Cellulosic protic ionic liquid hydrogel confined Pd nanoparticles for selective hydrogenation of α-angelica lactone and alkenes

Abstract

Hydrogenation is one of the important functional group conversion reactions in the chemical industry. In this study, a cellulosic protic ionic liquid hydrogel was firstly synthesized by adding mixed cyclic anhydrides into a cotton pulp cellulose solution in TMG (1,1,3,3-tetramethyl guanidine)/CO₂/DMSO to form the cellulosic protic ionic liquid hydrogel (CPILH) through an esterification reaction. The CPILH confined Pd nanoparticle (Pd@CPILH) catalyst was prepared by anchoring Pd²⁺ ions through the large functional groups on the CPILH (e.g., –COOH and TMG-based protic ionic liquids (TMGPILs)) and then an in situ reduction of Pd²⁺ to Pd NPs. TEM analysis revealed that the Pd NPs had a small size of 4.4 nm and were well dispersed within the matrix. As a result, catalytic hydrogenation of α-AL successfully formed GVL, with a conversion rate of 97.7% and 100% selectivity achieved within 3 hours at 50 °C in ethanol. Kinetics experiments were performed by adjusting the reaction temperature within the range of 30 to 65 °C, and the simulated data fitted well with the first-order kinetic law. The reaction rate constant (k) was determined to be 0.2226 min⁻¹ at 50 °C, and the reaction activation energy (E_a) was calculated to be 30.45 kJ mol⁻¹. The Pd@CPILH catalyst demonstrated remarkable recyclability, maintaining high conversion and selectivity even after 10 uses. Additionally, the catalyst exhibited excellent catalytic efficiency, achieving nearly 100% conversion and selectivity for common alkenes under moderate conditions. This work presents a straightforward and sustainable strategy for the synthesis of catalyst support materials, showcasing significant potential in the production of chemicals derived from biomass.