The impact of soot on NOx adsorption was studied over a Cu-modified hydrotalcite-derived lean NOx trap catalyst in a NO + O2 atmosphere. Powder X-ray diffraction, scanning electron microscopy, Raman scattering spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the surface properties of the pure catalyst and the soot/catalyst mixture. The adsorbed NOx species on the samples were evaluated by in situ diffuse reflectance Fourier transform spectroscopy. The soot coverage decreases the available adsorption sites on the surface of the catalyst, and a portion of active oxygen species are consumed by the soot oxidation during He pretreatment process. The NOx adsorption on two catalyst samples simultaneously undergoes two routes: the “nitrite route” and the “nitrate route”. The “nitrite route” is more dominant than the “nitrate route”. During NOx adsorption, the soot oxidation weakens the NO oxidation to NO2, and the released CO2 competes with NOx on the adsorption sites. Moreover, the temperature-programmed desorption tests indicate that the presence of soot reduces the NOx storage capacity of the catalyst and shifts the NO desorption peak to the lower temperature range by 50 °C.

This study reports the similarities and differences in the physicochemical properties of virgin soot generated in premixed methane flames and the corresponding extracted soot following removal of its soluble organic fraction (SOF). In addition, the correlations between these physicochemical properties and the SOF content are investigated. Soot samples were acquired at varying heights above the burner using a probe sampling technique, and surface functional groups (SFGs) and degree of graphitization were analyzed by Fourier transform infrared and Raman scattering spectroscopies. The oxidation reactivities of both the virgin and extracted soots were evaluated in terms of the characteristic oxidation temperatures and apparent activation energies based on thermogravimetric analysis. Both materials undergo similar changes in the concentrations of aliphatic and aromatic C–H, AD1/AG and AD3/AG ratios, and apparent activation energy with increasing height above the burner but differ in their AD4/AG ratios. The presence of the SOF does increase the relative concentrations of aliphatic and aromatic C–H groups. Moreover, at the same sampling position, the AD1/AG, AD3/AG, and AD4/AG ratios of the virgin soot are greater than those of the extracted soot, while the apparent activation energy values of the virgin soot are lower. These data indicate that the virgin soot possesses less graphitic organization and lower resistance to oxidation relative to the extracted soot. In addition, there is a definite correlation between the oxidation reactivity and the SOF content.

•Pollutant characteristics were measured under different MPI and PIR conditions.•Increasing MPI or PIR increased CO and THC emissions but decreased NOx.•Close and far post injections increased particle number and mass for high PIR.•Increasing MPI increased the particle number and mass for small PIR.•Applying post injection affected soot reactivity and its graphitization degree.This paper reports the effect of post-injection on pollutant emissions from a four-cylinder, direct-injection diesel engine fueled with biodiesel. Characteristics of exhaust pollutants were measured and evaluated for different main-post intervals (MPIs) and post-injection rates (PIRs). Measurements included emissions of carbon monoxide (CO), total hydrocarbons (THC), nitrogen oxides (NOx) and particulate matter (PM), the particle number concentration distribution, and the reactivity and graphitization degree of the soot particles. Increasing the MPI or PIR increased the emissions of CO and THC but decreased those of NOx. At both low and high MPI values, higher PM emissions and particle number concentrations were observed for the 12 and 20% PIRs. At a PIR of 4%, PM emissions and particle number concentration increased with the increase in MPI. The size distributions of exhaust particulates exhibited a trimodal character under the applied operating conditions. The particle geometric mean diameter decreased with the increase in MPI, probably as a result of an increased yield of soluble organic compounds. Post-injection significantly impacted the reactivity of emitted soot particles, as evidenced by changes in the graphitization degree of soot.

