Targeted supported noble metal catalyst and preparation method thereof

Abstract

The invention provides a targeted supported noble metal catalyst and a preparation method thereof, the targeted supported noble metal catalyst comprises a porous base material 2.0, a noble metal catalyst and a porous filter layer, the noble metal catalyst is supported in micropores of the base material 2.0, and the porous filter layer coats the outer surface of the base material 2.0. The preparation method of the supported noble metal catalyst comprises the following steps: carrying out charge modification on a nonporous catalyst substrate; forming pores for the non-porous catalyst base material to obtain a porous base material 2.0; loading a noble metal precursor on the base material 2.0; reducing the noble metal precursor to obtain a supported noble metal catalyst; and hydrolyzing the supported noble metal catalyst to obtain the targeted supported noble metal catalyst. The targeted supported noble metal catalyst disclosed by the invention has accurate gas targeted recognition capability, and targeted detection of different gases can be realized; and the sensitivity of carbon monoxide detection is superior to that of commercially available products.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation methods, and more specifically relates to a targeted supported noble metal catalyst and a preparation method thereof. Background Art

[0002] Carbon monoxide, a toxic and harmful gas produced by incomplete combustion of fossil fuels, is closely related to people's production and life. Carbon monoxide is usually a colorless, odorless, tasteless gas. Its binding ability with hemoglobin is 200 to 300 times higher than that of oxygen with hemoglobin, thus forming carboxyhemoglobin, which makes hemoglobin lose its oxygen-carrying ability and function, causing tissue asphyxiation. It is toxic to tissue cells throughout the body, especially the cerebral cortex. At higher concentrations, people will experience varying degrees of poisoning, endangering the brain, heart, liver, lungs and other organs, and endangering human health. Therefore, it is particularly important to detect the carbon monoxide content in a timely and accurate manner.

[0003] Among various carbon monoxide gas sensors, carbon monoxide sensors based on electrochemical principles are widely used due to their rapid response, high cost-effectiveness, strong robustness, and friendliness to environmental temperature and humidity. Carbon monoxide sensors based on electrochemical principles contain two core components: electrodes composed of catalysts and carriers, and electrolytes. The electrolyte acts as a medium for proton conduction, ensuring the closed-loop nature of the chemical reaction. The electrode is the place where the electrochemical reaction occurs, and is composed of a substrate and a catalyst. The substrate provides a support layer for the catalyst, and the catalyst realizes the redox reaction of the gas.

[0004] Currently, commonly used catalysts can be divided into two types. One is pure precious metal catalysts such as platinum black / palladium black; the other is supported precious metal catalysts generated by dispersing precious metal particles on different carriers such as carbon black. Regardless of the form of catalyst, it is a guarantee for chemical reactions to occur at room temperature. Domestic research on catalysts started late, and the gap in overall performance of catalysts with foreign manufacturers' products is still quite obvious. This is why domestic high-end electrochemical gas sensors mainly rely on imports. A good catalyst needs to have strong reactivity, good selectivity, strong stability, long service life and anti-poisoning ability. The preparation method of the catalyst directly determines the performance of the catalyst. A large number of catalyst preparation methods have been reported in the literature, the more typical ones include:

[0005] In the preparation method of platinum / carbon catalyst disclosed in U.S. Patent No. 6,689,505B1, the inventor uses water as a dispersion liquid, performs reduction at a medium temperature in a weakly alkaline environment, adds a precious metal precursor to a dispersion liquid at 90°C and pH = 9, and uses sodium formate as a reducing liquid for reduction to obtain a supported precious metal catalyst. The disadvantage of this method is that the catalyst loss is relatively high, with a loss rate of more than 20%, and when the prepared catalyst is used in a carbon monoxide sensor, the reaction activity with the target gas is about 30% lower than the ideal state.

[0006] Although the Chinese patent (application number 02118282.5) reduces the loss of precious metals during the preparation and post-processing process by introducing halides such as halogenated ammonium as anchoring agents, this method cannot fundamentally solve the problem of precious metal loss.

[0007] The method disclosed in US Pat. No. 6,686,308B2 for preparing precious metal catalysts using ethylene glycol as both a reducing agent and a dispersing agent has the advantage of small particles, but has a high reaction temperature, many by-products, difficulty in purification, and a long preparation cycle.

[0008] The reduction method using 7% hydrogen disclosed in US Pat. No. 6,703,150 B2 has the disadvantages of high risk and long reduction time.

[0009] The precious metal catalyst prepared by the method disclosed in Chinese Patent 200410028129.X, which uses ethylene glycol as a dispersant and sodium formate as a reducing agent, has outstanding advantages such as uniform particles, simple operation, and high raw material utilization rate. However, the selectivity of the catalyst is poor and it belongs to a broad-spectrum catalyst with strong catalytic properties for general toxic and harmful gases.

[0010] However, these traditional catalysts lack the ability to accurately identify gases in complex gas environments, making them susceptible to interference from other gases in carbon monoxide detection applications. This greatly reduces detection accuracy and makes it difficult to meet the current demand for high-precision carbon monoxide monitoring. Summary of the invention

[0011] In order to solve the problems existing in the prior art, the present invention provides a targeted supported noble metal catalyst and a preparation method thereof. The catalyst prepared by the method can achieve high-precision targeted detection of the gas to be detected.

[0012] A targeted supported precious metal catalyst comprises: a porous substrate 2.0, a precious metal catalyst and a porous filter layer, wherein the precious metal catalyst is supported in the micropores of the substrate 2.0, and the porous filter layer is coated on the outer surface of the substrate 2.0.

[0013] Furthermore, the noble metal catalyst is obtained by reducing a noble metal precursor; preferably, the noble metal is one or more of chloroplatinic acid, palladium dichloride, ruthenium trichloride, potassium chloroaurate, and iridium chloride.

[0014] Furthermore, the porous filter layer is a porous silicon dioxide filter layer or a titanium dioxide filter layer.

[0015] A method for preparing a targeted supported noble metal catalyst comprises the following steps:

[0016] Charge-modified nonporous catalyst substrates;

[0017] Creating pores in a non-porous catalyst substrate to obtain a porous substrate 2.0;

[0018] loading a noble metal precursor onto a substrate 2.0;

[0019] Reducing the noble metal precursor to obtain a supported noble metal catalyst;

[0020] The supported noble metal catalyst is hydrolyzed to obtain a targeted supported noble metal catalyst.

