Abstract
Soot-catalyst contact represents the main critical issue for an effective regeneration of catalytic (i.e., catalyst-coated) diesel particulate filters (DPFs). Most of the literature reviews on this topic have mainly been focused on studies dealing with powdered soot-catalyst mixtures. Although the results obtained on powders surely provide significant indications, especially in terms of intrinsic activity of materials towards soot oxidation, they cannot be directly extended to DPFs due to completely different soot-catalyst contact conditions generated during filtration and subsequent regeneration. In this work, attention is devoted to catalytic DPFs and, more specifically, studies on both catalyst dispersion and soot distribution inside the filter are critically reviewed from the perspective of soot-catalyst contact optimization. The main conclusion drawn from the literature analysis is that, in order to fully exploit the potential of catalytic DPFs in soot abatement, both a widespread and homogeneous presence of catalyst in the macro-pores of the filter walls and a suitably low soot load are needed. Under optimal soot-catalyst contact conditions, the consequent decrease in the temperature required for soot oxidation to values within the temperature range of diesel exhausts suggests the passage to a continuous functioning mode for catalytic filters with simultaneous filtration and regeneration, thus overcoming the drawbacks of periodic regeneration performed in current applications.
Highlights
Particulate matter (PM) emitted from diesel engines, which is mostly composed of carbonaceous particles called soot, represents a major concern for both human health and environment
On to the other hand, from the perspective of soot-catalyst contact optimization, the results shown the catalytic Diesel particulate filters (DPFs)
The most important developments in the field of the regeneration of catalytic DPFs have been reviewed, focusing on the dispersion of the catalyst inside the walls of the filter channels rather than on its intrinsic activity towards soot oxidation. The latter issue has been widely investigated under conditions of intimate soot-catalyst contact. These conditions are quite far from those of real catalytic DPFs, whose problems mainly stem from a rather weak solid-solid contact established during filtration and subsequent regeneration
Summary
Particulate matter (PM) emitted from diesel engines, which is mostly composed of carbonaceous particles called soot, represents a major concern for both human health and environment. The results obtained on powders surely provide significant indications, especially in terms of intrinsic activity of materials, they cannot be directly extended to DPFs due to different sootcatalyst contact conditions generated during filtration and subsequent regeneration. Their sacrificial burning produces catalyst particles embedded into soot particles, providing intimate soot-catalyst contact Such a solution, commercially applied since the early 2000s, has several drawbacks: the need for a second tank for continuous additive supply in the fuel; the accumulation of metal oxide ash inside the DPF; and the fate of catalyst particles after regeneration.
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