Diesel engines have gained immense popularity as compared to gasoline engines around the world due to their better fuel efficiency, lower operating cost, higher durability, and reliability, and they are the main power source for commercial (trucks, buses, trains, ships) and off-road industrial vehicles (excavation machinery, mining equipment) (Badini et al. 1998). However, a major environmental problem associated with diesel engines is the emission of particulate matter (PM)/soot consisting of carbonaceous soot and a soluble organic fraction (SOF) of hydrocarbons from their exhaust (Abdullah and Bhatia, 2008). Due to the carcinogenic properties of aromatic compounds, photochemical hazardous products of hydrocarbons and black carbon in PM could induce serious health problems and adverse impacts on the environment, such as global warming and climate change (Mishra and Prasad, 2017). Therefore, a possible solution to reduce PM emissions from vehicles is the use of diesel particulate filters (DPFs). The introduction of regenerative catalytic DPFs can reduce soot emission by 98% (Merkel et al. 2001). Among the existing catalytic systems for soot oxidation, noble metal-based catalysts are the most promising ones; however, they are very expensive and sensitive to sulfur poisoning. The key challenge is to find a catalyst that can decrease the combustion temperature of PM from above 600oC to the range of diesel exhaust (150-450oC) (Mishra and Prasad, 2014).
Due to the limited availability of noble metals more focus is on the development of non-precious catalysts i.e. CeO2, NiO, CuO, MoO3, MnO2, Co3O4, and Fe3O4. Among them, copper-ceria catalysts are widely accepted because of their high reducibility at low temperatures. This is due to the synergetic effect between copper and ceria which provides chemically and thermodynamically stable metal oxides (Tang et al. 2014). Wang et al. (2011) reported that nanomaterials have improved catalytic activity than conventional materials due to their higher surface-area-to-volume ratio. Pal et al. (2017) studied Nanostructured Cu-ceria in detail and suggested substantial oxidation ability, specific surface area, and oxygen storage capacity. Moreover, 1-D ceria nanomaterials have a lower agglomeration tendency, possess high porosity, and have an exceptionally high specific surface area. Hence, in recent years, one-dimensional (1-D) ceria nanomaterials, such as nanorods, nanotubes, nanowires, nanobelts, nanoribbons, nanofibers, have been fabricated for different catalytic applications.
Nanofibers can be synthesized by different methods, such as phase separation, template synthesis, and electrospinning. Among them, electrospinning is considered the most suitable method for nanofiber fabrication. Electrospinning is quite versatile because it produces continuous nanofibers at low cost and permits ease of production and flexibility and better control over fiber diameter, microstructure, and fiber arrangement (Cui et al. 2008).
There is no study reported on Cu-supported ceria nanofiber catalysts synthesized by electrospinning technique for diesel soot oxidation. In the present work we have designed fibrous structured Ceria and Cu-supported ceria catalysts with potentially enhanced trapping and soot oxidation properties. Due to special morphology these nanofibers increases the contact points with the soot particles compared to the layer of catalyst which is conventionally used in diesel particulate filter. In order to correlate the catalytic properties with the structure of nanofibers, the textural and spectral characterization was done. This paper additionally gets picture of the impact of working parameters for example i.e. catalyst-soot ratio, catalyst-soot contact condition, and airflow rate on diesel soot oxidation.