Showing papers on "Chemisorption published in 2016"

Oxide Defect Engineering Enables to Couple Solar Energy into Oxygen Activation

Abstract: Modern development of chemical manufacturing requires a substantial reduction in energy consumption and catalyst cost. Sunlight-driven chemical transformation by metal oxides holds great promise for this goal; however, it remains a grand challenge to efficiently couple solar energy into many catalytic reactions. Here we report that defect engineering on oxide catalyst can serve as a versatile approach to bridge light harvesting with surface reactions by ensuring species chemisorption. The chemisorption not only spatially enables the transfer of photoexcited electrons to reaction species, but also alters the form of active species to lower the photon energy requirement for reactions. In a proof of concept, oxygen molecules are activated into superoxide radicals on defect-rich tungsten oxide through visible-near-infrared illumination to trigger organic aerobic couplings of amines to corresponding imines. The excellent efficiency and durability for such a highly important process in chemical transformation can otherwise be virtually impossible to attain by counterpart materials.

β-Cyclodextrin modified graphitic carbon nitride for the removal of pollutants from aqueous solution: experimental and theoretical calculation study

Abstract: A novel β-cyclodextrin modified, multifunctional, layer-by-layer graphitic carbon nitride (g-C3N4/β-CD) was successfully synthesized and applied as an effective adsorbent for the removal of methyl orange (MO) and Pb(II) from aqueous solutions under various environmental conditions (e.g., solution pH, solid content, contact time and temperature). The kinetic results indicated that the adsorption was dominated by chemisorption, and the higher adsorption capacity of g-C3N4/β-CD was attributed to it having more oxygen-containing functional groups than g-C3N4. The Langmuir, Freundlich and Sips models were applied to simulate the adsorption isotherms of MO and Pb(II), and the results demonstrated that the adsorption of MO was attributed to multilayer adsorption, while the coverage adsorption of Pb(II) on the g-C3N4/β-CD was monolayer adsorption. The thermodynamic parameters showed that the adsorption of both MO and Pb(II) was spontaneous and endothermic. The DFT calculations further evidenced the surface complexation and electrostatic interaction of Pb(II) on the g-C3N4 and g-C3N4/β-CD, whereas, the interaction of MO with g-C3N4 and g-C3N4/β-CD was mainly attributed to hydrogen bonds and strong π–π interactions. The results demonstrated that g-C3N4/β-CD is a promising material for the efficient removal of organic and inorganic pollutants in environmental pollution remediation.

Degradation of benzotriazole by a novel Fenton-like reaction with mesoporous Cu/MnO2: Combination of adsorption and catalysis oxidation

Abstract: Degradation of benzotriazole (BZA) as an emerging contaminant by a novel Fenton-like reaction was investigated using a catalyst prepared by incorporating Cu into mesoporous MnO2 (mesoporous Cu/MnO2, MCM). Catalysts were synthesized with different Cu contents, and were characterized by N2 adsorption–desorption, X-ray photoelectron spectroscopy, ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, and temperature-programmed reduction (TPR)-H2. The MCM functioned via surface chemisorption and redox reaction that was confirmed by intermediates identification, XPS and TPR analysis, followed by a Fenton-like oxidation derived by surface Cu+ and Mn3+, to provide high degradation efficiency for BZA in solution. Fourier transform infrared (FT-IR) spectroscopy result also verified the surface adsorption and Fenton-like reaction. MCM exhibited much higher adsorption and catalytic activity in the Fenton reaction than pure MnO2 or CuO. The effect of Cu content in MCM, catalyst dose, H2O2 dose, and solution pH were investigated. BZA degradation was high in deionized water (removal efficiency = 89%) and moderate in wastewater treatment plant effluent (removal efficiency = 56%) after 60-min reaction at an initial pH of 7.13, which could be developed by adjusting the dose of catalyst or H2O2. A possible mechanism for the reaction is proposed. This involves surface adsorption with copper and a redox reaction with Mn3+, followed by a copper–manganese cycle-derived Fenton-like reaction.

