Transfer Hydrogenation in Mesoporous Palladium: Polar Hydrogen Engineering to Realize High Selectivity of Alkyne Semi‐Hydrogenation

Abstract

Semi-hydrogenation of alkynes to industrially important alkenes is earnestly desirable in the fine chemical industry but energetically unfavorable. Herein, it is reported that mesoporous palladium (meso-Pd) catalyst changes the hydrogenation pathways in ethanol with ammonium borane as the hydrogen source, realizing the high catalytic selectivity of ≈99% in semi-hydrogenation of alkynes. Mechanism studies reveal that the active polar hydrogen can be produced and reserved well in the electron-rich mesoporous channels of meso-Pd catalyst, resulting in a transfer hydrogenation pathway, which selectively semi-hydrogenates alkynes into alkenes without over-hydrogenating alkenes into alkanes. Moreover, it is demonstrated that the polar hydrogen engineering of meso-Pd catalyst is highly efficient in various alkyne semihydrogenation and chemoselective hydrogenation reactions. The results thus establish metal catalyst mesostructuring as an alternative route for engineering polar hydrogen in the transfer hydrogenation reactions, thus realizing the high catalytic selectivity in various selective catalysis.

Electrochemical Ultrathin Metal‐Atomic Layer Deposition for Silica Microenvironment‐Assisted Cu‐Based Catalysis

“…Amino-silica, involving Lewis basic amino groups, promote critical methanolysis step during the [Cu]-catalyzed proton transfer from methanol to the alkyne while [Cu] hydride (from NH 3 ⋅BH 3 ) completes the reduction into stereospecific Z-alkene in a concerted manner. [56] Although, we ob-served the evolution of H 2 gas during the reaction but its direct participation in the reduction of alkyne can be ruled out because of the inability of Cu(0) in activating H 2 . [58] Expectedly, replacing the NH 3 ⋅BH 3 by H 2 gas (1 atm) didn't result any alkene product.…”

“…Previous reports have also shown variable degrees of H-inclusion in the alkene products from the combined participation of metal-hydrides and protic solvent. [55,56] Further, replacing NH 3 ⋅BH 3 by ND 3 ⋅BH 3 resulted no detectable deuteration in the alkene, which ruled out any Lewis basic participation of ammonia (from NH 3 ⋅BH 3 ) in the methanolysis step. Surprisingly, deuteration of amino groups in EC-2DCu transferred ≈20% single deuterium in the produced Ealkene.…”

Enhanced Alkene Selectivity for Transfer Semihydrogenation of Alkynes over Electron-Deficient Pt Nanoparticles Encapsulated in Hollow Silica Nanospheres

“…Among the mentioned hydrogen donors, AB has attracted intense attention due to its high H 2 storage capacity of 19.6 wt %. For example, hydrogenation of PA with AB over Pt/TiO 2 could achieve 80.7% of ST selectivity at 92.8% of PA conversions at 30 °C and AB/PA ratio of 11:1, while that over Pd/UiO-66 (Hf) obtains ST selectivity of 100% at PA conversions of 50% under 100 °C. , According to the literature, − PA and AB are first adsorbed in metal active sites and then hydrogen species from the N–H and B–H bonds of AB directly attack the CC bond to produce styrene.…”

Effect of the Al2O3 Crystal Phase on the Supported Pd Performance of Semihydrogenation Alkynes

“…The focal point of the current research involves structurally regulating catalysts to enhance selectivity. Despite notable progress in Pd-based catalysts, achieving both high selectivity and conversion rates at elevated levels still presents a formidable challenge. − The key to solving the problem is to improve alkyne desorption to overcome over-hydrogenation. , The selective hydrogenation of phenylacetylene, a representative terminal alkyne, holds significant importance in both industrial production and the exploration of reaction mechanisms. , Considering that styrene is an intermediate product of the hydrogenation of ethynylbenzene, the selectivity could be adjusted by changing the adsorption properties of the catalyst surface. , To achieve this goal, it is necessary to make a complex adjustment on the geometric and electronic structure of Pd nanoparticles. , Support with various chemical and structural properties can also have a significant impact on the catalytic action of Pd, such as the construction of composite interfaces through metal–support interactions. , Among them, the metal–support interaction can change the state of the active element. With the aim of enhancing catalytic performance, the focus is on regulating reactive metal adsorption of reactants and products through modifications in the interaction forces between metals and oxide supports. , Metal oxides are used extensively as support materials in the hydrogenation industry and much progress has been made. − Liu et al showcases the pivotal influence of utilizing different metal oxides as a carrier for monatomic palladium catalysts.…”

“…17,18 Considering that styrene is an intermediate product of the hydrogenation of ethynylbenzene, the selectivity could be adjusted by changing the adsorption properties of the catalyst surface. 19,20 To achieve this goal, it is necessary to make a complex adjustment on the geometric and electronic structure of Pd nanoparticles. 21,22 Support with various chemical and structural properties can also have a significant impact on the catalytic action of Pd, such as the construction of composite interfaces through metal−support interactions.…”