A catalyst-loaded oil-in-water Pickering emulsion and its application in bubbling bed catalytic reaction

Abstract

The invention discloses a catalyst-loaded oil-in-water Pickering emulsion, a preparation method thereof, and an application thereof, comprising the following steps: (1) surface modification of SiO2 nanoparticles: weighing dried nano-SiO2, uniformly dispersing the mixture in toluene, and sequentially adding modifiers such as octyltrimethoxysilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, and 3-aminopropyltriethoxysilane; stirring under reflux at 100-110° C. for 3.5-6 hours, centrifuging to obtain a white solid, washing the solid with toluene, and drying the solid; (2) preparing a catalyst with interfacial activity; and (3) preparing a catalyst-loaded oil-in-water Pickering emulsion: weighing a catalyst, adding the mixture to deionized water, uniformly dispersing the mixture, and then adding chlorobenzene as a dispersed phase and mixing the mixture to obtain the catalyst-loaded oil-in-water Pickering emulsion.

Description

Technical Field

[0001] The invention relates to the technical field of Pickering emulsion and catalysis, and in particular to a catalyst-loaded oil-in-water Pickering emulsion and application thereof in a bubbling bed catalytic reaction. Background Art

[0002] Pickering emulsion refers to an emulsion obtained by using ultrafine solid particles as emulsifiers, also known as Pickering emulsion, which is divided into oil-in-water (O / W) and water-in-oil (W / O). The stability of the emulsion is related to the concentration, particle size, wettability, etc. of the solid particles. Compared with traditional surfactant-stabilized emulsions, Pickering emulsions have their own advantages: (1) the amount of emulsifier used is greatly reduced, saving costs; (2) the toxicity is much lower than that of surfactants; (3) it is environmentally friendly; (4) the stability is increased and it is not easily affected by factors such as temperature, pH value, salt concentration and oil phase composition. In recent years, Pickering emulsions and Pickering bubbles have received considerable attention in various fields such as chemical engineering, materials science, pharmaceutical engineering, drug delivery and biochemistry due to their advantages.

[0003] Liquid-liquid and gas-liquid two-phase catalytic systems in the industrial synthesis of fine chemicals have long suffered from low efficiency, forcing them to be carried out in batch reactors. Pickering emulsions, with their large reaction interface and easily regulated micro-nanointerfaces / spaces, can significantly improve the catalytic efficiency of two-phase reactions. More importantly, Pickering emulsions are extremely stable, allowing them to be packed into fixed-bed reactors like traditional solid particle catalysts, enabling continuous operation of liquid-liquid and gas-liquid two-phase catalytic reactions. This significantly improves the efficiency of enzyme-catalyzed and chemical-catalyzed reactions and promotes the development of two-phase catalytic systems towards application-oriented levels.

[0004] A fixed-bed catalytic reactor consists of a stationary bed of solid particles filled with catalyst particles within a tubular reactor. Gas and liquid reactants flow through the interstices between the particles, reacting chemically on the catalyst surface. To overcome the batch-like limitations of two-phase and emulsion catalysis, numerous researchers have dedicated themselves to developing continuous-flow catalytic reactions, a trend sought by industry. The novel Pickering emulsion fixed-bed catalysis concept addresses key challenges for homogeneous catalysts, particularly enzymes, such as catalytic efficiency, recycling, and continuous reaction. Currently, the Pickering emulsion fixed-bed concept has been successfully applied to a wide range of catalytic reactions, including biocatalytic chiral ester hydrolysis, chiral transesterification, ketone reduction to chiral alcohols, and transamination to chiral amines. It also encompasses reactions involving various types of homogeneous catalysts, such as acid-catalyzed, base-catalyzed, and ionic liquid-catalyzed reactions. Furthermore, by leveraging the easily tunable micro- and nano-interfaces / spaces of Pickering emulsions, it can also be applied to more complex biomimetic tandem catalytic systems.

[0005] Currently, reports on the application of Pickering emulsions in the field of catalysis technology typically involve intermittent reactions, although there are also reports of continuous flow reactions. For example, Chinese patent CN 107287181 B discloses a method for using a Pickering emulsion to immobilize an enzyme for a fixed-bed continuous reaction. This method uses nano-silica modified with dichlorodimethylsilane as an emulsion stabilizer, an ionic liquid containing an enzyme catalyst as the dispersed phase, and an organic solvent as the continuous phase. High-speed stirring forms an ionic liquid-in-oil (IL / Oil) Pickering emulsion. This enzyme-catalyzed Pickering emulsion is then loaded into a fixed-bed reactor, and a reactant solution is pumped from the upper end of the reactor via a constant flow pump. After flowing through the catalytic bed, the product flows out from the bottom of the reactor. This method has mild conditions, is simple and easy to use, can effectively improve the catalytic efficiency of the enzyme, and realizes the reuse and continuous operation of the enzyme; however, in the oil-in-ionic liquid (IL / Oil) Pickering emulsion prepared by this scheme, the dispersed phase ionic liquid has a high density, the emulsion droplets are deposited at the bottom of the bed, and the reactants diffuse into the emulsion by gravity to react. The reactant mass transfer efficiency is low, resulting in a low processing capacity of the reaction system.

