Effect Of Surface Species Research Articles

Effect of surface species on the alcohol-acid adsorption from FTS wastewater on graphene: A structure-capacity study

Fischer-Tropsch synthesis (FTS) wastewater retaining low-carbon alcohols and acids are organic pollutants as a limiting factor for FTS industrialization. In this work, the structure-capacity relationships between alcohol-acid adsorption and surface species on graphene were reported, shedding light into their intricate interactions. The graphene oxide (GO) and reduced graphene oxide (rGO) were synthesized via improved Hummers method with flake graphite (G). The physicochemical properties of samples were characterized via SEM, XRD, XPS, FT-IR, and Raman. The alcohol-acid adsorption behaviors and adsorption quantities on G, GO, and rGO were measured via theoretical and experimental method. It was revealed that the presence of COOH, C=O and CO species on graphene occupy the adsorption sites and increase the interactions of water with graphene, which are unfavorable for alcohol-acid adsorption. The equilibrium adsorption quantities of alcohols and acids grow in pace with carbon number. The monolayer adsorption occurs on graphene was verified via model fitting. rGO has the highest FTS modeling wastewater adsorption quantity (110 mg/g) due to the reduction of oxygen species. These novel findings provide a foundation for the alcohol-acid wastewater treatment, as well as the design and development of high-performance carbon-based adsorbent materials.

Probing the effects of plasma-induced surface species in ring-opening process of toluene decomposition via plasma-excited TPD and in situ DRIFTS

Aromatic ring-opening process is considered as the rate-determining step for catalytic toluene decomposition. However, the ring-opening pathway has not been fully revealed, especially the effect of the surface species in plasma catalytic hybrid system. Herein, a series of Mn based catalysts (with the low Mn content of 1 wt %), Mn/γ-Al2O3, Au-Mn/γ-Al2O3 and Ag-Mn/γ-Al2O3, were used to clarify the mechanism of plasma catalytic toluene degradation by a closely combined temperature-programmed desorption (TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Effects of plasma on surface oxygen species were investigated by a comparison study of O2-TPD and plasma-excited O2-TPD. A strong interaction between plasma and Ag-Mn/γ-Al2O3 could make better use of plasma-induced active oxygen species (i.e. O3, O*, O2* etc.) and considerably increase the amount of chemically adsorbed oxygen. Moreover, modified NH3-TPD experiments proved that O2 excited by plasma would greatly change the surface acidity of Ag-Mn/γ-Al2O3, resulting in the desorption activation energy (Ed) of toluene increasing to 19.5 kJ/mol. Finally, possible ring-opening mechanisms over different catalysts were proposed after the evolution of typical intermediates being systematically analyzed by in situ DRIFTS. It was found that the toluene ring-opening reaction on different catalysts might be selectively started at hydroquinone. The present work could provide both a more detailed toluene ring-opening process and new insights into the understanding of the plasma exciting effect on the surface species in VOCs decomposition.

Effects of surface species and homogeneous reactions on rates and selectivity in ethane oxidation on oxide catalysts

AbstractSelective alkane oxidations on metal oxide catalysts involve complex mechanisms with multiple reactions in series and parallel, different types of reduced and oxidized surface species, and potential contributions from gas‐phase reactions. Here, kinetics and thermodynamics of elementary steps involved in C2H6‐O2 reactions on SiO2‐supported small vanadium oxide domains are determined using density functional theory. These surface reactions together with gas‐phase mechanisms are incorporated in kinetic simulations to determine how surface and gaseous reactions interact and contribute to rates and selectivity. The results show that gas‐phase reactions within pore volumes in contact with the catalyst contribute significantly to C2H6 activation rates, even at conditions where gas‐phase reactions in empty volumes without catalyst are negligible. The majority of C2H6 activations occur on the surface, via H abstraction by vanadium oxo species present at terminal lattice oxygens. The gas‐phase activations via H‐abstraction by OH radicals also exhibit significant contributions. The reduced centers formed by reactions at vanadium oxo species are re‐oxidized rapidly and, therefore, are present in very small concentrations at reaction conditions. The re‐oxidation steps lead to the formation of HO2 radicals and surface peroxo species that are also rapidly consumed and are present in small concentrations. The peroxo species preferentially convert C2H4 to its epoxide product and influence selectivity even at low concentrations. The gas‐phase reactions decrease the concentrations of peroxo species and improve selectivity slightly. The effects of reaction conditions and catalyst site density provide further insights into how factors beyond conversions at lattice oxygens influence rates and selectivity in alkane oxidation reactions of significant industrial importance.

