Metallic Monolith Research Articles

Potential of metal monoliths with grown carbon nanomaterials as catalyst support in intensified steam reformer: a perspective

AbstractA monolithic catalytic support is potentially a thermally effective system for application in an intensified steam reforming process. In contrast to ceramic analogues, metal monoliths exhibit better mechanical strength, thermal conductivity and a thermal expansion coefficient equivalent to that of the reformer tube. A layer of carbon nanomaterials grown on the metal monolith’s surface can act as a textural promoter offering sufficient surface area for hosting homogeneously dispersed catalytically active metal particles. Carbon nanomaterials possess good thermal conductivities and mechanical properties. The future potential of this system in steam reforming is envisaged based on hypothetical speculation supported by fundamental carbon studies from as early as the 1970s, and sufficient literature evidence from relatively recent research on the use of monoliths and carbon in catalysis. Thermodynamics and active interaction between metal particle surface and carbon-containing gas have resulted in coke deposition on the nickel-based catalysts in steam reforming. The coke is removable through gasification by increasing the steam-to-carbon ratio to above stoichiometric but risks a parallel gasification of the carbon nanomaterials textural promoter, leading to nickel particle sintering. We present our perspective based on literature in which, under the same coke gasification conditions, the highly crystallised carbon nanomaterials maintain high chemical and thermal stability.

Cohesive strength measurement of catalyst layer: Uniform drying and on-line monitoring

Catalysed chemical reactions usually only occur on the surface of the catalyst, therefore the rate of reaction is dependent on the amount of surface area available. In order to achieve this, the active phase is distributed over a high surface area support material.In catalytic converters, automotive catalysts are deposited on the interior walls of a ceramic or metallic monolith in the form of a coating. The open structure of the monoliths allows the gases to pass through the catalyst without causing too much pressure drop. The strength of the coated layer is important for the life (and activity) of a catalytic converter. The coated catalyst layer can fail in both cohesive and adhesive manner, and the lack of methods to separately quantify the individual strength has become an issue. For this reason, the current paper proposes an improved method to measure the cohesive strength of a catalytic layer by implementing a uniform drying system for the preliminary method developed in a previous publication (Yang et al., 2016).The cohesive strength obtained was found to vary with particle size, pH of catalyst suspension, and drying rate of the suspension. In short, a suspension with d90 approximately of 9μm, pH=4 and dried under a low drying rate led to a layer with high cohesive strength. Variation in the cohesive strength is explained based on particle mobility and packing behaviour obtained from on-line monitoring of the drying process of a washcoat layer. In addition the cohesive strength is also in close agreement with the DLVO theory except at very low and high pHs where dissolution of the particles may have an influence. A combination of low resistance for particle movement and longer exposure to a drying environment was found to improve the cohesive strength. Particle mobility and packing behaviour which was retrieved on a micrometre length scale from on-line monitoring is one step further to understand the origin of cohesive strength of a coated layer beyond the widely investigated macroscopic preparation conditions such as viscosity and drying rate.

Recent Advances in Substrate Materials and Thermal Analysis of Catalytic Converters

Catalytic converters are employed in the automotive and chemical reactor application for reduction and oxidation of toxic by-products produced during the burning of fuels. Every industrial Nation is striving to achieve the stringent pollution norms for environment and safety. It has propelled the need to develop a simulated model of catalytic converter before being put in to action. This paper focusses on the history of development of the catalytic converter and the modifications taken place during the recent years. In earlier development ceramic and metallic monolith were used for making the substrate for catalytic convertor. In recent past, metallic foams were successfully tested for suitability as the alternative for the conventional substrate materials. An insight in to the pressure pattern, flow characteristics and the heat transfer capability of the catalytic converter shows that metallic foams have better heating ability which is convenient for cold starting of engines and improved heat transfer.