[0006] p-NP (4-NP, p-nitrophenol) is a priority pollutant for environmental control. Production discharges large quantities of high-concentration p-nitrophenol wastewater, which, if discharged directly, would severely pollute the environment. Therefore, p-NP-containing wastewater treatment is necessary. The catalytic hydrogenation of p-nitrophenol uses p-nitrophenol as the raw material and sodium borohydride as the reducing agent. Under the action of a catalyst (such as Pt, Pd, or Ni), hydrogenation reduction is performed under low and normal pressure to produce p-aminophenol (p-AP, 4-AP). p-Aminophenol (p-AP) is a very important pharmaceutical API and chemical intermediate. After the reaction, the majority of the product is typically crystallized by cooling. After distillation to remove most of the ethanol, water containing a small amount of ethanol and p-aminophenol remains.

[0007] In the catalytic reduction of 4-NP, NaBH4 is used as a reducing agent and nanometals are widely studied as catalysts. However, this type of catalyst is usually used in a batch reaction mode for the catalytic reduction of 4-NP, which has the following inherent disadvantages: 1) The product cannot be removed in time, and there is a serious product "inhibition effect", which makes it impossible to further improve the catalytic conversion rate. 2) After the reaction is completed, the product and catalyst need to be separated and recovered, and the entire process is energy-consuming and time-consuming. 3) The catalytic reaction can only be carried out in batches, and continuous and large-scale production is impossible. Therefore, it is a very valuable task to find a simple and effective method to convert the traditional batch reaction system into a continuous flow reaction system.

[0008] Bubble reactors are gas-liquid reactors with a liquid phase as the continuous phase and a gas phase as the dispersed phase. They include various structural types, including tank-type bubble reactors, bubble tube reactors, and bubble columns. Currently, there are few reports on the application of Pickering emulsions in bubble bed reactions or wastewater treatment. Summary of the Invention

[0009] The purpose of the present invention is to solve the above problems and provide a catalyst-loaded oil-in-water Pickering emulsion, a preparation method thereof and an application thereof in a bubbling bed catalytic reaction.

[0010] In order to achieve its purpose, the present invention adopts the following technical solutions:

[0011] A method for preparing a catalyst-loaded oil-in-water Pickering emulsion comprises the following steps:

[0012] (1) Surface modification of SiO2 nanoparticles:

[0013] Weigh dry nano-SiO2 and evenly disperse it in toluene. Then, add modifiers octyltrimethoxysilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, and 3-aminopropyltriethoxysilane in sequence. Reflux and stir at 100-110°C under inert gas for 3.5-6 hours, centrifuge to obtain a white solid, wash with toluene, and then dry to obtain solid SiO2 with interfacial activity. The dosage ratio of each substance is as follows: 320-340 μL octyltrimethoxysilane, 170-240 μL 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, and 100-150 μL 3-aminopropyltriethoxysilane are added to 1 g of nano-SiO2.

[0014] (2) Preparation of catalysts with interfacial activity:

[0015] The interfacially active solid SiO2 prepared in step (1) is weighed and added to toluene, and the mixture is evenly dispersed. A palladium-containing solution or a chloroplatinic acid solution is added, wherein the palladium-containing solution is a chloropalladium acid solution or a palladium acetate solution. After stirring and adsorption, the mixture is centrifuged to obtain a white solid, which is washed with toluene. The toluene solution is added to the washed white solid, and the mixture is evenly stirred. An ethanolic sodium borohydride solution is added thereto, and the solid is subjected to in-situ reduction at room temperature to reduce the palladium ions to a single palladium substance. After the reaction is completed, the solid is centrifuged, and the solid is washed with anhydrous ethanol and dried to obtain an interfacially active solid catalyst. The mass ratio of the catalyst palladium element or platinum element to SiO2 supported on the catalyst is 0.05-2%.

[0016] (3) Preparation of catalyst-loaded O / W Pickering emulsion:

[0017] The solid catalyst prepared in step (2) is weighed and added to deionized water, and dispersed evenly. Then, chlorobenzene is added as the dispersed phase and mixed to obtain an O / W type Pickering emulsion loaded with the catalyst. The mass ratio of each substance is 0.5-3% of the solid catalyst to chlorobenzene.

[0018] In the step (1), dried nano-SiO2 is weighed and uniformly dispersed in toluene, and then modifiers octyltrimethoxysilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, and 3-aminopropyltriethoxysilane are added in sequence; the mixture is refluxed and stirred for 4-6 hours under the protection of an inert gas at 100-110° C., and a white solid is obtained by centrifugation. The solid is washed with toluene and then dried to obtain SiO2 with interfacial activity; wherein the dosage ratio of each substance is as follows: 1 g of nano-SiO2 is dispersed in 4-6 mL of toluene, 320-340 μL of octyltrimethoxysilane, 180-240 μL of 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, and 100-130 μL of 3-aminopropyltriethoxysilane are added.

