Catalyst, method of manufacturing the same, and reaction using the catalyst

The present invention relates to a catalyst having a porous carrier, a buffer layer and an interface layer; a method for producing the catalyst; and a catalyst method using the catalyst.

This application is a partial continuation of US Patent Application No. 09 / 123,781, which is incorporated herein by reference.

Hydrogen and hydrocarbon conversion reactions, including, for example, steam reforming, water gas conversion, methanol synthesis and catalytic combustion are known. These reactions are usually carried out at temperatures between 150 ° C and 1000 ° C. Currently, these reactions are carried out industrially using catalytic pellets composed of active catalytic metals or catalytic metal oxides deposited on high surface area ceramic pellets.

<p><nplcit num="1"><text>ANPestryakov, AAFyodorov, VAShurov, MSGaisinovich, and LV.Fyodorova, React Kinet Catal.Lett, 53 [2] 347-352 (1994).</text></nplcit><nplcit num="2"><text>ANPestryakov, AAFyodorov, MSGaisinovich, VPShurov, lVFyodorova, and TAGubaykulina, React Kinet Catal.Lett., 54 [1] 167-172 (1995).</text></nplcit><nplcit num="3"><text>JRKosak. A Novel Fixed Bed Catalyst for the Direct Combination of H2 and O2to H2O2, MGScaros and MLPrunier, Eds., Catalysis of Organic Reactions, Marcel Dekker, Inc. (1995), p115-124.</text></nplcit><nplcit num="4"><text>OYPodyacheva, AAKetov, ZRlsmagilov, VAUshakov, A.Bos and HJVeringa, React. Kinet. Catal. Lett., 60 [2] 243-250 (1997).</text></nplcit><nplcit num="5"><text>ANLeonov, OLSmorygo, and VKSheleg, React Kinet Catal. Lett., 60 [2] 259-267 (1997).</text></nplcit><nplcit num="6"><text>MVTwigg and DEWebster. Metal and Coated-Metal Catalysts, A Cybulski is and JAMoulijn, Eds., Structured Catalysts and Reactors, Marcel Dekker, Inc. (1998), p59-90.</text></nplcit></p><p>As described in [1], foam catalysts or monolith catalysts having three layers, namely (1) a porous carrier, (2) an interface layer, and (3) a catalytic metal, are known. When producing these catalysts, the interface layer was deposited by a variety of methods, including solution impregnation. The catalyst layer can be deposited by a solution impregnation method. The interface layer has a larger surface area than the porous carrier, but the porous carrier has stronger mechanical strength than the interface layer. The porous carrier can be a metal or ceramic foam. Metal foams are highly thermally conductive and easy to machine. Due to the sponge-like mechanical properties, the reaction chamber can be easily sealed via mechanical contact. Metal foam and housing reaction Due to the tightly fitted thermal expansion between the chamber), cracking of the porous carrier is minimized at higher temperatures and gas drift around the porous carrier is minimized. Pestryakov et al. Prepared [1] and [2] metal foam-supported transition metal oxide catalysts with and without an intermediate gamma-alumina layer for oxidizing n-butane. Kosak [3] tested a number of methods for dispersing precious metals on various metal foams, pre-etching the surface with an HCl solution, and electroless plating best adheres the precious metal to the foam carrier. I reported that I would let you. Podyacheva et al. [4] also have a foam metal-supported LaCoO with a porous alumina intermediate layer for oxidizing methane.₃A perovskite catalyst was synthesized. Despite all the potential benefits of using metal foam-supported catalysts, metal foams have low corrosion resistance and poor adhesion to ceramic materials due to their non-porous and smooth web surface. Also, since these materials do not match the coefficient of thermal expansion, the interface layer tends to spall after the thermal cycle.</p><p>Ferritic steels have been secondary processed using methods such as alloy production by diffusion with Al, Cr and Si to increase corrosion resistance. The method is typically used to manufacture high temperature furnace components (about 1200 ° C) [5]. Appropriate heat treatment of aluminum-containing ferritic steel causes aluminum to migrate to the alloy surface, forming an oxide film that is resistant to oxygen diffusion and adheres strongly. Metal monoliths with&gt; 10 ppi (number of pores per inch) have been secondary processed using such ferritic steel foils [6]. However, studies on similar alloy foams with pores suitable for catalytic applications (&lt;20 ppi, preferably 80 ppi) have failed. It was due to both the immaturity of the method for producing finer Al-ferritic steel foams and the lack of alloy precursors to produce the foams.</p><p>Therefore, there is a need in technology for supported catalysts for porous carriers consisting of foams that are resistant to corrosion or oxidation and that suppress cracking of the interface layer.</p>

