Modification method for selectively passivating low-coordination-site platinum-carbon catalyst and platinum-carbon catalyst

Abstract

The invention belongs to the field of platinum-carbon catalyst modification, and particularly discloses a modification method of a platinum-carbon catalyst for selective passivation of low coordination sites and the platinum-carbon catalyst.The modification method comprises the steps that an initial platinum-carbon catalyst is subjected to reduction activation so as to fully expose the low coordination sites on platinum particles; enabling the passivator precursor to be adsorbed on the exposed low coordination sites, and then enabling the passivator precursor on the low coordination sites to be converted into a passivator through an activating agent, so as to obtain a passivator modified platinum-carbon catalyst precursor; and carrying out heat treatment on the platinum-carbon catalyst precursor in a reducing atmosphere to obtain the platinum-carbon catalyst. According to the method, the activity of low coordination sites of platinum particles in the platinum-carbon catalyst can be accurately inhibited, the stability of the platinum-carbon catalyst is improved, the intrinsic activity of the oxygen reduction reaction of the platinum-carbon catalyst can be further improved, and large-scale application is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of platinum-carbon catalyst modification, and more specifically, relates to a platinum-carbon catalyst modification method for selectively passivating low-coordination sites and a platinum-carbon catalyst. Background Art

[0002] Oxygen reduction reaction is one of the most important reactions in nature, such as biological respiration, and is also a key step in converting chemical energy into electrical energy, such as fuel cells. Unlike traditional internal combustion engines, fuel cells are energy conversion devices that are not restricted by the "Carnot cycle" and can be widely used in all aspects of production and life. Among many fuel cells, proton exchange membrane fuel cells have the characteristics of low operating temperature, high efficiency, green, zero greenhouse gas emissions, and miniaturization. They are the most promising hydrogen energy utilization devices. Proton exchange membrane fuel cells are mainly composed of gas diffusion layers, cathodes, proton exchange membranes, and anodes. The cathode undergoes a hydrogen oxidation half reaction, and the anode undergoes an oxygen reduction half reaction. Both the cathode and the cathode use precious metal platinum as a catalyst. Due to the kinetics, the reaction rate of the anode is too slow, so a large amount of precious metal platinum is required to maintain a high reaction rate. Early proton exchange membrane fuel cells used pure platinum black to catalyze the oxygen reduction process, which resulted in excessively high costs and was limited to applications in high-tech fields such as aerospace.

[0003] The emergence of supported platinum catalysts has effectively solved this problem, and the amount of platinum has been significantly reduced by more than 40%. Platinum-carbon catalysts with carbon as a carrier are currently recognized as the catalysts with the best comprehensive performance for oxygen reduction reactions, and are currently widely used in fuel cells for small passenger cars and heavy trucks. However, although platinum-carbon catalysts have been commercialized on a large scale, they still face huge challenges in further reducing the amount of precious metal platinum and improving its stability. The reason is that the strategy of reducing the amount of precious metal platinum by reducing the particle size has reached its limit: the reduction in the size of platinum particles will inevitably lead to an increase in its specific surface area, and the number of defect sites on the surface (i.e., low-coordination sites, including vertices, edge sites, step sites, etc.) will also increase significantly. A large number of studies have shown that low-coordination sites are the center of loss of catalytic activity and stability of platinum particles. Too many low-coordination sites will cause the platinum particles to deactivate quickly.

