In Situ Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy to Unravel Sequential Hydrogenation of Phenylacetylene over Platinum Nanoparticles

Abstract

Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is quickly developing into a powerful characterization tool in heterogeneous catalysis. In this work, we employ Pt catalysts supported on Au@SiO 2 shell-isolated nanoparticles to study hydrogenation reactions. First, we demonstrate the facile preparation of Pt/Au@SiO 2 and its characterization by using adsorption of CO as probe molecule. Next, we use the adsorption and hydrogenation of phenylacetylene as a model reaction for the interaction of triple bonds and aromatic rings with catalytic Pt surfaces. We show that the applicability of SHINERS is not limited to inherently gaseous compounds, thereby expanding the applicability of the technique to more complex systems. Furthermore, by using nonparticipating side groups as labels, we observe the sequential hydrogenation of phenylacetylene into styrene and ultimately ethylbenzene upon reaction with H 2 . Upon the absence of H 2 , the reverse reaction takes place with those molecules still adsorbed onto the catalyst surface, which allowed a more detailed understanding of the reaction mechanism and the assignment of Raman peaks. This strengthens the position of SHINERS as an easily applicable surface sensitive technique that can be used to study a wide variety of chemical reactions in the field of heterogeneous catalysis.

In SituShell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy of Nickel‐Catalyzed Hydrogenation Reactions

“…After reduction of the Ni(Pr), Ni(Col) and fresh Ni(SA) materials, CO was introduced into the Linkam Cell to probe the available catalytic surface, similarly to methods we have used before . Figure a shows spectra in the characteristic regions of CO adsorption on metal surfaces for both the low and high wavenumber region, that exhibit metal‐adsorbate and C−O stretching vibrations, respectively.…”

“…Studies are thus so far limited to noble metal catalysts, which are easily reduced to their metallic, active form, without the need for high temperatures . Some recent examples from our own group involve the hydrogenation of CO into higher hydrocarbons, including alcohols, over SHINERS‐active Rh/Au@SiO 2 and RhFe/Au@SiO 2 catalysts, as well as the hydrogenation of phenylacetylene into styrene and ethylbenzene over SHINERS‐active Pt/Au@SiO 2 …”

Hydrogenation of alkynyl substituted aromatics over rhodium/silica

“…In contrast end-on adsorption perpendicular to the surface found with phenylacetylene on Cu [30] (along with di-σ adsorbed) did not hydrogenate to styrene. Although this mode of adsorption has not been specifically identified on Rh with phenylacetylene, it has been identified on Pt [14] and for propyne adsorption on Rh [31]. Therefore, if the addition of a second component resulted in an increase in this mode of adsorption at the expense of the di-σ then the rate of hydrogenation would decrease.…”

“…Research has continued and over the last 15 years considerable advances have been made in our understanding of aliphatic alkyne and alkene hydrogenation over palladium [4][5][6][7] and aliphatic alkene hydrogenation and isomerization over platinum systems [8,9]. Aromatic alkyne hydrogenation historically has had much less attention but over recent years the number of publications has increased [10][11][12][13][14]. However, reactions where there is competition have had very little attention [15][16][17][18][19].…”

Operando Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy of the NO Reduction Reaction over Rhodium‐Based Catalysts

“…As a result, the Raman signal can be enhanced by factors over 10 6 . However, for practical application in catalysis, SERS substrates are required to be non‐invasive, [8] and the stability of the Ag and Au nanostructures must be improved [9] …”