Intermetallic PdZn nanoparticles catalyze the continuous-flow hydrogenation of alkynols to cis-enols

Abstract

Designing highly active and stable lead-free palladium-based catalysts without introducing surfactants and stabilizers is vital for large-scale and high-efficiency manufacturing of cis-enols via continuous-flow semi-hydrogenation of alkynols. Herein, we report an intermetallic PdZn/ZnO catalyst, designed by using the coupling strategy of strong electrostatic adsorption and reactive metal-support interaction, which can be used as a credible alternative to the commercial PdAg/Al2O3 and Lindlar catalysts. Intermetallic PdZn nanoparticles with electron-poor active sites on a Pd/ZnO catalyst significantly boost the thermodynamic selectivity with respect to the mechanistic selectivity and therefore enhance the selectivity towards cis-enols. Based on in situ diffuse reflectance infrared Fourier-transform spectra as well as simulations, we identify that the preferential adsorption of alkynol over enol on PdZn nanoparticles suppresses the over-hydrogenation of enols. These results suggest the application of fine surface engineering technology in oxide-supported metal (particles) could tune the ensemble and ligand effects of metallic active sites and achieve directional hydrogenation in fine chemical synthesis.

Intermetallic Palladium–Zinc Nanoparticles for the Ultraselective Hydrogenative Rearrangement of Furan Compounds

“…These results suggest that Pd-based catalysts can easily activate H 2 and that CO adsorption is the rate-determining step during hydrogenation. Meanwhile, the kinetic isotope experiments showed a lower times (1.22–1.45) of CO hydrogenation rate under the D 2 atmosphere than that under the H 2 atmosphere (Figure S8E,F), which further indicates that the H 2 activation step is rapid and not significantly included in the rate-determining step. , Previous studies have reported that intermetallic catalysts promote selective hydrogenation, such as the CC semihydrogenation of alkynols or acetylene to form enols or olefins, , CC hydrogenation of 1,3-butadiene to 1-butene, hydrogenation of CO 2 to methanol, NO 2 hydrogenation of nitrophenols to aminophenols, and N-methylation of N -methylaniline to N , N -dimethylaniline in organic solvents or solvent-free conditions via surface geometric and electronic effects. Furthermore, reactions conducted in isopropanol and cyclohexane only generated CO hydrogenated MFA with a selectivity of 99.9%; however, the MF conversion rates were <20% (Figure S8I).…”

“…Meanwhile, two obvious lattice spacings were observed at 0.231 and 0.219 nm, which were consistent with the [111] plane of Pd and PdZn nanoparticles, respectively (Figure S1D,F). , The compositions of intermetallic PdZn/ZnO were further confirmed by X-ray energy dispersive spectroscopy (EDS) mapping analysis (Figure S1G–J). High-angle annular dark-field TEM imaging of a representative particle revealed a periodic z-contrast bright–dark change, which indicated an ordered arrangement of Pd and Zn atoms, as well as the formation of highly ordered PdZn intermetallic nanoparticles (Figure B,C).…”

“…Adding Pd considerably reduced the reduction temperature of ZnO to 293 °C as a result of the hydrogen spillover from Pd to the neighboring ZnO, which promoted the reduction of ZnO to form PdZn nanoparticles (Figure S1A). , Inductively coupled plasma-optical emission spectroscopy (ICP-OES) spectra and N 2 adsorption/desorption isotherms showed that Pd/ZnO and PdZn/ZnO possessed similar Pd contents of 4.9–5.4 wt %, with Brunauer–Emmett–Teller (BET) specific surface areas of 9.6–10.7 m 2 ·g –1 (Figure S1B, Table S1). Powder X-ray diffraction (XRD) showed the disappearance of Pd peaks at 40.0° and the appearance of PdZn alloy peaks at 41.1° (Figure A). , Transmission electron microscopy (TEM) showed that the average PdZn nanoparticle size in PdZn/ZnO was 5.5 nm, which was slightly larger than that of the initial Pd nanoparticle seed in Pd/ZnO (5.0 nm) (Figure S1C,E).…”

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

“…This is confirmed by the fact that binding energy of Pd 0 has a positive shift (ca. 0.6 eV) due to strong metal-support interaction and formation of PdZn species [59]. In the case of palladium in oxidized state such shifting was not observed, confirming stabilization of PdO particles with the polymer.…”

Electron Divergence of Cuδ− and Pdδ+ in Cu3Pd Alloy-Based Heterojunctions Boosts Concerted C≡C Bond Binding and the Volmer Step for Alkynol Semihydrogenation

“…The selective semihydrogenation of alkynols to alkenols is of great significance in the industrial manufacture of fine and intermediate chemicals . Notably, the typical 2-methyl-3-buten-2-ol (MBE) serves as a crucial intermediate for vitamin E synthesis, with a global demand approximating 140,000 tons annually. − Metallic Pd-based catalysts (Lindlar catalysts) stand out as highly efficient hydrogenation catalysts in industrial alkynol hydrogenation using hydrogen molecules as hydrogen sources. , However, the strong interaction between Pd and sp 2 carbon within the C=C bond of alkenes usually leads to undesirable overhydrogenation. − Nevertheless, the pervasive use of excess hydrogen molecules imposes severe limitations on large-scale applications due to heightened safety and environmental concerns. Therefore, the pursuit of sustainable strategies is imperative to further decrease the economic and environmental footprints of the semihydrogenation process.…”