Promoter effect of Pd species on Mn oxide catalysts supported on rare-earth-iron mixed oxide
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 MnOx by a small amount of Pd. For CO oxidation, the catalytic activity of amorphous MnOx 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 MnOx 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 MnOx. Thus, an extremely small amount of Pd species serves to promote the catalytic and reduction functions of the MnOx species on Mn-h-YbFeO3. The establishment of such a promoter effect provides a guideline for decreasing the use of noble metal resources.