WO1995011752A1 - Structures de mousse a cellules ouvertes, supports pour catalyseur utilisant de telles structures et procede de production de ces structures - Google Patents

Structures de mousse a cellules ouvertes, supports pour catalyseur utilisant de telles structures et procede de production de ces structures Download PDF

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Publication number
WO1995011752A1
WO1995011752A1 PCT/US1993/010308 US9310308W WO9511752A1 WO 1995011752 A1 WO1995011752 A1 WO 1995011752A1 US 9310308 W US9310308 W US 9310308W WO 9511752 A1 WO9511752 A1 WO 9511752A1
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WO
WIPO (PCT)
Prior art keywords
open cell
micro
cell foam
highly porous
foam structure
Prior art date
Application number
PCT/US1993/010308
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English (en)
Inventor
Vladimir N. Antsiferov
Valentina I. Ovchinnikova
Aleksandr M. Makarov
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Scientific Dimensions Usa, Inc.
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Filing date
Publication date
Application filed by Scientific Dimensions Usa, Inc. filed Critical Scientific Dimensions Usa, Inc.
Priority to PCT/US1993/010308 priority Critical patent/WO1995011752A1/fr
Priority to AU55881/94A priority patent/AU5588194A/en
Publication of WO1995011752A1 publication Critical patent/WO1995011752A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
    • F01N3/2807—Metal other than sintered metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/11—Making porous workpieces or articles
    • B22F3/1103—Making porous workpieces or articles with particular physical characteristics
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/11—Making porous workpieces or articles
    • B22F3/1121—Making porous workpieces or articles by using decomposable, meltable or sublimatable fillers
    • B22F3/1137—Making porous workpieces or articles by using decomposable, meltable or sublimatable fillers by coating porous removable preforms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

  • This invention relates to highly porous open cell foam structures, to catalysts supported thereby and to methods of producing the same.
  • Effective catalytic systems are also required for preventing the build-up of hydrogen in nuclear power plants.
  • excessive hydrogen levels may be reduced by using devices employing high temperature catalytic systems or flames.
  • devices that use high temperature systems or flames to reduce the excessive hydrogen levels instead of reducing the risk, may actually increase the risk of a hydrogen explosion under certain circumstances.
  • Catalysts or catalyst supports based on open cell foam structures are known; J. Brockmeyer and J.F. Pizzirusso, "Ceramic Foam Offers Surprising Properties, " J. Materials Engineering, pp. 39-41, July 1988; J. McCallion, "New Materials, Applications Enter Booming Ceramic Scene," pp. 23, May 1988; and Antsiferov, V.N.
  • Open cell foam structures having an interconnected open cell structure may have a porosity of up to 99% and a permeability for liquid and gas substances of up to 10 "8 m 2 , Antsiferov, V.N. , Ovchinnikova, V.E., Porozova, S. Ya., Fedorova, E. F.; "Highly Porous Cellular Ceramic Materials,” Styeklo e Kyeramika, 1986, pp. 19-20.
  • Open cell foam structures may be prepared by using a reticulated polymeric foam as a substrate, e.g., reticulated polyurethane foam.
  • Reticulated foam substrates are disclosed, for example, in U.S. Patent No. 3,946,039.
  • a layer of ceramic or metallic material is deposited on the exposed surfaces of the reticulated foam substrate.
  • This deposition step may employ a variety of known techniques such as slip casting, chemical plating or galvanic plating.
  • the open cell foam structure is produced by heating the reticulated polymeric foam substrate containing the layer of ceramic or metallic material, which results in destruction and removal of the reticulated polymeric foam substrate, e.g., by evaporation. Agglomeration, e.g.
  • micro-structural elements are herein referred to as micro-rods.
  • the surface of the micro-rods forming the open cell foam structures normally appears smooth and is not very porous because the sintering processes typically used to produce these structures lead to surface configurations having a minimum free energy level, and thus, to surfaces having a low specific surface area. If such open cell foam structures are used as catalysts or as catalyst supports, the smooth surfaces of these micro-rods are considered to be a substantial drawback. This is generally understood to be due to the fact that heterogeneous catalysis becomes much less effective on surfaces having a low specific surface area.
  • micro-rods that form the open cell foam structures
  • micropores which constitute 20% to 80% of the total volume of the micro-rods.
  • Highly porous micro-rods having a surface micro-structure with a high specific surface area have a high capacity for water absorption. Since the catalytic effectiveness of a porous catalytic surface may be generally correlated with water absorption capacity of the surface, a high water absorption is indicative of more effective catalytic functioning.
  • open cell foam structures having micro-structural elements with 20-80% porosity have poor structural strength; Great Britain Patent No. 1,388,912 (1975) .
