Catalytic Performance of Polymer-Modified Pd/γ-Al2O3 Catalysts for Hydrogenation

In this work, 1%Pd/γ-Al2O3 catalysts modified with poly(4-vinylpyridine) (P4VP), polyacrylamide (PAM), and polyacrylic acid (PAA) were synthesized and evaluated for allyl alcohol hydrogenation. The effect of P4VP content was systematically investigated by varying the polymer loading, followed by comparison of the catalytic properties of the modified catalysts with that of the unmodified 1%Pd/γ-Al2O3 catalyst. The synthesized catalysts were characterized by TGA, IR spectroscopy, XRD, TEM, XPS, SEM/EDS, and viscosimetry to evaluate their structural, morphological, surface, and elemental properties. TEM analysis revealed that low P4VP loading preserved small Pd nanoparticles (3.9 nm), whereas higher polymer loadings promoted particle growth to 7.7 nm. All catalysts achieved complete conversion of allyl alcohol. At 5 wt.% polymer loading, the P4VP-modified catalyst exhibited a slightly higher hydrogenation rate than the PAA- and PAM-modified catalysts. Decreasing the P4VP content from 5 to 3 and 1 wt.% increased the hydrogenation rate from 8.3 × 10−6 to 13.9 × 10−6 and 22.9 × 10−6 mol/s, respectively, while propanol selectivity increased from 64 to 65 and 71%. The 1%Pd–P4VP(1%)/γ-Al2O3 catalyst exhibited higher catalytic activity than the unmodified 1%Pd/γ-Al2O3 catalyst and maintained good stability over 20 consecutive substrate additions. These findings demonstrate that the catalytic behavior of polymer-modified 1%Pd/γ-Al2O3 catalysts depends on the balance between polymer loading, Pd nanoparticle size, and active site accessibility.