[0004] Around this problem, in recent years, methods such as surface coating and non-precious metal doping have been developed to modify platinum-carbon catalysts. Among them, the core strategy of surface coating is to reduce the exposure of low-coordination sites by introducing a protective layer, thereby stabilizing platinum nanoparticles, including inorganic coating layers such as carbon, aluminum oxide, silicon oxide, etc., and organic coating layers such as pyridine, polyaniline, etc. Due to the lack of selectivity, the coating layer will cover the active center sites of the oxygen reduction reaction on the platinum particles while protecting the low-coordination sites, resulting in the loss of electrochemical active area of ​​the platinum particles, thereby reducing its intrinsic activity. The core strategy of non-precious metal doping is to introduce transition metal elements, such as iron, cobalt, nickel, etc., to form alloys with platinum, while further reducing the amount of platinum, regulating the distance between platinum atoms, thereby changing the adsorption characteristics of platinum for intermediate species in the oxygen reduction reaction and improving catalytic activity. Because the alloy itself is not stable, under complex and harsh working conditions such as strong acid and high overpotential, the transition metal elements are very easy to dissolve, destroying the overall structure of the alloy while catalyzing the decomposition of the proton exchange membrane, thereby causing the entire fuel cell to lose efficiency.

[0005] Therefore, how to accurately inhibit the activity of the low-coordination sites of platinum particles in platinum-carbon catalysts is the key to improving the stability of platinum-carbon catalysts, and there is currently no effective solution. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the present invention provides a method for modifying a platinum-carbon catalyst with selective passivation of low coordination sites and a platinum-carbon catalyst, the purpose of which is to accurately inhibit the activity of the low coordination sites of platinum particles in the platinum-carbon catalyst and improve the stability of the platinum-carbon catalyst.

[0007] To achieve the above object, according to one aspect of the present invention, a method for selectively passivating a platinum-carbon catalyst with a low coordination site is proposed, comprising the following steps:

[0008] S1, heat treating the initial platinum-carbon catalyst in a reducing atmosphere to achieve reduction activation and fully expose the low coordination sites on the platinum particles;

[0009] S2, adsorbing the passivating agent precursor on the exposed low-coordination site, and then converting the passivating agent precursor on the low-coordination site into a passivating agent by an activator to obtain a passivating agent-modified platinum-carbon catalyst precursor;

[0010] S3. Heat-treating the platinum-carbon catalyst precursor in a reducing atmosphere to obtain a platinum-carbon catalyst.

[0011] As further preferred, in step S1, the reducing atmosphere is hydrogen or a hydrogen-argon mixture with a concentration of 1% to 30%; and the heat treatment temperature is 200 to 500°C.

[0012] As further preferred, in step S1, before the initial platinum-carbon catalyst is heat-treated in a reducing atmosphere, the step further includes:

[0013] The initial platinum-carbon catalyst is firstly acid washed.

[0014] As further preferred, the acid washing of the initial platinum-carbon catalyst comprises: placing the initial platinum-carbon catalyst in a hot dilute acid solution saturated with an inert gas; the hot dilute acid solution is one or more of hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid solutions with a temperature of 30 to 100° C. and a concentration of 0.01 to 1.0 mol / L.

[0015] As further preferred, step S2 specifically includes the following steps:

[0016] Place the reduced activated platinum carbon catalyst into a fixture with two ends closed by filters, and then place the fixture into the furnace chamber;

[0017] The furnace chamber is evacuated, and a fluidizing gas is introduced from the bottom of the fixture to fluidize and suspend the platinum-carbon catalyst in the fixture;

[0018] The furnace chamber and the source bottle containing the passivation agent precursor are raised to a set temperature, and then the passivation agent precursor enters the fixture and is selectively adsorbed on the exposed low-coordination sites;

[0019] Then, an activator is introduced into the fixture to convert the passivating agent precursor adsorbed on the low coordination site into a stable passivating agent.

[0020] As further preferred, the set temperature of the furnace chamber is 25-300° C., and the set temperature of the source bottle is 25-200° C.; and the set temperature of the source bottle is not higher than the set temperature of the furnace chamber.

[0021] As further preferred, the passivator precursor is one or more of a compound containing a transition metal or an organic compound containing a metalloid; the activator is one or more of oxygen, ozone, hydrogen peroxide, water, hydrogen, and carbon monoxide; and the passivator is an oxide, hydroxide, or carbon oxide produced by decomposition of the passivator precursor.

[0022] As further preferred, the activator is hydrogen and / or carbon monoxide, and the metalloid is boron.

