T 0141/14 (NOx selective reduction/UMICORE) 25-05-2016

1. Main request - Amendments

1.1 For the board, the amendment of the feature "vanadium" to "vanadium oxide" does not meet the requirements of Rule 139 EPC, because the proposed correction is only one of several options which would occur to the skilled person.

1.1.1 According to the passage bridging pages 2 and 3 of the application as filed, the "solid acid system of titanium oxide and vanadium" is described as optionally further containing "at least one component selected from the group consisting of tungsten oxide (WO3), molybdenum oxide (MoO3), silicon dioxide, sulfate and zeolites", so a combination of vanadium and sulfate is clearly one of the options envisaged by the application as filed.

1.1.2 Appellant's argument that the system titanium oxide/ vanadium oxide was commonly known as solid acid and as SCR catalyst is accepted by the board. However, as long as there exists at least one further possibility of correction - for instance the one indicated in point 1.1.1 above - the criteria of Rule 139 EPC that "the correction must be obvious in the sense that nothing else would have been intended than what is offered as the correction" is not fulfilled.

1.2 Since there is no basis either in the application as filed for the amendment by which "vanadium oxide" replaces "vanadium", the subject-matter of claim 1 at issue extends beyond the content of the application as filed (Article 123(2) EPC).

1.3 It follows from the above considerations that the main request cannot be allowed.

2. First auxiliary request - Admissibility

This request is admitted into the appeal proceedings because the negative opinion of the board regarding the substitution of "vanadium oxide" for "vanadium" contradicts the contested decision, in which the above amendment was held to meet the requirements of both Rule 139 and Article 123(2) EPC.

Since the first auxiliary request remedies this deficiency in a simple manner, namely by deleting the alternative containing the deficiency, and since this amendment was filed one month before the oral proceedings, the board is of the opinion that the respondent had sufficient time to prepare its defence, and so the board exercises its discretion to admit this request into the proceedings.

3. First auxiliary request - Amendments

3.1 Claim 1 of this request differs from that of the main request in that the feature defining the SCR component as "a solid acid of titanium dioxide and vanadium oxide" has been deleted.

3.2 For the board, the amendment defining the catalyst (4) as "not contain[ing] catalytically active platinum group metals" has the following basis in the application documents as originally filed:

3.2.1 The invention as claimed in claim 1 is defined as an exhaust gas treatment unit for the selective catalytic reduction of nitrogen oxides under lean exhaust gas conditions containing:

- at least catalytically active component for selective catalytic reduction (SCR components), and

- at least one storage component for nitrogen oxides (NOx components).

Claim 4 (dependent on claim 1) discloses the SCR components as containing at least one zeolite, which may be present in the acid H form or exchanged with metal ions;

Claim 5 (dependent on claims 1 to 4) discloses the NOx storage components as containing at least one compound of elements selected from the group consisting of alkali metals, alkaline earth metals and cerium.

Claim 6 (dependent on claim 5) discloses the NOx storage components to be catalysed with at least one of the platinum group metals platinum, palladium, rhodium and iridium.

3.2.2 As an alternative to such an exhaust gas treatment unit in which the NOx component is associated with at least one platinum group metal, the passage at page 4, lines 8 to 21, discloses "an oxidation catalyst [...] located [...] upstream of the catalyst for selective catalytic reduction, which also oxidises nitrogen monoxide to nitrogen dioxide". In a preferred embodiment, this alternative is described (page 4, lines 12 to 16) as comprising an oxidation catalyst upstream of a catalyst according to the invention of which the NOx storage components comprise no catalytically active platinum group metals, with the oxidation of nitrogen monoxide to nitrogen dioxide solely occurring at the upstream oxidation catalyst which may contain platinum on active alumina.

3.2.3 Since in the application as filed, the catalyst "according to the invention" is the one defined in claim 1 as filed, i.e. a catalyst containing:

- at least catalytically active component for selective catalytic reduction (SCR components), and

- at least one storage component for nitrogen oxides (NOx components),

the above passage at page 4 is a direct and unambiguous disclosure in the application as filed of a catalyst as defined in claim 1 of the first auxiliary request.

3.2.4 Consequently, the board does not follow the respondent's argument that the application as filed described only the NOx storage component of the catalyst as not comprising catalytically active platinum metals.

