This work presented the influence of metal oxides as the support for silver-supported catalysts on the catalytic oxidation of diesel particulate matter (DPM). The supports selected to be used in this work were CeO₂ (reducible), ZnO (semiconductor), TiO₂ (reducible and semiconductor), and Al₂O₃ (acidic). The properties of the synthesized catalysts were investigated using XRD, TEM, H₂-TPR, and XPS techniques. The DPM oxidation activity was performed using the TGA method. Different states of silver (e.g., Ag° and Ag⁺) were formed with different concentrations and affected the performance of the DPM oxidation. Ag₂O and lattice oxygen, which were mainly generated by Ag/ZnO and Ag/CeO₂, were responsible for combusting the VOCs. The metallic silver (Ag°) formed primarily on Ag/Al₂O₃ and Ag/TiO₂ was the main component promoting soot combustion. Contact between the catalyst and DPM had a minor effect on VOC oxidation but significantly affected the soot oxidation activity.

In the present work, an experimental investigation is carried out on the use of waste plastic oil produced from waste poly(ethylene terephthalate) (PET) bottles (WPOB) as an alternative fuel for diesel engines. The physical and chemical properties of WPOB were analyzed, and it was found that it has fuel properties similar to those of petroleum fuels. The WPOB was tested in a diesel engine to evaluate the effect of WPOB on combustion and emissions characteristics. In addition, particulate matter (PM) emissions generated by the combustion of WPOB were analyzed. The combustion of WPOB was retarded with respect to diesel fuel, resulting in higher carbon-based emissions. The thermogravimetric analysis (TGA) results show that the temperature to reach the maximum rate of soot oxidation was lower with WPOB combustion. Because of the significant delay at the start of combustion and increase in emissions, the direct use of WPOB in the diesel engine is not recommended. It is suggested that WPOB can be used as a blend component to reduce the amount of diesel fuel used in diesel engines. Thus, further study on the effect of diesel fuel blended with WPOB on the combustion and emissions characteristics was performed. The results reveal that the maximum WPOB present in diesel fuel to avoid the increase in carbon-based emissions is 20% by volume to keep combustion and emissions characteristics similar to those of diesel fuel.

The effects of ethanol on combustion and emission were investigated on a single-cylinder unmodified diesel engine. The ethanol content of 10–50 vol % was chosen to blend with diesel and biodiesel fuels. Selective catalytic reduction (SCR) of nitrogen oxides (NO_x) in the passive mode was also studied under real engine conditions. Silver/alumina (Ag/Al₂O₃) was selected as the active catalyst, and H₂ (3000–10000 ppm) was added to assist the ethanol-SCR. The low cetane number of ethanol resulted in longer ignition delay. The diesel–biodiesel–ethanol fuel blends caused an increase in fuel consumption due to their low calorific value. The brake thermal efficiency of the engine fuelled with relatively low ethanol fraction blends was higher than that of diesel fuel. Unburned hydrocarbons (HC) and carbon monoxide (CO) increased, while NO_x decreased with ethanol quantity. The higher ethanol quantity led to increases in the HC/NO_x ratio which directly affected the performance of NO_x-SCR. Addition of H₂ considerably improved the activity of Ag/Al₂O₃ for NO_x reduction. The proper amount of H₂ added to promote the ethanol-SCR depended strongly on the temperature of the exhaust where a high fraction of H₂ was required at a low exhaust temperature. The maximum NO_x conversion of 74% was obtained at a low engine load (25% of maximum load), an ethanol content of 50 vol %, and H₂ addition of 10000 ppm.