A carbon-supported metal catalyst for low-temperature hydrogen reduction of N2O and its application

Abstract

The invention discloses a carbon-supported metal catalyst for reducing N2O at low temperature with hydrogen and its application, and belongs to the field of air pollution control. The method uses H2 as a reducing agent, uses commercial activated carbon or coconut shell carbon to load metal nitrate, so that the load of metal is about 3 10wt.%;After the mixture is dissolved and dried by deionized water, it is calcined under N2 atmosphere, and then the metal active phase is reduced to a simple state under H2 atmosphere, so that it has reaction activity, and the preparation of the catalyst is completed;Then, in H2 atmosphere, the medium and low temperature (40 200 DEG C) reduction of N2O is realized. The catalyst efficiency of the present invention is high, and the activated carbon surface after the metal Ni load can reach 90% N2O removal rate under the conditions of 160 DEG C, and is low in price, effectively reducing the reduction cost of N2O, and the reaction products are all environmentally friendly (H2O and N2), without secondary pollution, and the catalyst life is longer.

Description

Technical Field

[0001] The present invention relates to the technical field of air pollution purification, and in particular to a carbon-supported metal catalyst for low-temperature hydrogen reduction of N2O and applications thereof. Background Art

[0002] Currently NO x The main emission has gradually changed from being dominated by industrial sources to being dominated by both industrial sources and motor vehicles. On the one hand, the detection method of N2O in automobile exhaust focuses more on the emission of the engine under low speed and low load conditions (low exhaust temperature). On the other hand, the industrial sources are generally used to reduce NO x The SCR device is placed after the dust collector. The flue gas temperature entering the SCR device is typically between 100°C and 300°C. Reducing N2O at this flue gas temperature can save energy. Therefore, the development of high-efficiency, low-temperature denitrification catalysts is crucial for both mobile and stationary sources.

[0003] Current N2O decomposition catalysts are primarily categorized as precious metals, metal oxides, and zeolite-based catalysts. Precious metals are primarily used in nitric acid production and automobile exhaust emissions. They exhibit excellent catalytic performance at the lowest catalytic temperatures, between 240 and 320°C, but are expensive. A wide variety of metal oxide catalysts are widely used for N2O removal due to their low cost and excellent thermal stability. However, compared to precious metals, they require higher catalytic temperatures, achieving a 50% N2O reduction rate at approximately 300 to 500°C.

[0004] However, the catalytic reduction effects of both precious metals and metal oxides are significantly affected by the presence of O2 and H2O in the environment. Molecular sieve catalysts can be used in the petrochemical and acid industries and exhibit good environmental tolerance. When O2 is present in the reactor, the reduction efficiency of N2O is not significantly affected. However, they are expensive, the preparation process is complex, and the reduction temperature is generally high (T 50 Approximately between 400 and 650°C).

[0005] Since precious metals, metal oxides, and zeolite-based catalysts all have their own shortcomings, technicians need to find a new type of catalyst for reducing N2O. Carbon-based materials have been widely used in the adsorption and reduction of atmospheric pollutants in recent years due to their advantages such as low price, loose and porous surface, ability to form a dispersed catalyst active phase, and ability to recover active substances on their surface after the reaction. They are a viable alternative to existing catalytic carriers. Loading metals as active phases on carbon-based materials can greatly promote their catalytic ability to reduce N2O. However, at present, it is still unclear what kind of metals can achieve excellent catalytic effects on carbon-based materials. Loading precious metals on the carrier surface as active phases is still the main research content, which has seriously affected the development of N2O reduction catalysts.

[0006] In addition to factors inherent to the catalyst itself, the reaction atmosphere also significantly influences the N2O reduction process. During the N2O reduction process, the remaining oxygen atoms after the N2 is released from the catalyst surface occupy active sites on the surface, leading to catalyst deactivation. Selective catalytic reduction (SCR) technology may be a promising strategy to address this issue.

[0007] In practical applications and laboratory studies, the reducing agents commonly used in SCR solutions include H2, CO, HC x and NH3. CO, HC x Reducing agents such as CO or NH3 help remove surface oxygen species produced during the decomposition of N2O adsorbed on surface active sites. Currently, CO and NH3 dominate as reducing agents, but they have obvious shortcomings in practical applications, such as ammonia leakage, air heater fouling, catalyst poisoning, and high operating costs.

[0008] In contrast, hydrogen energy has become the clean energy with the greatest development potential in the world due to its advantages of being green, efficient and having a wide range of applications. As a non-toxic gas, H2 can selectively catalyze the reduction of NO x This green technology can be used for both stationary and mobile exhaust at low temperatures (<200°C). Compared to other reducing agents, H2 requires the lowest reaction temperature. Combustion of H2 in air produces H2O without CO2, resulting in no secondary pollution and a more environmentally friendly approach.

