HK1113811B

HK1113811B - Exhaust system comprising exotherm-generating catalyst

Info

Publication number: HK1113811B
Application number: HK08103767.7A
Authority: HK
Inventors: Bernard Paul Gabriel Ghislain Marie Oger; Paul Richard Phillips; Martyn Vincent Twigg; Andrew Peter Walker
Original assignee: Johnson Matthey Public Limited Company
Priority date: 2004-11-23
Filing date: 2005-11-22
Publication date: 2013-05-24

Description

Exhaust system comprising a catalyst generating an exotherm

Technical Field

The present invention relates to an exhaust system for a compression ignition engine, such as a diesel engine, and in particular it relates to an exhaust system comprising an exothermic-generating device consisting essentially of a catalyst and a device for injecting hydrocarbons into the exhaust gas for combustion on the catalyst.

Background

Diesel Oxidation Catalysts (DOCs) are designed to promote the chemical oxidation of carbon monoxide (CO) and Hydrocarbons (HC) as well as the Soluble Organic Fraction (SOF) portion of Particulate Matter (PM). Additional benefits include oxidation of individual non-regulated HC-derived emissions, such as aldehydes or Polycyclic Aromatic Hydrocarbons (PAHs), and reduction or elimination of diesel exhaust odor. HC is oxidized to form carbon dioxide (CO)₂) And steam to oxidize CO to CO₂. Generally, the DOC includes an active Platinum Group Metal (PGM), typically platinum.

DOCs comprising chromium oxide (chromiA), palladium (Pd) and platinum (Pt) are known from US-A-4,303,552.

Some of the oxidation reactions that may occur on the DOCUndesirable products are formed and actually work in opposition to the catalyst application. Sulfur dioxide (SO)₂) Can be oxidized to form gaseous sulfuric acid (H) which can be combined with water vapor₂SO₄) Sulfur trioxide (SO) of₃). The sulfuric acid vapor may combine with other water vapor to produce sulfuric acid particulates, which are detected as particulates in assessing total PM emissions from the engine. Sulfur can also poison the oxidation activity of DOC, and it is believed that this is an important reason why palladium catalysts are not more widely accepted in the market.

Exhaust gas temperatures are low (e.g., about 300 c) especially for compression ignition engines for diesel engines of light-duty diesel vehicles (as defined by the relevant legislation), and one such challenge facing catalyst developers is to develop robust catalyst formulations with low light-off temperatures. Although the sulphur derived from the fuel will be reduced in european union countries (from 1/2005, the maximum sulphur content in Euro 4 (approved type) diesel fuel will be reduced from 350ppm to 50ppm, whereas this rating will probably be reduced to 10ppm in 2010), the rating in the USA was not therefore reduced from their current 350ppm rating before 2007.

In order to meet current and future vehicle emission standards for particulate matter, it has been proposed to install a particulate filter in the exhaust system of a compression ignition engine powered vehicle. Suitable filter substrates may include ceramic wall-flow filters and sintered metal filters. It is also known to catalyze filters to reduce the combustion temperature of particulate matter so that it does not exceed or approach the exhaust gas temperature generated during normal driving conditions. However, the exhaust gas temperature of light-duty compression ignition engines is typically too low for the catalyzed filter to be passively regenerated, and so there has been a suggestion to actively regenerate the filter in the exotherm generated by combusting the hydrocarbon fuel on the catalyzed filter or on a separate catalyst upstream of the filter. Such an arrangement is described, for example, in GB-a-2064983.

US-A-4,686,827 describes an exhaust system for A diesel engine in which an electrically heated catalyst is used to generate an exotherm from hydrocarbon fuel injected into the exhaust gas for active regeneration of A downstream filter. In one embodiment, the electrically heated catalyst is platinum-palladium.

In our WO 2004/025093 we describe a compression ignition engine operable in a first mode and a second mode, the first mode being a normal running mode and the second mode producing exhaust gas comprising an increased level of CO relative to the first mode, and an apparatus which in use switches engine operation between the two modes, the engine comprising an exhaust system comprising a supported Pd catalyst in association with at least one alkali metal promoter and optionally a supported Pt catalyst in association with and/or downstream of the catalyst, wherein CO is oxidised by the supported Pd catalyst during operation in the second mode. According to this specification, increased CO can be produced: by injecting HC into the exhaust system, over a portion of the oxidation catalyst; by adjusting the ignition timing of at least one engine cylinder; and/or adjusting an engine air-fuel ratio of at least one engine cylinder. In one embodiment, the Pd catalyst and associated alkali metal and optional Pt catalyst components comprise a diesel oxidation catalyst.

