Showing papers on "Chemisorption published in 2015"
TL;DR: A sulfur electrode exhibiting strong polysulfide chemisorption using a porous N, S dual-doped carbon is reported, and the synergistic functionalization from the N and S heteroatoms dramatically modifies the electron density distribution and leads to much stronger polys sulfuride binding.
Abstract: A sulfur electrode exhibiting strong polysulfide chemisorption using a porous N, S dual-doped carbon is reported. The synergistic functionalization from the N and S heteroatoms dramatically modifies the electron density distribution and leads to much stronger polysulfide binding. X-ray photoelectron spectroscopy studies combined with ab initio calculations reveal strong Li(+) -N and Sn (2-) -S interactions. The sulfur electrodes exhibit an ultralow capacity fading of 0.052% per cycle over 1100 cycles.
676 citations
TL;DR: In this paper, a review of the structure and chemical reactions on well-defined cerium oxide surfaces is presented, and the growth, characterization and properties of these thin-films are also examined.
480 citations
TL;DR: A successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and 57Fe Mössbauer spectroscopy techniques is reported.
Abstract: Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and (57)Fe Mossbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity.
440 citations
TL;DR: Anatase TiO2-supported manganese and cobalt oxide catalysts with different Co/Mn molar ratios were synthesized by a conventional impregnation method and used for selective catalytic reduction (SCR) of NOx with NH3 as mentioned in this paper.
Abstract: Anatase TiO2-supported manganese and cobalt oxide catalysts with different Co/Mn molar ratios were synthesized by a conventional impregnation method and used for selective catalytic reduction (SCR) of NOx with NH3. The catalysts were characterized by N2 adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed desorption with NH3 and NOx. Characterization of the catalyst confirmed that by using Co3O4 over Mn/TiO2, we enhanced NO oxidation ability. From in situ diffuse reflectance infrared transform spectroscopy (DRIFTs) analysis of desorption and the transient reaction, we concluded that the addition of Co could remarkably lower the activation energy of NOx chemisorption on the catalyst surface. In addition, low-temperature SCR activity mainly results from a “fast SCR” reaction. We observed four NOx species (bidentate nitrates, gaseous NO2, linear nitrites, and monodentate nitrites) on the surface of Mn/TiO2 and Co–Mn/TiO2 catalysts that all participated in the...
283 citations
TL;DR: In this paper, 1H-pyrrole-2,5-dione derivatives were synthesized and their inhibitive action against the corrosion of carbon steel in 1 M HCl solution were investigated at 308 K by weight loss, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS) methods.
271 citations
TL;DR: None of the selected functionals hence provides a universally accurate treatment of chemisorption energies, and both the incorporation of van der Waals dispersive forces and the choice of the exchange functional have a key influence on the chem isorption energy.
Abstract: Molecular chemisorption at a metal surface is a key step for many processes, such as catalysis, electrochemistry, surface treatment, tribology and friction. Modeling with density functional theory is largely used on these systems. From a detailed comparison with accurate micro-calorimetric data on ten systems (involving ethylene, cyclohexene, benzene, naphthalene, CO, O2, H2, methane, ethane), we study the accuracy, for chemisorption on Pt(111), of five exchange–correlation functionals including one generalized gradient approximation functional (PBE) and four functionals that take into account van der Waals interactions (optPBE-vdW, optB86b-vdW, BEEF-vdW, PBE-dDsC). If the functionals used provide very similar geometries and electronic structures, as shown by projected density of states, they give strikingly different results for the adsorption energy of molecules on Pt(111). Among the set of chemisorption data, the lowest mean absolute deviations (MAD) are obtained with the optPBE-vdW and PBE-dDsC functionals (∼0.2 eV) while PBE and optB86b-vdW give twice larger MAD (∼0.45 eV). BEEF-vdW is intermediate with a MAD of 0.33 eV. For laterally π-bound unsaturated hydrocarbons (cyclohexene, benzene, naphthalene) the PBE and the BEEF-vdW functionals are severally under-bound, while optPBE-vdW and PBE-dDsC provide a good match with experiments. Hence both the incorporation of van der Waals dispersive forces and the choice of the exchange functional have a key influence on the chemisorption energy. Vertically bound ethylidyne and CO are in contrast over-bound with all functionals, the best agreement being obtained with BEEF-vdW. None of the selected functionals hence provides a universally accurate treatment of chemisorption energies.