[0021] Furthermore, the charge-modified nonporous catalyst substrate includes: mixing the nonporous catalyst substrate and a high boiling point solvent in a ratio of 0.01:1 to 0.1:1 to obtain a suspension; adding the charge modifier to the above suspension, wherein the amount of the charge modifier is 1 to 5 times the amount of the nonporous catalyst substrate, to form a nonporous catalyst substrate suspension with a charge.

[0022] Furthermore, the non-porous catalyst substrate is one or more of carbon black, graphene, titanium dioxide, carbon nanotubes, and other potentially applicable non-porous catalyst substrates; the high boiling point solvent is one or more of glycerol, diethylene glycol, diethyl oxalate, propylene glycol, and diethylene glycol; the charge modifier is one or more of sodium bicarbonate aqueous solution, sodium carbonate aqueous solution, sodium hypochlorite aqueous solution, and sodium sulfite aqueous solution.

[0023] Furthermore, the process of making pores in a non-porous catalyst substrate to obtain a porous substrate 2.0 includes: adding a first pore-forming agent with an opposite charge to the charged non-porous catalyst substrate suspension and stirring to obtain a porous catalyst substrate suspension; the amount of the first pore-forming agent added is 5% to 50% of the amount of the non-porous catalyst substrate; and filtering the porous catalyst substrate suspension and then sintering it to obtain a substrate 2.0.

[0024] Furthermore, the first pore-forming agent is one or more of sodium bicarbonate, aluminum nitrate, and ammonium bicarbonate.

[0025] Furthermore, the step of loading the noble metal precursor onto the substrate 2.0 includes: stirring a certain amount of the noble metal precursor, the substrate 2.0 and a high boiling point solvent to prepare a precursor solution.

[0026] Furthermore, the content of the noble metal precursor in the precursor solution is 10% to 70%, and the amount of the high boiling point solvent is 10 to 50 times the total weight of the noble metal precursor and the substrate 2.0; preferably, the noble metal precursor can be one or more of chloroplatinic acid, palladium dichloride, ruthenium trichloride, potassium chloroaurate, and iridium chloride.

[0027] Furthermore, the reduction of the precious metal precursor comprises: adding a rapid reducing agent to the precursor solution under low temperature conditions of 40 to 70° C. to obtain a solution containing a supported precious metal catalyst having a specific size, and filtering to obtain the supported precious metal catalyst.

[0028] Furthermore, the rapid reducing agent is one or more of hydrazine hydrate, sodium borohydride and formaldehyde.

[0029] Furthermore, the hydrolysis of the supported precious metal catalyst to obtain the targeted supported precious metal catalyst comprises the following steps: preparing a hydrolysis solvent, adding the supported precious metal catalyst powder, a hydrolysis source and a weak alkaline solution to the hydrolysis solvent to obtain a solid-liquid mixture; filtering the solid-liquid mixture to obtain the targeted supported precious metal catalyst.

[0030] Furthermore, the hydrolysis of the supported noble metal catalyst to obtain the targeted supported noble metal catalyst comprises the following steps:

[0031] S51, preparing a hydrolysis solvent: selecting water and short-chain alcohols to mix to obtain a hydrolysis solvent; the ratio of water to short-chain alcohols is 3:1 to 1:4;

[0032] S52, adding a supported noble metal catalyst: adding the supported noble metal catalyst to the hydrolysis solvent, stirring to form a solid-liquid mixture;

[0033] S53, adding a hydrolysis source: adding a hydrolysis source having a mass content of 3% to 20% to the solid-liquid mixture formed in step S52 to obtain a hydrolysis source solution;

[0034] S54, adding a second pore-forming agent: adding a second pore-forming agent to the hydrolysis source solution, mixing evenly, to obtain a second pore-forming agent solution;

[0035] S55, dripping weak alkaline solution and ultrasonic hydrolysis: slowly dripping weak alkaline solution into the second pore-forming agent solution to obtain a filter layer colloid;

[0036] S56, high temperature sintering molding: sintering the filter layer colloid to finally form a filter layer with a specific pore size; obtaining a targeted supported precious metal catalyst.

[0037] Furthermore, the hydrolysis source in S53 is ethyl silicate or butyl titanate; preferably, the second pore-forming agent is one or more of sodium bicarbonate, aluminum nitrate, and ammonium bicarbonate; preferably, the sintering temperature is 200-500°C.

[0038] Beneficial effects:

[0039] 1. Beneficial effects of targeted supported precious metal catalysts

[0040] (1) High selectivity: It has precise gas targeting recognition capability and can realize targeted detection of different gases. For example, a targeted supported precious metal catalyst with a silica filter layer on the surface only allows molecules smaller than carbon monoxide molecules to pass through, which can effectively avoid interference from other macromolecular gases and improve detection accuracy. In the application scenario of lithium battery thermal runaway detectors, compared with commercially available sensors, the relative sensitivity of the sensor of the present invention to 705 silicone rubber and freon is only 1%, while the commercially available sensors are as high as 96% and 19% respectively, which greatly reduces the possibility of false alarms caused by interfering substances.

[0041] (2) High sensitivity: sensitive to target gas, and better than commercially available products in detecting carbon monoxide. The carbon monoxide sensor made with the catalyst in Example 1 has a sensitivity of 3.2 nA / ppm for detecting carbon monoxide, which is higher than the 2.1 nA / ppm of commercially available sensors. It can more sensitively sense the presence of carbon monoxide and provide reliable data for detection and early warning.

[0042] 2. Beneficial effects of the preparation method

[0043] (1) Reducing the loss of precious metals: Through steps such as charge modification of the non-porous catalyst substrate, the problem of high loss of precious metals in the traditional preparation method is avoided. Reasonable control of the parameters of each step, such as the amount of charge modifier is 1 to 5 times the amount of non-porous catalyst substrate, can ensure that the non-porous catalyst substrate is fully modified, reduce self-agglomeration, and provide a good foundation for subsequent precious metal loading, thereby reducing the loss of precious metals in the preparation process.

