Simultaneous NOx-soot Removal Research Articles

Lanthanum-promoted copper-based hydrotalcites derived mixed oxides for NOx adsorption, soot combustion and simultaneous NOx-soot removal

La-promoted Cu-based hydrotalcites derived mixed oxides were prepared and their catalytic activities for NOx adsorption, soot oxidation, and simultaneous NOx-soot removal were investigated. The catalysts were characterized by XRD, DTG, BET, FTIR, H2-TPR, TPD and TPO techniques. The oxides catalysts exhibited mesoporous properties with specific surface area of 45–160m2/g. The incorporation of La and Cu decreased the amount of basic sites due to the large decrease in surface areas. Under O2 atmosphere, La incorporation is dominant for soot oxidation activity, while Cu favors high selectivity to CO2 formation. A synergetic effect between La and Cu for catalyzed soot oxidation lies in the improved redox property and suitable basicity. The presence of NO in O2 significantly promoted soot oxidation on the catalysts with the ignition temperature decreased to about 300°C. In O2/NO atmosphere, NO2 acts as an intermediate which oxidizes soot to CO2 at a lower temperature with itself reduced to NO or N2, contributing to the high catalytic performance in simultaneous removal of NOx and soot.

Performance of Ce substituted hydrotalcite-derived mixed oxide catalysts Co2.5Mg0.5Al1 − x%Cex%O used for soot combustion and simultaneous NOx-soot removal

The Co2.5Mg0.5Al1−x%Cex%O hydrotalcite-derived catalysts (CMACex) with different Ce/Al atomic ratios were synthesized by co-precipitation, which simultaneously possess multiple properties for soot combustion, lean-burn NOx storage and simultaneous NOx-soot removal. The techniques including XRD, EXAFS, BET, H2-TPR, O2-TPD and in-situ DRIFTS were used for catalyst characterization. It is found that Ce-substituted catalysts are much more active than Ce-free one for soot combustion, NOx storage and simultaneous NOx‐soot removal. Among the catalysts containing Ce, CMACe8 exhibits the highest performance, showing the lowest temperature of 384°C for the maximal soot oxidation rate (Tm), the largest NOx storage capacity (336μmolg−1), and the largest NOx reduction percentage of 15.4%. Compared with Ce-free sample, Ce-substitution increases the specific surface area, the redox properties and the amount of surface lattice oxygen species of the catalyst. The optimal Ce-substitution amount in Co2.5Mg0.5Al1−x%Cex%O is x=8. In-situ DRIFTS results reveal that NO is readily oxidized to NO2 and stored as nitrates over Ce-substituted catalysts, which are very reactive intermediates for simultaneous NOx-soot removal.

Highly efficient multifunctional dually-substituted perovskite catalysts La1−xKxCo1−yCuyO3−δ used for soot combustion, NOx storage and simultaneous NOx-soot removal

A series of K/Cu simultaneously substituted nanometric perovskite catalysts La1−xKxCo1−yCuyO3−δ (x=0, 0.1; y=0, 0.05, 0.1, 0.2, 0.3) were synthesized by citric acid complexation, which were employed for soot combustion, NOx storage and simultaneous NOx-soot removal. The physico-chemical properties of the catalysts were characterized by XRD, FT-IR, EXAFS, SEM, H2-TPR, Soot-TPR, TG/DTA, XPS and in situ DRIFTS techniques. When K and Cu are simultaneously introduced into LaCoO3, soot combustion is largely accelerated, decreasing the characteristic temperature (Tm) corresponding to the maximal soot combustion rate at least 80°C; moreover, NOx reduction by soot is also remarkably facilitated. Among all the catalysts La0.9K0.1Co0.9Cu0.1O3−δ shows the lowest Tm of 360°C, the highest NOx storage capacity (NSC) of 284μmolg−1 and the largest NOx reduction percentage of 32%; for soot combustion, it also exhibits the lowest activation energy (80.04kJmol−1). The XPS and Soot-TPR results reveal that the catalyst La0.9K0.1Co0.9Cu0.1O3−δ possesses more active and larger amount of surface oxygen species (O2− and O−), more tetravalent cobalt ions and better reducibility than others, which determines its better catalytic performance. Based on in situ DRIFTS and other characterization results, the potential mechanisms for soot combustion, NOx storage and simultaneous NOx-soot removal are proposed.

Simultaneous catalytic removal of NOx and soot particulates over CuMgAl hydrotalcites derived mixed metal oxides

A series of CuMgAl hydrotalcites derived oxides were prepared by co-precipitation and calcination methods and tested for the simultaneous catalytic removal of NOx and soot. The obtained samples were characterized by XRD, N 2 adsorption-desorption, H 2-TPR and ICP-AES techniques. The crystal phases, porous structures and redox properties of the catalysts were strongly influenced by Cu substitution contents and calcination temperatures. The CuMgAl mixed oxides with mesoporous properties exhibit high activity for the simultaneous NOx-soot removal. Among the tested catalysts, 3.0Cu-800 sample shows the best performance with the ignition temperature of soot = 260 °C and the total amounts of N 2 = 6.0 × 10 − 5 mol. Based on the experimental work, a primitive kinetics analysis was carried out from the non-steady (dynamic) TPR measurements. Linear Arrhenius plots of rates of CO 2, N 2 and N 2O formation were observed around the onset of formation curves where the substantial amount of the soot still remains in the soot/catalyst mixture and the effective area of the soot/catalyst contact can be regarded as constant. Finally, a compensation effect was found for the formation of CO 2, N 2 and N 2O over CuMgAl mixed oxides with CuO as the predominant phase.

