Nano-structured Pd catalysts with enhanced CH 3OH synthesis activities for CO 2 hydrogenation were prepared by integrating two different effects, i.e., incorporation of uniform mesoporous support such as MCM-41 and SBA-15 leading to small Pd nanoparticles inside nano-sized pore channels, and promotion by alkali/alkaline earth metal additives. Pd supported on these mesoporous silica without any promoters exhibited only weak activities for CH 3OH formation, while the addition of K, Mg and Ca significantly enhanced their activities. K(Ca)-promoted Pd supported on SBA-15 yielded CH 3OH 2-5 times as much as amorphous SiO 2-supported Pd catalysts. The formation rate of CH 3OH over the supported Ca/Pd varied as a function of average pore diameter of the support, and decreased in the order of MCM-41 > SBA-15 > MCM-48 > MSU-F ∼ amorphous SiO 2. In situ Pd K-edge EXAFS and H 2 chemisorption measurements of the reduced catalysts demonstrated that small mesopores of MCM-41 and SBA-15 worked as a template for the formation of small Pd 0 nanoparticles, leading to the higher activities for CH 3OH formation compared to the conventional amorphous silica supported counterpart.
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