[0023] As further preferred, in step S3, the reducing atmosphere is hydrogen, ammonia, a hydrogen-argon mixture or an ammonia-argon mixture, with a concentration of 1% to 30%; and the heat treatment temperature is 500 to 800°C.

[0024] According to another aspect of the present invention, there is provided a platinum-carbon catalyst obtained by using the above-mentioned platinum-carbon catalyst modification method for selectively passivating low-coordination sites.

[0025] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0026] 1. The present invention utilizes the high activity of the low coordination site in the platinum-carbon catalyst and uses it as the modification center. After the low coordination site is fully exposed through reduction activation, a passivating agent is introduced to selectively passivate it. This can accurately inhibit the activity of the low coordination site of the platinum particles in the platinum-carbon catalyst and improve the stability of the platinum-carbon catalyst. The operation is simple and can be mass-produced.

[0027] 2. When the initial platinum-carbon catalyst is pretreated, including the low-temperature hot pickling process and the low-temperature reduction process under inert gas protection, the low-coordination sites on the surface of the platinum particles attached by pollutants can be fully exposed and activated without causing sintering of the platinum particles. Specifically, the inert gas ensures that the surface of the platinum particles will not be oxidized and contaminated during the entire pickling process; if the pickling temperature is too low, the subsequent exposure of the low-coordination sites due to the attachment of impurities will not be thorough; and if the pickling temperature is too high, it will not only destroy the active sites on the surface of the platinum particles, but also corrode the carbon carrier, significantly affecting the stability of the platinum-carbon catalyst. Setting a reduction temperature of 200 to 500°C can ensure the full exposure of the low-coordination sites on the platinum particles, while avoiding the sintering and agglomeration of the platinum particles caused by excessively high temperatures, which reduces the electrochemical active area.

[0028] 3. When selectively passivating the platinum-carbon catalyst after reduction activation, by setting the temperature range of the source bottle, it can be ensured that the passivating agent precursor enters the furnace chamber in the state of gas, and the temperature of the source bottle is not higher than the temperature of the furnace chamber, so that the passivating agent precursor molecules are completely adsorbed on the fully exposed platinum catalyst sites. At the same time, by setting the furnace chamber temperature, it can be ensured that the passivating agent precursor is rapidly decomposed at the moment of contact with the activator, without damaging the activity of other sites.

[0029] 4. After the low coordination sites are fully exposed through reduction activation, a transition metal or metalloid passivator is introduced to selectively passivate them. By flexibly adjusting the type and amount of the passivator, not only can the stability of the platinum-carbon catalyst be improved, but the introduced transition metal will also form an alloy with platinum, significantly improving the intrinsic activity of the catalyst.

[0030] 5. In addition to selectively modifying and passivating the highly active low-coordination sites on the fully exposed platinum-carbon catalyst, the passivator will also be deposited at the contact interface between the platinum particles and the carbon carrier. When subjected to high-temperature thermal reduction at 500 to 800°C, the passivator at the interface will further inhibit the migration of the particles and the sintering growth between the particles through strong interactions with the platinum particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of a method for selectively passivating a platinum-carbon catalyst with a low coordination site according to an embodiment of the present invention;

[0032] Figure 2 A passivation reaction fixture according to an embodiment of the present invention;

[0033] Figure 3 (a) and (b) are cyclic voltammetry curves and polarization curves of the boron-modified platinum-carbon catalyst before and after the catalyst stability in Example 4 of the present invention;

[0034] Figure 4 (a) and (b) show the effect of different heat treatment temperatures on the crystal structure of the boron-modified platinum-carbon catalyst and the thermal sintering inhibition mechanism of interfacial boron in Examples 4-6 of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] The present invention provides a method for selectively passivating a low-coordination site platinum-carbon catalyst modification, such as Figure 1 As shown, the following steps are included:

[0037] S1. The initial platinum-carbon catalyst is subjected to acid washing and reduction activation pretreatment to fully expose the low coordination sites on the platinum particles.

