Kinetics Of CO Oxidation Research Articles

Kinetics and constraints of CO oxidation over hexameric copper nanocluster catalyst supported on carboxyl-functionalised MWCNT at high temperatures

Kinetics of CO oxidation over hexameric copper nanoclusters supported on carboxyl-functionalised multi-walled carbon nanotubes (Cu6/MWCNTCOOH) was studied between 400 and 475 °C. An excessive amount of O2 in the feed gas hindered access of CO molecules to the active sites (maximum CO conversion ~29% in O2-rich environment (CO:O2 = 1:10 v/v) cf. ~89% in O2-lean environment (CO:O2 = 1.0:1.2 v/v) at GHSV of 3,000–6,000 mL/(gcat·h)). The reaction temperature range was constrained by catalyst deactivation due to the formation of CuCO3 below the lower limit, and combustion of the MWCNT support in the oxidative environment above the upper limit. A kinetic model was developed based on assumptions that the reaction was CO-adsorption limited and followed the Langmuir–Hinshelwood mechanism for CO concentrations ≤14 vol% in the feed gas. The activation energy (Ea) was determined to be 54.3 kJ/mol in the temperature range studied.

Thermal decomposition of mixed calcium oxalate hydrates - kinetic deconvolution of complex heterogeneous processes.

Differential scanning calorimetry (DSC), thermogravimetry (TG) and in situ XRD were used to study dehydration and consequent decomposition reactions of mixed calcium oxalate hydrates. As the complex dehydration kinetics exhibited certain trends with respect to the applied heating rate, the modified multivariate kinetic analysis approach (based on averaged curve-by-curve optimizations) was employed to obtain a full kinetic description of the data. The Šesták-Berggren equation was used to model the two consequent dehydration reactions. Good agreement was found between the kinetic parameters calculated from the DSC and TG data - approximate values of activation energies were 68 and 81 kJ mol-1 for the trihydrate → monohydrate and monohydrate → anhydride transformations, respectively. A procedural methodology was developed to predict both dehydration kinetics and hydrate content ratios. For the calcium oxalate decomposition the TG technique provided very precise single-step prediction with an activation energy of 180 kJ mol-1. DSC on the other hand provided complex information on joint decomposition and carbon monoxide oxidation reactions - the proposed reaction mechanism includes completion of two reaction paths composed of consequent chemical reactions. A mechanistic view of the complex reaction path is discussed in terms of the diffusion barrier limiting the oxidation step.

Inverse temperature hysteresis and self-sustained oscillations in CO oxidation over Pd at elevated pressures of reaction mixture: Experiment and mathematical modeling

Studying the kinetics of CO oxidation over Pd foil at elevated CO and O2 pressures, we observed an inverse hysteresis: CO conversion was much lower under sample cooling than under foil heating. It was established that under heating the oxidation of metallic palladium to bulk palladium oxide occurred through formation of the palladium surface oxide. Under cooling the bulk oxide reduced directly to metallic species, and in this case some self-sustained oscillations of reaction rate were observed. The catalytic scheme including main various oxygen states of the palladium surface and bulk with transitions between them under reaction conditions in heating/cooling catalytic cycle was proposed. On the base of this scheme the kinetic model of CO oxidation reaction was developed. Both most important mechanisms: Langmuir- Hinshelwood and Mars-van Krevelen, were involved for description of the observed kinetic nonlinear phenomena. The performed simulations demonstrated the capability of this model to describe well the inverse hysteresis of CO oxidation rate together with its oscillatory behavior at constant temperature within the hysteresis loop.

