CN102380410A - Ferro-cobalt bimetallic catalyst for catalyzing nitrous oxide (N2O) decomposition - Google Patents

Abstract

The invention provides a cobalt-iron bimetallic loaded mordenite catalyst for catalyzing the decomposition of nitrous oxide and a preparation method thereof. When the space velocity is 30,000h ^-1 , the reaction temperature is 400-500°C, the concentration of N ₂ O is 0.1-30%, and the concentration of H ₂ O is 2-10%, it can discharge most or all of the pollutants in the system. The N ₂ O decomposes into N ₂ and O ₂ . Moreover, the catalyst has high stability, and the activity of the catalyst has not decayed after 100 hours of continuous operation under the simulated tail gas discharge of a nitric acid plant. The preparation process of the catalyst is simple, the cost is low, the catalytic decomposition activity of the nitrous oxide is high, and the stability is good. This technology has wide applicability and can be used in the reduction process of N ₂ O from many industrial sources (such as nitric acid production, adipic acid production, etc.), and its application prospect is very broad.

Description

A cobalt-iron bimetallic catalyst that catalyzes the decomposition of nitrous oxide

technical field

The invention relates to a nitrous oxide (N ₂ O) catalytic decomposition catalyst and its preparation, which belongs to the field of heterogeneous catalytic technology and its environmental protection, and specifically relates to a method for controlling air pollution, especially for tail gas treatment of nitric acid plants and adipic acid plants Contaminated catalysts and methods for their preparation.

Background technique

N ₂ O is a colorless gas with a faint sweet smell, which is not obviously toxic to the human body. Inhalation of a small amount excites people's nerves and causes laughter (so commonly known as laughing gas); inhalation of a large amount can cause people to lose consciousness, and it is sometimes used as an anesthetic for minor operations. At present, N ₂ O has been widely used in the fields of electronics industry and medicine, as well as semiconductor device manufacturing, pressure packaging and food industry and other fields. Because N ₂ O is stable in nature and has no obvious poisonous effect on the human body, it has not been regarded as a polluting gas for a long time, so it has not received attention from all walks of life. N ₂ O produced from natural activities and production processes is generally released into the atmosphere without restriction. However, studies in the past ten years have shown that N ₂ O can not only seriously damage the ozone layer, but also have a strong greenhouse effect. So far, the harm of N ₂ O to the environment has attracted widespread attention. N ₂ O is one of the six greenhouse gases (CO ₂ , N ₂ O, CH ₄ , HFC, PFC, SF ₆ ) stipulated in the Kyoto Protocol. It is generally believed that the contribution of N ₂ O to global warming is second only to CO ₂ and CH ₄ among the greenhouse gases in the atmosphere. Moreover, N ₂ O is very stable in the troposphere, has a long average lifetime, and its global warming potential is 310 times that of CO ₂ and 15 times that of CH ₄ . It is reported that the background concentration of N ₂ O in the atmosphere increased from 270ppb before the industrial revolution to 316ppb in 2000, with an annual growth rate of 0.2-0.3%. And the study found that human activities are the main reason for the increase of atmospheric N ₂ O concentration, and the main industrial sources of N ₂ O emissions include the production of fatty acids such as nitric acid and adipic acid, fertilizer production, and industrial processes using nitric acid as an oxidant. Therefore, it is of great practical significance to study technologies and methods that can efficiently remove N ₂ O produced in the production process of nitric acid and adipic acid.

N ₂ O catalytic direct decomposition technology is to directly decompose N ₂ O into N ₂ and O ₂ under the action of catalyst. Because the method is simple, low in cost, and does not need to add a reducing agent, it is considered to be an ideal method for eliminating N ₂ O. At present, the catalysts that catalyze the decomposition of N ₂ O mainly include metal oxide catalysts, such as MnO _x /MgO, etc. (US 5705136); hydrotalcite-derived composite oxides, such as Rh _0.01 Mg _0.71 Al _0.28 O _1.145 (EP 1262224B1); Stone structure composite oxides, such as CuAl ₂ O ₄ (US6723295B1), etc.; modified molecular sieve catalysts, such as Co-ZSM-5 (US 5171553). Among them, the ion-exchange cobalt molecular sieve catalyst has great advantages in treating N ₂ O tail gas emitted from the production process of nitric acid or adipic acid due to its high N ₂ O decomposition activity and anti-poisoning (NO, O ₂ , H ₂ O). High application value and research significance. Especially in the author's previous research, it was found that the cobalt-supported mordenite molecular sieve (Co-MOR) catalyst prepared by the ion exchange method has a very high catalytic activity for N ₂ O decomposition (higher than Co-ZSM-5), and the activity is higher than that of other remains high in the presence of gas. However, the ion exchange degree of the Co-MOR catalyst still cannot reach 100%, and the residual hydroxyl protons will cause the catalyst to be deactivated in the presence of water, and the stability needs to be further improved. On the other hand, Fe zeolites are also widely used in N ₂ O catalytic decomposition reactions due to their very high anti-poisoning (SO ₂ and H ₂ O, etc.) and excellent stability; however, their activity is lower than that of Co zeolites. Therefore, the present invention introduces two metals, Co and Fe, into molecular sieves successively through a two-step ion exchange method, and combines the characteristics of high stability of Fe ions and high activity of Co ions to prepare Co and Fe with higher catalytic activity and stability. Bimetallic supported MOR molecular sieve catalysts.