3.3 Dependent claims 2 to 11 have their basis in the dependent claims of the application as filed (this has not been contested by the respondent). It follows from the above considerations that the claims of this request meet the requirements of Article 123(2) EPC.

4. First auxiliary request - Sufficiency of disclosure

The respondent argued that the patent failed to disclose how the basic NOx storage component and the acidic SCR catalyst could be combined without being neutralised and significantly reducing the activity of both components. This argument does not convince the board, since the skilled person knows how neutralisation can be avoided, namely by providing the NOx component in a non-alkaline form, for instance by using a nitrate salt thereof, or alternatively, by providing it as a solid, in which case an intimate contact between the components, and so an acid-base reaction, is minimised or avoided.

In the absence of evidence to the contrary, the invention is sufficiently disclosed, since the claimed exhaust gas treatment unit is easily manufacturable by a person skilled in the art, e.g. by mixing the defined compounds or their precursors and converting them into active catalysts according to commonly known procedures.

The patent is thus in conformity with the requirements of Article 83 EPC.

5. First auxiliary request - Novelty

5.1 Document D1 (claims 16 and 17) discloses a system for the treatment of exhaust gases comprising:

- a catalyst for oxidation of at least NO to NO2;

- a filter for collecting soot and holding it for combustion with the NO2 in the gas;

- a NOx absorber containing a solid absorbent;

- means located downstream of the oxidation catalyst and upstream of the absorber for introducing intermittently a NOx-specific reactant;

- a catalyst system located downstream the absorber to promote reactions of HC and CO with O2 to H2O and CO2 and to react NOx to N2.

The system may be structured within a single housing or in separated housings (D1, page 2, lines 15 and 16) and the catalysts and absorbent are supported on a ceramic or metal honeycomb carrying a washcoat (page 2, lines 20 to 24).

The oxidation catalyst comprises generally a platinum group metal, especially platinum and/or palladium (page 2, lines 29 and 30).

The NOx absorbent may be selected from (a) compounds of alkali metals, alkaline earth metals, rare earth metals and transition metals and/or (b) adsorptive materials such as zeolites, carbons and high-area oxides (page 3, lines 17 to 27). Furthermore there may be present one or more catalytic agents, such as precious metals as reaction promoters (page 3, line 30 to page 5, line 2).

The NOx-specific reactant is preferably a nitrogen hydride, such as ammonia or hydrazine or their precursor, for example urea (page 4, lines 29 to 31).

In the examples, the NOx absorber consists of a monolith carrying a coating containing barium, platinum, rhodium and minor proportions of alumina, ceria and zirconia.

5.2 D1 fails to disclose the combination of an oxidation catalyst comprising platinum on active alumina with a platinum group metals-free catalyst containing at least one zeolite and at least one compound of elements selected from the group consisting of alkali metals, alkaline earth metals and cerium. The subject-matter of claim 1 is thus novel over D1.

5.3 As none of the other available documents discloses all the features of claim 1 at issue in combination (a fact which was not disputed by the respondent), it follows from the above considerations that claim 1 of this request, and by the same token claims 2 to 11, which depend on claim 1, meet the requirements of Article 54(1) and (2) EPC.

6. First auxiliary request - Inventive step

By applying the problem-solution approach, the board came to the conclusion that the subject-matter of claim 1 of this request involves an inventive step for the following reasons:

6.1 The invention relates to an exhaust gas treatment unit for the selective catalytic reduction of nitrogen oxides under lean exhaust gas conditions.

6.2 The closest state of the art is represented by document D1, the content of which is described in point 5.1 above. D1 discloses a catalytic unit for treating exhaust gases containing nitrogen oxides under lean exhaust gas conditions.

6.3 As to the problem underlying the contested patent, this is described at paragraph [0006] of the patent in suit as being to reduce the emission of nitrogen oxides from lean operated internal combustion engines even at exhaust gas temperatures below the light-off temperature for hydrolysis of urea and selective catalytic reduction.

6.4 As a solution to this problem, the contested patent proposes the exhaust gas treatment unit according to claim 1 at issue, which is in particular characterised in that:

- the oxidation catalyst comprises platinum on active alumina; and

- the catalyst downstream of the point of injection of urea contains

- at least one zeolite as an SCR component, and

- at least one compound of elements selected from the group consisting of alkali metals, alkaline earth metals and cerium as a NOx storage component, and

- it does not contain platinum group metals.