[0044] (2) Mild reaction conditions: The reduction of precious metal precursors is carried out at a low temperature of 40 to 70°C, which has many advantages over traditional methods. On the one hand, it is conducive to the generation of smaller precious metal particles, giving the catalyst higher catalytic activity; on the other hand, it can enable the precious metal precursors in the cave to be mildly reduced in situ, preventing the precious metal particles from escaping from the cave at high temperatures, ensuring the integrity and stability of the catalyst structure, and thus improving the overall performance and service life of the catalyst.

[0045] (3) Product performance is controllable: The parameters of each preparation step can be adjusted to achieve precise control of catalyst performance. For example, different filter layer particles can be generated by selecting different hydrolysis sources (ethyl silicate or butyl titanate), and different second pore-forming agents can be used to sinter at different temperatures (200-500°C) to generate filter layer pores of different sizes, thereby meeting the needs of detecting different gases and making the prepared catalyst more targeted and adaptable. DETAILED DESCRIPTION

[0046] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments.

[0047] A targeted supported noble metal catalyst comprises: a porous substrate 2.0, a noble metal catalyst and a porous filter layer, wherein the noble metal catalyst is supported in the micropores of the substrate 2.0, and the porous filter layer is coated on the outer surface of the substrate 2.0. The porous filter layer is a porous silicon dioxide filter layer or a titanium dioxide filter layer.

[0048] The method for preparing the above-mentioned targeted supported noble metal catalyst comprises the following steps:

[0049] S1. Charge-modified nonporous catalyst substrate: Mix the nonporous catalyst substrate and the high boiling point solvent in a ratio of 0.01:1 to 0.1:1, and use a high-speed stirrer to mix the two into a suspension at a speed of 800 to 1500 rpm. The addition ratio of the above-mentioned nonporous catalyst substrate and the high boiling point solvent can fully guarantee the effect of the following charge modifier and reduce the probability of self-agglomeration of the nonporous catalyst substrate. Add the charge modifier to the above-mentioned suspension and continue to stir at a speed of 800 to 1500 rpm to form a nonporous catalyst substrate suspension with a charge. The appropriate stirring speed can ensure the formation of a micro-vortex structure around the molecules of the nonporous catalyst substrate. After the charge modifier comes in, it will be locked in the micro-vortex structure to achieve the best modification effect; if the stirring speed is too low, part of the nonporous catalyst substrate will not be fully modified; if the stirring speed is too high, the modified nonporous catalyst substrate will cause the modified charge to be separated under high-speed stirring.

[0050] In the present invention, the non-porous catalyst substrate can be one or more of carbon black, graphene, carbon nanotubes, and other potentially applicable non-porous catalyst substrates. Among them, carbon black has a high specific surface area, good chemical stability, high conductivity, strong adsorption, low cost, and is easy to obtain and process. Graphene has an ultra-high specific surface area and excellent electrical conductivity, and can provide more active sites for the adsorption of subsequent precious metal precursors, which is beneficial to improving the activity of the catalyst. Carbon nanotubes have a regular pore structure and good chemical stability, and can better maintain the microporous morphology during high-temperature sintering, ensuring the structural stability of the catalyst.

[0051] In the present invention, the high boiling point solvent may be one or more of glycerol, diethylene glycol, diethyl oxalate, propylene glycol, and diethylene glycol. In the present invention, the charge modifier may be one or more of sodium bicarbonate aqueous solution, sodium carbonate aqueous solution, sodium hypochlorite aqueous solution, and sodium sulfite aqueous solution. The amount of the charge modifier is 1 to 5 times the amount of the non-porous catalyst substrate. This amount range has been carefully studied and verified in practice to achieve the best modification effect. When the amount of the charge modifier is within this range, it can ensure that the non-porous catalyst substrate is fully wrapped by the charge modifier. From all angles of three-dimensional space, the non-porous catalyst substrate has an equal chance of being modified, thereby comprehensively guaranteeing the uniformity and integrity of the modification effect. If the amount of the charge modifier is too much, due to the repulsion between like charges, the modifier cannot be tightly gathered around the non-porous catalyst substrate to form an effective wrapping. In this case, the contact between the modifier and the substrate is insufficient, which greatly reduces the modification effect and makes it difficult to achieve the expected modification target.

[0052] S2. Pore formation for non-porous catalyst substrate: add a first pore-forming agent of opposite charge to the above-mentioned non-porous catalyst substrate suspension with charge and stir at high speed to obtain a porous catalyst substrate suspension; the amount of the first pore-forming agent added is 5% to 50% of the amount of the non-porous catalyst substrate, and the amount of the first pore-forming agent added is not determined arbitrarily, but is an ideal dosage range found by the inventor after a lot of research. In the ideal preparation process, the number of pores generated should moderately exceed the load of the precious metal, just like carefully preparing an exclusive "habitat" for each precious metal molecule, so as to ensure that each precious metal molecule has a suitable attachment site, thereby laying the foundation for the efficient conduct of subsequent catalytic reactions. However, it is worth noting that the number of holes cannot exceed the loading capacity too much. Once it exceeds a reasonable limit, a series of thorny problems will arise in the subsequent generation process of precious metal catalysts: some reagents will be trapped in the holes, which will not only be difficult to be fully reduced in the reduction step, but also cannot be completely removed in the cleaning step. These residual reagents will not only affect the purity of the catalyst, but may also have a negative impact on its catalytic activity and selectivity, thereby reducing the performance of the entire precious metal catalyst; from a macroscopic perspective, the proportion of overall holes in the substrate cannot be too high, otherwise the rigidity of the catalyst substrate skeleton will be severely damaged. In the subsequent actual use process, this rigidity-damaged catalyst substrate is very likely to self-fragment, which will not only destroy the physical form of the catalyst and fail to maintain its original structure, but also cause the loss of active ingredients in the catalyst, greatly reducing the stability and service life of the catalyst, seriously restricting its effect in practical applications, and unable to meet the strict requirements for catalyst performance in industrial production and other fields.

[0053] After filtering the porous catalyst substrate suspension, it is placed in an inert gas protection environment at 400-1000°C for sintering. The first pore-forming agent is sintered away to produce micropores of appropriate size while retaining the electrical properties of the microenvironment inside the micropores. The obtained substrate with micropores is called substrate 2.0.

[0054] In the present invention, the first pore-forming agent may be one or more of sodium bicarbonate, aluminum nitrate, and ammonium bicarbonate.

