Promoter effect of Pd species on Mn oxide catalysts supported on rare-earth-iron mixed oxide

Abstract

To replace or reduce the use of precious metals, novel guidelines for designing base metal catalysts, such as Mn or Fe, are greatly desired for various environmental cleanup reactions. Here we report a unique metamorphosis of MnO_x by a small amount of Pd. For CO oxidation, the catalytic activity of amorphous MnO_x species on hexagonal YbFeO₃ (Mn-h-YbFeO₃) is comparable to that of Pd catalysts such as Pd/Al₂O₃, but loading a small amount of highly dispersed Pd on Mn-h-YbFeO₃ drastically enhances its catalytic activity. The catalytic activity of 0.5 wt% Pd/Mn-h-YbFeO₃ is exceptionally higher than that of 2.0 wt% Pd/Al₂O₃, despite the lower Pd loading. The reduction behavior of the MnO_x species, which are located on the ab plane of the hexagonal YbFeO₃, is greatly changed by the loading of highly dispersed Pd, resulting in the dramatic lowering of the reduction temperature of MnO_x. Thus, an extremely small amount of Pd species serves to promote the catalytic and reduction functions of the MnO_x species on Mn-h-YbFeO₃. The establishment of such a promoter effect provides a guideline for decreasing the use of noble metal resources.