US 2002/0053202 discloses a combined H₂Supply and SOF adsorption-oxidation catalysts including NO for co-downstream_xAt least one of Pt, Pd and/or rhodium (Rh) and cerium (Ce) which are periodically enriched with the air-fuel ratio of the exhaust gas are used in an adsorption catalyst. Example illustrates H₂Supplying and mixing Pt/CeO₂And Pt/La.SiO₂A SOF adsorption-oxidation catalyst of composition.

We have now found very unexpectedly that the combination of platinum and palladium is more active for generating an exotherm than either of the equivalent amounts of Pt or Pd alone. That is, there is a previously unrecognized synergy between platinum and palladium for generating an exotherm from a hydrocarbon fuel. This finding enables the platinum-palladium catalyst to be used without electric heating, so that the exhaust system is less complicated and the fuel burden from the electric heating catalyst is saved. Furthermore, we have recognized certain embodiments that are more resistant to sulfur poisoning, or that may be more easily devulcanized using the exotherm generated by the combustion of the hydrocarbon fuel.

Disclosure of Invention

According to one aspect, the present invention provides an apparatus comprising a compression ignition engine and an exhaust system therefor, comprising at least one exhaust system component for treating exhaust gas and means for generating an exotherm for heating the at least one exhaust system component, the exotherm generating means consisting essentially of a catalyst and means for injecting hydrocarbon into the exhaust gas for combustion on the catalyst, the catalyst consisting essentially of both a palladium (Pd) component and a platinum (Pt) component, and an optional support disposed on a substrate monolith.

The Pt component and the Pd component can be organized in any of a number of arrangements. In a first arrangement, the Pt and Pd components are in separate active layers (washcoat layers). In one embodiment of the first arrangement, both the Pd component and the Pt component are supported on the same support. In a second embodiment, the Pd component is supported on a first support and the Pt component is supported on a second support. In a third embodiment, the Pt component is disposed in a region on the upstream end of the substrate monolith and the Pd component is disposed on the downstream end of the substrate monolith.

In a second arrangement, the Pd component supported on the first support is within the first active layer and the Pt component supported on the second support is within the second active layer. In this latter arrangement, the first active layer may be disposed below the second active layer, or vice versa.

It will be appreciated that in arrangements in which the Pt component and the Pd component are closely associated, for example in the embodiment in which the Pd and Pt components are in the first arrangement on the same support, the Pt and Pd components may form an alloy. Typically, this results in an active component that exhibits the characteristics of both components. For example, the alloy is less metallic than Pt itself. This may be useful for applications where the catalyst is exposed to high temperatures, since the alloy is more resistant to sintering than Pt itself. Also, because Pd is a poor NO oxidation catalyst compared to Pt, the alloy can promote NO oxidation more effectively than Pd alone. Therefore, the alloy can maintain the oxidation activity of HC and CO better than sintered Pt.

In embodiments in which the Pt component is supported on a first support and the Pd component is supported on a second support, the first support may be different from the second support.

Optionally, in another arrangement, at least one of the Pt component and the Pd component is supported by the substrate monolith itself.

Suitable weight ratios of Pt to Pd in the oxidation catalyst may be from 6: 1 to 1: 6, alternatively from 4: 1 to 1: 2. Typical total content (loading) of Pt and Pd in the oxidation catalyst may be from 10 to 200gft^-3Alternatively 40-100gft^-3。

A problem with Pd-containing oxidation catalysts is that they can be poisoned by sulfur relatively quickly, which can be a controversial point for countries with higher dye sulfur. After studying ways to reduce or avoid this problem, we have found that one solution is to locate a Pt catalyst that is substantially free of Pd in a region at the end of the substrate monolith upstream of the exothermic Pt and Pd containing catalyst region. The substantially Pd-free Pt-containing region can be up to half the length of the substrate monolith or "stripe" type dimension.

In the above-described first arrangement of embodiments in which the Pt component zone is disposed on the upstream end of the substrate monolith and the Pd component zone is disposed on the downstream end thereof, the substantially Pd-free Pt-containing zone may comprise the Pt component zone, or alternatively it may be in addition to the Pt component zone. In later configurations, the Pt content in the substantially Pd-free Pt-containing region may be the same or different from the Pt content in the Pt-component region.

