Ceramic Monoliths Research Articles

Utilization of NiO/porous ceramic monolithic catalyst for upgrading biomass fuel gas

Catalytic steam reforming for producing high quality syngas from biomass fuel gas was studied over monolithic NiO/porous ceramic catalysts in a fixed-bed reactor. Effects of reaction temperature, steam to carbon (S/C) ratio, and nickel loading content on catalyst performance were investigated. Results indicated that the NiO/porous ceramic monolith catalyst had a good ability to improve bio-fuel gas quality. H2 yield, H2 + CO content, and H2/CO ratio in produced gas were increased when reaction temperature was increased from 550 to 700 °C. H2 yield was increased from 28.1% to 40.2% with S/C ratio increased from 1 to 2. And the yield of hydrogen was stabilized with the further increase of S/C ratio. Catalyst activity was not always enhanced with increased nickel content, when NiO loading content reaches 5.96%, serious aggregation and sintering of active composition on catalyst surface occur. The best performance, in terms of H2 yield, is obtained with 2.50% NiO content at reaction temperature of 700 °C and S/C ratio of 2.

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.

Gradient-Hierarchic-Aligned Porosity SiOC Ceramics

This work describes a simple technique to produce porous ceramics with aligned porosity having very high permeability and specific surface area. SiOC-based compositions were processed from blends of three types of preceramic polymer and a catalyst, followed by curing and pyrolysis. The heating applied from the bottom of molds promoted the nucleation, expansion and rising of gas bubbles, and the creation of a ceramic matrix with axially oriented channels interconnected by small round pores. The samples were analyzed by SEM, tomography, BET, water immersion porosimetry and permeation to gas flow. The resulting bodies presented levels of open porosity (69.9–83.4%), average channel diameter (0.59–1.25 mm) and permeability (0.56–3.83 × 10−9 m2) comparable to those of ceramic foams and honeycomb monoliths, but with specific surface area (4.8–121.9 m2/g) typical adsorbents, enabling these lotus-type ceramics to be advantageously used as catalytic supports and adsorption components in several environmental control applications.

Wicking into porous polymer-derived ceramic monoliths fabricated by freeze-casting

Silicon oxycarbide monoliths of different pore size distribution were fabricated by freeze-casting. The samples revealed a lamellar pore structure with an axial anisotropy. To evaluate the capillary transport abilities we performed wicking experiments. The sample weight measurement method was applied during the imbibition. The samples show deviations in permeability from 10% to 49% at different sample orientations that quantifies the impact of the anisotropy in the axial direction. The deviations were larger for the samples with smaller pore size. For these samples we also observed larger differences in the wicking behaviour. The samples with bigger pore size demonstrated higher permeability and faster wicking. Imbibition results at both sample orientations showed a good agreement with a prediction via the Lucas–Washburn equation with gravity effects. We demonstrate hereby, that our approach of macroscopic modelling predicts wicking behaviour in anisotropic structures reasonably well, providing a simple tool for further porous material investigations.

CO2 hydrogenation on Ru/Ce based catalysts dispersed on highly ordered micro-channelled 3YSZ monoliths fabricated by freeze-casting

The activity of Ru–Ce/3 mol% Y2O3 doped ZrO2 (3YSZ) catalysts was studied for the CO2 hydrogenation to form CH4 using catalyst-loaded freeze-cast ceramic monolith as possible substitute to conventional support fixed bed catalysts. Two set of three catalysts were elaborated by varying the Ru loading at 2.5, 5 and 7.5 wt% and by using as support (i) 3YSZ powder and (ii) 3YSZ hierarchically ordered and highly porous freeze-cast monolith. Freeze-cast monoliths present an interesting feature sought for catalytic devices, i.e., large and organized porosity boosting gas transport and minimizing pressure loss through it. The catalytic results reveal the adequate catalytic activity of both catalyst configurations and detail the beneficial effect of a monolith as support on CH4 selectivity and CO production. As expected thermodynamically, an increase in the H2 content in the reactor feed shifts the intermediate Reverse Water Gas Shift (RWGS) reaction to the equilibrium and thus improves CH4 yield. This improvement can be explained by the difference of packing between both configuration and at a similar GHSV, the monolith favors the RWGS reaction further in the monolith length which apparently does not occur in the same proportion in the conventional fixed-bed. Finally a study of the pressure drop through all the catalysts did not reveal any significant increase of pressure due to carbon deposition or high inlet flow.