Contents of the invention

The object of the present invention is to provide a cobalt-iron bimetallic supported mordenite molecular sieve catalyst (CoFe-MOR) for eliminating nitrous oxide emitted from industrial sources and a preparation method thereof.

The present invention utilizes a CoFe-MOR catalyst. Under test conditions, the space velocity is 30,000h ^-1 , the temperature is 400-500°C, the concentration of N ₂ O is 0.1-30%, the concentration of O ₂ is 5-10%, and the concentration of NO is 0.1- 1%, when H ₂ O is 2-10%, most or all of the N ₂ O in the system can be decomposed into N ₂ and O ₂ . And it has high stability, and the activity of the catalyst does not decrease significantly after being continuously carried out for 100 hours under the condition of simulating the tail gas of nitric acid.

In order to achieve the above purpose, the CoFe-MOR catalyst for N ₂ O decomposition provided by the present invention is prepared by using mordenite as the source molecular sieve, and successively loading Co and Fe active components by a two-step ion exchange method. The loading amounts of the active components Co and Fe in the MOR molecular sieve are 1-10% and 0.1-5% respectively. The best exchange sequence is Co first and then Fe. The specific preparation method is as follows:

1) At a certain pH value (such as a pH value of 2-9), exchange 0.01-2mol/L aqueous solution containing Co ²⁺ with mordenite (MOR) at room temperature for 24-48 hours, repeat 1-5 times , drying at 80-100°C for 15-25 hours, then raising the temperature to 500°C and roasting at a constant temperature in air for 4-6 hours to obtain cobalt-loaded mordenite (Co-MOR);

2) At a certain pH value (such as a pH value of 2-9), exchange 0.01-2mol/L aqueous solution containing Fe ³⁺ with Co-MOR for 24-48 hours, repeat 1-5 times, 80-100 drying at a temperature of 15-25 hours, and then raising the temperature to 500° C. and roasting at a constant temperature in air for 4-6 hours to obtain a cobalt-iron-loaded mordenite (CoFe-MOR) catalyst.

The preparation process of the catalyst of the invention is simple, the cost is low, and the catalytic decomposition activity for nitrous oxide is high, and the stability is good. It is suitable for the reduction process of N ₂ O in nitric acid production plants, and has broad application prospects. The present invention can also be applied to other industrial sources, such as N ₂ O emission reduction processes such as adipic acid plants.

Description of drawings

Figure 1: N 2 _O decomposition activities of CoFe-MOR, FeCo-MOR, Co-MOR and Fe-MOR catalysts at different temperatures (space velocity 30,000h ^-1 , N ₂ O concentration 0.5%).

Figure 2: CoFe-MOR N ₂ O decomposition activity under different atmospheres (space velocity 30,000h ^-1 , N ₂ O concentration 0.5%, N ₂ O 0.5%, O ₂ 5%, NO 0.1%, _H2O is 2%).

Figure 3: Test of N ₂ O decomposition stability of CoFe-MOR catalyst under simulated polluted atmosphere (space velocity is 30,000h ^-1 , N ₂ O concentration is 0.5%, O ₂ is 5%, NO is 0.1%, H ₂ O is 2%).

Detailed ways

Example 1: CoFe-MOR catalyst, the space velocity is 30,000 h ⁻¹ , the N ₂ O concentration is 0.5%, and the N ₂ O decomposition reaction activity at different temperatures. The reaction initiation temperature is 280°C, and the full conversion temperature is 430°C.

Preparation of CoFe-MOR: 1) Under the condition of pH 6, exchange MOR with 0.1mol/L aqueous solution containing Co ²⁺ for 24 hours, repeat 3 times, dry at 80°C for 24 hours, and then heat up to 500°C Calcined at constant temperature in air for 4 hours to obtain Co-MOR;

2) Under the condition of pH 6, exchange 0.1mol/L aqueous solution containing Fe ³⁺ with Co-MOR for 24 hours, repeat 3 times, dry at 80°C for 24 hours, then raise the temperature to 500°C in air Calcined for 4 hours to obtain a CoFe-MOR catalyst.