[0009] However, as a reducing agent in the SCR process, H2's current research focus remains on its ability to reduce NO. Research on H2's catalytic reduction of N2O is very limited, which also restricts related research on low-temperature N2O reduction.

[0010] In view of this, in order to realize the widespread application of N2O reduction technology, it is necessary to further explore low-temperature, high-efficiency and low-cost catalysts. Summary of the Invention

[0011] To address the aforementioned issues in the prior art, the present invention provides a carbon-supported metal catalyst for low-temperature hydrogen reduction of N2O and its application. The catalyst is highly efficient, with the activated carbon surface loaded with Ni metal achieving a 90% N2O removal rate at 160°C. Furthermore, it is inexpensive, effectively reducing the cost of N2O reduction. The reaction products (H2O and N2) are environmentally friendly, eliminating secondary pollution, and offer a long catalyst life.

[0012] The technical solutions of the present invention are as follows:

[0013] A carbon-based metal catalyst for low-temperature hydrogen reduction of N2O, wherein the catalyst is a metal-loaded carbon-based material, and the mass fraction of the metal element in the catalyst is 3-10 wt.%;

[0014] The preparation method of the catalyst is as follows:

[0015] S1. Dilute the modifier and immerse it in a 10-24 mesh carbon-based material, stir it magnetically at room temperature to ensure full contact, and remove impurities in the carbon-based material; then dry it in an oven overnight; after drying, wash the carbon-based material with deionized water to remove excess modifier until the washing water is neutral; and dry it in an oven overnight to obtain a catalyst precursor HNO3-Char;

[0016] S2. Dissolving a metal nitrate in deionized water at ambient temperature, then adding HNO3-Char to the aqueous solution of the metal nitrate to a metal loading of 3-10 wt.%; then magnetically stirring the mixture at room temperature to ensure full contact, and drying the mixed solution at room temperature;

[0017] S3. The obtained solid sample was calcined in a N2 atmosphere at 400°C for 2 hours; the calcined sample was then reduced at a H2 flow rate of 200 ml / min for 2 hours, and the reduction temperature was 250°C; the obtained catalysts were represented by Metal-char according to the different loaded metals.

[0018] Preferably, the supported metal is an alkali metal or a transition metal.

[0019] More preferably, the supported metal includes K, Ca, Na, Fe, Co, Ni or Cu.

[0020] Preferably, the carbon-based material in step S1 includes activated carbon or coconut shell carbon; impurities present in the activated carbon in step S1 include metals, minerals, etc.

[0021] Preferably, the modifier in step S1 is pure nitric acid reagent.

[0022] Preferably, the operation method of step S2 is: take 8 g of HNO3-Char material each time, calculate the mass of metal nitrate corresponding to the required metal loading amount, and dissolve it in 100 ml of deionized water.

[0023] The present invention also provides an application method of the catalyst, which comprises placing the catalyst in an environment containing N2O gas, introducing H2 or N2 atmosphere at a temperature of 40 to 200°C, thereby reducing N2O to H2O and N2.

[0024] Preferably, when H2 is used for catalytic reduction of N2O, the total gas flow rate is 3.2 L / min, wherein H2 is 2000 ppm, N2O is 400 ppm, and the rest is N2 as the balance gas.

[0025] The beneficial technical effects of the present invention are:

[0026] 1. Currently, research on catalyst supports for decomposing N2O mostly focuses on precious metals, metal oxides, and zeolite-based catalysts. In comparison, coal-based activated carbon is inexpensive, loose and porous, and has excellent catalytic performance. It is a good catalyst support and has good performance in reducing NO. Therefore, the present invention focuses on the efficiency of carbon-based materials in reducing N2O.

[0027] 2. Loading transition metals on the catalyst surface can also have a good promoting effect, but there is still no accurate conclusion as to which type of transition metal can achieve the best promoting effect. Currently, most metals used as active phases are precious metals, which are expensive. Therefore, based on the reduction of N2O by coal-based activated carbon, the present invention loads transition metals and alkali metals on its surface to promote its catalytic effect.