  • reactivity of the catalyst can be enhanced by depositing a support layer, such as 7- aluminum oxide on an open cell structure, (U.S. Patent No. 3,565,830).
  • the layer of 7-aluminum oxide is characterized by a highly developed surface structure with a specific surface area of up to 100 m 2 /g.
  • the high specific surface area provides for effective pick-up of the reactive components and for a high-quality dispersion of the active catalytic component.
  • the deposited carrier layer tends to be too thin, discontinuous and poorly adherent to the smooth surface. This layer is easily peeled off as a result of large or abrupt temperature changes.
  • Another problem of existing catalytic systems relates to the fact that carbon monoxide is one of the main contaminants of emission gas mixtures produced by transportation vehicles and power plants.
  • catalysts formed from platinum or palladium, or alloys thereof have been considered to be the most effective catalysts for removing CO, by oxidation, from emission gas mixtures.
  • the high cost of platinum- and palladium- containing materials can make the gaseous decontamination equipment quite expensive.
  • the development of lower cost non-platinum or non-palladium catalysts for CO oxidation could produce significant cost savings for programs directed toward reducing environmental pollution.
  • An object of the present invention is to provide highly porous open cell foam structures which overcome the above-mentioned problems of prior art catalytic systems.
  • Yet another object of the present invention is to provide high porosity catalytic systems having both high strength and high catalytic activity at high reagent flow rates.
  • a specific advantage of the present invention is that catalysts based on highly porous open cell copper foam structures can be produced which may be as effective as much more expensive platinum- or palladium-containing catalysts.
  • an open cell foam structure with a highly porous surface microstructure may be used either as a catalyst support or as the catalyst itself.
  • Still another advantage of the present invention is that catalytic systems based on open cell foam structures may be used to catalytically reduce excessive hydrogen levels without using high-temperature or flame-containing devices.
  • Another advantage of the present invention is that high efficiency catalytic systems can be produced that have high reaction rates due to high burning temperatures.
  • Still another advantage of the present invention is that a non-channeled open cell porous structure may be used as a physical filter to effectively trap noxious reagents.
  • an open cell foam structure having a three dimensional array of interconnected micro-rods forming the edges of the open cells of the open cell structure, the micro-rods having an inner core integrally bonded to a porous outer layer, the inner core comprising a first material and the porous outer layer comprising a second material, wherein the second material has a substantially higher porosity than the first material.
  • the open cell foam structures of the present invention may be formed by a method comprising preparing a first slip composition containing a first solvent, a first binding agent and a first ceramic material; coating a reticulated polymeric foam with the first slip composition to produce a coated polymeric foam having a first layer on the exposed surfaces of the reticulated polymeric foam; drying the coated polymeric foam to produce dried blanks of the coated polymeric foam; preparing a second slip composition containing a second solvent, a second binding agent, a second ceramic material and a pore-forming additive; coating the dried blanks with the second slip composition to produce a doubly-coated polymeric foam having a two-layer coating on the exposed surfaces of the polymeric foam; and heating and sintering the doubly-coated polymeric foam to form a highly porous open cell foam structure.
  • a highly porous metallic open cell foam structure may be prepared by a method comprising preparing a open cell foam structure wherein the structure comprises a three dimensional array of interconnected micro-rods forming the edges of the open cells of the open cell structure; oxidizing the surface of the micro-rods to form a porous surface microstructure that forms on the outer layer of micro-rods, and reducing the porous surface microstructure with hydrogen to form a highly porous open cell foam structure.
  • the micro-rods comprise copper.
  • a device for removing or reducing excessive hydrogen levels may be made by using a catalyst comprising a catalyst support; a carrier layer on the catalyst support; and a catalyst coated on the support layer; wherein the catalyst support comprises an open cell foam structure having a three dimensional array of interconnected micro-rods forming the edges of the open cells of the open cell structure, the micro-rods having an inner core integrally bonded to a porous outer layer, the inner core comprising a first material and the porous outer layer comprising a second material, wherein the second material has a substantially higher porosity than the first material.
  • the micro-rods comprise nickel and chromium
  • the catalyst support comprises 7-aluminum oxide
  • the catalyst comprises platinum and rhodium.
  • Fig. 1 An illustrative representation of the localized microstructure of an open cell foam structure.
  • Fig. 2 Schematic illustrations of the triangular cross-sections of the micro-rods disclosed herein.
  • FIG. 3 A representative illustration of the compression strength (MPa) vs. the porosity of the inner core (curve 1) and vs. the ratio of the inner core thickness to the total micro-rod thickness (curve 2) .
  • the basic unit of the macroscopic porous space of open cell foam structures may be generally represented by a cell that is typically shaped as a pentagon-dodecahedron. In terms of cubic symmetry, this corresponds to one of the simple shape types for which the class is designated as m3.