Effect of catalyst layer macroporosity in high-thermal-conductivity monolithic Fischer-Tropsch catalysts

In-house-fabricated aluminum monoliths were washcoated with Co-Re/Al2O3 catalysts for Fischer-Tropsch synthesis using two alumina supports with different texture. On one hand, a commercial mesoporous alumina support was used as reference material. On the other hand, a meso-macroporous alumina was prepared in the laboratory. The macropores were expected to act as transport pores and facilitate diffusion through the catalytic phase volume. Despite showing different porosities, both catalysts presented similar cobalt dispersions and maintained the textural properties observed in the slurried samples once they were deposited onto the metallic monoliths. Being made of a high-thermal-conductivity substrate, the structured catalysts behaved like isothermal reactors with no significant radial thermal gradient being observed inside them during the reactions. Under isothermal conditions, the catalytic differences in Fischer-Tropsch synthesis tests carried out at the same conversion values were ascribed to only diffusional effects imparted by the influence of the macropores. Methane selectivity increased and C5+ selectivity decreased linearly with catalyst loading. Moreover, for the highest catalyst loading used, methane selectivity was higher and C5+ selectivity was lower for the catalyst with transport pores. However, when the results of catalysis studies were analyzed asa function of the average catalyst layer thickness; thus under equivalent diffusion lengths, the catalyst containing transport pores showed lower methane selectivity and higher C5+ selectivity than the reference catalyst over the entire range of layer thicknesses studied. Therefore, the effect of macropores was observed to reduce the diffusion limitations, although at high catalyst loadings the layer thickness determined the selectivity results more than the macroporosity of the layer.

Catalytic oxidation of toluene: comparative study over powder and monolithic manganese-nickel mixed oxide catalysts

ABSTRACTThis paper is focused on development of the metal monolithic structure for total oxidation of toluene at low temperature. The well-adhered catalyst, based on the mixed oxides of manganese and nickel, is washcoated on the Al/Al2O3 plates as metallic support. For the comparison purposes, results observed for the manganese–nickel mixed oxide supported on the metallic monolith are compared with those obtained using powder type of the same catalyst. Prepared manganese–nickel mixed oxides in both configurations show remarkable low-temperature activity for the toluene oxidation. The reaction temperature T50 corresponding to 50% of the toluene conversion is observed at temperatures of ca. 400–430 K for the powder catalyst and at ca. 450–490 K for the monolith configuration. The appropriate mathematical models, such as one-dimensional (1D) pseudo-homogeneous model of the fixed bed reactor and the 1D heterogeneous model of the metal monolith reactor, are applied to describe and compare catalytic performances of both reactors. Validation of the applied models is performed by comparing experimental data with theoretical predictions. The obtained results confirmed that the reaction over the monolithic structure is kinetically controlled, while in the case of the powder catalyst the reaction rate is influenced by the intraphase diffusion.

Effect of the thermal conductivity and catalyst layer thickness on the Fischer-Tropsch synthesis selectivity using structured catalysts

Metallic monoliths composed of flat and corrugated foils were prepared in-house using two different alloys (Fecralloy® and aluminum) and cell densities (280 and 2300cpsi), and different loadings of a (20% Co–0.5% Re)/Al2O3 catalyst were deposited on their surface by washcoating, producing a wide range of average catalyst layer thicknesses. The obtained structured catalysts were tested in the Fischer-Tropsch synthesis, exhibiting increased selectivity for methane and decreased selectivity for C5+ fraction production with increasing average catalyst layer thickness. This effect was observed for all layer thicknesses in the case of aluminum monoliths with both cell densities and for Fecralloy® ones with a high cell density. Conversely, Fecralloy® monoliths with a low cell density exhibited a critical maximum catalyst layer thickness of ∼50μm, with diffusional and thermal limitations resulting in temperature and selectivity runaways at higher thicknesses. These results indicated the importance of high effective thermal conductivity of substrates for adequate temperature control in structured Fischer-Tropsch synthesis catalysts, which could be achieved by using highly conductive metallic monoliths (e.g., those made of aluminum) or increasing the cell density of less conductive alloys (e.g., Fecralloy®). Finally, the good thermal control observed for aluminum monoliths permitted to enhance the production of C5+ at higher temperatures without significantly increasing methane selectivity.

Flow resistance and heat transfer in short channels of metallic monoliths: Experiments versus CFD

Experimental and numerical studies were conducted on flow friction and heat transfer in short channels of triangular and sinusoidal cross-section assuming developing laminar air flow. Reynolds numbers range of 13–2880 was examined. Spatial distribution of the gas velocity, as well as the rates of local heat transfer between channel walls and gas stream, were determined on the basis of the computational fluid dynamics. It was shown that there is no flow stabilization over the whole channel length under the study conditions. The most intensive transfer and friction appears near the channel inlet, which causes the highest local heat transfer rates at the channel walls. It was also demonstrated that velocity profile is not entirely flat at channel inlet due to drag forces caused by frontal surface of channel wall. The numerical results based on the CFD tool FLUENT® agree reasonably well with the experimental data.

