Rate Of CO Oxidation Research Articles

Activation of a Au/CeO2 catalyst for the CO oxidation reaction by surface oxygen removal/oxygen vacancy formation

Applying quantitative temporal analysis of products (TAP) techniques, we demonstrate that after calcination, a Au/CeO2 catalyst is only slightly active for CO oxidation. The activity is significantly increased on removal of about 7% of the surface oxygen, whereas overreduction leads to initially lower activity. Reductive activation can occur either during reaction, in the (oxidative) reaction gas, or by controlled prereduction. This is the first experimental verification of a CO oxidation rate enhancement by oxygen surface vacancies on a realistic oxide-supported Au catalyst. Consequences for the reaction mechanism are discussed.

Indirect oxidation of Co(II) in the presence of the marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1.

Cobalt(II) oxidation in aquatic environments has been shown to be linked to Mn(II) oxidation, a process primarily mediated by bacteria. This work examines the oxidation of Co(II) by the spore-forming marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1, which enzymatically catalyzes the formation of reactive nanoparticulate Mn(IV) oxides. Preparations of these spores were incubated with radiotracers and various amounts of Co(II) and Mn(II), and the rates of Mn(II) and Co(II) oxidation were measured. Inhibition of Mn(II) oxidation by Co(II) and inhibition of Co(II) oxidation by Mn(II) were both found to be competitive. However, from both radiotracer experiments and X-ray spectroscopic measurements, no Co(II) oxidation occurred in the complete absence of Mn(II), suggesting that the Co(II) oxidation observed in these cultures is indirect and that a previous report of enzymatic Co(II) oxidation may have been due to very low levels of contaminating Mn. Our results indicate that the mechanism by which SG-1 oxidizes Co(II) is through the production of the reactive nanoparticulate Mn oxide.

Highly active surfaces for CO oxidation on Rh, Pd, and Pt

Studies show that the rate of CO oxidation on Pt-group metals at temperatures between 450 and 600 K and pressures between 1 and 300 Torr increases markedly with an increase in the O 2/CO ratio above 0.5. The catalytic surfaces, formed at discrete O 2/CO ratios >0.5, exhibit rates 2–3 orders of magnitude greater than those rates observed for stoichiometric reaction conditions and similar reactant pressures or previously in ultrahigh vacuum studies at any reactant conditions and extrapolate to the collision limit of CO in the absence of mass transfer limitations. The O 2/CO ratios required to achieve these so-called “hyperactive” states (where the reaction probabilities of CO are thought to approach unity) for Rh, Pd, and Pt relate directly to the adsorption energies of oxygen, the heats of formation of the bulk oxides, and the metal particle sizes. Auger spectroscopy and X-ray photoemission spectroscopy reveal that the hyperactive surfaces consist of approximate 1 ML of surface oxygen. In situ polarization modulation reflectance absorption infrared spectroscopy measurements coupled with no detectable adsorbed CO. In contrast, under stoichiometric O 2/CO conditions and similar temperatures and pressures, Rh, Pd, and Pt are essentially saturated with chemisorbed CO and exhibit far less activity for CO oxidation.

Cluster Chemistry: Size-Dependent Reactivity Induced by Reverse Spill-Over

In the present work, the CO oxidation rate on size-selected Pd clusters supported on thin MgO films is investigated in pulsed molecular beam experiments. By varying the cluster coverage independent of the cluster size, we were able to change the ratio of direct and diffusion flux (reverse spill-over) of CO onto the cluster catalyst and thus probe the influence of reverse spill-over on the reaction rate for different cluster sizes (Pd(8) and Pd(30)). The experimental results show that the change in reaction rate as a function of cluster coverage is different for Pd(8) and Pd(30). In order to explain these findings, the CO flux onto the clusters is modeled utilizing the collection zone model for the given experimental conditions. The results indicate that, for small clusters (Pd(8)), the reaction probability of an impinging CO molecule is independent of whether it is supplied by diffusion or direct flux. By contrast, for larger clusters (Pd(30)) a reduced reaction probability is found for CO supplied by reverse spill-over compared to CO supplied by direct flux.

