CH3OH Oxidation Research Articles

High-Temperature Shock Tube and Modeling Studies on the Reactions of Methanol with D-Atoms and CH3-Radicals

The shock tube technique has been used to study the hydrogen abstraction reactions D + CH3OH → CH2O + H + HD (A) and CH3 + CH3OH → CH2O + H + CH4 (B). For reaction A, the experiments span a T-range of 1016 K ≤ T ≤ 1325 K, at pressures 0.25 bar ≤ P ≤ 0.46 bar. The experiments on reaction B, CH3 + CH3OH, cover a T-range of 1138 K ≤ T ≤ 1270 K, at pressures around 0.40 bar. Reflected shock tube experiments, monitoring the depletion of D-atoms by applying D-atom atomic resonance absorption spectrometry (ARAS), were performed on reaction A using gas mixtures of C2D5I and CH3OH in Kr bath gas. C2D5I was used as precursor for D-atoms. For reaction B, reflected shock tube experiments monitoring H-atom formation with H-ARAS, were carried out using gas mixtures of diacetyl ((CH3CO)2) and CH3OH in Kr bath gas. (CH3CO)2 was used as the source of CH3-radicals. Detailed reaction models were assembled to fit the D-atom and H-atom time profiles in order to obtain experimental rate constants for reactions A and B. Total rate constants from the present experiments on D + CH3OH and CH3 + CH3OH can be represented by the Arrhenius equations kA(T) = 1.51 × 10(-10) exp(-3843 K/T) cm(3) molecules(-1) s(-1) (1016 K ≤ T ≤ 1325 K) and kB(T) = 9.62 × 10(-12) exp(-7477 K/T) cm(3) molecules(-1) s(-1) (1138 K ≤ T ≤ 1270 K). The experimentally obtained rate constants were compared with available rate data from the literature. The results from quantum chemical studies on reaction A were found to be in good agreement with the present results. The present work represents the first direct experimental study on these bimolecular reactions at combustion temperatures and is important to the high-temperature oxidation of CH3OH.

In Situ Ru K-Edge X-ray Absorption Spectroscopy Study of Methanol Oxidation Mechanisms on Model Submonolayer Ru on Pt Nanoparticle Electrocatalyst

In situ X-ray absorption spectroscopy (XAS) with electrochemical reaction control has enabled a detailed investigation of the mechanism of the methanol electrooxidation by a bimetallic PtRu catalyst. By the use of an original electrodeposition technique, ca. 0.3 monolayer of Ru was deposited on the surface of unsupported Pt nanoparticles (Ru@Pt). The presence of Ru atoms only at the surface of nanoparticles turns a bulk sensitive XAS technique into a surface methodology which permits correlation of the X-ray absorption fine structure at the Ru K-edge to the role of Ru atoms in the methanol oxidation process. In situ XAS spectra of the Ru@Pt nanoparticles were collected at various electrode potentials in background electrolyte, and then in 1 M solution of methanol (CH3OH) in the same electrolyte. Significant differences in the catalyst state have been revealed between these two environments. In the background electrolyte, Ru gradually oxidizes from mostly metallic to a Ru(III)/Ru(IV) mixture at the highest potentials. In the presence of CH3OH, the Ru oxidation state remains a mixture of metallic and Ru(III) even at the highest potentials. CO-type species were found adsorbed on Ru atoms at all potentials and coadsorbed with OH species at potentials 0.175 V vs Ag/AgCl and higher with steady number of near neighbors. The same potential correlates to the beginning of methanol oxidation reaction observed electrochemically. Therefore coadsorption of CO and OH groups on Ru atoms appears to be critical in the methanol oxidation process. The need for OH groups for CO removal from Pt sites was previously suggested by the bifunctional CH3OH oxidation mechanism; however, occupancy of Ru atoms with CO species and direct structural observations of the coadsorption of CO and OH on the same Ru atom is a novel finding resulting from this study. Other changes in the catalyst environment were observed, including decreased Ru–Ru and Ru–Pt bond distances, increased numbers of Ru–Pt near neighbors, and decreased number of Ru–Ru near neighbors.

