Monolithic Form Research Articles

Characterisation of Shear Creep and Stress Relaxation of Serrate Discontinuity in Rock Mass under Different Loading Paths

In engineering applications, rocks rarely exist in their monolithic form and discontinuities always occur in the rocks. Intuitively there is a considerable difference in rheological properties between monolithic rocks and rocks with discontinuities. The present paper aims to characterise the shear creep and stress relaxation of serrate discontinuity in rock mass under different loading paths. A comprehensive experimental program, including creep tests, stress relaxation tests and unloading tests, on serrate discontinuities, is developed with focus on the effect of the slope angle of the serrated surface of the discontinuity on its creep and stress relaxation. Empirical models for shear creep and stress relaxation are also developed. We found in the paper that the larger the slope angle of a discontinuity is the larger both the creep and stress relaxation are, and the stress-strain relation of discontinuities in rock masses can be different under different loading paths. The significance of the research is that it investigates the simultaneous shear creep and stress relaxation of a serrate discontinuity under various loading paths. The paper concludes that the empirical models for creep and stress relaxation developed in the paper can help geotechnical engineers to analyse and assess the behaviour of rock masses with discontinuities.

Phase field modeling of shearing processes of a dual-lobed γ″|γ′|γ″ coprecipitate

The Ni-based superalloy IN718 is one of the most widely used commercial alloy in the aerospace industry since its development in 1960s. The excellent mechanical properties have been attributed in a great deal to strengthening by coherent γ′ and γ″ precipitates. The deformation mechanisms of these two phases have been well studied individually. Recent experimental characterization has shown coprecipitates of these two phases in a variety of morphologies and it was argued that these coprecipitates may lead to improved strengthening as compared to their monolithic counterparts. However, the deformation mechanisms of these coprecipitates are still not well understood. In this study, we performed microscopic phase field simulations, with generalized-stacking-fault (GSF) energy surfaces from ab initio calculations as inputs, to systematically study the shearing processes of a periodical array of dual-lobed coprecipitates as well as monolithic precipitates. We found that the coupling between the γ′ and γ″ phases in the coprecipitates forces dislocations to take high energy shearing pathways in both phases that would not occur if they were in monolithic forms. The coupling also creates stacking fault configurations in the coprecipitates that require high stress to form. Thus, the presence of coprecipitates in general should increase the resistance to dislocation shearing and lead to higher strength levels. Various fault configurations observed during the shearing process are documented as a reference for future comparison with experimental observations. The link between stacking fault shearing and microtwinning is also discussed. The mechanisms analyzed in this study deepens our understanding of coprecipitation effects on alloy strength and may form a cornerstone for multi-precipitate strengthened alloy design strategies.

The Methyl Functionality of Monolithic Silica Xerogels Synthesized via the Co-Gelation Approach Combined with Surface Silylation.

The present research aims to investigate the chemical and morphological properties of the methylated silica xerogels produced via the co-gelation approach combined with surface silylation. In the sol-gel synthesis, methyltrimethoxysilane (MTMS) and tetraethylorthosilicate (TEOS) were utilized as silica precursors and trimethylchlorosilane (TMCS) served as a silylating agent. Structural changes were observed depending on the MTMS/TEOS molar ratio and on the post-synthesis-performed surface silylation of the xerogels. Post-synthesis silylation plays a critical role in the exchanging of the surface silanols with methyl groups, preserving the monolithic form. The morphological and structural changes were followed by SEM, 29Si-MAS-NMR, FTIR spectroscopy, nitrogen porosimetry, and contact angle measurements. The results have shown significant structural variations depending especially on the MTMS content. With an increasing MTMS content, the morphology of the samples has changed from a micro/mesoporous texture to a meso/macroporous texture. A higher degree of methyl substitution has been achieved for the silylated samples both confirmed by the FTIR and 29Si-NMR results. On the other hand, only the samples with a high MTMS content could preserve their structural integrity after evaporative drying, and all have exhibited a high degree of hydrophobicity with θ > 140°.

