Catalyst for production of nitric oxide

Abstract

The present invention provides a catalyst for production of nitric oxide from ammonia and oxygen. The catalyst has the composition A.sub.((n+1)x)B.sub.xC(n.sub.(1y))D.sub.nyO.sub.(3n+1)+d, wherein A is a lanthanide (La, Gd, Nd, Sm) or yttrium, B is an alkaline-earth cation (Ca, Sr or Ba), C is Fe and D is Cr, Mn, Ni, Ce, Ti, Co or Mg, wherein A, B, C and D are selected independent of each other. The catalyst has a high selectivity towards nitric oxide and a low ignition temperature in the reactor. Further the present invention relates to a method for the production of gas comprising nitric oxide by the catalyst of the present invention. The produced gas has a very low content of nitrous oxide.

Claims

1. A method for the production of a gas comprising nitric oxide, which comprises converting a gas blend comprising ammonia and oxygen in the presence of a catalyst comprising the composition A.sub.((n+1)x)B.sub.xC.sub.(n(1y))D.sub.nyO.sub.(3n+1)+d, to obtain the gas comprising nitric oxide, wherein: A is a lanthanide (La, Gd, Nd, or Sm) or yttrium, B is an alkaline-earth cation (Ca, Sr or Ba), C is Fe, D is Cr, Mn, Ni, Ce, Ti, Co or Mg, n is 5>n1, x is 1>x>0, y is 1>y>0, and d is 1>d>1.

2. The method according to claim 1, which comprises the steps of (a) continuously feeding said gas blend to a reactor comprising said catalyst, wherein a temperature of the feed before ignition, T.sub.a1, is increased until ignition of the reaction at temperature T.sub.b, and (b) thereafter adjusting a temperature of the feed after ignition, T.sub.a2, to achieve a defined temperature in the reactor, T.sub.c, during the reaction.

3. The method according to claim 2, wherein the ignition temperature T.sub.b of said gas blend is 330 to 450 C.

4. The method according to claim 1, wherein A is La and B is Sr.

5. The method according to claim 1, wherein n is 3>n1.

6. The method according to claim 5, wherein n is 2>n1.

7. The method according to claim 5, wherein n=1.

8. The method according to claim 3, wherein the temperature T.sub.b is 330 to 390 C.

9. The method according to claim 3, wherein the temperature T.sub.b is 330 to 370 C.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the experimental properties of LaSrFe.sub.0.75Co.sub.0.25O.sub.4+d, which is one embodiment of the catalyst of the present invention.

(2) FIG. 2 shows the selectivity calculated from FIG. 1 along with the catalyst bed temperature.

EXAMPLES

Example 1

(3) The catalysts were tested in an atmospheric pressure reactor, with an internal diameter of 8 mm. The catalyst bed (0.15 cm.sup.3), consisting of catalyst granules in the size range of 0.2 to 0.5 mm, was supported on a quartz frit. The gas feedstock, consisting of 10 volume % ammonia in air or 20% oxygen/80% argon was passed through the catalyst bed, at a rate of 3 N.1/min, and the product gas was analysed using infrared spectroscopy and mass spectrometry. The experimental procedure involved increasing the temperature of the gas feedstock at a rate of 5/min until the catalyst initiated combustion, defined as an increase in temperature in the catalyst bed (measured with a thermocouple placed in the catalyst bed) at a rate exceeding 20/second. After ignition, the temperature of the gas feedstock was adjusted to give a catalyst bed temperature of 900 C.

(4) The ignition temperatures towards formation of NO and NO.sub.2, of the catalysts described in Table 1, are shown in Table 2.

(5) TABLE-US-00002 TABLE 2 Ignition temperature ( C.) for La.sub.((n+1)x)Sr.sub.xFe.sub.(n(1y)Co.sub.nyO.sub.(3n+1)d, where n = 1 x y 0 0.5 1.0 0 416 0.25 354 428 395 0.5 388 415 376 0.75 383 377 349

(6) Table 3 shows concentrations of nitrous oxide achieved for the gases catalyst of the catalysts of the present invention.

(7) TABLE-US-00003 TABLE 3 N.sub.2O level for La.sub.((n+1)x)Sr.sub.xFe.sub.(n(1y)Co.sub.nyO.sub.(3n+1)+d, where n = 1 x y 0 0.5 1.0 0 5 0.25 14 3 0 0.5 21 0 0 0.75 7 0 0

(8) The selectivity towards formation of NO and NO.sub.2 of the catalysts described in table 1, are shown in table 4.

(9) TABLE-US-00004 TABLE 4 Selectivity towards NO + NO.sub.2 for La.sub.((n+1)x)Sr.sub.xFe.sub.(n(1y)Co.sub.nyO.sub.(3n+1)+d, where n = 1 X y 0 0.5 1.0 0 90.3 0.25 91.7 90.5 94.6 0.5 90.3 93.0 93.8 0.75 93.2 92.2 93.0

Example 2

(10) An oxide with the composition LaSrFe.sub.0.75Co.sub.0.25O.sub.4+d was prepared by complexation. 1 molar La(NO.sub.3).sub.3.6H.sub.2O, Sr(NO.sub.3).sub.2, Fe(NO.sub.3).sub.3).9H.sub.2O and Co(NO.sub.3).sub.2.6H.sub.2O solutions were mixed in 1:1:0.75:0.25 volume ratios. To 100 ml of the mixed-metal nitrate solution was added 25 ml of 64% HNO.sub.3, 100 ml of ethylene glycol and 211 g of citric acid. The resulting solution was heated to 150 C. with stirring until a highly viscous liquid/gel was obtained. The gel was heated in a muffle oven at 400 C. for 12 hours. The resulting solid was ground and calcined in a muffle oven at 900 C. for 12 hours.

(11) XRD analysis confirmed that this material was a single phase, mixed-oxide with the composition La.sub.((n+1)x)Sr.sub.xFe.sub.(n(1y)Co.sub.nyO.sub.4+d, where (n=1, x=1 and y=0.25) i.e. LaSrFe.sub.0.75Co.sub.0.25O.sub.4+d where d is between 0.5 and 0.

(12) The calcined catalyst was pressed into pellets which were crushed to produce a sieve fraction between 0.2 and 0.5 mm. These granules (0.2778 g) were loaded into the ammonia oxidation reactor, and were subjected to a test procedure described above. The temperature in the catalyst bed, concentrations of NH.sub.3, N.sub.2 and N.sub.2O are shown in FIG. 1. The catalyst bed temperature reaches 900 C. at time=100 minutes.

(13) It is observed that the catalyst ignites when the temperature of the oxygen-ammonia-argon gas feed reaches 395 C. After ignition, the ammonia level is observed to fall to zero %, indicating full combustion of the ammonia. The N.sub.2O levels are significantly reduced when compared to conventional platinum-based catalysts, in which N.sub.2O emissions are typically in the range of 1000 to 4000 ppm, depending on combustion conditions.

(14) From FIG. 2, we observe that a selectivity of LaSrFe.sub.0.75Co.sub.0.25O.sub.3+d towards NO+NO.sub.2 is circa 95%, at 900 C.