[0019] In the step (2),

[0020] The mass ratio of the catalyst palladium element or platinum element supported on the prepared catalyst to SiO2 is 0.05-1% or 0.05-0.8% or 0.05-0.6% or 0.05-0.4% or 0.06-0.3% or 0.07-0.2%;

[0021] The chloropalladium acid solution is a chloropalladium acid ethanol solution, the palladium acetate solution is a palladium acetate toluene solution, and the chloroplatinic acid solution is a chloroplatinic acid ethanol solution;

[0022] Preferably, chloropalladic acid ethanol solution is used;

[0023] The dosage ratio of each substance is as follows: 1 g of interfacially active SiO2 is added to 5-20 mL, 5-15 mL, or 9-12 mL of toluene, 0.7 mL-20 mL, 0.8 mL-10 mL, 0.9 mL-5 mL, or 0.9 mL-2 mL of a 5 mM chloropalladic acid ethanol solution is added, 8-12 mL of the toluene solution is added to the white solid obtained after washing with toluene, and the mixture is stirred uniformly, and 1-20 mL, 1-10 mL, 1-5 mL, or 2-4 mL of a 50 mM sodium borohydride ethanol solution is added thereto;

[0024] Preferably, in step (2), a palladium-containing solution or a chloroplatinic acid solution is slowly added through a syringe pump, and after stirring and adsorbing for 4-8 hours, a white solid is obtained by centrifugation, and a sodium borohydride ethanol solution is slowly added using a syringe pump, and a reduction reaction is carried out at room temperature for 3-6 hours, and the solid is washed with anhydrous ethanol and dried at 45-65°C.

[0025] In the step (3), the usage ratio of each substance is 0.022g-0.132g of catalyst is added to 1-8mL of deionized water, and then 1-8mL of chlorobenzene is added; preferably, the mass ratio of solid catalyst to chlorobenzene is 0.5-2% or 0.5-1.5% or 0.5-1.0%.

[0026] The preparation method of chloropalladate ethanol in step (2) is as follows: palladium chloride powder is weighed, and then diluted hydrochloric acid is added and heated to boil until the palladium chloride is completely dissolved, and then the volume is fixed with anhydrous ethanol after cooling to room temperature.

[0027] A catalyst-loaded oil-in-water Pickering emulsion is prepared by any of the above-mentioned preparation methods.

[0028] The catalyst-loaded oil-in-water Pickering emulsion is used in a bubbling bed catalytic reaction. The catalyst-loaded oil-in-water Pickering emulsion is loaded into a reaction column of a bubbling bed reactor. The catalyst loaded on the Pickering emulsion catalyzes the reaction of the reaction liquid in the reaction column.

[0029] In the above-mentioned technical solution for applying the catalyst-supported oil-in-water Pickering emulsion in a bubbling bed catalytic reaction, the reaction in the reaction column is a hydrogenation reaction requiring hydrogen, and the hydrogenation reaction is a nitrophenol hydrogenation reaction or an acetone hydrogenation reaction, and the nitrophenols include o-nitrophenol hydrogenation, m-nitrobenzene hydrogenation, and p-nitrophenol hydrogenation;

[0030] Hydrogen gas is bubbled into the reaction column from the bottom, or NaBH4 is added to the reaction solution to generate hydrogen gas.

[0031] A bubbling bed catalytic reaction method based on a Pickering emulsion comprises the following steps: loading the catalyst-loaded oil-in-water Pickering emulsion into a reaction column of a bubbling bed reactor; introducing a reaction liquid and hydrogen into the reaction column; wherein the reaction liquid is a solution containing nitrophenol or acetone; and the nitrophenol includes hydrogenated o-nitrophenol, hydrogenated m-nitrobenzene, and p-nitrophenol.

[0032] In the above-mentioned technical solution of the bubbling bed catalytic reaction method based on Pickering emulsion, the reaction liquid is an aqueous solution containing nitrophenol;

[0033] The hydrogen is generated by NaBH4 added to the reaction solution, and the reaction solution contains 0.1-1.5mM nitrophenol and 25-200mM NaBH4, preferably 0.1-1.3mM or 0.1-1.1mM nitrophenol, 25-150mM or 40-150mM or 40-130mM or 40-110mM or 50-100mM NaBH4.

[0034] The beneficial effects of the present invention are:

[0035] 1. The catalyst-loaded Pickering emulsion prepared by the present invention is an oil-in-water emulsion type and can be used in a bubbling bed continuous reactor. The reaction liquid is soluble in the continuous phase (deionized water) outside the emulsion solid particles. The reactants diffuse to the two-phase interface of the Pickering emulsion and are catalyzed by the catalyst there to react. The hydrogen bubbling improves the mass transfer performance of the catalyst interface, significantly increases the catalytic efficiency, and realizes a continuous reaction.