Adsorption of dyestuff by nano copper oxide coated alkali metakaoline geopolymer in monolith and powder forms: Kinetics, isotherms and microstructural analysis

To remove contaminants and pollutants from wastewater systems, adsorbents are widely used. Geopolymers offer a convenient alternative as adsorbents in the wastewater treatment system as they are low-cost, environmentally friendly, and safer. A new adsorbent material prepared by coating nano copper oxide on the surface of alkali-activated metakaolin showed a higher ability to remove methylene blue (MB) dye from wastewater, thus making them attractive in dye removal applications. First, nano copper oxide was prepared by sol gel method and metakaolin geopolymer was produced using sodium silicate solution having a Ms value of 1.1 (M). Afterwards, nano copper oxide (MC) was coated on the surface of the geopolymer. The ability of MB dye to bind to both pristine (Mp, MCp) and powder forms (Mpr, MCpr) of the geopolymer was evaluated. X-ray diffraction revealed that the halo found at 27.40°–31.077° (2θvalue) in both samples related to amorphous gel's composition and the major peaks of copper oxide in MCpr were sited at a 2θ value of 35.45° and 38.88°.The dye removal efficiency can be inferred from the increased adsorption capacity of 11.9 mg/g (Mp) and 14.4 mg/g (MCp) for the monolith form and 81.43 mg/g (Mpr) and 87.82 mg/g (MCpr) for the powder form. The adsorption of reused active sites was 73% for Mpr and 83% for MCpr up to the fifth cycle after regeneration by heat treatment at 400 °C. The models that best suited the adsorption data were pseudo-second-order and Freundlich isotherms, which indicated possible chemisorption with intra-particle diffusion. Furthermore, the binding energy is shifted to lower value in XPS spectra due to dye adsorption arising from electrostatic attraction. A higher electron density is formed due to interaction with an equal contribution of silanol Si–O–H and Si–O–Na/Cu(O1s). The adsorbents are effective over a wide pH range and their improved recycling capability increases their applications for a wide range of uses.

3D printing of powdered activated carbon monoliths: Effect of structuring on physicochemical and mechanical properties and its influence on the adsorption performance

Herein, a methodology for 3D printing of activated carbon powders in monolithic form using direct ink writing and carboxymethylcellulose as binder is reported, along with the effect on their physicochemical and mechanical properties. Monoliths with different wall diameters (0.42, 0.62, and 0.82 mm) and infill percentages (30, 50, and 70%) were designed and manufactured. The monoliths were heat-treated under a nitrogen atmosphere at 400 °C and 600 °C to remove the volatile material from the binder used. The monoliths showed a decrease in dimension of less than 8% from their designed values, attributed to the volatilization of water present in the binder solution in the drying and heat-treatment process. The printed monoliths presented pore distributions similar to those of their powdered counterparts. The isoelectric point of the monoliths increased relative to that of the powdered material and became more basic as the heat treatment temperature increased. The monoliths presented compressive strengths from 0.58 to 3.53 MPa. The analysis of variance of the compressive strength showed that the wall diameter and temperature are the most influential treatment parameters. The printed monoliths exhibited similar CO 2 adsorption capacity (0.37 mol Kg -1 at 10 kPa and 25°C) compared to the powder precursor. Fixed bed tests demonstrated that the 3D printed monoliths enhanced the mass transfer compared to conventionally extruded pelletswith same wall diameter.

Composition in the Aftermath of Hebrew Culture; The Musics of Betty Olivero and Chaya Czernowin

Ideally this article should be titled "decomposing Hebrewism," except that by the turn of the twenty-first century composers in Israel were past the point of opposing the tropes that constituted Hebrew culture and the territorial paradigms that had conditioned it. Still, the two composers under discussion here—Betty Olivero and Chaya Czernowin—do not offer more-of-the-same stand-ins in the monolithic form of representations or identities (gender identities included); nor are there common stylistic traits that could reason their joint appearance here (and their gender, needless to say, would be a poor excuse). In fact, it is despite their unequivocally different aesthetic penchants that we can point to artistic perceptions which mute national territorial tropes, disable the Zionist management of Jewish history, and opt for non-redemptive poetics—all while drawing on Jewish musical traditions or modern Hebrew literature. Looking at (and listening to) Olivero and Czernowin's works, this article discusses the modern and postmodern patrimonies that steer their writing while situating both in the aftermath of Hebrew Culture. Knowingly circumventing the playing of identity cards or the displaying of peripheral masks, Olivero and Czernowin's musics signal a constituent shift toward simultaneities, multiplicities, defacing of musical signifiers, and the unmarked semiotics of cultural spaces that are bluntly incongruent with the national.