Inverse gas chromatographic investigation of the active sites related to CO adsorption over Rh/SiO 2 catalysts in excess of hydrogen

In the present work, the novel methodology of reversed-flow gas chromatography (RF-GC) is extended in a topic of contemporary scientific and technological interest, such as the effect of hydrogen in the “ topography” of the active sites related to CO adsorption. This study concerns CO adsorption on a silica-supported Rh catalyst, at 90 °C. The topography of the catalyst in the absence of hydrogen consists of both randomly and islands of CO bound over chemisorbed CO molecules. In contrast, under H 2-rich conditions, the observed topography is almost entirely patchwise ascribed to long-range lateral attractions between adsorbate molecules. In excess of hydrogen, CO adsorption is shifted at higher lateral attractions values which correspond to weaker adsorbate–adsorbent interactions and lower surface coverage. This provides an indication of a H 2-induced desorption, which can be attributed to the formation of an H–CO complex desorbing from the catalyst surface below the temperature required for CO desorption, in the absence of H 2, and it may explain the well-known enhancement of the rate of selective CO oxidation in excess of hydrogen by H 2.

CO oxidation over structured carriers: A comparison of ceramic foams, honeycombs and beads

This work aims an experimental comparison of different packings on the basis of their pressure drop, mass and heat transfer properties. Ceramic foams, beads and a honeycomb monolith were used as carriers in the oxidation of carbon monoxide. The carriers were coated with active Pt/SnO 2. The CO oxidation rate was measured in the regime of external diffusion control at superficial gas velocities between 1 and 10 m/s. The volumetric rate coefficients and the pressure drop of packings with similar geometric surface area decreased in the sequence particles > foams > honeycomb. The magnitude of the temperature gradient along the catalytic bed decreased as going from honeycomb over larger particles to foams and small particles. Foams were superior over particle beds from the viewpoint of combined high mass transfer and low-pressure drop. The main advantage of foams as compared to honeycomb resided in the radial mixing enabling a better heat transfer to the reactor walls.

Effects of Pd particle size on the rates of oxygen back-spillover and CO oxidation under dynamic oxygen storage and release measurements over Pd/CeO2 catalysts

A kinetic mathematical model has been applied to investigate for the first time the effects of Pd particle size on the rates of oxygen back-spillover and CO oxidation during Oxygen Storage Capacity (OSC) measurements under dynamic conditions over Pd/CeO2 catalysts in the 500–700 °C range. The dependence of the intrinsic rate constant k1 of the CO oxidation reaction on PdO, and that of k 2 app of the oxygen back-spillover from ceria to Pd/PdO on the palladium particle size was estimated by performing curve-fitting of the experimental CO and CO2 pulse transient responses obtained. Activation energies of 8.0, 9.5 and 21.1 kJ/mol were calculated for the Eley–Rideal step of CO oxidation for the 1.3, 1.8 and 16.4 nm Pd particles, respectively, supported on CeO2. The transient rates of CO oxidation and oxygen back-spillover were found to decrease with increasing Pd particle size.

CO Oxidation Studied Using ‘Fast’ XPS and a Molecular Beam Reactor

We have combined the use of a molecular beam reactor with ‘fast’ XPS in order to correlate changes in the rate of CO oxidation with the coverages of the adsorbates and intermediates on the surface. In the reactor CO oxidation exhibits an isothermal ‘light-off’ phenomenon in which the rate autocatalytically increases with time. This is due to the desorption of CO which releases extra sites for O2 dissociation which, in turn, removes more CO, and hence the self-acceleration. In effect the reaction can be written as 2COa + O2g + 2S → 2CO2g + 4S, the acceleration coming from the release of extra adsorption sites, S, which are involved in the reaction itself. ‘Fast XPS’, carried out in-situ during the course of the reaction, shows domination of the surface by COa below 390 K and by Oa above that temperature, with a rapid change in surface coverage over a very narrow temperature window. This is an advance on earlier work, since our measurements are made in a single, continuous experiment, due to the high brightness of the synchrotron source. This also allows the data to be obtained at high energy resolution, in the presence of both gases, and without contamination. On high surface area samples this acceleration is further reinforced due to a rapid temperature increase because of the highly exothermic nature of the overall reaction.