Experimental and Kinetic Modeling Study of Methanol Ignition and Oxidation at High Pressure

ABSTRACTA detailed chemical kinetic model for oxidation of CH3OH at high pressure and intermediate temperatures has been developed and validated experimentally. Ab initio calculations and Rice–Ramsperger–Kassel–Marcus/transition state theory (RRKM/TST) analysis were used to obtain rate coefficients for , , , and . The experiments, involving CH3OH/O2 mixtures diluted in N2, were carried out in a high‐pressure flow reactor at 600–900 K and 20–100 bar, varying the reaction stoichiometry from very lean to fuel‐rich conditions. Under the conditions studied, the onset temperature for methanol oxidation was not dependent on the stoichiometry, whereas increasing pressure shifted the ignition temperature toward lower values. Model predictions of the present experimental results, as well as rapid compression machine data from the literature, were generally satisfactory. The governing reaction pathways have been outlined based on calculations with the kinetic model. Unlike what has been observed for unsaturated hydrocarbons, the oxidation pathways for CH3OH under the investigated conditions were very similar to those prevailing at higher temperatures and lower pressures. At the high pressures, the modeling predictions for onset of reaction were particularly sensitive to the reaction.

Impact of metal doping on the activity of Au/CeO2 catalysts for catalytic abatement of VOCs and CO in waste gases

Abstract The catalytic performance in the total oxidation of CO and methanol over gold catalysts supported on ceria doped by different metal oxides (Me = Fe, Mn and Co) was studied and a strong influence of the nature of dopant was observed. The activity towards the oxidation of CO and CH3OH was in the order: AuCeCo > AuCe > AuCeFe > AuCeMn. The characterization by XRD and HRTEM evidenced differences in the average size and the distribution of gold particles. AuCeCo catalyst exhibited superior low-temperature CO oxidation activity (100% conversion degree was obtained at 25 °C) and almost 100% total oxidation of CH3OH at about 40 °C. Higher hydrogen consumption was estimated by means of TPR over this catalyst. The effect of modification with Co3O4 of Au/CeO2 catalysts on their CO oxidation activity was further studied by varying of the dopant content (5, 10 and 15 wt.% Co3O4).

Thermal Decomposition and Oxidation of CH3OH

Thermal decomposition of CH(3)OH diluted in Ar has been studied by monitoring H atoms behind reflected shock waves of 100 ppm CH(3)OH + Ar. The total decomposition rate k(1) for CH(3)OH + M → products obtained in this study is expressed as, ln(k(1)/cm(3) molecule(-1) s(-1)) = -(14.81 ± 1.22) - (38.86 ± 1.82) × 10(3)/T, over 1359-1644 K. The present result on k(1) is indicated to be substantially smaller than the extrapolation of the most of the previous experimental data but consistent with the published theoretical results [Faraday Discuss. 2002, 119, 191-205 and J. Phys. Chem. A 2007, 111, 3932-3950]. Oxidation of CH(3)OH has been studied also by monitoring H atoms behind shock waves of (0.35-100) ppm CH(3)OH + (100-400) ppm O(2) + Ar. For the low concentration CH(3)OH (below 10 ppm) + O(2) mixtures, the initial concentration of CH(3)OH is evaluated by comparing evolutions of H atoms in the same concentration of CH(3)OH with addition of 300 ppm H(2) diluted in Ar. The branching fraction for CH(3)OH + Ar → (1)CH(2) + H(2)O + Ar has been quantitatively evaluated from this comparative measurements with using recent experimental result on the yield of H atoms in the reaction of (1,3)CH(2) + O(2) [J. Phys. Chem. A 2012, 116, 9245-9254]; i.e., the branching fraction for the above reaction is evaluated as, φ(1a) = 0.20 ± 0.04 at T = 1880-2050 K, in the 1.3 and 3.5 ppm CH(3)OH + 100 ppm O(2) samples. An extended reaction mechanism for the pyrolysis and oxidation of CH(3)OH is constructed based on the results of the present study combined with the oxidation mechanism of natural gas [GRI-Mech 3.0]; evolution of H atoms can be predicted very well with this new reaction scheme over a wide concentration range for the pyrolysis (0.36-100 ppm CH(3)OH), and oxidation (0.36-100 ppm CH(3)OH + 100/400 ppm O(2)) of methanol.

