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• Highly resolved species profiles in a porous catalyst pellet are measured operando. • The boundary layer surrounding the pellet is resolved. • The interaction of catalytic reactions and diffusion is probed experimentally. • Concentration profiles of the pellet in ignited and extinguished state are presented. • Numerical simulations show how distortions of the measurement method can be minimized. In the present work, we report on the direct measurement of spatially resolved concentration profiles inside a single catalyst pellet under reaction conditions using a capillary sampling method. CO oxidation on a platinum-coated, porous alumina cylinder was chosen as test reaction system. CFD simulations were conducted to probe the invasiveness of the method, which turned out to be acceptable for practical application. Spatially resolved CO 2 mole fraction profiles inside the particle are presented for different reaction conditions. Phenomena that result from the interplay between diffusion and reaction such as boundary layers, bifurcation, multiple steady states and kinetic oscillations are also shown. The method might allow the knowledge-based optimization of many industrial fixed-bed processes without requiring major changes to the process layout. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the three-dimensional corneal spatial profiles following small incision lenticule extraction (SMILE) based on corneal asphericity, thickness, and volume. Materials and methods: Eighty-three eyes in 83 patients who underwent SMILE were examined before and 1 and 6 months after surgery. The asphericity of the anterior and posterior corneal surfaces was analyzed. Corneal volume (CV) was measured in corneal regions measuring 3.0 mm, 5.0 mm, and 7.0 mm in diameter. Mean corneal thickness (CT) values were acquired at the apex (0.0 mm) and in four concentric radial zones from the apex (with diameters of 2.0, 4.0, 6.0, and 8.0 mm). Results: The mean anterior Q value increased from − 0.32 preoperatively to 0.67 at 1 month and 0.62 at 6 months postoperatively. The mean posterior Q value decreased from − 0.30 preoperatively to − 0.26 at 1 month and to − 0.25 at 6 months postoperatively. The CV increased by 0.05 ± 0.06 mm3 (1.40%), 0.06 ± 0.11 mm3 (0.83%), and 0.09 ± 0.17 mm3 (0.73%) along the radial zones with respective diameters of 3.0 mm, 5.0 mm, and 7.0 mm. The CT increased by 6.02 ± 6.48 µm (1.36%) at the apex and then decreased with increasing distance from the center, i.e., to 5.52 ± 6.31 µm (1.20%) at 2.0 mm, 4.72 ± 6.55 µm (0.92%) at 4.0 mm, 4.47 ± 7.86 µm (0.75%) at 6.0 mm, and 4.86 ± 10.31 µm (0.70%) at 8.0 mm. No correlations were observed between changes in CV and CT and refractive fluctuation between 1 month and 6 months postoperatively. Conclusions: The corneal profile displayed a less oblate shift on the anterior surface; however, the posterior surface showed a slight backward shift during the postoperative period. The CV and CT steadily increased after surgery and mainly within the operative zones. Refraction remained stable postoperatively and was not affected by the corneal remodeling. [ABSTRACT FROM AUTHOR]

Evidence shows that spatial interventions are successful in typical development. However, the potential of spatial interventions for Down syndrome (DS) populations is hindered by the lack of literature on spatial skills and their development in this group. This paper investigates (a) the profile of strengths and weaknesses in spatial abilities, and (b) the cross-sectional developmental trajectories of spatial skills, in DS relative to typical development. Participants included 33 individuals with DS (58% male; 10–35 years) and 131 typically developing (TD) children (53% male; 4–11 years) who completed spatial tasks assessing two spatial sub-domains. Despite weaknesses in spatial skill, the DS spatial profile aligned closely with that of mental-age matched TD children. Cross-sectional developmental trajectories revealed slower rates of spatial development for those with DS, relative to TD children. Collectively, these results indicate potential for improving spatial skills in DS through intervention. • We created a battery of suitable spatial tasks for use with people with Down syndrome. • We investigated spatial profiles and development in people with Down syndrome. • Across spatial tasks, people with Down syndrome performed broadly similarly to mental-age matched groups. • Spatial development shows qualitative differences in people with Down syndrome. • Spatial skills have potential as an intervention target in people with Down syndrome. [ABSTRACT FROM AUTHOR]

