Temperature-programmed Desorption Spectroscopy Research Articles

Study of the Role of Surface Oxygen Functional Groups on Carbon Nanotubes in the Selective Oxidation of Acrolein

AbstractCarbon nanotubes (CNTs) are promising candidates for metal‐based catalysts in the selective catalytic oxidation of acrolein. It has been proposed that the surface functional groups play an important role in this reaction. We employ the simple calcination and reduction method to selectively remove the oxygen functional groups on the CNT surface. With the assistance of different characterization techniques such as temperature‐programmed desorption and X‐ray photoelectron spectroscopy, epoxy and lactone oxygen groups on the CNT surface are recognized as the active sites for acrolein selective oxidation. Through adjusting the amount of epoxy and lactone groups, a top catalytic performance (51.2 % acrolein conversion and 79.7 % acrylic acid selectivity) is achieved. Our results indicate that CNTs can be selectively functionalized and used as catalysts for the selective oxidation reaction.

Deuterium retention in tungsten films deposited by magnetron sputtering

Deuterium retention in tungsten films deposited on polycrystalline bulk tungsten substrates was investigated and compared with deuterium retention in W films deposited on silicon and in polycrystalline bulk W alone. The structure of the deposited films was investigated by x-ray diffraction and scanning electron microscopy combined with focused ion beam cutting. D retention after implantation was measured by nuclear reaction analysis and temperature programmed desorption (TPD). The W films deposited on bulk W show a typical columnar epitaxial growth. After D implantation, high densities of blisters with diameters of about a hundred μm were formed. Interestingly, the blisters are located within the W substrate well below the interface of deposited film and substrate. TPD spectroscopy reveals two D2 release peaks at 510 and 700 K, indicating at least two different trap energies.

Vicinal Rutile TiO2 Surfaces and Their Interactions with O2

Slightly miscut TiO2(110) surfaces with high densities of step edges were studied by scanning tunneling microscopy (STM), temperature-programmed desorption (TPD), and ultraviolet photoemission spectroscopy (UPS). STM measurements provided information on the surface morphology and the density of defects and adstructures, whereas UPS measurements revealed information on the electronic structure and the surface reduction state before and after the conduction of O2 TPD experiments. It was found that the presence of step edges and adstructures has a strong influence on the O2–TiO2 interaction. The growth of TiOx islands occurred in the same way on stepped surfaces as on flat TiO2(110) surfaces, but the island densities were smaller. TPD measurements revealed that significantly less O2 desorbed between 300 and 410 K from stepped surfaces than from surfaces with large terraces. Importantly, the stepped TiO2 surfaces were characterized by clearly lower surface reduction states than flat TiO2(110) surfaces.

Molecular Hydrogen Formation from Photocatalysis of Methanol on Anatase-TiO2(101)

Photocatalysis of methanol (CH3OH) on anatase (A)-TiO2(101) has been investigated using temperature programmed desorption (TPD) method with 266 nm light at low surface temperatures. Experimental results show that CH3OH adsorbs on the A-TiO2(101) surface predominantly in molecular form, with only a small amount of CH3OH in dissociated form. Photocatalytic products, formaldehyde (CH2O) and methyl formate (HCOOCH3), have been detected under 266 nm light irradiation. In addition to H2O formation, H2 product is also observed by TPD spectroscopy. Experimental results indicate that H2 product is formed via thermal recombination of H-atoms on the BBO sites from photocatalysis of CH3OH on the A-TiO2(101) surface, and H2 production on the A-TiO2(101) surface is significantly more efficient than that on the rutile (R)-TiO2(110) surface.

Preparation of novel mesoporous Ce-Ni2P/SBA-15 catalysts and their catalytic performance for hydrodesulfurization of dibenzothiophene