198 citations
TL;DR: In this article, the first principles adsorption phenomena of nitrogen dioxide (NO 2 ) and nitrous oxide (N 2 O) molecules on the surface of pristine graphene and Al-doped graphene using density functional theory (DFT) calculations were studied.
181 citations
TL;DR: In this article, the adsorption behavior of Congo red (CR) from aqueous solution onto the as-prepared polyhedral cuprous oxide nanoparticles (Cu2O NPs) was systematically investigated.
176 citations
TL;DR: In this paper, the authors demonstrate very high adsorption capacity (qe = 72.2 mg g−1) of NH3-GO for uranyl ions in the presence of the above interfering species.
Abstract: Graphene oxide has recently emerged as an efficient adsorbent for removal of heavy metals including radionuclides from contaminated ground water. Here we demonstrate very high adsorption capacity (qe = 72.2 mg g−1) of graphene oxide for adsorption of uranyl ions. However, in the presence of common interfering cations (Ca2+, Mg2+, K+, Na+, Pb2+, Fe2+ and Zn2+) and anions (CO32−, HCO3−, Cl− and SO42−) that are expected in ground water, the adsorption capacity of uranyl ions on graphene oxide decreased drastically owing to poor selectivity. Here we also report a strategy for significantly improving selective adsorption of uranyl ions in the presence of the above interfering species. The graphene oxide is modified by liquid ammonia in the presence of a dehydrating agent (the material obtained is referred to as NH3-GO adsorbent) and thoroughly characterized by zeta potential measurement, Raman spectroscopy, Fourier transformed infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. The suitability of NH3-GO as an adsorbent of uranyl ions has been studied in batch mode as a function of pH, temperature, adsorbent dose and initial concentration of uranyl ions. The maximum experimental adsorption capacity at equilibrium conditions is found to be 40.1 mg g−1 at pH 6 at 298 K, which is not affected by the presence of most of the cations and anions. This marked improvement in the selectivity of uranyl ion adsorption is attributed to amidation of graphene oxide, rendering improved selectivity as compared to carboxylic acid groups. The maximum monolayer coverage (qmax) was deduced as 80.13 mg g−1, indicating it to be an excellent adsorbent. The mechanism of adsorption is studied in terms of adsorption isotherm models, kinetic models and thermodynamic studies, which indicated a dual mechanism of chemisorption and physisorption owing to more than one type of binding site in NH3-GO. It is concluded that the ammonia modified graphene oxide exhibited a highly selective adsorption property for uranyl ions at neutral pH.
128 citations
TL;DR: In this paper, the effect of flue gas temperature on mercury adsorption efficiency was explored in a fixed-bed reactor, where the bromine ion remains in the mesopore and the surface of activated carbon in the form of amorphous during modification process, leading to the reduction of mesopores volume and the increase of micropore volume.
124 citations
TL;DR: In this paper, the effects of prereduction temperature on catalyst dispersion and reducibility were examined. But the authors focused on the effect of temperature on catalytic activity and did not consider the impact of the temperature on phenol adsorption.
Abstract: Palladium supported on high-surface-area ceria effectively catalyzes the hydrogenation of phenol to cyclohexanone at atmospheric pressure and room temperature. Activation of H2 at Pd sites and phenol at surface ceria sites was investigated by probing the redox properties of the catalyst and studying the mechanism of phenol adsorption. Temperature-programmed reduction and pulsed chemisorption were used to examine the effects of prereduction temperature on catalyst dispersion and reducibility. A sharp effect of prereduction temperature on catalytic activity was observed. This dependence is rationalized as a result of interactions between palladium and ceria, which under reducing conditions enhance palladium dispersion and create different types of environments around the Pd active sites and of encapsulation of the catalyst caused by support sintering at high temperatures. Temperature-programmed diffuse reflectance infrared Fourier transform spectroscopy revealed that phenol undergoes dissociative adsorption...