How Pt Interacts with CeO2 under the Reducing and Oxidizing Environments at Elevated Temperature: The Origin of Improved Thermal Stability of Pt/CeO2 Compared to CeO2

Abstract: The interaction between Pt and CeO2 under reducing and oxidizing conditions as well as its effect on the thermal stability of Pt/CeO2 were extensively investigated by means of N2 adsorption/desorption, Raman spectroscopy, CO chemisorption, H2 TPR, XRD, and XPS techniques In situ and ex situ Raman spectroscopy showed that Pt is anchored with the surface oxygen of CeO2 by forming Pt–O–Ce bond during the oxidative treatment of Pt/CeO2 Under the reducing condition, the static CO chemisorption presented that the amount of CO adsorbed on CeO2 is almost equal to that on Pt/CeO2, implying that Pt atom is located on the oxygen vacancy generated on reduced CeO2 surface Strong Pt–O–Ce bond maintained the textural properties of Pt/CeO2 from oxidative treatment at temperature as high as 800 °C, as evidenced by the XRD patterns and BJH curves of the samples Selective removal of the surface oxygen of Pt/CeO2 resulted in the decreased thermal stability of Pt/CeO2 due to the loss of Pt–O–Ce bond Stronger interaction

Role of Hydroxyl Groups in the Preferential Oxidation of CO over Copper Oxide–Cerium Oxide Catalysts

Abstract: Model CuO/Ce0.8X0.2Oδ catalysts (with X = Ce, Zr, La, Pr, or Nd) have been prepared in order to obtain CuO/ceria materials with different chemical features and have been characterized by X-ray diffraction, Raman spectroscopy, N2 adsorption, and H2 temperature-programmed reduction. CO-PROX experiments have been performed in a fixed-bed reactor and in an operando DRIFTS cell coupled to a mass spectrometer. The CO oxidation rate over CuO/ceria catalysts correlates with the formation of the Cu+–CO carbonyl above a critical temperature (90 °C for the experimental conditions in this study) because copper–carbonyl formation is the rate-limiting step. Above this temperature, CO oxidation capacity depends on the redox properties of the catalyst. However, decomposition of adsorbed intermediates is the slowest step below this threshold temperature. The hydroxyl groups on the catalyst surface play a key role in determining the nature of the carbon-based intermediates formed upon CO chemisorption and oxidation. Hydrox...

2,4-Diamino-5-(phenylthio)-5H-chromeno [2,3-b] pyridine-3-carbonitriles as green and effective corrosion inhibitors: gravimetric, electrochemical, surface morphology and theoretical studies

Abstract: The inhibition of mild steel corrosion in 1 M HCl by three newly synthesized 2,4-diamino-5-(phenylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitriles (DHPCs) namely, 2,4-diamino-7-nitro-5-(phenylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitrile (DHPC-1), 2,4-diamino-5-(phenylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitrile (DHPC-2) and 2,4-diamino-7-hydroxy-5-(phenylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitrile (DHPC-3) was studied using weight loss method, electrochemical techniques, surface morphology (SEM, AFM) studies and theoretical (quantum chemical calculations and molecular dynamic simulation) methods. The weight loss and electrochemical measurements showed that the inhibition efficiency increases with increasing inhibitor concentration and the relative trend of inhibition performance is DHPC-3 > DHPC-2 > DHPC-1. A potentiodynamic polarization study reveals that the investigated DHPCs act as mixed type inhibitors. The adsorption of the DHPCs on the mild steel surface obeys the Langmuir adsorption isotherm and involves both physisorption and chemisorption modes. The presence of the electron releasing –OH group at position seven on the chromenopyridine ring is considered to be responsible for the highest inhibition efficiency of DHPC-3 among the studied compounds. Whereas the presence of the electron withdrawing nitro (–NO2) group at position seven on the chromenopyridine ring is responsible for the lowest inhibitive strength of DHPC-1. Quantum chemical calculations and molecular dynamic simulation studies were undertaken to provide mechanistic insight into the roles of the different substituents (–OH and –NO2) on the corrosion inhibition behavior of the studied inhibitors.

