LaCoO perovskite catalyst

The LaCoOs perovskite catalyst alone showed similar degradation compared with the stabilised platinum/alumina catalyst, whereas the addition of 0.2 mol% ruthenium to the perovskite catalyst led to stable performance. 

Selective CO oxidation reaction (SELOX) over cerium-doped LaCoOs perovskite catalysts. Appl. Catal., 388, 216-224. 

LaMnOs and Lao.8Ago.2Mn03) no structural modifications on the samples were observed (XRD analyses) contrarily to sulphur poisoned LaCoOs perovskites which dislocated [12]. Finally, it should be noted that, the preparation method has a great influence on the catalysts behaviour toward poisoning. 

Afterburning processes enable the removal of pollutants such as hydrocarbons and volatile organic compounds (VOCs) by treatment under thermal or catalytical conditions. Combinations of both techniques are also known. VOCs are emissions from various sources (e.g. solvents, reaction products etc. from the paint industry, enaml-ing operations, plywood manufacture, printing industry). They are mostly oxidized catalytically in the presence of Pt, Pd, Fe, Mn, Cu or Cr catalysts. The temperatures in catalytic afterburning processes are much lower than for thermal processes, so avoiding higher NOx levels. The catalysts involved are ceramic or metal honeycombs with washcoats based on cordierite, mullite or perovskites such as LaCoOs or Sr-doped LaCoOs. Conventional catalysts contain Ba-stabilized alumina plus Pt or Pd. 

Nguyen, S.V., Szabo, V., Trong-On, D., and Kaliaguine, S. (2002) Mesoporous silica supported LaCoOs perovskites as catalysts for methane oxidation. Microporous Mesoporous Mater., 54 (1-2), 51-61. 

From XPS analyses, the coexistence of Mn and Mn species was evidenced in LaMnOs material, while the LaCoOs one showed the presence of Co and Co " at the same time. Additionally, these authors established a higher Oads/Oiatt molar ratio on LaCoOs perovskite than that observed for the LaMnOs one. This phenomenon, observed at the surface of the material, improved the low-temperature reducibility of LaCoOs material, where the catalyst s properties claimed to be responsible for the remarkable catalytic performance of the cobalt-based perovskite in the CO oxidation reaction. Other authors have also remarked the importance of the presence of Co " species as active sites for the adsorption of CO [37-39]. For instance, by using DRIFT spectroscopy, Natile et al. [37]... 

Seyfi, B., Baghalha, M., and Kazemian, H. (2009) Modified LaCoOs nano-perovskite catalysts for the environmental application of automotive CO oxidation. Chem. Eng. 

L., Dujardin, C., and Granger, P. (2007) Structural regeneration of LaCoOs perovskite-based catalysts during the NO+H2+O2 reactions. Top. Catal,... 

It is well known that the major limitation of the application of perovskites as combustion catalysts is their lower surface area and their increased tendency to sinter. One solution to increase the contact surface between the VOC and the perovskite is to disperse it on a large surface area and thermally stable support. Thus, supported LaCoOs perovskites on CeZr02 have been studied recently. The use of a CeZr02 support for lanthanum cobalt perovskites promoted the catalytic activity with respect to the corresponding bulk perovskites, decreasing the temperature for complete toluene oxidation by more than 50 C. The increased activity was related to two factors (i) the larger exposed surface and (ii) the composition of the support which provided the increased oxygen mobility of the catalyst. 

Villoria JA, Alvarrez-Galvan MC, Al-Zahrani SM. Oxidative reforming of diesel fuel over LaCoOs perovskite derived catalysts influence of perovskite synthesis method on catalyst properties and performance. Appl Catal B Environ. 2011 105 276-88. 

