CN106881133B - Catalyst for synthesizing ammonia - Google Patents

Abstract

The present invention relates to a catalyst for the synthesis of ammonia, which comprises manganese nitride and related supports and additives. As a novel catalytic material, the invention shows good catalytic activity in ammonia synthesis reaction.

Description

A catalyst for the synthesis of ammonia

technical field

The invention relates to catalyst technology, and in particular provides a catalyst for synthesizing ammonia and its application in the reaction of synthesizing ammonia.

Background technique

Ammonia is the basic raw material for the production of important chemical products such as fertilizers, nitric acid, and plastics. Haber-Bosch realized the high-pressure synthesis of ammonia for the first time. Synthetic ammonia is of great significance in industrial production. At present, the catalysts widely used in the synthesis of ammonia are iron-based and ruthenium-based catalysts. A.Mittasch discovered K-promoted Fe-based catalysts; M.Muhler loaded metal ruthenium on the MgO carrier, added alkali (earth) metal additives Ba and Cs for ammonia synthesis, and achieved better ammonia synthesis activity [H. Bielawa, O. Hinrichsen, A. Birkner, M. Muler Angew. Chem. Int. Ed, 2001, 40, 6]. Although iron-based and ruthenium-based catalysts have been industrialized for ammonia synthesis, the process consumes a lot of energy, and how to improve the harsh conditions of high temperature and pressure required for the reaction is the main problem facing the development of the ammonia synthesis industry. According to the thermodynamic equilibrium of the reaction, the ammonia synthesis reaction can be carried out at normal temperature and pressure. Breaking out of the limitations of iron-based and ruthenium-based catalysts and exploring other metal-based catalysts is an effective way to develop a new generation of ammonia synthesis catalysts.

Contents of the invention

After full ball milling of MnN and LiH, the temperature was raised to above 250°C in a 1:3 N ₂ /H ₂ mixture, showing excellent ammonia synthesis performance, as shown in Figure 1. In ammonia synthesis reaction, the catalyst provided by the invention can achieve relatively ideal effect, and the reaction performance is better than that of the 5% Ru/MgO catalyst under the same conditions. The XRD results after the reaction showed that the samples were Mn nitrides and LiH, which further confirmed the catalytic effect of Mn-based catalysts and their promoters on the synthesis of ammonia.

Further studies have shown that catalysts formed by manganese nitrides (MnN, Mn ₃ N ₂ , Mn ₂ N, Mn ₄ N, Li ₇ MnN ₄ , etc.) combined with supports or additives have similar catalytic activities for ammonia synthesis.

The catalyst carrier for synthesizing ammonia provided by the present invention is composed of a main body and an additive, the above-mentioned main body is a nitrogen-containing compound of manganese, and the additive includes one or more of alkali/alkaline earth metal hydride, carrier or metal alloy;

The mass ratio of the catalyst body to the additive is in the range of 1000:1 to 1:500.

The manganese nitrogen-containing compound is one or a mixture of two or more of MnN, Mn ₃ N ₂ , Mn ₄ N, Mn ₂ N, Li ₇ MnN ₄ .

The carrier is Li ₂ O, MgO, CaO, SrO, BaO, Al ₂ O ₃ , BN, Si ₃ N ₄ , Mg ₃ N ₂ , Ca ₃ N ₂ , AlN, molecular sieve, carbon material, metal organic framework material (MOFs) of one or a combination of two or more.

The alkali/alkaline earth metal hydride is one or a mixture of two or more of LiH, NaH, KH, CsH, MgH ₂ , CaH ₂ , BaH ₂ .

The metal alloy is: a binary or ternary alloy formed between one or more of IVB, VB, VIB, VIIB or VIIIB group elements and Mn; the above-mentioned IVB, VB, VIB, VIIB or Group VIIIB elements are one or more of Ti, Zr, Cr, Mo, W, Fe, Ru, Co, Rh, Ir, Ni, Pd, and Pt.

The mass ratio of the catalyst body to the additive ranges from 200:1 to 1:100.