Electrocatalytic oxidation of methanol and carbon monoxide at platinum in protic ionic liquids

Oxidation of H2O, CO and CH3OH was investigated at Pt as a function of temperature in the protic ionic liquid diethylmethylammonium trifluoromethanesulfonate. Trace H2O oxidation in the ionic liquid results in coverage of the Pt with adsorbed oxides. Increasing the temperature significantly reduces the potential at which this reaction occurs. CH3OH and CO oxidation kinetics increased significantly with increasing temperature and oxidation of each species coincided with coverage of the Pt surface by the oxide. These observations indicate that surface oxides are required for complete oxidation of CH3OH to CO2 in the protic ionic liquid, in a similar way to that observed in conventional aqueous electrolytes. While the overpotential for CH3OH oxidation was drastically higher than that observed in purely aqueous electrolytes, it decreased with increasing water content of the ionic liquid. The results described here have implications for the development of protic ionic liquid electrolyte fuel cells and these implications are discussed.

Synthesis and photocatalytic properties of nanocrystalline Au, Pd and Pt photodeposited onto mesoporous RuO2-TiO2 nanocomposites

Noble metals (Au, Pd and Pt) have been photodeposited onto hexagonal mesoporous RuO2-TiO2 nanocomposites to study their influence on the photocatalytic activity under UV and visible lights by determination of the formation rate of HCHO generated by photooxidation of CH3OH in aqueous solution. X-ray diffraction (XRD) patterns and N2 sorption isotherms reveal that highly crystalline TiO2 and mesoporous structure have been formed with high surface area (150–180m2/g) and pore diameter ranging from 6.8 to 7.3nm. TEM measurements show that the framework of the highly crystalline mesoporous RuO2-TiO2 is composed of anatase phase grown along [101] direction. The dependence of HCHO formation rate on the noble metals/RuO2-TiO2 nanocomposites, behaves quite differently depending on noble metals as electrons sink. Under UV light, the findings reveal that Pd/RuO2-TiO2 offers an improvement in term photooxidation rate of CH3OH and photonic efficiencies over Pt/RuO2-TiO2 and Au/RuO2-TiO2. However, under visible light, the photocatalytic activity of mesoporous RuO2-TiO2 containing Au nanoparticles towards CH3OH oxidation is remarkable and the photonic efficiency of RuO2-TiO2 has been improved two times. Pt and Pd nanoparticles could not be observed in any improvement in photocatalytic activity of RuO2-TiO2 under visible light.

Mesoporous PdO–TiO2 nanocomposites with enhanced photocatalytic activity

Herein, we report a synthesis of mesoporous PdO–TiO2 nanocomposites at different PdO (0–3wt%) through simple one-step sol–gel reactions. Pd2+ ions have been immobilized into TiO2 networks by cross-linking triblock copolymer (Pluronic F123) as the structure-directing agents to develop highly efficient PdO–TiO2 photocatalyst. The produced PdO–TiO2 gel were calcined at 400°C for 4h to remove organic materials. TiO2 nanoparticles with an average diameter are 8–10nm and PdO nanoparticles are well dispersed and exhibit diameters of about 10–40nm based on the PdO content. Our prepared photocatalysts have been compared with Pd/Aeroxide TiO2-P25 by the determination of the initial rate of HCHO formation generated by the photooxidation of CH3OH in aqueous suspensions to calculate the corresponding photonic efficiencies. The newly prepared PdO–TiO2 nanocomposites showed a more effective and high efficient photocatalytic activities for CH3OH oxidation to HCHO ∼4 and 2 times than TiO2-P25 and Pd/TiO2-P25 respectively. In the present work, the photocatalytic activities of the obtained PdO–TiO2 nanocomposites were significantly higher than those of previously reported. To the best of our knowledge, the measured photonic efficiency ξ=19.5% of mesosporous PdO–TiO2 nanocomposites is found to be among the highest ξ-values reported up to now.

Direct methanol oxidation at low overpotentials using Pt nanoparticles electrodeposited at ultrathin conductive RuO2 nanoskins

Small (primarily 2–4 nm) Pt nanoparticles electrodeposited at Ti-supported RuO2 nanoskins, designated as Pt/RuO2(Ti), are highly active for electrocatalytic oxidation of methanol (CH3OH) in acid electrolyte, with peak potentials among the lowest reported anywhere for RuO2-supported Pt. The Pt-modified RuO2 nanoskin is equally effective for CH3OH oxidation whether one or both sides of the Ti-foil substrate is coated or whether the RuO2 nanoskin is electrolessly deposited at the Ti substrate as a single layer or in multiple layers. Current densities for methanol oxidation are ∼2× lower than previously reported, owing to a bimodal distribution of both highly active (2–4 nm) and less active larger (> 5 nm) Pt particles. The methods reported here comprise a means of expressing highly active, nanostructured, bifunctional electrocatalytic coatings on substrates of essentially any geometry and minimizing the quantity of RuO2 necessary.