The catalytic partial oxidation (CPOX) of several hydrocarbon mixtures, containing n-dodecane (DD), 1,2,4-trimethylbenzene (TMB), and benzothiophene (BT) as a sulfur compound was studied over a Rh/Al2 O3 honeycomb catalyst. The in-situ sampling technique SpaciPro was used in this study to investigate the complex reaction system which consisted of total and partial oxidation, steam reforming, and the water gas shift reaction. The mixtures of 83 vol % DD, 17 vol % TMB with and without addition of the sulfur compound BT, as well as the pure hydrocarbons were studied at a molar C/O-ratio of 0.75. The spatially resolved concentration and temperature profiles inside a central channel of the catalyst revealed three reaction zones: an oxidation zone, an oxy-reforming zone, and a reforming zone. Hydrogen formation starts in the oxy-reforming zone, not directly at the catalyst inlet, contrary to methane CPOX on Rh. In the reforming zone, in which steam reforming is the predominant reaction, even small amounts of sulfur (10 mg S in 1 kg fuel) block active sites. [ABSTRACT FROM AUTHOR]

In this paper, we report on the theoretical simulation and experimental investigation on a novel ultraviolet (UV) laser at 281 nm by second-harmonic generation (SHG) of a frequency-doubled nanosecond Nd:YAG laser in CsB3O5 (CBO) crystal. We firstly presented a numerical model that describes the nanosecond type-I SHG of CBO, accounting for pump depletion, beam divergence, beam spatial walk-off, linear absorption, and phase-mismatch in the Gaussian approximation of both spatial and temporal profiles. In experiment, we demonstrated the high average power UV at 281 nm up to 1.3 W by the cascaded SHG of an 1123-nm Nd:YAG laser to 561.5 nm in LBO at first SHG stage and then frequency-doubled again to 281 nm in CBO at second SHG stage. Moreover, we investigated the SHG efficiency and the UV 281-nm laser beam quality theoretically under the experimental conditions, and the calculations agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

This paper extends a previous investigation on the thermal behavior of CH-CPO reformers with honeycomb catalysts. Modeling and experimental studies on the short contact time catalytic partial oxidation (CPO) of CH to syngas from our and from other groups have shown that Rh-catalysts rapidly deactivate at the very high temperatures, close to 1000 °C, that establish in the inlet zone of the reactor. We have previously shown that a significant reduction of the surface hot-spot temperature can be obtained by properly designing the catalyst: beneficial effects are observed at increasing opening of the honeycomb channels, which decreases the rate of O inter-phase mass transfer, and at increasing catalyst activity, which promotes the rate of the endothermic reactions. In this work, we explore the effect of the reactor configuration, namely the effect of heat dispersion from the glowing front face of the monolith. Three reactor configurations were compared in CH-CPO experiments: (i) a configuration with perfect continuity between the front heat shield (FHS) and the catalytic module, which behaved close to an ideal adiabatic reactor, (ii) a configuration where the FHS was separated from the catalytic monolith and (iii) a configuration where the FHS was at large distance from the catalytic module. State of the art experimental tools, including the spatially resolved measurement of temperature and concentration profiles were used to characterize the thermal behavior of the various configurations. Detailed kinetic modeling supported the analysis of data. The results showed that, at the expense of a small loss of thermal efficiency, a very moderate loss of performance in terms of conversion and selectivity, but, remarkably, an important reduction of the surface inlet temperatures were achieved. Preliminary experiments with propane/air mixtures suggest that the adoption of a moderately dispersive reactor can represent a promising solution for the stable operation of catalytic units treating heavier fuels than methane. [ABSTRACT FROM AUTHOR]

