A rational design and precise construction method of hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes

Abstract

The invention discloses a macroporous-mesoporous hierarchical pore SiO2 for selective catalytic hydrogenation. 2 The rational design and precise construction method of the loaded metal microreactor comprises the following steps: Step 1: selecting a transition metal with catalytic hydrogenation activity as a catalytic active site, analyzing and calculating the intrinsic catalytic reaction rate of the active site for the selective hydrogenation of alkenes and alkynes; Step 2: determining the diffusion rate range of alkenes and alkynes in the catalyst that matches the intrinsic catalytic reaction rate of the metal obtained in Step 1; Step 3: accurately constructing a macroporous-mesoporous hierarchical SiO2 reactor that meets the diffusion rate according to the diffusion rate range obtained in Step 2. 2 carrier, so that the diffusion rate of the reactants in the carrier is within the diffusion rate range obtained in step 2; step 4: loading the metal active sites selected in step 1 on the hierarchical pore SiO 2 On top, obtain hierarchical pore SiO 2 The loaded metal microreactor is used as a catalyst to realize the selective catalytic hydrogenation of unsaturated alkenes and alkynes. 2 The carrier-loaded metal is used as a catalyst. According to the requirements of the intrinsic reaction rate of catalytic hydrogenation at different metal active sites, the corresponding macroporous-mesoporous SiO 2 In order to obtain the matching diffusion coefficient of alkenes and alkynes, rational design and precise construction of catalysts for efficient catalytic hydrogenation reactions can be achieved.

Description

Technical Field

[0001] The present invention belongs to the field of energy catalysis technology, and specifically relates to a rational design and precise construction method of a hierarchical pore SiO2-loaded metal microreactor for selective catalytic hydrogenation of alkenes and alkynes. Background Art

[0002] As an important chemical raw material, low-carbon monoolefins are widely used in the synthesis of polymers in industry. The main production method of low-carbon olefins is to crack petroleum hydrocarbons and crude oil including heavy fractions. However, the cracking process is carried out at high temperature. While generating low-carbon olefins, a small amount of impurities of diolefins and alkynes are also generated. The presence of diolefins / alkynes not only affects the deep processing of monoolefins, but also poisons the low-carbon monoolefin polymerization catalyst. Diolefins / alkynes impurities must be controlled below 10ppm in industry. Therefore, in industry, alkynes / diolefin impurities must be purified by heterogeneous selective catalytic hydrogenation on the surface of the supported metal catalyst to purify the low-carbon monoolefin raw materials.

[0003] The selective catalytic hydrogenation process of diene / alkyne impurities can be mainly divided into five series of steps: diffusion, adsorption, catalytic hydrogenation, desorption and diffusion of diene / alkyne reaction molecules in the catalyst. The catalytic reaction efficiency is mainly controlled by the catalytic reaction kinetics and molecular diffusion mass transfer. The former is mainly determined by the intrinsic properties of the metal catalytic active sites, while the latter is mainly determined by the pore structure of the catalyst.

[0004] At present, the regulation of high-performance selective catalytic hydrogenation catalysts focuses on the regulation of the intrinsic properties such as the component / structure of the metal active sites, from the introduction of the concept of metal active sites to the analysis of the active sites at atomic resolution in actual catalytic reactions; not only that, the structural sensitivity of supported metal catalysts also shows that the catalytic reaction rate will change with the different exposure ratios of the crystal faces. The introduction of catalytic activity description factors has deepened the understanding of the nature of active sites, and the theoretical calculation of kinetics has also connected the microscopic reaction mechanism with the macroscopic catalytic performance. The development of new and efficient heterogeneous catalysts based on catalytic reaction kinetics has prompted researchers to conduct a lot of research on active sites, and the influence of the component, structure, size, etc. of the metal active sites of selective hydrogenation catalysts on the reaction kinetics has become increasingly clear. However, due to the complexity of the heterogeneous catalytic reaction process and the dynamic changes in the rate-controlling steps of the catalytic reaction as the reaction proceeds, the design and optimization of supported metal catalysts from the perspective of catalytic reaction kinetics alone faces major challenges. Summary of the invention

[0005] In view of the problem that the existing catalysts for selective hydrogenation of low-carbon alkenes and alkynes are subject to diffusion limitation at high conversion rates, the present invention provides a rational design and precise construction method of a hierarchical pore SiO2-loaded metal microreactor for selective catalytic hydrogenation of alkenes and alkynes. The method uses a carrier hierarchical pore SiO2-loaded metal as a catalyst, and according to the intrinsic catalytic reaction rate requirements of different metals for selective catalytic hydrogenation of alkenes and alkynes, the macropore-mesoporous channels in the hierarchical pore SiO2 carrier are precisely controlled and constructed, so that the diffusion rate of the reactants in the carrier matches the intrinsic catalytic reaction rate of the metal active sites, eliminating the influence of diffusion on the catalytic reaction, thereby improving the efficiency of the catalytic reaction.