[0055] Substrate 2.0 has the advantages of higher controllability, better structural uniformity, more selective exposure of active sites, a wider range of starting material choices, and potentially higher stability and durability. Compared with porous substrates, it shows unique advantages in catalytic reaction applications.

[0056] S3, load the precious metal precursor onto the substrate 2.0: a certain amount of precious metal precursor, the above-mentioned substrate 2.0 and a high boiling point solvent are configured into a precursor solution, wherein the content of the precious metal precursor in the precursor solution is 10% to 70%. Among them, the amount of the high boiling point solvent is 10 to 50 times the total weight of the precious metal precursor and the substrate 2.0. The above-mentioned precursor solution is placed in a three-necked flask equipped with a thermometer and a vent, and stirred thoroughly to ensure that the precursor solution is adsorbed in the micropores of the substrate 2.0; an inert gas is introduced into the flask for protection; the flask is placed in an ultrasonic machine, the ultrasonic wave is turned on, and the micro energy and vibration generated by the ultrasonic wave are used to consolidate the micropore combination of the precious metal precursor and the substrate 2.0.

[0057] In the present invention, the noble metal precursor may be one or more of chloroplatinic acid, palladium dichloride, ruthenium trichloride, potassium chloroaurate, and iridium chloride.

[0058] S4. Reduce the precious metal precursor to obtain a supported precious metal catalyst: control the reaction temperature of the precursor solution in the flask at 40 to 70°C by a thermometer and a temperature feedback system. When the temperature reaches above 50°C, add a rapid reducing agent to the precursor solution so that the precious metal precursor undergoes an in-situ reduction reaction inside the micropores of the substrate 2.0. The amount of rapid reducing agent added is 3 to 10 times the amount of precious metal precursor added to ensure sufficient reduction. The entire reaction lasts for 10 to 100 seconds; turn off the ultrasonic wave, cool the above solution to room temperature under the protection of an inert gas, stop introducing the inert gas, and filter to obtain a supported precious metal catalyst of a specific size.

[0059] Under low temperature conditions of 40 to 70°C, there are significant advantages to slowly carrying out the reduction reaction. On the one hand, this reaction condition is conducive to the generation of smaller precious metal particles, and small-sized precious metal particles can give the catalyst higher catalytic activity, allowing it to exhibit better performance in the catalytic process. On the other hand, slow reduction at low temperature helps the precious metal precursors in the cave to undergo a mild reduction reaction in situ. Under high temperature conditions, the reaction is often too violent, which may cause the generated precious metal particles to break away from the cave where they were originally located and become free precious metal particles. The principle of slow reduction at low temperature effectively avoids this situation, ensuring that the precious metal particles can stably exist in the cave, ensuring the integrity and stability of the catalyst structure, and thus improving the overall performance and service life of the catalyst.

[0060] The rapid reducing agent may be one or more of hydrazine hydrate, sodium borohydride, and formaldehyde.

[0061] S5. Hydrolyze the supported precious metal catalyst to obtain a targeted supported precious metal catalyst: prepare a hydrolysis solvent, add the supported precious metal catalyst, a hydrolysis source and a weak alkaline solution into the hydrolysis solvent, and continue ultrasonication in an ice bath environment to uniformly generate a filter layer with a specific pore size on the outer surface of the supported precious metal catalyst by a low-temperature hydrolysis method to obtain a targeted supported precious metal catalyst.

[0062] Different filter layer particles can be generated by selecting different hydrolysis sources, and different second pore-forming agents can be used to sinter at different temperatures to generate filter layer pores of different sizes, thereby achieving the purpose of detecting different gases. Specifically, the following steps are included:

[0063] S51. Prepare hydrolysis solvent: Mix water with short-chain alcohols such as methanol, ethanol, and isopropanol to construct a reaction system for hydrolysis reaction and obtain hydrolysis solvent. The volume ratio of water and short-chain alcohols needs to be controlled so that it is in the range of 3:1 to 1:4, so as to subsequently generate filter layer particles of suitable size. Within this ratio range, when the water content is high, it is conducive to the generation of large-sized filter layer particles; when the alcohol content is high, it is easy to generate small-sized filter layer particles; the ratio of water and alcohol can be adjusted according to specific needs.

[0064] S52, adding a supported noble metal catalyst: adding the supported noble metal catalyst into the above hydrolysis solvent, stirring to form a solid-liquid mixture.

[0065] S53, adding a hydrolysis source: adding a hydrolysis source with a mass content of 3% to 20% to the solid-liquid mixture formed in step S52 to obtain a hydrolysis source solution. It is crucial to reasonably control the concentration of the hydrolysis source. If the concentration of the hydrolysis source is too low, the hydrolysis reaction is time-consuming and will significantly extend the reaction time; if the concentration of the hydrolysis source is too high, the generated filter layer particles are prone to self-agglomeration, causing the particle size of the filter layer particles to increase, thereby affecting the performance of the final product. In the present application, ethyl silicate (TEOS) can be selected as a hydrolysis source to hydrolyze to generate silicon dioxide filter layer particles; or butyl titanate (TBOT) can be selected as a hydrolysis source to hydrolyze to generate titanium dioxide filter layer particles.

[0066] S54, adding a second pore-forming agent: adding a second pore-forming agent to the above hydrolysis source solution, followed by stirring. The stirring time needs to be maintained at 8 to 24 hours to allow the second pore-forming agent and the hydrolysis source solution to be fully mixed and uniformly obtained to obtain a second pore-forming agent solution.

[0067] The second pore-forming agent may be one or more of sodium bicarbonate, aluminum nitrate, and ammonium bicarbonate. In the same embodiment, the type of the second pore-forming agent may be the same as or different from that of the first pore-forming agent.

[0068] S55, dripping weak alkaline solution and ultrasonic hydrolysis: slowly dripping weak alkaline solution such as ammonia solution or sodium hydroxide into the second pore-forming agent solution, and the amount of the weak alkaline solution added should account for 0.1% to 5% of the total amount of the above solvent. After the weak alkaline solution is dripped, it is fully stirred and then placed in an ice bath environment for ultrasonic treatment for 12 to 36 hours. In this process, the hydrolysis source undergoes a hydrolysis reaction to generate a filter layer colloid.