High rates of CO and hydrocarbon oxidation and NO reduction by CO over Ti0.99Pd0.01O1.99

This study aims at synthesizing a new by substituting 1atom% Pd2+ in ionic state in TiO2 in the form of Ti0.99Pd0.01O1.99 with oxide-ion vacancy. The catalyst was synthesized by solution combustion method and was characterized by XRD and XPS. The catalytic activity was investigated by performing CO oxidation, hydrocarbon oxidation and NO reduction. A reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. The model based on CO adsorption on Pd2+ and dissociative chemisorption of O2 in the oxide-ion vacancy for CO oxidation reaction fitted the experimental for CO oxidation. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide-ion vacancy fitted the experimental data. The rate parameters obtained from the model indicated that the reactions were much faster over this catalyst compared to other catalysts reported in the literature. The selectivity of N2, defined as the ratio of the formation of N2 and formation of N2 and N2O, was very high compared to other catalysts and 100% selectivity was reached at temperature of 350°C and above. As the N2O+CO reaction is an intermediate reaction for NO+CO reaction, it was also studied as an isolated reaction and the rate of the isolated reaction was less than that of intermediate reaction.

Anion re-adsorption and displacement at platinum single crystal electrodes in CO-containing solutions

Bulk CO oxidation experiments have been carried out in sulphuric and perchloric acid solutions on Pt(1 1 1) and Pt(1 1 0) electrodes under hanging meniscus rotating disk electrode (HMRDE) configuration. The comparison between the two different electrolytic media reveals an important influence of the anion in the oxidation kinetics. Once the adsorbed CO layer has been oxidized after the ignition peak, anions are re-adsorbed on the electrode surface and the presence of these anions affects the stationary currents measured at positive potentials. In the negative-going sweep, adsorbed anions are displaced from the surface when the CO oxidation rate is lower than the corresponding CO adsorption rate. The charge associated to this displacement has been measured at high scan rates and is in agreement with that expected from the CO displacement experiments performed at low potentials.

In situ ATR-IR study of CO adsorption and oxidation over Pt/Al 2O 3 in gas and aqueous phase: Promotion effects by water and pH

The adsorption and oxidation of carbon monoxide over a Pt/Al 2O 3 catalyst layer deposited on a ZnSe internal reflection element was investigated both in gas phase and water using attenuated total reflection infrared spectroscopy. A preparation method is described that results in a strongly attached layer that is stable for many days in a water flow. Both adsorption and oxidation of CO are largely affected by the presence of liquid water. It influences the metal particle potential as well as the CO molecule directly, which is reflected in large red shifts (45 cm −1) and a fourfold higher intensity when the experiments are carried out in water. Furthermore, the rate of CO oxidation changes significantly when carried out in water compared with gas phase. Finally, with increasing pH, CO stretching frequencies shift to lower wavenumbers, accompanied by a large increase in CO oxidation rate.

Enhancement of selectivity for preferential CO oxidation over SO 2-pretreated Ru/Al 2O 3 catalyst by the presence of sulfur compounds

The preferential CO oxidation on a monolith Ru/Al 2O 3 catalyst pretreated with SO 2 in the reactant gas was investigated in the presence/absence of 0.21–20 ppm sulfur compounds (SO 2 or H 2S). In the presence of 2.1 ppm sulfur compound, CO was preferentially oxidized over the SO 2-pretreated catalyst at 150 °C. On the other hand, in the absence of sulfur compounds, the H 2 oxidation was promoted. By in situ IR measurements, multicarbonyl species and SO 4 2− species were found on Ru in the presence of SO 2. The presence of multicarbonyl species at a high frequency (2154 cm −1) and that of SO 4 2− species on Ru suggested that Ru was oxidized. Since the rate of CO oxidation was low on oxidized Ru, the selectivity for CO oxidation was low over the SO 2-pretreated catalyst in the absence of sulfur compounds. On the other hand, the increase in the selectivity in the presence of sulfur compounds suggested that weakly adsorbed sulfur compounds suppressed the migration of dissociatively adsorbed H atom on Ru or decreased the H atoms next to adsorbed O atom for the H 2 oxidation.

