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1. Reaction pathways for HCN on transition metal surfaces

   https://doi.org/10.1039/C8CP07548D  

   Abdel-Rahman, Mohammed; Feng, Xu; Muir, Mark; Ghale, Kushal; Xu, Ye; Trenary, Michael (February 2019, Physical Chemistry Chemical Physics)

   The adsorption and decomposition of HCN on the Pd(111) and Ru(001) surfaces have been studied with reflection absorption infrared spectroscopy and density functional theory calculations. The results are compared to earlier studies of HCN adsorption on the Pt(111) and Cu(100) surfaces. In all cases the initial adsorption at low temperatures gives rise to a ν (C–H) stretch peak at ∼3300 cm −1 , which is very close to the gas phase value indicating that the triple CN bond is retained for the adsorbed molecule. When the Pd(111) surface is heated to room temperature, the HCN is converted to the aminocarbyne species, CNH 2 , which was also observed on the Pt(111) surface. DFT calculations confirm the high stability of CNH 2 on Pd(111), and suggest a bi-molecular mechanism for its formation. When HCN on Cu(100) is heated, it desorbs without reaction. In contrast, no stable intermediates are detected on Ru(001) as the surface is heated, indicating that HCN decomposes completely to atomic species. 

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2. Influence of the C + H ₂ O → H ₂ CO solid-state reaction on astrochemical networks and the formation of complex organic molecules

   https://doi.org/10.1051/0004-6361/202450958  

   Potapov, Alexey; Garrod, Robin T (December 2024, Astronomy & Astrophysics)

   Context. The solid-state reaction C + H₂O → H₂CO has recently been studied experimentally and claimed as a new ‘non-energetic’ pathway to complex organic and prebiotic molecules in cold astrophysical environments. Aims. We compared results of astrochemical network modelling with and without the C + H₂O surface reaction. Methods. A typical, generic collapse model in which a dense core forms from initially diffuse conditions was used along with the astrochemical kinetics model MAGICKAL. Results. The inclusion of the reaction does not notably enhance the abundance of formaldehyde itself; however, it significantly enhances the abundance of methanol (formed by the hydrogenation of formaldehyde) on the dust grains at early times, when the high gas-phase abundance of atomic C leads to relatively rapid adsorption onto the grain surfaces. As a result, the gas-phase abundance of methanol is also increased due to chemical desorption, quickly reaching abundances close to ∼10⁻⁹n_H, which decline strongly under late-time, high-density conditions. The reaction also influences the abundances of simple ice species, with the CO₂abundance increased in the earliest, deepest ice layers, while the water-ice abundance is somewhat depressed. The abundances of various complex organic molecules are also affected, with some species becoming more abundant and others less. When gas-phase atomic carbon becomes depleted, the grain-surface chemistry returns to behaviour that would be expected if there had been no new reaction. Conclusions. Our results show that fundamental reactions involving the simplest atomic and molecular species can be of great importance for the evolution of astrochemical reaction networks, thus providing motivation for future experimental and theoretical studies. 

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3. Computational Study of Solvent Incorporation into a Porphyrin Monolayer

   https://doi.org/10.1021/acs.jpcc.3c07274  

   Hipps, K.W.; Mazur, Ursula (February 2024, The Journal of Physical Chemistry C)