[0069] S56, high-temperature sintering molding: placing the filter layer colloid obtained in the above steps in a high-temperature environment for sintering, and the sintering temperature is controlled at 200-500°C, and finally forming a filter layer with a specific pore size to obtain a targeted supported precious metal catalyst.

[0070] The sintering temperature setting needs to be determined based on the type of the second pore former used and the desired pore size. Generally speaking, a lower sintering temperature is conducive to the formation of small pores, while a higher sintering temperature is conducive to the formation of large pores.

[0071] The size of the filter layer pore size can greatly improve the catalyst's selectivity for gas. For example, a targeted noble metal catalyst with a silica filter layer on the surface only allows molecules smaller than carbon monoxide molecules to pass through. Other large molecules cannot pass through the porous silica filter layer generated by hydrolysis, and cannot contact the noble metal catalyst, so they cannot be detected.

[0072] The targeted supported noble metal catalyst of the present invention has good selectivity and can realize targeted detection of different gases. In terms of selectivity, the gas sensor prepared by using the targeted supported noble metal catalyst is significantly better than the products on sale in the industry.

[0073] The core application of the targeted catalyst prepared by the present invention is in gas sensors based on electrochemical principles, among which carbon monoxide sensors are typical representatives.

[0074] It has demonstrated significant value in the industrial field. For example, in underground coal mining environments, it can accurately detect the concentration of carbon monoxide. Once the carbon monoxide concentration is abnormal, an early warning can be issued, thereby effectively warning of the risk of gas leakage and providing strong protection for the life safety of underground miners. In chemical production workshops, sensors supported by the catalyst can monitor the process in real time, and sensitively detect whether there is abnormal leakage of carbon monoxide, thereby ensuring the safe development of chemical production operations.

[0075] It also plays an important role in civilian use. In household gas alarms, it can quickly and accurately identify carbon monoxide leaks, protect the lives and health of residents, and avoid the harm caused by carbon monoxide poisoning; for indoor air quality monitoring equipment, the catalyst helps the equipment to achieve accurate control of air quality, thereby creating a healthy and comfortable living environment for people.

[0076] In the field of new energy, this targeted catalyst has unique application prospects and can be used in thermal runaway detectors for lithium batteries. It prevents the occurrence of malignant thermal runaway accidents and ensures the safety of lithium batteries by detecting the very early characteristic parameters of thermal runaway of lithium batteries, namely the content of carbon monoxide gas.

[0077] In addition, this catalyst technology has broad expansion potential and is expected to be used in the front-end detection link of the automobile exhaust purification system, assisting the system to accurately control the exhaust treatment process, thereby significantly improving the emission reduction effect and contributing to environmental protection; in the medical field, it can provide a highly sensitive detection method for the detection of carbon monoxide content in exhaled breath, assisting doctors in accurately diagnosing related diseases and providing important auxiliary information for medical diagnosis.

[0078] Example 1: Preparation of catalyst based on carbon black

[0079] A targeted supported precious metal catalyst comprises: a porous substrate 2.0, a precious metal catalyst and a porous filter layer, wherein the precious metal catalyst is supported in the micropores of the substrate 2.0, and the porous filter layer is coated on the outer surface of the substrate 2.0. The pore size of the substrate 2.0 is 3 to 5 nm, and the porosity is 35% to 40%; the pore size of the porous filter layer is less than 1.5 nm, and the porosity is 55% to 65%. The supported precious metal catalyst is used for selective detection of carbon monoxide, the porous substrate 2.0 is carbon black, and the porous filter layer is a silica filter layer.

[0080] The method for preparing the above-mentioned targeted supported noble metal catalyst comprises the following steps:

[0081] S1. Charge-modified nonporous catalyst substrate: 0.1 g of carbon black was mixed with 10 g of propylene glycol, and stirred into a suspension using a high-speed stirrer at a speed of 1200 rpm. 0.3 g of sodium bicarbonate aqueous solution (charge modifier) ​​was added to the suspension, and stirring was continued to form a carbon black suspension with a charge.

[0082] S2. Pore formation for a non-porous catalyst substrate: 0.05 g of sodium bicarbonate (the first pore-forming agent) was added to the above suspension and stirred at high speed. After filtering the suspension, the suspension was placed in a nitrogen protection environment at 600° C. for sintering to obtain a substrate 2.0 with micropores.

[0083] S3. Load the precious metal precursor onto the substrate 2.0: prepare a precursor solution by mixing 0.1 g of chloroplatinic acid (precious metal precursor), the above-mentioned substrate 2.0 and 5 g of propylene glycol. Place the precursor solution in a three-necked flask equipped with a thermometer and a vent, stir thoroughly, introduce nitrogen protection, put it into an ultrasonic machine, and turn on the ultrasonic wave.

[0084] S4. Reduce the noble metal precursor to obtain a supported noble metal catalyst: control the reaction solution in the flask at 50° C., add 0.03 g of hydrazine hydrate (rapid reducing agent), continue the reaction for 30 seconds, turn off the ultrasound, cool to room temperature under nitrogen protection, and then stop passing nitrogen.

[0085] S5. Hydrolyze the supported precious metal catalyst to obtain a targeted supported precious metal catalyst: prepare a hydrolysis solvent with a ratio of water to ethanol of 2:1, add the supported precious metal catalyst obtained in step S4 to the above hydrolysis solvent, stir to form a solid-liquid mixture; add ethyl silicate (hydrolysis source) with a mass content of 10% to the solid-liquid mixture, then add an appropriate amount of ammonium bicarbonate (a second pore-forming agent), stir for 16 hours, dropwise add an ammonia solution accounting for 2% of the total solvent, and perform ultrasonic treatment in an ice bath for 24 hours to generate a filter layer colloid, and sinter the filter layer colloid at 350°C to obtain a targeted supported precious metal catalyst.

[0086] Example 2: Preparation of catalyst based on graphene

[0087] A method for preparing a targeted supported noble metal catalyst comprises the following steps:

[0088] S1. Charge-modified nonporous catalyst substrate: 0.05 g of graphene was mixed with 5 g of diethylene glycol, stirred at 1200 rpm to form a suspension, 0.2 g of sodium carbonate aqueous solution was added, and stirred to form a charged graphene suspension.