Ni2P/SBA-15 precursors with Ni2P loadings of 25 wt% and initial P/Ni of 0.8 were prepared using nickel nitride as nickel source, diammonium hydrogen phosphide as phosphorus and mesopore molecular sieve SBA-15 as support. Then Ce was introduced into the Ni2P/SBA-15 precursor. The novel mesoporous Ce-Ni2P/SBA-15 catalysts were prepared after temperature-programmed reduction in flowing H2. The structure was characterized by X-ray diffraction, N2 adsorption–desorption isotherms, NH3 temperature-programmed desorption and X-ray photoelectron spectroscopy. The catalytic activities for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) were evaluated. The results showed that only Ni2P phase was formed in Ce-Ni2P/SAB-15 catalysts with Ce loadings of 0–5 wt%. Ni2P and Ni12P5 phases were existed in 7 wt% Ce-Ni2P/SBA-15 catalyst. The surface area and pore volume increased when Ce was added to Ni2P/SBA-15 catalyst. The strength of the acid sites and total acid amount of Ce-Ni2P/SBA-15 catalysts increased with increasing Ce loadings. Ce existed in the form of Ce3+and Ce4+, Ni existed in the form of Ni2+ and Niδ+, and P existed in the form of Pδ− and P5+. The addition of Ce to the Ni2P/SBA-15 catalyst decreased Niδ+ concentration in Ni2P/SBA-15 catalyst. The activity for HDS of DBT over Ni2P/SBA-15 catalysts was affected by the addition of Ce at 300–340 °C. The catalysts exhibited a good catalytic performance of deep hydrodesulfurization of dibenzothiophene and the conversion of DBT can reach 98.9 % at 380 °C. Biphenyl was the main product over Ce-Ni2P/SBA-15 catalysts and cyclohexylbenzene was the main product over Ni2P/SBA-15 catalyst at 380 °C.

The effect of H2–CCl4 mixture plasma treatment on TiO2 photocatalytic oxidation of aromatic air contaminants under both UV and visible light

The effect of H2–CCl4 mixture plasma treatment on TiO2 photocatalytic oxidation of aromatic air contaminants under both UV and visible light was reported. X-ray diffraction (XRD), UV–Vis spectroscopy, photoluminescence (PL), Temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared TiO2 nanoparticles. Carbon atoms were doped into TiO2 by replacing titanium atoms whereas chlorine located on TiO2 surface to form Ti–Cl bond via the coordination with Ti4+ sites by plasma treatment. The carbon doping amount and surface chlorine content of TiO2 under H2–CCl4 mixture plasma treatment were obviously higher than that under single CCl4 plasma treatment. H2–CCl4 mixture plasma treated catalyst exhibited much higher photocatalytic oxidation performances of benzene and toluene than that of single CCl4 plasma treated catalyst and P25 under both UV and visible light. Chlorine radicals formed under illumination are effective in oxidizing aromatic side groups, but ineffective in reactions with the aromatic ring, thus benzene conversions were lower than that of toluene under both UV and visible light. The possible mechanism was proposed.

Effects of M-promoter (M = Y, Co, La, Zn) on Cr2O3 catalysts for fluorination of perchloroethylene

The vapor phase fluorination of perchloroethylene (PCE) to synthesize 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123), 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124) and pentafluoroethane (HFC-125) was carried out on M-Cr2O3 catalysts with different promoters (M=Y, Co, La, Zn). The catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), Raman spectrum, Ammonia temperature-programmed desorption (NH3-TPD) and X-ray photoelectron spectroscopy (XPS) techniques. It was found that in the pre-fluorination process CrOx (x≥1.5) in M-Cr2O3 catalysts could be transformed into CrOxFy species. The highest activity was obtained on La-Cr2O3(F) catalyst with 90.6% of PCE conversion and 93.7% to total selectivity (HCFC-123+HCFC-124+HFC-125) at 300°C. The decline in surface acid sites density of the catalyst could improve the specific reaction rate, and the formation of surface CrOxFy species could enhance the selectivities to HCFC-123, HCFC-124 and HFC-125 for gas phase fluorination of PCE.

