More recently to explore the

Fortunately, the hydrogen protons of heteropoly acids can be substituted by larger monovalent cations to generate solid acid catalysts that are insoluble in water [154]. Recently, Tian et al. found that the substitution of H+ of H3PW12O40 with Cs+ could produce a series of cesium phosphotungstates (CsxH3 − xPW12O40, x = 1–3) and the various content of Cs would affect the catalytic activities for the hydrolysis of cellulose in aqueous solution [155].