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

[0007] A rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes comprises the following steps:

[0008] Step 1: Analyze the intrinsic catalytic reaction rate of metals: Select transition metals or alloys with catalytic hydrogenation activity as catalytic active sites, identify the kinetic control stage of the catalytic olefin and acetylene hydrogenation reaction of the corresponding metal active sites loaded on non-porous SiO2 (metal active sites are metals as catalytic active sites) according to the Arrhenius formula, and calculate the TOF value (unit: s) of metal-catalyzed selective hydrogenation of olefins and acetylene. -1 ), and then the intrinsic catalytic reaction rate of metal-catalyzed selective hydrogenation of alkenes and alkynes (unit: mol·s -1 );

[0009] Step 2: Determine the matching reactant diffusion rate: According to the intrinsic catalytic reaction rate of the metal-catalyzed selective hydrogenation of alkenes and alkynes obtained in step 1, determine the matching gas diffusion rate range;

[0010] Step 3: Select and accurately construct a macroporous-mesoporous structure carrier material with a corresponding diffusion rate: According to the gas diffusion rate range obtained in step 2, design and construct a macroporous-mesoporous hierarchical pore carrier that meets the gas diffusion rate; wherein the carrier is macroporous-mesoporous hierarchical pore SiO2, and independently regulating the combination of macropores and mesopores can satisfy the gas diffusion rate in the carrier within the gas diffusion rate range obtained in step 2;

[0011] Step 4: Loading of active metals: The metal selected in step 1 is loaded as a catalytic active site on the macroporous-mesoporous hierarchical pore SiO2 constructed in step 3 according to the loading amount set in step 1 to obtain a hierarchical pore SiO2 loaded metal microreactor, which is used as a catalyst to achieve selective catalytic hydrogenation of alkenes and alkynes.

[0012] According to the above scheme, the metal having catalytic hydrogenation activity includes but is not limited to Pt, Pd, Cu, Pd-Cu alloy, etc.

[0013] According to the above scheme, in step 1, the method for determining the intrinsic catalytic reaction rate (v) of the metal active site is: mainly using the Arrhenius formula to analyze the catalytic behavior of the non-porous structure SiO2 loaded with the corresponding metal during the temperature increase reaction, and identifying and selecting the conversion rate of the unit metal active site for the selective catalytic hydrogenation of alkynes / dienes per unit time in the kinetic control stage of the catalytic reaction, that is, the TOF value. Specifically, the supported catalysts with different metal loadings are prepared by conventional methods such as impregnation, and the catalytic hydrogenation performance is tested after calcination-reduction heat treatment. The Arrhenius formula is used to analyze the influence of the particle size and composition of the metal active site on the catalytic reaction performance, so as to accurately analyze the intrinsic catalytic activity of the metal active site, according to the formula:

[0014]

[0015] The TOF value (s) at this time is obtained -1 ), where C is the conversion rate of the reactants under the control of reaction kinetics, n (mol) is the total amount of reactants in the material, T (s) is the contact time between the reaction gas and the catalyst, and N is the number of surface atoms. Then, the loading amount of the metal on the carrier grade porous SiO2 is set, and the number of active sites of the metal is obtained according to the loading amount. Then, the intrinsic catalytic reaction rate (unit mol·s) of the metal-catalyzed selective hydrogenation of alkenes and alkynes is obtained by multiplying the number of active sites of the metal by the TOF value. -1 ).

[0016] According to the above scheme, in step 2, the gas diffusion rate (i.e., the diffusion rate of the reactant alkene and alkyne in the catalyst or microreactor) should be equal to the intrinsic catalytic reaction rate of the metal (mol·s -1 ) is 0.8 to 1.2 times of that in the catalyst reaction, which makes it easy to eliminate the influence of diffusion on the catalytic reaction.

[0017] According to the above scheme, in step 3, the macroporous-mesoporous hierarchical pore SiO2 is a block, and its construction method is: mainly through the metastable phase separation method of the oil / water interface, the surfactant molecules are introduced into the silica precursor during the hydrolysis process in the acidic environment, and then the silica precursor is treated with alkali after hydrolysis, so as to obtain a macroporous-mesoporous hierarchical pore structure SiO2 block with a through structure, preferably a cylindrical structure. By adjusting the acid concentration and the alkali treatment conditions, the pore size of the macropores and mesopores can be accurately controlled separately to achieve the regulation and optimization of the diffusion behavior of alkenes and alkynes; wherein, the macropore range is 0.5μm to 50μm, and the mesopore range is 5nm to 50nm. The size of the macropores and mesopores can be regulated within the corresponding size range by adjusting the pore preparation conditions.

[0018] According to the above scheme, in step 3, the macroporous-mesoporous SiO2 can make the gas diffusion rate between 0.5×10 -8 mol·s -1 ~5.0×10 -7 mol·s -1 within the range.