•In-cylinder soot from n-heptane and n-heptane/toluene fueled-diesel engine was studied.•Surface functional groups (SFGs) and sp3/sp2 hybridization ratios were assessed.•Adding toluene to n-heptane increased the concentrations of SFGs.•The sp3/sp2 hybridization ratio was obviously increased by toluene addition.•Aliphatic CH groups had a correlation with sp3/sp2 hybridization ratios.This work compared the surface functional group (SFG) types and concentrations and sp3/sp2 hybridization ratios of in-cylinder soot samples generated by a heavy-duty diesel engine when employing n-heptane and a toluene/n-heptane mixture (20% toluene by volume) as the fuels. In-cylinder soot samples were obtained from a total cylinder sampling system, and the SFGs and sp3/sp2 hybridization ratios were analyzed using Fourier transform infrared and X-ray photoelectron spectroscopy. Despite the differences in fuel formulation, both n-heptane and n-heptane/toluene soot exhibited similar trends in terms of changes in the SFGs concentrations and sp3/sp2 hybridization ratios during the combustion process. However, the addition of toluene to the n-heptane was found to increase the concentrations of all SFGs as well as the sp3/sp2 hybridization ratio. The COH and CO group concentrations exhibited a bimodal distribution for both the n-heptane and n-heptane/toluene soot throughout the combustion process, with the concentrations peaking in the premixed and diffusion combustion phases, respectively. In contrast, the relative amounts of aliphatic CH groups decreased in the premixed combustion phase, increased in the early diffusion combustion phase, and then decreased in the subsequent combustion phase. The sp3/sp2 hybridization ratios obtained from both fuel soot were observed to initially decrease, then to increase before a decrease during the combustion process. There was a definite correlation between the sp3/sp2 hybridization ratio and the relative concentration of aliphatic CH groups.

•Physicochemical characteristics of SIDI particles were studied at different AFRs.•Fractal dimensions decreased with increases in the AFR after an initial increase.•The largest average primary particle diameter was obtained at an AFR of 14.7.•The nanostructures of SIDI soot particles were affected by the AFR.•The soot particles at AFR = 14.7 exhibited the lowest sp2/sp3 hybridization ratio.This work studied the physicochemical characteristics of exhaust particles from a 1.48 L SIDI engine operating at different air–fuel ratios (AFRs). The morphology, fractal dimension, size and nanostructure were characterized using high-resolution transmission electron microscopy (HRTEM) in conjunction with electron energy-loss spectroscopy. The results indicate that SIDI aggregate particles produced at varying AFRs exhibit different morphologies. TEM images show that the aggregates obtained at an AFR of 14.7 are more compactly clustered than those generated under fuel-rich and fuel-lean conditions. The fractal dimension of SIDI aggregates at an AFR of 14.7 is found to be 2.21, a value that is larger than those from other AFRs. The primary particle sizes are distributed over a wide range of 5–55 nm at all AFRs, although the largest average primary particle diameter is found at an AFR of 14.7. Similar to diesel soot particles, SIDI soot particles also show characteristic shell-core and turbostratic structures at the nanoscale level. At an AFR of 14.7, the soot particles have a relatively short fringe length, a small fringe separation distance and high fringe tortuosity. As the AFR is increased, the sp2/sp3 hybridization ratios first gradually decrease and then increase, with a minimum value of 0.156 at AFR = 14.7. SIDI soot particles are likely more reactive than diesel soot particles because they possess the relatively short fringe length, large separation distance and high tortuosity.

•The evolutions of PAHs in the diesel engine combustion process were ascertained.•PAHs with five-membered ring structure were abundant in combustion process.•The evolutions of in-cylinder PAHs were varied after toluene addition.•Toluene addition generally reduced the ΣMPAHs during the combustion process.•Toluene addition was conducive to the growth of PAHs to form larger PAHs.This work studied the evolution of in-cylinder polycyclic aromatic hydrocarbons (PAHs) in a diesel engine fueled with n-heptane, and explored the effects of adding toluene to n-heptane on in-cylinder PAHs. In-cylinder PAHs were sampled in a direct injection diesel engine using a total cylinder sampling system. PAHs were analyzed by gas chromatography–mass spectrometry with programmed temperature vaporization in the solvent vent mode. For n-heptane, the mass of total in-cylinder PAHs (ΣMPAHs) increased in premixed and late diffusion combustion phases, and decreased in early diffusion and late combustion phases. Among the 16 PAHs detected, Naphthalene (Nap) was the most abundant. PAHs with two benzene rings and one five-membered ring, such as Acenaphthylene, Acenaphthene and Fluorene, were also plentiful, implying that PAHs with five-membered ring could play an important role in the growth of in-cylinder PAHs. When adding 20 vol.% toluene to n-heptane, the evolution of ΣMPAHs was varied. The ΣMPAHs for n-heptane/toluene increased in premixed and early diffusion combustion phases, and decreased in late diffusion and late combustion phases. Toluene addition reduced the ΣMPAHs in the premixed combustion phase by up to 48% but increased ΣMPAHs by 30% in the early diffusion combustion phase. In the subsequent combustion phase, the ΣMPAHs was reduced by approximately 67%. For in-cylinder individual PAHs, toluene addition generally reduced the percentages of Nap in ΣMPAHs during the engine combustion process but increased the percentages of larger PAHs, indicating that toluene addition was conducive to the growth of PAHs to form larger PAHs.

