Ceramic Foam Catalyst Research Articles

Continuous catalytic pyrolysis of waste oil to aromatics: Exploring the structure-performance relations of ZSM-5 based on different scale-up forms

Waste oil, a byproduct of oil industry, holds significant potential to valuable aromatics through catalytic pyrolysis. However, there is a lack of research on catalysts suitable for large-scale production, which requires scaling up powder catalysts to meet industrial requirements. In this study, structure-performance relations of four different scale-up ZSM-5 in waste oil catalytic pyrolysis to aromatics was evaluated in a continuous system. Notably, ZSM-5/SiC ceramic foam catalyst exhibited the smallest pressure loss across the catalytic reactor, which was 6 times lower compared to the powder catalysts. ZSM-5/SiC ceramic foam catalyst has excellent initial activity, maintaining aromatics selectivity above 99% for the first 30 min time-on-stream and retaining 73.63% selectivity after 1 h. The pelletized ZSM-5 showed the longest lifetime during six reaction-regeneration cycles. The deactivation mechanism of ZSM-5 was deduced. This study helps to better understand the process at the molecular level and also contribute to research in large-scale production.

Fabrication of a Ceramic Foam Catalyst Using Polymer Foam Scrap via the Replica Technique for Dry Reforming.

Megapores with spherical-like cells connected through windows and high porosities make up catalyst supports in the form of ceramic foams. These characteristics provide significant benefits for catalytic processes that are limited by mass or heat transport. This study focuses on the manufacture of ceramic foam using a polymeric sponge replica process and polymer foams as a template for catalyst supports, which are industrial waste from the packaging sector. To make ceramic foam catalysts, they were dipped in a catalyst solution, followed by a breakdown stage and a sintering process. Experiments focused on determinants that affect the desired characteristics of ceramic foams, such as the types of polymer foams that affect foam morphology, the rheology of catalyst solution that affects catalyst dispersion, and the polymer decomposition rate that affects catalytic performance during dry reforming of the methane process. The cell architectures of polyurethane and polyvinyl alcohol foams are attractive for catalyst support preparation because they have 98–99% porosity and typical cell sizes of 200 and 50 μm, respectively. The polyurethane performance was superior to the performance of polyvinyl alcohol in terms of higher porosity and better catalytic-solution absorption offering high catalyst active areas. The catalyst prepared from concentrated 10 wt % Ni/Al2O3–MgO (10NAM) slurry had the highest surface area (59.18 m2/g) and the highest metal oxide dispersion (5.65%). These results are relevant to the flow behavior of catalyst slurry which plays a key role in coating the catalyst gel on the polymer template. The thermal decomposition rate used to remove the polymer template from the catalyst structure is proportional to the ceramic foam structure (catalyst support structure). The slow decomposition rate bent and fractured foam-cell struts more than the faster rate. On the other hand, achieving good catalyst dispersion on catalyst supports necessitated a high sintering rate. When sintering was adjusted at a high sintering rate, the metal–particle dispersion was relatively high, around 7.44%, and the surface area of ceramic foam catalysts was 64.61 m2/g. Finally, the catalytic behavior toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions.

Wall heat transfer coefficient and effective radial conductivity of ceramic foam catalyst supports

In this work, different tubular solid-foam packed-beds were experimentally investigated under air flow in order to determine the effective conductivity and wall-to-bed heat transfer coefficient. Several foam types with different material, namely silicon carbide and alumina, and cell density were tested. Foam samples were experimentally studied using different air flow rates and wall temperatures ranging between 200 and 500°C. Axial and radial steady-state temperatures in the bed were experimentally measured and analysed with a two-dimensional, one-equation model. A Chilton–Colburn-type correlation based on the reactor diameter as characteristic dimension was proposed for the wall-to-bed heat transfer coefficient, which proved good to describe the behaviour of all tested foams. Effective radial thermal conductivity and pressure drop in the foams were also characterized.

Microwave-assisted catalytic co-pyrolysis of soybean straw and soapstock for bio-oil production using SiC ceramic foam catalyst

Microwave-assisted catalytic co-pyrolysis of soybean straw and soapstock was investigated by using silicon carbide ceramic foam as catalyst. The study determined the effects of catalytic temperature, feed-to-catalyst ratio, and soybean straw-to-soapstock ratio on product yield and chemical composition. Experimental results indicated high yield and ratio of hydrocarbon in bio-oil were observed at a catalytic temperature of 350 °C. The use of a catalyst enhanced the hydrocarbon proportion at the expense of decreased in bio-oil yield. A significant synergistic effect was observed during co-pyrolysis of soybean straw and soapstock, and this effect facilitated hydrocarbon production from bio-oil.