Synthesis of highly coke resistant Ni nanoparticles supported MgO/ZnO catalyst for reforming of methane with carbon dioxide

Abstract: Ni-nanoparticles supported on MgO promoted nanocrytalline zinc oxide catalyst was prepared by hydrothermal method in presence of cationic surfactant cetyltrimethylammonium bromide. The catalyst showed very good activity for the reforming of methane with carbon dioxide to produce synthesis gas, where H 2 /CO ratio was almost 1 and the catalyst showed no deactivation for more than 100 h. The prepared catalyst was characterized using the analytical techniques like N 2 -physisorption studies, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Temperature programmed desorption (TPD), Temperature programmed reduction (TPR), Temperature programmed oxidation (TPO), H 2 -chemisorpton, Thermo-gravimetric analysis (TGA), Inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), and Extended X-ray absorption fine structure (EXAFS). Transmission electron microscopy and H 2 -chemisorption analysis indicated that highly dispersed Ni nanoparticles with average size 5.7 nm, present on ZnO when MgO was added with the catalyst. The strong Ni–ZnO interaction was evidenced from TPR and EXAFS analysis. The presence of highly dispersed Ni nanoparticles and strong metal support interaction enhanced the reduction behaviour of the Ni-MgO/ZnO catalyst. The presence of MgO increased the adsorption behaviour of CO 2 , enhanced the dissociation of CO 2 and accelerated the carbon elimination.

Probing Surface Structures of CeO2, TiO2, and Cu2O Nanocrystals with CO and CO2 Chemisorption

Abstract: CO and CO2 chemisorption on uniform CeO2, TiO2, and Cu2O nanocrystals with various morphologies were comprehensively studied with in-situ diffuse reflectance infrared Fourier transform spectroscopy. The formed adsorbates were observed to be morphology dependent. CO or CO2 chemisorbed at the metal cation sites, and bidentate and bridged carbonates involving the O sites are sensitive to the surface composition and the local coordination environments of surface metal cations and O anions and can be correlated well with the surface structures of facets exposed on oxide nanocrystals. Carbonate and carbonite species formed by CO chemisorption can probe the different facets of CeO2. Carbonate species formed by CO chemisorption can probe the different facets of TiO2. Adsorbed CO and carbonate species formed by CO chemisorption can probe the different facets of Cu2O, and adsorbed CO2 formed by CO2 chemisorption can also probe the different facets of Cu2O. These results demonstrate chemisorption of probing molecule...

Adsorption and corrosion inhibition properties of N-{n-[1-R-5-(quinoxalin-6-yl)-4,5-dihydropyrazol-3-yl]phenyl}methanesulfonamides on mild steel in 1 M HCl: experimental and theoretical studies

Abstract: Six quinoxalinyl-dihydropyrazolyl-phenyl-methanesulfonamides were investigated for their adsorption characteristics and inhibition of mild steel corrosion in 1 M HCl medium. Tafel polarization measurements revealed that all the studied compounds are mixed-type inhibitors. Electrochemical impedance spectroscopy showed that the compounds form a pseudo-capacitive protective film on mild steel surface and protect the steel from direct acid attack. The inhibitors adsorb on mild steel in 1 M HCl via competitive physisorption and chemisorption mechanisms and their adsorption obeyed the Langmuir adsorption isotherm model. UV-vis spectra confirmed that the inhibitors interact with mild steel in solution to form Fe-inhibitor complexes. Scanning electron microscope (SEM) images also confirmed the protective efficacy of the studied compounds on mild steel in the acid. Quantum chemical calculations and quantitative structure activity relationship (QSAR) studies proposed good correlations between molecular quantum chemical descriptors and experimental inhibition efficiencies. Descriptors for protonated species correlate better than those of neutral species. Adsorption of the studied molecules was simulated on Fe(110) surface and the binding energies derived from molecular dynamics simulations corroborate experimental results. Compounds in which the sulfonamido group is attached to position 3 on the phenyl ring showed higher corrosion inhibition activities.

Role of the Cu-ZrO2 Interfacial Sites for Conversion of Ethanol to Ethyl Acetate and Synthesis of Methanol from CO2 and H2

Abstract: Well-defined Cu catalysts containing different amounts of zirconia were synthesized by controlled surface reactions (CSRs) and atomic layer deposition methods and studied for the selective conversion of ethanol to ethyl acetate and for methanol synthesis. Selective deposition of ZrO2 on undercoordinated Cu sites or near Cu nanoparticles via the CSR method was evidenced by UV–vis absorption spectroscopy, scanning transmission electron microscopy, and inductively coupled plasma absorption emission spectroscopy. The concentrations of Cu and Cu-ZrO2 interfacial sites were quantified using a combination of subambient CO Fourier transform infrared spectroscopy and reactive N2O chemisorption measurements. The oxidation states of the Cu and ZrO2 species for these catalysts were determined using X-ray absorption near edge structure measurements, showing that these species were present primarily as Cu0 and Zr4+, respectively. It was found that the formation of Cu-ZrO2 interfacial sites increased the turnover freque...

