Easily-Controlled Chemoselective Hydrogenation by using Palladium on Boron Nitride

Dynamic Modification of Palladium Catalysts with Chain Alkylamines for the Selective Hydrogenation of Alkynes

Selective hydrogenation of alkynes plays a pivotal role in the field of chemical production but still suffers from restrained catalytic activity and low alkene selectivity. Herein, a dynamic modification strategy was utilized by preferentially attaching diethylenetriamine (DETA) to the surface of the support to modify the Pd catalyst. The DETA-modified Pd catalyst demonstrates unprecedented reactivity (14,412 h^-1) and selectivity as high as 94% for the semihydrogenation of 2-methyl-3-butyn-2-ol at 35 °C, presenting a 36-fold higher reactivity than the Lindlar catalyst. Moreover, the yield exceeds 98.2% at full conversion under no solvent and organic adsorbate conditions, indicating the potential applications for industrial production. Systematic studies reveal that flexible DETA serves in a reversible "breathing pattern" for the molecular discrimination by constructing dynamic metal-support interaction (DMSI), enabling selective exclusion of alkenes from the Pd surface. DETA is competent to dynamically adjust the adsorption behaviors of reactants and effectively boost the intrinsic activity of the modified catalyst. Impressively, the DETA-modified Pd catalyst exhibits exceptional stability even after being recycled 20 times. This work sheds light on a novel and applicable method for the rational design of heterogeneous catalysts via DMSI.

Boron nitride-palladium nanostructured catalyst: efficient reduction of nitrobenzene derivatives in water

Boron nitride (BN) supported palladium (Pd) nanostructured catalyst, as an alternative support for heterogeneous reduction of nitrobenzene derivatives, was prepared by a mild reduction of a Pd precursor in water. The structural characteristics and distribution of the synthesized Pd nanoparticles (NPs) on BN support were investigated by transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy methods. The potential and efficiency of the BN supported Pd NPs as an active and stable nanostructured catalyst were verified in the reduction of nitroaromatics. Excellent yields of the corresponding aryl amines in water were obtained and due discussion were included about the catalytic activity of the synthesized catalyst. It was also indicated that the nanostructured catalyst can be recycled at least for six consecutive cycles in the reduction of nitrobenzene, without losing significant activity.

Carrier-Induced Modification of Palladium Nanoparticles on Porous Boron Nitride for Alkyne Semi-Hydrogenation

Chemical modifiers enhance the efficiency of metal catalysts in numerous applications, but their introduction often involves toxic or expensive precursors and complicates the synthesis. Here, we show that a porous boron nitride carrier can directly modify supported palladium nanoparticles, originating unparalleled performance in the continuous semi-hydrogenation of alkynes. Analysis of the impact of various structural parameters reveals that using a defective high surface area boron nitride and ensuring a palladium particle size of 4-5 nm is critical for maximizing the specific rate. The combined experimental and theoretical analyses point towards boron incorporation from defects in the support to the palladium subsurface, creating the desired isolated ensembles determining the selectivity. This practical approach highlights the unexplored potential of using tailored carriers for catalyst design.

Pd catalysts supported on dual-pore monolithic silica beads for chemoselective hydrogenation under batch and flow reaction conditions

Two different types of palladium catalysts supported on dual-pore monolithic silica beads [5% Pd/SM and 0.25% Pd/SM(sc)] for chemoselective hydrogenation were developed.

Polyethyleneimine-Modified Polymer as an Efficient Palladium Scavenger and Effective Catalyst Support for a Functional Heterogeneous Palladium Catalyst

The polyethyleneimine-modified polymers, polystyrene-divinylbenzene-based (TAs) and polymethacrylate-based polymers (TAm), were used as palladium scavengers to eliminate residual palladium species after palladium on carbon-catalyzed Sonogashira-type coupling reaction. Since both TAs and TAm indicated relatively favorable elimination abilities toward residual palladium species in the reaction mixture, the affinities of TAs and TAm for palladium species were used as supports for palladium catalysts. The TAm-supported palladium catalyst (Pd/TAm) indicated better catalyst properties for the chemoselective hydrogenation compared to those of the corresponding TAs-supported palladium catalyst (Pd/TAs). Aromatic benzyl ethers; aromatic and aliphatic N-Cbzs; and aromatic carbonyl groups were smoothly hydrogenated in the presence of 1-5 mol % of Pd/TAm in MeOH or 2-PrOH. In contrast, the hydrogenation of aromatic ketones was selectively suppressed in morpholine which act as appropriate catalyst poison and solvent. Furthermore, Pd/TAm-catalyzed chemoselective hydrogenation was applicable to continuous-flow reaction.

Boron Nitride as a Novel Support for Highly Stable Palladium Nanocatalysts by Atomic Layer Deposition

The ability to prepare controllable nanocatalysts is of great interest for many chemical industries. Atomic layer deposition (ALD) is a vapor phase technique enabling the synthesis of conformal thin films and nanoparticles (NPs) on high surface area supports and has become an attractive new route to tailor supported metallic NPs. Virtually all the studies reported, focused on Pd NPs deposited on carbon and oxide surfaces. It is, however, important to focus on emerging catalyst supports such as boron nitride materials, which apart from possessing high thermal and chemical stability, also hold great promises for nanocatalysis applications. Herein, the synthesis of Pd NPs on boron nitride (BN) film substrates is demonstrated entirely by ALD for the first time. X-ray photoelectron spectroscopy indicated that stoichiometric BN formed as the main phase, with a small amount of BNxOy, and that the Pd particles synthesized were metallic. Using extensive transmission electron microscopy analysis, we study the evolution of the highly dispersed NPs as a function of the number of ALD cycles, and the thermal stability of the ALD-prepared Pd/BN catalysts up to 750 °C. The growth and coalescence mechanisms observed are discussed and compared with Pd NPs grown on other surfaces. The results show that the nanostructures of the BN/Pd NPs were relatively stable up to 500 °C. Consequent merging has been observed when annealing the samples at 750 °C, as the NPs' average diameter increased from 8.3 ± 1.2 nm to 31 ± 4 nm. The results presented open up exciting new opportunities in the field of catalysis.

Amphipathic monolith-supported palladium catalysts for chemoselective hydrogenation and cross-coupling reactions

Monolithic polymer-supported, effective, and reusable palladium catalysts were developed for cross-coupling reactions and hydrogenation.