Influence of Hydrogen Annealing on the Photocatalytic Activity of Diamond-Supported Gold Catalysts

Fenton-treated diamond nanoparticles have been submitted to hydrogen reduction at 500 °C with the purpose of modifying the nature of the functional groups present on the diamond surface. The nature of the functional groups on the diamond samples was characterized by a combination of spectroscopic and analytical techniques. In particular, Fourier-transformed infrared spectroscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS) show the decrease in the population of carboxylic acids, esters, and anhydrides after hydrogen treatment. XPS also shows a decrease on the oxygen content after the hydrogen treatment of the diamond nanoparticles and lower electronegativity of the carbons as assessed by the lower binding energy values. Although Fenton-treated diamond colloids in water changes the zeta potential from positive to negative values as a function of the pH, hydrogen annealing and the disappearance of the carboxyl groups determines that the zeta potential of the resulting sample remains positive in the complete pH range. Deposition of gold nanoparticles was carried out by the polyol method consisting on the reduction of HAuCl4 by hot ethylene glycol in the presence of the support. TEM analysis shows a variation of the average gold nanoparticle size that decreases after hydrogen reduction of carboxylic groups and becomes smaller for low gold loadings. The catalytic activity of the diamond supported gold nanoparticles as a function of the surface annealing treatment and gold loading was evaluated for the natural sunlight-assisted peroxidation of phenol by H2O2. It was observed that the most efficient sample was the one having lower gold nanoparticle size that was obtained for diamond samples reduced by hydrogen at 500 °C after the Fenton treatment and having low gold loading (0.05 wt %). Turnover frequencies above 2400 and 940 h(-1) were obtained for phenol degradation and H2O2 decomposition, respectively.

XPS and TPD study of NO interaction with Cu(111): Role of different oxygen species

The adsorption and reaction of NO on clean and O-precovered Cu(111) has been studied using X-ray photoelectron spectroscopy and temperature-programmed desorption spectroscopy. By varying NO exposure and annealing temperature, two different types of chemisorbed oxygen species, with O 1 s binding energies (BE) of 531.0 (O 531 ) and 529.7 eV (O 529 ), were prepared on Cu(111). In the presence of O 531 species, the relative occupation of different NO adsorption states was largely affected, and most of the adsorbed NO(a) underwent dissociative desorption, releasing N 2 O and N 2 upon heating. In contrast, in the presence of O 529 species, the dissociative desorption of NO(a) was largely suppressed. Furthermore, the O 529 species show a more significant blocking effect on NO adsorption than the chemisorbed O 531 species. Our results reveal that the effect of precovered oxygen species on the adsorption and reaction of NO on Cu(111) is closely related to the type of oxygen species and oxygen coverage. 利用X射线光电子能谱和程序升温脱附谱研究了NO在清洁和预吸附氧的Cu(111)表面上的吸附和反应. 通过改变NO的暴露量和退火温度, 在Cu(111)表面可以制备出不同种类的化学吸附氧物种, 其O 1 s 的结合能分别位于531.0 eV (O 531 )和529.7 eV (O 529 ). 表面O 531 物种的存在对NO的不同吸附状态有着显著影响, 同时使得大部分NO吸附分子(NO(a))在加热过程中发生分解并以N 2 O和N 2 形式脱附; 而表面O 529 物种对NO(a)的解离脱附有着明显的抑制作用. 相对于O 531 物种来说, O 529 物种对NO吸附表现出更强的位阻效应. 上述结果表明, NO在Cu(111) 表面的吸附和分解行为与预吸附氧物种的种类和覆盖度密切相关. The adsorption and reaction behavior of NO on Cu(111) largely depends on the type of precovered oxygen species, which were prepared by varying NO exposure and annealing temperature.

Interactions of phenylglycine with amorphous solid water studied by temperature-programmed desorption and photoelectron spectroscopy

Temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) have been employed to study the interactions of phenylglycine (PheGly) with amorphous solid water (ASW) nanolayers (10–50ML). First, the adsorption and growth of PheGly layers on an AlOx/NiAl(110) surface have been examined. After that, mixed PheGly–ASW layers have been grown on the alumina surface at 110K. Alternatively, PheGly molecules (from submonolayer to multilayer coverages) have been deposited on top of the ASW surfaces. In mixed PheGly–ASW nanolayers the PheGly phase displays hydrophobic behavior and accumulates near the surfaces of the films, while top-deposited PheGly wets the ASW films forming closed overlayers at low coverages. H2O desorption from the PheGly–ASW films is strongly influenced by the PheGly molecules, i.e., the crystallization of ASW is partially inhibited in the vicinity of the amino acid and a lower desorption temperature of H2O molecules than from pure ASW layers was detected. Thicker PheGly overlayers on ASW provide a kinetic restriction to H2O desorption from the underlying ASW layers until the PheGly molecules become mobile and develop pathways for water desorption at higher temperatures. The results are discussed with respect to the previously obtained data for glycine–ASW layered systems. It has been demonstrated that the substitution of the hydrogen atom in glycine with a phenyl group does not lead to detectable changes in the pathways of ASW desorption. However, desorption of PheGly differs from the desorption of glycine from the similarly structured glycine–ASW nanolayers. The differences are interpreted in terms of adsorbate–adsorbate and adsorbate–substrate interactions.