[0038] Specifically, the initial platinum-carbon catalyst is a commercialized platinum-carbon catalyst product currently sold on the market for use in fuel cells, and its platinum loading is generally between 10% and 60%.

[0039] Furthermore, the initial platinum-carbon catalyst is pickled to remove various impurities attached thereto. Pickling specifically includes: placing the initial platinum-carbon catalyst powder in a hot dilute acid solution saturated with an inert gas. The hot dilute acid solution is one or more of hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid solutions with a temperature of 30 to 100°C and a concentration of 0.01 to 1.0 mol / L. The inert gas is one or more of nitrogen, argon, and helium. To achieve saturation, the inert gas must be continuously introduced into the solution during the entire pickling process and kept below the liquid level.

[0040] Furthermore, the reduction activation pretreatment specifically includes: placing the initial platinum carbon catalyst in a tubular furnace and heat treating it in a reducing atmosphere, which can not only achieve reduction activation, but also purge and strip off some impurities adsorbed on the surface of the platinum particles. The reducing atmosphere is pure hydrogen or a hydrogen-argon mixture with a concentration of 1% to 30%; the heat treatment temperature is 200 to 500°C.

[0041] S2, adsorbing the passivating agent precursor on the exposed low-coordination site, and then converting the passivating agent precursor on the low-coordination site into a passivating agent by an activator to obtain a passivating agent-modified platinum-carbon catalyst precursor;

[0042] Furthermore, step S2 specifically includes the following steps:

[0043] S21, placing the activated platinum-carbon catalyst into a fixture with both ends closed by steel wire filters, and then placing the fixture into the tubular furnace cavity;

[0044] S22, evacuating the furnace chamber, and introducing fluidizing gas from the bottom of the fixture to fluidize and suspend the platinum-carbon catalyst in the fixture, while heating the furnace chamber and the source bottle containing the passivating agent precursor;

[0045] S23, after the furnace chamber and the source bottle are raised to the set temperature, the source bottle is opened, and the passivation agent precursor enters the furnace chamber and the fixture in turn under the action of the carrier gas and vacuum, and is selectively adsorbed on the low-coordination sites of the platinum particles that have been fully exposed in the platinum-carbon catalyst, and the excess unadsorbed passivation agent precursor is extracted from the furnace chamber;

[0046] S24, introducing an activator into the furnace cavity to convert the passivator precursor adsorbed on the low coordination site into a stable passivator, and the excess activator is drawn out of the furnace cavity;

[0047] S25, using the same passivating agent precursor or changing the type of the passivating agent precursor, repeating steps S23 and S24, to obtain platinum-carbon catalyst precursors modified with different types and amounts of passivating agents.

[0048] Furthermore, the pore size of the wire filter is 300 to 30,000 meshes, the diameter and height ratio of the clamp is between 0.2 and 2, the diameter and height ratio of the tubular furnace chamber is between 0.2 and 2, and the diameter of the clamp is smaller than the diameter of the tubular furnace chamber.

[0049] Furthermore, in step S22, the furnace chamber is evacuated by a vacuum pump, and the background vacuum degree is 1-100 Pa; one or more of the fluidizing gases nitrogen, argon, and helium are introduced, and the flow rate is 10-2000 ccm.

[0050] Furthermore, in step S23, the set temperature of the furnace chamber is 25-300°C, and the set temperature of the source bottle is 25-200°C; and the set temperature of the source bottle is not higher than the set temperature of the furnace chamber.

[0051] Further, in step S23, the carrier gas is one or more of nitrogen, argon, and helium, and the flow rate is 1 to 1000 ccm.

[0052] Furthermore, in step S24, the flow rate of the activating agent is 10 to 2000 ccm, and the single duration is 1 to 600 s.

