The Effect of Polymer Matrix on the Catalytic Properties of Supported Palladium Catalysts in the Hydrogenation of Alkynols

Abstract

Palladium catalysts were obtained by the adsorption method involving the sequential deposition of polyvinylpyrrolidone (PVP) and then palladium ions on a modified zinc oxide surface without high-temperature calcination and reduction stages. The immobilized PVP-palladium catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), infrared spectroscopy (IRS), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and elemental analysis methods. It was found that the introduction of polymer into the catalyst’s composition promotes the dispersion and uniform distribution of active phase nanoparticles (PdO, Pd0) on the surface of zinc oxide. The catalysts were tested in the hydrogenation of complex acetylene alcohol, 3,7,11-trimethyldodecyn-1-ol-3 (C15-yn) under mild conditions (0.1 MPa, 40 °C). For comparison, studies on stereoselective hydrogenation of the short-chain alcohol 2-hexynol-1 were performed. It was shown that modification of the catalyst with polymer improves its catalytic properties. High C15-alkenol selectivity (98%), activity (W = 70 × 10−6 mol/s), and stability (turnover number (TON) 62,000) were achieved on a Pd-PVP/ZnO catalyst. Varying the active phase made it possible to reduce the metal content without deteriorating the catalytic performance of the catalyst.

Polysaccharide-Stabilized Pd-Ag Nanocatalysts for Hydrogenation of 2-Hexyn-1-Ol

“…The role of polymers is both to fix Pd and Ag species on zinc oxide surface and their stabilization. This is consistent with data obtained in our prior study for similar Pd-PVP/ZnO catalyst [53]. However, in case of Pd-HEC/ZnO a small amount of Pd was also interacted with ZnO forming PdZn species.…”

“…It should be noted that PdAg-HEC/ZnO catalyst demonstrated the higher surface area to compare with that of HEC/ZnO composite. This is consistent with data obtained for similar systems modified with polyvinylpirollidone (PVP) [53]. In [53] decreasing the surface area from ZnO to PVP/ZnO explained by blockage of micropores in inorganic material after modification with the polymer, while increasing the surface area from PVP/ZnO to Pd-PVP/ZnO explained by a decreasing the surface coverage of the ZnO with PVP shell through changing in an orientation of the polymer functional groups from ZnO to Pd.…”

“…This is consistent with data obtained for similar systems modified with polyvinylpirollidone (PVP) [53]. In [53] decreasing the surface area from ZnO to PVP/ZnO explained by blockage of micropores in inorganic material after modification with the polymer, while increasing the surface area from PVP/ZnO to Pd-PVP/ZnO explained by a decreasing the surface coverage of the ZnO with PVP shell through changing in an orientation of the polymer functional groups from ZnO to Pd. Another explanation for such changing the surface area from unmodified zinc oxide to polymer-modified catalyst can be in changing the degree of agglomeration of ZnO particles after modification with a polymer and following adsorption of metal ions on the polymer/ZnO composite.…”

“…In our prior studies [53,56] have been shown that interaction of polymers with metal ions on a support surface led to formation smaller active phase nanoparticles (~2 nm) to compare with those in similar unmodified supported catalysts. The transmission electron microscopy (TEM) image of Pd-HEC/ZnO catalyst showed the formation of finely dispersed palladium nanoparticles of ~2 nm evenly distributed on the surface of zinc oxide modified with HEC (Figure 3).…”

“…The initial reaction rate increased with increasing temperature up to 40°C. Further temperature increase to 50°C lead to a significant decrease in the reaction rate, which could be explained by the shrinking the surface polymer layer of the catalyst and blocking the active centers [53].…”