From a view of green chemistry, solid acids have the advantages of alternatives for harmful liquid acids such as H_2SO_4 with respect to corrosiveness, safety and quantity of waste. An acidic Cs salt of polyoxometalate, Cs_(2.5)H_(0.5)PW_(12)O_(40), shows an excellent performance in acid-catalyzed solid-liquid reactions due to the strong acidity and unique pore structure. While Cs_(2.5)H_(0.5)PW_(12)O_(40) retains its activity even in excess water to act as a water-tolerant acid catalyst, a small amount of polyanion is released from the catalyst . Cohen et al. reported insoluble polyanion (ZnW_9O_(34))_2]~(12-) tethered with organic polymers, which no longer have strong acidity. Here we wish to report that Cs_(2.5)H_(0.5)PW_(12)O_(40) combined with polyallylamine hydrochloride (PA) showed the porosity, good sedimentation and insolubility in water. This nanocomposite compound can be recovered from the water suspension by a simple filtration.
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