wherein, the structural formula of compound I-03 and hydrogen is as follows:

[0060]

[0061] The structural formula of compound II-03 is as follows:

[0062]

[0063] The obtained product was analyzed, and the analytical data were: White solid, 79% yield, 1 H NMR (500 MHz, CDCl 3 )δ7.60(d,J=5.0Hz,2H),7.51–7.42(m,4H),7.32(t,J=5.0Hz,1H),6.80–6.77(m,2H),3.74(s,2H). 13 C NMR (126 MHz, CDCl 3 )δ146.19,141.47,131.83,129.01,128.33,126.73,126.60,115.72.

[0064] <Example 4>

[0065] 0.5 mmol of compound I-04 and 2 mg of the 12R-Pd-NCs nanoparticles prepared above were added to a 10 mL reaction bottle, and then 0.1 MPa H 2 The raw material was subjected to static irradiation reaction under room temperature with sunlight (the illumination intensity of sunlight was equivalent to that of a 350W xenon lamp), and the reaction progress was detected by HPLC. After 4 hours, the reaction yield was 99%. The target compound II-04 was then purified by recrystallization or column chromatography to obtain a yellow solid.

[0066] Wherein, the structural formula of compound I-04 and hydrogen is as follows:

[0067]

[0068] The structural formula of compound II-04 is as follows:

[0069]

[0070] The obtained product was analyzed, and the analytical data were: A yellow solid, 91% yield, 1 H NMR (500 MHz, CDCl 3 )δ8.04(d,J=5.0Hz,1H),7.95(d,J=5.0Hz,1H),7.03–7.00(m,1H),6.95–6.88(m,1H),3.73(s,2H). 13 C NMR (126 MHz, CDCl 3 )δ143.01,140.01,137.64,124.03,121.72.

[0071] <Comparative Examples 1-3>

[0072] The synthesis process of <Comparative Examples 1-3> is basically the same as that of <Example 1>, except that the designed 12R Pd-NCs catalyst is replaced with Pd / C, Pd(OAc) 2 , the reaction results of the dodecyl palladium precursor mixture are as follows:

[0073] <Comparative Example 1> After the reaction was completed, the final yield was calculated to be 55%.

[0074] <Comparative Example 2> After the reaction was completed, the final yield was calculated to be 28%.

[0075] <Comparative Example 3> After the reaction was completed, the final yield was calculated to be 70%

[0076] <Comparative Examples 4-7>

[0077] The synthesis process of <Comparative Example 4-7> is basically the same as that of <Example 1>, except that the reaction environment is changed to a dark environment for static light-proof reaction.

[0078] The temperature was adjusted to 0°C, 25°C, 50°C and 100°C.

[0079] <Comparative Example 4> After the reaction was completed, the final yield was calculated to be 19%

[0080] <Comparative Example 5> After the reaction was completed, the final yield was calculated to be 50%

[0081] <Comparative Example 6> After the reaction was completed, the final yield was calculated to be 56%.

[0082] After the reaction of Comparative Example 7 was completed, the final yield was calculated to be 39%.

[0083] <Comparative Examples 8-11>

[0084] The synthesis process of <Comparative Examples 8-11> is basically the same as that of <Example 1>, except that: a xenon lamp is used to simulate sunlight, and the power of the xenon lamp is 15W, 60W, 100W and 300W respectively.

[0085] <Comparative Example 8> After the reaction was completed, the final yield was calculated to be 44%.

[0086] <Comparative Example 9> After the reaction was completed, the final yield was calculated to be 37%.

[0087] <Comparative Example 10> After the reaction was completed, it was calculated that the final yield was >99%.

[0088] <Comparative Example 11> After the reaction was completed, it was calculated that the final yield was >99%.