[0019] According to the above scheme, in step 4, the metal can be loaded on the macroporous-mesoporous hierarchical pore SiO2 by strong electrostatic adsorption. Specifically, the method for achieving metal loading on macroporous-mesoporous hierarchical pore SiO2 can be: the metal precursor solution is circulated through the macroporous-mesoporous hierarchical pore SiO2 by a peristaltic pump, and the positively charged metal precursor solution will undergo strong electrostatic adsorption with the negatively charged macroporous-mesoporous hierarchical pore SiO2 carrier to perform electrostatic self-assembly, and then washed with deionized water and dried to obtain a hierarchical pore SiO2-loaded metal catalyst, that is, a hierarchical pore SiO2-loaded metal microreactor, and the metal loading range is generally 0.0001wt% to 5wt%. Among them, the hierarchical pore SiO2 is fixed in a heat shrink tube; the metal precursor refers to an aqueous solution of a soluble salt of a metal, and the concentration of metal ions is 0.001mol·l -1 ~0.5mol·l -1 , the pH of the metal precursor solution satisfies 3<pH<11; the flow rate of the peristaltic pump is 0.2ml·min -1 ~0.35ml·min -1 , the circulation time is 2h~5h, and the deionized water cleaning time is 3h~6h. Further, the method of fixing the graded hole SiO2 in the heat shrink tube can be but not limited to: placing the graded hole SiO2 in the heat shrink tube (PTFE material), and then using a hot air gun to blow the graded hole SiO2 to tighten the heat shrink tube until the graded hole SiO2 is tightly wrapped by the heat shrink tube.

[0020] In the above scheme, the reaction gas for the selective catalytic hydrogenation of unsaturated alkenes and alkynes mainly includes dienes / alkynes (the number of carbon atoms in the main chain of the dienes / alkynes does not exceed 4) and hydrogen, wherein the dienes / alkynes are used as the main reaction gas and the hydrogen is used as the hydrogen source for the selective hydrogenation reaction; in addition, monoolefins can be used as the main system environmental gas in the reaction gas to verify the selective hydrogenation and impurity removal of dienes or alkynes under the condition of the presence of a large amount of monoolefins, such as ethylene, propylene, etc. The reaction gas for the selective catalytic hydrogenation of unsaturated alkenes and alkynes is generally a monoolefin produced by petroleum cracking. Since it contains a certain amount of alkynes or dienes as byproducts, the catalyst designed by the method of the present invention can be used for selective catalytic hydrogenation.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention searches for the reaction gas diffusion rate that matches the intrinsic catalytic reaction rate of the metal, thereby rationally screening out the macroporous-mesoporous hierarchical pore SiO2 structure of the carrier that best matches the diffusion rate, and then uses the macroporous-mesoporous hierarchical pore SiO2 as a carrier to load a metal catalyst for the selective catalytic hydrogenation of unsaturated alkenes and alkynes, which can eliminate the influence of diffusion on the reaction gas and the catalytic reaction, making the apparent reaction rate of the selective catalytic hydrogenation reaction better or maximum, thereby improving the efficiency of the reaction. Therefore, the present invention constructs an efficient hierarchical pore silica-loaded metal microreactor (i.e., catalyst) through the coupling effect of diffusion dynamics and reaction dynamics, which can solve the problem that a large number of trial and error experiments will cause a large time and cost cost, improve the screening speed, and provide direct theoretical guidance for experimental research, which is very meaningful for maximizing mass transfer and catalytic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is an analysis of the intrinsic catalytic reaction rate of Pt-loaded non-porous silica; Figure 1(a) is the catalytic performance of Pt-loaded non-porous silica; Figure 1(b) is the Arrhenius plot of the Pt-loaded non-porous silica catalyst.

[0024] Figure 2 The actual picture and electron microscope picture of macroporous-mesoporous SiO2.

[0025] Figure 3 shows the macropore mercury intrusion and mesopore N2 adsorption and desorption tests of SiO2 with different pore sizes. Figures 3(a) and 3(b) are respectively the N2 adsorption and desorption characteristics and N2 mercury intrusion characteristics of SiO2 with different pore sizes when the mesopore size is 13nm and the macropore size is different; Figures 3(c) and 3(d) are respectively the N2 adsorption and desorption characteristics and mercury intrusion characteristics of SiO2 with different pore sizes when the macropore size is 5μm and the mesopore size is different.

[0026] Figure 4 shows the test method of diffusion rate of SiO2 with different levels of pores and the relationship between flow rate and back pressure. Figure 4(a) is a schematic diagram of permeability test; Figure 4(b) is a graph showing the relationship between flow rate and back pressure when the mesopore size is 13nm and the macropore size is different, and the permeability test of SiO2 with different levels of pores is carried out; Figure 4(c) is a graph showing the relationship between flow rate and back pressure when the macropore size is 5μm and the mesopore size is different, and the permeability test of SiO2 with different levels of pores is carried out.

