Ammonia oxidation catalyst for the production of nitric acid based on yttrium-gadolinium ortho cobaltates

Abstract

The present invention relates to a catalytically active component of a catalyst, which comprises single phase oxides, based on a mixed yttrium-gadolinium ortho-cobaltate oxide systems, methods for the oxidation of ammonia and hydrocarbon in the presence of said catalytically active component and the use thereof.

Claims

1. A catalytically active component of a catalyst, comprising a stable, single phase oxide of a mixed yttrium-gadolinium ortho-cobaltate oxide system of the formula Y.sub.1XGd.sub.XCo.sub.1YM.sub.YO.sub.3, wherein 1>X>0, 0Y<1, and M is a metal selected from the group consisting of manganese, iron, chromium, vanadium, titanium, aluminum, a transition metal, and an alkaline earth metal.

2. The catalytically active component according to claim 1, wherein the oxide phase has the formula Y.sub.1XGd.sub.XCoO.sub.3wherein 1>X>0.

3. The catalytically active component according to claim 1, wherein the oxide phase has the formula Y.sub.0.75Gd.sub.0.25CoO.sub.3, Y.sub.0.5Gd.sub.0.5CoO.sub.3 or Y.sub.0.25Gd.sub.0.75CoO.sub.3.

4. The catalytically active component according to claim 1, wherein the oxide phase has the formula Y.sub.1XGd.sub.XCo.sub.1YMn.sub.YO.sub.3, wherein 1>X>0, 0<Y<1.

5. The catalytically active component according to claim 4, wherein the oxide phase has the formula Y.sub.0.25Gd.sub.0.75Co.sub.0.9Mn.sub.0.1O.sub.3, Y.sub.0.25Gd.sub.0.75Co.sub.0.8Mn.sub.0.2O.sub.3, or Y.sub.0.25Gd.sub.0.75Co.sub.0.7Mn.sub.0.3O.sub.3.

6. A catalyst for the oxidation of ammonia or a hydrocarbon, with a refractory support phase and a catalytically active single phase oxide, wherein the catalyst comprises a stable, single phase oxide of a mixed yttrium-gadolinium ortho-cobaltate oxide system of the formula Y.sub.1XGd.sub.XCo.sub.1YM.sub.YO.sub.3, wherein 1>X>0, 0Y<1, and M is a metal selected from the group consisting of manganese, iron, chromium, vanadium, titanium, aluminum, a transition metal, and an alkaline earth metal.

7. The catalyst according to claim 6, wherein the oxide phase has the formula Y.sub.1XGd.sub.XCoO.sub.3 wherein 1>X>0.

8. The catalyst according to claim 6, wherein the oxide phase has the formula Y.sub.0.75Gd.sub.0.25CoO.sub.3, Y.sub.0.5Gd.sub.0.5CoO.sub.3 or Y.sub.0.25Gd.sub.0.75CoO.sub.3.

9. The catalyst according to claim 6, wherein the oxide phase has the formula Y.sub.1XGd.sub.XCo.sub.1YMn.sub.YO.sub.3, wherein 1>X>0, 0<Y<1.

10. The catalyst according to claim 6, wherein the oxide phase has the formula Y.sub.0.25Gd.sub.0.75Co.sub.0.9Mn.sub.0.1O.sub.3,Y.sub.0.25Gd.sub.0.75Co.sub.0.8Mn.sub.0.2O.sub.3, or Y.sub.0.25Gd.sub.0.75Co.sub.0.7Mn.sub.0.3O.sub.3.

11. The catalyst according to claim 6, wherein the refractory support phase comprises cerium dioxide, zirconium dioxide, alumina, yttrium oxide, or gadolinium oxide, a mixed oxide of these oxides, silicon carbide, or sodium zirconium phosphate type phases.

12. A method involving an oxidation reaction, wherein the oxidation reaction is carried out in the presence of the catalytically active component according to claim 1.

13. A method for the oxidation of ammonia in an Ostwald process, comprising converting a gas blend comprising ammonia and oxygen in the presence of the catalytically active component according to claim 1.