[0028] 3. CO and HC in SCR technology x The inevitable escape of gases such as NO and NH3 will cause air pollution. In contrast, hydrogen energy has become the world's most promising clean energy source with its advantages of being green, efficient, and having a wide range of applications. H2 is a non-toxic gas that can be easily obtained from exhaust gas streams. Moreover, the oxidation product of H2 is eco-friendly, namely H2O, which can meet the requirements of carbon peak and carbon neutrality. Therefore, in the present invention, in an atmosphere of H2, by loading transition metals on coal-based activated carbon, catalytic reduction of N2O is carried out. This reaction condition exhibits excellent low-temperature denitrification, which provides technical guidance for the removal of N2O in actual industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the N2O removal efficiency of a carbon-based catalyst loaded with 3 wt.% transition metal in a H2 atmosphere;

[0030] Figure 2 The effect of the presence of H2 on the efficiency of N2O reduction by carbon-based catalysts;

[0031] Figure 3 The effect of the presence of carbon-based catalysts on the efficiency of H2 reduction of N2O;

[0032] Figure 4 Schematic diagram of the N2O removal efficiency of a carbon-based catalyst loaded with 3 wt.% alkali metal in a H2 atmosphere. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the accompanying drawings and embodiments. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, rather than all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0034] The raw materials used in the present invention are all purchased from the market, and the carbon-based material is commercial activated carbon or coconut shell carbon.

[0035] Example 1:

[0036] This embodiment provides several carbon-supported metal catalysts, and the preparation methods are as follows:

[0037] S1. Carbon Material: Commercial coconut shell carbon (10-24 mesh) was used. Pure nitric acid was diluted to 5 wt.% and then impregnated into the carbon material at a ratio of 10 g / ml. The carbon material was magnetically stirred at room temperature to ensure full contact. The activated carbon was then oven-dried overnight. After drying, the activated carbon was rinsed with deionized water to remove excess modifier until the wash water was neutral. The catalyst precursor, HNO3-Char, was obtained by oven-drying overnight.

[0038] S2. At ambient temperature, a predetermined mass of transition metal (Fe, Co, Ni, Cu) nitrate was dissolved in a predetermined amount of deionized water. A predetermined amount of HNO3-Char was then added to the solution, and the corresponding mass of metal nitrate was calculated with a target metal loading of 3 wt.%. The mixture was magnetically stirred at room temperature to ensure full contact, and the mixed solution was dried at room temperature.

[0039] S3. The obtained solid sample was calcined at 400° C. in a 400 ml / min N2 atmosphere for 2 hours to promote the interaction between the metal component and the carbon-based material support. The calcined sample was then reduced at a H2 flow rate of 200 ml / min for 2 hours at a reduction temperature of 250° C. The obtained catalysts are represented by "Metal-char" in the present invention according to the different supported metals. Thus, a selective catalytic reduction catalyst for NO was obtained.

[0040] The experimental system includes a furnace, temperature control system, gas distribution system, and flue gas analysis system. 2g of Metal-Char was placed in the reactor. The reaction gas mass flow was controlled to maintain a concentration of 400ppm N2O and 2000ppm H2. Ordinary nitrogen (N2) was used as the balance gas. These were evenly mixed and measured by a mass flow meter to create a simulated flue gas. The total reaction gas flow rate was 3.2L / min.

[0041] The simulated flue gas is passed through a vertically positioned reactor, which is heated in a furnace at a program-controlled temperature. The simulated flue gas enters the reactor tube, flows over the catalyst, and undergoes a N2O removal reaction at a constant temperature. After the reaction, the gas exits the reactor and is passed through a Gasmat for gas composition measurement. The N2O removal rate is calculated using the following equation:

[0042]

[0043] The reaction temperature was controlled in the range of 40-200°C, and the N2O removal rate corresponding to each 10°C increase in temperature was recorded.

[0044] The results show that the reaction rate of H2 reduction of N2O catalyzed by metal-loaded carbon-based materials is significantly improved. The detailed relationship between the reduction efficiency and temperature and the error bars are given by Figure 1 It is shown that the N2O reduction rate can reach more than 90% at 190℃.

[0045] The reaction's starting temperature was significantly reduced. When the Ni- and Co-loaded carbon-based materials catalyzed the reduction of N2O with H2, N2O reduction rates of 30% and 20% were achieved at 40°C. The corresponding temperatures for 50% N2O reduction dropped to between 90 and 140°C, respectively. The loading of different transition metals promoted the reaction differently, in the order of Ni-char > Co-char > Fe-char > Cu-char. No NO production was detected during the reaction, demonstrating the high selectivity of N2 during the N2O reduction process and avoiding secondary pollution caused by NO generation.

[0046] Comparative Example 1:

[0047] The reaction rate of reducing N2O by carbon-based materials without metal loading in H2 atmosphere was experimentally determined as a control group.

