Synthesis of Tetrahydrofuran Derivatives from 5-Hydroxymethylfurfural: Selective Ring Hydrogenation of HMF and Cascade Transformations over Pd Supported on Amino-Modified ITQ-2 Zeolite

5-Hydroxymethylfurfural (HMF) has been efficiently hydrogenated into the highly valuable 5-hydroxymethyltetrahydrofurfural (HMTHF) through the selective hydrogenation of the furan ring using Pd supported on pure silica ITQ-2 zeolite functionalized with amino groups (Pd-NITQ-2). Highly dispersed nanosized Pd nanoparticles were generated on the amino functionalized support, which exhibits high activity and selectivity to HMTHF. Yields up to 97% (99% selectivity) of HMTHF were achieved by working at room temperature under 10 bar hydrogen using ethanol as a solvent. Comparatively, Pd supported over nonfunctionalized ITQ-2 (Pd-ITQ-2) showed 17 times lower activity than Pd-NITQ-2. The IR of CO titration studies showed that on Pd-ITQ-2, catalyst oxophilic Pd species (Pdδ+) are generated, which is related to their lower activity in H2 activation and therefore their lower activity in the hydrogenation of the furan ring with respect to the Pd-NITQ-2 sample. The effect of Pd loading on NITQ-2, as well as the solvent effect, was studied. The optimized catalyst ((1%)-Pd-NITQ-2) was stable and could be reused for seven consecutive cycles, practically maintaining activity and selectivity. Finally, the optimized catalyst was applied to three different two-step cascade processes to obtain tetrahydrofuran substituted Knoevenagel adducts, N-substituted tetrahydrofurfurylamines, and tetrahydrofuran-substituted benzimidazole derivatives.