Typically, the Pt content in the catalyst at the upstream end may be 10 to 200g ft^-3Alternatively 30 to 150g ft^-3。

In one embodiment, the Pt in the catalyst at the upstream end is supported on a support.

Typically, the or each support is selected from alumina, silica, ceria, zirconia, titania and mixtures or mixed oxides of any two or more thereof. However, in particular embodiments, we have found it advantageous to use a more sulfur tolerant support for the Pd and Pt components of the exothermic catalyst behind the front of the substrate monolith and a more heat tolerant support for the Pt and Pd components in front of the back of the substrate monolith. This example derives from our observation that: when HC is injected into exhaust gas upstream of the exothermic catalyst, the temperature in the rear of about the first third (first third) from the front of the substrate monolith is generally kept low. It is therefore advantageous to locate more sulfur tolerant catalyst in this region because it is more difficult to increase the temperature within the associated catalyst for purposes of desulfurization.

In contrast, the temperature towards the rear of the substrate monolith can reach 1000 ℃ during HC injection, where desulfurization will occur without significant difficulty. However, the heat resistance of the catalyst in this location is more of an issue and therefore the catalyst can be formulated for heat resistance with advantage.

Suitable supports for washcoat of the upstream sulfur tolerant catalyst zone may be selected from titania, zirconia, silica, mixtures or mixed oxides of any two or more thereof, and mixed oxides or composite oxides of alumina and at least one of titania, zirconia or silica, with alumina being a more suitable support to provide increased heat resistance to the catalyst formulation at the downstream end of the substrate monolith.

"composite oxide" as defined herein means an amorphous oxide material comprising primarily at least two component oxides, which are not truly mixed oxides consisting of at least two components.

Where the oxidation catalyst comprises a substantially Pd-free Pt-containing region upstream of the Pd-and Pt-containing exothermic catalyst-generating region, the region of the sulfur-tolerant support need not correspond to that of the substantially Pd-free Pt-containing region and the same is the case for the Pd-and Pt-containing region and the region of the heat-tolerant support.

At least one exhaust system component may comprise an optionally catalysed particulate filter, NO_xAbsorbent, Selective Catalytic Reduction (SCR) catalyst or depleted (lean) NO_xA catalyst. NO_xThe absorbent (typically an oxide of an alkaline earth metal such as barium, calcium or strontium, or an oxide of an alkali metal such as potassium or caesium) may form NO_xFraction of collector, NO_xThe collector typically comprises a Pt oxidation catalyst and a rhodium reduction catalyst coated on a flow-through monolith substrate. Optionally, NO as defined above_xThe sorbent may be loaded on the particulate filter. Including NO in the filter_xAbsorbent, oxidation catalyst and NO_xWhere the collector is reducing catalyst, this arrangement is often referred to as a 'four-way' catalyst or FWC.

In fact, NO is included in the exhaust system_xWhere the absorbent is to be regenerated, suitable control means are intermittently incorporated to reduce the oxygen concentration in the exhaust gas to regenerate NO_xAbsorbent and reduction of such emissions in NO_xReduction of NO on a catalyst_x. Such control means are well known to those skilled in the art and include varying the timing of fuel injection into one or more of the engine cylinders or injectors for injecting a suitable reductant such as HC directly into NO_xIn the exhaust gas upstream of the absorbent. According to the invention for producingThe heat-generating fuel injector may be used for this purpose with NO therein_xThe absorber and exothermic catalyst are in the same substrate monolith embodiment as described below.

In one exemplary embodiment, the substrate monolith is a ceramic or metal flow-through monolith disposed upstream of at least one exhaust system component. In such an arrangement, the catalyst may be configured as a DOC for treating CO and HC between exotherm generation events. It should be understood, however, that the catalyst is activity-adjusted for low HC light-off to achieve its primary function as an exothermic catalyst. In one embodiment, at least one exhaust system component is a filter, and the means for generating an exotherm facilitates filter regeneration at preselected regular intervals or in response to sensor input such as backpressure across the filter.

According to another embodiment, at least one exhaust system component is NO_xCollector, it will be appreciated that there is an optimal temperature window (window) for NO_xAbsorption and NO_xRegeneration of absorbent and for NO_xAnd (4) reducing. The heat-generating device may be operated in response to the detected NO_xTrap temperature to maintain NO_xThe collector temperature is within a desired temperature range.

In an alternative embodiment, at least one exhaust system component comprises a substrate monolith. The substrate monolith may be a flow-through monolith or a particulate filter, depending on the characteristics of at least one exhaust system component.