14. The method according to claim 13, wherein the catalytically active component has a selectivity towards NOx (NO+NO.sub.2) exceeding 90%, and a selectivity towards N.sub.2O less than 0.05%.

15. A method for the complete oxidation of a hydrocarbon to CO.sub.2, comprising carrying out an oxidation reaction in the presence of a the catalytically active component according to claim 1.

16. The method according to claim 15, wherein the oxidation reaction is carried out at temperatures below 600 C.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The current invention is a catalyst for high temperature ammonia oxidation, which is resistant to the hydration issues of lanthanum containing mixed oxides as discussed above. An evaluation of the hydration resistance of large metal ions that may adopt a trivalent oxidation state shows that the following are candidates; Scandium, yttrium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium and lutetium.

(2) Scandium is eliminated as it is too small to form an ortho-cobaltate phase. Terbium, dysprosium, holmium, erbium, ytterbium and lutetium are suitable in terms of their ionic radii and hydration resistance, but they are very expensive. However, yttrium and gadolinium meet the set requirement in terms of ionic radii, when in the trivalent oxidation state, and their hydration resistance.

(3) Yttrium and cobalt, in a 1:1 mole ratio form a stable orthorhombic phase YCoO.sub.3yttrium ortho-cobaltate. When this mixed oxide phase is tested under industrially relevant ammonia oxidation conditions (a feed-stock containing 10% ammonia, 18% oxygen and a balance of inert gas or nitrogen, at a temperature of 900 C.), it combusts ammonia to a mixture of NOx (NO+NO.sub.2), N.sub.2 and N.sub.2O. However, the selectivity towards the nitrogen containing oxides that are desired in the production of nitric acid (NOx) is lower than that obtained by platinum-based catalysts and is in the range of 91.3%.

(4) Examination of the YCoO.sub.3 phase prior to and after the ammonia oxidation test, using X-ray powder diffraction, shows clearly that there has been a reduction of the YCoO.sub.3 phase
2YCoO.sub.3.fwdarw.Y.sub.2O.sub.3+2CoO (1)
It is known that the CoO phase demonstrates some activity towards ammonia oxidation, but the selectivity towards desired NOx products is low-high levels of N.sub.2 and N.sub.2O are produced.

(5) Thermo-gravimetric analysis of the YCoO.sub.3, in air shows that the YCoO.sub.3 phase reduces according to equation 1, at a temperature of 970 C. When combusting ammonia at 900 C., as in industrial plants, the 900 C. temperature is that of the product gas directly downstream of the catalyst. The temperature of the catalyst is significantly higher than the gas temperature. Therefore, pure YCoO.sub.3 is not sufficiently stable for use as an industrial ammonia oxidation catalyst.

(6) Gadolinium and cobalt in a 1:1 mole ratio form a monoclinic phase GdCoO.sub.3. When this mixed oxide phase is tested under industrially relevant ammonia oxidation conditions, as described above, it combusts ammonia to a mixture of NOx (NO+NO.sub.2), N.sub.2 and N.sub.2O. However, the selectivity towards the nitrogen containing oxides that are desired in the production of nitric acid (NOx) is lower than that obtained by platinum-based catalysts and is in the range of 84.8%. Such catalysts are for example described in WO 2006010904 A1, where several perovskite oxidation catalysts are disclosed.

(7) The invention will be further described through the following non-limiting examples:

EXAMPLE 1

(8) Samples of the Y.sub.1XGd.sub.XCoO.sub.3 catalysts were tested for their catalytic performance towards ammonia combustion, in a laboratory test reactor system. They were found to be active towards ammonia combustion with a high selectivity towards the desired NOx product.