6.5 The question whether the problem identified in point 6.3 above is solved by the proposed solution is positively answered, since the compounds of alkali or alkaline metals and/or cerium are known to store the NOx at lower temperatures, and release NOx at higher temperatures for it to be converted by the SCR component, i.e. the zeolite, into harmless nitrogen.

6.6 However, as the exhaust gas treatment unit of D1 also makes use of a NOx absorber, the problem addressed in the patent in suit and defined under point 6.3 above has in fact already been solved. Therefore, the objective technical problem must be reformulated as the provision of an alternative exhaust gas treatment unit for the selective catalytic reduction of nitrogen oxides under lean exhaust gas conditions.

6.7 As to the question of obviousness, it has to be determined whether the proposed solution was obvious in the light of the state of the art, in particular in the light of documents D6, D7 or D8, as argued by the respondent.

6.7.1 D6 (claims 1, 3, 4 and 10; Figure 1) discloses an exhaust gas treatment system for diesel engine exhaust comprising:

- a first upstream catalyst comprising platinum and gamma-alumina as nitrogen oxide absorbent, with the exhaust gases being oxidised and the nitrogen oxides being absorbed at lower temperatures and released at higher temperatures;

- a second downstream catalyst comprising a lean-NOx catalyst or a selective reduction catalyst to convert the nitrogen oxides to nitrogen or nitrous oxide;

- an injection zone of a reductant (hydrocarbon, urea or ammonia) between the first and second catalysts.

According to paragraph [0026]:

(a) the lean-NOx catalyst uses a hydrocarbon for the reduction reaction of NOx and is exemplary

Cu-ZSM-5, Fe-ZSM-5, Co-ZSM-5, or supported Rh;

(b) the SCR catalyst uses urea or ammonia and is exemplary a base metal zeolite, such as Cu-ZSM-5 or Ce mordenite.

For the board, the skilled person seeking an alternative to the exhaust gas treatment unit of document D1 and taking document D6 into consideration would not arrive at the subject-matter of claim 1 at issue, because D6 teaches to locate the NOx adsorbent upstream of the SCR catalyst, and not on the same catalyst, as in claim 1 at issue. Furthermore, D6 (paragraph [0017]) teaches away from using alkali or alkaline earth metal compounds as the NOx adsorbent.

6.7.2 D7 (claims 1 and 2) discloses an exhaust gas treatment system for lean-burn engines comprising in sequence:

- a catalyst for oxidising NO (in the examples this catalyst is platinum on stabilised alumina);

- an injection point for urea;

- a catalyst for hydrolysing urea into NH3 and H2O comprising a mixture of TiO2, Al2O3, SiO2, ZrO2, Nb2O5, Ta2O5, WO3 and/or a zeolite in the H form; and

- a reduction catalyst.

In the board's view, the skilled person would not arrive at the claimed invention in view of D7, because the latter does not teach to use on the same catalyst a zeolite and one compound of elements selected from the group consisting of alkali metals, alkaline earth metals and cerium to achieve a selective catalytic reduction of NOx.

6.7.3 D8 (claim 1, 7, 8 and 9) discloses a process for removing nitrogen oxides from an oxygen-containing gas by conversion to nitrogen and water, comprising a contacting step with an oxidation catalyst (preferably platinum and/or palladium), adding ammonia to the gas leaving this catalyst, and thereafter contacting said gas stream with a reduction catalyst. In preferred embodiments (claims 15, 17 or 19), the reduction catalyst is a mixture of at least two metal oxides, such as a mixture of titania and vanadia or a mixture of titania, vanadia, alumina and ceria.

D8 does not describe the use of a zeolite, let alone the combination of a zeolite with one compound of elements selected from the group consisting of alkali metals, alkaline earth metals and cerium, to achieve the selective reduction of NOx compounds, so the skilled person faced with the problem of providing an alternative to the exhaust gas treatment unit of D1 would not arrive in an obvious manner at the wording of claim 1 at issue on the basis of the content of this document either.

6.7.4 The other documents in the proceedings also do not disclose or suggest the solution as defined in claim 1 at issue to the problem defined in point 6.3 above.

6.8 It follows from the above considerations that the subject-matter of claim 1 of the first auxiliary request involves an inventive step (Article 56 EPC).

The same applies to claims 2 to 11, which depend on claim 1 at issue.

7. Since the claims of the first auxiliary request meet the requirements of the EPC, there is no need to consider the lower-ranking requests.