However, diesel engines entail a more challenging reduction of pollutant emissions. Particulate matter (PM) is a complex aerosol composed of nanosized carbonaceous particles (called soot) on which soluble hydrocarbons, sulphates

and metals adhere through complex filtration and oxidation phenomena. These particulates have diameters that range from a few nanometers to hundreds of nanometers and beyond [1]. This means serious problems in terms of human respiratory diseases and environmental issues [2, 3]. Driven by compulsory legislation, the reduction in PM emission is currently a technological challenge from both the engine and the catalyst points click here of view. In the past, many efforts were devoted to the development of catalytic diesel particulate filters

(DPF), in order to achieve a cheaper and more effective solution than fuel-borne catalysts (FBC), which had proved to produce more pulmonary intrusion particles [4]. The DPF is a ceramic filter with alternate-plugged channels, in which the flue gases enter the open channels at the inlet, cross the porous ceramic wall of the channel, where soot particles are retained, and finally exit the filter from the neighbouring channels. The soot particles deposit in the pores of the ceramic walls and progressively form a soot layer on top of the wall, which is called cake[5]. The latter generates a drop in pressure across the filter, which becomes unsustainable for the engine; therefore, the cake periodically needs to be burned

off, selleck kinase inhibitor in order for the filter to regenerate. Regeneration is currently achieved through the post-injection of fuel from the engine [6, 7], which causes a relevant fuel penalty for modern engines. Currently, the combination of a trap with an oxidative catalyst is commonly adopted. This involves the deposition of noble metals on carriers with Pyruvate dehydrogenase a high surface area, such as zeolites or γ-alumina, or those with redox properties, like ceria (CeO2) in pure or doped form [8, 9]. It is common knowledge that rare earth metals, like ceria, are less expensive than classic noble metals and leave a lower transformation carbon footprint, which makes these materials more sustainable. Replacing noble metals with rare earth ones, or lowering the content of the former, would be a remarkable result in economic and environmental terms. In this work, ceria-based catalysts have been investigated as active carriers to improve soot oxidation. In particular, three different morphologies have been proposed. Having redox properties, the Ce4+/Ce3+ cycle can store oxygen in lean conditions and then provide it in rich conditions to promote oxidation at the soot-catalyst interface [10]. This ability depends to a great extent on the intrinsic activity of the catalyst and on the properties of the reaction surfaces [11].