<p>The present invention includes a catalyst having at least three layers: (1) a porous carrier, (2) a buffer layer, (3) an interfacial layer, and optionally (4) a catalytically active layer. In some embodiments, the buffer layer disposed between the porous layer and the interface layer comprises at least two compositionally distinct sublayers. The buffer layer typically provides a coefficient of thermal expansion transition from the porous carrier to the interface layer, thereby reducing thermal expansion strain when the catalyst is heated and cooled to high operating temperatures. The buffer layer also reduces corrosion and oxidation of the porous carrier and minimizes side reactions catalyzed by the surface of the porous carrier.</p><p>The present invention also provides a catalyst having a porous carrier, a buffer layer arranged between the porous carrier and the interface layer, and an interface layer; in which case, the catalyst is at 580 ° C. in air. It has oxidation resistance such that when heated for 2500 minutes, it gains weight by less than 5%. Alternatively, the catalyst is also characterized by its resistance to flaking during the thermal cycle.</p><p>Furthermore, the present invention provides a method of converting at least one reactant to at least one product. In the method, the reactant is passed through a reaction chamber containing a catalyst.</p><p>The method of the present invention for producing a multilayer catalyst (at least three layers) is (1) a step of selecting a porous carrier, (2) a step of depositing a buffer layer on the porous carrier, and (3) a step thereof. It comprises the steps of arranging the interface layer on top and optionally (4) arranging the catalytically active layer on or integrated with the interface layer; and in that case, the buffer layer It is arranged between the porous carrier and the interface layer. Better results can be obtained by depositing a buffer layer. The catalytically active layer can be deposited after and during the deposition of the interface layer.</p><p>The advantages of the present invention, including a porous carrier with a buffer layer and an interface layer, are: better adaptation of coefficient of thermal expansion and better stability to temperature changes, such as reduced side reactions such as coking, desired. Metal-oxide interactions, strong binding to high surface area interface layers, and enhanced protection of the underlying porous carrier.</p><p>The subject matter of the present invention is specifically pointed out and explicitly claimed in the conclusions of this specification. However, by referring to the following description of the accompanying drawings where the same reference numbers refer to the same elements, it is best to understand both the configuration and method of operation, as well as the further advantages and objectives of the present invention. it can.</p>

<figref num="1">It is an enlarged cross-sectional view of a catalyst.</figref><figref num="2a">FIG. 2a is a graph of weight gain (due to oxidation) over time for stainless steel foam (top line) and titanium-coated stainless steel foam (bottom line) at 580 ° C (dashed line).</figref><figref num="2b">FIG. 2b is a graph of weight gain (due to oxidation) over time for nickel foam (top line) and nickel foam coated with titania at 500 ° C.</figref><figref num="3">It is a pair of photomicrographs comparing the effects of thermal cycles on a stainless steel foam with a titania buffer layer and an alumina thin coating (left) and a stainless steel foam with an alumina thin coating (no buffer layer, right).</figref>