[0036] 2. Based on the catalyst-loaded Pickering emulsion prepared by the present invention, a bubbling bed continuous reaction system based on Pickering emulsion was constructed for the first time. Compared with the traditional Pickering emulsion fixed bed continuous reaction system, in this reaction system, the reactants enter from the bottom of the reactor, and the gas introduced into the reaction system causes a certain disturbance to the entire emulsion system, which fully improves the mass transfer performance of the catalyst interface. This provides a new method for the application of Pickering emulsion in the field of catalysis and provides new ideas for the large-scale and continuous treatment of organic wastewater or the production of various chemicals.

[0037] 3. The Pickering emulsion preparation method and application method of the present invention are simple and low-cost, and can achieve high catalytic efficiency at a low catalyst loading. The catalyst is easy to recover and reuse, and is easy to scale production. The application method is simple to operate and has low equipment requirements, making it suitable for industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is SiO2 with interfacial activity prepared by mixing different modifiers.

[0039] Figure 2 This is the EDS element distribution map of the catalyst (Pd / SiO2) with interfacial activity.

[0040] Figure 3 Fluorescence microscope (a) and optical microscope (bd) photos of Pickering emulsion: (ab) 1 wt% Pickering emulsion, (c) 2 wt% Pickering emulsion (d) 3 wt% Pickering emulsion.

[0041] Figure 4 It is a characterization experiment diagram of each product in Example 1.

[0042] Figure 5 It is a schematic structural diagram of the Pickering emulsion-based bubbling bed continuous flow catalytic system constructed in Example 2.

[0043] Figure 6 It is the catalytic efficiency result of Pickering emulsion with different catalyst ratios.

[0044] Figure 7 These are the experimental results on the effect of different sodium borohydride concentrations in the reaction solution on the catalytic efficiency.

[0045] Figure 8 These are the catalytic performance results of the bubble bed reactor under different conditions. DETAILED DESCRIPTION

[0046] The present invention will be further described below with reference to the embodiments, but the present invention is not limited thereto.

[0047] The experimental methods in the following examples are conventional methods unless otherwise specified; the chemical reagents and materials used are conventional reagents and materials in the art and are commercially available unless otherwise specified.

[0048] Example 1 Preparation and Characterization of Pickering Emulsion

[0049] 1. Preparation of Pickering emulsion

[0050] Follow these steps:

[0051] (1) Surface modification of SiO2 nanoparticles to prepare SiO2 with interfacial activity:

[0052] Weigh 1g of nano-SiO2 (30nm) and dry it at 125℃ for 4h (to remove the moisture contained in it and prevent the contained water from affecting subsequent experiments). Use a mixer to disperse 1g of dried nano-SiO2 in 5mL of toluene, and then add the first modifier octyltrimethoxysilane (CAS No.: 3069-40-7), the second modifier 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (CAS No.: 35141-30-1) and the third modifier 3-aminopropyltriethoxysilane (CAS No.: 919-30-2) in sequence; reflux and stir at 110℃ under nitrogen protection for 4h, centrifuge to obtain a white solid, wash three times with toluene, and vacuum dry to obtain the modified SiO2 with interfacial activity.

[0053] According to the above steps, experimental groups with different modifier ratios were prepared simultaneously, and a total of 4 experimental groups of interfacially active SiO2 were prepared as shown in Table 1:

[0054] Table 1

[0055]

[0056] The surface active silica modified in experimental groups 1-4 was used to prepare Pickering emulsions: 2 mL of deionized water, 2 mL of chlorobenzene, and 0.022 g of modified silica were mixed to obtain Pickering emulsions such as Figure 1 As shown in the figure: Experimental groups 1, 2, and 4 can all prepare stable O / W Pickering emulsions; the emulsion obtained in experimental group 3 is too lipophilic (this is because octyltrimethoxysilane contains a large number of hydrophobic methyl groups, and its excessive use makes the emulsifier too hydrophobic). Experimental group 3 cannot form an O / W Pickering emulsion, and the W / O emulsion droplets it forms float on the oil phase (the oil phase is heavy - chlorobenzene, with a density of 1.1, and the aqueous phase is light - deionized water, with a density of 1), and cannot be used for catalytic reactions.