Morphology of the solid water synthesized through the pathway D + O2 studied by the sensitive TPD technique

We report on an experimental study on the formation of water, through the D + O2 pathway, on a sample of amorphous solid water, i.e. a realistic analogue of the surface of the interstellar grains of dense clouds. For improving our experimental conditions we use deuterium instead of hydrogen. We obtain, using both Temperature-Programmed Desorption Spectroscopy and Infrared Spectroscopy, that the morphology of the nascent water ice is mostly compact. We compare our results with those obtained previously by Oba et al. and show that the first technique is more effective in probing the morphology of amorphous water ice. We propose that the formation of compact ice is due to the heat of reactions which lead to the formation of water molecules. Water is synthesized, through the D + O2 pathway, on a film of compact amorphous solid water and on a porous substrate for comparison purposes. We show that in this latter case a gradual compaction of the sample takes place upon formation of new water molecules. We compare this reduction of water ice porosity with that one obtained by Accolla et al., due to recombination of deuterium atoms sent on the surface of an amorphous porous ice sample, and show that the compaction of the sample as a consequence of the water formation appears clearly more efficient.

CO oxidation on nanoporous gold: A combined TPD and XPS study of active catalysts

Disks of nanoporous gold (np-Au), produced by leaching of silver from AgAu alloy and prepared as active catalysts for CO oxidation in a continuous-flow reactor, were investigated in detail by x-ray photoelectron spectroscopy and temperature-programmed desorption spectroscopy in ultra-high vacuum. Np-Au exhibits several oxygen species on and in the surface: Chemisorbed oxygen (Oact), probably generated at residual silver sites at the surface, is readily available after np-Au preparation and consumed by CO oxidation. It can be replenished on activated np-Au by exposure to O2. In addition, strongly bound oxygen, probably at subsurface sites, is present as a major species and not consumed by CO oxidation. Pronounced CO desorption at temperatures above 200K observed after exposing np-Au to CO at 105K indicates an additional, more stable type of CO binding sites on np-Au as compared to pure gold. Only CO at these binding sites is consumed by oxidation reaction with Oact. It is proposed that the presence of strongly bound subsurface oxygen stabilizes CO adsorption on np-Au, thereby being as crucial for the observed catalytic activity of np-Au as residual silver.

Interaction between H2O and Preadsorbed D on the Stepped Pt(553) Surface

We have studied the interaction of Pt(553) with varying coverages of preadsorbed D and H2O and compare results to those from the similar Pt(533) surface. We have used temperature programmed desorption spectroscopy in combination with isotopic labeling to monitor H–D exchange. Similar to results for Pt(533), on Pt(553) small amounts of D weaken the H2O–metal bonding at steps. Larger D coverages also weaken the stability of the water overlayer at the (111) terraces. However, in contrast to Pt(533), water wets the Pt(553) surface at all D-coverages and the surface does not become hydrophobic. We attribute the difference in the long-range ordering of water to the difference in bond energy of deuterium to (100) and (110) step sites. This also affects HOD formation by H–D exchange. The exchange increases with H2O and Dad coverage, although less than proportional. Availability of bare Pt sites for both adsorbates is key to obtaining high reactivity.

