Diesel engines have been widely used due to their
high thermal efficiency, good environmental adaptability, wide power adjustment
range, convenient maintenance and long service life. However, the application
of diesel engines is also facing a serious problem; that is, the emission of nitrogen oxides and particulate matter is
serious. For marine diesel engine emission requirements, MARPOL Convention
Annex VI imposes strict restrictions on the emission of atmospheric pollutants.
The limit emission of nitrogen oxides in the Tier III emission standards
mandated by IMO is 3.4 g/kWh. Therefore, in
order to meet the requirements of international conventions and countries and
regions, it is necessary to control the emissions of diesel engines. The NOx in
the exhaust gas is mostly a thermal type of nitrogen oxide which is produced
under high temperature and high pressure conditions formed during compression
and combustion strokes. The diesel engine relies on the compression energy of
the mixture to ignite, and the good injection atomization effect is not
achieved. The distribution of the detonation point is not uniform, and local
high temperature points are generated in some areas, which increases the NOx
formation. The main means of reducing NOx emissions are organic internal
control and post-treatment. However, the use of internal control technology to
reduce the internal temperature of the machine will deteriorate the fuel
combustion conditions, so that the fuel cannot be completely burned, and the
emissions of incomplete combustion products such as PM and CO increase. It is
difficult to achieve NOx reduction by simply
relying on the internal control technology, so it is necessary to use
post-processing technology. The combined use of different emission reduction
technologies is also a hot topic in emissions control research. The
post-treatment methods for NOx emission reduction include direct catalytic
decomposition, selective non-catalytic reduction, selective catalytic
reduction, lean-burn adsorption catalytic reduction, and low-temperature plasma
assisted technology. The current research and application schemes in the
industry are SCR selectivity. Catalytic reduction and LNT lean combustion
adsorption reduction. In this paper, the partial replacement of Ce by La is
carried out to modify the Ce/Zr composite oxide. The mass fraction of La2O3 in the prepared La/Ce/Zr composite oxide was 5%, and the physicochemical
properties of La/Ce/Zr composite oxide powder were analyzed by ICP, OSC, SEM
and TPR techniques. The experiment found that: 1) La can refine the grain and inhibit the grain growth, so that the powder
obtains a higher specific surface area and a smaller particle size
distribution. 2) The addition of La reduces
the sintering of cerium-zirconium and improves the heat aging resistance of the
catalyst under the inhibition of high temperature. 3) After doping La, it enhances the migration of surface lattice oxygen and
enhances the oxygen storage capacity; the addition of La enhances the NO
adsorption capacity of cerium-zirconium and improves the catalytic activity of
the catalyst. The light-off temperature and the highest activity temperature of
PM decrease, and the reduction rate of No is 19.2%.