Abstract: The rigorous estimation of the temperature of the surface of a working catalyst is an issue of fundamental and practical relevance, especially in the case of high temperature reactions. In the present article, the potentialities and complexities of an optical technique, consisting of an optical fiber connected to an infrared pyrometer, are explored with respect to the catalytic partial oxidation of CH4 performed over Rh honeycomb catalysts. The case of a 400cpsi cordierite honeycomb support is analyzed. The effects of different geometrical configurations of the fiber probe are measured and the associated optical artifacts are analyzed. By comparing the experimental results with a predictive numerical model, it is confirmed that the expected surface temperatures are closely captured with a 45° angled optical fiber specifically calibrated and that the use of a thermocouple, sliding from the front face, reveals the temperature of the gas phase. This latter can be dramatically different from that of the solid phase at the reactor inlet, where heat and mass transfer control the kinetics. The application of a non contact infrared device to measure the solid surface temperature is therefore essential, provided that its application is minimally intrusive both with respect of the catalytic volume and of the reactor set-up. [Copyright &y& Elsevier]

Abstract: Spatially resolved species and temperature profiles measured for a wide range of inlet stoichiometries and flowrates are compared with microkinetic numerical simulations to investigate the effect of transport phenomena on the catalytic partial oxidation of methane on Rh foam catalysts. In agreement with the experimental data, the species profiles calculated at different C/O inlet stoichiometries show that both partial oxidation products (H2, CO) and total oxidation products (H2O, CO2) are formed in the presence of oxygen. At the leaner stoichiometries, both oxygen and methane react in the diffusive regime at the catalyst entrance. At the richest methane stoichiometry (high C/O), surface temperatures are lower and methane consumption is only partly determined by transport. For all stoichiometries, a kinetically controlled regime prevails in the downstream reforming zone after O2 is fully consumed. The effect of increasing the flowrate shifts all species profiles downstream and also slightly modifies the shapes of the axial profiles, due to the different effectiveness of heat and mass transfer. Despite enhanced mass transfer and increased surface temperature, the shortened contact time causes a reduced CH4 conversion at high flowrates. The effect of flowrate on the dominant regime is investigated, for both reactants, comparing the resistances calculated in the pure transport regime and in the pure kinetic regime. From a chemical point of view, the model allows for the analysis of the reaction path leading to hydrogen. Due to inhibition of H2O re-adsorption, it can be proven that H2 can be a primary product even in the presence of gas phase O2. The analysis of the surface coverages shows analogous effects on the profiles when decreasing C/O or increasing flow, because in both cases the surface temperature is increased. Syngas selectivity was also evaluated, both from measured and calculated profiles. SH2 is well described by the model at each stoichiometry and flowrate, while SCO is underestimated in every case. From this work, it is also indicated that the Rh catalyst works with CO (measured) selectivities higher than equilibrium. Carbon dioxide only forms in the oxidation zone, for C/O=1 and 1.3, but in the rest of the catalyst zone, there is no further production despite what would be expected from equilibrium. This confirms Rh does not catalyze the water gas shift reaction. On the other hand, at C/O=0.8, this reaction becomes active, due to the higher temperature, and the CO2 is also produced in the reforming zone. This suggests that CO2 will not rise after the oxidation section if the surface temperature is kept sufficiently low. Sensitivity analyses to the active catalytic surface and to the kinetic parameters are provided. [Copyright &y& Elsevier]

Abstract: Spatially resolved autothermal experiments of CH4 catalytic partial oxidation (CPO) performed over Rh-coated foams were analyzed using a detailed reactor model and a novel, thermodynamically consistent C1 microkinetic scheme. The effect of depositing Rh (5wt%) on an 80 ppi α-Al2O3 foam directly or after washcoating with γ-Al2O3 washcoat (2wt%) was examined. For the first time, a fully predictive approach was adopted in the numerical analysis by introducing in the model the experimentally estimated catalyst metal surface area and state of the art correlations for heat and mass transfer in foams. Characterization of the catalysts by H2 pulse chemisorption and SEM microscopy revealed that the washcoat addition increased the metal area by almost one order of magnitude, from 74cm2/g Foam on Rh foams to 630cm2/g Foam on washcoated foams. The numerical results showed that the model is able to quantitatively account for the axial evolution of the species and the temperature profiles of the solid and the gas phase within the catalyst volume. In line with previous results, it was confirmed that the consumption of O2 is strictly governed by mass transfer and that the co-presence of O2 and syngas in the bulk of the gas phase is exclusively due to mass transfer limitations. Reaction path analysis showed that CH4 is activated via pyrolytic decomposition and its main oxidizer is OH* and not O*, both in the oxidation zone and in the reforming zone of the catalyst. By application of the most up-to-date experimental and numerical tools, the present results provide a clear picture of CH4 CPO and emphasize the importance of modeling spatially resolved experiments in order to properly interpret the high density of information that these kinds of data provide. [ABSTRACT FROM AUTHOR]

