Preparation and Catalytic Performance of Metal-Rich Pd Phosphides for the Solvent-Free Selective Hydrogenation of Chloronitrobenzene

Aromatic Ethers Induced Electronic Structure Reconstruction on Encapsulated Nickel Catalysts for High-Performance Catalytic Hydrogenation

Carbon-encapsulated metal (CEM) catalysts effectively address supported metal catalyst instability by protecting the active metal with a shell. However, mass transfer limitations lead to reduced activity for catalytic hydrogenation reaction over most CEM catalysts. Herein, we introduce a dopant strategy aimed at incorporating nickel metal within graphene-like shells (GLS) featuring oxygen-containing functional groups (OFGs). The core of this strategy involves precise control of GLS modification and the demonstrated pivotal influence of aromatic ether linkages (═C-O-C) in GLS for significant enhancement of catalytic performance. The introduction of ═C-O-C into GLS with stability was beneficial to improve the work function of the catalyst and promoted electron transmission from Ni metal core to GLS, further elevating the catalytic activity, based on the Mott-Schottky effect. In addition, the experimental characterization and density functional theory (DFT) calculations showcased that the ═C-O-C reconstructed the electronic state of GLS, imparting it highly specific for the adsorption of hydrogen and para-chloronitrobenzene (p-CNB) to obtain para-chloroaniline (p-CAN) with high selectivity. This work manifested a feasible direction for the precise modulation and design of the OFGs in CEM catalysts to achieve highly efficient catalytic hydrogenation.

Support Engineering for the Stabilisation of Heterogeneous Pd3 P-Based Catalysts for Heck Coupling Reactions

Herein we report the use of a supported Pd3 P catalyst for Heck coupling reactions. For the stabilisation of Pd3 P and Pd, as reference system, the silica support material was modified via phosphorus doping (0.5 and 1 wt % P). Through this so-called support engineering approach, the catalytic activity of Pd3 P was clearly enhanced. Whereas an iodobenzene conversion of 79 % was witnessed for Pd3 P@SiO2 in the coupling of styrene and iodobenzene in 1 h, 90 % conversion could be achieved using Pd3 P@1P-SiO2 . This improved catalytic activity probably stems from an electronic modulation of the support surface via the introduction of phosphorus. Simultaneously, the recyclability was boosted and the Pd3 P@1P-SiO2 catalyst has shown to maintain its catalytic activity over several recovery tests. Hereby, metal leaching could almost be suppressed completely to 3 % by the use of a P-modified silica support.

A Supported Palladium Phosphide Catalyst for the Wacker-Tsuji-Oxidation of Styrene

The substitution of pure metal particles by metal phosphides in catalysis represents a promising opportunity to lower the required metal quantity in the context of a sustainable use of metal resources. Herein we show the synthesis of palladium phosphide, Pd₃ P, supported on silica, which is tested as catalyst for the Wacker-Tsuji-oxidation of styrene to acetophenone. The synthesized catalyst is characterized by PXRD, SEM-EDX, FTIR, ICP-AES and XPS measurements. Four different reaction systems are investigated in this study including different co-catalysts and reaction media. Conversions of styrene up to 95 % with a selectivity of 73 % towards acetophenone are observed using Pd₃ P/SiO₂ as catalyst, CuCl₂ as co-catalyst and O₂ as oxidant. An enhanced selectivity up to 100 % towards acetophenone is obtained in other reaction systems. The use of Pd₃ P/SiO₂ leads to an optimized selectivity and conversion in the oxidation reaction in comparison with the purely Pd-based system Pd/SiO₂ . These results give an insight on how the incorporation of phosphorus has a great effect on the performance of heterogeneous catalysts.

Electron-Enriched Pd Nanoparticles for Selective Hydrogenation of Halonitrobenzenes to Haloanilines

Selective hydrogenation of halonitrobenzenes into haloanilines represents a green process to replace the environmentally unfriendly non-catalytic chemical reduction process in industry. However, this transformation often suffers from serious dehalogenation due to the easy break of carbon-halogen bonds on metal surfaces. Modulations of the electronic structure of the supported Pd nanoparticles on Lewis-basic layered double hydroxides have been demonstrated to promote catalytic activity and selectivity for hydrogenation of halonitrobenzenes into haloanilines. Mechanism studies suggest that Pd with the enhanced electron density not only improves the capability for hydrogen activation, but also generates the partially negative-charged hydrogen species to suppress the electrophilic attack on the carbon-halogen bond and avoid the dehalogenation.