Modification of the supported Cu/SiO2 catalyst by alkaline earth metals in the selective conversion of 1,4-butanediol to γ-butyrolactone

The promotion effects of alkaline earth metals (Mg, Ca, Sr, Ba) on the catalytic property of the Cu/SiO2 catalyst for the gas phase dehydrogenation of 1,4-butanediol were investigated. The addition of Ca, Sr or Ba to the Cu/SiO2 catalyst resulted in the improvements of the catalytic activity and the γ-butyrolactone selectivity, and the Cu-Ba/SiO2 catalyst gave 99.6% yield of γ-butyrolactone even after 900h running. The catalysts were prepared by co-impregnation and characterized by N2 physisorption, X-ray diffraction (XRD), SEM, TEM, H2-temperature programmed reduction (H2-TPR), N2O-decomposition, ammonia temperature-programmed desorption (NH3-TPD), CO2-TPD, XPS, and FTIR spectroscopy of adsorbed pyridine and CO. On the base of the experimental results, two types of copper species on the reduced catalyst were proposed. The Cu° account for the dehydrogenation of 1,4-butanediol, while the electropositive copper species (Cu+) is suggested to be the strong Lewis acid site to catalyze side reactions. The selectivity of γ-butyrolactone was increased with the increasing of the Cu0/Cu+ ratio, and the yield of γ-butyrolactone was increased with copper surface area. The main byproduct 2,3-dihydrofuran may be formed from 1,4-butanediol by the metal/acid–base concerted catalysis.

Depletion of Monolayer Liquid Lubricant Films Induced by Laser Heating in Thermally Assisted Magnetic Recording

In this study, lubricant depletion due to high-frequency pulsed-laser heating, with a heating rate of ~108–109 K/s, was investigated for lubricant films with thicknesses of greater than and less than one monolayer. The conventional lubricants, Zdol2000 and Ztetraol2000, were used. It was found that the critical temperature at which the lubricants begin to deplete was strongly dependent on the lubricant film thickness. For lubricant film thicknesses of less than one monolayer, this temperature was approximately 170 °C higher than that for thicknesses of greater than one monolayer. To analyze the lubricant depletion mechanism, we examined the tested lubricant films, using temperature-programmed desorption (TPD) spectroscopy, in which the heating rate was 0.3 K/s. It was found that the lubricant depletion characteristics could be explained using the experimental TPD results for the tested lubricant films. The depletion mechanism involves the desorption or decomposition of the lubricant molecules, which interact with the diamond-like carbon thin films when the lubricant film thickness is less than one monolayer. Therefore, we concluded that the TPD results were highly effective for evaluating the lubricant depletion characteristics induced by rapid laser heating, even though the heating rates are substantially different.

NiMo/γ-Al2O3 Catalysts from Ni Heteropolyoxomolybdate and Effect of Alumina Modification by B, Co, or Ni

A hydrotreating NiMo/γ-Al2O3 catalyst (12 wt% Mo and 1.1 wt% Ni) was prepared by impregnation of the support with the Anderson-type heteropolyoxomolybdate (NH4)4Ni(OH)6Mo6O18. Before impregnation of the support, it was modified with an aqueous solution of H3BO3, Co(NO3)2, or Ni(NO3)2. The catalysts were investigated using N2 adsorption, O2 chemisorption, X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, temperature-programmed reduction, temperature-programmed desorption, and X-ray photoelectron spectroscopy. The addition of Co, Ni, or B influenced the Al2O3 phase composition and gave increased catalytic activity for 1-benzothiophene hydrodesulfurization (HDS). X-ray photoelectron spectroscopy confirmed that the prior loading of Ni, Co or B increased the degree of sulfidation of the NiMo/γ-Al2O3 catalysts. The highest HDS activity was observed with the NiMo/γ-Al2O3 catalyst with prior loaded Ni.

Probing the active sites for CO dissociation on ruthenium nanoparticles

The active sites for CO dissociation were probed on mass-selected Ru nanoparticles on a HOPG support by temperature programmed desorption spectroscopy using isotopically labelled CO. Combined with transmission electron microscopy we gain insight on how the size and morphology of the nanoparticles affect the CO dissociation activity. The Ru nanoparticles were synthesized in a UHV chamber by gas-aggregation magnetron sputtering in the size range from 3 to 15 nm and the morphology was investigated in situ by scanning tunneling microscopy and ex situ by high resolution transmission electron microscopy. Surprisingly, it was found that larger particles were more active per surface area for CO dissociation. It is suggested that this is due to larger particles exposing a more rough surface than the smaller particles, giving rise to a higher relative amount of under-coordinated adsorption sites on the larger particles. The induced surface roughness is proposed to be a consequence of the growth processes in the gas-aggregation chamber.