[0048] The selective catalytic reduction of N2O catalyst is prepared by the following process:

[0049] Commercial coconut shell carbon (10-24 mesh) was used as the carbon material. Pure nitric acid was diluted to 5 wt.% and then impregnated into the carbon material at a ratio of 10 g / ml. The mixture was magnetically stirred at room temperature to ensure full contact and then oven-dried overnight. After drying, the activated carbon was rinsed with deionized water to remove excess modifier until the wash water was neutral. The catalyst precursor, HNO3-Char, was obtained by oven-drying overnight.

[0050] The experimental system includes a furnace, temperature control system, gas distribution system, and flue gas analysis system. 2g of HNO3-Char was placed in the reactor. The reaction gas mass flow was controlled to maintain a concentration of 400ppm N2O and 2000ppm H2. Ordinary nitrogen (N2) was used as the balance gas. These were evenly mixed and measured by a mass flow meter to create a simulated flue gas. The total reaction gas flow rate was 3.2L / min.

[0051] The simulated flue gas was introduced into a vertically positioned reactor, which was heated in a furnace at a program-controlled temperature. The simulated flue gas entered the reactor tube, passed over the catalyst, and then underwent a NO removal reaction at a constant temperature. After the reaction, the gas exited the reactor and was passed through a Gasmat for gas composition analysis. The NO removal rate was calculated using the formula in Example 1.

[0052] The reaction temperature was controlled in the range of 40-200°C, and the N2O removal rate corresponding to each 10°C increase in temperature was recorded.

[0053] The results show that when the carbon-based catalyst is treated only with HNO3 without modifying the metal active phase (HNO3-char), and when the reaction gas contains 2000 ppm of H2, N2O reduction can only be carried out at medium and high temperature stages, and there is basically no reducing ability below 300°C, indicating that the energy barrier of the reaction is high and a large amount of energy is required to reduce N2O.

[0054] The N2O reduction rate increases rapidly in the process of 300℃~400℃. At 400℃, 60% of N2O can be reduced, and at 500℃, 95% of N2O can be reduced. The detailed relationship between reduction efficiency and temperature is shown in Figure 2 This comparative example shows the effect of reducing N2O in the presence of a carbon-based catalyst without metal modification and H2 reducing agent, and serves as a control group for the following examples.

[0055] Comparative Example 2:

[0056] The reaction rate of reducing N2O by carbon-based materials without metal loading in N2 atmosphere was experimentally determined as a control group.

[0057] The selective catalytic reduction of N2O catalyst is prepared by the following process:

[0058] Using commercial coconut shell carbon (10-24 mesh), pure nitric acid was diluted to 6 wt.% and then impregnated into the carbon material at a ratio of 10 g / ml. The carbon was then magnetically stirred at room temperature to ensure thorough contact and oven dried overnight. After drying, the activated carbon was rinsed with deionized water to remove excess modifier until the wash water was neutral. The catalyst precursor, HNO3-Char, was obtained by oven drying overnight.

[0059] The experimental system and method were the same as those in Comparative Example 1. 2g of HNO3-Char was placed in the reactor. The mass flow rate of the reaction gas was controlled to maintain a gas concentration of 400ppm of N2O. The remainder was ordinary nitrogen (N2). After uniform mixing and metering using a mass flow meter, the simulated flue gas was prepared. The total reaction gas flow rate was 3.2L / min.

[0060] The simulated flue gas was introduced into a vertically positioned reactor, which was heated in a furnace at a program-controlled temperature. The simulated flue gas entered the reactor tube, passed over the catalyst, and then underwent a NO removal reaction at a constant temperature. After the reaction, the gas exited the reactor and was passed through a Gasmat for gas composition analysis. The NO removal rate was calculated using the formula in Example 1.

[0061] The results show that the reaction rate of N2O reduction in N2 atmosphere is significantly reduced. At a high temperature of 400℃, only 20% of N2O is reduced. The N2O reduction rate changes little with temperature. At a high temperature of 500℃, about 65% of N2O is reduced. The detailed relationship between reduction efficiency and temperature is shown in Figure 2 This example and comparative example 1 verify each other and can prove the promoting effect of H2 on the N2O reduction process.

[0062] Comparative Example 3:

[0063] The reaction rate of H2 homogeneous reduction of N2O without using a catalyst was experimentally determined as a control group.

[0064] The experimental system and method are the same as those in Comparative Example 1. The mass flow rate of the reaction gas is controlled to ensure a gas concentration of 400 ppm N2O and 2000 ppm H2. The rest is ordinary nitrogen (N2). After uniform mixing and metering by a mass flow meter, the simulated flue gas is prepared. The total flow rate of the reaction gas is 3.2 L / min.