[0057] Nano-silicon dioxide is widely available, inexpensive, and has a surface rich in silanol groups (hydrophilic groups, so unmodified silicon dioxide itself is quite hydrophilic), making it easy to functionalize and modify the surface. Therefore, the present invention selects silicon dioxide as the substrate material for modification. 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane and 3-aminopropyltriethoxysilane are relatively hydrophilic because they have amino groups (-NH2) (the former modifier has a higher amino content, while the latter has a lower amino content. In addition, another important purpose of the grafted amino group is to better adsorb palladium particles). Solid particles with medium wettability can be adsorbed on the oil / water interface to form a Pickering emulsion. The present invention also uses hydrophobic octyltrimethoxysilane (this modifier contains methyl-CH3, where methyl is a hydrophobic group) to modify silicon dioxide particles. By finely adjusting the ratios of the three modifiers, silicon dioxide nanoparticles with good interfacial activity are prepared to stabilize the O / W Pickering emulsion. The present invention selects two amino-containing modifiers to finely control the grafting amount of amino groups. By adjusting the grafting ratio of amino groups to methyl groups, solid particles with medium wettability are obtained, and the solid particles are subsequently used to prepare a stable O / W Pickering emulsion.

[0058] (2) Preparation of catalysts with interfacial activity:

[0059] Weigh 1g of the interfacially active SiO2 prepared in Experimental Group 1 in step (1) and add it to 10mL of toluene solution. Stir magnetically to disperse it evenly. Then, slowly add (so that PdCl4 2-Complex ions are more evenly dispersed in the solvent and more evenly loaded on the silica surface) 1mL of 5mM chloropalladic acid ethanol solution (5mM, weigh 0.04434g of palladium chloride (PdCl2) powder in a 50mL small volume flask, then add 5mL of 0.2M dilute hydrochloric acid and heat to boil until the palladium chloride is completely dissolved. After cooling naturally to room temperature, dilute to 50mL with anhydrous ethanol to obtain 5mM chloropalladic acid ethanol solution), stir and adsorb for 6h, centrifuge to obtain a white solid, and wash three times with toluene. Add 10mL of toluene solution to the washed white solid, stir evenly, and use a syringe pump (40μl / min) to pass 3mL of sodium borohydride (NaBH4) solution (the solvent is anhydrous ethanol, concentration 50mM) (sodium borohydride is a strong reducing agent that can reduce PdCl4 adsorbed on the silica surface) 2- The complex ions are completely reduced to reduce the palladium ions to palladium element, completing the in situ synthesis of Pd nanoparticles), and then reduced at room temperature for 4 hours and centrifuged, washed three times with anhydrous ethanol, and vacuum dried at 55°C for 6 hours to obtain a catalyst with interfacial activity. The palladium loading of this catalyst was quantitatively detected by ICP-OES to be 0.07wt%, that is, 696mg of palladium element was loaded on 1kg of silica, which is equivalent to about 0.7mg of palladium element loaded on 1g of silica. The mass ratio of palladium element to silica of this catalyst is 0.07%. This catalyst is recorded as Pd / SiO2-0.07% catalyst.

[0060] Chloropalladic acid ethanol solution is used because: sodium borohydride is soluble in ethanol, and ethanol is soluble in toluene, which can better perform reduction; sodium borohydride aqueous solution is not used because: 1. Water is insoluble in toluene and cannot be fully reduced; 2. Silicon dioxide will partially agglomerate when it comes into contact with water, and the palladium particles cannot be better and evenly loaded on the silicon dioxide surface.

[0061] A Pd / SiO2-0.2% catalyst was prepared using the same method, using 2.86 mL of a 5 mM chloropalladic acid-ethanol solution. The remaining reagents were the same as those used to prepare the Pd / SiO2-0.07% catalyst. Quantitative analysis by ICP-OES revealed a palladium-to-silica mass ratio of 0.2% in the prepared Pd / SiO2-0.2% catalyst.

[0062] Since the catalyst content in the Pd / SiO2-0.07% catalyst is too low to be conducive to elemental analysis, the prepared Pd / SiO2-0.2% catalyst with interfacial activity was subjected to EDS elemental analysis. The EDS element distribution diagram is shown in the figure. Figure 2 As shown in the figure, Pd atoms are evenly distributed on the surface of the modified silica. This is because a large number of amino groups are successfully grafted onto the surface of the modified silica. The presence of amino groups allows Pd nanoparticles to better adsorb on the surface of the silica particles.

[0063] (3) Preparation of catalyst-loaded O / W Pickering emulsion:

[0064] 0.044 g of the catalyst prepared in step (2) was weighed and added to 4 mL of deionized water, ultrasonically dispersed uniformly, and then 4 mL of chlorobenzene (mass 4.4 g, density 1.1 g / mL) was added and vigorously shaken for 1 min to obtain a catalyst-loaded O / W Pickering emulsion. According to the mass ratio of catalyst to dispersed phase chlorobenzene, the Pickering emulsion prepared with this ratio was recorded as 1 wt% Pickering emulsion. 0.5 wt% Pickering emulsion, 2 wt% Pickering emulsion, and 3 wt% Pickering emulsion were prepared in the same manner. The masses of the catalyst prepared in step (2) weighed during the preparation of the 0.5 wt%, 2 wt%, and 3 wt% Pickering emulsions were 0.022 g, 0.088 g, and 0.132 g, respectively.