[0089] S2. Making pores for a non-porous catalyst substrate: Add 0.02 g of aluminum nitrate (the first pore-forming agent) to the above suspension, stir and filter, and sinter at 800° C. in an argon environment to obtain a substrate 2.0.

[0090] S3. Loading the precious metal precursor onto the substrate 2.0: 0.03 g of palladium dichloride, the above substrate 2.0 and 3 g of diethylene glycol are prepared into a precursor solution, which is put into a three-necked flask, stirred, protected by argon gas, and then ultrasonicated.

[0091] S4. Reduce the noble metal precursor to obtain a supported noble metal catalyst: control the temperature of the reaction solution at 60° C., add 0.02 g of sodium borohydride (rapid reducing agent), react for 40 seconds, and then cool in a conventional manner.

[0092] S5. Hydrolyze the supported precious metal catalyst to obtain a targeted supported precious metal catalyst: prepare a hydrolysis solvent with a ratio of water to isopropanol of 1:3, add the supported precious metal catalyst obtained in step S4 to the above hydrolysis solvent, stir to form a solid-liquid mixture; add butyl titanate (hydrolysis source) with a mass content of 15% to the solid-liquid mixture, and then add an appropriate amount of aluminum nitrate (a second pore-forming agent), stir for 20 hours, add dropwise a sodium hydroxide solution accounting for 3% of the total solvent, perform ice bath ultrasound for 30 hours to generate a filter layer colloid, and sinter the filter layer colloid at 400° C. to obtain a targeted supported precious metal catalyst.

[0093] Example 3: Preparation of catalyst based on carbon nanotubes

[0094] A method for preparing a targeted supported noble metal catalyst comprises the following steps:

[0095] S1. Charge-modified nonporous catalyst substrate: 0.08 g of carbon nanotubes and 8 g of diethyl oxalate were mixed, stirred at 900 rpm to form a suspension, 0.4 g of sodium hypochlorite aqueous solution was added, and stirred to form a charged suspension.

[0096] S2. Making pores for a non-porous catalyst substrate: adding 0.03 g of ammonium bicarbonate (the first pore-forming agent) to the above suspension, stirring and filtering, and sintering at 700° C. in a nitrogen environment to obtain a substrate 2.0.

[0097] S3. Loading the precious metal precursor onto the substrate 2.0: 0.04 g of ruthenium trichloride, the above substrate 2.0 and 4 g of diethyl oxalate are prepared into a precursor solution, placed in a three-necked flask, stirred, and protected by nitrogen, followed by ultrasonication.

[0098] S4. Reduce the noble metal precursor to obtain a supported noble metal catalyst: control the temperature of the reaction solution at 45° C., add 0.025 g of formaldehyde (rapid reducing agent), react for 50 seconds, and cool in a conventional manner.

[0099] S5. Hydrolyze the supported precious metal catalyst to obtain a targeted supported precious metal catalyst: prepare a hydrolysis solvent with a ratio of water to methanol of 3:1, add the supported precious metal catalyst obtained in step S4 to the above hydrolysis solvent, stir to form a solid-liquid mixture; add ethyl silicate (hydrolysis source) with a mass content of 8% to the solid-liquid mixture, then add an appropriate amount of ammonium bicarbonate (a second pore-forming agent), stir for 12 hours, dropwise add an ammonia solution accounting for 1% of the total solvent, and perform ultrasonic treatment in an ice bath for 18 hours to generate a filter layer colloid, and sinter the filter layer colloid at 250°C to obtain a targeted supported precious metal catalyst.

[0100] Example 4: Preparation of catalysts from various noble metal precursors

[0101] A method for preparing a targeted supported noble metal catalyst comprises the following steps:

[0102] S1. Charge-modified nonporous catalyst substrate: 0.06 g of carbon black was mixed with 6 g of propylene glycol, and stirred at 1100 rpm to form a suspension, and 0.3 g of sodium sulfite aqueous solution was added and stirred to form a charged suspension.

[0103] S2. Making pores for a non-porous catalyst substrate: Add 0.03 g of sodium bicarbonate (the first pore-forming agent) to the above suspension, stir and filter, and sinter at 500° C. in an argon environment to obtain a substrate 2.0.

[0104] S3. Loading the precious metal precursor onto the substrate 2.0: Prepare a precursor solution by mixing 0.02g of chloroplatinic acid, 0.02g of potassium chloroaurate, the above substrate 2.0 and 4g of propylene glycol, and put it into a three-necked flask. Stir, pass argon gas for protection, and then perform ultrasound.

[0105] S4. Reduce the noble metal precursor to obtain a supported noble metal catalyst: control the temperature of the reaction solution at 55° C., add 0.03 g of hydrazine hydrate (rapid reducing agent), react for 60 seconds, and cool in a conventional manner.

[0106] S5. Hydrolyze the supported precious metal catalyst to obtain a targeted supported precious metal catalyst: prepare a hydrolysis solvent with a ratio of water to ethanol of 1:2, add the supported precious metal catalyst obtained in step S4 to the above hydrolysis solvent, stir to form a solid-liquid mixture; add butyl titanate (hydrolysis source) with a mass content of 12% to the solid-liquid mixture, add a suitable second pore-forming agent, stir for 18 hours, dropwise add a sodium hydroxide solution accounting for 4% of the total solvent, perform ice bath ultrasound for 28 hours to generate a filter layer colloid, sinter the filter layer colloid at a temperature of 300°C to obtain a targeted supported precious metal catalyst.

[0107] Example 5: Preparation of targeted catalysts for different application scenarios

[0108] A method for preparing a targeted supported noble metal catalyst comprises the following steps:

[0109] S1. Charge-modified nonporous catalyst substrate: 0.1 g of graphene was mixed with 10 g of diethylene glycol, and stirred at 1300 rpm to form a suspension, and 0.4 g of sodium carbonate aqueous solution was added and stirred to form a charged suspension.

[0110] S2. Making pores for a non-porous catalyst substrate: adding 0.04 g of aluminum nitrate (the first pore-forming agent) to the above suspension, stirring and filtering, and sintering at 900° C. in a nitrogen environment to obtain a substrate 2.0.

[0111] S3. Loading the precious metal precursor onto the substrate 2.0: 0.03 g of palladium dichloride, the above substrate 2.0 and 3 g of diethylene glycol are prepared into a precursor solution, which is put into a three-necked flask, stirred, and protected by nitrogen, followed by ultrasonication.