Growth of Rhodospirillum rubrum on synthesis gas: Conversion of CO to H2 and poly‐β‐hydroxyalkanoate

To examine the potential use of synthesis gas as a carbon and energy source in fermentation processes, Rhodospirillum rubrum was cultured on synthesis gas generated from discarded seed corn. The growth rates, growth and poly-beta-hydroxyalkanoates (PHA) yields, and CO oxidation/H(2) evolution rates were evaluated in comparison to the rates observed with an artificial synthesis gas mixture. Depending on the gas conditioning system used, synthesis gas either stimulated or inhibited CO-oxidation rates compared to the observations with the artificial synthesis gas mixture. Inhibitory and stimulatory compounds in synthesis gas could be removed by the addition of activated charcoal, char-tar, or char-ash filters (char, tar, and ash are gasification residues). In batch fermentations, approximately 1.4 mol CO was oxidized per day per g cell protein with the production of 0.75 mol H(2) and 340 mg PHA per day per g cell protein. The PHA produced from R. rubrum grown on synthesis gas was composed of 86% beta-hydroxybutyrate and 14% beta-hydroxyvalerate. Mass transfer of CO into the liquid phase was determined as the rate-limiting step in the fermentation.

Role of Rotational Alignment in Dissociative Chemisorption and Oxidation: O2 on Bare and CO‐Precovered Pd(100)

The adsorption of gas-phase molecules that approach solid surfaces in well-defined quantum states represents a fundamental step for the understanding of heterogeneous chemical reactions and for better control over the growth of selfassembled layers. This objective has been achieved only in a few cases to date (NO, H2, [5] CH4 ). Vibrational excitations and conversion of translational to vibrational energy were thereby found to account for strong enhancements in the dissociation probability. Less attention has been devoted to rotations because they involve less energy, and are therefore important only for physisorption. We show here that rotations as well as the alignment of the rotational axis play a role in the dissociative chemisorption of O2 onto a CO Pd(100) surface. The effect, which arises from the requirements needed to pass through the CO adlayer, leads to different sticking probabilities and average O CO distances, and has possible general applications for controlling reactions and film growth. The alignment of rotational angular momentum can be exploited to investigate stereodynamical effects in molecular adsorption processes. 11–13] Such an alignment, which consists of a propensity of molecules to populate specific helicity states (defined by the quantum number M, the projection of the rotational angular momentum along the propagation direction) can be naturally induced by collisions in seeded supersonic molecular beams (MBs). Diatomic, linear, and linear-like molecules flying in the MB with M= 0 behave as cartwheels when impinging on the surface at normal incidence, while when M is maximum they move in a helicopterlike manner. In particular, it has been shown that for the interaction of C2H4 with an O2-precovered Ag(100) surface, 11] and for C3H6/Ag(100), [12] molecules with helicopterlike motion adsorb more efficiently than cartwheeling ones only at intermediate hydrocarbon coverage. The stereoinsensitivity of the initial sticking probability S0 and its coverage dependence indicated that the effect is due to the collision between trapped molecules, which still remember about their original alignment, and preadsorbed ones, which lie flat on the surface. Rotational alignment was found to be ineffective for more strongly bound systems such as s-bonded C2H4/Pd(100) [13] and O2/Ag(100) (interactions mediated via a chemisorbed molecular precursor). This result was attributed to steering forces turning the incoming molecule into the most favorable configuration and causing it to lose memory of its initial state. For O2 on CO-precovered Pd(100), however, we find that molecules moving as cartwheels stick better than those with helicopter-like motion and that molecular alignment also affects the initial sticking probability. The system under investigation is important because of the effective rate of CO oxidation on Pd(100) when exposed to molecular oxygen. Herein we focus on stereodynamical effects of O2 on the S0 value and on the production of CO2. According to Ref. [14], rotational alignment of O2 is generated by collisions during a supersonic seeded expansion of O2 diluted in lighter and faster carrier atoms, typically He and Ne. Under these conditions most of the oxygen molecules in the MB are relaxed in the ground rotational level (K= 1) and cartwheeling motion prevails on average over helicopterlike motion. In addition, as demonstrated by the use of a high-resolution mechanical velocity selector (consisting of eight rotating slotted disks) the angular momentum of the O2 molecules belonging to the slow tail (ST) of the velocity distribution are nearly randomly oriented (ca. 33% inM= 0), while those in the fast tail (FT) fly mostly with cartwheeling motion (> 80%). In the present experiment (see the Experimental Section and the Supporting Information) the fraction moving as cartwheels are approximately 0.4 and 0.7 for the ST and FT regions, respectively. Figure 1 shows the partial pressure of O2 in the chamber, measured by a quadrupole mass spectrometer (QMS), during exposure of the Pd(100) sample at 394 K to the STor FTof the O2 supersonic MB seeded in He at normal incidence. The sample is initially shielded by an inert cover (flag), so that no direct adsorption occurs. The background pressure typically increases by 2 C 10 10 mbar, mostly because of He, so that adsorption from the background over the time scale of an experiment (< 100 s) is also negligible. When the flag is removed (t1) the beam strikes the reactive surface of the sample. The relative decrease in the QMS signal corresponds to the O2 sticking probability S. [16] The lower traces refer to the interaction with bare Pd(100). No difference is observed between the FT and ST experiments, thus indicating either that steering is efficient in turning the molecule into the most favorable configuration for dissociation or that the interaction [*] Dr. A. Gerbi, Dr. L. Savio, Dr. L. Vattuone Dipartimento di Fisica CNISM Unit) di Genova Universit) di Genova Via Dodecaneso 33, 16146 Genova (Italy) Fax: (+39)010-314-218 E-mail: vattuone@fisica.unige.it Homepage: http://www.fisica.unige.it/~ vattuone

