Synthesis of La-hexaaluminate catalyst for methane combustion by a reverse SDS microemulsion

Abstract

La-hexaaluminate catalyst for methane catalytic combustion was synthesized by a reverse microemulsion. Pseudo-ternary phase diagrams of a quaternary microemulsion system of sodium dodecyl sulfate (SDS), n-pentanol, n-octane, and water (or Al(NO 3 ) 3 solution) were presented. The effects of alcohol chain length, cosurfactant-to-surfactant ratio, and salt concentration on the formation and stability of the microemulsion system were studied. The phenomenon that the conductivity changed with water supported the phase behavior of the microemulsion system. La(Mn x /Fe x )Al 12−x O 19−δ catalysts, applied in methane combustion and with high-temperature stability, were synthesized within the stable areas of the phase diagram of the microemulsion system, when SDS was chosen as surfactant, n-pentanol as cosurfactant, and n-octane as oil phase. The physical properties and structure of the catalysts were characterized by BET method, transmission electron microscope (TEM), and X-ray diffraction (XRD). A micro-fixed-bed reactor was used to measure the catalytic activity of hexaaluminates in methane combustion. The results show that the reverse microemulsions can be used to produce discrete La-hexaaluminate nanoparticles that display excellent methane combustion activity owing to their high surface area and high thermal stability.

Clear microstructure–performance relationships in Mn-containing perovskite and hexaaluminate compounds prepared by activated reactive synthesis

“…By contrast, hexaaluminate mixed oxides with the general formula of AB x Al 12Àx O 19Àd (A x+ and B y+ stand respectively for lanthanide and transition/noble metal cations) have gained increased attention for their exceptional resistance to sintering at high temperature. [8][9][10] Their ability to maintain phase stability and high surface area is considered to be of great interest. Therefore, perovskites and hexaaluminates are undeniably the most promising catalytic materials among MOs.…”

ZrO 2 -modified Ni/LaAl 11 O 18 catalyst for CO methanation: Effects of catalyst structure on catalytic performance

“…In addition, the two peaks at 23.4° and 48.0° correspond to (111) and (024) planes of perovskite LaAlO3 (JCPDS 01-082-0478), respectively, indicating that the as-synthetized LaHA sample contained a small amount of the LaAlO3 phase [42,43]. As previously reported, it is difficult to obtain pure LaHA [19,44] because the solid-state formation of LaHA by the reaction between LaAlO3 and Al2O3 is extremely slow even at high temperatures. After the NiO addition, new diffraction peaks at 43.3° and 62.8° appeared in their XRD patterns, which correspond to the (012) and (110) planes of NiO (JCPDS 00-044-1159), respectively.…”

“…Hexaaluminate (HA) materials are highly stable at high temperatures because of their unique layered structure of alternately stacked spinel blocks separated by mirror planes [5,17] and have been used as catalysts or catalyst supports for high-temperature reactions such as methane catalytic combustion [18,19], methane reforming reaction [20], and CO methanation [5,17]. In addition, the rare-earth oxide La2O3 has been widely used as an excellent promoter for various catalysts because of its unique properties, such as neutralization of acid sites [21], stabilization of the support [22][23][24], enhancement of the catalytic performance [25], and suppression of carbon deposition by activating adsorbed H2O and CO2 [26,27].…”

La-Doped Alumina, Lanthanum Aluminate, Lanthanum Hexaaluminate, and Related Compounds: A Review Covering Synthesis, Structure, and Practical Importance

“…Even for unstabilized, that is, unsubstituted La- or Ba-HA, formation temperatures below 1200 °C are occasionally reported. Examples are 1100 °C by the research groups of Arai, Järås, Ying, and Groppi , , , and 1050 °C by Yu et al…”

“…The surface areas obtained by sol–gel synthesis (entries 47–53) , , − , , are in the upper range of those reported for coprecipitation. Higher surface areas are clearly seen for samples prepared in microemulsions (entries 54–58) ,,− (e.g., 67 m 2 /g in entry 58). Further methods to obtain LHA include precipitation (as opposed to coprecipitation, entry 26), solid-state reactions (entries 1–6), ,,,,,− ion-exchange or impregnation of aluminas or alumoxane with decomposable La-salts (entries 7–14), ,, , , , ,, Pechini method (entries 15, 17, 18), , , , carbon templating (entries 19–21), , , , as well as combustion and oxidation routes (entries 22–25). , , , With respect to surface areas, only a combined Pechini/carbon-templating route (entry 18, 90 m 2 /g) can compete with synthesis in microemulsions.…”