[0065] The Pickering emulsion prepared using Pd / SiO2-0.07% catalyst was characterized by fluorescence microscopy (to further confirm the type of Pickering emulsion) and optical microscopy (to characterize the morphology of the Pickering emulsion), as shown in Figure 2. Figure 3 As shown, Figure 3 a The dispersed phase was fluorescently stained with the oil-soluble fluorescent dye Nile red (insoluble in water), and then characterized by fluorescence microscopy. The characterization results showed that the Pickering emulsion type was O / W type. Figure 3 b-3d 1wt%, 2wt%, and 3wt% Pickering emulsions were prepared using Pd / SiO2-0.07% catalyst for morphological characterization. It can be seen from the figure that with the increase of catalyst dosage, the emulsion droplet size gradually decreases.

[0066] 2. Characterization

[0067] Characterize the products prepared above:

[0068] 1. The contact angles of unmodified silica, the interfacially active silica modified with the modifier prepared in Experimental Group 1 in Step 1 (1), and the Pd / SiO2-0.07% catalyst prepared in Step 1 (2) were measured: Figure 4 a shows that the three-phase contact angle of unmodified silica nanoparticles is 25°, showing strong hydrophilicity and unable to stabilize O / W Pickering emulsion; Figure 4 b shows that the interfacially active silica modified with three modifiers has appropriate wettability with a contact angle of 77°, which can well stabilize the O / W Pickering emulsion. Figure 4c shows that the interfacial active catalyst after loading palladium particles still has appropriate wettability, with a contact angle of 75°, and can also stabilize the O / W Pickering emulsion well, which lays the foundation for its application in the catalytic system.

[0069] 2. The unmodified silica, the interfacially active silica modified with the modifier prepared in Experimental Group 1 in Step 1 (1), and the Pd / SiO2-0.07% catalyst prepared in Step 1 (2) were tested:

[0070] Figure 4 d shows the FT-IR (Fourier transform infrared spectroscopy: analysis of specific functional groups) spectra of unmodified and modified SiO2 particles. Compared with unmodified SiO2 nanoparticles, the modified SiO2 particles have a higher FT-IR wavelength at 3200-3400 cm -1 The absorption peak in the range of 2800-3000 cm is reduced, which is because the -OH groups on the SiO2 surface are reduced; -1 The vibration peaks in the range are attributed to the stretching vibration of saturated C-H bonds, indicating that the SiO2 nanoparticles were successfully grafted with methyl groups.

[0071] Figure 4 e shows the XPS elemental full spectrum analysis of three different forms of silica particles (unmodified, modified, and in Pd / SiO2-0.07% catalyst). The C and N elements are the characteristic elements of methyl (-CH3) and amino (-NH2), respectively, further proving the successful grafting of methyl and amino groups. Because the palladium content is very low, its signal is very weak, so the experiment also uses ICP-OES to quantitatively detect the actual Pd loading on the silica surface.

[0072] Figure 4 f is the 3d peak spectrum (XPS) of Pd in ​​Pd / SiO2-0.07% catalyst, which further proves the successful loading of palladium nanoparticles. In addition, partially oxidized Pd was observed, which may be due to the oxidation of the sample when it comes into contact with oxygen in the air.

[0073] Example 2: Treatment of p-NP-containing wastewater by continuous reaction in a bubbling bed reactor based on a Pickering emulsion

[0074] 1. Construction of a Bubbling Column Reaction System Based on Pickering Emulsion and Screening of Catalyst Content Ratio in Pickering Emulsion

[0075] 1. Prepare the reaction solution: Take 240 mL of wastewater containing p-NP (p-NP concentration is 1 mM), add 0.228 g of NaBH4 (i.e., the NaBH4 concentration in the wastewater is 25 mM), and mix well to prepare a reaction solution.

[0076] 2. Bubbling bed catalytic reaction for wastewater treatment

[0077] Wastewater treatment experiments were conducted using 0.5wt%, 1wt%, 2wt%, and 3wt% Pickering emulsions prepared using the Pd / SiO2-0.07% catalyst in Example 1. The Pd / SiO2-0.07% catalyst has a palladium to silicon dioxide mass ratio of 0.07%, while the 0.5wt%, 1wt%, 2wt%, and 3wt% Pickering emulsions refer to the mass ratios of the catalyst to the dispersed phase, chlorobenzene.

[0078] The structural diagram of the Pickering emulsion-based bubbling bed continuous flow catalytic system constructed in this example is shown in FIG. Figure 5 shown.