A versatile approach for quantification of surface site fractions using reaction kinetics: The case of CO oxidation on supported Ir single atoms and nanoparticles

Supported metal single-atom catalysts have shown unique activity and selectivity for several reactions. Investigating the reaction mechanism on single-atom catalysts and unambiguous assignment of the activity and selectivity requires catalysts with exclusively single atoms. However, it is challenging to prepare pure single-atom catalysts with conventional impregnation methods, which typically result in a mixture of single atoms and nanoparticles. Here, we show that owing to different reaction mechanisms on single atoms and nanoparticles, reaction kinetics can serve as a surface sensitive characterization technique for quantifying their surface site fractions. As a case study, we use CO oxidation kinetics on Ir/MgAl2O4 to quantify the surface site fractions of single atoms and nanoparticles and the results are consistent with aberration-corrected scanning transmission electron microscopy, X-ray absorption fine structure and infrared spectroscopies. Additionally, by carefully choosing the reaction conditions, the activity of single atoms (or nanoparticles) can be made dominant, enabling detection of a small fraction, or allowing a study of their reaction mechanism on a catalyst containing a mixture of single atoms and nanoparticles. These results are general and could be applied to other systems where two types of sites have different reaction mechanisms.

Catalytic Enhancement of CO Oxidation on LaFeO3 Regulated by Ruddlesden-Popper Stacking Faults.

The influence of planar defects, in the form of stacking faults, within perovskite oxides on catalytic activity has received little attention because controlling stacking-fault densities presents a major synthetic challenge. Furthermore, stacking faults in ceramics are not thought to appreciably impact surface chemistry, which partly explains why their direct effect on catalysis is generally ignored. Here, we show that Ruddlesden-Popper (RP) stacking faults in otherwise stoichiometric LaFeO3 can be broadly controlled by modulating the ceramic synthesis route. Electronic structure calculations along with electron microscopy and spectroscopy show that energetically favorable RP faults occur both near the surface and in bunches and enhance CO oxidation kinetics. Density functional theory (DFT) + U shows that subsurface RP faults strengthen the adsorption and co-adsorption of CO, O, and O2, which could lower the apparent activation energy of CO oxidation on faulted catalysts compared to that on their pristine counterparts. Our work suggests that planar defects should be considered a new and useful feature in hierarchal nanoscale design of future catalysts.

Bimetallic palladium-supported halloysite nanotubes for low temperature CO oxidation: Experimental and DFT insights

The design and fabrication of novel metal-supported catalysts for energy conversion and heterogeneous catalysis is a pivotal theme. Herein, we present the synthesis of bimetallic palladium nanoalloys supported on halloysite nanotubes, PdM@HNTs, where M = Co, Cu, and Ni and their catalytic performance towards CO oxidation. The synthesis procedure involves simple co-reduction of the metals precursors using NaBH4 on halloysite nanotubes support. The synthesized catalysts retain the tubular morphology of halloysite support with surface area of 90–107 m2 g−1. Transmission electron microscopy (TEM) revealed smaller size for bimetallic nanoparticles (6–8 nm) compared to Pd (14 nm). PdNi displayed the highest catalytic activity towards CO oxidation. Moreover, PdCo and PdNi demonstrated enhanced CO oxidation kinetics compared to PdCu and PdNi as revealed from the calculated activation energies. DFT calculations revealed that the order of catalytic activity is PdNi > PdCo > PdCu > Pd which is in agreement with the experimental results and that the adsorption energy of CO2 on the different catalysts has no apparent role in the whole activity of the catalyst.In conclusion, PdM@HNTs catalysts expressed homogeneous distribution for metallic nanoparticles as well as high dispersion and expressed promising potential to be applied in real flare control processes.

Kinetics of CO oxidation and redox cycling of Sr2Fe1.5Mo0.5O6-δ electrode for symmetrical solid state electrochemical devices

Resultsof the redox cycling of the Sr2Fe1.5Mo0.5O6-δ electrode in contact with the LaGaO3-based electrolyte at 800°С in air - CO/CO2 - Ar/H2 are presented for the first time. The electrochemical impedance method was used to demonstrate that the electrode polarization resistance at fast gas cycling remained almost unchanged. In the long-term cycling from oxidizing to reducing atmospheres (and vice versa) the polarization resistance equilibrated rapidly (slowly). The kinetics of the CO oxidation in CO/CO2 gas mixtures at 800°С (pO2 ≈ 10−16 – 10−19 atm) near the equilibrium electrode potential was studied. By means of a complex approach to the impedance spectra analysis using the distribution of relaxation times and non-linear least squares methods, it was determined that the CO oxidation is limited by three steps: CO adsorption (CO2 desorption) at the electrode surface, oxygen hetero-exchange and the oxygen ion transport in the electrode bulk. We assume that the charge transfer and the gas diffusion do not limit the CO oxidation reaction on the Sr2Fe1.5Mo0.5O6-δ electrode.