[0053] Furthermore, the passivator precursor is one or more of a compound containing a transition metal and an organic compound containing a metalloid, and the compound containing a transition metal may be an organic complex containing a transition metal. The passivator is an oxide, hydroxide, carbon oxide, etc. produced after the decomposition of the passivator precursor. The transition metal is iron, cobalt, nickel, tin, manganese, titanium, zinc or gallium; the metalloid is boron, silicon, germanium, arsenic, antimony or tellurium, preferably boron.

[0054] The activator is one or more of oxygen, ozone, hydrogen peroxide, water, hydrogen, and carbon monoxide; preferably, when the set temperature of the furnace chamber is 160-300°C, the activator is hydrogen and / or carbon monoxide to avoid oxidation of the carbon carrier when the furnace chamber temperature is too high during the treatment process.

[0055] S3. Heat-treating the platinum-carbon catalyst precursor in a reducing atmosphere to restore activity at sites other than the low-coordination sites, thereby obtaining a platinum-carbon catalyst.

[0056] Further, in step S3, the platinum-carbon catalyst precursor is placed in a tubular furnace and heat-treated in a reducing atmosphere, wherein the reducing atmosphere is pure hydrogen, pure ammonia, a hydrogen-argon mixture or an ammonia-argon mixture with a concentration of 1% to 30%; the heat treatment temperature is 500 to 800°C.

[0057] The following are specific embodiments:

[0058] Example 1

[0059] A method for selectively passivating platinum low coordination sites in a platinum-carbon catalyst comprises the following steps:

[0060] S1. A commercial platinum-carbon catalyst with a platinum content of 20% is first hot pickled with dilute sulfuric acid, and then pre-treated with reduction activation in a 10% hydrogen-argon mixture at 200°C to fully expose the low coordination sites on the platinum particles, wherein the concentration of the dilute sulfuric acid is 0.5 mol / L, the temperature is 60°C, and the pickling process is carried out in an argon atmosphere.

[0061] S21, placing the activated commercial platinum-carbon catalyst into a fixture with a width-to-length ratio of 0.5, which is closed at both ends by a 3000-mesh steel wire filter, and then placing the fixture into a tubular furnace cavity with a width-to-length ratio of 0.8;

[0062] S22, evacuate the furnace chamber to 5 Pa, and introduce nitrogen gas at a rate of 200 ccm from the bottom of the fixture to fluidize and suspend the commercial platinum-carbon catalyst in the fixture, and heat the furnace chamber and the source bottle containing the titanium passivating agent precursor 4,2-methylamidotitanium to 160° C. and 60° C. respectively;

[0063] S23, when the furnace chamber and the source bottle are raised to the set temperature, the source bottle is opened, and the titanium passivation agent precursor 4,2-methylamidotitanium enters the furnace chamber and the fixture in turn under the action of 100ccm nitrogen and vacuum, and is selectively adsorbed on the low-coordination sites of the platinum particles that have been fully exposed in the catalyst, and the excess unadsorbed 4,2-methylamidotitanium precursor is extracted from the furnace chamber;

[0064] S24, oxygen is introduced into the furnace chamber at a rate of 500 ccm to convert the 4,2-methylaminotitanium precursor adsorbed on the low coordination site into a stable titanium oxide compound, and excess oxygen activator is extracted from the furnace chamber.

[0065] S3. The obtained titanium oxide-modified platinum-carbon catalyst precursor is placed in a tubular furnace, heated to 600° C. in a 5% ammonia-helium atmosphere, and cooled to obtain a highly stable commercial platinum-carbon catalyst modified with titanium nitride.

[0066] Example 2

[0067] A method for selectively passivating platinum low coordination sites in a platinum-carbon catalyst comprises the following steps:

[0068] S1. The commercial platinum-carbon catalyst with a platinum content of 20% is first hot pickled with dilute sulfuric acid, and then pre-treated with reduction activation at 10% hydrogen-argon mixed gas at 350°C to fully expose the low coordination sites on the platinum particles, wherein the concentration of the dilute sulfuric acid is 0.5 mol / L, the temperature is 60°C, and the pickling process is carried out in an argon atmosphere.

