Cyanide adsorption on gold electrodes : a combined surface enhanced Raman spectroscopy and density functional theory study

A combined SERS and DFT study of cyanide adsorption on a gold electrode is presented. From our analysis, the high-frequency mode at 2100 cm-1 is ascribed to the C–N stretching frequency at (1 0 0) and (1 1 0) sites. The lower frequency modes at 370 and 300 cm-1 are ascribed to the Au–CN stretching and bending modes, respectively. The Stark tuning slopes of these modes agree well with the DFT computations. The bending mode at 300 cm-1 has a very small Stark tuning slope of 4 cm-1 V-1, experimentally, compared to 1 cm-1 V-1, computationally. The Au–CN stretching frequency has a Stark tuning slope of 15 cm-1 V-1, experimentally, compared to 16–22 cm-1 V-1, computationally. The positive Stark tuning slopes suggest that cyanide adsorbs as an anion, with a bond polarity between that of the Au–Cl and Au–Br surface bonds. The anionic character of the Au–CN bond is also confirmed by different charge analyses based on the DFT computations. The ordering in binding strength on the three different surfaces is the same as the ordering in bond ionicity. The C–N stretching frequency has two different Stark tuning slopes in the SERS experiments: 14 cm-1 V-1 in the more negative potential region corresponding to cyanide adsorption, and 35 cm-1 V-1 in the more positive potential region corresponding to gold dissolution. The computational result of 8 cm-1 V-1 agrees well with the lower Stark tuning slope. The higher Stark tuning slope is presumably related to the formation of gold–cyanide complexes in the double layer

Cyanide adsorption on gold electrodes : a combined surface enhanced Raman spectroscopy and density functional theory study

A combined SERS and DFT study of cyanide adsorption on a gold electrode is presented. From our analysis, the high-frequency mode at 2100 cm-1 is ascribed to the C–N stretching frequency at (1 0 0) and (1 1 0) sites. The lower frequency modes at 370 and 300 cm-1 are ascribed to the Au–CN stretching and bending modes, respectively. The Stark tuning slopes of these modes agree well with the DFT computations. The bending mode at 300 cm-1 has a very small Stark tuning slope of 4 cm-1 V-1, experimentally, compared to 1 cm-1 V-1, computationally. The Au–CN stretching frequency has a Stark tuning slope of 15 cm-1 V-1, experimentally, compared to 16–22 cm-1 V-1, computationally. The positive Stark tuning slopes suggest that cyanide adsorbs as an anion, with a bond polarity between that of the Au–Cl and Au–Br surface bonds. The anionic character of the Au–CN bond is also confirmed by different charge analyses based on the DFT computations. The ordering in binding strength on the three different surfaces is the same as the ordering in bond ionicity. The C–N stretching frequency has two different Stark tuning slopes in the SERS experiments: 14 cm-1 V-1 in the more negative potential region corresponding to cyanide adsorption, and 35 cm-1 V-1 in the more positive potential region corresponding to gold dissolution. The computational result of 8 cm-1 V-1 agrees well with the lower Stark tuning slope. The higher Stark tuning slope is presumably related to the formation of gold–cyanide complexes in the double layer

Ab Initio calculations of intermediates of oxygen reduction on low-index platinum surfaces

Properties of the oxygen molecule, atomic oxygen, and intermediate products of its reduction, OH, OOH, H2O2 on (111), (100), and (110) Pt surfaces have been investigated using periodic density functional theory. The Pt surfaces are modeled as four-layer slabs. Adsorption energies and geometries, as well as the charge-transfer properties are calculated. Computed characteristics of the adsorbed oxygen reduction intermediates supply known tendencies of the low index Pt surface activities under different experimental conditions. Electric field dependencies of the properties of all species adsorbed on a Pt9(111) cluster have been also studied. Lowering the field causes an increase of the O-O bond length of O2ads, attracting the molecule to the Pt surface and increasing the charge transfer from Pt to 2* orbitals of the oxygen molecule. The weakening of the O-O bond is evidenced by a decrease of the O-O stretching frequency. The charge-transfer from the Pt9 cluster to the adsorbates is observed for all species. In our calculations hydrogen peroxide was unstable on all three low-index Pt surfaces and dissociated into two hydroxyls or a water molecule and atomic oxygen. The results of the calculations are discussed in the context of the mechanism of oxygen reduction

Characterization of the microporosity of chromia- and titania-pillared montmorillonites differing in pillar density. I. Adsorption of nitrogen