[0089] As can be seen from the above data, sunlight is essential for driving the spontaneous synthesis of solid aromatic amines from solid nitro reactants. The new nanoclusters designed in the present invention can significantly enhance this effect through photothermal conversion. Although light is essential for the reaction, its role as a heat source is another important consideration. The reaction results at different temperatures under dark conditions indicate that temperature effects are unlikely to be the controlling factor in the process. The hypothesis of a "gradient-driven" phenomenon seems to be a more reasonable hypothesis. Due to the different properties of light and heat (in the dark), the temperature "gradients" produced are significantly different. According to thermal measurements, these gradients are larger ( Figure 6 ). This is important because it is the gradient, not the uniformity, that drives the motion of molecules or particles. The presence of the gradient facilitates the preferential migration of the catalyst relative to the reactants / products, thereby achieving complete conversion. This is something that heat alone cannot achieve without a gradient driving the motion. The importance of the gradient is also indicated by experimental data at different light intensities, which show that there is a critical light level above which the dynamics required for high yields can be achieved, that is, the gradient needs to exceed a threshold of "local motion inhibition" ( Figure 1 The change in the physical form of the reaction is also consistent with the higher yields caused by the motion induced by the temperature gradient, i.e., the physical form of the reaction mixture changes dramatically during the reaction from a highly aggregated crystalline structure to a foamy appearance ( Figure 2 ).

[0090] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a palladium nanocatalyst, characterized in that: 4-dodecylaniline diazonium salt is prepared by using 4-dodecylaniline, tetrafluoroboric acid and sodium nitrite; The palladium nanocatalyst is prepared by using palladium acetate, 4-dodecylaniline diazonium salt and sodium borohydride.

2. A method for preparing a palladium nanocatalyst as claimed in claim 1, characterized in that, The following steps are involved: S1: 4-dodecylaniline and tetrafluoroboric acid are mixed at 0-5°C and a sodium nitrite aqueous solution is slowly added, and after stirring, the mixture is filtered and washed to obtain 4-dodecylaniline diazonium salt, which is then dried and stored at 0-5°C; S2: Mix the methanol solution of palladium acetate and the tetrahydrofuran solution of 4-dodecylaniline diazonium salt at 0°C and slowly add the methanol solution of sodium borohydride. Stir vigorously at 0-5°C to react. After the reaction is completed, remove the methanol and tetrahydrofuran and dissolve in dichloromethane. After washing and drying, filter and remove the solvent.

3. A method for preparing a palladium nanocatalyst as claimed in claim 2, characterized in that: The method further comprises step S3: dispersing the product after suction filtration and removal of the solvent in anhydrous ethanol, discarding the supernatant after centrifugal treatment, and drying the obtained solid to obtain a palladium nanocatalyst.

4. A method for preparing a palladium nanocatalyst as claimed in claim 2, characterized in that: In the step S1, the molar ratio of the added amounts of 4-dodecylaniline, sodium nitrite and tetrafluoroboric acid is 1:4.5:

21.

5. A method for preparing a palladium nanocatalyst as claimed in claim 2, characterized in that: In the step S2, the molar ratio of palladium acetate, 4-dodecylaniline diazonium salt and sodium borohydride added is 1:1:

5.

6. A palladium nanocatalyst, characterized in that: The invention is prepared by the method described in any one of claims 1 to 5.

7. Use of the palladium nanocatalyst as claimed in claim 6 in the spontaneous synthesis of solid aromatic amines by solid reactants driven by solar energy.

8. The use of the palladium nanocatalyst in the spontaneous synthesis of solid aromatic amines by solid reactants driven by solar energy as claimed in claim 7, characterized in that: At room temperature and in a H2 atmosphere, solid aromatic amine compounds were synthesized by using palladium nanomaterials as catalysts and statically irradiating solid nitro compounds with sunlight.

9. The use of the palladium nanocatalyst in the spontaneous synthesis of solid aromatic amines by solid reactants driven by solar energy as claimed in claim 8, characterized in that: The molar ratio of the solid nitro compound to the palladium nanomaterial is 1:0.0001-0.

1. Preferably, the molar ratio of the solid nitro compound to the palladium nanomaterial is 1:0.

01.

10. The use of the palladium nanocatalyst in the spontaneous synthesis of solid aromatic amines by solid reactants driven by solar energy as claimed in claim 8, characterized in that: The reaction is detected to be complete by HPLC, and then purified by recrystallization or column chromatography to obtain a solid aromatic amine compound.

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