In a particular embodiment in which the substrate monolith is a particulate filter, the exothermic catalyst is disposed within a "stripe" or zone configuration on the front end of the substrate monolith and a substantially Pd-free Pt catalyst is coated downstream thereof, wherein the Pt support may be alumina. This configuration is useful in high temperature applications in that the sintering of Pt/alumina due to the effect of Pt: Pd alloying can promote NO oxidation more effectively than the sintering of exothermic catalysts.

The means for injecting HC into the exhaust gas may comprise an injector for injecting HC directly into the exhaust gas upstream of the exothermic catalyst, or alternatively an injector in one or more cylinders of the engine.

In one embodiment, the compression ignition engine may be a diesel engine, optionally a light duty diesel engine.

According to a second aspect, the present invention provides a method of heating at least one component in an exhaust system of a compression ignition engine, the method comprising generating an exotherm for heating the at least one exhaust system component by contacting a catalyst consisting essentially of both a palladium (Pd) component and a platinum (Pt) component and an optional support disposed on a substrate monolith with exhaust gas comprising an increased concentration of hydrocarbons relative to the concentration of hydrocarbons present in the exhaust gas during normal operating conditions.

Drawings

In order that the invention may be more fully understood, the following examples are provided by way of illustration only and with reference to the accompanying drawings, in which:

FIG. 1 is a graph showing the HC reduction (ppm) versus time for a Pt-only oxidation catalyst, a Pd-only oxidation catalyst, and a Pt: Pd 1: 1 oxidation catalyst before, during, and after HC injection upstream of the catalyst at 7,000ppm (C3) during steady state conditions at an inlet temperature of 275 ℃;

FIG. 2 is a graph showing the HC reduction (ppm) versus time for three oxidation catalysts of different Pt: Pd before, during, and after injection of HC upstream of the catalyst at 7,000ppm (C3) during steady state conditions at an inlet temperature of 275 ℃;

3A, 3B, 3C and 3D show a series of schematic diagrams illustrating embodiments of the present invention according to a feature of a separate exothermic catalyst disposed upstream of an exhaust system component; and

fig. 4A and 4B show schematic diagrams illustrating an embodiment of the invention in which the exhaust system component comprises an exothermic catalyst.

Detailed Description

Referring to fig. 3, 10 generally refers to an exhaust system for a compression ignition engine according to the present invention, and 12 represents a system for delivering exhaust gas from the engine to various components of the exhaust system for exhaust gas aftertreatment and/or for engine noise abatement before the exhaust gas is passed to the atmosphere. Arrows indicate the direction of exhaust flow in the system and "upstream" and "downstream" should be construed accordingly.

In fig. 3A, 13 refers to a flow-through monolith substrate comprising a catalyst coating 14, the catalyst coating 14 being characterized by separate active layers of particulate support supporting both a Pt component and a Pd component. Alternatively, the catalyst washcoat 14 may include a Pt component and a Pd component, each supported on separate and optionally mutually different supports within a separate active layer. The arrangement of the catalyst coating 14 may also include a supported Pt component in the first active layer, on which a second active layer of a supported Pd component is coated, or the Pd component may be in a layer below the Pt component layer. The part identified as 15 is an injector for delivering combustible HC into the exhaust gas upstream of 13, this injector being controlled by suitably programmed control means of an optional part of the Engine Control Unit (ECU). Part 16 is at least one exhaust system component, such as an optionally catalyzed particulate filter, SCR catalyst, NO_xTrap, four-way catalyst or depleted NO_xA catalyst.

Fig. 3B, 3C and 3D illustrate alternative embodiments of the flow-through monolith substrate 13. In fig. 3B, 18 represents the Pt component of the exothermic catalyst and 20 is the Pd component thereof. FIG. 3C shows an alternative arrangement for a fuel containing higher amounts of sulfur, where a "stripe" of substantially Pd-free Pt catalyst 22 higher than the Pt content of 18 is positioned at the upstream end of the flow-through substrate monolith 13, except for the components 18 and 20. Of course, FIG. 3B may also represent a composite embodiment characterized by a substantially Pd-free Pt catalyst at substantially the same Pt content as the Pt component of the exothermic catalyst, i.e., the "stripe" of substantially Pd-free Pt catalyst on the upstream side of the Pt component 18 is contiguous with the Pt component 18 where the Pt content in 22 is greater than or equal to the Pt content in 18. Figure 3D illustrates an embodiment in which a substantially Pd-free Pt catalyst 22 is positioned on the upstream side of any of the embodiments of 14 described above.