[0069] The subsequent steps are consistent with Example 1, except that the activator in S24 is replaced by ozone. The 4,2-methylaminotitanium precursor is rapidly converted into a stable titanium oxide compound after contacting water, and the excess ozone is extracted from the furnace chamber.

[0070] Example 3

[0071] A method for selectively passivating platinum low coordination sites in a platinum-carbon catalyst comprises the following steps:

[0072] S1. A commercial platinum-carbon catalyst with a platinum content of 20% is first hot pickled with dilute sulfuric acid, and then pre-treated with reduction activation in a 10% hydrogen-argon mixture at 500°C to fully expose the low coordination sites on the platinum particles, wherein the concentration of the dilute sulfuric acid is 0.5 mol / L, the temperature is 60°C, and the pickling process is carried out in an argon atmosphere.

[0073] The subsequent steps are consistent with Example 1, except that the activator in S24 is replaced by water. The 4,2-methylaminotitanium precursor is rapidly converted into a stable titanium hydroxide upon contact with water, and excess water is pumped out of the furnace chamber.

[0074] For Examples 1-3, when the reduction temperature of step S1 is 200°C, 350°C, and 500°C, the corresponding final products have average platinum particle sizes of 2.12nm, 2.21nm, and 2.25nm, respectively, and the grain size growth of the platinum catalyst is limited. It can be seen that the appropriate reduction temperature can not only maintain a high exposure rate of low coordination sites, but also effectively avoid thermal sintering of the platinum catalyst. At the three reduction temperatures and different activators, 4,2-methylamidotitanium can be finally converted into titanium oxide to modify the high-activity low coordination sites on the platinum-carbon catalyst.

[0075] Example 4

[0076] A method for selectively passivating platinum low coordination sites in a platinum-carbon catalyst comprises the following steps:

[0077] S1. The commercial platinum-carbon catalyst with a platinum content of 40% is first hot pickled with dilute sulfuric acid, and then pre-treated with reduction activation at 300°C in a 10% hydrogen-argon mixture to fully expose the low coordination sites on the platinum particles, wherein the concentration of the dilute sulfuric acid is 0.5 mol / L, the temperature is 60°C, and the pickling process is carried out in an argon atmosphere.

[0078] S21, placing the activated commercial platinum-carbon catalyst into a fixture with a width-to-length ratio of 0.5, which is closed at both ends by a 3000-mesh steel wire filter, and then placing the fixture into a tubular furnace cavity with a width-to-length ratio of 0.8;

[0079] S22, evacuate the furnace chamber to 5 Pa, and introduce nitrogen gas at a rate of 200 ccm from the bottom of the fixture to fluidize and suspend the commercial platinum-carbon catalyst in the fixture, heat the furnace chamber to 120° C., and do not heat the source bottle;

[0080] S23, when the furnace chamber rises to the set temperature, the source bottle containing trimethyl borate is opened, and the boron passivation agent precursor trimethyl borate enters the furnace chamber and the fixture in turn under the action of vacuum, and is selectively adsorbed on the low-coordination sites of platinum particles that have been fully exposed in the catalyst, and the excess unadsorbed trimethyl borate precursor is extracted from the furnace chamber;

[0081] S24, oxygen is introduced into the furnace chamber at a rate of 200 ccm to convert the trimethyl borate precursor adsorbed on the low coordination site into a stable boron oxide compound, and excess oxygen activator is extracted from the furnace chamber;

[0082] S25. Repeat steps S23 and S24 five times to obtain a platinum-carbon catalyst precursor passivated with boron oxide having a boron content of 3%.

[0083] S3. The obtained boron oxide-modified platinum-carbon catalyst precursor is placed in a tubular furnace, heated to 500° C. in a 10% hydrogen-argon atmosphere, and cooled to obtain a highly stable boron-modified commercial platinum-carbon catalyst.

