Catalytic activity of Mn-substituted barium hexaaluminates for methane combustion

• 来源期刊: 中国科学B辑（英文版）
• 年，卷（期）: 2008,（3）
• 页码范围: 211-217
• 页数: 7页
• 语种: 英文
• DOI: 10.1007/s11426-008-0043-2

摘要

The catalysts of hexaaluminate (BaMnxAl12-xO19-δ, x= 1.0, 2.0, 3.0, 4.0) to be used in methane combus-tion have been successfully synthesized by co-precipitation method and supercritical drying. The crystalline structure and surface area of catalyst were characterized by X-ray diffraction (XRD) and ni-trogen adsorption analysis of BET method. BET analysis revealed that the preparing and drying method proposed here provides stable materials with higher surface area of 51.4 m2/g in comparison to mate-rials prepared using conventional ambient drying method for BaMnxAl12-xO19-δ calcined at 1200℃ under oxygen. XRD analysis indicated that formation of a pure single phase BaMnxAl12-xO19-δ occurred up to x= 3 in the case of Mn-substituted barium hexaaluminates, incorporation of Mn in excess leads to BaAl2O4 phase formation. As far as the valence state of Manganese ions was concerned, the introduced Mn ions were either divalent or trivalent. The first Mn ions were introduced in the matrix essentially as Mn2+ and only for BaMnxAl12-xO19-δ does manganese exist exclusively as Mn3+; the higher the Mn concen-tration, the higher the proportion of Mn3+. Catalytic activity for methane combustion has been measured for Mn-substituted barium hexaaluminates, light-off temperature was observed in the 512-624℃ range.The highest activity was obtained for catalysts containing 3 Mn ions per unit cell, which reveals that theBaMnxAl12-xO19-δ catalyst was a promising methane combustion catalyst with high activity and good thermal stability. Temperature programmed reduction (TPR) under hydrogen has been used to correlate the catalytic activity with the amount of easily reducible species.