Hydrophilic–Hydrophobic Regulation of the Cellulose Suspending Ionic Liquid Hydrogel/Palladium Nanocomposite Catalyst for Hydrogenation

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)/CO2 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 Pd2+ 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.