Role of CO2 methanation into the kinetics of preferential CO oxidation on Cu/Co3O4

In the present study, cobalt oxide (Co3O4) and Cu substituted Co3O4 were synthesized using sonochemical method. The role of Cu substitution was studied for CO oxidation in absence of H2 as well as in H2 rich conditions (PrOx). The synthesized catalysts were characterized by XRD, XPS, TEM and BET. The role of side reactions such as H2 oxidation and CO2 methanation in inhibiting the CO oxidation reaction were discussed. H2 – TPR and in situ FTIR were conducted to understand the reducible nature of the support and reaction mechanism. The intermediate species such as carbonates, bicarbonates, formates play an important role for CO oxidation under H2 rich conditions. Further, the utilization of atomic hydrogen by surface CO2 species, enhanced the methane formation. A detailed reaction mechanism was proposed for both CO oxidation and PrOx conditions with the insights obtained from in situ FTIR. 3% Cu/Co3O4 showed high stability for CO oxidation under hydrogen rich conditions for 50 h at 170 °C as well as in methanation prone region at 200 °C.

Reaction mechanism and kinetics of CO oxidation over a CuO/Ce0.75Zr0.25O2-δ catalyst

The CuO/Ce0.75Zr0.25O2-δ and Ce0.75Zr0.25Oδ catalysts were prepared by the sol-gel method, and Cu0.07Ce0.75Zr0.25O2-δ was obtained by treating CuO/Ce0.75Zr0.25O2-δ with nitric acid to remove the well-dispersed CuO on the surface. Various characterizations were used to reveal the different active sites, such as surface-dispersed CuO and Cu-Ce-Zr-Oδ solid solutions in CuO/Ce0.75Zr0.25O2-δ, Cu-Ce-Zr-Oδ solid solutions in Cu0.07Ce0.75Zr0.25O2-δ and Ce-Zr-Oδ solid solutions in Ce0.75Zr0.25Oδ. The Raman and O2-TPD results showed that the concentration of oxygen vacancies in Cu-Ce-Zr-Oδ solid solutions was higher than that in Ce-Zr-Oδ solid solutions. CO oxidation testing suggested that the catalytic activity decreases in the order of CuO/Ce0.75Zr0.25O2-δ > Cu0.07Ce0.75Zr0.25O2-δ > Ce0.75Zr0.25Oδ. Combined with the in situ diffuse-reflectance Fourier transform (in situ DRIFT) results, the reaction sensitivity followed the order of CO linear chemisorption onto dispersed CuOx species (Mars-van Krevelen mechanism) > carbonate species onto a Cu-Ce-Zr-Oδ solid solution (Langmuir-Hinshelwood mechanism) > carbonate species onto a Ce-Zr-Oδ solid solution (Langmuir-Hinshelwood mechanism). Kinetic studies suggested that the power-law rate expressions and apparent activation energies were r = 6.02 × 10−7×PCO0.68PO20.03 (53 ± 3 kJ/mol) for CuO/Ce0.75Zr0.25O2-δ, r = 5.86 × 10−7×PCO0.8PO20.07 (105 ± 5 kJ/mol) for Cu0.07Ce0.75Zr0.25O2-δ and r = 5.7 × 10−7×PCO0.75PO20.12 (115 ± 6 kJ/mol) for Ce0.75Zr0.25Oδ. The Mars-van Krevelen mechanism should be the crucial reaction pathway over CuO/Ce0.75Zr0.25O2-δ in CO interfacial reactions, although the Langmuir-Hinshelwood mechanism cannot be ignored, and the Langmuir-Hinshelwood mechanism mainly occurred over the Cu0.07Ce0.75Zr0.25O2-δ and Ce0.75Zr0.25Oδ catalysts, where the contribution from the Mars-van Krevelen mechanism was negligible due to the absence of surface CuOx species.