The microporosity of chromia- and TiO2-pillared clays differing in pillar d. was explored. Nitrogen adsorption data detd. at very low relative pressures were used. These data were analyzed by the as method and the BET, Langmuir, Dubinin-Radushkevich and Dubinin-Stoeckli approaches. The applicability of these methods for detn. of the PILCs' microporosity was studied. The surface area calcd. by the as method can be considered as a total surface area of the materials studied. The BET method underestimates, whereas the Langmuir approach overestimates, the total surface area of these solids. The Dubinin-Radushkevich method can be applied only to characterize textural features of PILCs exhibiting homogeneously distributed narrow micropores

Characterization of the microporosity of chromia- and titania-pillared montmorillonites differing in pillar density. I. Adsorption of nitrogen

The microporosity of chromia- and TiO2-pillared clays differing in pillar d. was explored. Nitrogen adsorption data detd. at very low relative pressures were used. These data were analyzed by the as method and the BET, Langmuir, Dubinin-Radushkevich and Dubinin-Stoeckli approaches. The applicability of these methods for detn. of the PILCs' microporosity was studied. The surface area calcd. by the as method can be considered as a total surface area of the materials studied. The BET method underestimates, whereas the Langmuir approach overestimates, the total surface area of these solids. The Dubinin-Radushkevich method can be applied only to characterize textural features of PILCs exhibiting homogeneously distributed narrow micropores

Physicochemical and catalytic characterization of non-hydrothermally synthesized Mg-, Ni- and Mg-Ni-saponite-like materials

Saponite-like materials with Mg2+ or Ni2+ ions and their mixt. in the octahedral sheet were non-hydrothermally synthesized. Their protonic forms were prepd. through deammoniation or by treatment with HCl. The products were characterized by phys. methods, gas-phase adsorption of amines and the catalytic transformation of 2-propanol and cumene via pulse and flow methods. The materials have a house-of-card' texture composed of platelets with small lateral dimensions and exhibit a high surface area and pore vol. Subsequent deammoniation resulted in the formation of non-framework Ni2+ and possibly Mg2+ ions. Mg-saponite, prepd. in this way, shows predominantly non-framework species formed by tetrahedrally coordinated Al3+ ions whereas its acid-treated counterpart contains Al3+ in both framework and non-framework positions.Deammoniated Ni-saponite exhibits a peculiar catalytic behavior, which manifests itself in the fact that the activity in the 2-propanol decompn. in a pulse expt. is low while under flow conditions it becomes the most active. This is ascribed to generation during the reaction of new acidic centers due to the dissociative adsorption of produced water on site pairs formed by coordinatively unsatd. non-framework Ni2+ and framework oxygen ions. Cumene conversion tests confirm this explanation. The high activity and stability of acid-treated Mg-saponite in cumene dealkylation underlines its potential use for high-temp. acid-catalyzed reactions. The Bronsted acidity of the saponite-like materials is related to their layer charge, cation exchange capacity and diminished with increasing Ni content, whereas the Lewis acidity increased. Both the gas-phase amine chemisorption and catalytic tests provide the same order of protonic acidity: Mg > MgNi > Ni. The origin of the acidic sites from deammoniation or HCl treatment is discussed. [on SciFinder (R)

The protoadamantane radical cation

DFT (B3LYP) and MP2 computations with a 6-31G* basis set show that a unique protoadamantane radical cation (1·+) structure with an elongated, half-broken C6-H bond prevails both in the gas phase and in solution. This is in agreement with the observed regioselectivity of the single electron-transfer oxidation of protoadamantane (1) with photoexcited 1,2,4,5-tetracyanobenzene, which only gives 5-(6-protoadamantyl)-1,2,4-tricyanobenzene (5), for which the X-ray crystal structure is reported. The regioselectivities for the functionalizations of 1 with electrophiles support this oxidation pathway. The H-coupled electron-transfer mechanism recently proposed for the C-H activation of alkanes with electrophilic oxidizers explains the high C6 positional selectivities in the functionalization of 1 in electrophilic media

The protoadamantane radical cation

DFT (B3LYP) and MP2 computations with a 6-31G* basis set show that a unique protoadamantane radical cation (1·+) structure with an elongated, half-broken C6-H bond prevails both in the gas phase and in solution. This is in agreement with the observed regioselectivity of the single electron-transfer oxidation of protoadamantane (1) with photoexcited 1,2,4,5-tetracyanobenzene, which only gives 5-(6-protoadamantyl)-1,2,4-tricyanobenzene (5), for which the X-ray crystal structure is reported. The regioselectivities for the functionalizations of 1 with electrophiles support this oxidation pathway. The H-coupled electron-transfer mechanism recently proposed for the C-H activation of alkanes with electrophilic oxidizers explains the high C6 positional selectivities in the functionalization of 1 in electrophilic media