[0079] At room temperature, a Pickering emulsion was loaded into a bubbling bed reactor (with an inner diameter of 1.6 cm) for a continuous flow catalytic reaction. The reaction solution was transported from the bottom of the reaction column, and the reaction solution flow rate was precisely controlled by a peristaltic pump (at a flow rate of 150 μL / min). Before entering the reaction column, the NaBH4 in the reaction solution undergoes a hydrolysis reaction with water to produce H2. Therefore, the reaction solution entering the reaction column forms a gas-liquid two-phase flow. The upward movement of H2 bubbles within the reaction column causes local displacement between the Pickering emulsion droplets, fully contacting the reactants with the catalytically active centers, strengthening the mass transfer process of the reactants, fully improving the mass transfer performance of the catalyst interface, and significantly increasing the catalytic efficiency. The resulting products (p-aminophenol (p-AP) and water) diffuse to the top of the reaction column due to concentration differences. The products can be continuously collected at the top of the reactor, and the products are regularly collected from the top to measure the conversion rate (i.e., the ratio of p-NP to p-AP).

[0080] The results are as follows Figure 6 As shown, 1 wt% Pickering emulsion has the best catalytic efficiency, so subsequent experiments were conducted using 1 wt% Pickering emulsion.

[0081] 2. Effect of Sodium Borohydride Concentration in the Reaction Solution on Catalytic Efficiency

[0082] An experiment was conducted using a 1 wt% Pickering emulsion prepared using the Pd / SiO2-0.07% catalyst in Example 1 to detect the effect of the sodium borohydride concentration in the p-NP wastewater on the catalytic efficiency. The concentrations of NaBH4 in the 1 mM p-NP wastewater were set to 25, 50, 100, and 200 mM, respectively. The remaining experimental conditions and parameter settings were the same as those in step 1 of this embodiment.

[0083] The results are as follows Figure 7As shown, the catalytic conversion rate is highest when the sodium borohydride concentration is 100mM. The catalytic efficiency is lowest when the sodium borohydride concentration is 25mM. This is mainly because the hydrolysis of low-concentration sodium borohydride produces less hydrogen, which does not effectively disturb the entire emulsion bed. When the sodium borohydride concentration is too high (200mM), the amount of hydrogen generated by its hydrolysis is too large, causing significant damage to the emulsion bed and ultimately resulting in lower conversion rate.

[0084] 3. Catalytic performance test of catalysts with different Pd loading rates

[0085] Experiments were conducted on p-NP wastewater treatment using 1 wt% Pickering emulsions prepared using the Pd / SiO2-0.07% and Pd / SiO2-0.2% catalysts, respectively, as described in Example 1. Experiments were conducted at different reaction flow rates (150 μL / min, 250 μL / min, and 350 μL / min). The p-NP concentration in the p-NP wastewater reaction solution was 1 mM, and the NaBH4 concentration was 100 mM. The remaining procedures were identical to those in Step 1 of this example.

[0086] The results are as follows Figure 8 As shown:

[0087] Figure 8 a is a p-NP wastewater treatment experiment without the addition of Pickering emulsion (i.e., blank control). The absorption peaks of the nitrophenol stock solution and the reaction solution were detected by Fourier ultraviolet spectrometer, showing that the maximum absorption peak of the p-NP solution is located at 317nm. After adding NaBH4 to the solution, the maximum absorption peak shifted to 400nm. This is because the p-NP molecules are converted into p-NP ions under alkaline conditions. In addition, Figure 8 a also shows that the reaction will not occur in the absence of a catalyst.

[0088] Figure 8 Figures b and c tested the effect of flow rate on reaction conversion at different catalyst loadings (Pd / SiO2-0.07% and Pd / SiO2-0.2%). At a constant flow rate, a higher catalyst loading resulted in more catalytically active sites and higher catalytic efficiency. At the same catalyst loading, a lower reaction flow rate resulted in a longer residence time of the reactants in the bed and higher catalytic efficiency.

[0089] Figure 8 d is a stability test under different catalyst loadings. When Pd / SiO2-0.2% catalyst is used, the reaction system can operate continuously for 60 hours and the conversion efficiency is higher than 98.5%, indicating that the Pickering emulsion bubbling bed continuous flow catalytic system of the present invention has good catalytic efficiency and durability, and can achieve high-efficiency catalysis at low cost.

[0090] The Pickering emulsion-based bubbling bed reaction system constructed in this embodiment enables continuous flow catalytic reaction, with the reaction solution continuously fed into the reactor. This allows for high-speed catalysis of p-NPs in wastewater at low cost and high efficiency. The emulsion is centrifuged after the reaction to obtain catalyst particles that can be used in the next round of catalytic reaction, allowing for recycling of the catalyst, further reducing costs.

[0091] It is well known to those skilled in the art that palladium can be used to catalyze the hydrogenation of o-nitrophenol, m-nitrobenzene, p-nitrophenol, and acetone. In this embodiment, after replacing p-nitrophenol with o-nitrophenol hydrogenation, m-nitrobenzene hydrogenation, or acetone, efficient catalysis of the reaction can be achieved.

