MCM -41 supported H3PW12O40(PW) catalysts were prepared and characterized. PW crystal phase was not observed in X - ray diffraction patterns at PW loading as high as 70% (quality fraction). The chemical interaction between PW and the support was stronger on MCM - 41 than on amorphous SiO2. The acid sites in bulk PW were uniform and strong with differential heat of NH3 adsorption in the range of 160 ~ 180 kJ/mol, whereas in PW/MCM - 41 catalysts the acid sites became less uniform and weaker due to the strong...