[0084] like Figure 3 As shown in the figure, the stability of the platinum-carbon catalyst is significantly improved after boron modification, which is specifically manifested in that the area of ​​the electrochemical active area marked by the dotted box in the cyclic voltammetry curve diagram is significantly reduced after the use of boron-modified Pt / CB than after the use of unmodified Pt / C; the half-wave potential of the electrochemical current marked by the dotted arrow in the polarization curve diagram is significantly shifted to the left after the use of boron-modified Pt / CB than after the use of unmodified Pt / C.

[0085] Example 5

[0086] A method for selectively passivating platinum low coordination sites in a platinum-carbon catalyst, the main steps of which are consistent with Example 4, except that the heating temperature in S3 is changed to 800°C.

[0087] Example 6

[0088] A method for selectively passivating platinum low coordination sites in a platinum-carbon catalyst, the main steps of which are consistent with Example 4, except that the heating temperature in S3 is changed to 700°C.

[0089] For Examples 4-6, Figure 4 As shown, the XRD main peaks of the corresponding platinum-carbon catalysts at different heat treatment temperatures have hardly changed significantly, indicating that the grain size of platinum is extremely stable within 500-800°C, proving that boron modification can not only improve the electrochemical corrosion resistance of platinum-carbon catalysts, but also significantly inhibit the thermal sintering of platinum particles during high-temperature thermal reduction treatment, which is due to the strong interaction between the excess boron and the platinum particles at the interface between the platinum particles and the carbon carrier.

[0090] Example 7

[0091] A method for selectively passivating platinum low coordination sites in a platinum-carbon catalyst comprises the following steps:

[0092] S1. The commercial platinum-carbon catalyst with a platinum content of 20% is first hot pickled with dilute nitric acid, and then pre-treated with reduction activation at 400°C in a 10% hydrogen-argon mixture to fully expose the low coordination sites on the platinum particles, wherein the concentration of the dilute nitric acid is 0.2 mol / L, the temperature is 80°C, and the pickling process is carried out in an argon atmosphere.

[0093] S21, placing the activated commercial platinum-carbon catalyst into a fixture with a width-to-length ratio of 0.5, which is closed at both ends by a 3000-mesh steel wire filter, and then placing the fixture into a tubular furnace cavity with a width-to-length ratio of 0.8;

[0094] S22, evacuate the furnace chamber to 5 Pa, and introduce nitrogen gas at a rate of 200 ccm from the bottom of the fixture to fluidize and suspend the commercial platinum-carbon catalyst in the fixture, heat the furnace chamber to 180° C., and heat the source bottle to 80° C.;

[0095] S23, when the furnace chamber is heated to the set temperature, the source bottle containing tetrakis(dimethylamino)tin is opened, and the tin passivation agent precursor tetrakis(dimethylamino)tin enters the furnace chamber and the fixture in turn under the action of vacuum, and is selectively adsorbed on the low-coordination sites of platinum particles that have been fully exposed in the catalyst, and the excess unadsorbed tetrakis(dimethylamino)tin precursor is extracted from the furnace chamber;

[0096] S24, hydrogen is introduced into the furnace chamber at a rate of 200 ccm to convert the tetrakis(dimethylamino)tin precursor adsorbed on the low coordination site into single tin. Meanwhile, hydrogen can prevent the carbon carrier from being oxidized at high temperature, and excess hydrogen is extracted from the furnace chamber;

[0097] S25, repeating steps S23 and S24 several times to obtain a platinum-carbon catalyst precursor passivated with a specific content of tin;

[0098] S3. The obtained tin-modified platinum-carbon catalyst precursor is placed in a tubular furnace, heated to 600° C. in a 10% hydrogen-argon atmosphere, and cooled to obtain a highly stable tin-modified commercial platinum-carbon catalyst.

[0099] Example 8

[0100] A method for selectively passivating low-coordination sites of platinum in a platinum-carbon catalyst, the main steps of which are consistent with Example 7, except that the activator in S24 is replaced with weakly oxidizing carbon monoxide, which can reduce tetrakis(dimethylamino)tin to a divalent intermediate tin without oxidizing the carbon carrier.