Iron and Ruthenium Heterobimetallic Carbonyl Complexes as Electrocatalysts for Alcohol Oxidation: Electrochemical and Mechanistic Studies

Carbonyl-containing Ru and Fe heterobimetallic complexes were prepared and tested as electrocatalysts for the oxidation of methanol and ethanol. GC analysis of the electrolyte solution during bulk electrolysis indicated that CpRu(CO)(μ-I)(μ-dppm)PtI2 (1), CpFe(CO)(μ-I)(μ-dppm)PtI2 (2), and CpRu(CO)(μ-I)(μ-dppm)PdI2 (3) were catalysts for the electrooxidation of methanol and ethanol, while CpFe(CO)(μ-I)(μ-dppm)PdI2 (4), CpRu(CO)I(μ-dppm)AuI (5), and CpFe(CO)I(μ-dppm)AuI (6) did not function as catalysts. The oxidation of methanol resulted in two- and four-electron oxidation to formaldehyde and formic acid, respectively, followed by condensation with unreacted methanol to yield dimethoxymethane and methyl formate as the observed products. The oxidation of ethanol afforded 1,1′-diethoxyethane as a result of two-electron oxidation to acetaldehyde and condensation with excess ethanol. FTIR analysis of the headspace gases during the electrochemical oxidation of methanol indicated formation of CO2. Isotopic labeling experiments demonstrated that the CO2 resulted from oxidation of the CO ligand instead of complete oxidation of CH3OH.

Carbonylation of Nitrobenzene in Methanol with Palladium Bidentate Phosphane Complexes: An Unexpectedly Complex Network of Catalytic Reactions, Centred around a Pd–imido Intermediate

The reactivity of palladium complexes of bidentate diaryl phosphane ligands (P(2)) was studied in the reaction of nitrobenzene with CO in methanol. Careful analysis of the reaction mixtures revealed that, besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MPC), N,N'-diphenylurea (DPU), aniline, azobenzene (Azo) and azoxybenzene (Azoxy)], large quantities of oxidation products of methanol were co-produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H(2)O, and CO). From these observations, it is concluded that several catalytic processes operate simultaneously, and are coupled via common catalytic intermediates. Starting from a P(2)Pd(0) compound formed in situ, oxidation to a palladium imido compound P(2)Pd(II)=NPh, can be achieved by de-oxygenation of nitrobenzene 1) with two molecules of CO, 2) with two molecules of CO and the acidic protons of two methanol molecules, or 3) with all four hydrogen atoms of one methanol molecule. Reduction of P(2)Pd(II)=NPh to P(2)Pd(0) makes the overall process catalytic, while at the same time forming Azo(xy), MPC, DPU and aniline. It is proposed that the Pd-imido species is the central key intermediate that can link together all reduction products of nitrobenzene and all oxidation products of methanol in one unified mechanistic scheme. The relative occurrence of the various catalytic processes is shown to be dependent on the characteristics of the catalysts, as imposed by the ligand structure.

Processing Nanomaterials in Molten Salts: Partially Electrometallized TiO2 as Pt Support for Enhanced Catalytic Oxidation of CO and CH3OH

Processing Nanomaterials in Molten Salts: Partially Electrometallized TiO2 as Pt Support for Enhanced Catalytic Oxidation of CO and CH3OH

Formaldehyde production from methanol and methyl mercaptan over titania and vanadia based catalysts

The results of selective oxidation of CH3OH and CH3SH to produce formaldehyde are presented and the effect of the reaction conditions on the CH2O yield is evaluated. The yield of formaldehyde was evaluated by thermodynamic calculations by using the HSC Chemistry® and Aspen Plus® simulation programmes. Oxidation of CH3OH and CH3SH was investigated by calculating the system equilibrium composition. Based on the modelling results, the yield of formaldehyde was almost zero with all the reactants present, i.e. the CH3OH, CH3SH and CH3OH+CH3SH mixture, which was also supported by the experiments. Catalytic experiments were performed over TiO2, V2O5/SiO2 and V2O5/(SiO2+10% TiO2) catalysts to evaluate the effect of feed concentration, reaction temperature and catalyst loading on the formaldehyde yield. Both CH3OH and CH3SH were oxidized separately and as mixtures. The V2O5/(SiO2+10% TiO2) catalyst was the most active catalyst in formaldehyde production. At optimal reaction conditions, 88% yield of CH2O was achieved at 413°C in a feed mixture of 1000ppm of CH3OH+CH3SH with the space velocity of 94,000h−1. The catalysts showed no activity loss when tested for 6h.