The operating conditions when the catalyst is used to synthesize ammonia are as follows: the sample is raised to a certain reaction temperature in the reaction atmosphere, and the composition of the product is analyzed online by using a conductivity meter; the above reaction atmosphere is a mixed gas of N ₂ and H ₂ .

Description of drawings

Figure 1. The synthetic ammonia reactivity of the MnN/LiH (molar ratio is 1:5) prepared in Example 1 under normal pressure conditions.

Fig. 2. Ammonia synthesis reaction activity of Li ₇ MnN ₄ prepared in Example 2 under normal pressure conditions.

Fig. 3. Ammonia synthesis reaction activity of MnCl ₂ /LiH prepared in Example 3 under normal pressure conditions.

specific embodiment

In order to further illustrate the present invention, the following specific examples are cited, but it does not limit the scope of the invention defined by the appended claims.

Example 1:

In an argon glove box, accurately weigh 1.0000 g of manganese nitride (MnN) and 0.5797 g of LiH, and place them in a self-made stainless steel ball mill jar. After closing the ball milling tank, put it into a planetary ball mill (Fischt PM400), and the ball milling condition is 150rpm ball milling for 3 hours. That is, the sample MnN/LiH (molar ratio 1:5) was obtained.

In an argon glove box, 0.0690 g of MnN/LiH (molar ratio 1:5) was accurately weighed and placed in a fixed-bed quartz tube reactor. The sample was heated up to the required temperature in the reaction atmosphere (1:3N ₂ /H ₂ mixed gas), the flow rate of the reaction gas was controlled at 20mL/min, and samples were taken for analysis after 30 minutes. The test results are shown in Figure 1. The rate of ammonia gas generation reaches the maximum at 275℃, and then the rate of ammonia gas generation decreases as the temperature rises.

Example 2:

In an argon glove box, accurately weigh 0.1598g of Li ₃ N and 0.1082g of Mn powder in a stainless steel reactor, pressurize N ₂ to 10MPa, raise the temperature to 750°C and react in a closed system for 24h. The reaction product was collected to obtain Li ₇ MnN ₄ .

In an argon glove box, accurately weigh 0.0200 g of Li ₇ MnN ₄ and place it in a fixed-bed quartz tube reactor. The sample was heated to the required temperature in the reaction atmosphere (1:3N ₂ /H ₂ mixed gas), the flow rate of the reaction gas was controlled at 33mL/min, and samples were taken for analysis after 30 minutes. The test results are shown in Figure 2. Starting from 300°C, the rate of ammonia gas generation increases with increasing temperature, and reaches the maximum rate at 375°C.

Example 3:

In an argon glove box, accurately weigh 0.504 g of MnCl ₂ and 0.192 g of LiH, and place them in a self-made stainless steel ball mill jar. After closing the ball milling tank, put it into a planetary ball mill (Fischt PM400), and the ball milling condition is 200rpm ball milling for 3 hours. The sample MnCl ₂ /LiH was obtained. In an argon glove box, accurately weigh 0.0400 g of MnCl ₂ /LiH, and place it in a fixed-bed quartz tube reactor. The sample was heated up to the required temperature in the reaction atmosphere (1:3N ₂ /H ₂ mixed gas), the flow rate of the reaction gas was controlled at 30mL/min, and samples were taken for analysis after 30 minutes. The test results are shown in Figure 3. The catalyst has good ammonia synthesis activity in the low temperature region, and the reaction activity increases with the increase of temperature.

Claims (2)

1. A manganese catalyst for use in ammonia synthesis, characterized by: the catalyst consists of a main body and an additive, wherein the main body is a nitrogen-containing compound of manganese, and the additive is LiH;

the mass ratio of the catalyst body to the additive is in the range of 200:1 to 1:100, respectively;

The nitrogen-containing compound of manganese is one or a mixture of MnN or Li7MnN 4.

2. Use of a catalyst according to claim 1, wherein: the operating conditions of the catalyst for synthesizing ammonia are as follows: the sample is heated to a certain reaction temperature in the reaction atmosphere, and the composition of the product is analyzed on line by a conductivity meter; the reaction atmosphere is mixed gas of N2 and H2.