An Environmental Approach in Production of Activated Carbon Monolithic Derived from Garlic Peels for Supercapacitor Application

An environmental approach is needed in the production of activated carbon as electrode material in supercapacitor applications. Activated carbon provides high specific surface area and well-developed pore structures. These circumstances compromise high electrochemical performance for supercapacitor. Therefore, this research focusses on fabricating the activated carbon derived from garlic peels through the chemical activation of potassium hydroxide under various concentrations, combined with 1-integrated stage pyrolysis. The morphology of activated carbon was observed using scanning electron microscopy (SEM), embedded in energy dispersive X-ray (EDS) for analyzing the elemental status. The crystalline degree of the activated carbon was observed using X-ray diffraction (XRD). The electrochemical performances of cell supercapacitor-based-ACM electrodes were evaluated with cyclic voltammetry (CV) and galvanostatic charging-discharging (GDC). The activated carbon was prepared in monolithic form without binder materials and shows a sponge liked-porous structure with high electrochemical performance, including specific capacitance of 204 F g−1, with energy and power of 28.58, 71.16 W kg−1 under current densities 1 A g−1, in the 2-electrode system of 1 M H2SO4 electrolyte. The results showed that using an environmental approach in the production of activated carbon monolithic derived from garlic peels has high electrochemical performance.
 HIGHLIGHTS
 
 Activated carbon was performed in monolithic form
 Activated carbon monolithic was prepared in low chemically activated
 ACM was produced without binder material
 ACM exhibits high specific capacitance of 204 F g-1
 
 GRAPHICAL ABSTRACT

Silica gel doped with cobalt oxide prepared by sol-gel technique; improving dielectric charge storage

The structural, morphology and magnetic properties of Cobalt oxide embedded in silica gel with 10 mol. %, in monolith form, sintered at different temperature ranging from 60 up to 1300ºC, respectively recorded as (SC(60-1300) were prepared by a modified sol gel technique. The sintering temperature effect on the crystallization, surface morphology and magnetic behaviors of the prepared samples will be study, Phase identification by using surface morphology and X-ray diffraction will be study by using Transmission electron microscope (TEM) and Field emission scanning electron microscope imaging (FESEM). The nano-scale presence and the formation of the α-cristobalyte tetragonal phase of silica gel as well as the doped samples with cobalt oxide crystallinity enhancement were detected using the mentioned techniques. FTIR spectra were being study. The saturation magnetization (Ms), remnant magnetization (Mr) and coercive force (Hc), was founded to be equl to 0.183,0.031 emu/g and 46.7Oe respectively. The A. C. conductivity increased by increasing the temperature .Therefore, by increasing the sintering temperature of the silica gel network doped withCo3O4are applicant for several electronic and industrial devices with improved dielectric charge storage capacity and strength.

Get the light & keep the warmth - A highly insulating, translucent aerogel glass brick for building envelopes

Silica aerogels are thermal superinsulation materials that have found increasing application in the building sector in the last ten to fifteen years. While the most common material types are opaque insulating blankets and renders, in its monolithic form silica aerogel can be almost transparent, allowing for composite translucent insulating building system.Here, we developed and characterized a novel modular, translucent and thermally insulating building component based on silica aerogel granules, the aerogel glass brick. Both thermal and mechanical properties were tested and the former were compared to a 3D simulation of the heat transfer through the brick. The glass brick has a measured thermal conductivity of 53 mW/(m·K), corresponding well to the simulation results of 51 mW/(m·K), and a compressive strength of almost 45 MPa. This makes the glass brick the insulating brick with the highest insulation performance reported in literature or available on the market, and at the same time adds the feature of light transmission.The aerogel glass brick is suitable when the requirements combine daylighting, glare protection and the need to protect privacy, e.g. offices, libraries, museums; an analysis of the materials costs indicates that the insulating glass brick can be competitive in such applications. The glass brick provides architecture with new design opportunities to increase daylight inside buildings.

Selective Impact of MTMS-Based Xerogel Morphology on Boosted Proliferation and Enhanced Naphthoquinone Production in Cultures of Rindera graeca Transgenic Roots.