Synthesis gas production by catalytic partial oxidation of natural gas using ceramic foam catalyst

Catalytic partial oxidation (CPOX) of natural gas was investigated over granule and ceramic foam Rh/CeO2+ZrO2+MgO catalysts under high throughput (GHSV of 180,000–1,600,000h−1) conditions at various pressures from 0.1 to 2.1MPaA. The application of ceramic foam as the substrate of Rh/CeO2+ZrO2+MgO catalyst improved the stability of the catalytic performance. It was found that the catalyst deactivation occurred when Reynolds number for flow through the catalyst bed exceeded around 20 and flow in the void of the catalyst bed changed from laminar flow regime to transitional flow regime. This change of fluid flow causes the acceleration of the mass transfer of the reactants from the gas phase to the catalyst surface and a rapid increase of the exothermic surface reaction rates over the catalyst, leading to hot spot formation. Due to larger void and smaller strut diameter of the ceramic foam, the configuration of the foam catalyst can make linear velocity lower in the catalyst bed and maintain laminar flow regime up to higher GHSV conditions than the granule catalyst, resulting in higher stability of the foam catalyst by suppression of hot spot formation. Chemical species measurements in the ceramic foam catalysts by means of a capillary sampling method revealed that the consumption rates of CH4 and O2 over Rh/CeO2+ZrO2+MgO were much lower than those over Rh/MgO and mild exothermic oxidation reaction over Rh/CeO2+ZrO2+MgO proceeds in wide region of the catalyst bed. High resistance to oxidation of Rh surface over CeO2+ZrO2+MgO even in the presence of O2 during CPOX reaction is considered to change the rates of both complete combustion reaction and reforming reaction, and to increase a contribution of another way to produce syngas.

Catalytic co-pyrolysis of waste vegetable oil and high density polyethylene for hydrocarbon fuel production

In this study, a ZrO2-based polycrystalline ceramic foam catalyst was prepared and used in catalytic co-pyrolysis of waste vegetable oil and high density polyethylene (HDPE) for hydrocarbon fuel production. The effects of pyrolysis temperature, catalyst dosage, and HDPE to waste vegetable oil ratio on the product distribution and hydrocarbon fuel composition were examined. Experimental results indicate that the maximum hydrocarbon fuel yield of 63.1wt. % was obtained at 430°C, and the oxygenates were rarely detected in the hydrocarbon fuel. The hydrocarbon fuel yield increased when the catalyst was used. At the catalyst dosage of 15wt.%, the proportion of alkanes in the hydrocarbon fuel reached 97.85wt.%, which greatly simplified the fuel composition and improved the fuel quality. With the augment of HDPE to waste vegetable oil ratio, the hydrocarbon fuel yield monotonously increased. At the HDPE to waste vegetable oil ratio of 1:1, the maximum proportion (97.85wt.%) of alkanes was obtained. Moreover, the properties of hydrocarbon fuel were superior to biodiesel and 0# diesel due to higher calorific value, better low-temperature low fluidity, and lower density and viscosity.

Preparation and Characterization of ZrO2 Polycrystalline Ceramic Foam Catalyst for Production of Biodiesel

Characteristics of ZrO2 polycrystalline ceramic foam catalyst including crystal structure, phase composition, and microstructure were analyzed by Py-IR, XRD, SEM, and BET. Effects of preparation conditions such as calcination temperature, calcination time, ZrO2 (catalyst matrix), Al2O3 (flux), TiO2 (stabilizer), NaHCO3 (low-temperature pore-forming agents), and NaCl (high-temperature pore-forming agents) on catalytic activity were investigated. The optimum composition of ZrO2 polycrystalline ceramic foam catalyst were optimized using response surface methodology (RSM) to be 88.47% ZrO2, 9.62% Al2O3, 3.31% TiO2, 10% NaHCO3, and 25% NaCl (compared with the standard number 100). After calcination at 1550°C for 120 min, fatty acid methyl ester conversion rates were substantially maintained at around 97.31%, The FAME content in the product oil exceeded 97% after five successive reuses of the catalyst. In addition, catalytic activity did not significantly fluctuate. The proposed catalyst presents a new type of solid catalyst with excellent catalytic activity and stability.