Abstract: Using a spatially resolved sampling technique, the catalytic partial oxidation of CH4 to synthesis gas was investigated over 80 ppi α-Al2O3 foams coated with three catalytic formulations: 5 wt% Rh, 5 wt% Rh/2 wt% γ-Al2O3 washcoat and 5 wt% Rh–2 wt% Ce/2 wt% γ-Al2O3 washcoat. Experiments were performed at atmospheric pressure and ∼8 millisecond contact time, with 20% v/v CH4 and C/O ratio equal to 1. Data show that the length of the oxidative zone (∼2 mm) is unaffected by the composition of the catalyst. The addition of γ-Al2O3 washcoat to Rh coated monoliths allows the reaction to reach adiabatic equilibrium by increasing the rates of steam reforming and water gas shift. Additionally, both the maximum and the gradients in the temperature profiles decrease significantly with the addition of washcoat. Data collected on Rh–Ce/washcoat show that the adiabatic equilibrium composition is reached through a different kinetic route: the consumption of CH4 becomes slower, the production of CO2 exhibits a maximum, and the production of H2O is drastically moderated, suggesting that Ce has an active role in the CPO reaction kinetics. The features presented could be detected exclusively with spatially resolved measurements. [Copyright &y& Elsevier]

Using spatially resolved measurements of temperature and concentration, we critically analyzed the chemistry and transport limitations in the partial oxidation of methane (POM) reaction carried out on Rh, supported on a foam catalyst. The analysis was based on two models, both sharing a detailed surface chemistry but with different gas–surface transport processes. The simulation neglecting transport limitations correctly predicts the outlet concentrations, apparently because of the approach to equilibrium, but significant disagreement was found along the catalysts, particularly in the initial region, demonstrating the existence of regions in which strong diffusive limitations prevail. We developed a pseudo-1D model that can differentiate the species and temperature in the bulk of the gas and at the surface and describe heat (including radiation) and mass transport through correlations with ad hoc parameters based on experimental studies. With this model, we correctly predicted the profiles along the reactor for all species. Only CO2 had a relevant relative error, but its composition was very low. The solid temperature was well reproduced as well, whereas the gas temperature was somewhere higher than the experimental temperature, possibly due to overestimation of the heat transport coefficient. Analysis of the transport limitations found that O2 and H2O had large concentration gradients between gas and surface due to their involvement in the total oxidation, which is a very fast reaction. The analysis thus demonstrated that production and consumption rates at the catalytic surface were frequently sufficiently high so as to enter a diffusive regime. Accordingly, we highlight the need to augment the implementation of detailed surface chemistry with some accounting of the transport processes of both mass and heat. In addition, we show that the Chilton–Colburn analogy can be seriously misleading under these conditions of locally fast heterogeneous kinetics. [Copyright &y& Elsevier]

We have presented measurements of spatial profiles of electron induced emission coefficients for the 777.4 nm radiation of oxygen in low current discharges. Measurements were performed by the drift tube technique in low-current self-sustained Townsend type discharges. We have also compared results for the delay distance for electrons in oxygen calculated using Monte Carlo simulation code and results from a semi-empirical formula adjusted to fit the oxygen data. Finally, from the spatial profiles we have determined ionization coefficients. The spatial profiles of emission provide us also with information on heavy particle excitation and on the reflection of electrons from the anode. The absolutely calibrated spatial profiles of emission may be used to separate the effects of electrons and heavy particles in excitation at high E/N values and obtain the cross sections for fast neutral excitation. [ABSTRACT FROM AUTHOR]