Claims

1. A method for preparing a catalyst-loaded oil-in-water Pickering emulsion, characterized in that: The steps include: (1) Surface modification of SiO2 nanoparticles: Weigh dry nano-SiO2 and evenly disperse it in toluene. Then, add modifiers octyltrimethoxysilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, and 3-aminopropyltriethoxysilane in sequence. Reflux and stir at 100-110°C under inert gas for 3.5-6 hours, centrifuge to obtain a white solid, wash with toluene, and dry to obtain solid SiO2 with interfacial activity. The dosage ratio of each substance is as follows: 320-340 μL octyltrimethoxysilane, 180-240 μL 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, and 100-130 μL 3-aminopropyltriethoxysilane to 1 g nano-SiO2. (2) Preparation of solid catalysts with interfacial activity: The solid SiO2 with interfacial activity prepared in step (1) is weighed and added to toluene, and the mixture is evenly dispersed. A palladium-containing solution or a chloroplatinic acid solution is added, wherein the palladium-containing solution is a chloropalladium acid solution or a palladium acetate solution. After stirring and adsorption, the mixture is centrifuged to obtain a white solid, which is washed with toluene. The toluene solution is added to the washed white solid, and the mixture is evenly stirred. A sodium borohydride ethanol solution is added thereto, and in-situ reduction is performed at room temperature. After the reaction is completed, the mixture is centrifuged, washed with anhydrous ethanol, and dried to obtain a solid catalyst with interfacial activity. The mass ratio of the palladium element or platinum element supported on the solid catalyst to the SiO2 is 0.05-1%. (3) Preparation of catalyst-loaded oil-in-water Pickering emulsion: The solid catalyst prepared in step (2) is weighed and added to deionized water, and dispersed evenly. Then, chlorobenzene as a dispersed phase is added and mixed to obtain a catalyst-loaded oil-in-water Pickering emulsion. The usage ratio of each substance is: the mass ratio of the solid catalyst to chlorobenzene is 0.5-3%.

2. The preparation method according to claim 1, wherein: In step (2), The mass ratio of palladium element or platinum element supported on the solid catalyst to SiO2 is 0.05-0.6%; The chloropalladium acid solution is a chloropalladium acid ethanol solution, the palladium acetate solution is a palladium acetate toluene solution, and the chloroplatinic acid solution is a chloroplatinic acid ethanol solution; The proportions of the various substances are as follows: 1 g of solid SiO2 with interfacial activity is added to 5-20 mL of toluene, followed by 0.7 mL-20 mL of a 5 mM chloropalladic acid ethanol solution. 8-12 mL of the toluene solution is added to the white solid obtained after washing with toluene, and the mixture is stirred evenly. 1-20 mL of a 50 mM sodium borohydride ethanol solution is then added thereto. In step (2), a palladium solution or a chloroplatinic acid solution is slowly added through a syringe pump, and after stirring and adsorbing for 4-8 hours, a white solid is obtained by centrifugation. A sodium borohydride ethanol solution is slowly added using a syringe pump, and an in situ reduction reaction is carried out at room temperature for 3-6 hours. The solid is washed with anhydrous ethanol and dried at 45-65°C.

3. The preparation method according to claim 1, wherein: In step (3), The dosage ratio of each substance is: 0.022g-0.132g of solid catalyst is added to 1-8mL of deionized water, and then 1-8mL of chlorobenzene is added; the mass ratio of solid catalyst to chlorobenzene is 0.5-1.5%.

4. The preparation method according to claim 2, wherein: The preparation method of the chloropalladic acid ethanol solution in step (2) is as follows: palladium chloride powder is weighed, and then dilute hydrochloric acid is added and heated to boil until the palladium chloride is completely dissolved, and then the volume is fixed with anhydrous ethanol after cooling to room temperature.

5. A catalyst-loaded oil-in-water Pickering emulsion, characterized in that: The preparation method according to any one of claims 1 to 4 is used.

6. Use of the catalyst-supported oil-in-water Pickering emulsion according to claim 5 in a bubbling bed catalytic reaction, characterized in that: The catalyst-loaded oil-in-water Pickering emulsion is loaded into a reaction column of a bubbling bed reactor, wherein the catalyst loaded on the Pickering emulsion catalyzes a reaction of a reaction liquid in the reaction column; the reaction in the reaction column is a hydrogenation reaction requiring hydrogen, wherein the hydrogenation reaction is a nitrophenol hydrogenation reaction or an acetone hydrogenation reaction, and the nitrophenol includes o-nitrophenol, m-nitrophenol, or p-nitrophenol; Hydrogen gas is bubbled into the reaction column from the bottom, or NaBH4 is added to the reaction solution to generate hydrogen gas.

7. A bubbling bed catalytic reaction method based on Pickering emulsion, characterized in that: The catalyst-supported oil-in-water Pickering emulsion of claim 5 is loaded into a reaction column of a bubbling bed reactor, and a reaction liquid and hydrogen are introduced into the reaction column to carry out a hydrogenation reaction, wherein the reaction liquid is an aqueous solution containing nitrophenol; The hydrogen gas is generated by adding NaBH4 into the reaction solution, and the reaction solution contains 0.1-1.5 mM nitrophenol and 25-200 mM NaBH4.

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