•Cerium substitution at A-site in Mn100 enhances the catalytic activity.•Cerium substitution leads to the formation of the CeO2 phase.•Cobalt substitution at B-site in Ce20Mn generally decreases the catalytic activity.•Cerium substitution increases the α-O2 amount and low-temperature reducibility.•Cobalt substitution decreases the α-O2 amount and low-temperature reducibility.La1−xCexMn1−yCoyO3 catalysts were prepared by the “glucose method”. The structures and physico-chemical properties for these catalysts were characterized using X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR), H2-temperature-programmed reduction (H2-TPR) and O2-tempreature-programmed desorption (O2-TPD). Results showed that cerium substitution at the A-site in LaMnO3 produced a CeO2 phase. The cobalt can be introduced into the B-site in La0.8Ce0.2MnO3 at any substitution ratio because of the similar ionic radii between cobalt and manganese. The catalytic activity for soot combustion in air was evaluated using a TG/DTA analyzer. Cerium substitution at A-site enhances the catalytic activity, while cobalt substitution at B-site inhibits the catalytic activity. The activation energy for soot combustion was calculated using the Horowitz method. The activation energy for non-catalytic soot combustion was 164.1 kJ mol−1. The addition of catalysts decreased the activation energy by about 26–63 kJ mol−1. Among the applied catalysts, Ce20Mn exhibited the lowest activation energy (101.1 kJ mol−1).

•Reductions in CBC emissions were assessed for CFT diesel.•Significant reductions in emissions of total and individual CBCs were obtained.•The percentage reduction in the total CBCs decreased with an increase in engine load.•The percentage reduction in the total CBCs increased with increase in engine speed.•The ozone formation potential of CBCs emitted was strongly reduced with use of CFT.The reduction in carbonyl compound emissions was evaluated using diesel engines running on Fischer–Tropsch diesel fuel synthesized from coal (CFT). A four-cylinder light-duty diesel engine fuelled with CFT and diesel fuel (DF) was used, and 13 individual carbonyl compounds identified in the exhaust. Tests were performed in the constant speed/varying load mode and in the constant load/varying speed mode. Under the engine operating conditions used, formaldehyde and acetaldehyde were the dominant carbonyl compounds for both test fuels. There was no significant difference in the profiles of total carbonyl emissions between CFT and DF. However, the use of CFT resulted in a remarkable reduction in carbonyl emissions in comparison with using DF. A 27.2–44.6% reduction in total carbonyls and a 6.0–100% reduction in individual carbonyls in the constant speed/varying load test mode, were observed. In addition, there was an 18.0–35.8% reduction in total carbonyls and a 3.4–100% drop in individual carbonyls in the constant load/varying speed test mode. CFT had 16.5–44.1% lower ozone formation potential of the carbonyl compounds present than DF under the identical operating conditions.

The laminar burning velocities were measured for mixtures of CH4/O2/N2/carbon black particle with equivalence ratio values in the range of 0.8–1.2. The data were acquired at an initial pressure of 0.1 MPa and initial temperatures of 303, 353, and 403 K. High-speed schlieren visualization, used to monitor flame growth following ignition, provided a direct determination of the laminar flame velocity. The data were corrected for flame stretch, providing the unstretched laminar burning velocities and burned gas Markstein lengths. The values measured for CH4/O2/N2 flames were compared to those previously reported in the literature and computational prediction using the full mechanism. These comparisons revealed reasonable similarity in the data and demonstrated the reliability of the current experimental system and the accuracy of the full mechanism for CH4/O2/N2 flames. A decline in the Markstein lengths and burning velocities and an enhancement of the thermal diffusive instability upon the addition of carbon black particles were shown by the data. An early onset of cellularity preceded by the formation of toroidal cells for CH4/O2/N2/carbon black particle flames indicated particle mediated alteration of the cellular flame structure. The key reactions involved in the observed changes in the laminar burning velocities were identified on the basis of the sensitivity analysis.