[0027] Figure 5 shows the permeability and diffusion rate of SiO2 with different pore sizes. Figure 5(a) shows the relationship between the permeability coefficient K and the diffusion rate of SiO2 with different pore sizes when the mesopore size is 13nm and the macropore size is different; Figure 5(b) shows the relationship between the permeability coefficient K and the diffusion rate of SiO2 with different pore sizes when the macropore size is 5μm and the mesopore size is different.

[0028] Figure 6 is an evaluation of the catalytic performance of Pt loaded on hierarchical pore SiO2. Figure 6(a) and Figure 6(b) are TEM images of Pt loaded on hierarchical pore SiO2 and catalytic performance at different diffusion rates when the mesopore size is 13 nm and the macropore size is different.

[0029] Figure 7 is an evaluation of the catalytic performance of hierarchical pore SiO2 loaded with Cu. Figures 7(a), 7(b), and 7(c) are TEM images of hierarchical pore SiO2 loaded with Cu when the macropore size is 5 μm and the mesopore size is different, and the catalytic performance and stability under different diffusion coefficients.

[0030] In the above figures, Macro represents macropores, with the unit of μm; Meso represents mesopores, with the unit of nm. DETAILED DESCRIPTION

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

[0032] In the following embodiment, the preparation method of macroporous-mesoporous hierarchical pore SiO2 for realizing selective catalytic hydrogenation of alkenes and alkynes is as follows:

[0033] (1) Add nitric acid and polyethylene glycol to water, stir for 10 to 15 minutes, then add tetraethyl orthosilicate, stir in an ice water bath for 30 to 90 minutes, and put the resulting mixture into a mold; wherein, by mole, the tetraethyl orthosilicate is 0.8 to 1.2 parts, the polyethylene glycol is 0.4 to 0.8 parts, the nitric acid is 0.15 to 0.35 parts, and the water is 13 to 15 parts.

[0034] (2) placing the mold in a water bath and treating it at 30-60° C. for 48-96 hours to cause the water and ethyl orthosilicate therein to undergo sol-gel transformation and phase separation to generate an unevenly distributed water phase and silicon phase, and removing the water phase to obtain silicon dioxide with a macroporous structure;

[0035] (3) demolding the silica gel having a macroporous structure, washing it to neutrality, and then treating it in ammonia water to perform Ostward aging at a temperature of 30 to 90° C. for a time of 12 to 36 hours, thereby generating mesopores to obtain mesoporous-macroporous silica; wherein the concentration of ammonia water is 0.05 mol·l -1 ~0.2mol·l -1 ;

[0036] (4) Wash the mesoporous-macroporous silica to neutral dryness, and then calcine the mesoporous-macroporous silica at 550° C. to 700° C. for 16 hours to obtain macroporous-mesoporous hierarchical pore SiO2.

[0037] In the preparation process of the above-mentioned hierarchical pore SiO2, the macropores can be regulated by changing the amount of HNO3 used in the preparation process, affecting the hydrolysis rate of tetraethyl orthosilicate, thereby changing the size of the macropores. The pore size of the macropores can be regulated between 0.5μm and 14μm; the mesopores can be regulated by changing the temperature and NH3·H2O concentration of the NH3·H2O treatment in the preparation process of the hierarchical pore SiO2, affecting the Ostward ripening conditions of the SiO2 macroporous skeleton and thus changing the size of the mesopores. The pore size of the mesopores can be regulated between 9nm and 36nm.

[0038] Specifically, the preparation process of hierarchical pore SiO2 with a mesopore size of 13nm and a macropore size of 2.1μm is as follows: 20g of tetraethyl silicate (TEOS) is weighed and then placed at -19°C overnight; 24.56g of deionized water is poured into a 100mL conical flask, and then 2.651g of nitric acid is added, stirred at room temperature for 5min, and then 2.534g of polyvinyl alcohol (PEO) is added, and stirred at room temperature for 30min until PEO is completely dissolved. The resulting mixed solution is placed at -19°C for 10min to cool the solution but not freeze it, and then the pre-frozen TEOS is added, and then placed in an ice bath and stirred evenly. A polystyrene (PS) tube with a diameter of 10 mm and a length of 75 mm was placed in a -19°C refrigerator for 30 min, and then the mixture in the conical flask was filled in the PS tube, reinforced and sealed, and placed in a constant temperature water bath at 40°C for 3 days, and then the rod-shaped solid was taken out of the PS tube and placed in a 40°C 1L water bath at room temperature, and the water was changed every 2 hours until the pH reached neutral (about 6 washes). Then the rod-shaped solid was immersed in a beaker containing 1L ammonia water (0.1 mol / L), sealed with plastic wrap and rubber band, and placed in a constant temperature water bath at 40°C for 24 hours to obtain rod-shaped silica. The obtained rod-shaped silica was placed in a 1L, 40°C water bath, and the water was changed every 2 hours until the pH reached neutral (about 8 washes), then dried, and calcined in air at 550°C for 8 hours to remove the remaining PEO, and a hierarchical pore SiO2 with a mesopore size of 13 nm and a macropore size of 2.1 μm was obtained.