In situ extraction is a method for separating plant secondary metabolites from in vitro systems of plant biomass cultures. The study aimed to investigate the MTMS-based xerogels morphology effect on the growth kinetics and deoxyshikonin productivity in xerogel-supported in vitro culture systems of Rindera graeca hairy root. Cultures were supplemented with three types of xerogel, i.e., mesoporous gel, microporous gel, and agglomerated precipitate, in the disintegrated or monolithic form. Structure, oil sorption capacity, and SEM analyses for xerogel-based additives were performed. Application of monolithic macroporous xerogel resulted in the highest biomass proliferation, i.e., 5.11-fold fresh biomass increase after four weeks of the screening culture. The highest deoxyshikonin production (i.e., 105.03 µg) was noted when hairy roots were maintained with particles of disintegrated mesoporous xerogel. The detailed kinetics investigations (6-week culture) revealed the highest growth of hairy root biomass and secondary metabolite production, equaling 9.46-fold fresh weight biomass and 204.08 µg deoxyshikonin, respectively. MTMS-based xerogels have been recognized as selective biocompatible scaffolds for boosting the proliferation of transgenic roots or for productivity enhancement of naphthoquinones without detrimental effects on biomass growth, and their successful applicability in in situ removal of secondary plant metabolites has been experimentally confirmed.

On the seismic behaviour of monolithic lunar arches subjected to moonquakes

AbstractWith a new era emerging in the field of lunar exploration and habitation, there is a need for research on structural forms made of local soil material (regolith), which will be able to endure the extreme conditions in harsh environments (e.g., extreme temperature fluctuations, solar and cosmic radiation, meteor showers, strong ground motions, etc.). The present work focuses on understanding the dynamic and seismic behaviour of certain structural typologies of monolithic arches by means of finite element analysis (FEA). These typologies were extensively investigated previously, using static analyses accounting for the reduced gravitational field on the moon, and proved to be of the optimum shape against certain loading scenarios. Specifically, these optimal monolithic arch forms (named enhanced varying‐thickness arches – EVTAs) examined herewith, are described by varying‐thickness geometry, properly enhanced at certain weak points for increasing their structural stability. Aiming at a fair comparison, the seismic behaviour of EVTAs is contrasted to that of their corresponding monolithic constant‐thickness (CTAs) counterparts (having the same amount of structural material). After defining an appropriate damage state, the authors conduct preliminary pushover analyses to determine the structural capacity of the arches against lateral loading. Subsequently, the modal analysis of the EVTAs shows that the second/vertical mode exhibits a natural period almost equal to that of their first/translational mode and substantially longer than the corresponding second/vertical mode of their CTA counterparts, indicating a potential vulnerability along the vertical excitation. Furthermore, taking into account that shallow moonquakes are comparable to intraplate earthquakes in terms of hazard potential, the authors produce sets of stochastic seismic excitations used as time histories for seismic analyses. The probability of exceedance of the defined damage state as a function of the peak ground acceleration (PGA) is presented through indicative fragility curves, where the structural superiority of EVTAs against their CTA counterparts is demonstrated.

Interlayer fracture behaviour of functionally layered concrete

Automatization and additive manufacturing provide a platform to move away from traditional monolithic concrete forms towards more material efficient functionally-graded or structural composite elements. This has a great potential to tailor the element’s mechanical or thermal performance which allows to efficiently use material and furthermore safe costs and reduce the environmental footprint of an element. However, the deposition of different wet-on-wet and wet-on-hardened concrete layers introduces the risk of a weak interlayer zone (ILZ). Furthermore, functionally layered concrete made of multi-mixes introduces a new dimension whereby the mix compositions and the deposition delay times potentially interact to influence the interlayer behaviour.To provide a better insight on the interlayer zone behaviour of functionally graded concrete, a detailed investigation of the interlayer fracture properties of multi-mix concrete elements cast in layers and the effect of the pour delay between layers is presented. Wedge-splitting-tests are used to infer the fracture behaviour of layered specimens fabricated using three different concrete mixes in single and multi-mix combinations. The influence of a pour delay between layers of up to 4.0 h is also interrogated. The results show that the multi-mix fracture behaviour depends on not only the mix compositions but also on the pour delay time. Cases where the fracture properties were at least as good as, or even better, than those of the comparator weaker single mix suggest that judicious mix designs and controlled fabrication processes for functionally layered concrete can mitigate the formation of weak ILZs.