[0101] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for selectively passivating a low-coordination site platinum-carbon catalyst modification, characterized in that: The steps include: S1, heat treating the initial platinum-carbon catalyst in a reducing atmosphere to achieve reduction activation and fully expose the low coordination sites on the platinum particles; S2, adsorbing the passivating agent precursor on the exposed low-coordination site, and then converting the passivating agent precursor on the low-coordination site into a passivating agent by an activator to obtain a passivating agent-modified platinum-carbon catalyst precursor; S3. Heat-treating the platinum-carbon catalyst precursor in a reducing atmosphere to obtain a platinum-carbon catalyst.

2. The method for selectively passivating a low-coordination site platinum-carbon catalyst modification according to claim 1, characterized in that: In step S1, the reducing atmosphere is hydrogen or a hydrogen-argon mixture with a concentration of 1% to 30%; the heat treatment temperature is 200 to 500°C.

3. The method for selectively passivating a low-coordination site platinum-carbon catalyst modification according to claim 1, characterized in that: In step S1, before the initial platinum-carbon catalyst is heat-treated in a reducing atmosphere, the process further comprises: The initial platinum-carbon catalyst is firstly acid washed.

4. The method for selectively passivating a low-coordination site platinum-carbon catalyst modification according to claim 3, characterized in that: The acid washing of the initial platinum-carbon catalyst comprises: placing the initial platinum-carbon catalyst in a hot dilute acid solution saturated with an inert gas; the hot dilute acid solution is one or more of hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid solutions with a temperature of 30 to 100° C. and a concentration of 0.01 to 1.0 mol / L.

5. The method for selectively passivating a low-coordination site platinum-carbon catalyst modification according to claim 1, characterized in that: Step S2 specifically includes the following steps: Place the reduced activated platinum carbon catalyst into a fixture with two ends closed by filters, and then place the fixture into the furnace chamber; The furnace chamber is evacuated, and a fluidizing gas is introduced from the bottom of the fixture to fluidize and suspend the platinum-carbon catalyst in the fixture; The furnace chamber and the source bottle containing the passivation agent precursor are raised to a set temperature, and then the passivation agent precursor enters the fixture and is selectively adsorbed on the exposed low-coordination sites; Then, an activator is introduced into the fixture to convert the passivating agent precursor adsorbed on the low coordination site into a stable passivating agent.

6. The method for selectively passivating a low-coordination site platinum-carbon catalyst modification according to claim 5, characterized in that: The set temperature of the furnace cavity is 25-300° C., and the set temperature of the source bottle is 25-200° C.; and the set temperature of the source bottle is not higher than the set temperature of the furnace cavity.

7. The method for selectively passivating a low-coordination site platinum-carbon catalyst modification according to claim 1, characterized in that: The passivator precursor is one or more of a compound containing a transition metal and an organic compound containing a metalloid; the activator is one or more of oxygen, ozone, hydrogen peroxide, water, hydrogen, and carbon monoxide; and the passivator is an oxide, hydroxide, or carbon oxide produced by decomposition of the passivator precursor.

8. The method for selectively passivating a low-coordination site platinum-carbon catalyst modification according to claim 7, characterized in that: The activator is hydrogen and / or carbon monoxide, and the metalloid is boron.

9. The method for selectively passivating a low-coordination site platinum-carbon catalyst modification according to any one of claims 1 to 8, characterized in that: In step S3, the reducing atmosphere is hydrogen, ammonia, a hydrogen-argon mixture or an ammonia-argon mixture, with a concentration of 1% to 30%; and the heat treatment temperature is 500 to 800°C.

10. A platinum-carbon catalyst, characterized in that The catalyst is obtained by using the platinum-carbon catalyst modification method for selectively passivating low coordination sites as described in any one of claims 1 to 9.

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