TL;DR: In this article, the authors show that the concentrations of nitric acid do not significantly change the specific surface area and textural property of coconut shell activated carbon (AC), but the oxygenated groups which result in acidic properties, such as lactone, carboxyl and phenol groups, are formed on AC surface during the acid treatment process and increase with the increasing concentration of Nitric acid.
Abstract: Coconut shell activated carbon (AC) is treated by nitric acid and used as a support to prepare nano-copper heterogeneous catalysts for oxidative carbonylation of methanol to dimethyl carbonate. AC supports and their corresponding catalysts are characterized intensively by BET, XPS, XRD, TEM, N 2 O chemisorption, CO adsorption, and TPR. The results show that the concentrations of nitric acid do not significantly changes the specific surface area and textural property of AC. But the oxygenated groups which result in acidic properties, such as lactone, carboxyl and phenol groups, are formed on AC surface during the acid treatment process and increase with the increasing concentration of nitric acid. The increased surface oxygenated groups not only influence the dispersion but also the valence distributions of copper species. When copper supported on the AC treated by 4 M HNO 3 , the Cu/AC catalyst shows the optimal catalytic performance for oxidative carbonylation of methanol to dimethyl carbonate, which might be ascribed to the highest dispersion of Cu + and Cu 0 species. The average conversion of methanol and space-time yield of DMC (STY DMC ) within 10 h for the catalyst have reached 9.2% and 229 mg g −1 h −1 , respectively. The deactivation of Cu/AC catalysts is attributed to the agglomeration of copper species. Besides, the STY DMC of per S(Cu + + Cu 0 ) for the acid treated Cu/AC catalysts is very similar and less than that of the original Cu/AC catalyst which may be induced by the AC surface oxygenated groups itself but not the ratio of Cu + /Cu 0 .
TL;DR: In this paper, the authors used density functional electronic structure methods to design a catalyst for producing formic acid from CO2 and H2 via a two-step pathway having low reaction barriers.
Abstract: Efficient catalytic reduction of CO2 is critical for the large-scale utilization of this greenhouse gas. We have used density functional electronic structure methods to design a catalyst for producing formic acid from CO2 and H2 via a two-step pathway having low reaction barriers. The catalyst consists of a microporous metal organic framework that is functionalized with Lewis pair moieties. These functional groups are capable of chemically binding CO2 and heterolytically dissociating H2. Our calculations indicate that the porous framework remains stable after functionalization and chemisorption of CO2 and H2. We have identified a low barrier pathway for simultaneous addition of hydridic and protic hydrogens to carbon and oxygen of CO2, respectively, producing a physisorbed HCOOH product in the pore. We find that activating H2 by dissociative adsorption leads to a much lower energy pathway for hydrogenating CO2 than reacting H2 with chemisorbed CO2. Our calculations provide design strategies for efficient ...
TL;DR: In this article, a facile and green method was employed to synthesize the tannic acid functionalized graphene nanocomposite (TA-G), which could alter graphene surface physicochemical properties to improve the adsorption efficiency.
TL;DR: In this paper, a series of CuO-ZnO−ZrO2 catalysts were synthesized by a surfactant-assisted co-precipitation method and tested for the synthesis of methanol from CO2 hydrogenation.
TL;DR: In this article, a highly efficient and robust Cu/SiO2 catalyst from a pure-phase copper phyllosilicate precursor was successfully fabricated by the ammonia evaporation hydrothermal (AEH) method.
TL;DR: A mesoporous silica-grafted graphene oxide (GO-SBA-15) was synthesized by covalently binding graphene oxide to SBA and the features of the material were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infra-red (FT-IR) spectroscopy as discussed by the authors.
TL;DR: In this article, two preparation methods, controlled adsorption and dry impregnation, are implemented to explore the effect of preparation method on the formation of active sites on alumina supported nickel catalysts.
