Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

The adsorption properties of sulfated aluminum oxide (9% SO ₄ ^2- /γ-Al₂O₃) and a cobalt-containing composite (0.5%Сo/SO ₄ ^2- /γ-Al₂O₃) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C₆–C₈), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO ₄ ^2- /γ-Al₂O₃ in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25–120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2–4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al₂O₃ promoted by cobalt salt.     

Influence of chemisorbed carbon monoxide on the oxidation of molecular hydrogen at smooth platinum in sulfuric acid solution

Potentiostatic current—potential curves of hydrogen oxidation were measured at 0.5 mV s^?1 on two smooth platinum electrodes of different shape in the presence of various coverages with chemisorbed carbon monoxide in 0.5 M H₂SO₄, stirred with molecular hydrogen at 1 cm³ s^?1. Carbon monoxide coverages up to 0.6 have a small influence. The hydrogen oxidation remains controlled by convective diffusion of molecular hydrogen. Above coverages of 0.6, a kinetic step becomes increasingly predominant. The effect of chemisorbed carbon monoxide on the H₂ oxidation is similar to that on hydrogen adsorption, studied previously. The correlation between the rate of the kinetic step and the free energy of hydrogen adsorption in the Temkin model of the surface is established and discussed.     

Tin-sulfur based catalysts for acetylene hydrochlorination

In the present work, tin-sulfur based catalysts were prepared using Na₂SO₃ and (CH₃SO₃)₂Sn and were tested in acetylene hydrochlorination. Based on the analysis of experiments results, the acetylene conversion of (CH₃SO₃)₂Sn/S@AC is still over 90%after a 50 h reaction, at the reaction conditions of T = 200 ^oC, V_HCl/V_C2H2 = 1.1:1.0 and C₂H₂-GSHV = 15 h^–1. According to the results of X-ray photoelectron spectroscopy (XPS), HCl adsorption experiments, and acetylene temperature programmed desorption (C₂H₂-TPD), it is reasonable to conclude that the interaction between Sn and S not only can retard the oxidation of Sn²⁺ in catalysts but also strengthen the reactant adsorption capacity of tin-based catalysts. Furthermore, results obtained from nitrogen adsorption/desorption and XPS proved that the CH₃SO₃- can effectively decrease the coke deposition of (CH₃SO₃)₂Sn/AC and thus prolong the lifetime of (CH₃SO₃)₂Sn/AC.     

Dissociation rate measurements in SO2 + Ar mixtures behind incident shock waves

Dissociation rates of SO₂ in SO₂ + Ar mixtures at 6%, 11%, 15% and 20% of SO₂ were measured behind incident shock waves over a temperature range 4000–6000 K at initial pressures 1.0 to 2.5 Torr. The recorded laser schlieren signals exhibited two exponentials, the faster one due to vibrational relaxation and the slower one due to dissociation. The initial dissociation rate was calculated from the value of the density gradient at the point of intersection of the two exponentials. A least-squares analysis of the experimental data yielded the following empirical relations: k_SO2Ar = 3.34 × 10¹⁵ exp(?107.6 kcal mole^?1/RT) cm³/mole s, k_SO2SO2 = 5.02 × 10¹⁴ exp(?66.6 kcal mole^?1 kcal mole^?1/RT) cm³/mole s.     

Reaction rate constant of SO3 + CH3OH in the gas phase

The reaction rates of SO₃ with CH₃OH in He were measured at total pressures of 0.7–1.6 torr in flow tubes. The concentration of SO₃ was monitored by the SO₂* fluorescence from excitation of SO₃ at 147 nm. The reaction rate constant of SO₃ + CH₃OH in the gas phase is determined to be (1.17 ± 0.16) × 10^?13 cm³ molec^?1 s^?1 at room temperature.     

Adsorption of SO2 on alumina

The adsorption of SO₂ on alumina used in the aluminium industry, the so-called smelter-grade alumina, was studied in the temperature range 15–120°C. It was found that at temperatures lower than 40°C, sulphur dioxide was bonded to alumina reversibly by physical forces, and the adsorption could be described satisfactorily by the Langmuir adsorption isotherm. The heat of adsorption was estimated to be −33 kJ mol⁻¹. At temperatures ranging from 80°C to 120°C, which prevail in dry scrubbers in the aluminium industry, the heat of adsorption was determined to be −56 kJ mol⁻¹. When SO₂ was adsorbed at temperatures higher than 80°C, about 30 % of the SO₂ could not be desorbed even if the samples were heated up to 250°C. In the presence of SO₂ and oxygen, the formation of sulphate was observed at temperatures above 90°C.     