The catalytic reaction adopts a fixed-bed continuous flow reaction evaluation device. When the initial concentration of N ₂ O is 0.5%, the space velocity is 30,000h ^-1 , and the temperature is 280°C, the conversion of N ₂ O starts, and the conversion rate reaches 50% at 355°C. Full conversion.

Example 2: Iron-cobalt-loaded mordenite (FeCo-MOR) catalysts prepared by different exchange sequences, with a space velocity of 30,000 h ^-1 , an N ₂ O concentration of 0.5%, and N ₂ O decomposition activities at different temperatures. The reaction initiation temperature is 325°C, and the full conversion temperature is 525°C.

Preparation of FeCo-MOR: 1) Under the condition of pH 6, exchange MOR with 0.1mol/L aqueous solution containing Fe ³⁺ for 24 hours, repeat 3 times, dry at 80°C for 24 hours, and then heat up to 500°C Roasting at constant temperature in air for 4 hours to obtain iron-loaded mordenite (Fe-MOR);

2) Under the condition of pH 6, exchange 0.1mol/L aqueous solution containing Co ²⁺ with Fe-MOR for 24 hours, repeat 3 times, dry at 80°C for 24 hours, then heat up to 500°C and roast at constant temperature in air After 4 hours, FeCo-MOR catalyst was obtained.

The catalytic reaction adopts a fixed-bed continuous flow reaction evaluation device. When the initial concentration of N ₂ O is 0.5%, the space velocity is 30,000h ^-1 , and the temperature is 350°C, the conversion of N ₂ O begins, and the conversion rate reaches 50% at 455°C. Full conversion.

Example 3: CoFe-MOR catalyst, the space velocity is 30,000h ^-1 , the N ₂ O concentration is 0.5%, the decomposition activity of N ₂ O at different temperatures under different interfering atmospheres (NO, O ₂ , H ₂ O). The results show that the 50% conversion temperature of N ₂ O is 355, 350, 375 and 380℃ when NO, O ₂ and H ₂ O exist alone and together.

The catalyst is the CoFe-MOR catalyst in Example 1, and the evaluation is carried out on the device in Example 1. The amount of catalyst is 0.1g, the space velocity is 30,000h ^-1 , adjust the flow of various gases and balance gas He gas flow, so that the initial concentration of N ₂ O is 0.5%, O ₂ is 5%, NO is 0.1%, H ₂ O 2%. The temperature was programmed to rise from 200-600°C, and the conversion rate of N ₂ O was investigated. The results show that the 50% conversion temperature of N ₂ O is 355, 350, 375 and 380℃ when NO, O ₂ and H ₂ O exist alone and together.

Example 4: Evaluation of CoFe-MOR catalyst activity and stability. The catalyst and evaluation apparatus used in Example 3 were the same. The space velocity is 30,000 h ^-1 , the N ₂ O concentration is 0.5%, the N ₂ O is 0.5%, the O ₂ is 5%, the NO is 0.1%, and the H ₂ O is 2%. The N ₂ O conversion _rate was 71% at 375°C, 92% at 400°C, and 100% at 425°C; and the activity of _the catalyst did not decrease significantly after the reaction was continued for 100 hours .

Claims (2)

1. the catalyst that decomposes of the inferior nitrogen of a catalytic oxidation is characterized in that being is carrier with modenite (MOR) molecular sieve, and load bimetallic Co and Fe are active component.The developed by molecule formula is: CoFe-MOR, each constituent content is: Co is that 1-10%, Fe are that 0.1-5%, MOR are 80-98%.

2. Preparation of catalysts method as claimed in claim 1 is characterized in that catalyst passes through the two step load C o of aqueous solution ion-exchange elder generation, and back loading Fe active component prepares to the MOR molecular sieve, and concrete steps are following:

1) be 2-9 in the pH value, with the Co that contains of 0.01-2mol/L ²⁺The aqueous solution and MOR at room temperature exchange 24-48 hour, repeat 1-5 time, 80-100 ℃ of down oven dry 15-25 hour in 500 ℃ of air constant temperature calcining 4-6 hour then, obtains the MOR (Co-MOR) of cobalt load;

2) be 2-9 in the pH value, with the Fe that contains of 0.01-2mol/L ³⁺The aqueous solution and Co-MOR at room temperature exchange 24-48 hour, repeat 1-5 time, 80-100 ℃ of down oven dry 15-25 hour in 500 ℃ of air constant temperature calcining 4-6 hour then, obtains above-mentioned catalyst.

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