Catalyst for ammonia synthesis and ammonia decomposition

Abstract

The present invention relates to a catalyst for ammonia synthesis and ammonia decomposition. The catalyst includes a nitrogen-containing compound of a main group element and a related support and an additive. The present invention is a novel catalytic material, which exhibits good catalytic activity in ammonia synthesis and ammonia decomposition reactions.

Claims

1. A catalyst for ammonia synthesis, comprising: at least one compound of a main group element, wherein the at least one compound of the main group element is a hydride of the main group element; one or more selected from the group consisting of transition metal nitrides and transition metal alloys; and a support.

2. The catalyst according to claim 1, wherein the at least one compound of the main group element is represented by formula MH.sub.x, wherein M is an IA, IIA, or IIIA group element, x is 1, 2, or 3 and equals a valence of M.

3. The catalyst according to claim 1, wherein the main group element is one selected from the group consisting of Li, Na, K, Cs, Mg, Ca, Ba, Al, and a mixture thereof.

4. The catalyst according to claim 1, wherein the support is one selected from the group consisting of Li.sub.2O, MgO, CaO, SrO, BaO, Al.sub.2O.sub.3, BN, Si.sub.3N.sub.4, Mg.sub.3N.sub.2, Ca.sub.3N.sub.2, AlN, molecular sieve, carbon material, Metal-organic Frameworks (MOF), and a mixture thereof.

5. The catalyst according to claim 1, wherein the transition metal nitrides are nitrides of Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, and Co.

6. The catalyst according to claim 1, wherein the transition metal alloys are selected from the group consisting of binary or ternary alloys comprising two or three of Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd and Pt, or alloy comprising C, B, and one or more element selected from the group consisting of Ti, Zr, Cr, Mo, W, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, and Pt.

7. The catalyst according to claim 1, wherein a mass ratio of the one or more selected from the group consisting of compounds of a main group element to the one or more selected from the group consisting of transition metal nitrides or transition metal alloys or the support ranges from 200:1 to 1:100.

8. The catalyst of claim 1, comprises LiNH.sub.2, Li.sub.2NH, KNH.sub.2, Fe.sub.2NKNH.sub.2, Fe.sub.2NLiNH.sub.2, LiH, FeKH, RuLiH, or KNH.sub.2Ru/LiH.

9. A method for ammonia synthesis, comprising: contacting a gas mixture comprising N.sub.2 and H.sub.2 with the catalyst of claim 1 at a temperature ranging from 300 C. to 550 C.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the temperature programmed desorption of LiNH.sub.2 (Ar-TPD).

(2) FIG. 2 shows the temperature programmed reaction of Li.sub.2NH in 5% NH.sub.3/Ar (NH.sub.3-TPR).

(3) FIG. 3 shows the activities of Li.sub.2NH, KNH.sub.2 and Fe.sub.2N in the 5% NH.sub.3/Ar.

(4) FIG. 4 shows the reaction activities of Fe.sub.2N/LiNH.sub.2 (molar ratio is 0.5:2) and Fe.sub.2N/KNH.sub.2 (molar ratio is 0.5:2) in the 5% NH.sub.3/Ar.

(5) FIG. 5 shows the reaction activities of Fe.sub.2N/LiNH.sub.2 (molar ratio is 0.5:3) and Fe.sub.2N/KNH.sub.2 (molar ratio is 0.5:2) in pure ammonia.

DETAILED DESCRIPTION

(6) To further describe the present invention, the following specific embodiments are listed, but do not limit the invention scope defined by all appended claims.

Embodiment 1

(7) In an argon glovebox, Li.sub.2NH of 0.0300 g is accurately taken in a fixed bed stainless steel reactor. The sample is heated to 400 C. in argon atmosphere, and the argon flow rate is 30 mL/min. After 20 min, 5% NH.sub.3/Ar mixture is introduced, the reactant flow rate is controlled between 1.8 L/h and 3.6 L/h, and after 30 min, the sampling analysis is conducted. The measurement results are shown in FIG. 3. The NH.sub.3 conversion rate increases approximately linearly as the temperature increases, and the NH.sub.3 conversion rate can reach 35% at 450 C.

Embodiment 2

(8) In the argon glovebox, KNH.sub.2 of 0.0300 g is accurately taken in the fixed bed stainless steel reactor. The sample is heated to 400 C. in argon atmosphere, after 20 min, 5% NH.sub.3/Ar mixture is introduced, the reactant flow rate is controlled between 1.8 L/h and 3.6 L/h, and after 30 min, the sampling analysis is conducted. The measurement results are shown in FIG. 3. The ammonia conversion rate increases approximately linearly as the temperature increases. At the same reaction temperature, the activity thereof is a little more than that of the Li.sub.2NH, and the NH.sub.3 conversion rate can reach 35% at 440 C.

Embodiment 3

(9) In the argon glovebox, Fe.sub.2N of 1.0000 g and LiNH.sub.2 of 0.7300 g are accurately taken in a homemade stainless steel ball mill tank. After the ball mill tank is sealed, the sample Fe.sub.2N/LiNH.sub.2 (molar ratio is 0.5:2) is prepared by ball-milling Fe.sub.2N and LiNH.sub.2 under ball mill condition of 200 rpm in a planetary ball mill (Fischt PM400) for 5 h.