[0065] The simulated flue gas is introduced into a vertically positioned reactor, which is heated in a furnace at a program-controlled temperature. The simulated flue gas enters the reactor tube, where it undergoes a homogeneous reduction of N2O with H2 at a specific temperature. After the reaction, the gas exits the reactor and is passed through a Gasmat for gas composition monitoring. The reaction temperature is controlled within a range of 40-200°C, and the N2O removal rate is recorded for each 10°C increase in temperature.

[0066] The results show that when there is no carbon-based catalyst in the reaction system and H2 and N2O are reduced in the same phase, the reaction is almost impossible to proceed. At 500℃, the N2O reduction rate is always 0. The reaction requires a lot of energy to maintain. At 550℃, only 10% of N2O is reduced. At a high temperature of 600℃, only 20% of N2O is reduced. The detailed relationship between reduction efficiency and temperature is shown in Figure 3 given.

[0067] This comparative example and comparative example 1 verify each other and can prove the promoting effect of carbon-based catalysts on the N2O reduction process. H2 reduction of N2O requires heterogeneous reduction on the surface of carbon-based catalysts, and homogeneous reduction cannot proceed due to the high energy barrier. Therefore, in the process of reducing N2O, H2 and char both play an important promoting role.

[0068] Example 2:

[0069] This embodiment provides several carbon-supported metal catalysts, and the preparation methods are as follows:

[0070] The catalyst precursor HNO3-Char was obtained according to the preparation method of Example 1. At ambient temperature, a certain mass of transition metal (Fe, Co, Ni, Cu) nitrate was dissolved in a certain amount of deionized water. Then, a certain amount of HNO3-Char was added to the solution. The corresponding mass of metal nitrate was calculated with a metal loading of 6 wt.% as the target.

[0071] The mixture was stirred magnetically at room temperature to ensure full contact, and the mixed solution was dried at room temperature. The obtained solid sample was calcined at 400°C in a 400ml / min N2 atmosphere for 2 hours to promote the interaction between the metal component and the carbon-based material support. The calcined sample was then reduced at a flow rate of 200ml / min H2 for 2 hours at a reduction temperature of 250°C. The obtained catalysts are represented by Metal-char in this embodiment according to the different supported metals.

[0072] The experimental system and method were the same as in Example 1. 2 g of Metal-Char was placed in the reactor. The mass flow rate of the reaction gases was controlled to ensure a gas concentration of 400 ppm N₂O and 2000 ppm H₂. Ordinary nitrogen (N₂) was used as the balance gas. These gases were uniformly mixed and measured using a mass flow meter to form a simulated flue gas. The total reaction gas flow rate was 3.2 L / min.

[0073] The simulated flue gas is introduced into a vertically positioned reactor, which is heated in a furnace at a program-controlled temperature. The simulated flue gas enters the reactor tube, flows over the catalyst, and undergoes a NO removal reaction at a constant temperature. After the reaction, the gas exits the reactor and is passed through a Gasmat for gas composition monitoring.

[0074] The reaction temperature was controlled in the range of 40-200°C, and the N2O removal rate corresponding to each 10°C increase in temperature was recorded.

[0075] The results showed that the metal-loaded carbon-based materials significantly increased the reaction rate of H2 reduction of N2O, achieving N2O reduction rates exceeding 90% at 180°C. The increase in metal loading also resulted in a corresponding increase in the reduction rate under the same conditions.

[0076] The starting temperature of the reaction was significantly reduced. When the carbon-based materials loaded with Ni and Co catalyzed the reduction of N2O with H2, the N2O reduction rates reached 35% and 25% at 40°C. The corresponding temperatures for N2O reduction dropped to between 80 and 135°C, respectively. The loading of different transition metals promoted the reaction differently, with the order remaining as Ni-char > Co-char > Fe-char > Cu-char. No NO generation was detected during the reaction, demonstrating the high selectivity of N2 during the N2O reduction process and avoiding secondary pollution caused by NO generation.

[0077] Example 3:

[0078] This embodiment provides several carbon-supported metal catalysts, and the preparation methods are as follows:

[0079] The catalyst precursor HNO3-Char was obtained according to the preparation method of Example 1. At ambient temperature, a certain mass of transition metal (Fe, Co, Ni, Cu) nitrate was dissolved in a certain amount of deionized water. Then, a certain amount of HNO3-Char was added to the solution. The corresponding mass of metal nitrate was calculated with a metal loading of 10 wt.% as the target.