[0112] S4. Reduce the noble metal precursor to obtain a supported noble metal catalyst: control the temperature of the reaction solution at 65° C., add 0.02 g of sodium borohydride (rapid reducing agent), react for 35 seconds, and cool in a conventional manner.

[0113] S5. Hydrolyze the supported precious metal catalyst to obtain a targeted supported precious metal catalyst: prepare a hydrolysis solvent with a ratio of water to isopropanol of 2:3, add the supported precious metal catalyst obtained in step S4 to the above hydrolysis solvent, stir to form a solid-liquid mixture; add ethyl silicate (hydrolysis source) with a mass content of 18% to the solid-liquid mixture, then add an appropriate amount of aluminum nitrate (a second pore-forming agent), stir for 22 hours, dropwise add an ammonia solution accounting for 2.5% of the total solvent, perform ice bath ultrasound for 32 hours to generate a filter layer colloid, sinter the filter layer colloid at 450°C to obtain a targeted supported precious metal catalyst for front-end detection of automobile exhaust purification systems.

[0114] Test Case

[0115] In the actual application scenarios of lithium battery thermal runaway detectors, traditional lithium battery packs are usually sealed with 705 silicone rubber. However, during the normal operation of lithium batteries, the gas contained in the silicone rubber will continue to evaporate. Due to this characteristic, the carbon monoxide sensor used in this scenario must have a strong ability to resist the interference of 705 silicone rubber. If the carbon monoxide sensor cannot meet this requirement, it is very easy to have false alarms during on-site use, which will cause serious interference to the normal operation and safety monitoring of the system.

[0116] The carbon monoxide sensor made of the targeted supported noble metal catalyst in Example 1 was used to test the relative sensitivity of carbon monoxide, 705 silicone rubber and freon. The test results are shown in the following table:

[0117] Table 1 Comparison of material detection performance based on the present invention and commercially available sensors

[0118]

[0119] The sensitivity of the sensor of the present invention (3.2nA / ppm) is higher than that of commercially available sensors (2.1nA / ppm), which indicates that the sensor of the present invention has better response performance when detecting carbon monoxide and can more keenly sense the presence of carbon monoxide, thereby providing a more reliable data basis for subsequent detection and early warning.

[0120] The relative sensitivity of the sensor of the present invention is only 1% (S silicone rubber / SCO*100%), while the relative sensitivity of the commercially available sensor is as high as 96%. This fully demonstrates that the sensor of the present invention performs well in resisting the interference of 705 silicone rubber. In contrast, the commercially available sensor is very susceptible to the interference of the volatile gas of 705 silicone rubber, which may lead to false alarms, while the sensor of the present invention can effectively reduce the risk of false alarms caused by the interference of 705 silicone rubber.

[0121] The relative sensitivity of the sensor of the present invention is also only 1% (SR32 / SCO*100%), while that of the commercially available sensor is 19%. This means that the sensor of the present invention also shows a significant advantage in resisting the interference of Freon, and can better avoid the false alarm caused by the presence of Freon, providing a more stable and accurate monitoring environment for practical applications.

[0122] In summary, by comparing the relative sensitivity test results of the sensor of the present invention and commercially available sensors to carbon monoxide, 705 silicone rubber and Freon, it can be seen that the sensor of the present invention not only has improved carbon monoxide detection sensitivity, but more importantly, has shown excellent performance in resisting interference from 705 silicone rubber and Freon, which greatly reduces the possibility of false alarms due to interfering substances in the application scenarios of lithium battery thermal runaway detectors, and improves the reliability and accuracy of the detector.

[0123] The details shown herein are presented as examples only and for the purpose of illustrative discussion of preferred embodiments of the invention, and are presented for the purpose of providing what is believed to be the most useful and easy-to-understand description of aspects of the principles and concepts of various embodiments of the invention. In this regard, no attempt is made to show the structural details of the invention in more detail than is necessary for a basic understanding of the invention, and the description in conjunction with the examples makes it clear to those skilled in the art how several forms of the invention are embodied in practice. Therefore, before describing the disclosed methods and apparatus, it should be understood that the aspects described herein are not limited to specific embodiments, instruments or configurations, and therefore can certainly be changed. It should also be understood that the terms used herein are only for the purpose of describing specific aspects, and are not intended to be limiting unless expressly defined herein.

[0124] The terms "a", "an", "the" and similar references used in the context of describing the present invention (especially in the context of the claims below) should be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values ​​herein is merely intended to serve as a shorthand method of referring individually to each individual value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. It will be further understood that the endpoints of each range are significant not only in relation to the other endpoints, but also independently of the other endpoints.

[0125] All methods described herein can be performed in the order of any suitable steps, unless otherwise indicated herein or clearly contradictory to the context. The use of any and all embodiments provided herein, or exemplary language (e.g., "such as") is intended only to better illustrate the present invention and does not set limitations on the scope of the present invention otherwise claimed. No language in the specification should be interpreted as indicating any unclaimed elements essential to the practice of the present invention.

[0126] Unless the context clearly requires otherwise, throughout the specification and claims, the wording 'comprising

[0127] The terms "herein," "above," and "below," and words of similar meaning, when used in this application, shall refer to this application as a whole and not to any particular portion of this application.

[0128] As will be understood by one of ordinary skill in the art, each embodiment disclosed herein may comprise, consist essentially of, or consist of the specifically identified elements, steps, ingredients, or components thereof. As used herein, the transitional terms "comprise" or "comprises" are meant to include, but are not limited to, and permit the inclusion of unspecified elements, steps, ingredients, or components, even in large quantities. The transitional phrase "consisting of" excludes any unspecified elements, steps, ingredients, or components. The transitional phrase "consisting essentially of" limits the scope of the embodiment to the identified elements, steps, ingredients, or components and those that do not materially affect the embodiment.

[0129] Unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0130] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors resulting from the standard deviation found in their respective testing measurements.

[0131] The grouping of the optional elements or embodiments of the invention disclosed herein should not be construed as limiting. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements present herein. It is expected that one or more members of the group may be included in the group, or deleted from the group, due to convenience and / or patentable reasons. When any such inclusion or deletion occurs, it is considered that the specification contains the modified group, and therefore satisfies the written description of all Markush groups used in the appended claims.