Abstract: We compare Rh and Pt as catalysts for the partial oxidation of methane to syngas at millisecond contact times. The basis for the comparison are species and temperature profiles, with a spatial resolution of about 300 μm measured along the centerline of an adiabatically operated metal-coated α-Al2O3 foam using a capillary sampling technique with mass spectrometric species measurement. Gas temperature profiles are measured with a thermocouple. Investigated stoichiometries range from C/O=0.6 to 2.6 at constant flow rate of 4.7 slpm and atmospheric pressure. Rh and Pt are compared with respect to (i) profile development at syngas stoichiometry, (ii) profile development at varying stoichiometries from C/O=0.6–2.6, (iii) product selectivities and yields in the oxidation zone, (iv) contribution of partial oxidation and steam reforming to the final syngas yield, (v) mass transport limitations, and (vi) approach to thermodynamic equilibrium. Independent of C/O and metal, all profiles show an oxidation zone and a steam-reforming zone. H2 and CO are formed in the presence of gas-phase oxygen by partial oxidation and in the absence of gas-phase oxygen by steam reforming. CO2 reforming is not observed. At the same C/O, H2 and CO selectivities and yields are higher in the oxidation zone on Rh than on Pt. As the C/O ratio increases, the catalyst temperature decreases and selectivities to H2 and CO in the oxidation zone decrease. The decrease is larger on Pt than on Rh. Because Rh is also the better steam-reforming catalyst, H2 and CO yields are generally higher on Rh than on Pt. The rate of O2 conversion at the catalyst entrance is largely mass transport-controlled on Rh but not on Pt. In the oxidation zone on Pt, the methane CPO is kinetically controlled with a constant reaction rate. An average O2 mass transport coefficient is calculated and compared with literature values on foam catalysts. Finally, exit species flow rates and temperatures are compared with thermodynamic calculations at constant pressure and enthalpy. Rh brings the methane oxidation close to equilibrium if , whereas Pt reaches equilibrium only at very high catalyst temperatures if . At higher C/O, deviations from equilibrium are observed mainly because steam-reforming slows, but also because water–gas shift equilibrium is not established. [Copyright &y& Elsevier]

Spatially resolved species and temperature profiles have been measured for the catalytic partial oxidation of on autothermally operated Rh-coated foams in both steady state and transient mode. A probe consisting of a thin quartz capillary and a thermocouple was moved with sub-mm resolution through the catalyst/heat shield stack to sample the gases into a mass spectrometer and measure temperature. The probe was also used to follow the relaxation of the system upon perturbation by stepping the stoichiometry of the reactants periodically. The spatial profiles in steady state show that and CO are formed in presence of gas phase oxygen (oxidation zone) and after total oxygen conversion by steam reforming (reforming zone). The stepwise change of the reactant stoichiometry in the transient experiments allowed decoupling chemistry (ms timescale) and temperature (s timescale). By exposing a catalyst, initially operating very hot at , suddenly to a rich feed , it was possible to follow how the integral and CO production rates decrease with decreasing temperature of the catalyst. The reverse switch from to 0.6 showed how the integral and CO production rates increased with increasing temperature of the catalyst. Differential reaction rates were obtained by performing these transients spatially resolved at two adjacent points in the catalyst. For , and CO formation show a strict linear Arrhenius behavior over the entire temperature range from to . For , the Arrhenius plots show two straight segments, a steep increase in the formation rate from to and a weak increase from to. In both cases, formation is more activated than CO formation indicating two different rate determining steps. [Copyright &y& Elsevier]