[0039] The same preparation method as that of hierarchical pore SiO2 with a mesopore size of 13 nm and a macropore size of 2.1 μm is adopted, except that the masses of nitric acid are 1.779 g, 2.046 g, 2.313 g, 2.980 g and 0.335 g, respectively, thus obtaining hierarchical pore SiO2 with a mesopore size of 13 nm and macropore sizes of 14 μm, 6 μm, 3.4 μm, 1.1 μm and 0.5 μm, respectively.

[0040] Specifically, the preparation process of hierarchical pore silica with a mesopore size of 16nm and a macropore size of 5μm is as follows: weigh 20g of tetraethyl silicate (TEOS) and place it at -19°C overnight; pour 24.56g of deionized water into a 100mL conical flask, then add 2.150g of nitric acid, stir at room temperature for 5min, then add 2.534g of polyvinyl alcohol (PEO), stir at room temperature for 30min, until PEO is completely dissolved. The resulting mixture is placed in a refrigerator at -19°C for 10min to cool the solution without freezing, then continue to add pre-frozen TEOS, and then put it in an ice bath and stir evenly. Then a polystyrene (PS) tube with a diameter of 10 mm and a length of 75 mm was placed in a -19°C refrigerator for 30 min, and then the mixture in the conical flask was filled in the PS tube, reinforced and sealed, and placed in a constant temperature water bath at 40°C for 3 days, and then the rod-shaped solid was taken out of the PS tube and placed in a 1L water bath at room temperature, and the water was changed every 2 hours until the neutral pH was reached. Then the rod-shaped solid was immersed in a beaker filled with 1L ammonia water (0.1 mol / L), sealed with plastic wrap and rubber band, and placed in a constant temperature water bath at 60°C for 24 hours to obtain rod-shaped silica. The obtained rod-shaped silica was placed in a 1L water bath, and the water was changed every 2 hours until the pH reached neutral, then dried, and calcined in air at 550°C for 8 hours to remove the remaining PEO, and a hierarchical pore SiO2 with a mesopore size of 16 nm and a macropore size of 5 μm was obtained.

[0041] The same preparation method as that of hierarchical pore SiO2 with a mesopore size of 16nm and a macropore size of 5μm is adopted, except that the temperature during ammonia treatment is 40℃, 70℃, 80℃ and 90℃, thereby obtaining hierarchical pore SiO2 with a macropore size of 5μm and a mesopore size of 9nm, 24nm, 30nm and 36nm respectively.

[0042] like Figure 2 The macrostructure and micromorphology of the hierarchical pore SiO2 prepared above are about 70 mm in length and 6.7 mm in diameter, with a macroporous-mesoporous structure.

[0043] like Figure 3a and Figure 3b As shown, the macropore sizes of the hierarchical SiO2 prepared above are 14, 6, 3.4, 2.1, 1.1, and 0.5 μm, respectively, and the mesopore sizes are all 13 nm. Figure 3c and Figure 3d As shown, the macropore size of the hierarchical pore SiO2 prepared above is 5 μm, and the mesopore sizes are 9, 16, 24, 30, and 36 nm respectively.

[0044] The diffusion coefficient of graded pore SiO2 with different pore sizes was tested by the test method of Figure 4(a), and the pressure difference at both ends of the catalyst at different flow rates was obtained by changing the flow rate of butadiene, such as Figure 4(b) , 4(c) As shown. Since the way butadiene enters the catalyst at this time is fluid penetration, according to the formula of Darcy's law:

[0045]

[0046] Where Q is the gas flow rate, k is the permeability, A is the cross-sectional area, and L is the length. The permeability k in Figure 5(a) and Figure 5(b) can be calculated; then according to the formula of the permeability coefficient K:

[0047]

[0048] Where K is the permeability coefficient, k is the permeability, η is the gas viscosity coefficient, and p is the gas density. The diffusion coefficient K shown in Figure 5(a) and Figure 5(b) can be obtained; according to the formula of the diffusion rate D:

[0049]

[0050] Where V is the volume of hierarchical porous silica, the diffusion rate D in Figure 5(a) and Figure 5(b) can be obtained.

[0051] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0052] Example 1

[0053] A rational design and precise construction method of a hierarchical pore SiO2-supported Pt microreactor for selective catalytic hydrogenation of alkenes and alkynes with Pt as the catalytic active site, the specific steps of which are as follows:

[0054] Step 1 Analysis of the intrinsic catalytic reaction rate of Pt metal: Select metal Pt, and use the impregnation method to prepare Pt-loaded non-porous silica catalysts with loading amounts of 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, and 0.35wt%, respectively. These catalysts are heated to 200℃ at 5℃ / min, and after in-situ reduction for 2h in a H2 atmosphere, butadiene, hydrogen and propylene are reacted with a volume ratio of 2:5:30 as a mixed reaction gas. The catalytic performance of these catalysts is evaluated as shown in Figure 1(a); as shown in Figure 1(b), the catalytic performance of these catalysts is analyzed according to the Arrhenius formula, and the control stage belonging to its reaction kinetics is obtained. At this stage, the TOF value (s) of the Pt metal is calculated according to formula (1). -1 ).