Effect of surface species and structure on the performance of CeO2 and SO42− doped MCM-41 catalyst toward NH3-SCR

The different structure and surface species on the SCR activity of CeO2 and SO42− doped MCM-41 catalysts toward NO reduction by NH3 were investigated. The sulfated species generated over Cat-A and Cat-B except for Cat-C.

Effective Enhancement of TiO2 Photocatalysis by Synergistic Interaction of Surface Species: From Promoters to Co-catalysts

The enhancement of TiO2-based catalyst activity by effect of surface species is analyzed in the photoelimination of toluene in a complex, ternary system having ceria and Mn-modified carbon nitride in contact with a major anatase phase. With a combination of kinetic and spectroscopic tools applied to the ternary system and corresponding binary/single references, this study delineated a method to quantitatively analyze the quantum yield or reaction rate through a strict measurement of the effect of each component of the ternary system in the generation of the active OH-related radical species of the reaction and the subsequent influence in photocatalytic observables. Using this procedure, the study allows elucidating the role and significance of the surface species in the reaction and, in particular, the important and unique role of a cationic Mn species in modifying the behavior of the carbon-containing species, a fact exclusively occurring in the ternary system and not in the corresponding parent binary/single ones. The method unveils a transformation of such surface species role from that of a promoter to that of a co-catalyst through the synergistic/cooperative interaction of all present phases at the catalyst and establishes a general scheme to measure and interpret the interaction of components in multicomponent photocatalysts.

Effect of surface species on Cu-TiO 2 photocatalytic activity

The Cu-TiO 2 nanoparticles with different Cu dopant content were prepared by sol–gel method. The structure of the as-prepared catalysts and the surface species of Cu-TiO 2 were determined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflection spectroscopy (DRS). The relationship between the photocatalytic activity and the surface species of Cu-TiO 2 was revealed via the measurement of surface photovoltage spectroscopy (SPS) as well as the degradation of the rhodamine B (RhB). The experimental results suggest that the Cu-TiO 2 photocatalysts with appropriate content of Cu (about 0.06 mol%) possess abundant electronic trap, which effectively inhibits the recombination of photoinduced charge carriers, improving the photocatalytic activity of TiO 2. While at high Cu dopant region (>0.06 mol%), the excessive oxygen vacancies and Cu species can become the recombination centers of photoinduced electrons and holes. Meanwhile, at heavy Cu doping concentration, excessive P-type Cu 2O can cover the surface of TiO 2, which leads to decrease in the photocatalytic activity of photocatalyst. The photocatalytic experimental results are in good agreement with the conclusions of SPS measurements, indicating that there is a close relationship between the photocatalytic activity and the intensity of SPS spectra.

The effect of surface species on the rate of H sorption into nanostructured Pd

Studies of the hydrogen region of nanostructured H1-e Pd films in 1 M sulfuric acid in the presence of crystal violet, or when small amounts of Pt are deposited on to the surface, show that the adsorption of hydrogen onto the metal surface is suppressed but that at the same time the kinetics of absorption of hydrogen into the Pd to form the β-hydride are significantly enhanced suggesting that the strongly adsorbed hydrogen on the Pd surface acts as a blocking layer for absorption of hydrogen into the Pd lattice.

Atomic Layer Deposition of SiO2 and TiO2 in Alumina Tubular Membranes: Pore Reduction and Effect of Surface Species on Gas Transport

The pore diameters in alumina tubular membranes were progressively reduced via SiO2 and TiO2 atomic layer deposition (ALD) using sequential surface reactions. The SiO2 ALD was accomplished using alternating exposures of SiCl4 and H2O. The TiO2 ALD was achieved using alternating exposures of TiCl4 and H2O. The reduction of the pore diameter was observed using in situ N2 conductance measurements. The total conductance, Ct = Q/ΔPt, was measured using a mass flow controller to define a constant gas throughput, Q, and two capacitance manometers to monitor the total pressure drop, ΔPt. These N2 conductance measurements revealed that the SiO2 and TiO2 ALD progressively reduced the pore diameter from an initial diameter of 50 A to molecular diameters. Using an aperture model for the conductance, the pore diameter was found to decrease at a rate of 1.3 ± 0.1 A per SiCl4/H2O AB cycle during SiO2 deposition and 3.1 ± 0.9 A per TiCl4/H2O AB cycle during TiO2 deposition. The N2 conductance measurements were also very ...