[0080] The mixture was stirred magnetically at room temperature to ensure full contact, and the mixed solution was dried at room temperature. The obtained solid sample was calcined at 400°C in a 400ml / min N2 atmosphere for 2 hours to promote the interaction between the metal component and the carbon-based material support. The calcined sample was then reduced at a flow rate of 200ml / min H2 for 2 hours at a reduction temperature of 250°C. The obtained catalysts are represented by Metal-char in this embodiment according to the different supported metals.

[0081] The experimental system and method were the same as in Example 1. 2 g of Metal-Char was placed in the reactor. The mass flow rate of the reaction gases was controlled to ensure a gas concentration of 400 ppm N₂O and 2000 ppm H₂. Ordinary nitrogen (N₂) was used as the balance gas. These gases were uniformly mixed and measured using a mass flow meter to form a simulated flue gas. The total reaction gas flow rate was 3.2 L / min.

[0082] The simulated flue gas is introduced into a vertically positioned reactor, which is heated in a furnace at a program-controlled temperature. The simulated flue gas enters the reactor tube, flows over the catalyst, and undergoes a NO removal reaction at a constant temperature. After the reaction, the gas exits the reactor and is passed through a Gasmat for gas composition monitoring.

[0083] The reaction temperature was controlled in the range of 40-200°C, and the N2O removal rate corresponding to each 10°C increase in temperature was recorded.

[0084] The results show that the metal-loaded carbon-based materials significantly increase the rate of H2 reduction of N2O, achieving N2O reduction rates exceeding 90% at 175°C. Increasing the metal loading corresponds to a slight increase in the reduction rate under the same conditions, but the change is not significant.

[0085] The starting temperature of the reaction was significantly reduced. When the carbon-based materials loaded with Ni and Co catalyzed the reduction of N2O with H2, the N2O reduction rates reached 35% and 25% at 40°C. The corresponding temperatures for N2O reduction dropped to between 80 and 130°C, respectively. The loading of different transition metals promoted the reaction differently, with the order remaining as Ni-char > Co-char > Fe-char > Cu-char. No NO production was detected during the reaction, demonstrating the high selectivity of N2 during the N2O reduction process and avoiding secondary pollution caused by NO generation.

[0086] Example 4:

[0087] This embodiment provides several carbon-supported metal catalysts, and the preparation methods are as follows:

[0088] The catalyst precursor HNO3-Char was prepared according to the preparation method of Example 1, wherein the carbon-based material was commercial activated carbon. A certain mass of alkali metal (K, Ca, Na) nitrate was dissolved in a certain amount of deionized water at ambient temperature. Subsequently, a certain amount of HNO3-Char was added to the solution. The corresponding mass of metal nitrate was calculated with a target metal loading of 3 wt.%. The resulting catalysts are represented in this example as Metal-Char, depending on the loaded metal.

[0089] The experimental system and method were the same as in Example 1. 2 g of Metal-Char was placed in the reactor. The mass flow rates of the reaction gases were controlled to ensure a gas concentration of 400 ppm N₂O and 2000 ppm H₂. Ordinary nitrogen (N₂) was used as the balancing gas. These gases were uniformly mixed and measured using a mass flow meter to create a simulated flue gas. The total reaction gas flow rate was 3.2 L / min.

[0090] The simulated flue gas is introduced into a vertically positioned reactor, which is heated in a furnace at a program-controlled temperature. The simulated flue gas enters the reactor tube, flows over the catalyst, and undergoes a NO removal reaction at a constant temperature. After the reaction, the gas exits the reactor and is passed through a Gasmat for gas composition monitoring.

[0091] The reaction temperature was controlled in the range of 40-200°C, and the N2O removal rate corresponding to each 10°C increase in temperature was recorded.

[0092] The results show that the reaction rate of H2 reduction of N2O catalyzed by metal-loaded carbon-based materials is significantly improved. The detailed relationship between the reduction efficiency and temperature and the error bars are given by Figure 4 It is shown that the N2O reduction rate can reach more than 90% at 200℃.

[0093] The reaction's initial temperature was significantly reduced, reaching between 125°C and 145°C for 50% N₂O reduction. The reaction was promoted differently by different transition metal loadings, in the order of Ca-char > K-char > Na-char. No NO production was detected during the reaction, demonstrating high N₂ selectivity during the N₂O reduction process and avoiding secondary pollution caused by NO production.

[0094] pass Figure 1 Comparisons show that carbon-based materials loaded with transition metals exhibit stronger catalytic performance, enabling lower N2O reduction temperatures. Regardless of the metal loading, N2O reduction rates exceeding 90% can be achieved at 200°C.