Methanol Dehydrogenation and Oxidation on Pt(111) in Alkaline Solutions

Adsorption, dehydrogenation, and oxidation of methanol on Pt(111) in alkaline solutions has been examined from a fundamental mechanistic perspective, focusing on the role of adsorbate-adsorbate interactions and the effect of defects on reactivity. CO has been confirmed as the main poisoning species, affecting the rate of methanol dehydrogenation primarily through repulsive interactions with methanol dehydrogenation intermediates. At direct methanol fuel cell (DMFC)-relevant potentials, methanol oxidation occurs almost entirely through a CO intermediate, and the rate of CO oxidation is the main limiting factor in methanol oxidation. Small Pt island defects greatly enhance CO oxidation, though they are effective only when the CO coverage is 0.20 ML or higher. Large Pt islands enhance CO oxidation as well, but unlike small Pt islands, they also promote methanol dehydrogenation. Perturbations in electronic structure are responsible for the CO oxidation effect of defects, but the role of large Pt islands in promoting methanol dehydrogenation is primarily explained by surface geometric structure.

Carbon Monoxide Adsorption and Oxidation on Monolayer Films of Cubic Platinum Nanoparticles Investigated by Infrared−Visible Sum Frequency Generation Vibrational Spectroscopy

The adsorption and oxidation of CO on monolayer films of cubic Pt nanoparticles synthesized by a modified solution-phase polyol process were examined by sum frequency generation (SFG) vibrational spectroscopy in total internal reflection (TIR) geometry. Extremely low incident laser power (approximately 5 microJ/pulse of infrared) yields sufficient SFG intensity in TIR geometry and reduces destructive interference. Because TIR-SFG spectroscopy does not require correction for bulk gas absorption, CO spectra can be collected over a wide pressure range (<1 mTorr up to 700 Torr). Poly(vinylpyrrolidone)-capped Pt nanoparticles deposited on single-crystal sapphire were monitored under high-pressure reaction conditions in a combined spectroscopy-catalytic reactor cell. The effect of the capping polymer on the position and intensity of the CO peak was studied before and after low-temperature calcination. The polymer decreased the amount of CO adsorption and caused a slight red-shift of the atop CO band relative to a surface treated in oxygen at 373 K. Oxidation rates were determined by measuring the intensity of the atop CO peak as a function of time in the presence of flowing oxygen. The activation energy (approximately 19.8 kcal/mol) determined from the SFG data is close to that obtained from gas chromatography (GC) measurements of CO oxidation rates at different temperatures. The SFG and GC results are in good agreement with published data for Pt(100) surfaces.

Dynamics of Surface Catalyzed Reactions; the Roles of Surface Defects, Surface Diffusion, and Hot Electrons