Monoliths: A Review of the Basics, Preparation Methods and Their Relevance to Oxidation

Considerable research has been conducted on monolithic catalysts for various applications. Strategies toward coating monoliths are of equal interest and importance. In this paper, the preparation of monoliths and monolithic catalysts have been summarized. More specifically, a brief explanation for the manufacturing of ceramic and metallic monoliths has been provided. Also, different methods for coating γ-alumina, as a secondary support, are included. Techniques used to deposit metal-based species, zeolites and carbon onto monoliths are discussed. Furthermore, monoliths extruded with metal oxides, zeolites and carbon are described. The main foci are on the reasoning and understanding behind the preparation of monolithic catalysts. Ideas and concerns are also contributed to encourage better approaches when designing these catalysts. More importantly, the relevance of monolithic structures to reactions, such as the selective oxidation of alkanes, catalytic combustion for power generation and the preferential oxidation of carbon monoxide, has been described.

Washcoating of Ni/MgAl2O4 Catalyst on FeCralloy Monoliths for Steam Reforming of Methane

In this study, the effect of different process variables on the washcoating of Ni/MgAl2O4 on FeCralloy foils and monoliths has been investigated and the washcoated monolith tested for the steam reforming of methane. Washcoating parameters, such as calcination temperature after washcoating, addition of binders, particle size of the slurry after ball milling, and rheological properties of the slurry, not only affected the loading and adherence of the washcoat, but also significantly affected the physicochemical properties of the catalyst. Slurry milled for 48 h (average particle size ∼2 μm) of pH 2–4 was found to be most stable and resulted in homogeneous washcoating. Increasing the calcination temperature after washcoating from 600 to 800 °C decreased the weight loss observed during adhesion test. However, the weight loss of the washcoat was still significant. Furthermore, typical procedures for sol coating of the metal monolith, before slurry washcoating, did not improve adhesion of Ni/MgAl2O4 washcoating...

Enhancement of washcoat adhesion for SCR catalysts to convert nitrogen oxide using powder spray coating of TiO2 on metallic honeycomb substrate

A novel powder spray coating method was applied to form intermediate layers on metallic honeycomb substrates to improve the adhesion property of ceramic-based washcoat layer without any binder addition. Washcoating of SCR catalysts for abatement of nitrogen oxides was performed with different numbers of coating and different amounts of washcoat loading. Metallic monoliths with the intermediate layer showed much better washcoat adhesion property than monoliths without the layer even with high washcoat loading. The surface-modified monoliths had better NO conversion performance than the samples without the intermediate layer after ultrasonic vibration test to measure adhesion property of the washcoat layers.

Ru-coated metal monolith catalyst prepared by novel coating method for hydrogen production via natural gas steam reforming

Ru-coated FeCrAlloy monolith catalysts were prepared by a deposition-precipitation (DP) method with different solution pHs and evaluated the catalytic activity in natural gas steam reforming (NGSR) reaction for H2 production. The characteristics of prepared monolith catalysts as to the crystallite size, surface area, pore size distribution, metal dispersion, and morphology of Ru particles were analyzed by XRD, BET, BJH, CO-chemisorption, and SEM, respectively. The solution pH had a major effect on the precipitation formation and the particle size and dispersion of Ru catalyst coated on the monolith surface. At pH 7, nano-sized Ru particles with high BET surface area (112m2/g) and metal dispersion (23.5%) were formed uniformly on the monolith surface. Among the prepared monolith catalysts, the monolith catalyst prepared at pH 7 showed the highest CH4 conversion in NGSR. Despite the less amount of Ru metal coated on the metal monolith, the monolith catalyst showed a good catalytic performance equivalent to the 2wt% Ru/Al2O3 pellet catalyst due to the high availability of the Ru active metal in NGSR. It was also confirmed that the Ru catalyst layer coated on the FeCrAlloy monolith had good adhesion via ultrasonic vibration test.