Si-B-C-N monoliths with LaB6-induced well-developed BN(C) flakes

Si-B-C-N ceramic monoliths with LaB6 additive were prepared by mechanical alloying followed by spark plasma sintering. The microstructures and mechanical properties were investigated compared to LaB6-free Si-B-C-N counterparts. After sintered at 1900°C/50MPa, the La/Si-B-C-N monoliths provide well-developed BN(C) flakes (≤100nm in thickness) and improved fracture toughness, while the BN(C) ones show no lamellar microstructures in Si-B-C-N systems. The solid-solution of La in BN(C) grains promotes ordered arrangement of BN(C) along the (0002) plane causing in situ growth of BN(C) thus leading to an increase in toughness by 40% (from 5.6 to 7.8MPam−1/2).

Monolithic translucent BaMgAl10O17:Eu2+ phosphors for laser-driven solid state lighting

With high power light emitting diodes and laser diodes being explored for white light generation and visible light communication, thermally robust encapsulation schemes for color-converting inorganic phosphors are essential. In the current work, the canonical blue-emitting phosphor, high purity Eu-doped BaMgAl10O17, has been prepared using microwave-assisted heating (25 min) and densified into translucent ceramic phosphor monoliths using spark plasma sintering (30 min). The resulting translucent ceramic monoliths convert UV laser light to blue light with the same efficiency as the starting powder and provide superior thermal management in comparison with silicone encapsulation.

CO-PrOx over nano-Au/TiO2: Monolithic catalyst performance and empirical kinetic model fitting

In this work, the performance of ceramic monoliths washcoated with Au/TiO2 is studied on CO preferential oxidation (CO-PrOx) reaction in H2-rich environments under a wide range of operating conditions of practical interest. The parameter estimation of a nonlinear kinetic empirical model representing this system is made via genetic algorithms by fitting the model predictions against our laboratory observations. Parameter uncertainty leading to inaccurate predictions is often present when kinetic models with nonlinear rate equations are considered. Here, after the fitting was concluded, a statistical study was conducted to determine the accuracy of the parameter estimation. Activation energies of ca. 30 kJ/mol and 55 kJ/mol were adjusted for CO and H2 oxidations, respectively. The catalyst showed appropriate activity and selectivity values on the CO oxidation on a H2-rich environment. After ca. 45 h on stream the catalyst showed no deactivation. Results show that the model is suitable for reproducing the behavior of the CO-PrOx reactions and it can be used in the design of reactors for hydrogen purification.

Ceramic monolith supported Mn–Ce–M ternary mixed-oxide (M=Cu, Ni or Co) catalyst for VOCs catalytic oxidation

The MOx (M=Cu, Ni or Co) modified manganese-cerium mixed-oxide catalysts supported on ceramic monolith were prepared by sol-gel method and examined for the catalytic combustion of o-xylene. Results show that the addition of CuOx could significantly enhance the catalytic properties of the monolithic catalysts, which may be correlated with the Mn-Cu synergistic interaction. The effects of the preparation parameters including the Cu content, the total amount of active phase and the calcination temperature and time, as well as the reaction conditions, i.e., the space velocity and concentration of o-xylene, on the catalytic performance for the combustion of o-xylene were also investigated. It is shown that the MnCeCu0.4/monolith catalyst with the active phase loading of 11.4wt% and calcined at 500°C for 3h displays the highest catalytic activity. When the concentration of o-xylene is 1000ppm and the space velocity is 10,000h−1, the temperature at which 90% o-xylene conversion is reached is 277°C. It is also seen that the optimum catalyst has a good catalytic stability and exhibits an excellent activity not only at a rather high space velocity but also within a wide range of o-xylene concentration. Furthermore, the optimum catalyst also show the high combustion performance for other hydrocarbons, e.g., n-butanol and styrene.