Three LaCoOs samples (1,11, and 111) with different specific surface areas were prepared by reactive grinding. In the case of LaCoOs (1), only one step of grinding was performed. This step allowed us to obtain a erystalline LaCoOs phase. LaCoOs (11) and LaCoOs (111) were prepared in two grinding steps a first step to obtain perovskite crystallization and a second step with additive to enhanee speeific surface area. The obtained compounds (perovskite + additive) were washed repeatedly (with water or solvent) to free samples from any traee of additive. The physical properties of the three catalysts are presented in Table 10. LaCoOs (1) was designed to present a very low specific surface area for comparison purposes. NaCl used as the additive in the case of LaCoOs (11) led to a lower surface area than ZnO used for LaCoOs (111), even if the crystallite size calculated with the Sherrer equation led to similar values for the three catalysts. The three catalysts prepared were perovskites having specific surface areas between 4.2, 10.9 and 17.2 m /g after calcination at 550 °C. A second milling step was performed in the presence of an additive, yielding an enhanced specific surface area. 

Li et al. developed a solid-state reaction process to synthesize perov-skite-type LaCoOs NCs with grain diameters of 15 0 run (Li et al., 2002). In the first step of the preparation, 5 run composite hydroxide NPs were s)mthesized by grinding metal nitrates liquid paste and mixing with KOH. Then the composite powders were calcined at 800 °C, yielding a single-phase oxide. Tien-Thao et al. prepared LaCo Cui J.O3 x < 0.3) by mechano-synthesis (Tien-Thao et al., 2008). The sample has various distinct Co " " ions in the perovskite lattice, which are more reducible. The reduced catalyst surface comprising cobalt and copper atoms is very selective for the hydrogenation of CO. 

Among the cobalt containing perovskites GdCoO, SmCoO, NdCoO, PrCoO, and LaCoO, tested as catalyst precursors for the partial oxidation of methane the Gd-Co-0 system showed exceptionally better performance for synthesis gas formation (Figs. 6A-6C). At 1009 K a steady-state methane conversion of 73% with selectivities of 79 and 81% for CO and H., respectively, is observed for the catalyst Gd-Co-O. The catalysts Sm-Co-O and Nd-Co-0, of lower activity, show similar steady-state methane conversions in the temperature range studied. On the other hand, the H, and CO selectivities are much higher over Sm-Co-O. 

XRD analyses of the used catalysts Gd-Co-O and Sm-Co-O showed similar patterns to the reduced catalysts with very strong and sharp peaks for the sesquioxides Gd,0, and Sm20,. On the other hand, the XRD analysis of the La-Co-O catalyst after reaction at 1023 K for 19 h clearly showed the formation of the perovskite LaCoO,. Therefore, it is not surprising that the only reaction products observed were water and carbon dioxide. This agrees with previous works on this perovskite and other forms of cobalt oxide which have been shown to be active catalysts for methane combustion and also for CO and H, oxidation [19], The high Co/Ln surface ratio determined by XPS for the used catalyst is expected for a perovskite like surface. 

Slagten and Olsbye [ 10] studied the perovskite LaCoO, (containing some impurities of La O, and COiOj) for the partial oxidation of methane to syngas and observed the production of mainly CO,. If the catalyst was kept at 1073 K after 30 h on-stream the activity changed to give mainly CO which they assigned to the in situ reduction of cobalt. The XRD for Nd-Co-O after reaction revealed the presence of the phases Nd,0, and also the perovskite NdCoO,. For all used catalysts no clear evidence for the presence of simple cobalt oxides such as CoO, COjO, and CO3O4 could be found by XRD. 

The pure perovskites are all more active for CO + O2 than CO + NO reactions. The best catalysts for both reactions are LaMnOs and LaCoOs. The activity of the different pervoskites for CO oxydation can be linked semiquantitatively with the ease of anionic vacancy formation in the lattice, described by the B-O bond energy (Figure 3). 

The addition of Ce to the perovskites leads to different effects depending on the nature of B ions and on the relative amount of Ce. It has to be emphasized, that Ce02 itself is also a good catalyst for CO oxidation with O2 (97 mol % CO conversion at 300°C). This activity is equal to that of LaMnOs, but it is inferior to the activity of LaCoOs. 

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