Referring to fig. 4A, items sharing the same reference numbers as in fig. 3A-D represent the same parts as described above. Reference numeral 23 denotes a particulate filter substrate monolith and is coated with a single or double layer washcoat arrangement 24 similar to those described with reference to part 14 in fig. 3A-D. Figure 4B illustrates the embodiment of figure 4A in which a "strip" of substantially Pd-free Pt catalyst 22 having a higher Pt content than 24 is positioned on the upstream end of the filter substrate 23 of the exotherm generating catalyst 24. NO coated on filter substrate 23 with a composition comprising Pt and Pd components of an exothermic catalyst, e.g. barium oxide_xWhere the absorbent and the rhodium reduction catalyst are present, the catalyst composition is referred to as a four-way catalyst 26.

Example 1

A set of catalyst samples, each supported on a ceramic flow-through substrate monolith, was prepared, the monoliths having the following dimensions: 267mm (10.5inch) diameter by 152mm (6 inch) length and 8.5 litre (519 inch)³) At 62 cell cm^-2(400 cell inch^-2) And a wall thickness of 0.15mm (0.06 inch). The formulation of the catalyst sample was as follows: (i) only Pt; (ii) only Pd; (iii) 2: 1 of Pt: Pd; (iv) 1: 1 of Pt: Pd; and (v) 1: 2 Pt: Pd. In each case, the Pt and/or Pd are supported on an alumina-based support and the total PGM content (loading) is for all catalysts comprising (i) to (v)The samples were equal. Prior to testing, the catalyst samples were aged in air at 700 ℃ for 200 hours, followed by further aging in air at 750 ℃ for 200 hours. For testing, the catalyst samples were positioned in a 10 liter (litre) exhaust duct, and the turbocharged engine on the test bench had thermocouples mounted 25mm forward of the inlet face and 25mm aft of the outlet face. The engine was run at steady speed and the load was adjusted to 45,000hr^-1The hourly gas space velocity (GHSV) produced an inlet temperature to the catalyst of 275 ℃. A separate diesel fuel injector is disposed in the exhaust conduit upstream of the catalyst in a position that ensures a uniform, well-distributed injection of fuel in front of the catalyst sample.

Once stable conditions were achieved, about 7,000ppm Hydrocarbon (HC) (C3) was continuously injected into the catalyst for about 700 seconds, causing the outlet temperature of the catalyst to rise to about 600 ℃. The amount of HC at the catalyst outlet (ppm) was measured during all injections.

Fig. 1 shows the HC reduction rate (slip) of the catalyst samples (i), (ii) and (iv). It can be seen that the Pd-only catalyst allows a higher degree of HC reduction rate when injection starts than the Pt-only catalyst, but this reduces the catalyst temperature rise faster. The Pt-only catalyst, although the initial HC reduction rate was smaller, allowed more time for HC to pass through (through with time) and the rate of HC reduction rate became constant to a higher degree than the Pd-only catalyst. The outlet temperature of the Pt only catalyst (not shown) was also lower than the Pd containing catalyst sample tested in either of them, probably due to coking of the catalyst surface. The 1: 1 Pt: Pd catalyst showed a more or less constant, low HC reduction rate throughout the duration of the injection and is therefore a significant improvement over both containing separate metal samples.

FIG. 2 shows the results of comparing Pt: Pd catalyst samples (ii), (iv) and (v), all of which show similar performance, although the Pt: Pd catalyst samples at a ratio of 1: 2 reacted somewhat slower and stabilized for a longer time when HC began to be injected than the samples containing at least equal amounts of Pt.

Example 2

The experiments were carried out with different sets of catalyst samples coated on a flow-through monolith having a diameter of 152mm (6 inch) x a length of 152mm (6 inch) and 2.8 litre (170 inch)³) At 62 cell cm^-2(400 cell inch^-2) And 0.15mm (0.06inch) wall thickness. The catalyst formulation consisted of (vi) of Pt only and (vii) of 1: 1 Pt: Pd, both on the same alumina support and at the same total PGM content. Prior to testing, the catalyst was aged for 400 hours in a similar manner to example 1. They were then installed in the exhaust duct of a 6.0 litre turbocharged engine on a test rig with a separate diesel fuel injector positioned upstream of the catalyst as in example 1. The inlet temperature was measured at 25mm (l inch) into the front of the catalyst substrate using a thermocouple and by adjusting the engine load, the engine was run at four steady state speeds for 10 minutes to produce temperatures of 225 ℃, 250 ℃, 275 ℃ and 300 ℃ the space velocity range varied from 25 to 35,000 GHSV as a function of load.

