Comparative Study of Methanol Activation by Different Small Mixed Silicon Clusters Si₂M with M = H, Li, Na, Cu, and Ag

Abstract

High-accuracy quantum chemical calculations were carried out to study the mechanisms and catalytic abilities of various mixed silicon species Si 2 M with M = H, Li, Na, Cu, and Ag toward the first step of methanol activation reaction. Standard heats of formation of these small triatomic Si clusters were determined. Potential-energy profiles were constructed using the coupled-cluster theory with extrapolation to complete basis set CCSD(T)/CBS, and CCSD(T)/aug-cc-pVTZ-PP for Si 2 Cu and Si 2 Ag. The most stable complexes generated by the interaction of methanol with the mixed clusters Si 2 M possess low-spin states and mainly stem from an M–O connection in preference to Si–O interaction, except for the Si 2 H case. In two competitive pathways including O–H and C–H bond breakings, the cleavage of the O–H bond in the presence of all clusters studied becomes predominant. Of the mixed clusters Si 2 M considered, the dissociation pathways of both O–H and C–H bonds with Si 2 Li turns out to have the lowest energy barriers. The most remarkable finding is the absence of the overall energy barrier for the O–H cleavage with the assistance of Si 2 Li. The breaking of O–H and C–H bonds with the assistance of Si 2 H, Si 2 Li, and Si 2 Na is kinetically preferred with respect to the Si 2 Cu and Si 2 Ag cases, apart from the case of Si 2 Na for O–H cleavage. In comparison with other transition-metal clusters with the same size, such as Cu 3 , Pt 3 , and PtAu 2 , the energy barriers for the O–H bond activation in the presence of small Si species, especially Si 2 H and Si 2 Li, are found to be lower. Consequently, these small mixed silicon clusters can be regarded as promising alternatives for the expensive metal-based catalysts currently used for methanol activation particularly and other dehydrogenation processes of organic compounds. The present study also suggests a further extensive search for other doped silicon clusters as efficient and more realistic gas-phase catalysts for important dehydrogenation processes in such a way that they can be experimentally prepared and implemented.

Mechanistic Study on Water Splitting Reactions by Small Silicon Clusters Si3X, X = Si, Be, Mg, Ca

“…Improved geometrical parameters are then reoptimized using the same functional but with the larger correlation consistent aug-cc-pVTZ (denoted hereafter as aVTZ) basis set. The B3LYP functional has been shown to provide energetic data in line with experiment, or high accuracy wave function methods such as the coupled-cluster theory CCSD­(T) in previous investigations for both pure and doped silicon clusters ,,− and the reactions of water dimer. , Harmonic vibrational frequency analyses are performed at the same level to confirm the nature of the stationary structures and to evaluate the zero-point correction energies (ZPE). Intrinsic reaction coordinate (IRC) profiles are computed at the B3LYP/aVTZ level to make sure that each transition structure (TS) located is correctly connected with two energy minima.…”

“…In fact, an appropriate dopant can dramatically change some properties of the resulting doped clusters, namely electronic, chemical, and optical features . Earth-alkaline metals have been suggested to be efficient catalyst in many processes. − Our recent studies , also revealed that small earth-alkali mixed silicon clusters Si n M with n = 2,3 and M = Be, Mg, Ca, can be regarded to be promising alternatives for the expensive metal-based catalysts used for methanol dissociation and other dehydrogenation processes of organic compounds. In particular, the energy barriers for the cleavage of O–H bond in the presence of doped Si clusters has been found to be lower than all previously reported values on various types of elemental clusters, metal surfaces, or metal oxides.…”

A theoretical investigation of the adsorption capacities of HCHO, HCOOH, CH3OH on M4 clusters (M = Au, Pd, Pt)

“…The result obtained are suitable with the previous studies about the decomposition of CH3OH on metal surfaces of Pt, Pd, Co, etc. [14,[16][17][18][19][20]22,24] Therefore, considering the CH3OH adsorbent, the highest catalytic adsorption efficiency belongs to the Pt4 cluster, leading to the formation of M-O bonds.…”

“…[2] Other works relate to the decomposition of methanol and formaldehyde to form hydrogen on Pt/Al2O3, Ru-Pt, Pt3/Ni(1 0 0), Zn/Cu(1 1 1), Pd/Zn(1 1 1), Pt13, Pt7, Pt3Cu4, Cu7, etc. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]32] The O-H cleavage or C-H cleavage occurs first depending on the catalytic material used. For instance, Desai and co-workers examined the adsorption of methanol over Pt(1 1 1) in vacuum and concluded that dehydrogenation pathways starting from the activation of the C-H bond are easier than these of the O-H bond.…”

Synthesis of picolinates via a cooperative vinylogous anomeric-based oxidation using UiO-66(Zr)-N(CH2PO3H2)2 as a catalyst

“…1–5 These frameworks, characterized by high thermal stability and large surface area, have found extensive use as catalysts in coupling, cross-coupling, nitration, multi-component, oxidation-reduction, and Diels–Alder reactions. 6–11 Crystalline porous frameworks consist of an inorganic sector comprising metal cations as nuclei and an organic sector serving as ligand connectors. 12,13 These frameworks possess highly active surfaces and offer a wide range of functional groups, enabling the design of highly efficient catalysts.…”