  • the coordination number as determined by the number of adjacent neighbors for each given cell, is 12.
  • a coordination number of 12 is evidence that the repeating units in the open cell foam structure are characterized by a high packing density of polyhedron cells.
  • Open cell foam structures in general, have areas of local short-range order in the macroscopic structure formed by the polyhedron cells. Long-range order does not normally exist in the types of open cell foam structures described herein.
  • the three-dimensional region of local short-range order in open cell foam structures may typically have a size that includes four to five polyhedron cells. This results in channels being present in the structure wherein the channels may have a thickness which is 0.3 to 0.5 times as thick as the cell diameter.
  • the channels in the pore space structure of open cell foam structures are typically built up from short straight-line channels which, on average, are 4 to 6 times as long as the cell diameter.
  • the herein-described channel-type porosity which is characteristic of the macroscopic structure of highly porous open cell foam structures, simultaneously accounts for the high permeability of highly porous open cell foam structures as well as for the reduced chance for the reactant materials, e.g. noxious components, to pass through such structures without reacting.
  • reactant materials e.g. noxious components
  • micro-rods the microstructural elements forming the edges of the cells of the open cell foam structure are herein referred to as micro-rods.
  • the cross-sectional configuration of these micro-rods plays an important role in affecting the overall physical properties, such as strength, water absorption, reactivity, etc., of the highly porous open cell structures.
  • Each micro-rod typically has an axial pore of triangular cross-section.
  • the axial pores are formed, as described below, by removal of the reticulated polymeric foam substrate that may be used to produce the open cell foam structures.
  • These axial pores form an inter-linked capillary system inside the micro-rods, wherein the total volume occupied by the capillaries may be about 3 volume percent of the micro-rod volume.
  • Fig. 1 shows the localized microstructure, as schematically represented in U.S. Patent No. 4,569,821, of an open cell foam structure (1) having micro-rods (2) forming the edges of the open cells (3).
  • Figs. 2(a), 2(b) and 2(c) show schematic illustrations of the triangular cross-sections of the micro-rods disclosed herein.
  • FIG. 2(a) shows the axial pore (4) and micropores (5) in the low porosity material, shown as (6) of Fig. 2(b), of the inner core.
  • Fig. 2(b) shows the highly porous layer (7) that surrounding the inner core.
  • Fig. 2(c) shows a carrier layer (8) on the highly porous layer with a catalyst layer (9) coated on the carrier layer.
  • the preferred method for making the highly porous open cell foam structures of the subject invention is slip casting.
  • the slip casting process may be carried out using any of a large number of different methods.
  • a reticulated polyurethane foam is used as a substrate wherein the polyurethane foam is imbedded with what is generally referred to as a slip composition.
  • the slip from the slip composition adheres to the exposed surfaces of the micro-structural elements of the reticulated polyurethane foam substrate.
  • the slip composition may be a slurry or dispersion, for example, of a solvent containing particles of a starting material that is a ceramic or metal powder mixed or dispersed together with a binding agent.
  • the binding agent is an organic binder.
  • the slip composition may include still other components such as a pore-forming additive.
  • the solvent, which is not to react with the reticulated polymeric foam substrate or the pore-forming additive may typically be water or ethanol.
  • the metals or ceramic materials that may be used as the starting materials in the present invention may include any of the very large number of metals and materials that have been used to produce porous metal or ceramic foam products.
  • Such metals or ceramic materials include Cu, Ni, Fe, Mo, W, Ni-Cr alloys, Ni-Fe alloys, or other alloys thereof, stainless steel, porcelain, A1 2 0 3 , Si0 2 , Mo 2 C, WC or Cr 3 C.
  • the preferred metal of the present invention is copper, or an alloy of nickel and chromium, and the preferred ceramic material is porcelain.
  • the metallic or ceramic materials used to make the highly porous open cell foam structures may initially be in the form of a powder or particles, or any other form which may be used to produce highly porous foam products.
  • the materials may be obtained from any of many known suppliers.
  • the materials may be further characterized as being sphere-shaped particles to provide convenient fluidity and slip filling.
  • the starting materials used to make both the first and the second slip compositions comprise materials having substantially the same ceramic or metallic composition.
  • the binding agents that may be used in the slip composition include polyvinyl alcohol and isopropanol.
  • the preferred binding agent of the present invention is polyvinyl alcohol, which may be obtained from any of many known suppliers.
  • the reticulated polymeric foam substrate may be selected from many different polymers, including polyurethanes, polyureas, polyesters, polyamides, polyethers, polystyrenes, polyvinyl chlorides, polyethylene or polypropylene.
  • the preferred polymeric foam substrate is polyurethane foam.
  • the slip composition may be prepared by mixing the metal or ceramic starting material with the solvent and the binding agent to produce a slurry or dispersion.
