Palladium catalysts supported on CsXH3-XPW12O40/MCF (Pd/CsXPW/MCF (X = 1.7, 2.0, 2.2, 2.5, and 2.7)) were prepared with a variation of cesium content (X), and they were applied to the direct synthesis of hydrogen peroxide from hydrogen and oxygen. Conversion of hydrogen over Pd/CsXPW/MCF catalysts showed no great difference, while selectivity for hydrogen peroxide and yield for hydrogen peroxide over the catalysts showed volcano-shaped curves with respect to cesium content. Acidity of Pd/CsXPW/MCF catalysts also showed a volcano-shaped trend with respect to cesium content. It was revealed that yield for hydrogen peroxide increased with increasing acidity of Pd/CsXPW/MCF catalysts. Among the catalysts tested, Pd/Cs2.5PW/MCF catalyst with the largest acidity showed the highest yield for hydrogen peroxide. It is concluded that Pd/CsXPW/MCF efficiently served as an alternate acid source and as an active metal catalyst in the direct synthesis of hydrogen peroxide. (C) 2011 Elsevier B.V. All rights reserved.