(9) TABLE-US-00001 TABLE 1 Performance of Y.sub.1-xGd.sub.xCoO.sub.3 mixed yttrium-gadolinium ortho-cobaltates, sintered at 900 C., towards ammonia combustion. N.sub.2O Ignition temperature Selectivity emission Sample C. towards NOx % ppm YCoO.sub.3 271 91.3 50 Y.sub.0.75Gd.sub.0.25CoO.sub.3 272 94.6 20 Y.sub.0.5Gd.sub.0.5CoO.sub.3 311 96.3 40 Y.sub.0.25Gd.sub.0.75CoO.sub.3 241 94.6 44 GdCoO.sub.3 279 84.8 55

(10) Table 1 also shows the selectivity towards NOx and N.sub.2O emissions for YCoO.sub.3 and GdCoO.sub.3 for comparison. These compounds are not part of the invention.

(11) We observe that mixed yttrium-gadolinium ortho-cobaltate (Y.sub.1XGd.sub.XCoO.sub.3) exhibits both high selectivity towards the desired NOx product, and low levels of the powerful N.sub.2O greenhouse gas. X-ray powder diffraction analysis of the fresh and used yttrium-gadolinium ortho-cobaltates show that these phases had not undergone a reduction towards:
2Y.sub.1XGd.sub.XCoO.sub.3.fwdarw.(1X/2)Y.sub.2O.sub.3+(X/2)Gd.sub.2O.sub.3+2CoO (2)

(12) Thus the doping of yttrium ortho-cobaltate with a reduction resistant gadolinium, leads to high selectivity towards NOx and low levels of the undesired N.sub.2O, under industrially relevant oxidation conditions. The catalysts may be prepared by co-precipitation, complexation, combustion synthesis, freeze-drying or solid-state routes, or by other state-of-the-art methods of producing mixed-metal oxides.

(13) In this context the composition Y.sub.1XGd.sub.XCoO.sub.3 should be understood as the catalytically active component of a catalyst for use in a process for the oxidation of ammonia or the oxidation of hydrocarbons.

EXAMPLE 2

(14) Samples of Y.sub.1XGd.sub.XCo.sub.1yMn.sub.yO.sub.3 catalysts were tested for their catalytic performance towards ammonia combustion, in the laboratory test reactor system. Table 2 shows the selectivity towards NOx and N.sub.2O emissions for Y.sub.1XGd.sub.XCo.sub.1yMn.sub.yO.sub.3 where X=0.75 and Y=0, 0.1, 0.2 or 0.3.

(15) TABLE-US-00002 TABLE 2 Performance of Y.sub.1-xGd.sub.xCo.sub.1-yMn.sub.yO.sub.3 mixed yttrium-gadolinium ortho-cobaltates, sintered at 900 C., towards ammonia combustion. Ignition N.sub.2O temperature Selectivity emission Sample C. towards NOx % ppm Y.sub.0.25Gd.sub.0.75CoO.sub.3 241 94.6 44 Y.sub.0.25Gd.sub.0.75Co.sub.0.9Mn.sub.0.1O.sub.3 290 80.8 22 Y.sub.0.25Gd.sub.0.75Co.sub.0.8Mn.sub.0.2O.sub.3 265 93.3 23 Y.sub.0.25Gd.sub.0.75Co.sub.0.7Mn.sub.0.3O.sub.3 258 83.2 5
The selectivity towards NOx is lower for these samples containing Mn since there was some NH.sub.3 slippage in these tests. However the N.sub.2O levels are very low for these tests.

(16) The catalysts according to the present invention can be used to catalyse several reactions. Examples of such uses are: I. The catalysts may be used as oxidation catalysts, II. as a catalysts for the selective oxidation of ammonia III. as a catalysts for the oxidation of hydrocarbons IV. as a catalysts for the complete oxidation of hydrocarbons to CO.sub.2, in gas turbine power generation applications V. as a catalysts for the complete oxidation of hydrocarbons to CO.sub.2, at temperatures below 600 C., for the abatement of hydrocarbon emissions from vehicle exhaust gases.

(17) Thus, the present invention also involves methods involving oxidation wherein a catalyst comprising the catalytically active component is used.

(18) The present invention further involves the use of catalysts comprising the catalytically active component for e.g. the abatement of hydrocarbon emissions from vehicle exhaust gases.