Polymeric Material Application for The Production of Ceramic Foam Catalyst

Ceramic foams are prepared as positive images corresponding to a plastic foam structure which exhibits high porosities (85–90%). This structure makes the ceramic foams attractive as a catalyst in a dry reforming process, because it could reduce a high pressure drop problem. This problem causes low mass and heat transfers in the process. Furthermore, the reactants would shortly contact to catalyst surface, thus low conversion could occur. Therefore, this research addressed the preparation of dry reforming catalysts using a sol-gel catalyst preparation via a polymeric sponge method. The specific objectives of this work are to investigate the effects of polymer foam structure (such as porosity, pore sizes, and cell characteristics) on a catalyst performance and to observe the influences of catalyst preparation parameters to yield a replica of the original structure of polymeric foam. To accomplish these objectives industrial waste foams, polyurethane (PU) and polyvinyl alcohol (PVA) foams, were used as a polymeric template. Results indicated that the porosity of the polyurethane and polyvinyl alcohol foams were about 99% and 97%. Their average cell sizes were approximate 200 and 50 micrometres, respectively. The cell characteristics of polymer foams exhibited the character of a high permeability material that can be able to dip with ceramic slurry, which was synthesized with various viscosities, during a catalyst preparation step. Next, morphology of ceramic foams was explored using scanning electron microscopy (SEM), and catalyst properties, such as; temperature profile of catalyst reduction, metal dispersion, and surface area, were also characterized by H2TPR and H2-TPD techniques, and BET, respectively. From the results, it was found that metal-particle dispersion was relatively high about 5.89%, whereas the surface area of ceramic foam catalysts was 64.52 m 2 /g. Finally, the catalytic behaviour toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions. The approaches from this research provide a direction for further improvement of marketable environmental friendly catalyst production.

Hydrogenation of commercial polystyrene on Pd/TiO2 monolithic ceramic foam catalysts: catalytic performance and enhanced internal mass transfer

Monolithic TiO2 ceramic foam (CF) supported palladium nanoparticles, possessing three-dimensional structure with open accessible pores, were developed as effective catalysts for the hydrogenation of commercial polystyrene. The monolithic CF was synthesized through uniform coating of TiO2 on synthetic template and partial sintering. The mechanical and structural properties of CF were investigated. The distribution and texture of Pd nanoparticles on the CF and their hydrogenation performances were studied. Furthermore, the internal mass transfer analysis of PS coils during the hydrogenation was evaluated. The results showed that the TiO2 CF-0.652 possessed interconnected cell windows of 400–600 μm and macropores of 200–300 nm on the struts. In 0.06 wt% Pd/CF-0.652, Pd nanoparticles (5.0 nm) were located on the surface of the TiO2 ceramic base, the dispersion of Pd was 34.3 %. As the Pd loading increased, the dispersion of Pd on the Pd/CF significantly decreased. The activity of Pd for PS hydrogenation slightly increased when the Pd loading increased from 0.06 to 0.45 wt%, which could be explained by the existence of interaction between Pd atoms and TiO2 CF at low metal loadings. For Pd/CF-0.652 catalysts, the Weisz modulus was calculated to be less than 0.30, indicating that internal diffusion limitation inside the Pd/CF-0.652 catalysts could be neglected for unique macropores on the struts.

A simplified model for natural-gas vehicle catalysts with honeycomb and foam substrates

A mathematical model is developed for the simulation of the chemical and transport phenomena in three-way catalysts for natural-gas vehicles, with honeycomb and foam substrates. The chemical phenomena are modelled on the basis of a simplified approach, which assumes that pollutant conversion is governed by oxygen storage and release dynamics. The transport phenomena, i.e. heat transfer, gas-phase mass transfer, washcoat diffusion, and pressure drop, are modelled on the basis of correlations adapted from the literature. The model is validated using lambda scan tests and a cold-start driving cycle, carried out with a honeycomb catalyst and a ceramic foam catalyst. The experimental data show a decline in methane conversion for lean mixtures, which is modelled by an inhibition term of methane oxidation from nitric oxide. The proposed model may capture the performance of both substrates with sufficient accuracy, both under cold-start and under hot-mode conditions. The model-based comparison of the two substrates shows that the ceramic foam presents inferior carbon monoxide conversion in the extra-urban part of the cycle. Although the gas-phase mass transfer in the ceramic foam is faster than with the honeycomb monolith, diffusion in the washcoat pores is much slower. As a result, the mass-transfer-limited conversion efficiency of the foam is lower. This is primarily attributed to the higher washcoat thickness of the foam sample tested.

