Continuous diesel soot control with minimal back pressure penatly using conventional flow substrates and active direct soot oxidation catalyst disposed thereon

Abstract

There is disclosed high cell density or tortuous / turbulent flow through monolithic catalyst devices for the direct catalytic, and (semi) continuous oxidation of diesel particulate matter. The catalysts relate to OIC / OS materials having a stable cubic crystal structure, and most especially to promoted OIC / OS wherein the promotion is achieved by the post-synthetic introduction of non-precious metals via a basic (alkaline) exchange process. The catalyst may additionally be promoted by the introduction of Precious Group Metals.

Description

REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of provisional application 61 / 308,879, filed Mar. 27, 2008, and is a continuation-in-part of application Ser. No. 12 / 240,170 filed Sep. 29, 2008, and application Ser. Nos. 12 / 363,310 and 12 / 363,329, both filed Jan. 30, 2009, all of which are relied on and incorporated herein by reference.INTRODUCTION AND BACKGROUND[0002]Over the last thirty years increasingly stringent legislative limits have been introduced to regulate the emissions from both petrol (gasoline) and diesel internal combustion engines. See Regulation (EC) No 715 / 2007 of the European Parliament and of the Council, 20 Jun. 2007, Official Journal of the European Union L 171 / 1, see also Twigg, Applied Catalysis B, vol. 70 p 2-25 and R. M. Heck, R. J. Farrauto Applied Catalysis A vol. 221, (2001), p 443-457 and references therein. In the case of diesel / compression ignition engines this has led to the implementation of the Diesel Oxidation Catalyst (...

AI Technical Summary

Benefits of technology

[0015]The use of high cell density / turbulent flow through monoliths is also required to provide sufficient interaction and subsequent reaction between the entrained soot particles within the exhaust flow and the active catalytic coating. The term high cell density is consistent with preformed flow through monolith substrates with a large (≧600) number of individual cells of flow channels per square inch. It is proposed that this high cell density firstly introduces turbulence at the inlet to maximise possible soot collisions with the active wash-coated walls of the monolith. Secondly, the high cell density restricts the flow path through the monolith, again increasing the potential for particulate collisions and retention / reaction on the active wash-coat, but without the large backpressure penalties associated with the conventional DPF. Moreover the use of the flow-through substrate removes existing constraints regarding total washcoat loading, or the use of layered technologies with specific functionalities, e.g. soot combustion catalyst in one layer (overcoat) and SCR catalyst in a second layer (undercoat), equally it enables the use of an undercoat rich in Al2O3 to provide high washcoat adhesion, but with low intrinsic catalytic function, onto which a second pass containing all required OS, PGM and NOx trap etc. active components may be dispersed. In this second example, the overcoat would under normal conditions present lower adhesion and would conventionally be diluted with binder, e.g. Al2O3, however, the incorporation of binder results in a decrease in activity due to dilution of the active phase, hence the layered design is preferred. This layering ensures the surface coating that would interact / react with the soot as it passed through the flow-through substrate would exclusively consist of active material and would therefore maximize catalytic action. The enabling of higher washcoat loads when using the flow through monolith also provides the capability of employing higher concentrations of active materials to be coated on the substrate thereby further enhancing the performance and hydrothermal durability of the technology without the catastrophic back pressure penalty such an approach would present using the conventional DPF. Hence by use of the flow through substrate washcoat load could be increased from 10 g / l to 180 g / l or higher concomitantly increasing the effective geometric surface area for catalyst to soot contact to again increase in combustion efficiency.

[0019]b) Particulate control system without requirement for DPF substrate thereby removing associated substrate cost, back pressure constraints, canning and space requirements and ancillary systems associated with conventional DPF;

[0022]e) Ability to employ multilayer technologies with specific functionalised layers to providing additional catalytic properties and functions from a single monolith and to potentially achieve further chemical synergies and performance advantages previously impossible when employing the conventional DPF.

[0023]f) Synergistic operation between the active washcoat and high cell density substrate to facilitate rapid oxidation of soot and soluble organic fraction to thereby circumvent the potential for ‘face plugging’, a phenomenon associated with the use of conventional high CPSI monoliths with conventional catalyst formulations.

Problems solved by technology

Secondly, the high cell density restricts the flow path through the monolith, again increasing the potential for particulate collisions and retention / reaction on the active wash-coat, but without the large backpressure penalties associated with the conventional DPF.

However, the use of this ‘hyper-milling’ to obtain the very small particles for in-wall coating has been found to be extremely destructive to the activity, stability and surface areas of the OS and alumina components employed in typical formulations.

As a result such a process can adversely affect the rate of release and total Oxygen Storage capacity of the OS.

In addition the hyper-milling can result in cation extraction and phase disproportionation for the OS with further poisoning of any PGM function arising from the deposition of extracted cations.

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