[0055] Specifically, for a Pt-supported nonporous silica catalyst with a loading of 0.3 wt%, based on the volume of the catalyst being 0.056 cm 3 , the flow rate of butadiene is 0.0017 cm 3 ·s -1 , we know that T(s) is 33.25s. Then according to the contact time and the flow rate of butadiene, the amount of butadiene passing through is calculated to be 4.63×10 -6 mol; From the Arrhenius plot, it can be seen that the reaction is controlled by reaction kinetics when the butadiene conversion rate is 11.93%; According to the mass of the loaded Pt 0.0003g, the surface atomic density of Pt is 12.5 / nm 2 It can be seen that the number of atoms on the surface is 3.67×10 -7 mol, calculated the TOF value of Pt metal (s -1 ) is 0.00585s -1 According to the above method, the TOF values ​​of other loadings of 0.05wt%, 0.1wt%, 0.2wt% and 0.35wt% are 0.00584, 0.00581, 0.00589 and 0.00581s -1 It can be seen that when nonporous silica is used as a carrier and the metal loading amount is different, within the loading amount range required by the present invention, the TOF value of metal-catalyzed selective hydrogenation of alkenes and alkynes is basically the same.

[0056] On the basis of the above, the loading amount of hierarchical pore SiO2 (0.12 g) is set to 0.05%, and the mass of Pt is 0.0006 g, and the number of active sites of Pt is 3.08×10 -6 mol, then the intrinsic catalytic reaction rate of Pt loaded on hierarchical pore SiO2 is equal to the TOF value of Pt (0.0058s -1 value) multiplied by the number of active sites (3.08×10 -6 mol), the intrinsic catalytic reaction rate of Pt is calculated to be about 1.8×10 -8 mol·s -1 ;

[0057] Step 2: Calculate the matching reactant diffusion rate: Based on the intrinsic catalytic reaction rate of the metal obtained in step 1, the reaction gas diffusion rate is 1 to 1.1 times the intrinsic catalytic reaction rate of the metal, and the reaction gas diffusion rate is 1.8×10 -8 mol·s -1 ~1.98×10 -8 mol·s -1 within the scope;

[0058] Step 3: Select a carrier that meets the reaction diffusion rate: According to Figure 5(a), it is known that the carrier has a macropore size of 2.1 μm and a mesopore size of 13 nm (diffusion rate of 1.9×10 -8 mol·s -1 ) has a higher matching degree, so the hierarchical pore SiO2 with a macropore size of 2.1μm and a mesopore size of 13nm is selected.

[0059] Step 4: Loading of metal Pt: First, prepare a precursor solution of metal Pt and add 1 g H 12 Dissolve N4PtCl2-xH2O in a 100ml volumetric flask, then take 100μL of H 12 An aqueous solution of N4PtCl2-xH2O (the mass of metal Pt is 0.00006g, and the material is fed according to the loading amount of Pt of 0.05%) and 15mL of deionized water are mixed, and the pH is adjusted to about 8 with aqueous ammonia; the hierarchical pore SiO2 (cylindrical, 1cm in length, 0.66cm in bottom circle diameter, and 0.12g in mass) screened in step 3 is loaded into a PTFE heat shrinkable tube, and the heat shrinkable tube is heated so that it is tightly wrapped by the heat shrinkable tube, and then the heat shrinkable tube is fixed to a peristaltic pump using an adapter, and the precursor solution is circulated through the hierarchical pore SiO2 described in step 3 at a flow rate of 0.25mL / min, circulated for 2h, and then rinsed in one direction with deionized water at the same flow rate for 3h, and after drying, a catalyst of hierarchical pore SiO2 loaded with metal Pt, i.e., a microreactor of hierarchical pore SiO2 loaded with metal Pt, is obtained.

[0060] In step 4, hierarchical SiO2 with different mesopore sizes can be used to prepare microreactors (i.e., catalysts) with hierarchical SiO2 loaded with metal Pt with different diffusion rates, and then connected to a GC gas chromatograph for catalytic performance testing. In this test, butadiene, hydrogen, and propylene with a volume ratio of 2:5:30 are used as mixed reaction gases. After in-situ reduction for 2 hours (5°C / min) in a H2 atmosphere at 200°C, the catalyst is heated in an oil bath to evaluate the catalytic performance of microreactors with different hierarchical pores SiO2 loaded with metal Pt for selective hydrogenation of butadiene, including activity and olefin selectivity.

[0061] As shown in Figure 6(a), the active sites of Pt in the microreactors with hierarchical pore SiO2 loaded with metal Pt of different diffusion rates are consistent and are all single-atom metals. The difference in catalytic performance is mainly related to the diffusion rate of the carrier.