SO2 Surface Chemistry on Metal Substrates

The surface chemistry, induced by thermal and non-thermal methods, of SO₂ on metal substrates is reviewed. The substrate temperature during dosing is important; regardless of metal, adsorption is dissociative at 300 K and molecular at 100 K. On Ni, Pd, and Pt, molecular adsorption occurs through the S and one O atom, and the molecular plane is perpendicular to the surface. However, on Ag and Cu, adsorption occurs only through the S with the molecular plane perpendicular to the surface. The differences can be attributed to the structure of the metal's molecular orbitals and their interactions with the SO₂ orbitals. Upon heating, SO₂ dissociates on all transition metal surfaces with the exception of Ag, Au, and Cu, where only molecular desorption occurs. On Pt, Fe, and Pd, additional reactions are observed between SO₂ and its dissociation products. The nonthermal reactions induced by photons and electrons for monolayer coverages of SO₂ on Ag (111) are dominated by molecular desorption. Desorption cross sections for 313 nm photons and 50eV electrons were 2.8 × 10^?20 cm² and ?1 × 10^?16 cm², respectively. Nonthermal excitation mechanisms and quenching processes as well as interesting characteristics of SO₂ under irradiation are also reviewed.     

New Composite Sorbent for Removal of Sulfate Ions from Simulated and Real Groundwater in the Batch and Continuous Tests

The evaluation of groundwater quality in the Dammam formation, Faddak farm, Karbala Governorate, Iraq proved that the sulfate (SO₄²⁻) concentrations have high values; so, this water is not suitable for livestock, poultry and irrigation purposes. For reclamation of this water, manufacturing of new sorbent for permeable reactive barrier was required through precipitation of Mg and Fe hydroxides nanoparticles on the activated carbon (AC) surface with best Mg/Fe molar ratio of 7.5/2.5. Mixture of 50% coated AC and 50% scrap iron was applied to eliminate SO₄²⁻ from contaminated water with efficiency of 59% and maximum capacity of adsorption equals to 9.5 mg/g for a time period of 1 h, sorbent dosage 40 g/L, and initial pH = 5 at 50 mg/L initial SO₄²⁻ concentration and 200 rpm shaking speed. Characterization analyses certified that the plantation of Mg and Fe nanoparticles onto AC was achieved. Continuous tests showed that the longevity of composite sorbent is increased with thicker bed and lower influent concentration and flow rate. Computer solution (COMSOL) software was well simulated for continuous measurements. The reclamation of real contaminated groundwater was achieved in column set-up with efficiency of 70% when flow rate was 5 mL/min, bed depth was 50 cm and inlet SO₄²⁻ concentration was 2301 mg/L.     

SIFDT study of the SO+2/H2 H-atom abstraction reaction

The exothermic H-atom abstraction reaction of SO⁺₂ with H₂ has been studied in a selected ion flow drift tube (SIFDT) over a range of center-of-mass energies from thermal (300 K) to about 0.12 eV. The measured rate coefficient at 300 K is 4.2 × 10⁻¹² cm³ s⁻¹ which is very much less than the Langevin capture rate. The increase in rate coefficient with ion kinetic energy gives a linear Arrhenius-type plot with a slope that indicates a barrier of ∼5 kJ mol⁻¹ exists on the potential surface. The H₂SO⁺₂ potential surface is also explored in an ab initio investigation using the G2 procedure. An (SO⁺₂.H₂)¹ transition state between reactants and products is identified, corresponding to the barrier found from experiments.     

Electrochemical Condensation of Methylviologen on Specifically‐adsorbed Anion Layers

The adsorption of methylviologen dications (MV²⁺) on single‐crystalline Au electrodes in both H₂SO₄ and HClO₄ was examined. MV²⁺ strongly interacted with sulfate and bisulfate anions adsorbed on the Au(111) electrode surface in 0.05 M H₂SO₄ under a controlled potential of 1.25 V vs. the reversible hydrogen electrode (RHE). A characteristic non‐Faradaic current was observed at 1.10 V vs. RHE. When adsorption of MV²⁺ was carried out in 0.1 M HClO₄, the electrochemical response of MV²⁺ was less than that obtained in H₂SO₄. The results show that the formation of a highly ordered sulfate/bisulfate adlayer plays an important role in the formation of condensed MV²⁺ layers. Examination of polycrystalline Au and Au(100) electrodes revealed a poor electrochemical response due to the surface roughness of the Au substrate, but the electrochemical detection was applicable to polycrystalline Au electrodes. A systematic investigation of the structural dependency of viologen derivatives showed that molecular size is important for electrostatic interactions with a highly ordered sulfate/bisulfate adlayer. The findings of the present study demonstrate successful detection of MV²⁺ at a concentration of ≤1 pM with a non‐Faradaic current.     