Comparative Studies of Cellular Permeable Solids as Catalyst Supports

Metallic and ceramic foam catalyst supports and catalysts were manufactured. Comparative studies of the foam-structure catalyst supports and straight-channel catalysts supports were performed. Affect of the catalyst support pore structure upon the catalyst operational performance was analyzed.

Fundamentals and Applications of Structured Ceramic Foam Catalysts

This paper reviews the use of ceramic foams as structured catalyst supports. They are open-cell ceramic structures that may be fabricated in a variety of shapes from a wide range of materials, and they exhibit very high porosities with good interconnectivity. These characteristics result in a lower pressure drop than that observed with packed beds and high convection in the tortuous megapores, which, in turn, enhances mass and heat transfer. They are easily coated with high-surface-area catalytic components, using well-established techniques. Research in the past decade has produced a large amount of fundamental information that elucidates the desirable properties of ceramic foams. In addition, many applications involving important reactions have appeared in the open and patent literature, especially for catalytic processes that suffer certain limitations, such as those encountered in relieving high pressure drop with low-contact-time reactions at high space velocities or with narrow reactors in heat-transfer-limited systems and in controlling axial and radial temperature profiles in highly exothermic and endothermic reactions. These important contributions are discussed, and the advantages and shortcomings of using ceramic foams as structured catalyst supports to benefit commercial operations are considered.

Properties of ceramic foam catalyst supports: one-dimensional and two-dimensional heat transfer correlations

Properties of ceramic foam catalyst supports: one-dimensional and two-dimensional heat transfer correlations

Properties of ceramic foam catalyst supports: one-dimensional and two-dimensional heat transfer correlations

Ceramic foam catalyst supports in structured reactors promise higher external surface areas, lower pressure drop and increased heat transfer than beds of packed particles, especially for reactions limited to the external surface. Heat transfer is an important factor in highly endothermic and exothermic reactions, with the latter more compelling since hot spots, once started, propagate through the bed and lead to catalyst deactivation and decreased selectivity. In this research, we report experimental data from which heat transfer parameters are determined for one- and two-dimensional models, suitable for reactor modeling and analysis. In the 1-D experiments, axial temperature profiles in a 1.27 cm bed of 30-PPI α-Al 2O 3 foam, covering a temperature range of 25–400 °C and up to air flow rates of 7 SLPM, were used to derive a correlation for the overall heat transfer coefficient comprising radiation and convective terms. The convective term is proportional to the Reynolds number and is greater than that of an equivalent bed of glass spheres by about a factor of two. This convective term is also sensitive to the roughness of the surface, since adding γ-Al 2O 3 washcoat resulted in a further increase by about a factor two. In the 2-D measurements, at 5 cm diameter cylinder was embedded with thermocouples to measure the radial temperature profile a various axial positions. Data for 150–550 °C and 3–20 SLPM were used to extract the effective bed conductivity and the wall heat transfer coefficient as functions of the temperature and Reynolds number. Comparison of these parameters with beds of particles and structured packing show the foam gives the highest effective bed conductivity and external surface areas, confirming that foams are excellent candidates for reactions occurring on the surface of non-porous surfaces, resulting in high activities per unit volume, low-pressure drop and superior heat transfer. Enhanced mixing and turbulence indicates less susceptibility to hot spot development in exothermic reactions with foams, especially when compared to monolith supports.

Production of hydrogen for fuel cells by catalytic partial oxidation of ethanol over structured Ru catalysts

A series of Ru catalysts supported on cordierite monoliths, ceramic foams and γ-Al 2O 3 pellets were prepared and tested for the production of hydrogen by catalytic partial oxidation of ethanol. The catalyst supported on a cordierite monolith exhibited excellent catalytic performance for a wide variety of process conditions and excellent long-term stability with low coke formation. The effect of the steam to ethanol molar ratio on conversion and selectivities was relatively small. A more pronounced effect was observed for the oxygen to ethanol ratio. Overall, catalysts on all three supports were able to completely convert ethanol with high selectivities towards the desired products. The Ru supported on a ceramic foam catalyst provided comparatively better performance, probably due to the smaller pore sizes and higher tortuosity of this support.