  • the reticulated polymeric foam substrate for example, polyurethane foam, may be dipped or sprayed with the slip composition and the excess slip composition is then removed before drying to produce dried blanks having a single layer of the slip on the exposed surfaces of the micro-structural elements of the reticulated polymeric foam substrate.
  • a second slip composition is then prepared using substantially the same ingredients as above, but also including a pore-forming additive.
  • the dried blanks of the polyurethane foam having the single layer formed by the first slip composition may be dipped or sprayed with the second slip composition containing the pore- forming additive.
  • the solvent is removed by drying to produce a polyurethane foam having a double coating on the exposed surfaces of the polyurethane foam.
  • the doubly-coated polyurethane foam may then be heated to destroy and remove the polyurethane foam and the pore- forming additive and to sinter the ceramic or metallic materials to form what is herein referred to as a highly porous open cell structure having a three dimensional array of interconnected micro-rods forming the edges of the open cells of the open cell structure.
  • This heating and sintering may be carried out using many different methods known in the art.
  • the pore-forming additive is typically an organic constituent that is destroyed and removed with the reticulated polymeric foam.
  • the pore-forming additive produces pores within the outer layer of the micro-rods.
  • the pore-forming additives that may be used include polystyrene, polyethylene and polymethyl ethacrylate.
  • the preferred pore-forming additive of the present invention comprises particles of polymethyl methacrylate.
  • the particle size of the pore-forming additives may be from about 10 microns (micrometers) to about 100 microns in average diameter.
  • the preferred particle size is from about 20 microns to about 30 microns in average diameter.
  • the weight percent of the particles of polymethyl methacrylate is from about 10 weight percent to about 90 weight percent of the total weight of the material used to form the outer layer of the micro-rods.
  • the particles of polymethyl methacrylate are substantially spherical.
  • the highly porous open cell structures produced using the methods of the present invention comprise micro-rods having an inner core of a low porosity material surrounding an axial pore.
  • the axial pore at the center of the micro-rod is produced by destruction and removal of the reticulated polymeric foam.
  • the low porosity material of the inner core is integrally bonded to an outer layer that is preferably comprised of substantially the same metallic or ceramic composition but having substantially higher porosity than the low porosity material in the inner core.
  • the higher porosity of the outer .layer may be produced by use of pore-forming additives in the second slip composition.
  • the degree of porosity may be varied by varying the weight percent of the pore-forming additive in the second slip composition.
  • the low porosity material in the inner core described herein refers to materials that have a porosity of about 0.5% to about 10% and the high porosity material of the outer layer refers to materials that have a porosity of about 20% to about 80%. Most preferably, the high porosity material of the outer layer has a porosity of about 40% to about 70%.
  • the high porosity material of the outer layer provides the micro-rod with a highly porous surface microstructure.
  • the highly porous surface microstructure is preferred for achieving effective heterogeneous catalysis.
  • 15 open cell foam catalysts and catalyst supports may be produced having both high permeability and high reactivity with noxious components, while still retaining the high structural strength and integrity of a high capacity catalyst.
  • micro-rods is from about 0.1 mm to about 3 mm. Most preferably, the thickness of the micro-rods is from about 0.5 mm to about 2 mm. In addition, the inner core preferably has a thickness of about 60% to about 80% of the total micro-rod thickness, and the porous outer layer
  • 25 preferably has a thickness of about 40% to about 20%, respectively, of the total micro-rod thickness.
  • 35 material of the inner core may be strengthened by appropriate selection of the ceramic or metal materials used in the slip composition and by the heating and sintering conditions used to produce the highly porous open cell foam materials.
  • the starting materials of the first and second slip compositions are substantially the same except for addition of an appropriate quantity of the pore-forming additive in the second slip composition.
  • the preferred ceramic composition of the present invention is porcelain.
  • Porcelain is typically comprised of Si0 2 , A1 2 0 3 , CaO , MgO , Ti0 2 , Fe 2 0 3 , Na 2 0 and K 2 0 .
  • the highly porous surface microstructure of porcelain micro- rods typically has a high specific surface area that provides for effective pick-up of reactive components as well as for high-quality dispersion of the active catalytic component.
  • the specific surface area of the catalytic support prepared from porcelain using the methods of the present invention is typically in the range from about 2.0 to about 10 m/g.
  • the highly porous open cell foam structures of the present invention may be used either as catalysts or as catalyst supports. Whenever, the highly porous open cell foam structures are used as catalyst supports, the highly porous open cell foam structures may be combined with a catalyst by covering the micro-rods of a metallic open cell foam structure with a support layer comprised of metal oxides such as A1 2 0 3 , Zr0 2 or Ti0 2 and then coating the surface of the support layer with a catalyst such as platinum, platinum-rhodium, palladium, cerium, Cu, Ni, etc.