Computation-Guided Development of Platinum Alloy Catalyst for Carbon Monoxide Preferential Oxidation

Carbon monoxide preferential oxidation (PROX) in an H2-rich stream represents one promising H2 purification technology but requires the development of active and selective catalysts to make the technology viable. We conducted density functional theory simulations of CO PROX catalysis on model Pt alloy systems to establish correlations between the catalyst parameters and the catalytic properties, which validated EA,COOR and EA,HOR as descriptors for CO oxidation and H2 oxidation kinetics, ΔEA as a descriptor for CO PROX selectivity, and ed as a catalyst parameter descriptor for the activation energy barriers. We discovered an interesting compromising relationship between the CO PROX activity and selectivity properties. Pt-Ni and Pt-Mn nanoparticle catalysts were selected for synthesis on the basis of the computational data and tested for their properties, which matched well with the DFT calculations and verified the effectiveness of the computational findings. The use of computation-guided methods and the ...

Interactions between aftertreatment systems architecture and combustion of oxygenated fuels for improved low temperature catalysts activity

Diesel engine vehicles, despite their good fuel economy and reduced CO2, are receiving significant attention and negative publicity in recent years due to their difficulties in achieving the emissions regulations. This has widely been linked to undesirable environmental impact and health effects.The lower exhaust gas temperatures associated with modern and more efficient hybrid powertrain and diesel engines makes current technology catalytic aftertreatment systems less efficient under range of vehicle operating conditions. This study, demonstrates how changes in the commonly used aftertreatment system architecture and changes in fuel composition in this case through the addition of oxygenated fuels (i.e. butanol) in diesel fuel can provide meaningful low temperature catalyst activity improvements.The catalyst oxidation kinetics of CO and HC species were improved (reduced the light-off temperature by around 20 °C) when a diesel particulate filter (DPF) was placed upstream of the DOC, while the combination of DPF and combustion of oxygenated fuel in diesel led to up to 80 °C improvement in catalyst activity. The prevention of soot reaching the DOC active sites increases the rate of reactions and the species accessibility to the active sites of the catalyst, and thereby the oxidation of emissions (CO, HC, and NO) can occur at lower catalyst temperatures. The combustion of diesel-butanol blend further improved the DOC low temperature activity. The major contributors to the improved catalyst light-off, are the reduced level of soot and hydrocarbon emissions as well as the higher reactivity of the hydrocarbons species emitted under butanol blend combustion.

The Mechanism of Low-Temperature Oxidation of Carbon Monoxide by Oxygen over the PdCl₂-CuCl₂/γ-Al₂O₃ Nanocatalyst.

The state of palladium and copper on the surface of the PdCl2–CuCl2/γ-Al2O3 nanocatalyst for the low-temperature oxidation of CO by molecular oxygen was studied by various spectroscopic techniques. Using X-ray absorption spectroscopy (XAS), powder X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), freshly prepared samples of the catalyst were studied. The same samples were also evaluated after interaction with CO, O2, and H2O vapor in various combinations. It was shown that copper exists in the form of Cu2Cl(OH)3 (paratacamite) nanophase on the surface of the catalyst. No palladium-containing crystalline phases were identified. Palladium coordination initially is comprised of four chlorine atoms. It was shown by XAS that this catalyst is not capable of oxidizing CO at room temperature in the absence of H2O and O2 over 12 h. Copper(II) and palladium(II) are reduced to Cu(I) and Pd(I,0) species, respectively, in the presence of CO and H2O vapor (without O2). It was found by DRIFTS that both linear (2114 cm−1, 1990 cm−1) and bridging (1928 cm−1) forms of coordinated CO were formed upon adsorption onto the catalyst surface. Moreover, the formation of CO2 was detected upon the interaction of the coordinated CO with oxygen. The kinetics of CO oxidation was studied at 18–38 °C at an atmospheric pressure for CO, O2, N2, and H2O (gas) mixtures in a flow reactor (steady state conditions).

