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 methane in an exhaust gas from a natural gas combustion engine, wherein the exhaust gas comprises 5 to 12 wt % water, wherein the catalyst article comprises a doped palladium-on-alumina catalyst, wherein the palladium-on-alumina catalyst is doped with zinc, wherein the catalyst article has a palladium loading of from 100 to 200 g/ft.sup.3, wherein the catalyst article has a zinc loading of from 20 to 80 g/ft.sup.3.

2. The catalyst article according to claim 1, wherein the catalyst article has a total loading of Zn of from 40 to 60 g/ft.sup.3.

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

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

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

Description

FIGURES

(1) The invention will be described further in relation to the following non-limiting Figures, in which:

(2) 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).

(3) 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

(4) The invention will now be described further in relation to the following non-limiting examples.

Example 1

(5) A catalyst composition comprising 1 wt % Mn-2.85 wt % Pd/on undoped alumina (SCFA 140) was prepared as follows.

(6) 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.

(7) 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

(8) A further catalyst composition comprising 1 wt % Zn-2.85 wt % Pd/on undoped alumina (SCFA 140) was prepared as follows.

(9) 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.

(10) 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.

(11) Catalyst Testing

(12) Pelletised samples (0.2-0.4 g, 250-300 ?m) 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 45 k at a range of temperatures (ramped from 150 to 450? C. at a ramp rate 10-15? C./minute).

(13) For water tolerance testing, the following inlet gas mixtures were employed:

(14) Dry: 4000 ppm CH.sub.4, 8% O.sub.2, balance N.sub.2

(15) Wet: 4000 ppm CH.sub.4, 8% O.sub.2, 10% H.sub.2O, balance N.sub.2

(16) 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.

(17) 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.

(18) 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.