  • the highly porous metallic open cell structures may be formed from metals such as Ni, Cr, Mo, Co, W, alloys thereof, or stainless steel.
  • an open cell copper foam structure initially having a low porosity throughout the micro- rods, may be prepared by chemical or electrochemical deposition of copper on a permeable open cell polyurethane foam.
  • the porosity of the micro-rods prepared using this method may be in the range of 0.5 to 1% and the exposed surface of these micro-rod structural elements is smooth. The smooth surface results in a relatively low reactivity of this material even when used at higher temperatures as a catalyst for CO oxidation, as shown below: % oxidation temperature °C
  • oxidation of an open cell copper foam structure having low porosity micro-rods may be carried out in air at temperatures from 300-800 °C to produce a structure having a high porosity outer layer on a low porosity inner core.
  • the oxidation is carried out at temperatures from 400-600 °C. If the oxidation temperature is too low, a sufficiently thick active outer layer is not formed and, thus, catalytic activity is too low. If oxidation is performed at too high a temperature, the oxidation is too great and causes an unacceptable loss in strength of the overall open cell copper foam structure.
  • a reduction step is carried out in the presence of hydrogen at temperatures about 200-300 °C less than the oxidation temperature.
  • a reduction temperature that is too high causes sintering of the high porosity outer layer and, thus, a loss in the active surface area and a reduction in catalyst efficiency.
  • a high porosity outer layer is formed on and integrally bonded to a low porosity inner core.
  • the porous outer layer is 20-40% of the micro-rod thickness and has a porosity of 50-80%.
  • the low porosity material of the inner core has a porosity of about 0.5 to about 3%.
  • the low porosity material of the inner core has a porosity of about 0.5 to about 1%.
  • the first example shows that the micro-rod structure of the present invention may be used to produce highly porous open cell foam structures having, unexpectedly, both high structural strength and high water absorption.
  • the high water absorption is indicative of high catalytic effectiveness.
  • the second example relates to a method for preparing highly porous open cell foam structures •having a micro-rod structure wherein the highly porous open cell foam structure is comprised of copper.
  • the third example shows how highly porous open cell structures having a micro-rod structure of the present invention may be prepared and used as a catalyst support.
  • Example 1 Polyurethane foam having an average cell diameter of 2.5- 3 mm was cut to prepare blanks with dimensions of 35 x 35 x 25 mm.
  • the polyvinyl alcohol had an average molecular weight of 500 and was obtained from Fluka Chemie A.G. (Switzerland) .
  • the polyurethane foam blanks were soaked in the slip composition to coat the exposed surfaces of the polyurethane foam with slip. The excess slip was removed by squeezing and the blanks were allowed to dry to form dried blanks having a density of 0.1, 0.2, 0.3, 0.4 and 0.5 g/cm 3 , respectively.
  • a second slip composition containing substantially the same- composition as the first slip composition, that is, a porcelain compound mixed in a water solution containing polyvinyl alcohol, but which, in addition, also included a pore-forming additive, polymethyl methacrylate (PMMA) .
  • PMMA polymethyl methacrylate
  • the particles of PMMA were 10 to 100 microns in size, predominantly 20 to 30 microns in size, and amounted to 15, 30, 50, 80 and 85 weight percent of the total quantity of ceramic powder.
  • Slip from the second slip composition was deposited on the dried blanks by dipping or spraying and the coated blanks were provided with a heat treatment that sintered the materials to produce the highly porous open cell foam structures to be used as catalysts or catalyst supports.
  • the heat treatment conditions were selected so as to provide a gradual burn-out of the polyurethane foam blanks and of the particles of PMMA used as the pore- forming additive.
  • the heat treatment was also intended to insure that the shape and permeability remained unchanged.
  • the highly porous open cell foam structures prepared from the porcelain mixture were sintered at temperatures from 1320 to 1420 °C.
  • the compression strength was measured by Instron universal testing equipment, (Instron Limited, England) .
  • the water absorption was measured by weighing.
  • Table 1 show that an outer layer thickness of about 20% to about 40% of the total micro-rod thickness does not, surprisingly, cause a substantial decrease in compression strength but still provides much higher water absorption than the open cell foam structures not having the high porosity outer layers.
  • an outer layer thinner than about 20% of the total micro-rod thickens does not provide for good water absorption and an outer layer thicker than about 40% of the total micro- rod thickness causes an unacceptable decrease in strength.
  • the porosity of the outer layer is less than about 20%, high catalytic reactivity cannot be achieved and if the porosity is greater than about 80%, the outer layer may be easily peeled off, thus causing catalytic reactivity to decrease.
  • the highly porous open cell foam structures of the present invention maintain surprisingly high compression strength while still having high water absorption.