Kinetics of CO Oxidation over Unloaded and Pd-Loaded α-Fe2O3 Spherical Submicron Powder Catalysts: Photoacoustic Investigations at Low Pressure

In this study, α-Fe2O3 spherical particles with an average diameter of approximately 200 nm were synthesized by a solvothermal method for use as both a catalyst and medium for a Pd catalyst. The kinetics of CO oxidation over powders of α-Fe2O3 spherical particles and 14 wt % Pd/α-Fe2O3 spherical particles were measured in a static reactor by using a CO2 laser-based photoacoustic technique. The total pressure was fixed at 40 Torr for the CO/O2/N2 mixture for temperatures in the range of 225–350 °C. The variation in the CO2 photoacoustic signal with the CO2 concentration during CO oxidation was recorded as a function of time, and the CO2 photoacoustic data at the early reaction stage was used to estimate the rates of CO2 formation. Based on plots of ln(rate) vs. 1/T, apparent activation energies were calculated as 13.4 kcal/mol for the α-Fe2O3 submicron powder and 13.2 kcal/mol for the 14 wt % Pd/α-Fe2O3 submicron powder. Reaction orders with respect to CO and O2 were determined from the rates measured at various partial pressures of CO and O2 at 350 °C. The zero-order of the reaction with respect to Po2 was observed for CO oxidation over α-Fe2O3 submicron powder, while 0.48 order to Po2 was observed for CO oxidation over Pd/α-Fe2O3 submicron powder. The partial orders with respect to PCO were determined as 0.58 and 0.54 for the α-Fe2O3, and the Pd/α-Fe2O3 submicron powders, respectively. The kinetic results obtained from both catalysts were compared with those for the α-Fe2O3 fine powder catalysts and were used to understand the reaction mechanism.

CO Oxidation Kinetics over Au/TiO2 and Au/Al2O3 Catalysts: Evidence for a Common Water-Assisted Mechanism.

The mechanism of CO oxidation over supported gold catalysts has long been debated, with two prevailing mechanisms dominating the discussion: a water-assisted mechanism and a mechanism involving O-defect sites. In this study, we directly address this debate through a kinetic and mechanistic investigation of the role of water in CO oxidation over Au/TiO2 and Au/Al2O3 catalysts; the results clearly indicate a common water-assisted mechanism to be at work. Water adsorption isotherms were determined with infrared spectroscopy; the extracted equilibrium constant was essentially the same for both catalysts. Added water decreases CO adsorption on Au/TiO2, likely by blocking CO binding sites at the metal-support interface. Reaction kinetics (CO, O2, and H2O reaction orders) were essentially the same for both catalysts, as were measured O-H(D) kinetic isotope effects. These data indicate that the two catalysts operate by essentially the same mechanism under the conditions of these experiments (ambient temperature, significant amounts of water available). A reaction mechanism incorporating the kinetic and thermodynamic data and accounting for different CO and O2/COOH binding sites is proposed. The mechanism and kinetic data are treated with an active site (Michaelis-Menten) approach. This indicated that water adsorption does not significantly affect reaction rate constants, only the number of active sites available at a given water pressure. Extracted water and O2 binding constants are similar on both catalysts and consistent with previous DFT calculations. Water adsorption constants are also similar to independently determined equilibrium constants measured by IR spectroscopy. The likely roles of water, surface carbonates, and oxygen vacancies at the metal-support interface are discussed. The results definitively show that, at least in the presence of added water, O vacancies cannot play an important role in the room-temperature catalysis, and that the water-assisted mechanism is far more consistent with the preponderance of the kinetic data.

