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The aim of this study is to synthesize the catalysts of Fe-and Mn-substituted hexaaluminate by reverse microemulsion medium for methane catalytic combustion application. Pseudo-ternary phase diagrams in quaternary microemulsion systems of cetyltrimethylammonium bromide (CTAB), n-butanol, n-octane, and water [or Al(NO 3 ) 3 solution] were presented. The effects of the alcohol chain length, ratio of surfactant to cosurfactant, and salt concentration on the formation and stability of microemulsion systems were studied. The phase behavior of microemulsion systems was confirmed through the varying of the conductivity with the water content. The performance and structure of the catalysts, La(Mn x /Fe x )Al 12−x -O 19−δ synthesized with the optimal parameter in the phase diagrams of microemulsions systems were characterized by BET, TG-DTA, and XRD. The micro fix-bed reactor was used to measure the catalytic activities of catalysts to methane combustion. The results showed that this synthesis method could yield non-agglomerated and highly dispersed precursors that would undergo crystallization at the lower temperature of 950℃. When temperature was raised up to 1050℃, the complete crystalline La-hexaaluminate was shaped. The hexaaluminate substituted with Fe had high-catalytic activity and stability at high temperature, while the Mn-substituted had higher catalytic activity at lower temperature. When the cooperation of Fe and Mn occurred, i.e., LaFeMnAl 10 O 19−δ exhibited a high surface area and catalytic activity to CH 4 combustion, the CH 4 light-off temperature was only 475℃ and the complete combustion temperature was 660℃. This was attributed to the synergistic effect between Fe and Mn. methane catalytic combustion, hexaaluminate catalysts, reverse microemulsion, phase diagram

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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.

Co-based nanoalloys showp otential applications as nanocatalysts for the oxygen reduction reaction (ORR), but improving their activity is stillagreat challenge. In this paper,astrategy is proposed to design efficient Co-M (M = Au, Ag, Pd, Pt, Ir,a nd Rh) nanoalloys as ORR catalysts by using density functional theory (DFT) calculations. Through the Sabatier analysis, the overpotential as af unction of DG OH *i si dentified as aq uantitative descriptor for analyzing the effect of dopantsa nd atomics tructures on the activity of the Co-based nanoalloys. By adopting the suitable dopants anda tomic structures, DG OH *a ccompanied by overpotential could be adjusted to the optimal range to enhance the activity of the Co-based nanoalloys. With this strategy, the core-shell structuredA g 42 Co 13 nanoalloy is predicted to have the highest catalytic activity for ORR among these Cobased nanoalloys. To give ad eeper insight into the properties of Ag-Co nanoalloys, the structure, thermals tability,a nd reactionm echanism of Ag-Co nanoalloys with different compositions are also studied by using molecular simulations and DFT calculations. It is found that core-shell Ag 42 Co 13 exhibits the highest structural and thermals tability among these Ag-Co nanoalloys. In addition, the core-shell Ag 42 Co 13 showst he lowest ORR reactione nergy barriers among these Ag-Co nanoalloys. It is expected that this kind of strategy could provide av iable way to design highly efficient heterogeneous catalysts in extensive applications.