[0132] Some embodiments of the present invention are described herein, including the best mode known to the inventor for carrying out the present invention. Of course, for those skilled in the art, when reading the foregoing description, variations of the embodiments described will become clear. The inventor expects that a skilled person will adopt such variations as appropriate, and the inventor intends to practice the present invention in a manner other than the specific description herein. Therefore, the present invention includes all modifications and equivalents of the subject matter recorded in the appended claims as allowed by applicable law. In addition, the present invention includes any combination of the elements described above in all possible variants thereof, unless otherwise indicated herein or clearly contradictory to the context.

[0133] Throughout this specification, a number of patents and printed publications are cited. Each of the cited references and printed publications is incorporated herein by reference in its entirety.

[0134] In addition, it should be understood that the embodiments of the invention disclosed herein are illustrative of the principles of the present invention. Other modifications that may be adopted are within the scope of the present invention. Therefore, by way of example, but not as a limitation, alternative configurations of the present invention may be used consistent with the teachings herein. Therefore, the present invention is not limited to what is precisely shown and described.

Claims

1. A targeted supported noble metal catalyst, characterized in that: include: A porous substrate 2.0, a precious metal catalyst and a porous filter layer, wherein the precious metal catalyst is loaded in the micropores of the substrate 2.0, and the porous filter layer is coated on the outer surface of the substrate 2.

0.

2. The targeted supported noble metal catalyst according to claim 1, characterized in that: The noble metal catalyst is obtained by reducing a noble metal precursor; preferably, the noble metal is one or more of chloroplatinic acid, palladium dichloride, ruthenium trichloride, potassium chloroaurate, and iridium chloride; preferably, the porous filter layer is a porous silica filter layer or a titanium dioxide filter layer.

3. A method for preparing a targeted supported noble metal catalyst, characterized in that: The steps include: Charge-modified nonporous catalyst substrates; Creating pores in a non-porous catalyst substrate to obtain a porous substrate 2.0; loading a noble metal precursor onto a substrate 2.0; Reducing the noble metal precursor to obtain a supported noble metal catalyst; The supported noble metal catalyst is hydrolyzed to obtain a targeted supported noble metal catalyst.

4. The method for preparing a targeted supported noble metal catalyst according to claim 3, characterized in that: The charge-modified non-porous catalyst substrate comprises: mixing the non-porous catalyst substrate and a high boiling point solvent in a ratio of 0.01:1 to 0.1:1 to obtain a suspension; adding the charge modifier to the suspension, wherein the amount of the charge modifier is 1 to 5 times the amount of the non-porous catalyst substrate, to form a non-porous catalyst substrate suspension with a charge.

5. The method for preparing a targeted supported noble metal catalyst according to claim 4, characterized in that: The non-porous catalyst substrate is one or more of carbon black, graphene, carbon nanotubes, and other potentially applicable non-porous catalyst substrates; the high boiling point solvent is one or more of glycerol, diethylene glycol, diethyl oxalate, propylene glycol, and diethylene glycol; the charge modifier is one or more of sodium bicarbonate aqueous solution, sodium carbonate aqueous solution, sodium hypochlorite aqueous solution, and sodium sulfite aqueous solution.

6. The method for preparing a targeted supported noble metal catalyst according to claim 3, characterized in that: The method of making pores for a non-porous catalyst substrate to obtain a porous substrate 2.0 includes: adding a first pore-forming agent with an opposite charge to the charged non-porous catalyst substrate suspension and stirring to obtain a porous catalyst substrate suspension; the amount of the first pore-forming agent added is 5% to 50% of the amount of the non-porous catalyst substrate; and filtering the porous catalyst substrate suspension and then sintering it to obtain the substrate 2.

0.

7. The method for preparing a targeted supported noble metal catalyst according to claim 3, characterized in that: The process of loading the precious metal precursor onto the substrate 2.0 includes: stirring a certain amount of precious metal precursor, the substrate 2.0 and a high boiling point solvent to form a precursor solution; preferably, the content of the precious metal precursor in the precursor solution is 10% to 70%, and the amount of the high boiling point solvent is 10 to 50 times the total weight of the precious metal precursor and the substrate 2.0; preferably, the precious metal precursor can be one or more of chloroplatinic acid, palladium dichloride, ruthenium trichloride, potassium chloroaurate, and iridium chloride.

8. The method for preparing a targeted supported noble metal catalyst according to claim 3, characterized in that: The reducing of the noble metal precursor comprises: adding a rapid reducing agent to the precursor solution under a low temperature condition of 40 to 70° C. to obtain a solution of a supported noble metal catalyst with a specific size, and filtering to obtain the supported noble metal catalyst.

9. The method for preparing a targeted supported noble metal catalyst according to claim 3, characterized in that: The hydrolysis of the supported precious metal catalyst to obtain the targeted supported precious metal catalyst includes the following steps: preparing a hydrolysis solvent, adding the supported precious metal catalyst powder, a hydrolysis source and a weak alkaline solution into the hydrolysis solvent to obtain a solid-liquid mixture; filtering the solid-liquid mixture to obtain the targeted supported precious metal catalyst.

10. The method for preparing a targeted supported noble metal catalyst according to claim 3, characterized in that: The method of hydrolyzing the supported noble metal catalyst to obtain the targeted supported noble metal catalyst comprises the following steps: S51, preparing a hydrolysis solvent: selecting water and short-chain alcohols to mix to obtain a hydrolysis solvent; the ratio of water to short-chain alcohols is 3:1 to 1:4; S52, adding a supported noble metal catalyst: adding the supported noble metal catalyst to the hydrolysis solvent, stirring to form a solid-liquid mixture; S53, adding a hydrolysis source: adding a hydrolysis source having a mass content of 3% to 20% to the solid-liquid mixture formed in step S52 to obtain a hydrolysis source solution; S54, adding a second pore-forming agent: adding a second pore-forming agent to the hydrolysis source solution, mixing evenly, to obtain a second pore-forming agent solution; S55, dripping weak alkaline solution and ultrasonic hydrolysis: slowly dripping weak alkaline solution into the second pore-forming agent solution to obtain a filter layer colloid; S56, high temperature sintering molding: sintering the filter layer colloid to finally form a filter layer with a specific pore size; obtaining a targeted supported precious metal catalyst.

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