CH3OH Oxidation Activities of an Unsupported PtxRuy Powder Catalyst before and after Different Electrochemical Treatments

An unsupported Pt75Ru25 powder was synthesized by co-reducing the corresponding precursor salts rapidly. An alloy powder of Pt75Ru25 composition was formed in this manner. The catalyst powders were subjected to various electrochemical treatments in either 0.5 M H2SO4 or 0.5 M CH3OH + 0.5 M H2SO4 solutions. Applying specific electrochemical treatments in respect to time (e.g., the potential cycling number) relative to the E+ value result in either a decrease or increase in the CH3OH oxidation activity of this catalyst. The differently treated catalyst powders were further studied using EDX, XPS and CO adsorbed (COads) stripping voltamograms and transients. The results suggest that removal of surface Ru-oxides result in an increase in CH3OH electro-oxidation activity, while extensive loss of Ru from the catalyst surface results in a decrease in CH3OH oxidation activity. Refluxing this as-prepared catalyst powder in an excess of boiling 0.5 M H2SO4 did neither result in the removal of the surface Ru-oxides nor improve the CH3OH oxidation activity.

Platinum–polytyramine composite material with improved performances for methanol oxidation

Polytyramine (PTy) is shown to be a possible alternative to other conducting polymers as a support material for fuel cell electrocatalysts such as platinum. In this work, a Pt–PTy composite was prepared via potentiodynamic deposition of polytyramine on graphite substrate, followed by the electrochemical deposition of Pt nanoparticles. The material obtained by this straightforward method exhibited, for platinum loadings as low as ca. 0.12 mg cm−2, a specific electrochemically active surface area of the electrocatalyst of ca. 54 m2 g−1, together with a good electrocatalytic activity for methanol oxidation in acidic media, thus ensuring better efficiency of Pt utilization. The system Pt–PTy appears to be worthy of development for methanol fuel cell applications also because the results suggested that, when deposited as small particles in a PTy matrix, platinum is less sensitive to fouling during CH3OH oxidation.

Hydrogen production by photocatalytic steam reforming of methanol on noble metal-modified TiO 2

The photocatalytic production of hydrogen by methanol steam reforming was studied over a series of pristine or noble metal (Ag, Au, Au–Ag alloy and Pt) – modified TiO 2 photocatalysts, synthesised by flame spray pyrolysis or by the deposition of preformed noble metal nanoparticles on TiO 2. A closed recirculation apparatus was employed, with the photocatalyst bed continuously fed with methanol/water vapours. Methanol underwent oxidation up to CO 2 through the formation of formaldehyde and formic acid. Carbon monoxide, methane, methyl formate, acetaldehyde and dimethyl ether were identified as side products. Hydrogen evolved at constant rate, which significantly increased upon noble metal addition, Pt being the most effective co-catalyst, followed by gold and silver, according to their work function values. A systematic investigation into the effects of the inlet gas composition gave valuable information on the prevailing reaction paths and on the conditions of process optimisation, also in terms of distribution of CH 3OH oxidation products.

Photo-oxidation of ethylene in gas phase and methanol and formic acid in liquid phase on synthesized TiO 2 and Au/TiO 2 catalysts