Recently emerging advancements in polymeric cryogel nanostructures and biomedical applications

Cryogels are interlinked macroporous substrates or materials which have undergone processing from a monomeric solution below zero temperatures. Due to their exceptional features including biocompatibility, sensitivity, and physical inhibition, cryogels appear as injectable gels, powders, column, monolithic, beads, spheres, and membrane forms and are utilized in biomedical applications. Therefore, this paper elucidates recently emerging trends in cryogels structures for biomedical and pharmaceutical applications including drug delivery, cell transplantation, tissue engineering, therapeutic, immunotherapy, cell transplantation, and so on.

Photocatalytic degradation of atrazine by an N-doped TiO2/polymer composite: catalytic efficiency and toxicity evaluation

Monolithic composite aerogel based on N-doped TiO2 (NdT) photocatalyst dispersed into syndiotactic polystyrene (sPS) matrix was used for atrazine (ATZ) degradation under ultra-violet (UV) and visible light (Vis) irradiation. sPS/NdT composite aerogel, with a polymer/photocatalyst 90/10 wt ratio, was achieved by super critical CO2 extraction of chloroform from the relative sPS/NdT gel. Testing of the sPS/NdT photocatalytic activity was performed by using initial ATZ concentration of 0.1 mg/L and a sPS/NdT composite in monolithic aerogel form. ATZ removal was equal to 47% and 25% under UV or Vis light, respectively, after 180 min of irradiation. The efficiency of the photocatalytic process was also investigated by monitoring the ecotoxicity of the treated water to Aliivibrio fischeri, Raphidocelis subcapitata, and Daphnia magna. The results indicated that, for both UV and Vis irradiation, even for high ATZ removal efficiency (i.e., UV treatment), the toxicity of process effluent is greater than the initial one, most likely because of the generation of toxic by-products. The UV treatment was effective only after 72 h when the solution appeared not toxic to D. magna and presented a very low effect to R. subcapitata. On the other hand, under Vis light irradiation, a very high level of toxicity was still detected after 72 h of treatment time. Toxicity tests are confirmed as an indispensable tool for a correct assessment of the environmental impact of water treatment processes.

Selective Ru Adsorption on SnO2/CeO2 Mixed Oxides for Efficient Destruction of Multicomponent Volatile Organic Compounds: From Laboratory to Practical Possibility.

Ru-based catalysts have been extensively employed for the catalytic destruction of chlorinated volatile organic compounds (VOCs), but their versatility for other routine VOCs' destruction has been less explored. Herein, we show that Ru-decorated SnO2/CeO2 mixed oxides can sustain H2O and HCl poisonings and are endowed with extraordinary versatility for a wide range of VOCs' destruction. Selective adsorption of Ru on the cassiterite SnO2 and CeO2 nanorods through a Coulomb force can rationally tune the oxidation and dechlorination centers on decorated catalysts, where the epitaxial growth of RuOx on top of SnO2 is endowed with excellent dechlorination ability and that on CeO2 is functional as an oxidation center; the latter could also activate H2O to provide sufficient H protons for HCl formation. Our developed Ru/SnO2/CeO2 catalyst can steadily destruct mono-chlorobenzene, ortho-dichlorobenzene, trichloroethylene, dichloromethane, epichlorohydrin, N-hexane, ethyl acetate, toluene, and their mixtures at an optimum temperature of 300 °C, and its monolithic form is also functional at this temperature with few dioxins being detected in the off-gas. Our results imply that the Ru-decorated SnO2/CeO2 catalyst can meet the demands of regenerative catalytic oxidation for the treatment of a wide range of VOCs from industrial exhausts.

Effects of ultrasound/microwave irradiation on the sol-gel synthesis of titanium dioxide nanoparticles for photocatalyc application

TiO2 nanoparticles were synthesized by the sol-gel method with the purpose of optimizing their morphological and structural properties, for their application in photocatalysis by varying the thermal treatment in the crystallization stage. Each sample was prepared according to the case with microwave irradiation (MO), ultrasound (US), combined mode (microwave-ultrasound (MC)) or conventional method (reflux), where the MC method has not been reported. It was found that the optical (edge energy (Eg)), textural and morphological properties depend on the type of irradiation during the crystallization stage. The SEM micrograms (scanning electron microscopy) showed two morphologies, one in the form of monoliths and the other as aggregates of lobular particles. In the case of MO and reflux, it is made up of aggregates of lobular particles, for US in the form of monoliths and finally for MC, the dominant morphology is due to the effect of US. For the evaluation in photocatalysis, it was observed in the samples studied that the higher the percentage of anatase phase, surface area, volume and pore size, all at the same Eg value, the greater the photodegradation of methyl orange. Therefore, TiO2 synthesized by the combined MC method was the best material obtained for photodegradation.