Study of Cu-Zn and Au/TiO2 Catalysts on Anodized Aluminum Monoliths for Hydrogen Generation and Purification

Abstract This work reports the preparation of Cu-Zn and Au/TiO2 catalysts on anodized aluminum monoliths (AAM). The structured catalysts were studied for the generation of H2 by methanol steam reforming (MSR) and its purification by preferential oxidation of CO (CO-PrOx). Initially, it was possible to generate a surface with whiskers and larger surface area by hydrothermal treatment of the AAM. Subsequently, the structured catalysts were synthesized by incipient wetness impregnation (IWI) and hydrothermal synthesis (HS). IWI synthesis allowed for the deposition of a larger amount of catalytic material than HS, with very good adhesion. The TiO2-IWI structured catalyst presented a homogeneous catalytic coating, with the presence of agglomerated particles. On the other hand, Cu-Zn-IWI showed good dispersion of the deposited particles with a homogeneous surface coating. EDX analysis corroborated the presence of Ti, Cu and Zn in all the catalytic surfaces. The incorporation of Au over TiO2-IWI structured catalysts was successfully performed by IWI using a colloidal solution of gold nanoparticles. MSR was studied over the developed metallic monoliths functionalized with Cu-Zn by the IWI method. The samples showed promising results in terms of activity, selectivity, and stability. Both diluted and concentrated methanol + water feeds were assayed. Complete methanol conversion was achieved for the diluted feed. Maximum methanol conversions of 55 % with 60 % H2 yield were measured when the concentrated feed was selected. Promising results were also achieved for the Au-based structured catalysts in the CO-PrOx in an H2-rich atmosphere. Although CO conversions of approximately 60 % were achieved, operating with higher catalyst loadings would be recommended to reach the high CO conversions required for PrOx catalysts.

Effect of the thermal conductivity of metallic monoliths on methanol steam reforming

We have studied the influence of cell density of two sets of metal monoliths coated with different amounts of Pd/ZnO in the methanol steam reforming (MSR). The results indicate that the conversion increases with increasing size of the channels that is accompanied by a decrease in the monoliths cell density. To explain this unexpected result, the longitudinal and radial temperature profiles were measured. It was observed that the thermal conductivity increased with increasing cell density and temperature profiles became more marked with increasing catalyst loading on the monolith. This last result was explained by the increase of the heat required for the reaction to maintain a constant space velocity. Being fixed central temperature of the monolith and being the MSR an endothermic reaction, the average temperature increases with decreasing thermal conductivity. To assess whether this increase in average temperature justifies the observed increase in conversion, a CFD modeling of the system was performed. The simulation results showed an excellent agreement with experimental values. This confirms the fundamental role of thermal conductivity, which is mainly controlled by the cell density of the monolith.

Structuring hybrid palladium nanoparticles in metallic monolithic reactors for continuous-flow three-phase alkyne hydrogenation

Ligand-modified palladium nanoparticles are stabilised in the microchannels of an alumina-coated metallic monolith and advantageously used in the continuous-flow three-phase semi-hydrogenation of acetylenic compounds.

Catalytic Converter Developed By Washcoat Of γ-Alumina On Nickel Oxide (Nio) Catalyst In FeCrAl Substrate For Exhaust Emission Control : A Review

Automobile exhaust emission control is one of the trending issues in automobile research field. The existing catalytic converter using the noble metals of platinum (Pt), palladium (Pd) and rhodium (Rd) recently were in limited supply and higher in cost. There is a need for the automotive industry to produce ultra-low emitting vehicles at a reasonable cost. The objective of this study is to investigate the effectiveness of methods of fabrication of modified catalytic converter by approaching FeCrAl as a substrate which treated using ultrasonic bath technique to improve the exhaust emission control. The modified catalytic converter preparation will involve the ultrasonic bath process of FeCrAl foil which has fabricated as metallic monolith coated by γ-Al 2 O 3 powder. Nickel as catalyst material will be prepared using electroplating process. The oxidation test will be conducted using a tube and automatic furnace in temperature of 1100°C for 100 hours. Mitsubishi 4G93 1800cc Petrol E.F.I with a multi -gas analyzer equipped with a hydraulic dynamometer will be used for emission measurements of HC, CO, and NO x in varying speed and load for both conditions with and without catalytic converter. The result will expect the γ-Al 2 O 3 as the washcoat material that fully embedded to FeCrAl substrate with the combination of ultrasonic and electroplating technique will effectively convert the CO, NO x and HC to CO 2 , NO 2 and H 2 O which means that catalytic converter is effective to improve exhaust emission control of diesel engine. The FeCrAl substrate as a metallic catalytic converter which coated by γ-Al 2 O 3 using ultrasonic and nickelelectroplating technique may improve the exhaust emission control.