The mechanism that controls bond breaking at transition metal surfaces has been studied with sum frequency generation (SFG), scanning tunneling microscopy (STM), and catalytic nanodiodes operating under the high-pressure conditions. The combination of these techniques permits us to understand the role of surface defects, surface diffusion, and hot electrons in dynamics of surface catalyzed reactions. Sum frequency generation vibrational spectroscopy and kinetic measurements were performed under 1.5 Torr of cyclohexene hydrogenation/dehydrogenation in the presence and absence of H(2) and over the temperature range 300-500 K on the Pt(100) and Pt(111) surfaces. The structure specificity of the Pt(100) and Pt(111) surfaces is exhibited by the surface species present during reaction. On Pt(100), pi-allyl c-C6H9, cyclohexyl (C6H11), and 1,4-cyclohexadiene are identified adsorbates, while on the Pt(111) surface, pi-allyl c-C6H9, 1,4-cyclohexadiene, and 1,3-cyclohexadiene are present. A scanning tunneling microscope that can be operated at high pressures and temperatures was used to study the Pt(111) surface during the catalytic hydrogenation/dehydrogenation of cyclohexene and its poisoning with CO. It was found that catalytically active surfaces were always disordered, while ordered surface were always catalytically deactivated. Only in the case of the CO poisoning at 350 K was a surface with a mobile adsorbed monolayer not catalytically active. From these results, a CO-dominated mobile overlayer that prevents reactant adsorption was proposed. By using the catalytic nanodiode, we detected the continuous flow of hot electron currents that is induced by the exothermic catalytic reaction. During the platinum-catalyzed oxidation of carbon monoxide, we monitored the flow of hot electrons over several hours using a metal-semiconductor Schottky diode composed of Pt and TiO2. The thickness of the Pt film used as the catalyst was 5 nm, less than the electron mean free path, resulting in the ballistic transport of hot electrons through the metal. The electron flow was detected as a chemicurrent if the excess electron kinetic energy generated by the exothermic reaction was larger than the effective Schottky barrier formed at the metal-semiconductor interface. The measurement of continuous chemicurrent indicated that chemical energy of exothermic catalytic reaction was directly converted into hot electron flux in the catalytic nanodiode. We found the chemicurrent was well-correlated with the turnover rate of CO oxidation separately measured by gas chromatography.

Efficient CO Oxidation at Low Temperature on Au(111)

The rate of CO oxidation to CO2 depends strongly on the reaction temperature and characteristics of the oxygen overlayer on Au(111). The factors that contribute to the temperature dependence in the oxidation rate are (1) the residence time of CO on the surface, (2) the island size containing Au-O complexes, and (3) the local properties, including the degree of order of the oxygen layer. Three different types of oxygen--defined as chemisorbed oxygen, a surface oxide, and a bulk oxide--are identified and shown to have different reactivity. The relative populations of the various oxygen species depend on the preparation temperature and the oxygen coverage. The highest rate of CO oxidation was observed for an initial oxygen coverage of 0.5 monolayers that was deposited at 200 K where the density of chemisorbed oxygen is maximized. The rate decreases when two-dimensional islands of the surface oxide are populated and further decreases when three-dimensional bulk gold oxide forms. Our results are significant for designing catalytic processes that use Au for CO oxidation, because they suggest that the most efficient oxidation of CO occurs at low temperature--even below room temperature--as long as oxygen could be adsorbed on the surface.

Synthesis, characterization and catalytic properties of CuO nanocrystals with variousshapes

CuO nanocrystals with different shapes, i.e. irregular nanoparticles, nanobeltsand nanoplatelets, have been synthesized by controlling a few critical synthesisparameters to explore their catalytic properties. It was found that the rate ofCO oxidation on the nanoplatelets is over six times higher than that on thenanoparticles and about three times higher than that on the nanobelts at110 °C. Based on combined characterizations, such as BET, XRD, TEM, HRTEM and COtemperature-programmed reduction, the relationship between the catalytic reactivity andthe shape as well as the predominantly exposed crystal planes of the CuO nanocrystals hasbeen discussed.

Energy conversion from catalytic reaction to hot electron current with metal-semiconductor Schottky nanodiodes

Exothermic catalytic reactions induce electronic excitation at the metal surface, leading to the production of energetic hot electrons. We monitored the flow of hot electrons for over several hours using two types of metal-semiconductor Schottky diodes, Pt∕TiO2 or Pt∕GaN, during the platinum catalyzed oxidation of carbon monoxide. The thickness of Pt film used as the catalyst was 5nm, less than the electron mean free path, resulting in the ballistic transport of hot electrons through the metal. The electron flow was detected as a chemicurrent if the excess electron kinetic energy generated by the exothermic reaction was larger than the effective Schottky barrier formed at the metal-semiconductor interface. The measurement of continuous chemicurrent indicated that chemical energy of exothermic catalytic reaction was directly converted into hot electron flux in the catalytic nanodiode. The chemicurrent was well correlated with the turnover rate of CO oxidation separately measured by gas chromatography, suggesting the possibility of application as chemical sensors with high sensitivity.