Role of N-Containing Surface Species on NO Reduction by Carbon

In order to understand the mechanism of C−NO reaction, the detailed material balance was established by analyzing all the gas species produced during the reaction with mass spectroscopy and gas chromatography. The amount of nitrogen-containing surface species was estimated in the temperature range between 600 and 950 °C and with NO concentration of, mainly, 540 ppm. Then the effect of surface species on the reaction rate was examined. The step response experiments were carried out by switching the feed gas from 14N16O to 15N18O. The results reveal not only the reaction mechanism but also the depletion rate of surface nitrogen species during the experiment. N2 formation rate was correlated with NO concentration and the amount of surface nitrogen species. It is concluded that N2 is mainly formed by the first-order reaction between C(N) and NO.

Effects of surface oxide species on the electropolymerization of o-aminophenol on pretreated glassy carbon electrodes

The effects of surface species (e.g. surface oxide species, etc.) on electropolymerization of o-aminophenol on pretreated glassy carbon electrodes are investigated. It is found that surface oxide species can affect the electropolymerization of conducting polymer and electron-transfer rate on the electrochemically pretreated electrode substrate. It is also shown that electropolymerization rate increases with pretreatment potential. However, it is found that nitro groups formed by a chemical method on the electrode surface have a negative effect on the electropolymerization of o-aminophenol. The possible mechanisms are also proposed and discussed.

The effect of surface species on the photoluminescence of porous silicon

The photoluminescence of porous Si immersed in alcohol exhibits a blue shift and a marked decrease in intensity relatively to dry, as-anodized wafers. However, when the immersed samples are treated with ultraviolet (UV) light for a few minutes, the photoluminescence (PL) peak shifts to longer wavelength. Fourier transform infrared spectroscopy reveals that alkoxy surface species and silicon hydride species backbonded to oxygen atoms appear on the UV-treated samples. Furthermore, the PL characteristics and surface species of the UV-treated samples can be recovered to those of as-anodized wafers by dipping in hydrofluoric acid. These results point out the importance of surface chemistry in the luminescence process of porous Si.

Effect of surface species on activity and selectivity of MoO3/SiO2 catalysts in partial oxidation of methane to formaldehyde

The effect of the nature of surface species on the activity and selectivity of MoO3/SiO2 catalysts has been investigated for the partial oxidation of methane to formaldehyde. Characterization techniques including BET surface area, ambient and in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction were used in conjunction with steady-state reaction studies to relate the presence of different surface species to the activity and selectivity of the catalyst. Results of these experiments indicate the presence of a highly dispersed silicomolybdic species with terminal Mo=O sites appearing at lower MoO3 loadings. As the weight loading increases, these sites are transformed into polymolybdate species, forming more Mo-O-Mo bridging sites at the expense of Mo=O sites. At high weight loadings, crystalline MoO3 begins to form. The abundance of the Mo=O sites is believed to affect activity and selectivity in the partial oxidation of methane to formaldehyde.

The surface state and catalytic properties of Pt black after O2-H2 cycles

XPS and UPS of a Pt black catalyst after customary H2-O2 regeneration shows considerable amounts of residual C as well as surface OH/H2O species. Surface C could not be removed even by O2 at 800 K. Oxygenates are stable even after H2 treatment up to 750 K. Their chemical state has been tentatively identified by comparing XPS and UPS results. Catalytic transformations of n-hexane on Pt black treated analogously is reported and the effect of surface species on catalytic properties discussed. Possible consequences of the presence of stable surface OH/H2O species on H2-O2 titrations are mentioned.

Effects of different surface species on the infrared spectrum of CO adsorbed on Rh/Al2O3

The effects of surface species (formed in the hydrogenation of CO and CO2 on supported Rh catalysts) on the bonding of chemisorbed CO on Rh have been investigated by infrared spectroscopy. It appeared that neither the intensities nor the locations of the bands of adsorbed CO and formate were influenced by each other, indicating that the adsorption sites for CO and formate species at 300 K on Rh/Al2O3 are basically different. The adsorption of ethylene (or its fragments) lowered the amount of CO adsorbed on Rh. It left the position of the Rh(CO)2 bands unaltered, but it caused a red shift in the band of Rh—CO species. The deposition of carbon on the surface also changed the structure and adsorptive properties of Rh, and shifted the Rh—CO bond to lower frequency.