Theoretical Study of the Adsorption of 2-Propanol onto Silica Surfaces on the Basis of Ab Initio and Density Functional Calculations

Abstract

The adsorptive interactions of 2-propanol (2-PrOH) molecules with silica surfaces were investigated using ab initio and density functional calculations. Two cluster models of silica were chosen to represent the terminal ≡SiOH groups and the siloxane bridges ≡Si-(O) 2-Si≡ on the silica surface. The Hartree-Fock (HF) and Density Functional Theory (DFT) approaches, employing a 6-31G(d) basis set, were used to calculate the geometries, electronic structures, vibrational frequencies and adsorption energies of the adsorption complexes formed. The calculated adsorption energies were corrected for zero-point vibrational energies (ZPVE) and basis set superposition errors (BSSE). The results favoured a most likely surface configuration for the physisorbed species in which 2-PrOH molecules are bound to exposed silanol groups via two hydrogen bonds, with the alcoholic-OH group acting simultaneously as a proton acceptor and donor. Moreover, bonding of 2-PrOH with strained surface siloxane bridges (≡Si-O-Si≡) was shown to lead to chemisorption of the alcohol molecule. These findings have been shown to help interpreting reported infrared spectroscopic results of in-situ experimental studies.

The Role of Surface Complexes in Ketene Formation from Fatty Acids via Pyrolysis over Silica: from Platform Molecules to Waste Biomass

“…However, it is determined only by the reactivity of the pentanoic acid molecule itself and the coordination capabilities of the silicon atoms on the surface. The formation of such a surface complex was also shown by Abdallah and coauthors . Additionally, the existence of two types of water in the IR spectra until the complete conversion of acid into ketene provides additional evidence of the bonding of acids with strained siloxane bridges …”

“…The formation of such a surface complex was also shown by Abdallah and coauthors. 55 Additionally, the existence of two types of water in the IR spectra until the complete conversion of acid into ketene provides additional evidence of the bonding of acids with strained siloxane bridges. 44 Figure 8 schematically shows all types of adsorption complexes obtained as a result of DFT modeling.…”

Iridium‐Catalyzed Dehydrogenation in a Continuous Flow Reactor for Practical On‐Board Hydrogen Generation From Liquid Organic Hydrogen Carriers

“…This is further supported by apparent activation enthalpies (6.3 kcal mol À 1 for batch reactor [11b] vs 14.0 kcal mol À 1 for flow reactor) indicating less contribution of mass transfer and higher contribution of bond-breaking in the β-elimination step in the flow reactor case, and also by a reaction order of one in iridium centers in the flow reactor compared to 0.5 in the batch reactor. Plausibly, support effects, such as differential interaction of the supports with acetone and isopropanol (that are adsorbed) [25][26][27] and hydrogen (that is not adsorbed) [25] may give rise to the observed effects, but further studies are needed to confirm or disprove this hypothesis.…”

Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect

“…For comparison, Abdallah et al (2009 ) found that, with the same B3LYP/6-31G(d) level of theory, bond lengths for hydrogen bonds were 1.7 Å and 1.9 Å for the physical adsorption of isopropanol on a silica surface. For THF adsorbed on the silica surface, not only the identical bond lengths, but also the localization of the Si–OH proton between the oxygen of the silanol group and the oxygen of the THF ( Figure 9 ) indicate the formation of a hydrogen bond.…”

“…As a model system for calculations, a 32 T (tetrahedral) silica cluster (cell size of approximately 1 nm × 1 nm) has been used in its non-hydroxylated and hydroxylated forms (no OH group and 2 OH groups/nm 2 , respectively), which resulted in a Si 32 O 68 H 8 composition (108 atoms as a whole). The SiO 2 cluster model and the adsorption structures of different probe molecules were optimized in the gas phase at the B3LYP/6-31G (d) level of theory, which seems to be a reliable method for studying the structures and stabilities of silica materials ( Abdallah et al, 2009 ; Rimola et al, 2013 ). This computational model has also been successfully used in our previous works ( Bauer et al, 2017 ; Bauer et al 2019 ; Bauer et al 2021 ).…”