Novel intense metallic monolith for automotive applications: Experimental versus numerical studies

Three-dimensional numerical analysis for simultaneously developing fluid flow and heat transfer through triangular and sinusoidal channels is simulated in this paper. ANSYS FLUENT 12 was used for simulations. Numerical results were compared with experimental ones for the same channels dimensions. The research was conducted to verify that very short metallic monoliths could be applied to engine pre-turbo catalytic converters. It was shown that short monoliths have high potential to reduce HC/CO emissions due to higher temperatures and flow velocities in front of the turbocharger, resulting in increased heat and mass transfer and reaction kinetics accompanied with reduced flow resistance.

Facile synthesis of porous silver monoliths with excellent catalytic activity

In this study, novel porous silver (Ag) monoliths have been successfully prepared via a facile process by combining an aging treatment with a thermal-induced reduction reaction. The obtained Ag samples display distinct morphologies via simply adjusting reaction conditions such as aging temperature and precursor’s concentrations. More interestingly, the as-made porous Ag samples exhibit superior catalytic activity and durability in the catalysis over reduction of P-nitrophenol (4-NP). Remarkably, the synergistic effects of stabilizing and oxidative etching agents should be responsible for the fabrication of hierarchical metallic monoliths, which highlight significant advantages over the existing techniques given that the present method is facile, inexpensive, environmentally benign, and amenable to scale-up process.

Catalytic Combustion of Ethyl Acetate over Manganese Oxides Deposited on Metallic Monoliths

AbstractMnOx/AISI 304 austenitic stainless‐steel monolithic catalysts were prepared by impregnation with aqueous solutions of manganese nitrate or acetate. The preparation method was satisfactory in terms of reproducibility and adherence of the deposited phase. The use of different precursors led to significantly dissimilar results. With manganese nitrate, the formation of Mn‐Cr‐O mixed phases on the surface was favored, whereas with manganese acetate, Mn2O3 was the predominant active phase. The Mn‐Cr‐O mixed phases would be highly dispersed but their catalytic activity was low. The major catalytic behavior was obtained with monoliths impregnated with manganese acetate.

Au/CeO2 metallic monolith catalysts: influence of the metallic substrate

Ceria-based gold catalysts were successfully deposited on ferritic stainless steel (Fecralloy) and aluminium monoliths. The prepared monolithic and reference powder catalysts were characterized by means of S BET, X-ray diffraction, glow discharge optical emission spectroscopy and scanning electron microscopy–energy dispersive X-ray analysis techniques and tested in the CO oxidation reaction. Characterization results put in evidence the diffusion of cations from the catalytic layer on the surface of the monoliths to the metallic oxide scale and inversely, from the oxide scale to the catalysts, thus altering the catalytic formulation and affecting the CO oxidation properties of the catalytic device. The extension and nature of the modifications produced depend on the nature of the catalysts and the metallic substrate, as well as the reaction conditions applied. These facts must be considered when gold catalysts are supported on metallic-structured devices.

Structured catalysts based on Mg–Al hydrotalcite for the synthesis of biodiesel

The performance of metallic (Fecralloy®) monoliths based on Mg–Al hydrotalcite for the synthesis of biodiesel through the methanolysis of sunflower oil is reported for the first time. A Mg–Al hydrotalcite was synthesized and the oxides obtained after calcination at 500°C were employed for preparing the slurries used for washcoating the monoliths. Using methanol as the solvent and sepiolite as binder allowed to reach 96% adherence after sonication. The positive effect of sepiolite on adherence seems to be related with its fibrous nature and ability for crosslinking with the hydrotalcite particles. However, catalytic tests have shown a negative effect of sepiolite on the methanolysis activity that can be attributed to the partial neutralization of the basic sites and/or masking of the hydrotalcite particles. The performance of the structured catalysts has been investigated in a monolithic stirrer reactor under very mild conditions (60°C and 1atm). Using 2wt.% of catalyst allowed reaching 62–77% oil conversion after 10h. However, the poor adherence of the coating in the reaction mixture prevented the effective reutilization of the catalysts. Further work is required concerning the formulation of the coating slurries to improve adherence in the chemically aggressive medium involved in the synthesis of biodiesel.