Fischer–Tropsch diesel fuel has desirable physicochemical properties, with the potential to significantly reduce diesel exhaust emissions. This paper evaluates the effects of the use of Fischer–Tropsch diesel fuel synthesized from coal (CFT) on diesel exhaust emissions. A four-cylinder common-rail direct-injection diesel engine fueled with Fischer–Tropsch diesel fuel synthesized from coal, diesel fuel, and blends of the two (15, 30, and 50% CFT by volume) was used. Tests were conducted using the European stationary cycle (ESC) and constant speed/varying load test modes. In the ESC test mode, the brake-specific regulated emissions were reduced by increasing the proportion of CFT in the fuel, achieving reductions of 3.2–33.9% for carbon monoxide, 3.6–39.3% for total unburned hydrocarbon, 0.1–11.8% for nitrogen oxides, and 1.0–25.5% for particulate matter; also, a marginal decrease in the brake-specific carbon dioxide was observed. In the constant speed/varying load test modes, the use of CFT also resulted in a general reduction of regulated emissions. The percentage reductions of carbon monoxide, total unburned hydrocarbon, and nitrogen oxide emissions at low engine speed were much lower than those observed at medium and high engine speeds, while there was no significant difference in the percentage reduction of particulate matter to be observed between the three levels of engine speed. At medium and high engine speeds, the percentage reduction of carbon monoxide showed a decreasing trend with an increasing engine load, and the percentage reduction of particulate matter at light engine loads was higher than at medium or high engine loads. In addition, the geometric mean diameter of particles exhibited a slight drop as the CFT ratio in the fuel was increased. CFT has a weak ability in reducing the total particulate count when compared to Fischer–Tropsch diesel fuels synthesized from natural gas.

Cobalt-containing catalysts supported on ZSM-5 zeolite and mesoporous siliceous SBA-15 were prepared and characterized by nitrogen sorption, X-ray diffraction, scanning electron and transmission electron microscopies, energy-dispersive X-ray, Fourier transform infrared, ultraviolet–visible diffuse reflectance, X-ray photoelectron spectroscopies, and temperature-programmed desorption of ammonia measurement. The effect of cobalt loading ratio on the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia was investigated. The existing Brønsted acid sites contributed to the cobalt species finely dispersed within the ZSM-5 zeolite, either as isolated cobalt ions anchored at α, β, and γ sites, or as amorphous cobalt oxides enriched on the ZSM-5 surface. NOx conversion profiles of Co/ZSM-5 exhibited two peaks. The low-temperature peak (<300 °C) was induced by cobalt ions at β and γ sites, while the high-temperature peak (>300 °C) was assigned to the amorphous and crystalline cobalt oxides. With increasing cobalt content, the intensity of low-temperature peak was enhanced monotonously, and the peak position remained constant. Increasing cobalt content promoted the high-temperature peak to shift toward lower temperatures. NOx conversion profiles of Co/SBA-15 only exhibited a high-temperature peak. For Co/SBA-15, the poor dispersion of cobalt species was derived from the absence of Brønsted acid sites. The activity of Co/SBA-15 catalysts was lower than that of the Co/ZSM-5 catalysts due to inactive cobalt ions anchored on isolated Si–OH groups, and agglomerated cobalt oxides within the SBA-15 channels blocking the reactant pathway to active sites.