Abstract: Nickel catalysts prepared by a variety of different methods are commonly used for reforming reactions such as methane dry reforming. Two preparation methods, controlled adsorption and dry impregnation, are implemented to explore the effect of preparation method on the formation of active sites on alumina supported nickel catalysts. By varying only the preparation method, comparison of catalysts that differ primarily in metal–support interactions, strong metal–support interaction (controlled adsorption) and weak metal–support interactions (dry impregnation), are obtained. For controlled adsorption, optimal synthesis conditions are identified using point of zero charge measurements, pH-precipitation experiments, and adsorption isotherms. Using these conditions, a catalyst with a higher dispersion and strong metal–support interactions is prepared. Physicochemical characterization by N2 physisorption, H2 chemisorption, temperature programmed reduction (TPR), transmission electron microscopy (TEM), and environmental TEM (ETEM) shows that the types of nickel sites formed strongly depend on the synthesis method. Methane dry reforming reactivity studies show stable catalytic performance for at least 9 h and provide additional insight into the types of active centers present. After reductive pretreatment, the nickel catalyst prepared by dry impregnation is found to primarily have nickel present as a surface NiAl2O4. In contrast, the active centers for the nickel catalyst prepared by controlled adsorption consist of nickel particles that are encapsulated by a nickel aluminate layer with 1–2 nm in thickness. Combustion analysis and XPS of spent catalysts reveal different amounts and nature of carbonaceous deposits as a function of the synthesis method.
TL;DR: In this article, the surface entropy of Fh is estimated by analyzing the surface enthalpy, entropy, and Gibbs free energy of the principal interfaces of H2O, i.e. ice-water-gas, and it is shown that the surface Gibbs free energies of metal (hydr) oxides increase with the mean metal coordination number of oxygen in the lattices.
TL;DR: In this paper, the structure, adsorption energy, charge transfer and the electronic states of CO, CO 2, H 2 O molecules on the surface of pristine and Al-doped graphene sheets using density functional theory calculations.
TL;DR: In this paper, the effect of temperature on the adsorption process was assessed through thermodynamic and statistical methods, and it was revealed that the reaction is endothermic and spontaneous.
Abstract: The conventional method for the estimation of ΔG0 through the van't Hoff equation was critically analysed. The development of an analytical framework for the determination of the thermodynamic parameters for the adsorption process had been attempted in this work. A calcined Ca–Al–(NO3) layered double hydroxide was employed for the adsorptive removal of fluoride. The effect of the temperature on the adsorption process was assessed through thermodynamic and statistical methods. The adsorption equilibrium was described by Freundlich and linear isotherms. The isotherm constants were used in the van't Hoff equation by the proposed method. The thermodynamic assessment revealed that the adsorption reaction is endothermic and spontaneous. Furthermore, the ΔH0, Ea, Ead, and ΔHx values confirmed that the adsorption process is in between physisorption and chemisorption in nature. The interactive effect of the temperature with other important process parameters, i.e., pH, initial fluoride concentration and adsorbent dose, was evaluated through response surface methodology. The solution pH had very little effect on the adsorption. On the contrary, the adsorbent dose and initial concentration influenced the adsorption process significantly. The interactive effect of temperature was prominent at a lower adsorbent dose and a higher initial concentration. The highest adsorption capacity, obtained in the RSM study, was 59.60 mg g−1. However, the highest Kf value from Freundlich isotherm was 8.48 (mg g−1) (L mg−1)1/n at 50 °C.
TL;DR: In this article, the applicability of the d-band center theory to nonuniform catalytic systems, such as core-shell nanoparticles, was evaluated for formic acid oxidation.
Abstract: Theoretical DFT calculations suggest that chemisorption energy, activation barrier, and energy of dissociation of small molecules on metal surface can be correlated to the d-band center of gravity of that metal. This holds true for many systems and reactions, but there are also reports where significant discrepancies were found. Here we present the critical assessment of applicability of the d-band center theory to nonuniform catalytic systems, such as core–shell nanoparticles. For Pt-core–Pd-shell nanoparticles we found a significant enhancement of catalytic activity toward formic acid oxidation, which was assigned to observed changes of density of states close to the Fermi level, in general in agreement with d-band center theory. However, at the same time the changes in d-band center for Pt-core–Pd-shell nanoparticles were contrary to those predicted by theory due to incorporation of Pt valence electrons to the overall band structure, which shifted the d-band center in the direction opposite to that pre...