Removal of sulfate from wastewater via synthetic Mg–Al layered double hydroxide: An adsorption,kinetics, and thermodynamic study

Sulfate-contaminated water is a major environmental problem that alters the taste of water, disturbs the digestive systems of animals and humans, and erodes both soil and metals. In this study, the layered double hydroxide LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ were prepared using a co-precipitation technique, and applied in the adsorption of SO₄^2- from an aqueous solution. The reaction is well described by the Langmuir adsorption model. LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ afforded maximum SO₄^2- adsorption values of 135.14 and 92.59 ​mg/g, respectively. The reaction is best explained by a pseudo-second-order mechanism, which suggests that chemisorption is the rate-determining step. The activation energies of LDH 4Mg2Al·NO₃ and LDH 8Mg2Al·NO₃ indicate that the adsorption of SO₄^2- on synthetic LDHs predominantly follows an anion-exchange mechanism, wherein SO₄^2- ions in the aqueous medium replaces intercalated NO₃^- ions in the synthetic LDHs. The thermodynamic parameters (ΔH̊, ΔS̊, and ΔG̊) were also calculated. The reaction was endothermic, and the synthetic LDHs afforded feasible and spontaneous adsorption of SO₄^2-.     

A pulse radiolysis and flash photolysis study of the radicals SO-2, SO-3, SO-4 and SO-5

Pulse radiolysis and laser-flash photolysis have been used to generate the radicals SO^-₂, SO^-₃, SO^-₄ and SO^-₅. Optical absorption spectra for these radicals and rate constants for their self-reactions have been derived. The decay of SO^-₂, SO^-₃, and SO^-₄ follow simple second-order kinetics; the decay of SO^-₅ is slower and does not follow a second-order rate law when the radical is generated by the pulse radiolysis of an oxygenated sulfite or bisulfite solution, but is second-order when generated by the flash photolysis of an oxygenated dithionate solution. SO^-₂ reacts rapidly with O₂ and a rate constant of 2.4 × 10⁹ M^-1 s^-1 was derived. SO^-₃ also reacts rapidly with O₂ and a rate constant of 1.1 × 10⁹ M^-1 was derived for this reaction. The rate constant for the reaction of H with SO₂ was determined to be 2.9 × 10⁹ M^-1 s^-1.     

AB initio calculations and matrix ftir studies of the sulfur trioxide radical anion

The structures and vibrational frequencies of SO⁻₃ (C_3v) and SO⁻₂ (C_2v) have been calculated at the UHF SCF/3-21 + G¹ level. By cocondensation of Cs atoms and SO₃ in an Ar matrix the FTIR spectrum of Cs₄SO₃ has been measured. The molecule is proposed to have C_s symmetry with SO₃ binding to Cs in a bidentate fashion.     

Calorimetric study of the adsorption of air pollutants on alumina-supported tin and gallium oxides

The differential enthalpies of adsorption of air pollutants such as SO₂, NO₂, NO on aluminasupported tin and gallium oxides were measured by calorimetry coupled with isothermal volumetry. Whatever the amount of tin or gallium on alumina, the enthalpies of adsorption of SO₂ at low coverage were of the same order of magnitude or up to 50 kJ/mol lower than those of the support. The amount of SO₂ adsorbed decreased with increasing SnO₂ loading and increased with increasing Ga₂O₃ loading on the alumina. The differential enthalpies of adsorption of NO₂ are close to those on the support whatever the amount of tin or gallium (around 120–130 kJ/mol). NO is only reversibly adsorbed on the samples. The calorimetric data of ammonia adsorption are given for comparison.     