Development of a syngas-fired catalytic combustion system for hybrid solar-thermal applications

This paper describes the development and operation of a catalytic combustion system for use with syngas as an important component of a hybrid heating source for solar-thermal power generation. The reactor consists of a cylindrical ceramic monolith with porous alumina washcoat in which platinum is distributed as the catalyst. Two fuel-rich equivalence ratios were studied over a range of flow rates. The fuel-rich conditions permit low temperature combustion without the problem of hotspots likely to occur under fuel-lean conditions with hydrogen-containing fuels. Experimental data of temperature and species concentration at the exit of the reactor have been reported for a maximum fuel thermal input of 34kW. The system exhibited quick start-up with a light-off time of around 60s and a steady-state time of around 200s as determined from the transient temperature profiles. The experimental results have also been complemented with detailed two-dimensional numerical simulations for improved understanding of the combustion characteristics in the reactor. The simulations suggest that the combustion system can be operated at a turn-down ratios far in excess of 1.67, which is the maximum value that has been investigated in the present setup. Stable operation, quick startup, and high turn-down ratio are some of the key features that enable the proposed combustion system to accommodate the transients in solar-thermal applications.

Ni/CeO2-thin ceramic layer depositions on ceramic monoliths for syngas production by Oxy Steam Reforming of biogas

Ni-CeO2 catalysts (metals load equal to 7.5wt.%) as thin oxide layers on ceramic monoliths have been obtained by support dip-coating into acid-free stable catalyst dispersion. Ni-based catalysts were prepared by precipitation-dry-impregnation method or solution combustion synthesis and characterized by XRD, BET, CO-Chemisorption, TPR, TEM and SEM-EDX techniques.Coating load (15–20wt.%) was controlled by multiple depositions on the basis of the slurry rheological behavior. Procedure goodness was evaluated in terms of coating load and adhesion performance. Homogeneous and well adherent layers of ca. 10–20μm were found. The performance of final structured systems was evaluated towards biogas oxy-steam reforming (OSR) reaction, highlighting the influence of morphological and structural properties of synthesized Ni-based powders on the catalytic activity. Catalytic tests demonstrated superior performances of solution combustion synthesized Ni/CeO2 catalyst washcoated on monolith, especially at high space velocity.

Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis

A ceramic monolith heat exchanger has been learnt for finding out heat transfer performance and effectiveness on computing numerically and ξ-NTU method. In entire domain computation numerically has been performed along with fluid region in rectangular ducts of exhaust gas side, ceramic core and rectangular duct fluid region in air side with the air exhaust in direction of cross flow. Additionally, the heat exchanger has been examined for estimating the functionality via ξ-NTU technique that is conventional along numerous Nusselt number links for rectangular duct flow for the literature. Based on the research, it has been performed on the ceramic heat exchangers and on the ceramic materials and the demand in utilizing the ceramic materials in heat exchangers. Then the recuperator is modeled by using GAMBIT and it is analyzed using FLUENT. The effectiveness and the heat transfer rate are also calculated. Then those outcomes have been assessed along the experimental data. By comparison of both functionality by computing numerically and the ξ-NTU technique, the efficiency by ξ-TU technique has been identified to be nearest to product by the numerical computation among the associative of 2.15% when Stephan's Nusselt number association has been adapted to the ξ-NTU technique within numerous connections. The total heat transfer and effectiveness by ξ-NTU method relative errors utilizing five Nusselt number correlations from literature have been lesser than 14.5% comparative to numerical computation. Associated to Nusselt number correlations, the entire heat transfer utilizing ξ-NTU technique with Stephan's correlation is highly nearest to numerical computation. For that reason, the exit temperature by ξ-NTU method with Stephan's correlation simulates within 1.2% of the relative error for exhaust exist temperature and 0.45% for the air exit temperature assessed against the numerical computation. Overall heat transfer coefficient's relative errors by ξ-NTU technique utilizing five Nusselt number correlations for the literature have been more than 17.5% to that on computing numerically.