(10) In the argon glovebox, Fe.sub.2N/LiNH.sub.2 (molar ratio is 0.5:2) of 0.0350 g is accurately taken in the fixed bed stainless steel reactor. The sample is heated to a desired temperature in reaction atmosphere (5% NH.sub.3/Ar mixture), the reactant flow rate is controlled between 1.8 L/h and 3.6 L/h, and after 30 min, the sampling analysis is conducted. The measurement results are shown in FIG. 4. The NH.sub.3 conversion rate gradually increases as the temperature increases, and the NH.sub.3 conversion rate can reach 22% at 380 C.; when the temperature is higher than 380 C., the catalyst activity decreases; and when the temperature is higher than 400 C., the NH.sub.3 conversion rate increases gradually as the temperature increases.

Embodiment 4

(11) In the argon glovebox, Fe.sub.2N of 1.0000 g and KNH.sub.2 of 0.7300 g are accurately taken in a homemade stainless steel ball mill tank. After the ball mill tank is sealed, the sample Fe.sub.2N/KNH.sub.2 (molar ratio is 0.5:2) is prepared by ball-milling Fe.sub.2N and KNH.sub.2 under ball mill condition of 200 rpm in the planetary ball mill (Fischt PM400) for 5 h.

(12) In the argon glovebox, Fe.sub.2N/LiNH.sub.2 (molar ratio is 0.5:2) of 0.0350 g is accurately taken in the fixed bed stainless steel reactor. The sample is heated to a desired temperature in reaction atmosphere (5% NH.sub.3/Ar mixture), the reactant flow rate is controlled between 1.8 L/h and 3.6 L/h, and after 30 min, the sampling analysis is conducted. The measurement results are shown in FIG. 4. The NH.sub.3 conversion rate increases gradually as the temperature increases during the temperature range of 300 to 400 C. The NH.sub.3 conversion rate can reach 16% at 380 C., which is lower than that of the sample Fe.sub.2N/LiNH.sub.2 (molar ratio is 0.5:2).

Embodiment 5

(13) In the argon glovebox, Fe.sub.2N/LiNH.sub.2 (molar ratio is 0.5:3) of 0.0400 g is accurately taken in the fixed bed stainless steel reactor. The sample is heated to the desired reaction temperature in pure ammonia atmosphere, the reactant flow rate is controlled at 2.4 L/h, and after 30 min, the sampling analysis is conducted. The measurement results are shown in FIG. 5. The NH.sub.3 conversion rate increases as the temperature increases during the temperature range of 400 to 475 C., and the NH.sub.3 conversion rate is measured to be 9.2 kg NH.sub.3 g.sub.cat.sup.1 h.sup.1 at 470 C.

Embodiment 6

(14) In the argon glovebox, Fe.sub.2N/KNH.sub.2 (molar ratio is 0.5:2) of 0.0400 g is accurately taken in the fixed bed stainless steel reactor. The sample is heated to the desired reaction temperature in pure ammonia atmosphere, the reactant flow rate is controlled at 2.4 L/h, and after 30 min, the sampling analysis is conducted. The measurement results are shown in FIG. 5. The NH.sub.3 conversion rate increases as the temperature increases during the temperature range of 300 to 400 C. The NH.sub.3 conversion rate is measured to be 6.9 kg NH.sub.3 g.sub.cat.sup.1 h.sup.1 at 470 C., which is slower than that of the sample Fe.sub.2N/LiNH.sub.2 (molar ratio is 0.5:3).

Embodiment 7

(15) In the argon glovebox, a ball-milled LiH sample of 0.0300 g is accurately taken in a fixed bed stainless steel high-pressure reactor. The sample is heated to 400 C. in N.sub.2/H.sub.2 mixture (volume ratio of N.sub.2 to H.sub.2 is 1:3), the total pressure is 1 atm, the reactant flow rate is 1.8 L/h, and the NH.sub.3 synthesis rate is detected by using the conventional conductivity method. The NH.sub.3 synthesis rate is measured to be 95 umol g.sub.cat.sup.1 h.sup.1 under reaction condition.

Embodiment 8

(16) In the argon glovebox, a Fe/KH sample of 0.0300 g prepared by a ball-milling method is accurately taken in the fixed bed stainless steel high-pressure reactor. The sample is heated to 400 C. in N.sub.2/H.sub.2 mixture (volume ratio of N.sub.2 to H.sub.2 is 1:3), the total pressure is 1 atm, the reactant flow rate is 1.8 L/h, and the NH.sub.3 synthesis rate is detected by using the conventional conductivity method. The NH.sub.3 synthesis rate is measured to be 120 umol g.sub.cat.sup.1 h.sup.1 under reaction condition.

Embodiment 9

(17) In the argon glovebox, a 5 wt % Ru/LiH sample of 0.0560 g homemade by an impregnation method is accurately taken in the fixed bed stainless steel high-pressure reactor. The sample is heated to 400 C. in N.sub.2/H.sub.2 mixture (volume ratio of N.sub.2 to H.sub.2 is 1:3), the total pressure is 10 atm, the reactant flow rate is 2.4 L/h, and the NH.sub.3 synthesis rate is detected by using the conventional conductivity method. The NH.sub.3 synthesis rate is measured to be 75 umol g.sub.cat.sup.1 h.sup.1 under reaction condition.

Embodiment 10

(18) In the argon glovebox, a KNH.sub.2-promoted 5 wt % Ru/LiH sample of 0.1390 g homemade by the impregnation method is accurately taken in the fixed bed stainless steel high-pressure reactor. The sample is heated to 340 C. in N.sub.2/H.sub.2 mixture (volume ratio of N.sub.2 to H.sub.2 is 1:3), the total pressure is 1 atm, the reactant flow rate is 2.4 L/h, and the NH.sub.3 synthesis rate is detected by using the conventional conductivity method. The NH.sub.3 synthesis rate is measured to be 5010 umol g.sub.cat.sup.1 h.sup.1 under reaction condition.