Identifying Metal–Halogen Bonding for Hydrogen-Induced Acid Generation in Bifunctional Catalysis

Abstract

Within conventional bifunctional catalysts, active metal sites are associated with metal components, while acid sites are usually localized over oxide supports. The modification of metal sites by halogens provides an opportunity to generate acidity via the heterolytic dissociation of hydrogen directly over metal sites. Herein, we report the results of high-throughput screening of the combinations of different metals (Co, Ni, Ru, Pt, Pd, Rh) and halogens (Cl, Br, I) for acid site generation from hydrogen in the hydrogenation of furfural and 5-hydroxymethylfurfural. The results demonstrate that only Pd and Pt catalysts demonstrate the formation of acid sites by interaction with Br, Cl, and I. The characterization in combination with density functional theory (DFT) modeling indicates hydrogen heterolytic dissociation over halogens localized at the edges and corners of Pd and Pt nanoparticles with an increase in strength of the acid sites with an increase of electronegativity of the halogen.

Role of the In Situ Generated Acidic Protons and Cl Species for 2,5-Hexanedione Production from the New Platform Molecule 5-(Chloromethyl)furfural

“…Transmission electron microscopy (TEM) images indicated that Pd NPs had excellent dispersion on Al 2 O 3 (Figure S3a, and Figure b), and the average size of the metal decorated by Cl species increased from 5.70 to 6.56 nm (Figure S3b and Figure c). High-resolution TEM (HRTEM) images showed a 0.22 nm lattice spacing, which was related to the (111) plane of metallic Pd NPs (Figure S3c and Figure d). , The Cl species were clearly located by high-angle annular dark-field scanning TEM (HAADF-STEM) and energy dispersive X-ray analysis (EDX) element mapping images (Figure e–i). As expected, a much more intense Cl EDX signal on Pd NPs was detected rather than on the Al 2 O 3 support.…”

“…High-resolution TEM (HRTEM) images showed a 0.22 nm lattice spacing, which was related to the (111) plane of metallic Pd NPs (Figure S3c and Figure 5d). 38,39 The Cl species were clearly located by high-angle annular dark-field scanning TEM (HAADF-STEM) and energy dispersive X-ray analysis (EDX) element mapping images (Figure 5e−i). As expected, a much more intense Cl EDX signal on Pd NPs was detected rather than on the Al 2 O 3 support.…”

Coupling Cu+ Species and Zr Single Atoms for Synergetic Catalytic Transfer Hydrodeoxygenation of 5-Hydroxymethylfurfural

“…At present, DMF is principally synthesized in the presence of exogenous hydrogen and substantial achievements have been accomplished in the HDO of HMF to DMF with molecular hydrogen, affording high DMF yield when using various noble ( e.g., Pd, − Pt, − and Ru − ) and non-noble metal catalysts ( e.g., Co, , Ni, − and Cu − ). Compared to the H 2 -driven HDO process, catalytic transfer hydrodeoxygenation (CTHDO) with alcohols as the hydrogen donor can be a more convenient and safer alternative, which has merely received cursory attention for the HMF-to-DMF transformation.…”