Direct and efficient conversion of cellulose to levulinic acid catalyzed by carbon foam-supported heteropolyacid with Brønsted–Lewis dual-acidic sites - Xiaofen Xu; Beiling Liang; Ying Zhu; Jiashuo Chen; Tao Gan; Huayu Hu; Yanjuan Zhang; Zuqiang Huang; Yuben Qin (Bioresource Technology, 2023)