Structure‐Dependent Selective Hydrogenation of α,β‐Unsaturated Aldehydes over Platinum Nanocrystals Decorated with Nickel

Abstract

The shape sensitivity of monometallic Pt and bimetallic PtÀNi nanocrystals in a,b-unsaturated aldehydes is studied by using a cubic shape enclosed by six {100} facets as well as an octahedral shape surrounded by eight {111} facets. Compared with monometallic Pt and bimetallic PtÀNi cubic/octahedral shapes, Pt 3 Ni cubes enhanced the selective hydrogenation of the C=O double bond and suppressed the selective hydrogenation of the C=C double bond of the a,b-unsaturated aldehyde. The Pt, Pt 3 Ni, or PtNi octahedral shape is an unfavorable structure for C=O hydrogenation and enables the activation of the whole conjugated system of the molecule, which leads to complete hydrogenation to form the saturated alcohol product. The synergistic effects of the surface structure and electronic properties of Pt or PtÀNi nanocrystals play a key role in controlling the selective hydrogenation of C=C and C=O bonds of a,b-unsaturated aldehydes.Great effort has been made to control the selective hydrogenation of C=O and C=C bonds of a,b-unsaturated aldehydes or ketones for valuable industrial products. [1][2][3][4][5] The difference in bond energy-715 kJ mol À1 for the energy of the C=O double bond and 615 kJ mol À1 for the C=C double bond-makes the hydrogenation of the C=O bond more difficult than hydrogenation of the C=C bond, yet the resulting unsaturated alcohol products from C=O hydrogenation are valuable intermediates for the production of perfumes and flavorings. [6][7][8][9] Selective hydrogenation of a,b-unsaturated aldehydes/ketones is often used as a structure-dependent reaction to investigate the capability of the hydrogenation of C=O and C=C bonds over model catalysts. As we already know, the catalytic activity and selectivity are affected by several factors, including catalyst preparation and activation procedures, the geometric structure of catalysts, as well as the electronic structure of catalysts. [10][11][12][13][14][15] Therefore, many attempts have been made to promote the hydrogenation of the C=O double bond by taking advantage of the synergistic effects of metallic catalysts, in which bimetallic catalysts with particular geometric and electronic structures display strongly structure-dependent behavior. [16][17][18][19][20] In particular, Pt-based bimetallic nanocrystals such as pure Pt crystals exhibit defined crystallographic planes and can be used to explore the structure sensitivity of liquid-phase reactions. [21][22][23][24][25][26] Benzene hydrogenation was used as a example to demonstrate that both cyclohexene and cyclohexane formed on cuboctahedral Pt nanoparticles, and only cyclohexane formed on cubic Pt nanoparticles. [27] In this study, monometallic Pt and bimetallic PtÀNi (Pt atoms replaced with Ni atoms) nanocrystals with a well-defined cubic shape enclosed by six {100} facets as well as an octahedral shape surrounded by eight {111} facets were synthesized. Herein, the replacement of one atom of every four Pt atoms or two Pt atoms with one Ni atom (referred to as Pt 3 Ni and PtNi) can be effectively ...

Selective Hydrogenation of the Carbonyls in Furfural and 5-Hydroxymethylfurfural Catalyzed by PtNi Alloy Supported on SBA-15 in Aqueous Solution Under Mild Conditions

“…On one hand, the electron-rich Pt δ− species in PtNi nanoalloys favors the adsorption and activation of C=O bond via donating electrons to the carbonyl groups. It has been found in reported literatures that the electron-rich species of bimetallic catalyst favors adsorption and activation of C=O bond in α,β-unsaturated aldehydes ( Jiang et al, 2014 ; Tan et al, 2019 ; Wu et al, 2019 ). Due to strong Pt(5d)-CO(2π*) bonding interactions, the probability of C=O bond activation increases ( Jiang et al, 2014 ).…”

“…It has been found in reported literatures that the electron-rich species of bimetallic catalyst favors adsorption and activation of C=O bond in α,β-unsaturated aldehydes ( Jiang et al, 2014 ; Tan et al, 2019 ; Wu et al, 2019 ). Due to strong Pt(5d)-CO(2π*) bonding interactions, the probability of C=O bond activation increases ( Jiang et al, 2014 ). Meanwhile, the high electron density of Pt δ− also weakens the strength of Pt-(C=C) interaction and decreases the activity of the C=C bond through an increase in the repulsive four-electron interaction ( Jiang et al, 2014 ).…”

“…The bimetallic nanoalloys are significantly different from the two bulk metals and take on intrinsic features, including tunable components and ratios, variable constructions, reconfigurable electronic structures, and optimizable performances. In addition, the bimetallic synergy effect in nanoalloy adjusts the spatial structure and electronic state around the metal active center, which could make the dispersion of active sites higher and further improve the catalytic hydrogenation ability to obtain the target product ( Kijenski and Winiarek, 2000 ; Wu et al, 2012 ; Jiang et al, 2014 ; Fang et al, 2018 ). Among the various bimetallic nanoalloys, PtNi nanoalloys with high activity and stable properties were widely used to catalyze C=O hydrogenation reactions ( Wu et al, 2012 ; Jiang et al, 2014 ).…”

“…In addition, the bimetallic synergy effect in nanoalloy adjusts the spatial structure and electronic state around the metal active center, which could make the dispersion of active sites higher and further improve the catalytic hydrogenation ability to obtain the target product ( Kijenski and Winiarek, 2000 ; Wu et al, 2012 ; Jiang et al, 2014 ; Fang et al, 2018 ). Among the various bimetallic nanoalloys, PtNi nanoalloys with high activity and stable properties were widely used to catalyze C=O hydrogenation reactions ( Wu et al, 2012 ; Jiang et al, 2014 ). For example, Jiang et al reported that PtNi alloys enhanced the selective C=O hydrogenation of cinnamaldehyde in alcohol, and the hydrogenation of C=C double bond of the α,β-unsaturated aldehydes was suppressed ( Jiang et al, 2014 ).…”

“…Among the various bimetallic nanoalloys, PtNi nanoalloys with high activity and stable properties were widely used to catalyze C=O hydrogenation reactions ( Wu et al, 2012 ; Jiang et al, 2014 ). For example, Jiang et al reported that PtNi alloys enhanced the selective C=O hydrogenation of cinnamaldehyde in alcohol, and the hydrogenation of C=C double bond of the α,β-unsaturated aldehydes was suppressed ( Jiang et al, 2014 ). Wu et al (2021) reported that PtNi hollow nanoframes could catalyze the FF hydrogenation with 99% yield of FFA at 373 K in isopropanol solution.…”