TL;DR: It is proposed that the acid-base adsorption mode involving the Ni(2+) cation is responsible for the sulfite species on the NMC surface, and the surface reactivity was clearly decreasing after Al2O3 coating.
Abstract: The role of the transition metal nature and Al2O3 coating on the surface reactivity of LiCoO2 and LiNi1/3Mn1/3Co1/3O2 (NMC) materials were studied by coupling chemisorption of gaseous probes molecules and X-ray photoelectron (XPS) spectroscopy. The XPS analyses have put in evidence the low reactivity of the LiMO2 materials toward basic gaseous probe (NH3). The reactivity toward SO2 gaseous probe is much larger (roughly more than 10 times) and strongly influenced by the nature of metal. Only one adsorption mode (redox process producing adsorbed sulfate species) was observed at the LiCoO2 surface, while NMC materials exhibit sulfate and sulfite species at the surface. On the basis of XPS analysis of bare materials and previous theoretical work, we propose that the acidbase adsorption mode involving the Ni2+ cation is responsible for the sulfite species on the NMC surface. After Al2O3 coating, the surface reactivity was clearly decreasing for both LiCoO2 and NMC materials. In addition, for LiCoO2, the coating modifies the surface reactivity with the identification of both sulfate and sulfite species. This result is in line with a change in the adsorption mode from redox toward acidbase after Al/Co substitution. In the case of NMC materials, the coating induced a decrease of the sulfite species content at the surface. This phenomenon can be related to the cation mixing effect in the NMC.
TL;DR: In this article, the effects of the weight ratios of Gel to MCM-41, amine loadings, adsorption temperatures, and CO 2 partial pressures at different temperatures were investigated in a self-assembled fixed bed reactor.
TL;DR: Thermodynamic analysis showed that mercury adsorption by the biochars was exothermic process and apparent adsorptive energy was 43.3 kJ/mol in the range of chemisorption.
TL;DR: In this paper, the performance impact and poisoning mechanism of arsenic on commercial V2O5-WO3/TiO2 SCR catalysts were studied and the results showed that As2O3 would be adsorbed on the catalyst surface and most oxidized by surface chemisorption oxygen.
TL;DR: In this paper, the effects of pH, contact time, sorbent dosage, metal concentration, and temperature on the adsorption energy (8.2 kJ/mol) calculated from the Dubinin-Radushkevich model indicated that the sorption process occurred via chemisorption.
Abstract: The prepared chitosan-coated diatomite (CCD) was characterized using Fourier transform infrared spectroscopy and SEM techniques. The effects of pH, contact time, sorbent dosage, metal concentration, and temperature on the adsorption (%) of mercury (Hg(II)) from aqueous solution using the CCD sorbent were studied systemically. The monolayer sorption capacities of raw diatomite and CCD sorbents at pH 5 were found to be 68.1 and 116.2 mg/g, respectively. The mean adsorption energy (8.2 kJ/mol) calculated from the Dubinin–Radushkevich (D–R) model indicated that the sorption process occurred via chemisorption. The modified sorbent had good adsorption and desorption performance with respect to reusability after 10 repeated cycles. The thermodynamic calculations revealed that the sorption was viable, spontaneous, and exothermic in nature under the conditions studied. The kinetic calculations indicated that the sorption mechanism was well-explained by a pseudo-second-order model. All results demonstrated that the...
TL;DR: In this paper, the adsorption of Pb(II) ions onto a biopolymer based composite, chitosan blended polyacrylonitrile (chitosans/PAN), has been studied in a batch mode operation.
TL;DR: In this article, triazolyl-acyl-hydrazone derivatives as inhibitors were developed to inhibit corrosion of copper in chloride solutions, and electrochemical techniques, morphological characterization and measurements of contact angle, electrochemical quartz crystal microbalance and Fourier transform infrared spectroscopy were combined to investigate the inhibition mechanism and performance.
TL;DR: In this article, the newly discovered B 40 fullerene is a suitable candidate for capture, storage and separation of CO 2, which is validated by the high adsorption energy, large charge transfer, and kinetic feasibility for B 40 (CO 2 ) complexes.