Structure of the SO42−/TiO2 solid acid catalyst and its catalytic activity in cellulose acetylation

SO42−/TiO2 solid acid catalyst, a kind of green catalyst, was introduced as an alternative of sulfuric acid in the synthesis of cellulose acetate (CA). It has been investigated that SO42−/TiO2 presented prominent catalytic activity during this process. The degree of polymerization of CA obtained using SO42−/TiO2 catalyst was 1.7 times higher than that using H2SO4, which could influence the mechanical properties of CA considerably. In addition, the SO42−/TiO2 solid acid catalyst exhibited perfect reusability in the acetic acid system for cellulose acetylation, with traces of SO42− leached during the reaction confirmed by NH3-TPD. It was investigated by XRD that the polymorphic of catalyst transformed from amorphous TiO2 to anatase TiO2 with the increase of calcination temperature and prolongation of calcination time, improving the catalytic activity of SO42−/TiO2 solid acid catalyst. The higher crystallinity it had, the better catalytic activity the SO42−/TiO2 catalyst exhibited. However, due to the decomposition of SO42− on the catalyst surface, confirmed by TG-MS analysis, the catalytic activity of SO42−/TiO2 catalyst decreased sharply when the calcination temperature was above 550 °C. The structure of SO42−/TiO2 solid acid catalyst has been investigated by FT-IR, and it can be confirmed that the SO42− group was bidentate coordinated with TiO2.