A systematic investigation of acetylene activation and hydracyanation of the activated acetylene on Au_n(n = 3–10) clusters via density functional theory

Abstract

A systematic investigation of the selective catalytic conversion of poisonous HCN gas through hydracyanation of C2H2 activated on Au clusters, presented here for the first time, is of paramount importance from both scientific and technological perspectives. Hydracyanation of activated acetylene on an Au-cluster based catalyst leads to vinyl isocyanide (H2C[double bond, length as m-dash]CHNC) formation, a versatile chemical intermediate. Using density functional theory, bond activation of acetylene and selective catalytic hydracyanation of activated acetylene on small gold clusters Aun (n = 3-10) have been studied through a detailed analysis of the geometric and electronic structures. Different possible complexes of Aun-CHCH have been studied and two possible modes of adsorption of acetylene over the gold clusters, namely, the π- and di-σ modes, have been observed. The hydracyanation of the acetylene molecule is found to occur via the cleavage of one of acetylene triple bonds at the cost of formation of two Au-C bonds followed by the binding of HCN to the activated C[double bond, length as m-dash]C bond via nitrogen's lone pair. Preferential binding sites for HCN and C2H2 are analyzed through Fukui function calculations, frontier molecular orbital analysis and natural population charge distribution analysis. Based on adsorption energies, odd-sized Aun clusters are found to be significantly more favorable for C2H2 adsorption with the C-C bond stretching up to 1.31 Å with respect to the C-C triple bond length of 1.21 Å in the gas phase. The stretching frequency of adsorbed complexes, C2H2/Aun, (3460 cm(-1)), decreases notably relative to the frequency of the free acetylene molecule (7948 cm(-1)), which is a signature of the bond activation of the acetylene molecule over the Au clusters. The high adsorption energy of HCN on the Au9-C2H2 complex implies the considerable binding strength and activation of C2H2 and HCN on the Au9 clusters. Due to the importance of polymerization/cyclotrimerization of C2H2 in synthetic fiber industries, the capability of Au9 clusters to adsorb up to four acetylene molecules, (C2H2)n (n = 1-4), on adjacent sites without affecting the planarity/structure of Au9 is demonstrated here for the first time. Our findings provide valuable guidance for choosing a suitable substrate/support for realizing these Aun-catalyzed reactions in practical applications.

On the Limited Role of Electronic Support Effects in Selective Alkyne Hydrogenation: A Kinetic Study of Au/MOx Catalysts Prepared from Oleylamine‐Capped Colloidal Nanoparticles

“…For simplicity, only one dissociated water molecule was used in this model. Two adsorption modes were simulated based on the predominant literature for alkyne adsorption on Au 10 (Figures and S20): the triple‐bonded carbon atoms bound to the same atom in Au 10 (π‐mode), or two separate atoms in Au 10 (di‐σ mode) …”

“…The metal surface generates an image dipole that cancels out the effect of the dipole change originating in the vibrating molecule . The Au nanoparticles are 2–4 nm, and linear alkynes are thought to adsorb parallel to the Au surface, so 1‐octyne species adsorbed to Au may not be detectable with FTIR.…”

Theoretical insights into the structural, relative stable, electronic, and gas sensing properties of PbnAun (n = 2–12) clusters: a DFT study

“…It is well known that the properties of Au n clusters are very sensitive to both size n and geometrical structure. According to the theoretical calculations, [16][17][18][19][20][21][22] the ground-state structures of Au n clusters demonstrate a transition from two-dimensional structures to three-dimensional structures due to the strong relativistic effects in Au atoms. 23,24 In general, Au n (n ¼ 3-13) clusters favor planar structures, whereas those Au n clusters exhibit three-dimensional structures when the size n is larger than 13.…”

“…However, the promising applications of Au n clusters are also particularly interesting to scholars. For example, Gautam et al 18 systematically investigated the C 2 H 2 activation and hydrogenation of C 2 H 2 activated on small Au n (n ¼ 3-10) clusters using DFT calculations. Zhou et al 26 performed ultrafast spectroscopic investigations on atomically precise thiolate-protected Au n nanoparticles, the Au n nanoparticles show three distinct states, including metallic, transition regime and non-metallic or excitonic states and their catalytic properties were obviously changed.…”

π⋅⋅⋅H+⋅⋅⋅π Hydrogen Bonds and Their Lithium and Gold Analogues: MP2 and CASPT2 Calculations

“…Studies related to the above gold and lithium complexes are rather rare. For example, acetylene–Au n ( n =3–10) clusters were optimized theoretically to analyze acetylene adsorption on gold surfaces . The complexes between Cu + , Ag + , and Au + and ethylene were analyzed theoretically, but, in these early studies, low‐level calculations were carried out .…”