Theoretical Study and Analysis on Performance Enhancement of a Ceramic Monolith Heat Exchanger

Background/Objectives: Ceramic heat exchangers are preferred in most high temperature applications due to its high temperature stability and corrosion resistance. Evaluation of performance of the heat exchanger under different circumstances helps us to select suitable design for certain application. Methods/Statistical Analysis: This work investigated the functioning capability of a ceramic heat exchanger, determining pressure drop and the heat transfer theoretically by Ɛ-NTU method by using silicon carbide and aluminium nitride as heat exchanger material. The performance of both the ceramic material under the desired condition was compared. A heat exchanger possess ducts that is rectangular to exhaust gas, ducts which are rectangular for air and exhaust gases, a core made of ceramic along with air in the cross-flow direction. Findings: Heat exchanger has been investigated involving conventional Ɛ-NTU technique with numerous Nusselt number correlations from the literature for characterizing the rectangular duct flow. Theoretical analyses reveal that, while using aluminium nitride as the heat exchanger material the performance parameters such as overall heat transfer got increased by 4.5-5%, effectiveness by 3% and heat transfer rate by same 3% relative to silicon carbide as the heat exchanger material. Applications/Improvements: Analysis on performance enhancement of all other heat exchanger.

Self-Assembled Gyroidal Mesoporous Polymer-Derived High Temperature Ceramic Monoliths

Polymer-derived ceramics (PDCs) have enabled the development of nonoxide ceramic coatings and fibers with exceptional thermo-mechanical stability. Here, we report the self-assembly based synthesis of gyroidal (space group Q230, Ia3d) mesoporous silicon oxynitride ceramic monoliths by pyrolysis of blends of commercially available preceramic polysilazane with a structure-directing triblock terpolymer up to temperatures of 1000 °C. Monoliths had pore diameters of 9.4 ± 1.1 nm and surface area of 160 m2/g. The three-dimensionally (3D) ordered periodic pore structure of the as-made hybrids acts to relieve stresses by allowing the escape of gases formed during ceramization. This process in turn enables the retention of smooth monoliths during ceramization under ammonia, a process that both adds nitrogen to the material and removes carbon pyrolysis products. The monoliths are appealing for high-temperature applications such as catalyst supports and microelectromechanical system (MEMS) devices including gas and ...

Polymeric liquid precursor of multi-component ZrC–SiC ceramic

Polymeric liquid ceramic precursors for the production of multi-component ZrC–SiC ceramics were prepared by reactive blending of polyzirconoxanesal, phenylacetylene-terminated polysilane and bisphenol-A type benzoxazine. The polymeric liquid precursors of ZrC–SiC ceramic have the processing capability of Precursor-Infiltration-and-Pyrolysis technique in ceramic composites fabrication. The thermal cure reactions included by the catalytic polymerisation of ethynyl groups, the ring opening polymerisation of benzoxazine rings, and the condensation of zirconate with phenolic hydroxyl and Si–H at 200–350°C. The monolithic ceramics were formed upon pyrolysis at 1000, 1200 and 1600°C in a yield of 65, 62 and 40%, respectively. X-ray diffraction and SEM–EDS results revealed that almost pure, elemental, uniformly distributed ZrC–SiC multi-component ceramic monolith was obtained through pyrolysis at 1600°C via carbothermal reduction of ZrO2.

Structured carbons as supports for hydrogenation hybrid catalysts prepared by the immobilization of a Rh diamine complex

A CNF-monolith sample (carbon nanofibres grown on a ceramic monolith), and a granular carbon xerogel have been used as supports for hybrid catalysts where the active species is an Rh diamine complex. The advantages of these supports are their open porous structure and their morphology, which make catalyst handling easier and avoid difficult separation processes. The obtained catalysts are noticeably more active than the homogeneous Rh complex and are stable against leaching. At first use, partial reduction of the Rh complex takes place and nanometer-sized Rh particles develop, which increases the catalyst activity. Despite the open porous structure, mass transport limitations are present, especially in the case of the carbon xerogel based catalyst. Differences in internal mass transfer limitations are essentially due to the different diffusional path lengths.