Perovskite-type La1–xKxCoO3 and LaCo1–yFeyO3 catalysts were prepared and characterized by nitrogen sorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Catalytic activity for the simultaneous removal of NOx and soot was investigated using temperature-programmed reactions. For the La1–xKxCoO3 series, the introduction of K ions into the A-site caused the enhancement of Co valence state, which was beneficial to improving the catalytic activity. Excess K ions produced a Co3O4 phase adhering to the perovskite crystals, but the rhombohedral perovskite structure was well-maintained. In contrast, the B-site could be substituted by Fe ions with the doping ratio changing from null to 0.5, and no secondary phases were detected. With increasing K substitution, NOx conversion in the La1–xKxCoO3 series showed a declining trend after an initial ascent. The Co3O4 particles produced at high K content were responsible for this falling catalytic activity. For the LaCo1–yFeyO3 series, catalytic performances showed a monotonously decreasing trend as a function of Fe substitution. Among all of the perovskite oxides tested in this study, the La0.6K0.4CoO3 sample exhibited the highest catalytic activity for the simultaneous removal of NOx and soot.

La0.9K0.1CoO3 perovskite type oxide fibers have been prepared by a sol−gel process combined with electrospinning procedure. The reactions during the calcination process of fibers have been tracked and characterized by TG, IR, and XRD. The prepared La0.9K0.1CoO3 fibers are composed of nanoparticles and the BET surface area is 7.1 m2/g. The scanning electron microscopy (SEM) results indicate that each individual fiber is uniform in cross section, and the average diameter of this sample is 600 nm. The catalytic activity for the combustion of soot particulate is evaluated by the technique of the temperature-programmed reaction, and the combustion temperature of carbon is indeed significantly lower than that of noncatalytic combustion under loose contact conditions.

This study examines the similarities and dissimilarities in the physical properties of in-cylinder soot obtained during combustion of n-heptane and a toluene/n-heptane mixture (TRF20, 20% toluene by volume) in a heavy-duty diesel engine. A total cylinder sampling system was used to sample the in-cylinder soot during different combustion phases. For each sample, the morphology, size, fractal dimension and nanostructure of the soot particles were analyzed using high-resolution transmission electron microscopy and Raman scattering spectrometry. The oxidation reactivity of soot particles was also evaluated in terms of apparent activation energy using thermogravimetric analysis. Throughout the combustion process, soot aggregates from the combustion of TRF20 generally exhibited more primary particles and larger-sized clusters than the n-heptane soot aggregates. Despite the different fuel formulations, both n-heptane and TRF20 showed similar trends during the combustion process in terms of changes in fractal dimension of soot aggregates, mean primary particle size and nanostructure (as characterized by fringe length, separation distance and tortuosity). The presence of toluene, however, led to a decrease in the fractal dimensions of the aggregates and a concurrent increase in the mean size of primary particles. Moreover, in the same combustion stages, the mean fringe length for the TRF20 soot was smaller than that for the n-heptane soot, while the mean separation distance and tortuosity for the TRF20 soot were both larger than those for the n-heptane soot. Relative to the n-heptane soot, the TRF20 soot had less graphitic organization and lower resistance to oxidation.

Zirconium doped Cu/ZSM-5 catalysts were prepared and characterized in this investigation. Catalytic activity during soot combustion was determined in both O2/He and NO/O2/He atmospheres by temperature-programmed oxidation. The use of zirconium reduces the temperature of maximum soot oxidation rate by 229 °C in O2/He atmosphere and 270 °C in NO/O2/He atmosphere. The promoting effect of zirconium is discussed in terms of surface dispersion, enrichment of active components, and creation of oxygen vacancies where molecular oxygen or NOx is adsorbed forming basic surface oxygen species active for soot oxidation. The NO2 formed at the copper–zirconium interface sites leads to the ignition temperature being significantly decreased to 93 °C, which is inside the exhaust temperature range of diesel engines. To understand the combustion reaction kinetics, the activation energy and reaction order of soot combustion were evaluated. According to the Redhead method, the activation energy for non-catalyzed reaction is 164 kJ/mol under the O2/He atmosphere. For the Cu/ZSM-5 and Cu–Zr/ZSM-5, the activation energies under the O2/He atmosphere (134–151 kJ/mol) are slightly higher than those under the NO/O2/He atmosphere (128–135 kJ/mol). The Freeman–Carroll method is suitable to describe the soot combustion in the NO/O2/He atmosphere, with the activation energies for the catalysts in the range of 97–112 kJ/mol and the average value of reaction order equal to 1.36.