[0062] As shown in Figure 6(b), the hierarchical pore SiO2-loaded metal Pt microreactor with a macropore size of 3.4 μm and a mesopore size of 13 nm achieved complete conversion at 90°C compared to other samples, and its performance was greatly improved. It is the same as the hierarchical pore SiO2 screened out in step 3 of this embodiment, thereby verifying the feasibility of the design and construction method of the hierarchical pore SiO2-loaded metal microreactor for selective catalytic hydrogenation provided by the present invention.

[0063] Example 2

[0064] A design and construction method of a hierarchical pore SiO2-loaded Cu metal microreactor for selective catalytic hydrogenation, the specific steps of which are as follows:

[0065] Step 1 Analysis of the intrinsic catalytic reaction rate of Cu metal: Select metal Cu, and use the impregnation method to prepare Cu-loaded non-porous silica catalysts with loading amounts of 1wt%, 3wt%, 4wt%, 6wt%, and 7wt%, respectively. The catalytic performance of these catalysts is evaluated. Referring to Example 1, it is calculated that when the loading amount is 5wt%, the intrinsic catalytic reaction rate of Cu metal is 4.8×10 -8 mol·s -1 ;

[0066] Step 2: Calculate the matching reactant diffusion rate: Based on the intrinsic catalytic reaction rate of the metal obtained in step 1, the reaction gas diffusion rate is 4.75×10 -8 mol·h -1 ~5×10 -8 mol·h -1 within the scope;

[0067] Step 3: Select a carrier that meets the reaction diffusion rate: According to Figure 5(b), the gas diffusion rate is related to the macropore size of 5 μm and the mesopore size of 16 nm (diffusion rate 4.9×10 -8 mol·h -1 ) has a higher matching degree, so the graded pore SiO2 with a macropore size of 5μm and a mesopore size of 16nm is selected.

[0068] Step 4 Loading of metallic Cu: First, prepare the precursor solution of metallic copper. Dissolve 3.6 g of Cu(NO3)2·3H2O in a 20 ml volumetric flask, and then take 126 μL An aqueous solution of Cu(NO3)2·3H2O (the mass of metal Cu is 0.006g, and the material is fed at a loading of 5wt%) and 20mL of deionized water are mixed, and then 200μL of concentrated ammonia water is added to adjust the pH value of the solution to about 12; the hierarchical pore SiO2 (cylindrical, with a bottom circle diameter of 6.7mm, a length of 10mm, and a mass of 0.12g) screened in step 3 is taken and loaded into a PTFE heat shrinkable tube, and a hot air gun is aimed at the hierarchical pore SiO2 and purged in the heat shrinkable tube for 2min so that it is tightly wrapped by the heat shrinkable tube, and then the heat shrinkable tube is fixed to a peristaltic pump using an adapter, and the precursor solution is circulated through the hierarchical pore SiO2 at a flow rate of 0.25mL / min, circulated for 2h, and then rinsed in one direction with deionized water at the same flow rate for 3h, and after drying, a catalyst of hierarchical pore SiO2 loaded with metal Cu, i.e., a microreactor of hierarchical pore SiO2 loaded with metal Cu is obtained.

[0069] In step 4, hierarchical pore SiO2 with different macropore sizes can be used to prepare hierarchical pore SiO2-loaded metal Cu microreactor (i.e., catalyst) samples with different diffusion rates, which are respectively connected to a GC gas chromatograph for catalytic performance testing. The testing method is the same as that in Example 1, and the catalytic performance of the hierarchical pore SiO2-loaded metal Cu microreactor for selective hydrogenation of butadiene is evaluated, including activity, olefin selectivity and stability.

[0070] As shown in Figure 7(a), in the microreactors of graded porous SiO2 loaded with metal Pt with different diffusion rates, the sizes of the loaded copper particles are basically the same, so the influence of their active sites is basically eliminated. It can be seen that the difference in their catalytic performance as catalysts is caused by diffusion.

[0071] As shown in Figure 7(b), the hierarchical pore SiO2 loaded metal Cu microreactor with a macropore size of 5μm and a mesopore size of 16nm is completely converted at 110°C compared to other samples, showing the best catalytic performance, which is the same as the hierarchical pore SiO2 screened in this example, thereby verifying the feasibility of the design and construction method of the hierarchical pore SiO2 loaded metal microreactor for selective catalytic hydrogenation provided by the present invention. In addition, it can be seen from Figure 7(c) that the prepared microreactor has excellent catalytic stability.