Ultra‐Low Threshold Titanium‐Doped Sapphire Whispering‐Gallery Laser (Advanced Optical Materials 8/2022)

A fresh approach is taken to titanium sapphire by manufacturing it into a whispering-gallery laser. In article number 2102137, Farhan Azeem, Luke S. Trainor, Harald G. L. Schwefel and co-workers show that the new monolithic form factor allows lasing at a record low threshold power with a high slope efficiency. Gain in the active resonator is accurately measured through the linewidth of the whispering-gallery modes. The photo shows the resonator fluorescing when pumped evanescently through a prism with green laser light.

Composite membranes with ultrathin and conformal passivation for universal microfiltration compatible with organic solvents

The development of porous membranes with excellent solvent resistances is an important technical task in relation to environmental and energy issues, including chemical waste treatment in the semiconductor industry. However, common polymer membranes, except for Teflon-based membranes, do not guarantee universal resistance to various organic solvents. In this study, a universal strategy is proposed to improve the solvent resistances of polymeric porous membranes through conformal passivation of ultrathin metal oxide layers via atomic layer deposition. Conformal ZnO shells with a thickness below ∼62 nm can significantly improve the inherently low resistances of nitrocellulose, polyethersulfone, and polycarbonate membranes to organic solvents without significantly degrading the flux. Although the polymer core is gradually dissolved by the organic solvent penetrating through the native cracks of the ZnO shell as the time of exposure to the organic solvent increases, the rigid porous network composed of hollow ZnO can well maintain its monolithic form for more than 1 week. Thus, it is possible to effectively filter pollen grains and heavy metal microparticles dispersed in harsh organic solvents without expensive Teflon-based membranes. This study opens new opportunities for selection of organic solvent-compatible membranes for microfiltration.

Conversion of Salam leaves (Syzygium polyanthum (Wight) Walp.) bio-kitchen waste as functional activated carbon for sustainable supercapacitor electrodes

Porous carbon based on bio/organic waste is a very popular raw material used in high-level applications due to its advantages of high porosity, high electrical conductivity, suitable pore structure, and good stability. In this study, bio-kitchen waste is used as a precursor to obtaining high functional activated carbon which is applied to electrochemical energy storage applications. This kitchen waste is focused on Salam leaves (Syzygium polyanthum (Wight) Walp.). Precursors are converted to porous carbon through a simple technique and a green approach without the addition of synthetic materials. In addition, activated carbon is designed in a new form of monolith without a binder. The material properties were thoroughly investigated through monolith dimension reduction and X-ray diffraction. The dimensions of the monolith are reviewed based on mass, thickness, and diameter. The activated carbon obtained shows porosity and amorphous properties which are useful in supporting its electrochemical natures. Furthermore, the electrochemical properties of carbon electrodes were reviewed using standard cyclic voltammetry and galvanostatic charge-discharge methods in a two-electrode system. In addition, a 1M H2SO4 aqueous electrolyte was selected to enhance the supercapacitor cell performance and it exhibit high specific capacitance of 145 F g−1. Based on these results, it is surprising that bio-kitchen waste has great potential as a high-carbon material for high-level applications.

Catalyst optimization in a catalytic flow reversal reactor for lean methane combustion

This paper describes a detailed catalyst configuration study for a catalytic flow reversal reactor for lean methane combustion using computational modelling. The design is based on the use of a platinum group metals catalyst in the form of a washcoated monolith. A small-scale pilot plant reactor is used as the basis for the study. The computational model is based on the fundamental conservation equations of mass and energy that are solved using the finite element method with commercial software. Extensive model validation is performed using experimental data previously obtained on the pilot plant system. It is found that catalyst activity and length of the reaction section play key roles in the stable operation and performance of the system. For methane feed concentrations above about 0.5% by volume, the catalyst activity plays a relatively small role. For concentrations down to about 0.2% both the catalyst activity and reactor length become increasingly important. The complete transient history of the reactor also plays an important role in determining whether or not a stable stationary state can be achieved for a given set of inlet conditions. Computational modelling is shown to be an extremely valuable tool for the design of the reactor system.