Properties of ceramic foam catalyst supports: mass and heat transfer

Mass and heat transport properties have been determined for 30 PPI α-Al 2O 3 ceramic foam containing 6 wt.% γ-Al 2O 3 washcoat. The foam was loaded with 5 wt.% platinum and the rate of carbon monoxide oxidation measured for a 0.3 cm cylindrical segment of the foam operating with mass transfer controlling at 550 °C. This gave a mass transfer factor versus Reynolds number correlation that was equivalent to a packed bed of particles. A correlation for the radial heat transfer coefficient in a bed of ceramic foam was determined by measuring outlet temperatures achieved when air at varying flow rates and inlet temperatures was passed through a bed of foam pellets. Correlation parameters of a 1D model were fitted from 700 to 1000 °C using a Simplex optimization routine. Radial heat transfer coefficients were two to five times higher than those predicted from packed bed correlations.

Theory and Applications of Ceramic Foam Catalysts

Reticulated ceramic foams can now be prepared from a range of materials, and they have characteristics that make them desirable as substrates for structured heterogeneous catalysts. They exhibit extremely high porosities, with a significant degree of interconnectivity that results in low pressure-drop. High convection in the tortuous megapores gives enhanced mass and heat transfer. Furthermore, ceramic foam catalysts, unlike their honeycomb monolithic counterparts, have a considerable degree of radial mixing, which is an advantage in processes limited by heat transfer and can even out flow distribution. The low surface areas of ceramic foams means they have to be coated with a higher surface area material, and this increases the pressure drop and radial heat transfer conductivity in a predictable way. Reactions that require short contact times to control product selectivity and processes that are limited by heat transfer to or from the catalyst bed can benefit from the use of foam-based catalysts. This is particularly true if the effectiveness factor for a specific reaction with conventional catalyst particles is low. Examples of reactions of this type include many industrially important processes, such as the partial oxidation of hydrocarbons, water gas shift, methanol synthesis, methanation and Fischer-Tropsch synthesis. In this paper, the structure of ceramic foam catalysts, and correlations for estimating their transport properties are reviewed, and their use to potential applications are considered.

Technical Features of Ceramic Foam Catalyst Carriers in Relation to their Manufacture

Technical Features of Ceramic Foam Catalyst Carriers in Relation to their Manufacture

Properties of ceramic foam catalyst supports: pressure drop

Ceramic foams are prepared as positive images of corresponding plastic structures and exhibit bed porosities as high as 80–90%. This makes them attractive as catalyst supports in processes where high pressure drop in the reactor tube is a problem. In this research, pressure drop relationships were examined for 10, 30, 45 and 65 pores per inch (PPI) ceramic foam samples made from 92.0 and 99.5% α-Al 2O 3 and from ZrO 2 stabilized with Mg, Ca, and La 2O 3. Pore distributions were determined with imaging analysis, using digital techniques. Pressure drop measurements confirmed that ceramic foams follow the Forscheimer relationship and may be interpreted with the Ergun model, in which the pressure drop is the sum of viscous and inertial terms. The Ergun parameters, α and β, are not constant, α decreases from 8.05 to 2.88 and β increases from 0.0338 to 0.111 as the pore density increases from 10 to 65 PPI. Empirical equations were developed for these parameters in terms of the mean pore size and the bed porosity, and these indicated a dependence on the media properties. Calculated pressure drop from these equations were within 15% of measured values. Up to 15 wt.% γ-Al 2O 3 washcoat was added to 30 PPI samples of α-Al 2O 3 foams. Nitrogen BET surface areas increased from about 2 m 2 g −1 in the unwashcoated samples to almost 15 m 2 g −1 at the highest loading. Both α and β increase linearly with the BET surface area, α by only about 50% but β by a factor of 8. This suggests that roughness introduced by the washcoat plays a dominant role in the turbulent resistance.

ChemInform Abstract: Preparation and Properties of Ceramic Foam Catalyst Supports

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