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and changes without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes, characterized in that: The following steps are involved: Step 1: Select a metal with catalytic hydrogenation activity as a catalytic active site, identify the kinetic control stage of the catalytic olefin and alkyne hydrogenation reaction of the non-porous structure SiO2 loaded with the corresponding metal active site according to the Arrhenius formula, and calculate the TOF value of the metal-catalyzed selective hydrogenation of alkynes during the reaction kinetic control stage; set the loading amount of the corresponding metal on the carrier grade pore SiO2, obtain the number of active sites of the metal according to the loading amount, and then obtain the intrinsic catalytic reaction rate of the metal-catalyzed selective hydrogenation of alkynes by multiplying the number of active sites of the metal by the TOF value; Step 2: According to the intrinsic catalytic reaction rate of the metal-catalyzed selective hydrogenation of alkenes and alkynes obtained in step 1, determine a gas diffusion rate range that matches the intrinsic catalytic reaction rate; wherein the diffusion rate of the reaction gas is 0.8 to 1.2 times the intrinsic catalytic reaction rate of the metal; Step 3: According to the gas diffusion rate range obtained in step 2, construct a macroporous-mesoporous grade pore structure carrier that meets the gas diffusion rate range; wherein the carrier is macroporous-mesoporous grade pore SiO2, and the combination of macropores and mesopores satisfies that the gas diffusion rate in the carrier is within the gas diffusion rate range obtained in step 2; Step 4: The metal selected in step 1 is loaded as a catalytic active site on the macroporous-mesoporous hierarchical pore SiO2 constructed in step 3 according to the loading amount set in step 1 to obtain a hierarchical pore SiO2 loaded metal microreactor, which is used as a catalyst to realize the selective catalytic hydrogenation of alkenes and alkynes.

2. The rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes according to claim 1, characterized in that: In step 1, the method for determining the TOF value of metal-catalyzed selective hydrogenation of alkenes and alkynes is as follows: the Arrhenius formula is used to analyze the catalytic behavior of the corresponding metal loaded on the non-porous structure SiO2 during the temperature-increasing reaction as the conversion rate of alkenes and alkynes changes with temperature, the kinetic control stage of the catalytic reaction is identified and selected, and the conversion number of the selective catalytic hydrogenation of alkenes and alkynes per unit metal active site per unit time is calculated, that is, the TOF value.

3. The rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes according to claim 1, characterized in that: In step 3, the macropore range of the macroporous-mesoporous graded SiO2 is between 0.5 μm and 50 μm, and the mesopore range is between 5 nm and 50 nm.

4. The rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes according to claim 1, characterized in that: In step 3, the method for constructing macroporous-mesoporous hierarchical pore SiO2 is as follows: surfactant molecules are introduced into the silica precursor during hydrolysis in an acidic environment to generate macropores through the metastable phase separation method at the oil / water interface, and mesopores are generated by Oswald ripening of silica in an alkaline solution to obtain a macroporous-mesoporous hierarchical pore structure SiO2 block with a through structure; wherein, the acid concentration and the alkaline treatment conditions are adjusted to accurately control the pore sizes of macropores and mesopores respectively, so as to achieve a pore size between 0.5μm and 50μm and a mesopore size between 5nm and 50nm.

5. The rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes according to claim 1, characterized in that: In step 3, the gas diffusion rate of the macroporous-mesoporous SiO2 is calculated based on Darcy's law by recording the front-rear pressure difference of the macroporous-mesoporous SiO2 carrier along the gas flow direction at different gas volume flow rates.

6. The rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes according to claim 1, characterized in that: In step 3, the gas diffusion rate is 0.5×10 -8 mol·s -1 ~5.0×10 -7 mol·s -1 within the range.

7. The rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes according to claim 1, characterized in that: In step 1 and step 4, the metal having catalytic hydrogenation activity includes but is not limited to one or more of Pt, Pd, Cu, and Pd-Cu alloy.

8. The rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes according to claim 1, characterized in that: In step 4, the metal loading method adopts the electrostatic adsorption method, and the metal precursor solution is circulated through the macroporous-mesoporous hierarchical SiO2 fixed in the heat shrink tube by a peristaltic pump. The positively charged metal precursor solution will undergo strong electrostatic adsorption with the negatively charged hierarchical SiO2 carrier to perform electrostatic self-assembly. Then, after washing with deionized water and drying, the hierarchical SiO2-loaded metal catalyst, i.e., the hierarchical SiO2-loaded metal microreactor, can be obtained; wherein, the metal loading amount ranges from 0.0001wt% to 5wt%, and the pH of the metal precursor solution satisfies 3<pH<11; the flow rate of the peristaltic pump is 0.2ml·min -1 ~0.35ml·min -1 The cycle time is 2h to 5h.

9. The rational design and precise construction method of a hierarchical pore SiO2-supported metal microreactor for selective catalytic hydrogenation of alkenes and alkynes according to claim 1, characterized in that: The reaction gas for the selective catalytic hydrogenation of alkenes and alkynes mainly includes a mixed reaction gas of dienes, alkynes, monoolefins and hydrogen, wherein dienes and / or alkynes are used as main reactants, hydrogen is used as a hydrogen source for the selective hydrogenation reaction, and monoolefins are used as the main system environmental gas in the reaction gas.

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