Proton conduction in AIII0.5BV0.5P2O7 compounds at intermediate temperatures

Proton conductors capable of operation between 100 and 400 °C are attractive electrochemical materials due to their high utility value in energy and environmental applications. However, such proton conductors have not yet made headway in the marketplace, due to insufficient proton conductivity. Here, we present new types of metal pyrophosphates as promising candidates for intermediate temperature proton conductors. A series of AIII0.5BV0.5P2O7 (AIIIBV = InSb, SbSb, FeSb, GaNb, FeNb, YNb, GaTa, AlTa, FeTa, YTa, BiTa, and SmTa) compounds were synthesized, of which In0.5Sb0.5P2O7, Fe0.5Nb0.5P2O7, and Fe0.5Ta0.5P2O7 exhibited the highest proton conductivities in the temperature ranges of 50–100 °C (0.045 S cm−1@100 °C), 100–200 °C (0.12 S cm−1@150 °C), and 200–400 °C (0.18 S cm−1@250 °C), respectively, in unhumidified air. The proton conductivity of these three compounds was further enhanced by the introduction of AIII or BV deficiency into the bulk. Consequently, Fe0.4Ta0.5P2O7 exhibited the highest proton conductivity of 0.27 S cm−1 at 300 °C in unhumidified air. Such high proton conductivity values were also observed under fuel cell operating conditions. The environments of protons in the bulk of these compounds were monitored using Fourier transform infrared (FT-IR) spectroscopy, temperature-programmed desorption (TPD), and proton magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Protons were incorporated into the compounds for charge-compensation of the deficient AIII or BV cations, which results in an increase in the quantity of protons. More importantly, the mobility of the protons was also enhanced. Various electrochemical measurements demonstrate that proton conduction is dominant in these compounds, where the protons migrate according to a hopping mechanism.

Effect of Sr addition to La-based perovskite-type oxide as an electrode material for zirconia-based amperometric-type NOx sensor

The sensing characteristics of an amperometric NOx sensor with yttria-stabilized zirconia and a La-based perovskite-type oxide sensing electrode were examined. La1-xSrxMO3 (M = Co, Mn, x = 0, 0.2, 0.4, 0.6) were synthesized using the spray pyrolysis method. The NO2 response of a sensor fabricated with La1-xSrxMnO3 increased with increasing amount of Sr, and the trend was in contrast to that of the sensors fabricated with La1-xSrxCoO3. LaSr0.2MnO3 was determined to be the most appropriate material for the sensor in terms of a high NO2 response and low O2 current. In order to discuss the effects of Sr addition to La-based perovskite oxides for the sensor, NO adsorption and desorption properties of oxides and the relationship between the oxidation number of the B-site cation and Sr substitution were examined using temperature-programmed desorption and X-ray photoelectron spectroscopy, respectively.

Effects of the crystal reduction state on the interaction of oxygen with rutile TiO2(1 1 0)

The interaction of O2 with reduced rutile TiO2(110)–(1×1) has been studied by means of scanning tunneling microscopy (STM), temperature-programmed desorption (TPD) and photoelectron spectroscopy (PES). It is found that the interaction of O2 with TiO2(110) depends strongly on the reduction state of the TiO2(110) crystal. High-resolution STM studies revealed that the energy barrier for the non-vacancy-assisted, 2nd O2 dissociation channel decreases with increasing crystal reduction. Additionally, it is found in the STM studies that the Ti interstitial diffusion is slightly more facile in high-reduced TiO2(110) crystals compared to low-reduced ones. Accompanying TPD studies revealed that the line shape of the O2-TPD peak occurring between ∼360K and ∼450K depends on the crystal reduction state. For high-reduced TiO2(110) crystals characterized by large terraces most O2 molecules desorb at ∼386K, whereas O2 desorption is peaking at ∼410K for low- and medium-reduced crystals. Furthermore, the O2-TPD experiments revealed a highly non-linear behavior of the O2 desorption peak integrals as function of the crystal reduction state. The presented results point to an ionosorption model where the adsorbates withdraw the excess charge (Ti3+) from the near-surface region at temperatures<∼360K and where Ti interstitials react with oxygen species on the surface at temperatures≥∼360K.