[0095] Example 5:

[0096] This embodiment provides several carbon-supported metal catalysts, and the preparation methods are as follows:

[0097] The catalyst precursor HNO3-Char was prepared according to the preparation method of Example 1, wherein the carbon-based material was commercial activated carbon. A certain mass of alkali metal (K, Ca, Na) nitrate was dissolved in a certain amount of deionized water at ambient temperature. A certain amount of HNO3-Char was then added to the solution. The corresponding mass of metal nitrate was calculated based on a target metal loading of 6 wt.%. The resulting catalysts are represented in this example as Metal-Char, depending on the loaded metal.

[0098] The mixture was stirred magnetically at room temperature to ensure full contact, and the mixed solution was dried at room temperature. The obtained solid sample was calcined at 400°C in a 400ml / min N2 atmosphere for 2 hours to promote the interaction between the metal component and the carbon-based material support. The calcined sample was then reduced at a flow rate of 200ml / min H2 for 2 hours at a reduction temperature of 250°C. The obtained catalysts were represented by Metal-char according to the different supported metals.

[0099] The experimental system and method were the same as in Example 1. 2 g of Metal-Char was placed in the reactor. The mass flow rates of the reaction gases were controlled to ensure a gas concentration of 400 ppm N₂O and 2000 ppm H₂. Ordinary nitrogen (N₂) was used as the balancing gas. These gases were uniformly mixed and measured using a mass flow meter to create a simulated flue gas. The total reaction gas flow rate was 3.2 L / min.

[0100] The simulated flue gas is introduced into a vertically positioned reactor, which is heated in a furnace at a program-controlled temperature. The simulated flue gas enters the reactor tube, flows over the catalyst, and undergoes a NO removal reaction at a constant temperature. After the reaction, the gas exits the reactor and is passed through a Gasmat for gas composition monitoring.

[0101] The reaction temperature was controlled in the range of 40-200°C, and the N2O removal rate corresponding to each 10°C increase in temperature was recorded.

[0102] Results show that the metal-loaded carbon-based materials significantly increase the rate of H2 reduction of N2O, achieving over 90% N2O reduction at 200°C. The reaction's initial temperature is significantly reduced, with the corresponding temperature for 50% N2O reduction dropping to between 125 and 140°C. The effect of different transition metal loadings on the reaction is different, with the order being Ca-char > K-char > Na-char. No NO production was detected during the reaction, demonstrating high N2 selectivity during the N2O reduction process and avoiding secondary pollution caused by NO generation.

[0103] Example 6:

[0104] This embodiment provides several carbon-supported metal catalysts, and the preparation methods are as follows:

[0105] The catalyst precursor HNO3-Char was prepared according to the preparation method of Example 1, wherein the carbon-based material was commercial activated carbon. A certain mass of alkali metal (K, Ca, Na) nitrate was dissolved in a certain amount of deionized water at ambient temperature. Subsequently, a certain amount of HNO3-Char was added to the solution. The corresponding mass of metal nitrate was calculated based on a target metal loading of 10 wt.%. The resulting catalysts are represented in this example as Metal-Char, depending on the loaded metal.

[0106] The experimental system and method were the same as in Example 1. 2 g of Metal-Char was placed in the reactor. The mass flow rate of the counter-reactant gas was controlled to ensure a gas concentration of 400 ppm N₂O and 2000 ppm H₂. Ordinary nitrogen (N₂) was used as the balancing gas. These were uniformly mixed and measured using a mass flow meter to form a simulated flue gas. The total flow rate of the reaction gas was 3.2 L / min.

[0107] The simulated flue gas is introduced into a vertically positioned reactor, which is heated in a furnace at a program-controlled temperature. The simulated flue gas enters the reactor tube, flows over the catalyst, and undergoes a NO removal reaction at a constant temperature. After the reaction, the gas exits the reactor and is passed through a Gasmat for gas composition monitoring.

[0108] The reaction temperature was controlled in the range of 40-200°C, and the N2O removal rate corresponding to each 10°C increase in temperature was recorded.

[0109] The results show that the reaction rate of the H2 reduction of N2O by the metal-loaded carbon-based materials is significantly increased. The N2O reduction rate can reach over 90% at 200°C. The starting temperature of the reaction is significantly reduced, and the corresponding temperature for 50% N2O reduction is reduced to between 120 and 140°C. The loading of different transition metals has different promoting effects on the reaction, in the order of Ca-char > K-char > Na-char. Furthermore, no NO generation was detected during the reaction, demonstrating the high selectivity of N2 during the N2O reduction process, avoiding secondary pollution caused by NO generation. The efficiency of the carbon-based materials catalyzing the H2 reduction of N2O under different metal loading concentrations is not much different.