Propene induced reversible deactivation effects in diesel oxidation catalysts

By applying different transient test protocols in a lab reactor, it is demonstrated that in the presence of C3H6 a Pt/Pd based oxidation catalyst experiences a persistent deactivation that can be attributed to the accumulation of propene partial oxidation products on the catalyst surface. The deactivation can be reversed by treating the catalyst at higher temperature in a hydrocarbon free atmosphere. The three most important scenarios giving rise to the activation/deactivation phenomenon are:(1) Consecutive heat-up/cool-down cycles: If several consecutive heat-up/cool-down cycles are performed with a catalyst pretreated in a propene free oxidative atmosphere, a lower ignition temperature is observed during the first heating ramp than during the following cycles. The effect can be explained by a reversible blocking of active sites by hydrocarbon (HC) intermediates, which are formed during the ignition branch, then entirely are removed after the HC ignition is completed and finally are formed again during the extinction branch, providing a deactivated state of the catalyst for the following ignition. The deactivation can be completely reversed either by a conditioning in an oxidizing HC free gas mixture at temperatures above 110°C or a conditioning in N2 above 140°C. The deactivation effect is more pronounced under conditions that lead to a low light-off temperature and completely disappears at conditions leading to higher light-off temperatures, i.e. high CO concentrations or high space velocities.(2) Light-off tests with varying temperature ramp rate: For faster ramp rates, CO/propene ignition is observed at lower inlet temperatures. This is the opposite behavior than would be expected based on thermal considerations and can be explained by a higher accumulation of HC intermediates during the slower ramp.(3) Transient observation of the deactivation effect: If an initially clean catalyst is operated at a constant temperature in the light-off range, a transient decrease in CO/HC conversion is observed that can be attributed to the gradual build-up of the blocking HC intermediates.A kinetic model is presented which considers not only the standard CO and hydrocarbon oxidation kinetics, but also the formation of site blocking intermediates by partial oxidation of propene and the removal of these blocking intermediates either by total oxidation with O2 or by thermal desorption. The model nearly quantitatively reproduces the experimental results of the different test protocols.

Observation of temperature-dependent kinetics for catalytic CO oxidation over TiO2-supported Pt catalysts

TiO2-supported Pt catalysts were prepared for the study of CO oxidation kinetics at reaction conditions of pressures (1–100Torr) and temperatures (300–500K). We find two distinct temperature ranges with different reaction kinetics distinguished by an abrupt slope change at around 380K in the Arrhenius plot only with the excess O2, not with the stoichiometric O2/CO ratio. We propose that Pt oxides are formed during the catalytic reactions with increasing temperatures under the oxidizing condition and the origin of the slope change is due to the changes in the reaction pathways of CO oxidation due to the Pt oxide formation.

Spectroscopic and kinetic insights of Pt-dispersion over microwave-synthesized GO-supported Pt-TiO2 for CO oxidation

This study explores the effect of Pt and TiO2 dispersion on the catalytic activity and analyzes the kinetics of CO oxidation over a novel catalyst consisting of ultrafine Pt-particles decorated on GO-supported TiO2. Its catalytic activity is compared with catalysts synthesized by decorating Pt nanoparticles on (i) TiO2 (Aeroxide, P25), and TiO2 prepared by using (ii) sol-gel (TiO2-SG) and (iii) microwave techniques (TiO2-MW). A 99.9% conversion of CO to CO2 is observed at 150°C on Pt-TiO2-GO, while it occurs at significantly higher temperatures over other catalysts. Detailed characterization of the catalysts using XRD, TEM, TGA, ICP-MS and BET suggests that this enhanced catalytic activity is because of the uniform dispersion of Pt-TiO2 nanoparticles on the high surface area GO sheets. A combination of DRIFTS and CO-TPD is used to develop a catalytic reaction pathway and is supported by a kinetic model. This study establishes that ensuring a uniform support and noble metal dispersion can be used to develop highly active catalysts.