High-temperature oxidation behavior of polymer-derived SiHfBCN ceramic nanocomposites

Within this study, the oxidation behavior of SiHfBCN ceramic powders and monoliths was studied at temperatures from 1200 to 1400°C. Both powder and monolithic samples exhibited parabolic oxidation behavior characterized by very low rates (10−9–10−8mg2cm−4h−1). The activation energy of 112.9kJmol−1, which was determined for the SiHfBCN powder, is comparable to that of other silica formers such as silicon or SiC and relates to the diffusion of molecular oxygen through silica scale. Whereas, the values determined for the SiHfBCN ceramic monoliths (174 and 140kJmol−1, depending on the Hf content) indicate the complex nature of their oxidation process, leading at temperatures below 1300°C to a continuous oxide scale consisting of borosilicate, silica, m-and t-HfO2. At higher temperatures, the oxide scale consists of silica, HfSiO4 as well as m-and t-HfO2 and becomes discontinuous, probably due to the evaporation of boria.

Dissolution of Ceramic Monolith of Spent Catalytic Converters by Using Hydrometallurgical Methods / Rozpuszczanie Monolitu Ceramicznego Zużytych Katalizatorów Na Drodze Hydrometalurgicznej

Catalytic converters contain the catalytic substance in their structure, which is a mixture of Platinum Group Metals (PGMs): platinum, palladium and rhodium. The prices of these metals and a growing demand for them in the market, make it necessary to recycle spent catalytic converters and recovery of PGMs. The ceramic monolith of catalytic converters is still a predominant material in its construction among of multitude of catalytic converters which are in circulation. In this work attempts were made to leach additional metals (excluding Pt) from comminuted ceramic monolith. Classic leachant oxidizing media 10M H2SO4, HCl and H3PO4 were used considering the possibility of dissolution of the ceramic monolith.

Hierarchically ordered micro/meso/macroporous polymer-derived ceramic monoliths fabricated by freeze-casting

A hierarchically-ordered macro/meso/microporous SiOC monolith was obtained via freeze-casting using commercial polysiloxane as a raw material and silica sol as a binder and template source. The pre-ceramic polymer polysiloxane was pyrolyzed at 600°C to produce a hydrophilic surface; higher temperatures would fully decompose the organic groups. When silica sol and polysiloxane precursor were combined in freeze-casting method, after pyrolysis a polymer-derived SiOC ceramic monolith with a lamellar pore morphology and a hierarchically-ordered pore structure was obtained. Decomposition of the polysiloxane precursors results in the development of micropores, and particle packing is believed to be responsible for the mesopore formation. Macro/mesoporous hierarchically-ordered ceramics with a specific surface area of 74 m2/g are preserved at pyrolysis temperatures as high as 1000°C. The influence of H44-derived filler amount (10wt–40wt%), freezing temperature (−20°C, −80°C, −150°C), and pyrolysis temperature (600°C, 700°C, 1000°C) on open porosity, pore size distribution, and surface characteristics were investigated.

Crystallization Behavior of Amorphous Si2BC3N Ceramic Monolith Subjected to High Pressure

The crystallization behavior of amorphous Si2BC3N monoliths by heating at 1000°C–1400°C and 5 GPa was investigated with the special attention to the nucleation mechanisms of β‐SiC and BN(C) phases. Nanoscale puckered structures arising in particle bridging areas were found and its evolution behavior well reflected the nucleation process of nanocrystallites. The temperature‐dependent crystallization of amorphous Si2BC3N monoliths at 5 GPa passes through four stages: The material remains amorphous below 1100°C. It undergoes partial phase segregation (1100°C–1200°C), followed by initiation of nucleation (1200°C–1250°C), and then nucleation and growth of β‐SiC and turbostratic BN(C) crystallites (>1250°C). The first principles calculation indicates the nucleation precedence of BN(C) phase over β‐SiC. BN(C) nucleates preferentially at bridges between ceramic particles causing SiC to concentrate in particle interiors thus forming capsule‐like structures.