  • Fig. 3 shows the compression strength (MPa) plotted against the porosity (%) of the inner core (curve 1) and against the ratio of the inner core thickness to the total micro-rod thickness (curve 2) for a porcelain open cell foam structure having an average cell size of about 2 mm and a density of about 0.5 g/cm 3 .
  • An increase in porosity above about 10% for the inner core material produces an unacceptable decrease in the overall strength of the highly porous open cell foam structure.
  • a micro- rod thickness wherein the low porosity material of the inner core is greater than about 60% of the total micro- rod thickness is required to achieve a material strength greater than about 2 MPa.
  • a material strength of at least about 2 MPa is required for satisfactory application of these materials as catalyst supports.
  • Table 1 if the thickness of the inner core is greater than about 80% of the total micro-rod thickness, there is a reduction of outer layer porosity and this accounts for an unacceptable drop in water absorption.
  • Samples of a highly porous copper open cell foam structure comprising micro-rods were prepared by first forming an open cell structure having a single-layer micro-rod structure. In the first step, copper was chemically deposited on an open cell polyurethane foam. Dried blanks were prepared and then the dried blanks were heated and sintered at temperatures from about 500 to about 900 °C. The material in the single layer micro-rod structure had a porosity of about 0.5 to about 1%.
  • These single-layer micro-rod open cell structures were then oxidized in air at a temperature from about 300 to about 500 °C for 1.4 hours.
  • the oxidized open cell structures were then reduced in hydrogen for about 1-3 hours at temperatures from about 200 to about 300 °C to produce highly porous copper open cell foam structures having a two-layer micro-rod structure.
  • the high porosity outer layer had a thickness of about 20% to about .40% of the total micro-rod thickness and a porosity of about 50% to about 80%.
  • the low porosity material of the inner core retained the original porosity of about 0.5 to about 1%.
  • the catalytic reactivity was tested by means of a microcatalytic reactor.
  • the stoichiometric catalytic conversion of CO to C0 2 by the subject catalyst was compared with the catalytic reactivity of a surface on which a 0.3% layer of palladium had been deposited.
  • the comparison was carried out using a helium carrier gas having a flow rate of 20-60 cm 3 /min.
  • the output gas mixture was chromatographically analyzed using a method such as described in "Applied Industrial Catalysis, Vol. 1, edited by Bruce E. Leach, Conoco Inc. Research and Development, Poonca City, Oklahoma, 1983.
  • the kinetic characteristics of this process are summarized in Table 2.
  • the initial temperature during CO oxidation on the copper-based catalyst was about 110 °C and about 90 °C for catalysts prepared using a one-cycle and a two-cycle oxidation-reduction process, respectively.
  • the apparent activation energy of the process equaled 77 KJ/mole for a highly porous open cell copper foam catalyst after a two- cycle oxidation-reduction process.
  • the corresponding data were found to be 100 °C and 64 KJ/mole, respectively.
  • the catalytic reactivity of a unit volume of the highly porous open cell copper foam catalyst using micro-rods was comparable to the catalytic reactivity level of the reference palladium catalyst.
  • a highly porous open cell foam structure having a micro- rod structure of a nickel-chromium alloy was prepared using the slip casting process.
  • the slip compositions were prepared from a mixture of nickel and chromium powders wherein the nickel was about 82 weight percent of the total metal powder and chromium was about 18 weight percent.
  • the powders had an average particle size of about five microns in diameter. These powders were mixed in water solutions wherein polyvinyl alcohol was used as the binding agent.
  • the pore-forming additive used to produce the porous outer layer of the micro-rod was polymethyl methacrylate.
  • the first slip composition was coated on a polyurethane foam and then dried to produce dried blanks which were then coated with a slip composition containing the pore- forming additive. These doubly-coated blanks were then processed in hydrogen at temperatures from about 1100 °C to about 1300 °C to produce highly porous open cell foam structures comprised of nickel-chromium micro-rods.
  • the nickel-chromium micro-rod surfaces were then coated with a carrier layer of 7-aluminum oxide by submerging the highly porous nickel-chromium open cell foam structure in a saturated solution of sodium aluminate at 60-70 °C for three hours.
  • a layer of Al(OH) 3 was subsequently formed by swirling with distilled water until the hydrolysis reaction was completed.
  • the specimen was then heated in air for three hours at about 500 °C to form a 7-aluminum oxide carrier layer having a thickness of about 60-100 microns and a specific surface area of about 200 m 2 /g. About 20 g/mm 2 of the 7-aluminum oxide adhered to the surface of the nickel-chromium micro-rods.
  • a platinum-rhodium catalytic layer was then formed on the surface of the 7-aluminum oxide carrier layer by impregnating the specimen in a 0.5% solution of platinum chloride and rhodium chloride and subsequently reducing at 60-80 °C in a 1% solution of sodium formate to produce a finely dispersed metallic layer of platinum-rhodium.