Table 1 summarizes the stable temperature rise over the catalyst and the approximate percent elimination of HC during the injection time. The data confirms that the Pt: Pd catalyst produces a higher temperature rise at a lower inlet temperature and a lower HC reduction rate than the Pt system, thus showing excellent fuel combustion characteristics for regeneration of the particulate filter.

TABLE 1

Claims

1. An apparatus comprising a compression ignition engine and an exhaust system (10) therefor, comprising at least one exhaust system component (16) for treating exhaust gas and means for generating an exotherm for heating the at least one exhaust system component, the means for generating an exotherm consisting essentially of a catalyst (14) and means (15) for injecting hydrocarbon into exhaust gas for combustion on said catalyst, the catalyst consisting essentially of both a palladium (Pd) component and a platinum (Pt) component, and optionally a support, and being disposed on a substrate monolith in one of the following arrangements:

(i) the Pt component is disposed in a zone (18) on an upstream end of the substrate monolith and the Pd component is disposed in a zone (20) on a downstream end of the substrate monolith; and

(ii) the Pt component and the Pd component are disposed on a downstream end of the substrate monolith, and an upstream end (22) of the substrate monolith comprises the Pt component substantially free of Pd.

2. The apparatus of claim 1, wherein the Pd component and the Pt component are both supported on the same support.

3. The apparatus of claim 1, wherein the Pd component is supported on a first support and the Pt component is supported on a second support.

4. The apparatus of claim 3, wherein the Pd component supported on the first support is in a first layer and the Pt component supported on the second support is in a second layer.

5. The apparatus of claim 4, wherein the first layer is below the second layer.

6. The apparatus of claim 3, 4 or 5, wherein the first carrier is different from the second carrier.

7. The apparatus of any one of claims 1-5, wherein the weight ratio of Pt to Pd in the catalyst is from 5: 1 to 1: 5.

8. The apparatus of any one of claims 1 to 5, wherein the catalyst is heated in the presence of a heating elementThe total content of Pt and Pd in the catalyst is 10-200 gft^-3。

9. The apparatus of any one of claims 1-5, wherein in arrangement (ii), the Pt content in the upstream-end catalyst is 10 to 200gft^-3。

10. An apparatus according to any one of claims 1 to 5, wherein the or each support is selected from alumina, silica, ceria, zirconia, titania and mixtures or mixed oxides of any two or more thereof.

11. The apparatus of any one of claims 1-5, wherein the substrate monolith comprises an upstream zone and a downstream zone, wherein the support in the upstream zone is selected from titania, zirconia, silica, a mixture or mixed oxide of any two or more thereof, and a mixed oxide or composite oxide of alumina and at least one of titania, zirconia, or silica, and the support in the downstream zone comprises alumina.

12. The apparatus of any of claims 1-5, wherein the at least one exhaust system component is selected from a particulate filter, NO_xAbsorbent, Selective Catalytic Reduction (SCR) catalyst and depleted NO_xA catalyst.

13. The apparatus of claim 12, wherein the NO is_xAn absorbent is on the particulate filter.

14. The apparatus of any of claims 1-5, wherein the substrate monolith is a flow-through monolith disposed upstream of the at least one exhaust system component.

15. The apparatus of claim 14, wherein the at least one exhaust system component comprises the substrate monolith.

16. The apparatus of claim 12, wherein the substrate monolith is the particulate filter.

17. An apparatus according to any one of claims 1-5, wherein the means for injecting hydrocarbons into the exhaust gas comprises an injector for injecting the hydrocarbons into the exhaust gas immediately upstream of the substrate monolith.

18. The apparatus of any of claims 1-5, wherein the means for injecting hydrocarbons into the exhaust gas comprises an injector within one or more cylinders of the engine.

19. The apparatus according to any one of claims 1-5, characterised in that the compression ignition engine is a diesel engine.

20. A method of heating at least one component in an exhaust system of a compression ignition engine, the method comprising generating an exotherm for heating the at least one exhaust system component by contacting a catalyst consisting essentially of both a palladium (Pd) component and a platinum (Pt) component, and optionally a support, with exhaust gas comprising an increased concentration of hydrocarbons relative to the concentration of hydrocarbons present in the exhaust gas during normal operating conditions, the catalyst being disposed on a substrate monolith in one of the following arrangements: