Special Issue "Structured Catalysts for Catalytic Processes Intensification"

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Environmental Catalysis".

Deadline for manuscript submissions: closed (30 September 2018)

Special Issue Editor

Guest Editor
Dr. Vincenzo Palma

Univ Salerno, Dept Ind Engn, Via Giovanni Paolo 2,132, I-84084 Fisciano, SA, Italy
Website | E-Mail
Interests: structured catalysts and reactors; monoliths; foams; coating; catalytic layer; reforming reactions

Special Issue Information

Dear Colleagues,

Process intensification is ‘‘any chemical engineering development that leads to a substantially smaller, cleaner and more energy-efficient technology’’. In this direction, in the present issue, we want to report the application of structured catalysts as a viable solution in the process intensification.

In recent years, the spread of structured catalysts even in the most traditional processes of the chemical industry has certainly been one of the most interesting technological innovations in heterogeneous catalysis.

In particular, the possibility of making such carriers with different complex geometric structures, and with different types of materials with very well defined physical properties, generated many considerations on the potential effects on the performances of the catalytic reactor.

Several papers evidenced that structured catalysts (honeycomb, foams) improve heat and material transfer mechanisms between gaseous and solid phases.

In particular, by selecting a high thermal conductive structured substrate, an optimal thermal management in the catalytic volume will be achieved. Such aspect on one hand improves endothermic processes, by maximizing heat transfer from heating medium to the catalytic volume and by reducing the temperature gradient due to the reaction endothermicity.

On the other hand in exothermic processes, the possibility to realize a heat back-diffusion through the carrier structure of the catalytic bed, apart to allow a better exploiting of the catalytic volume, helps to mitigate temperature rising of the process, minimizing risks of hot-spot phenomena.  

Considering that another source of initiation of explosion could be a hotspot at the catalyst surface, the use of a structured carrier may enhance operating of difficult to control reactions in a wider range of operation conditions.

Such aspects, on one hand improve catalytic performances, and on the other increase catalyst lifetime, as well as the intrinsic safety of a chemical process, so resulting in an effective process intensification.

The special issue covers a wide range of different aspects related structured catalysts and reactors, starting by catalyst preparation and characterization, experimental tests results and mathematical modeling, and innovative applications as membrane catalytic reactors.

Dr. Vincenzo Palma
Guest Editor

Manuscript Submission Information

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Keywords

  • structured catalysts and reactors
  • monoliths
  • foams
  • coating
  • catalytic layer
  • thermal properties
  • membrane catalytic reactor

Published Papers (7 papers)

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Research

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Open AccessArticle Metal Micro-Monoliths for the Kinetic Study and the Intensification of the Water Gas Shift Reaction
Catalysts 2018, 8(12), 594; https://doi.org/10.3390/catal8120594
Received: 12 November 2018 / Revised: 24 November 2018 / Accepted: 27 November 2018 / Published: 30 November 2018
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Abstract
A kinetic study of the water gas shift (WGS) reaction has been carried out on a Pt-based catalyst promoted by a Zr-based proton conductor. The investigation was first performed on powders with diluted feed mixtures and then extended to more severe and representative [...] Read more.
A kinetic study of the water gas shift (WGS) reaction has been carried out on a Pt-based catalyst promoted by a Zr-based proton conductor. The investigation was first performed on powders with diluted feed mixtures and then extended to more severe and representative conditions by using a catalyst coated metallic micromonolith. Temperature measurements reveal that isothermal conditions were obtained along the micromonolith during the tested conditions. In addition, the very thin catalytic layer allows for the discarding of intraporous resistances, providing excellent conditions to analyse the kinetics of the WGS reaction under the integral regime. The proposed rate expression accounts for independence on CO concentration, an inhibiting effect of H2 and a promoting effect of H2O; kinetic orders on CO and H2 are in line with those reported in the literature for the Pt-based catalyst. Instead, the obtained reaction order of water (0.36) is significantly lower than that reported for unpromoted catalysts (typically 0.77–1.10) in good agreement with the proposed water-enhancer effect of the proton conductor on the rate-limiting step. Metallic micromonoliths turn out to be a powerful tool for the kinetic investigation, due to the absence of mass and heat transport limitations and represent a strategy for the intensification of the WGS unit for future applications of fuel processors in small mobile devices. Full article
(This article belongs to the Special Issue Structured Catalysts for Catalytic Processes Intensification)
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Open AccessArticle The Influence of the Washcoat Deposition Process on High Pore Density Open Cell Foams Activation for CO Catalytic Combustion
Catalysts 2018, 8(11), 510; https://doi.org/10.3390/catal8110510
Received: 28 September 2018 / Revised: 25 October 2018 / Accepted: 30 October 2018 / Published: 2 November 2018
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Abstract
Spin coating was evaluated as alternative deposition technique to the commonly used dip coating procedure for washcoat deposition on high-porosity metallic substrates. By using spin coating, the washcoating of metallic open cell foams with very high pore density (i.e., 580 μm in cell [...] Read more.
Spin coating was evaluated as alternative deposition technique to the commonly used dip coating procedure for washcoat deposition on high-porosity metallic substrates. By using spin coating, the washcoating of metallic open cell foams with very high pore density (i.e., 580 μm in cell diameter) was finely controlled. Catalytic performances of samples prepared with conventional dip coating and spin coating were evaluated in CO catalytic combustion in air, using palladium as active phase and cerium oxide as carrier. The incipient wetness method was used to prepare catalytic powder, which was dispersed by means of an acid-free dispersing medium. After washcoating, deposited layers were evaluated by optical microscopy and adhesion test. In comparison to dip-coated samples, the use of spin coating demonstrated better performances from both catalytic and coating quality points of view, highlighting the possibility of the industrial adoption of these supports for process intensification in several catalytic applications. Full article
(This article belongs to the Special Issue Structured Catalysts for Catalytic Processes Intensification)
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Open AccessArticle Comparative Study Between Aluminum Monolith and Foam as Carriers for The Intensification of The CO Water Gas Shift Process
Catalysts 2018, 8(11), 489; https://doi.org/10.3390/catal8110489
Received: 29 September 2018 / Revised: 17 October 2018 / Accepted: 18 October 2018 / Published: 24 October 2018
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Abstract
A comparison between the effect of different highly thermal conductive carriers on the performance of Pt/CeO2/Al2O3-based structured catalysts in a water–gas shift reaction, was reported. The structured catalysts were prepared by means of washcoating two carriers, a [...] Read more.
A comparison between the effect of different highly thermal conductive carriers on the performance of Pt/CeO2/Al2O3-based structured catalysts in a water–gas shift reaction, was reported. The structured catalysts were prepared by means of washcoating two carriers, a flow through aluminum monolith and an open cell aluminum foam, with the same contact surface and the same chemical composition of the washcoat. The experiments were carried out under stressful conditions (no dilution and high space velocity), so as to minimize the thermal dispersions and to highlight the effect of the thermal conductivity of the carriers and the material transport phenomena. Both of the catalysts showed a substantially flat thermal profile, while the carbon monoxide conversion was higher with the foam-based catalyst, as a result of the higher temperatures reached. The experimental results were validated with a computational fluid dynamics (CFD) simulation by using the finite elements software, COMSOL Multiphysics®. Through the simulation results, it was also possible to investigate the effects of transport phenomena on the two catalytic systems, such as mass and heat transfer. Full article
(This article belongs to the Special Issue Structured Catalysts for Catalytic Processes Intensification)
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Open AccessArticle Honeycomb Structured Catalysts for H2 Production via H2S Oxidative Decomposition
Catalysts 2018, 8(11), 488; https://doi.org/10.3390/catal8110488
Received: 28 September 2018 / Revised: 16 October 2018 / Accepted: 23 October 2018 / Published: 24 October 2018
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Abstract
Cordierite honeycomb structured catalysts were studied for the reaction of H2S decomposition in the presence of oxygen to obtain H2 and sulphur. An Al2O3-based washcoat was deposited on the honeycomb monolith by a dip-coating procedure. In [...] Read more.
Cordierite honeycomb structured catalysts were studied for the reaction of H2S decomposition in the presence of oxygen to obtain H2 and sulphur. An Al2O3-based washcoat was deposited on the honeycomb monolith by a dip-coating procedure. In particular, three different washcoat percentages (15, 20 and 30 wt%) were deposited on the structured carrier and the obtained samples were characterized by N2 adsorption and SEM analysis. The evaluation of the catalytic performance of the three samples was carried out at two different temperatures (1000 °C and 1100 °C). The sample with 30 wt% washcoat content showed the lowest SO2 selectivity at 1000 °C (<0.4%), whereas the H2S conversion and H2 yield values were very similar to those achieved for the samples at 15 and 20 wt% washcoat loading. Based on these results, additional tests were carried out on the catalyst with 30 wt% Al2O3-based washcoat loading, varying the contact time and the H2S inlet concentration to identify the operating conditions that minimize the SO2 formation, obtaining good H2S conversion and H2 yield. The comparison of the structured catalyst with the powder alumina sample has shown the same catalytic performance, exhibiting lower SO2 selectivity. Full article
(This article belongs to the Special Issue Structured Catalysts for Catalytic Processes Intensification)
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Open AccessArticle Rh/CeO2 Thin Catalytic Layer Deposition on Alumina Foams: Catalytic Performance and Controlling Regimes in Biogas Reforming Processes
Catalysts 2018, 8(10), 448; https://doi.org/10.3390/catal8100448
Received: 10 September 2018 / Revised: 5 October 2018 / Accepted: 8 October 2018 / Published: 11 October 2018
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Abstract
The application of ceramic foams as structured catalyst supports is clearly expanding due to faster mass/heat transfer and higher contact efficiency than honeycomb monoliths and, mainly, packed beds. In this paper, alumina open-cell foams (OCFs) with different pore density (20, 30 and 40 [...] Read more.
The application of ceramic foams as structured catalyst supports is clearly expanding due to faster mass/heat transfer and higher contact efficiency than honeycomb monoliths and, mainly, packed beds. In this paper, alumina open-cell foams (OCFs) with different pore density (20, 30 and 40 ppi) were coated with Rh/CeO2 catalyst via a two steps synthesis method involving: (i) the solution combustion synthesis (SCS) to in-situ deposit the CeO2 carrier and (ii) the wet impregnation (WI) of the Rh active phase. The catalytic coatings were characterized in terms of morphology and adhesion properties by SEM/EDX analysis and ultrasounds test. Permeability and form coefficient were derived from pressure drop data. Catalytic performance was evaluated towards biogas Steam Reforming (SR) and Oxy-Steam Reforming (OSR) processes at atmospheric pressure by varying temperature (800–900 °C) and space velocity (35,000–140,000 NmL·g−1·h−1). Characteristics time analysis and dimensionless numbers were calculated to identify the controlling regime. Stability tests were performed for both SR and OSR over 200 h of time-on-stream (TOS) through consecutive start-up and shut-down cycles. As a result, homogenous, thin and high-resistance catalytic layers were in situ deposited on foam struts. All structured catalysts showed high activity, following the order 20 ppi < 30 ppi ≈ 40 ppi. External interphase (gas-solid) and external diffusion can be improved by reducing the pore diameter of the OCF structures. Anderson criterion revealed the absence of internal heat transfer resistances, as well as Damköhler and Weisz-Prater numbers excluded any internal mass transfer controlling regime, mainly due to thin coating thickness provided by the SCS method. Good stability was observed over 200 h of TOS for both SR and OSR processes. Full article
(This article belongs to the Special Issue Structured Catalysts for Catalytic Processes Intensification)
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Open AccessArticle Wetting Fraction in a Tubular Reactor with Solid Foam Packing and Gas/Liquid Co-Current Downflow
Catalysts 2018, 8(9), 396; https://doi.org/10.3390/catal8090396
Received: 5 August 2018 / Revised: 7 September 2018 / Accepted: 12 September 2018 / Published: 14 September 2018
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Abstract
The performance of fixed-bed reactors with structured catalysts depends heavily on the gas–liquid–solid contacting pattern. For a broad range of flow conditions, the liquid phase does not cover the solid surface of the packing homogeneously; this is known as partial wetting. The wetting [...] Read more.
The performance of fixed-bed reactors with structured catalysts depends heavily on the gas–liquid–solid contacting pattern. For a broad range of flow conditions, the liquid phase does not cover the solid surface of the packing homogeneously; this is known as partial wetting. The wetting fraction in solid foams was obtained using a modified electrochemical measurement method with adaption of the limiting-current technique in different pre-wetting scenarios. The external wetting fraction, which is defined as fraction of the external solid-foam area covered by the liquid phase to the total external solid-foam area, is directly linked to the overall rate of reaction through the overall liquid mass transfer rate. The wetting fraction decreased with an increase in foam density, a process which was related to decreasing the strut thickness, increasing foam surface area, and consequently, decreasing the wetted area. Additionally, the results indicate that a better distribution of liquid and an increased wetting fraction occurred when a spray nozzle distributor was applied. A new wetting correlation for solid foams is proposed to estimate the wetting fraction with consideration of foam morphology and flow regime. Full article
(This article belongs to the Special Issue Structured Catalysts for Catalytic Processes Intensification)
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Review

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Open AccessReview Policies and Motivations for the CO2 Valorization through the Sabatier Reaction Using Structured Catalysts. A Review of the Most Recent Advances
Catalysts 2018, 8(12), 578; https://doi.org/10.3390/catal8120578
Received: 10 October 2018 / Revised: 8 November 2018 / Accepted: 16 November 2018 / Published: 22 November 2018
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Abstract
The current scenario where the effects of global warming are more and more evident, has motivated different initiatives for facing this, such as the creation of global policies with a clear environmental guideline. Within these policies, the control of Greenhouse Gase (GHG) emissions [...] Read more.
The current scenario where the effects of global warming are more and more evident, has motivated different initiatives for facing this, such as the creation of global policies with a clear environmental guideline. Within these policies, the control of Greenhouse Gase (GHG) emissions has been defined as mandatory, but for carrying out this, a smart strategy is proposed. This is the application of a circular economy model, which seeks to minimize the generation of waste and maximize the efficient use of resources. From this point of view, CO2 recycling is an alternative to reduce emissions to the atmosphere, and we need to look for new business models which valorization this compound which now must be considered as a renewable carbon source. This has renewed the interest in known processes for the chemical transformation of CO2 but that have not been applied at industrial level because they do not offer evident profitability. For example, the methane produced in the Sabatier reaction has a great potential for application, but this depends on the existence of a sustainable supply of hydrogen and a greater efficiency during the process that allows maximizing energy efficiency and thermal control to maximize the methane yield. Regarding energy efficiency and thermal control of the process, the use of structured reactors is an appropriate strategy. The evolution of new technologies, such as 3D printing, and the consolidation of knowledge in the structing of catalysts has enabled the use of these reactors to develop a wide range of possibilities in the field. In this sense, the present review presents a brief description of the main policies that have motivated the transition to a circular economy model and within this, to CO2 recycling. This allows understanding, why efforts are being focused on the development of different reactions for CO2 valorization. Special attention to the case of the Sabatier reaction and in the application of structured reactors for such process is paid. Full article
(This article belongs to the Special Issue Structured Catalysts for Catalytic Processes Intensification)
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