  • the content of platinum and rhodium was about 0.25 and 0.1 weight percent, respectively, as compared to the total weight of the catalyst.
  • the catalytic activity of the specimen was measured using a gas reactor and an infra-red spectrometer.
  • the degree of conversion of CO into C0 2 was used to characterize the degree of catalytic activity.
  • the measurements were carried out under pulse conditions using the SLONDI 64'1 method, which is described in "Applied Industrial Catalysis, " supra.
  • the results were compared with the results obtained with a Volvo-740 catalytic converter after it had been used in an automobile that had traveled about one thousand kilometers .
  • the exhaust gases were measured at a gas mixture flow rate of 30 liters/hour.
  • the degree of conversion of CO to C0 2 at T(°C) was prepared according to Example 3 and the reference was a VOLVO-740 catalytic converter.

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Abstract

L'invention concerne des structures en mousse (1) à cellules ouvertes très poreuses (3) ainsi que des procédés de préparation de ces structures en mousse à cellules ouvertes très poreuses (3), lesquelles sont destinées à des systèmes catalytiques améliorés. Plus particulièrement, cette invention concerne des structures en mousse (1) à cellules ouvertes très poreuses (3) présentant un réseau tridimensionnel de micro-tiges reliées entre elles (2). Les micro-tiges (2) consistent en un matériau central interne solidaire d'une couche externe poreuse, laquelle est constituée d'un matériau ayant une porosité beaucoup plus élevée que le matériau central interne.
PCT/US1993/010308 1993-10-27 1993-10-27 Structures de mousse a cellules ouvertes, supports pour catalyseur utilisant de telles structures et procede de production de ces structures WO1995011752A1 (fr)

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PCT/US1993/010308 WO1995011752A1 (fr) 1993-10-27 1993-10-27 Structures de mousse a cellules ouvertes, supports pour catalyseur utilisant de telles structures et procede de production de ces structures
AU55881/94A AU5588194A (en) 1993-10-27 1993-10-27 Open cell foam structures, catalysts supported thereby and method of producing the same

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Cited By (18)

* Cited by examiner, † Cited by third party
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US5976454A (en) * 1996-04-01 1999-11-02 Basf Aktiengesellschaft Process for producing open-celled, inorganic sintered foam products
US5998317A (en) * 1996-11-21 1999-12-07 Basf Aktiengesellschaft Open-celled porous sintered products and their production
US6171532B1 (en) 1996-05-17 2001-01-09 Basf Aktiengesellschaft Method of stabilizing sintered foam and of producing open-cell sintered foam parts
EP1095792A2 (fr) * 1999-10-29 2001-05-02 Pentel Kabushiki Kaisha Corps de vanne et réservoir de stockage de liquide pour appareil d'éjection de liquide utilisant ce corps de vanne
EP1272303A1 (fr) * 2000-02-02 2003-01-08 Materials And Electrochemical Research (Mer) Corporation Structures alveolaires et procedes de fabrication correspondants
US6977095B1 (en) * 1997-10-01 2005-12-20 Wright Medical Technology Inc. Process for producing rigid reticulated articles
DE10083881B3 (de) * 1999-01-19 2012-02-16 Utc Fuel Cells, Llc (N.D.Ges.D. Staates Delaware) Kompakte Brennstoffgas-Reformeranordnung
JP2013537847A (ja) * 2010-09-08 2013-10-07 ジョンソン、マッセイ、パブリック、リミテッド、カンパニー 触媒製造方法
WO2014143098A1 (fr) * 2013-03-12 2014-09-18 Hrl Laboratories, Llc Matériau cellulaire à microcouches contraint à rigidité et amortissement élevés
CN107614142A (zh) * 2015-04-24 2018-01-19 住友电气工业株式会社 复合材料及其制造方法
US10035174B2 (en) 2015-02-09 2018-07-31 United Technologies Corporation Open-cell reticulated foam
US10612441B1 (en) * 2019-05-17 2020-04-07 James R. Cartiglia Catalytic converter having foam-based substrate with nano-scale metal particles
US10619543B1 (en) * 2019-05-17 2020-04-14 James R. Cartiglia Catalytic converter with foam-based substrate having embedded catalyst
US10835888B1 (en) 2019-05-17 2020-11-17 James R. Cartiglia Foam-based substrate for catalytic converter
WO2020236321A1 (fr) * 2019-05-17 2020-11-26 Cartiglia James Support catalytique à base de mousse de carbone