Quinoxaline derivatives as corrosion inhibitors for mild steel in hydrochloric acid medium: Electrochemical and quantum chemical studies

Abstract: The corrosion inhibition potential of four quinoxaline derivatives namely, 1-[3-(4-methylphenyl)-5-(quinoxalin-6-yl)-4,5-dihydropyrazol-1-yl]butan-1-one (Me-4-PQPB), 1-(3-(4-methoxyphenyl)-5-(quinoxalin-6-yl)-4,5-dihydropyrazol-1-yl)butan-1-one (Mt-4-PQPB), 1-[3-(3-methoxyphenyl)-5-(quinoxalin-6-yl)-4,5-dihydropyrazol-1-yl]butan-1-one (Mt-3-PQPB) and 1-[3-(2H-1,3-benzodioxol-5-yl)-5-(quinoxalin-6-yl)-4,5-dihydropyrazol-1-yl]butan-1-one (Oxo-1,3-PQPB) was studied for mild steel corrosion in 1 M HCl solution using electrochemical, spectroscopic techniques and quantum chemical calculations. The results of both potentiodynamic polarization and electrochemical impedance spectroscopic studies revealed that the compounds are mixed-type inhibitors and the order of corrosion inhibition efficiency at 100 ppm is Me-4-PQPB>Mt-3-PQPB>Oxo-1,3-PQPB>Mt-4-PQPB. Fourier transform infrared (FTIR) and ultraviolet–visible (UV–vis) spectroscopic analyses confirmed the presence of chemical interactions between the inhibitors and mild steel surface. The adsorption of the inhibitor molecules on mild steel surface was found to be both physisorption and chemisorption but predominantly chemisorption. The experimental data obey Langmuir adsorption isotherm. Scanning electron microscopy studies revealed the formation of protective films of the inhibitors on mild steel surface. Quantum chemical parameters obtained from density functional theory (DFT) calculations support experimental results.

Studies on CO2 Adsorption and Desorption Properties from Various Types of Iron Oxides (FeO, Fe2O3, and Fe3O4)

Abstract: Various type iron oxides of FeO, Fe2O3, and Fe3O4 were used for carbon dioxide (CO2) capture at room temperature and pressure by studying its adsorption–desorption properties. Several interactions of carbonate species were detected on its surface. The morphology of carbonate formation shows different structures on FeO (grooves-like), Fe2O3 (fine sharp particles), and Fe3O4 (aggregated nanoparticles). CO2 chemisorption discovered a potential adsorbent of Fe2O3 with an adsorption capacity of 3.95 mgCO2/gadsorbent. The adsorption capacity increased up to 62.8% by using concentrated 99.9% CO2 for adsorption. At higher concentration of CO2 exposure, it partially turns to red color which indicated the less stable Fe3O4 was easily oxidized to Fe2O3 after CO2 regeneration with temperatures up to 500 °C. Hence, Fe2O3 possessed the highest basicity strength (1.26 cm3/g), and the adsorption capacity after four cycles was not significantly reduced by 8.6% indicating an effective chemical or physical adsorption in CO2...

Interaction of Adatoms and Molecules with Single-Layer Arsenene Phases

Abstract: Recent studies have shown that arsenic can form single-layer phases in buckled honeycomb as well as symmetric washboard structures, named as arsenene. These structures are stable even in freestanding form and are nonmagnetic semiconductors in the energy range which is suitable for various electronic applications. In this study we investigated the adsorption of selected adatoms (H, Li, B, C, N, O, Al, Si, P, Cl, Ti, Ga, Ge, As, Se, and Sb) and physisorption of molecules (H2, O2, and H2O) to these two arsene phases. Since the interaction of these adspecies with arsenene are studied using large supercells, the coupling between adspecies is minimized, and hence our results can be interpreted to mimic the effects of isolated adatom or physisorbed molecule. It is found that the adatoms form strong chemisorption bonds and hence modify the atomic structure and physical properties locally. Some of the adatoms give rise to significant local reconstruction of the atomic structure. Electronic states of some adatoms b...