Performance of K and Ni substituted La1−xKxCo1−yNiyO3−δ perovskite catalysts used for soot combustion, NOx storage and simultaneous NOx-soot removal

The nanometric substituted perovskite catalysts La1−xKxCo1−yNiyO3−δ (x=0, 0.1; y=0, 0.05, 0.1) were synthesized by citric acid complexation method, and employed for soot combustion, NOx storage and simultaneous NOx-soot removal. Their structures and physico-chemical properties were characterized by XRD, EXAFS, BET, SEM, H2-TPR, and XPS techniques. When K and Ni are simultaneously introduced into LaCoO3 catalyst, soot combustion is largely accelerated, with the temperature (Tm) for maximal soot conversion lowered by at least 50°C; moreover, NOx reduction by soot is also facilitated. The La0.9K0.1Co0.95Ni0.05O3−δ catalyst exhibits not only the lowest Tm (367°C) temperature but also the highest soot combustion rate (67.3μg/sg catalyst). Meanwhile, the NOx reduction percentage over this catalyst can reach 21%. The kinetic results show that the activation energy for soot combustion over La0.9K0.1Co0.95Ni0.05O3−δ (81.34kJmol−1) is much lower than that over LaCoO3 (107.7kJmol−1). The H2-TPR and XPS results show that the La0.9K0.1Co0.95Ni0.05O3−δ catalyst possesses better redox properties, more tetravalent cobalt ions and larger amount of surface adsorbed oxygen species, which determines its novel performance for soot combustion, NOx storage and soot-NOx removal.

LaCo1−x Pd x O3 Perovskite-Type Oxides: Synthesis, Characterization and Simultaneous Removal of NO x and Diesel Soot

A series of naometric perovskite catalysts LaCo1−x Pd x O3 (x = 0, 0.01, 0.03) were prepared via a solution combustion synthesis route using metal nitrates as oxidizers and urea as fuel. It is essential to add a certain amount of ammonia aqueous solution to Pd2+ ions solution in the catalyst preparation process. Homogeneous nanoparticles LaCo1−x Pd x O3 catalysts with the sizes in the range of 68–122 nm were obtained and characterized by using of XRD, BET, H2-TPR, XPS, SEM and TEM. Pd was successfully introduced into the LaCoO3 perovskite lattices. Further information was obtained by using XPS upon the LaCo0.97Pd0.03O3 (with NH4OH) sample after H2-TPR. The results revealed that surface Pd was reduced to the metallic state at the end of the first step in the H2-TPR experiment, and some surface Co could be reduced to metallic Co simultaneously. The catalytic properties were investigated for simultaneous NO x -soot removal reaction. The performance of LaCo1−x Pd x O3 catalysts were greatly improved by the partial substitution of Pd. The maximum NO conversion into N2 and the ignition temperature of soot are 32.8% and 265 °C, respectively.

Reaction mechanism of simultaneous catalytic removal of NOx and diesel soot particulates

Reactions of diesel soot and NOx with and without O2 were carried out over CuFe2O4 catalyst. The ignition temperature of soot with the NO+O2 feed was lower than that in O2 or NO but close to those in NO2 and NO2+O2, indicating the implication of NO2 especially in decreasing the ignition temperature. On the other hand, the reduction of NOx into N2 was enhanced by coexisting O2. Based on these results and mechanisms of O2-soot and NO-soot reactions, the possible reaction mechanism of the simultaneous NOx-soot removal with the NO+O2 feed has been proposed.

Identification of Active Crystalline Phase in La-K-Cu-V Mixed Oxide for the Simultaneous Removal of Nitrogen Oxides and Diesel Soot

Abstract The oxide catalyst having an overall metal composition of La/K/Cu/V = 9/1/7/3 (denoted as LKCVO) showed an excellent selectivity to NOx reduction into N2 in the simultaneous NOx-soot removal reaction, though it was a mixture of several crystalline phases. In order to identify the real active phase, LKCVO was characterized by X-ray diffraction (XRD) and by elemental analysis of individual grains in a transmission electron microscope (TEM) equipped with an energy dispersive spectrometer (EDS). LKCVO was found to be composed of CuO and mixed metal oxides analogous to La2CuO4, LaVO4, and La3VO7. By comparing the catalytic activity of LKCVO with those of single-phase oxides synthesized according to the results of XRD and TEM/EDS, (La2−xKx)(Cu0.95V0.05)O4 with 0.05 ≤ x ≤ 0.1 was identified to be the real active phase in LKCVO for the simultaneous NOx-soot removal reaction.