   Density functional theory (DFT) is used to investigate the conversion from a solvent incorporated pseudo-polymorph into a single component monolayer. Calculations of thermodynamic properties both for the surfaces in contact with gas phase and with solvent are reported. In the case of wetted surfaces, a simple bond-additivity model, first proposed by Campbell and modified here, is used to augment the DFT calculations. The model predicts a dramatic reduction in desorption energies in solvent as compared to gas phase. Eyring’s reaction rate theory is used to predict limiting desorption rates for guest (solvent) molecules from the pockets in the pseudo-polymorph and for cobalt octaethylporphyrin (COEP) molecules in all structures. The pseudo-polymorph studied here is a nearly rectangular lattice (REC) composed of two CoOEP and 2 molecules of either 1,2,4-trichlorobenzene (TCB) or toluene (TOL) supported on 63 atoms of Au(111). At sufficiently high initial concentrations of CoOEP, only a hexagonal unit cell (HEX) with two molecules of CoOEP, supported on 50 atoms of gold is observed. Experimentally, the TCB-REC structure is more stable than the TOL-REC structure existing in solution at initial mM concentrations of CoOEP in TCB as opposed to initial M concentration of CoOEP in toluene. Calculations here show that the HEX structure is the thermodynamically stable structure at all practical concentrations of CoOEP. Once the REC structure forms kinetically at low concentration because of the vast excess of solvent on the surface, it is difficult to convert to the more stable HEX structure. The difference in stability is primarily due to the difference in electronic adsorption energy of the solvents (TOL or TCB) and to the very low desorption rate of CoOEP. The adsorption energy of TCB has two important contributors: the adsorption energy onto Au alone, and the intermolecular interactions between TCB and the CoOEP host lattice. Neither factor can be neglected. We also find that planar adsorption of both TOL and TCB on Au(111) is the energetically preferred orientation when space is available on the surface. Rates of desorption are very sensitive to the solvent free activation energy and to the thermodynamic parameters required to convert the solvent free activation energy to one for the solvated surface. Small changes in the computed energy (of the order of 5%) can lead to one order of magnitude change in rates. Further, the solvation model used does not provide the barrier to adsorption in solution needed to determine values for the desorption activation energy. Thus, the rates computed here for desorption into solvent are limiting values. 

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4. Surface structure sensitivity of hydrodeoxygenation of biomass-derived organic acids over palladium catalysts: a microkinetic modeling approach

   https://doi.org/10.1039/D1CY01029H  

   Kundu, Subrata Kumar; Vijay Solomon, Rajadurai; Yang, Wenqiang; Walker, Eric; Mamun, Osman; Bond, Jesse Q.; Heyden, Andreas (January 2021, Catalysis Science & Technology)

   null (Ed.)

   Microkinetic models based on parameters obtained from density functional theory and transition state theory have been developed for the hydrodeoxygenation (HDO) of propanoic acid, a model lignocellulosic biomass-derived organic acid, over the flat Pd(100) and Pd(111) surfaces in both vapor and liquid phase reaction conditions. The more open Pd(100) surface was found to be 3–7 orders of magnitude more active than the Pd(111) surface in all reaction environments, indicating that the (111) surface is not catalytically active for the HDO of propanoic acid. Over Pd(100) and in vapor phase, liquid water, and liquid 1,4-dioxane, propanoic acid hydrodeoxygenation follows a decarbonylation (DCN) mechanism that is facilitated by initial α- and β-carbon dehydrogenation steps, prior to the rate controlling C–OH and (partially rate controlling) C–CO bond dissociations. Only over Pd(111) and aqueous reaction environments is the decarboxylation (DCX) preferred over the DCN with the C–CO 2 step being rate controlling. 

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5. Surface chemistry of monochloramine catalyzed by Fe(111)

   https://doi.org/10.1016/j.susc.2025.122890  

   Agbelusi, Oloruntoba S; Pandey, Subash; Sonam; Goel, Neetu; Tharaka, RM_D Naveen; Lopez, Journey A; Perrine, Kathryn A (November 2025, Surface Science)

   Monochloramine (NH2Cl) is a secondary disinfectant used for water purification and interacts with iron materials in various environments. Iron surfaces undergo reduction-oxidation and corrosion, where zero-valent iron sites are produced at complex interfaces. The initial stages of the reaction of monochloramine (NH2Cl) have been studied on Fe(111), as a model for iron pipelines and mineral surfaces, at the gas/solid interface in ultra-high vacuum conditions. Using in situ infrared reflection absorption spectroscopy, NH2Cl was found to adsorb molecularly at -160 °C, by observation of amine vibrational signatures. Auger electron spectroscopy was used to detect the presence of chloride to amine in a 3:1 ratio. Upon annealing, the NH2Cl multilayer was found to desorb from Fe(111) at -120 °C, and the monolayer also undergoes molecular dissociation. At 34 °C, NH2Cl primarily binds through the chloride species, thus blocking sites for NH2 adsorption. Density functional theory computations and X-ray photoelectron spectroscopy confirmed two favorable chemisorbed orientations, both through binding of chloride. Further annealing allowed for chloride desorption before 400 °C, suggesting decomposition. The NH2Cl is found to undergo a dechlorination mechanism, similar to chlorohydrocarbon reactions on iron surfaces. These findings reveal the mechanism of the chloramine disinfectant on metallic iron interfaces and its role in pipelines and water systems. 

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