Rapid microwave assisted sol-gel synthesis of CeO2 and CexSm1-xO2 nanoparticle catalysts for CO oxidation

CeO2 and CexSm1-xO2 nanoparticle mixed oxides have been synthesized by microwave assisted sol-gel (MW sol-gel) and conventional sol-gel synthesis carried out at 60°C (typical sol-gel) and 100°C (approaching the MW temperature). Different characterization techniques, namely, XRD, BET, Raman, SEM, FTIR, TEM, XPS, H2-TPR, CO2-TPD, and XPS have been employed to understand the process-structure-properties relationship of the catalysts. The CO oxidation performance has been determined both in the absence and in the presence of H2 in the feed gas stream. Microwave heating yields a more thermally stable precursor material, which preserves 75% of its mass up to 600°C, attributable to the different chemical nature of the precursor, compared to the typical sol-gel material with the same composition. Varying the synthesis method has no profound effect on the surface area of the materials, which is in the range 4–35m2/g. Conventional sol-gel synthesis performed at 60 and 100°C yields CeO2 particles with a crystallite size of 29nm and 24nm compared to 21–27nm for MW sol-gel synthesis (at different power values). The MW sol-gel CexSm1-xO2 catalysts exhibit a smaller crystallite size (12–18nm). The pure ceria nanoparticles were shown to have a stoichiometry of approximately CeO1.95. The presence of Ce3+ and Sm3+ in the mixed oxide particles facilitates the presence of oxygen vacant sites, confirmed by Raman. Oxygen mobile species have been traced using H2-TPR studies and a compressive lattice strain in the 0.45–1.9% range of the cubic CexSm1-xO2 lattice were found to be strongly correlated with the CO oxidation performance in the presence and absence of H2 in the oxidation feed stream. MW sol-gel synthesis led to more active CeO2 and Ce0.5Sm0.5O2 catalysts, demonstrated by T50 (temperature where 50% CO conversion is achieved), being reduced by 131°C and 47°C, respectively, compared to typical sol-gel catalysts. Conventional synthesis performed at 100°C leads to a CeO2 catalyst of initially higher activity at a certain temperature window (220–420°C), though with a slower increase of XCO as a function of temperature compared to the MW synthesized catalyst. MW sol-gel synthesized Ce0.8Sm0.2O2 exhibited a high performance (∼90%) for CO oxidation over a period of more than 20h in stream. In addition the effect of reaction temperature and contact time (W/F) on the activity of the CeO2-based materials for CO oxidation kinetics were investigated. The activation energy of the reaction was found to be in the range 36–43kJ/mole depending on the catalyst composition.

Research Update: Ionotronics for long-term data storage devices

Data storage materials suffer from limited lifetime. Thus, there is a necessity for new data storage systems for archiving purposes. Systems based on chemical reactions such as the oxidation of corrosion-resistant metals are attractive candidates because they offer in principle very long-term stability. We have therefore investigated oxidation kinetics of Cr, Al, Ti, V, Zn, Ni, and Co. Here we present the results and discuss in detail fundamental issues of thin film oxidation, the limits of diffusion controlled oxidation, and possible ways to increase the oxidation rate constants. Co showed the highest oxidation rate constant (kp = 2.5 × 10−9 cm2/s at 540 °C) and is therefore considered as a promising candidate for data archiving.

New insight of the Mars-van Krevelen mechanism of the CO oxidation by gold catalyst on the ZnO(1 0 1) surface

We performed theoretical studies of the Mars-van Krevelen (M-vK) mechanism of the CO oxidation by gold catalyst supported on ZnO(101) surface. The activities of the lattice oxygen at the Au/ZnO interface are related with its coordination and orientation. The 3-coordinated O3c″ shows the highest activity because of the feasible achievement of the analogous single-atom catalytic active site of Au/CeO2. However, the CO2 desorption does not determine the kinetics of CO oxidation for Au/ZnO that is different from the case of Au/CeO2. Thus, the M-vK reactivity of CO oxidation cannot be measured by the vacancy formation energy of the lattice oxygen of Au/ZnO. Rather, the high reactivity is found closely related with the large interfacial AuAu bond distortion in the transition states, which can be used to depict the M-vK reactivity of the CO oxidation on Au/ZnO.