US10960383B2 (en) 2019-05-17 2021-03-30 James R. Cartiglia Emission control devices
WO2021058705A1 (fr) 2019-09-25 2021-04-01 Evonik Operations Gmbh Catalyseur supporté sur mousse métallique et son procédé de production
US12076790B2 (en) 2019-09-25 2024-09-03 Evonik Operations Gmbh Metal foam bodies and process for production thereof

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US3408180A (en) * 1966-09-12 1968-10-29 Gen Foam Corp Method of producing an inorganic foam and product
US3946039A (en) * 1967-10-30 1976-03-23 Energy Research & Generation, Inc. Reticulated foam structure
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Cited By (29)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5976454A (en) * 1996-04-01 1999-11-02 Basf Aktiengesellschaft Process for producing open-celled, inorganic sintered foam products
US6171532B1 (en) 1996-05-17 2001-01-09 Basf Aktiengesellschaft Method of stabilizing sintered foam and of producing open-cell sintered foam parts
US5998317A (en) * 1996-11-21 1999-12-07 Basf Aktiengesellschaft Open-celled porous sintered products and their production
US6977095B1 (en) * 1997-10-01 2005-12-20 Wright Medical Technology Inc. Process for producing rigid reticulated articles
US7740897B2 (en) * 1997-10-01 2010-06-22 Wright Medical Technology, Inc. Process for producing rigid reticulated articles
DE10083881B3 (de) * 1999-01-19 2012-02-16 Utc Fuel Cells, Llc (N.D.Ges.D. Staates Delaware) Kompakte Brennstoffgas-Reformeranordnung
EP1095792A2 (fr) * 1999-10-29 2001-05-02 Pentel Kabushiki Kaisha Corps de vanne et réservoir de stockage de liquide pour appareil d'éjection de liquide utilisant ce corps de vanne
EP1095792A3 (fr) * 1999-10-29 2003-06-04 Pentel Kabushiki Kaisha Corps de vanne et réservoir de stockage de liquide pour appareil d'éjection de liquide utilisant ce corps de vanne
EP1272303A1 (fr) * 2000-02-02 2003-01-08 Materials And Electrochemical Research (Mer) Corporation Structures alveolaires et procedes de fabrication correspondants
EP1272303A4 (fr) * 2000-02-02 2006-03-29 Mat & Electrochem Res Corp Structures alveolaires et procedes de fabrication correspondants
US9278338B2 (en) 2010-09-08 2016-03-08 Johnson Matthey Plc Catalyst manufacturing method
US9272264B2 (en) 2010-09-08 2016-03-01 Johnson Matthey Plc Catalyst manufacturing method
JP2013537847A (ja) * 2010-09-08 2013-10-07 ジョンソン、マッセイ、パブリック、リミテッド、カンパニー 触媒製造方法
US9839907B2 (en) 2010-09-08 2017-12-12 Johnson Matthey Plc Catalyst manufacturing method
WO2014143098A1 (fr) * 2013-03-12 2014-09-18 Hrl Laboratories, Llc Matériau cellulaire à microcouches contraint à rigidité et amortissement élevés
US9217084B2 (en) 2013-03-12 2015-12-22 Hrl Laboratories, Llc Constrained microlayer cellular material with high stiffness and damping
US10035174B2 (en) 2015-02-09 2018-07-31 United Technologies Corporation Open-cell reticulated foam
CN107614142A (zh) * 2015-04-24 2018-01-19 住友电气工业株式会社 复合材料及其制造方法
EP3287206B1 (fr) * 2015-04-24 2023-08-16 Sumitomo Electric Industries, Ltd. Matériau composite et procédé pour sa production
US10619543B1 (en) * 2019-05-17 2020-04-14 James R. Cartiglia Catalytic converter with foam-based substrate having embedded catalyst
US10835888B1 (en) 2019-05-17 2020-11-17 James R. Cartiglia Foam-based substrate for catalytic converter
WO2020236321A1 (fr) * 2019-05-17 2020-11-26 Cartiglia James Support catalytique à base de mousse de carbone
US10926244B2 (en) 2019-05-17 2021-02-23 James R. Cartiglia Foam-based substrate for catalytic converter
US10933402B2 (en) 2019-05-17 2021-03-02 James R. Cartiglia Carbon foam-based catalyst support
US10960383B2 (en) 2019-05-17 2021-03-30 James R. Cartiglia Emission control devices
US10612441B1 (en) * 2019-05-17 2020-04-07 James R. Cartiglia Catalytic converter having foam-based substrate with nano-scale metal particles
WO2021058705A1 (fr) 2019-09-25 2021-04-01 Evonik Operations Gmbh Catalyseur supporté sur mousse métallique et son procédé de production
WO2021058719A1 (fr) 2019-09-25 2021-04-01 Evonik Operations Gmbh Élément en mousse métallique contenant du cobalt et son procédé de production
US12076790B2 (en) 2019-09-25 2024-09-03 Evonik Operations Gmbh Metal foam bodies and process for production thereof

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