CATALYST ARTICLE FOR EXHAUST SYSTEM OF NATURAL GAS ENGINE

Abstract

The present invention relates to a catalyst article for the exhaust system of a natural gas engine with improved sulphur and/or water tolerance. The catalyst article comprises a doped palladium-on-alumina catalyst, wherein the palladium-on-alumina catalyst is doped with manganese and/or zinc. The invention further relates to an exhaust gas treatment system, a natural gas combustion engine and to a method for the treatment of an exhaust gas from a natural gas combustion engine.

Claims

1. A catalyst article for the treatment of an exhaust gas from a natural gas combustion engine, the catalyst article comprising a doped palladium-on-alumina catalyst, wherein the palladium-on-alumina catalyst is doped with manganese and/or zinc.

2. The catalyst article according to claim 1, wherein the catalyst article has a Pd loading of from 50 to 300 g/ft.sup.3.

3. The catalyst article according to claim 1, wherein the catalyst article has a total loading of Mn and/or Zn of from 5 to 100 g/ft.sup.3.

4. The catalyst article according to claim 1, wherein a ratio of the Pd loading to the total loading of Mn and/or Zn from 1:1 to 10:1.

5. The catalyst article according to claim 1, wherein the doped palladium-on-alumina catalyst is provided as a washcoat on a substrate.

6. The catalyst article according to claim 1, wherein the doped palladium-on-alumina catalyst is provided as a component of an extruded substrate.

7. The catalyst article according to claim 1, wherein the substrate is a flow-through ceramic monolith.

8. The catalyst article according to claim 1, wherein the doped palladium-on-alumina catalyst further comprises platinum, preferably in loading of from 50 to 300 g/ft.sup.3.

9. The catalyst article according to claim 8, wherein the ratio by weight of Pt to Pd is from 1:2 to 1:10.

10. The catalyst article according to claim 1, wherein the doped palladium-on-alumina catalyst comprises one or more further dopant elements selected from Se, Cu, Cd, Ge, Ba, Sr and Sn.

11. The catalyst article according to claim 10, wherein the one or more further dopant elements is present in a loading of from 5 to 100 g/ft.sup.3.

12. The catalyst article according to claim 10, wherein the one or more further dopants is present in a mass ratio to the total amount of Mn and/or Zn of less than 1:1.

13. An exhaust gas treatment system comprising the catalyst article according to claim 1.

14. A natural gas combustion engine comprising the exhaust gas treatment system according to claim 13.

15. A method for the treatment of an exhaust gas from a natural gas combustion engine, the method comprising contacting the exhaust gas with the catalyst article according to claim 1.

16. The method according to claim 15, wherein the exhaust gas is obtained by the combustion of a natural gas, the exhaust gas comprising at least 0.5 ppm sulphur dioxide and/or from 5 to 12 wt % water.

17. The method according to claim 15, wherein during the step of contacting the exhaust gas with the catalyst article, a temperature of the exhaust gas is less than 550° C.

Description

FIGURES

[0042] The invention will be described further in relation to the following non-limiting Figures, in which:

[0043] FIG. 1 shows the methane conversion (%) as a function of temperature under dry and wet conditions. In this figure, from left to right at 50% conversion, the lines are Zn doped (dry), Mn doped (dry), undoped (dry), Pt-doped (dry), and then Zn doped (wet), Mn doped (wet), undoped (wet), and Pt-doped (wet).

[0044] FIG. 2 shows the methane conversion (%) as a function of temperature using a 0.5 ppm SO.sub.2 reaction gas feed. In this figure, at 425° C., the best conversion is obtained with Mn and then with Zn.

EXAMPLES

[0045] The invention will now be described further in relation to the following non-limiting examples.

Example 1

[0046] A catalyst composition comprising 1 wt %Mn-2.85 wt %Pd/on undoped alumina (SOFA 140) was prepared as follows.

[0047] 0.9 g manganese nitrate tetrahydrate was dissolved in minimum amount of water and added to 3.75 g Pd nitrate followed by further dilution with ˜1 ml water. The mixture was added dropwise to 20 g of the alumina support with constant stirring followed by rinsing. The mixture was dried in oven for 3 h followed by calcined at 500° C. for 2 h. The total loading of Pd in this catalyst was approximately 128 g/ft.sup.3 and the total loading of Mn was approximately 45 g/ft.sup.3.

Example 2

[0048] A further catalyst composition comprising 1 wt Zn-2.85 wt %Pd/on undoped alumina (SOFA 140) was prepared as follows. 0.9 g zinc nitrate hexahydrate was dissolved in minimum amount of water and added to 3.77 g Pd nitrate followed by further dilution with ˜1 ml water. The mixture was added dropwise to 20 g of the alumina support with constant stirring followed by rinsing. The mixture was dried in oven for 3 h followed by calcined at 500° C. for 2 h.

[0049] The total loading of Pd in this catalyst was approximately 128 g/ft.sup.3 and the total loading of Zn was approximately 45 g/ft.sup.3.

[0050] Catalyst Testing

[0051] Pelletised samples (0.2-0.4 g, 250-300 μm) of the catalyst compositions prepared in Examples 1 and 2 were tested in a synthetic catalytic activity test (SCAT) apparatus for water and sulphur tolerance using the inlet gas mixtures described below with a space velocity (SV) of 45k at a range of temperatures (ramped from 150 to 450° C. at a ramp rate 10-15° C/minute).

[0052] For water tolerance testing, the following inlet gas mixtures were employed:

[0053] Dry: 4000 ppm CH.sub.4, 8% O.sub.2, balance N.sub.2

[0054] Wet: 4000 ppm CH.sub.4, 8% O.sub.2, 10% H.sub.2O, balance N2

[0055] For sulphur tolerance testing, the following inlet gas mixture was employed: 4000 ppm CH.sub.4, 30 ppm C.sub.3H.sub.8, 100 ppm C.sub.2H.sub.6, 1000 ppm CO, 5%CO.sub.2, 500 ppm NO, 8% O.sub.2, 10% H.sub.2O, 0.5 ppm SO.sub.2, balance N.sub.2.

[0056] Both of these examples showed improved sulphur resistance, improved moisture resistance and better catalytic activity compared to an undoped Pd-catalyst, as shown in the figures.

[0057] Although preferred embodiments of the disclosure have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the disclosure or of the appended claims.