Methods are presented to measure axial species and temperature profiles within catalytic partial oxidation foam monoliths at atmospheric pressure with 0.3 mm spatial resolution using a capillary sampling technique with a quadrupole mass spectrometer. The system allows sampling within the catalyst with negligible interference in flow or temperature by using a 0.6 mm quartz capillary containing a thermocouple and possessing a 0.3 mm side orifice. The capillary tightly fills a concentric channel drilled within the 10 mm long ceramic foam minimizing gas bypass. This technique has been used to measure axial catalyst species profiles at temperatures up to 1300 °C for catalytic partial oxidation of methane and ethane to synthesis gas and ethylene, respectively. CH4 and O2 conversion are approximately twice as fast on Rh than on Pt. For C2H6 the reaction products at the catalyst entrance are H2, H2O, CO, and CO2. Ethylene production begins only after ~4 mm into the catalyst after most of the O2 has reacted. Transient operation where the feed composition is varied stepwise between different C/O ratios has also been used to characterize these systems. The capillary sampler has a time resolution of ~0.05 s, and C/O step changes within 0.5 s have been achieved using mass flow controllers. For switches from C/O = 0.6 to 1.4, sharp overshoots are observed for syngas (H2 and CO) and similar undershoots for combustion products (H2O and CO2). By placing the sampling orifice at different positions and stepping the C/O ratio, spatio-temporal profiles can be obtained. Spatio-temporal profiles are extremely important in validating detailed reaction mechanisms because their information content is much higher compared to integral steady state measurements at the reactor outlet. The spatial profiles show where and how quickly different species are formed or consumed along the catalyst axis. Transient profiles provide additional diagnostics of mechanisms and surface coverages because they show how temperature and species concentrations follow a perturbation from steady state. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism for the catalytic partial oxidation of CH4 on Rh-coated α-Al2O3 foam monoliths was investigated by measuring species and temperature profiles along the catalyst axis and comparing them with numerical simulations. A thin quartz capillary connected to a quadrupole mass spectrometer was moved through the catalyst with a spatial resolution of ∼0.3 mm. Profiles were measured under autothermal operation for C/O ratios of 0.7, 1.0 and 1.3. The influence of the flow rate (5 vs. 10 l min−1) was studied for syngas stoichiometry (C/O=1). Numerical simulations were performed with a 38 step surface mechanism using both a porous 2D-model with mass and heat transfer and a simple plug-flow model. The experimental profiles reveal complete O2 conversion within 2 mm of the catalyst entrance for all C/O ratios and flows. H2 and CO are formed partly in the oxidation zone and partly after O2 is fully converted by steam reforming. CO2 is formed in small amounts in the oxidation zone and remains constant thereafter, except for C/O=0.7, where some water gas shift is observed. CO2 reforming does not occur under the experimental conditions. Based on the experimental findings, a two-zone picture of the reaction mechanism is proposed. The 2D numerical simulations and the measured profiles agree qualitatively for all experimental conditions. Quantitative agreement is best for syngas stoichiometry (C/O=1.0) at 5 and 10 l min−1 flow rate. Some quantitative differences are observed for C/O=0.7 and 1.3. The plug flow model is for all conditions inferior to the 2D model. The importance of spatial profiles for mechanism and reactor model validation is highlighted. [Copyright &y& Elsevier]

In a stirred laboratory reactor a biofilm was grown on a gas-permeable silicone membrane. Xylene was added to the bulk fluid as the only carbon source and oxygen was supplied through the membrane. For 66 days the reactor was operated under varying experimental conditions. The concentrations of five components in the reactor effluent and of two in the gas outlet were measured almost daily, the biofilm thickness was determined several times. The measured time series were used to calibrate a mathematical model which calculates pH, aerobic degradation of xylene, and microbial growth, decay and conversion to inert particulate material. The calibrated model was then used to analyze the spatial distribution and dynamics of the xylene-degrading heterotrophic population in the biofilm. The analysis revealed that as long as oxygen was supplied as air heterotrophic cells only grew within a thin zone of about two hundred micrometers near the membrane. Upon the change from air to pure oxygen this zone shifted instantaneously by half of the biofilm thickness of about two millimeters towards the biofilm surface. The immediate ability of the biofilm to convert xylene in a zone which so far had been strictly anaerobic, indicates the presence of a heterotrophic population in this zone. The conclusion is that this population had been transported from the aerobic to the anaerobic zone and that transport and growth of microbial cells are processes which are equally important in biofilms. [ABSTRACT FROM AUTHOR]