Variations in the Overall Charge and Open-Circuit Potential of a Palladium Electrode during the Adsorption of Iodine and Iodide Anions

Transients of the current and the open-circuit potential during the adsorption of I^– and I₂ on Pd/Pt (supporting electrolyte 0.5 M H₂SO₄) are measured and so are potentiodynamic and galvanostatic charging curves, in the presence and absence of adlayers. Dependences of the overall electrode charge on potential are constructed. After the adsorption of both I^– and I₂, values of the electrode surface charges at potentials of the double-layer region turn negative and considerably differ in their magnitude. The latter is connected with different character of adlayers, which is shown by experiments on the adsorption of silver atoms at underpotentials after a preliminary adsorption of I^– and I₂ on the electrode surface. Certain discrepancies between experimentally-found and theoretically-expected values of transients are attributed to a substantial increase in the irreversibility of sorption and desorption of hydrogen and oxygen in the presence of iodine atoms adsorbed on the surface.     

Adsorption of SO2 and chlorobenzene on activated carbon

Activated carbon is very effective for simultaneous removal of multiple pollutants. The adsorption of SO₂ and chlorobenzene modeling of VOCs on activated carbon was investigated in a fixed-bed reactor by four kinds of activated carbon. The results show that the SO₂ adsorption is affected by the BET surface and basic functional groups as C=O and π–π* groups of the carbon, while the chlorobenzene adsorption is strongly affected by the carbon pore structure, with the micropore volume deciding the adsorption amount and larger pores increasing the adsorption rate. The chlorobenzene adsorption is little affected by the chemical properties of activated carbon as the O/C ratio detected by XPS. The effect of SO₂ on the chlorobenzene adsorption was investigated, with the results showing the SO₂ seriously restricts the individual chlorobenzene adsorption and this effect becomes smaller in the presence of O₂. The adsorption products were analyzed by TPD-MS and the initial decomposition temperatures are 380 K for chlorobenzene and 500 K for SO₂, showing that SO₂ is much more stable adsorbed than chlorobenzene. The changes of the carbon functional groups that the CO₂ desorption peak emerges at 700 K and decreases at 1000 K with the chlorobenzene adsorption, were observed by TPD-MS, indicating that the lactone and quinone groups on the carbon are likely to combine with the chlorobenzene and form weakly chemisorbed chlorobenzene.     

Electrochemical reduction of sulphur dioxide on inert electrodes in acetonitrile solutions

The reduction of SO₂ on Pt and glassy carbon electrodes in acetonitrile-0.1 M LiBr solutions is studied by chronopotentiometric and chronovoltamperometric techniques in a wide range of SO₂ concentrations. It is found that the reduction process involves an irreversible adsorption of the reaction products followed by a fast formation of a weakly soluble dithionate film which passivates the electrode surface. At sweep rates >0.1 V s^?1 the electric charge associated with cathodic reaction corresponds to that of a monolayer. The dependencies of the peak current and the peak potential on the sweep rate are in agreement with the requirements of the adsorption pseudocapacitance theory. The strong effect of water on the height of the cathodic peaks is indicative of the depassivation of the electrode by some active species formed in the presence of water, SO₂ and LiBr by a slow reaction.     

Adsorption of -histidine on copper surface as evidenced by surface-enhanced Raman scattering spectroscopy

The adsorption of -histidine on a copper electrode from H₂O- and D₂O-based solutions is studied by means of surface-enhanced Raman scattering (SERS) spectroscopy. Different adsorption states of histidine are observed depending upon pH, potential, and the presence of the SO²⁻₄ and Cl⁻ ions. In acidic solutions of pH 1.2 the imidazole ring of the adsorbed histidine remains protonated and is not involved in the chemical coordination with the surface. The SO²⁻₄ and Cl⁻ ions compete with histidine for the adsorption sites. In solutions of pH 3.1 three different adsorption states of histidine are observed depending on the potential. Histidine adsorbs with the protonated imidazole ring oriented mainly perpendicularly to the surface at potentials more positive than −0.2 V. Transformation of that adsorption state occurs at more negative potentials. As this takes place, histidine adsorbs through the α-NH₂ group and the neutral imidazole ring. The Cl⁻ ions cause the protonation and detachment of the α-NH₂ group from the surface and the formation of the ion pair NH⁺₃ … Cl⁻ can be observed. In the neutral solution of pH 7.0 histidine adsorbs through the deprotonated nitrogen atom of the imidazole ring and the α-COO⁻ group at E ≥ −0.2 V. However, this adsorption state is transformed into the adsorption state in which the α-NH₂ group and/or neutral imidazole ring participate in the anchoring of histidine to the surface, once the potential becomes more negative. In alkaline solutions of pH 11.9 histidine is adsorbed on the copper surface through the neutral imidazole ring.