Photo-catalytic activity of TiO 2 and Au/TiO 2 was studied in gas phase oxidation of ethylene (C 2H 4) in the presence of air over TiO 2 and Au/TiO 2 supported on glass surfaces using 350 nm photo-light separately. Around 20 nm-sized TiO 2 synthesized by hydrothermal process and Au/TiO 2 synthesized through photolysis of TiO 2 (laboratory-prepared) with Au III ions solutions were used for photo-catalytic oxidation experiments. CO 2 was found as photolysis product and its yield was found to be increasing with the increase in C 2H 4 concentration up to 0.47 mM (with respect to irradiation vessel/apparatus) in TiO 2 system, subsequently the CO 2 yield decreased, which might be due to the decrease in O 2/C 2H 4 ratio. However, in Au/TiO 2 (0.3–7.5 wt.% gold) system, the rate of photo-catalytic oxidation of C 2H 4 was reduced to half (0.05 ml min −1) as compared to pure TiO 2 system (0.08 ml min −1). Besides this, studies on the photo-catalytic oxidation of CH 3OH and HCOOH in the presence of suspended TiO 2 and Au/TiO 2 in water were carried out separately to evaluate the extent of oxidation properties between two different phases’ viz. gaseous and condensed phases. Our studies demonstrated the enhancement in photo-catalytic oxidation of CH 3OH and HCOOH over Au/TiO 2 in aqueous systems on contrary to the gas phase oxidation of C 2H 4.

The internal energy of CO2 produced by the catalytic oxidation of CH3OH by O2 on polycrystalline platinum

The dynamics of steady state catalytic methanol oxidation on a polycrystalline Pt surface over a range of surface temperatures and reactant flow conditions were investigated by monitoring the kinetics with mass spectrometry and the internal state distribution of nascent CO(2) with tunable diode laser absorption spectroscopy. The results indicate that CO(2) formation proceeds via three distinct reaction pathways. The first produced CO(2), which is vibrationally excited relative to CO(2) in thermal equilibrium with the surface and shows preferential excitation in the asymmetric stretch. This pathway proceeds via the decomposition of CH(3)OH and the subsequent oxidation of nascent CO adsorbed to Pt in a weakly held precursor state. CO(2) production via this pathway is favored at high surface temperatures and high oxygen coverage. The second forms CO(2), which is vibrationally deactivated relative to CO(2) in thermal equilibrium with the surface and exhibits no preferential excitation among its three nondegenerate vibrational modes or the rotational energy. This pathway involves the decomposition of CH(3)OH and subsequent oxidation of nascent CO adsorbed to Pt in a more strongly held chemisorbed state. CO(2) production via this pathway is favored at low surface temperatures and low oxygen coverage. The third forms CO(2) with preferential excitation in the asymmetric stretch but with less overall vibrational excitation than CO(2) from the first pathway and more vibrational excitation than CO(2) from the second. This third pathway occurs via the complete dehydrogenation of CH(3)OH and subsequent oxidation of nascent CO adsorbed to Pt in a bridged state bound through both ends of the molecule. CO(2) production via this pathway is favored at intermediate surface temperatures and oxygen coverage, conditions which favor overall oxidation to form CO(2).

Preparation and Characterization of DMFC Electrodes and MEAs

A stencil method, that utilizes a dried powder made of the catalyst and the Nafion ionomer phase, is used to make catalyst layers and membrane electrode assemblies (MEAs). The influence of different hot-pressing conditions on the DMFC performance and various properties of the MEAs, in particularly on the properties of the anode, are investigated and compared to MEAs made by the conventional spray method. The highest DMFC performance is achieved using MEAs made by stenciling. It is also found that the membrane resistance (Rm), the resistance to proton transport within the catalyst layer (Rp) and the charge transfer resistance (Rct) towards the CH3OH oxidation reaction are lower for stenciled vs. sprayed anodes.

Nature of the Oxidizing Species Formed upon UV Photolysis of C-TiO2 Aqueous Suspensions

UV photolysis of aerated aqueous suspensions of C-TiO2 (KRONOS vlp 7000) or TiO2 (KRONOS uvlp 7500, Degussa P25) containing CH3OH produces HCHO and H2O2, and the latter accumulates only in the case of C-TiO2. The UV photolysis of C-TiO2 in aerated suspensions produces holes, which oxidize CH3OH to •CH2OH leading to the formation of HCHO in the presence of oxygen. H2O2 produced via the oxidation of CH3OH to HCHO and through the reduction of O2 by the conduction band or trapped electrons is adsorbed by all titania. Catalase, which catalyzes CH3OH oxidation by H2O2, substantially increases the rate of HCHO formation only in the case of C-TiO2. This observation indicates that the electrons produced upon UV excitation of C-TiO2 differ from those of unmodified TiO2 with respect to their reactivity toward the photolytically generated H2O2. The holes produced in P25 behave differently from those formed in C-TiO2 and uvlp 7000 with respect to their reaction with added H2O2. This difference is, at least in part, du...