The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NOx and soot emissions requires a catalytic system with great complexity, size of units, and number of units, as well as increased fuel consumption. Thus, an after-treatment device for a diesel vehicle requires the use of an integrated catalyst technology for a reduction in the individual emissions of exhaust gas. The representative technologies devoted to the reduction of NOx under lean-burn operation conditions are selective catalytic reduction (SCR) and the lean NOx trap (LNT), while soot removal is mainly performed by filters (DPF). These devices are normally used in sequence, or a combination of them has been proposed to overcome the drawbacks of the individual devices. This review summarizes the current state of NOx and soot abatement strategies. The main focus of this review is on combined technologies for NOx removal (i.e., LNT–SCR) and for the simultaneous removal of NOx and soot, like SCR-on-Filter (SCRoF), in series LNT/DPF and SCR/DPF, and LNT/DPF and SCR/DPF hybrid systems.
Influence of the process parameters for the industrially relevant reaction of free fatty acid (FFA) with glycerol is investigated. Furthermore, several drying techniques are investigated and a novel method is suggested that can provide more realistic experimental conditions. Silica as an absorbent is found to be a more suitable method for water removal than distillation or carrier gas. Using response surface methodology, important parameters are identified and optimal conditions found. Empirical correlation is developed to account for the most important parameters. Both oil:glycerol ratio and temperature have optimal values for which the highest conversion can be achieved. Interestingly, the highest conversion can be obtained at 220°C; above this temperature the conversion decreases. It is found that the influence of oil:glycerol ratio also exhibits anomalous behavior, where conversion is constant and decreases above a certain value. At optimal conditions, the FFA is reduced to 1.6% from the initial 8.6%.
In the framework of nowadays challenges in the automotive catalysis, directed to the mitigation of pollution caused by the emissions of internal combustion engines, a series of LaAl1-xCoxO3 perovskites were investigated with the purpose of enhancing the oxidation of soot in the presence of NOx. Perovskite oxides LaAl1-xCoxO3 (x=0; 0.25; 0.5; 0.75 and 1) were synthesized by a solgel route and characterized by different methods: X-Ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), N2-sorption, O2/NOx-temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The perovskite oxides were tested as catalysts for NO oxidation in isothermal mode and for NOx-assisted soot oxidation in temperature programmed reaction. Structural results reveal that Co is well incorporated in the perovskite structure expanding the unit cell, and doping Co may result in the distortion of the BO6 octahedra of the general ABO3 perovskite structure. An increase in Co substitution with x up to 0.75 remarkably promotes the oxidation activity, whereas total replacement of Al by Co degrades the catalytic performance. Among the prepared solids, LaAl0.25Co0.75O3 is the most active for NO oxidation, with a conversion of 78% at 320 °C, and it also exhibits the highest activity for NOxassisted soot oxidation, with a T10% of 377 °C while maintaining high NO2 production (71%). The outstanding performance of LaAl0.25Co0.75O3 is associated with the high mobility of lattice oxygen species and the role of surface adsorbed oxygen seems not to be prominent. The strong correlation of catalytic activity with NOx-TPD profiles suggests that NOx adsorption on catalyst surface is an essential step in soot oxidation. It is also shown that higher calcination temperature promotes the crystallinity of perovskite phase and leads to the improvement in the catalytic activity. The present work indicates that the prepared perovskite catalysts are competitive with noble-metal rivals for NOx-assisted soot oxidation and outperform them in NO2 production for further NOx abatement.
In manipulation and utilization of biodiesel and its mixtures, especially in the winter period, one of the most serious problems is relatively poor low-temperature flow properties. Classic methods of transesterification solve this problem, so biodiesel quality can be improved only by additives (cold flow improvers). This research examines the effect of commercial additives on the improvement of low-temperature characteristics of biodiesel. Namely, cold filter plugging point (CFPP), pour point (PP) and cloud point (CP) were tested in accordance with EN 116 and ISO 3015 standards. The influence of additives on different types of biodiesel, its different age and influence on the mixture of 5 % biodiesel and fossil diesel were examined. A better effect of additivation to "fresh" biodiesel (made using rapeseed oil), compared to "aged" biodiesel was noted. Improvement of additivation was achieved by mixing additives with an organic solvent (toluene). It was demonstrated that different types of additives are suitable for different types of biodiesel as well as mixtures of biodiesel and fossil diesel. Additives in which solvent is compatible with the type of biodiesel were found to exhibit better performance.
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