Hydrophilic–Hydrophobic Regulation of the Cellulose Suspending Ionic Liquid Hydrogel/Palladium Nanocomposite Catalyst for Hydrogenation
Hongrun Li, Xianyi Zhu, Tianlong He, Changsheng qu, Qiuling Tian, Haibo Xie, Lijie Hu, Songmiao Liang, Lihua Zhang, Jili Yuan
Abstract
Catalytic processes have been widely involved in the chemical industry; thus, the design and preparation of sustainable, highly active, and recyclable catalysts is significant toward a sustainable chemical industry. Herein, by taking the particular solution properties of cellulose solution in a 1,1,3,3-tetramethyl guanidine (TMG)/dimethyl sulfoxide (DMSO)/CO 2 solvent system, a straightforward “one-pot” method was developed to prepare the cellulose-suspending TMG-based protic ionic liquid (PIL) hydrogel (CPILH-X) with hydrophilic–hydrophobic changes by simply tuning the molar ratio of succinic anhydride (SA) and 2-dodecen-1-ylsuccinic anhydride (DSA), in which the TMG was not only a solvent component for cellulose dissolution but also a green organo-catalyst for the reaction of cellulose with SA and DSA, as well as a cation component in the formed CPILH-X. CPILH-X was identified as the support for palladium nanoparticles (Pd NPs) by the impregnation and reduction method, yielding a series of CPILH-X/Pd NPs (Pd@CPILH-X) catalyst. The structure of Pd@CPILH-X was systematically characterized by various characterization technologies. The suspended TMG-based PILs were capable of stabilizing Pd 2+ as a nucleation center in the reduction to Pd NPs process, making the Pd NPs well-dispersed in the framework of CPILH-X. Moreover, not only the DSA could improve the hydrophobicity of Pd@CPILH-X but also its long chain structure was capable of preventing the aggregation of Pd NPs. It was found that the catalytic activity of the Pd@CPILH-X was significantly correlated to their hydrophilic/hydrophobic properties when they were used as a catalyst in hydrogenation reaction, and the Pd@CPILH-5 with the highest hydrophobicity exhibited 99% catalytic conversion efficiency in 30 min and superior catalytic recyclability for the typical hydrogenation of styrene.