[0110] After carefully considering the current situation and current industrial factors, the inventors chose to combine carbon-based materials with metal-loaded materials and H2 catalysis for N2O reduction. Carbon-based materials and their loaded metals are inexpensive, and China is currently strongly encouraging the development of hydrogen energy based on carbon neutrality and peak carbon emissions. H2 is also used industrially as a gas for the production of NH3. This combination is inexpensive, environmentally friendly, and has excellent N2O reduction effectiveness at low temperatures.

[0111] The excellent catalytic properties inherent in carbon-based materials make them promising catalysts. Furthermore, the addition of metals as active phases on their surfaces can further lower reaction temperatures. Furthermore, the use of H2 as a traditional reducing agent for the selective catalytic reduction of N2O on the surfaces of metal-supported carbon-based materials is a viable approach to reduce environmental pollution. While limited research is currently underway, this method holds promise for industrial application.

[0112] During the experiment, the inventors fully considered the safety of H2 as a reducing gas, compared the effect of H2 concentration on N2O removal performance, and found that 2000ppm of H2 can achieve excellent catalytic effects. The continued increase in H2 concentration has no significant effect on the performance improvement. This concentration of H2 is within the safe range. For low-temperature removal of N2O on the mobile end, this method can replace the current mainstream precious metal catalysts. For industrial source tail gas treatment devices, the tail gas input is generally around 300°C. This method does not require additional energy for industrial source tail gas treatment, saving energy. Therefore, the present invention has a wide range of applications.

[0113] The inventors conducted sufficient experiments to verify the effect of the carbon-based material treatment process on the reduction of N2O, including the type of carbon-based material, the effect of metal loading, the time and temperature of N2 calcination, the concentration, temperature and time of H2 reduction, etc.

[0114] The types of carbon-based materials include coal-based activated carbon and biomass-based coconut shell carbon, the metal loading includes 3wt.%, 6wt.%, 10wt.% and other variations, the N2 calcination time includes 1h, 2h and other times, the N2 calcination temperature includes 400℃, 500℃, 600℃ and other temperatures, the H2 reduction concentration includes 200ml / mim, 300ml / mim, 400ml / mim, etc., the H2 calcination time includes 1h, 2h, etc., the H2 calcination temperature includes 200℃, 300℃, 400℃, etc., and multiple groups of cross experiments were carried out to explore what preparation conditions can achieve the optimal catalytic efficiency.

[0115] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. An application method of a carbon-based metal catalyst for low-temperature hydrogen reduction of N2O, wherein the catalyst is a metal-loaded carbon-based material, characterized in that: The catalyst is placed in an environment containing N2O gas, and H2 atmosphere is introduced at a temperature of 40-200°C, thereby reducing N2O to H2O and N2; The mass fraction of the metal element in the catalyst is 3-10wt%; The preparation method of the catalyst is as follows: S1. Dilute the modifier and immerse it in a 10-24 mesh carbon-based material, stir it magnetically at room temperature to ensure full contact, and remove impurities in the carbon-based material; then dry it in an oven overnight; after drying, wash the carbon-based material with deionized water to remove excess modifier until the washing water is neutral; and dry it in an oven overnight to obtain a catalyst precursor HNO3-Char; S2. Dissolving a metal nitrate in deionized water at ambient temperature, then adding HNO3-Char to the aqueous solution of the metal nitrate to a metal loading of 3-10 wt %; then magnetically stirring the mixture at room temperature to ensure full contact, and drying the mixed solution at room temperature; S3. The obtained solid sample was calcined in a N2 atmosphere at 400°C for 2 hours; the calcined sample was then reduced at a H2 flow rate of 200 ml / min for 2 hours at a reduction temperature of 250°C; the obtained catalysts were represented by Metal-char according to the different supported metals; The loaded metal is Co, Ni or Fe; The carbon-based material in step S1 is coconut shell carbon.

2. The application method according to claim 1, characterized in that: The modifier in step S1 is pure nitric acid reagent.

3. The application method according to claim 1, characterized in that: The operation method of step S2 is: take 8 g of HNO3-Char material each time, calculate the mass of metal nitrate corresponding to the required metal loading amount, and dissolve it in 100 ml of deionized water.

4. The application method according to claim 1, characterized in that: When H2 is used for catalytic reduction of N2O, the total gas flow rate is 3.2 L / min, of which H2 is 2000 ppm, N2O is 400 ppm, and the rest is N2 as the balance gas.

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