The catalyst of the present invention having the porous carrier 100, the buffer layer 102, the interface layer 104, and optionally the catalyst layer 106 is shown in FIG. Both layers can be continuous or discontinuous in the form of spots or dots, or in the form of layers with gaps or holes. The porous carrier 100 can be in the form of a porous ceramic or metal. Other porous carriers suitable for use in the present invention include carbides, nitrides, and composites. Prior to layer deposition, the porous carrier has a porosity of at least 5% as measured by the mercury intrusion method and an average pore size of 1 μm to 1000 μm as measured by light microscopy and scanning electron microscopy. It has the total pore diameter / number of pores). The porous carrier preferably has a porosity of about 30% to about 99%, more preferably 70% to 98%. Preferred forms of porous carriers are foams, felts, wads and combinations thereof. Foam is a structure with continuous walls that define pores throughout the structure. Felt is a fiber structure with gaps between them. Wads are a structure of intertwined strands like steel wool. Although less preferred, the porous carrier may also include other porous media, such as pellets and honeycombs, provided that it has the above-mentioned porosity and pore size characteristics. Open air bubbles in metal foam cells) preferably have a number of pores per inch of about 20 (ppi) to about 3000 ppi, more preferably about 40 to about 120 ppi. PPI is defined as the maximum number of pores per inch (for isotropic materials, the measurement direction is irrelevant; for anisotropic materials, the measurement is performed in the direction of maximum number of pores). .. In the present invention, ppi is measured with a scanning electron microscope. We have found that porous carriers offer a number of advantages in the present invention, including low pressure reduction, improved thermal conductivity over traditional ceramic pellet carriers, and ease of loading / unloading in chemical reactors. ..

The buffer layer 102 has a different composition and / or density than both the carrier and the interface layer, and preferably has a coefficient of thermal expansion intermediate between the porous carrier and the interface layer. Preferably, the buffer layer is a metal carbide of a metal oxide. Applicants have found that the vapor deposition layer exhibits better adhesion and resistance to flaking even after a number of thermal cycles. More preferably, the buffer layer is Al₂O₃, TiO₂, SiO₂And ZrO₂Or a combination of them. More specifically, Al₂O₃Is α-Al₂O₃, γ-Al₂O₃And their combination. α-Al₂O₃Is even more preferred because of its excellent resistance to oxygen diffusion. Therefore, it is expected that the resistance to high temperature oxidation can be improved by the alumina coated on the porous carrier 100. The buffer layer can also be made from two or more compositionally different sublayers. When the porous carrier 100 is a metal, such as a stainless steel foam, a preferred embodiment has a buffer layer 102 formed from two compositionally different sublayers (not shown). The first sublayer (which is in contact with the porous carrier 100) shows good adhesion to the porous carrier 100 and is therefore preferably TiO.₂Is. Preferably, the second sublayer is TiO₂Α-Al placed on₂O₃Is. In a preferred embodiment, α-Al₂O₃The sublayer is a high density layer that provides excellent protection against the underlying metal surface. A lower density high surface area alumina interface layer can then be deposited as a carrier for the catalytically active layer.

Typically, the coefficient of thermal expansion of the porous carrier 100 is different from that of the interface layer 104. Thus, for high temperature catalysts (T&gt; 150 ° C), the buffer layer 102 needs to transition between the two coefficients of thermal expansion. The coefficient of thermal expansion of the buffer layer can be adjusted by adjusting the composition of the buffer layer in order to obtain a coefficient of thermal expansion compatible with the coefficient of thermal expansion of the porous carrier and the interface layer. Another advantage of the buffer layer 102 is that it provides resistance to side reactions caused by exposed metal foam surfaces, such as caulking or cracking. For chemical reactions that do not require large surface area carriers, such as catalytic combustion, the buffer layer 102 stabilizes the catalytic metal by a strong metal-to-metal oxide interaction. For chemical reactions that require a large surface area carrier, the buffer layer 102 provides a stronger bond to the high surface area interface layer 104. Preferably, the buffer layer is free of holes and pinholes, which provides excellent protection against the underlying carrier. More preferably, the buffer layer is non-porous. Also, the buffer layer has a thickness of less than 1/2 of the average pore size of the porous carrier. Preferably, the buffer layer has a thickness of about 0.05 μm to about 10 μm, more preferably less than 5 μm. The buffer layer should exhibit thermal and chemical stability at high temperatures.

The interface layer 104 can include nitrides, carbides, sulfides, halides, metal oxides, carbons and combinations thereof. The interface layer provides a high surface area and / or provides the desired catalytic carrier interaction for the supported catalyst. The interface layer can contain any material conventionally used as a catalyst carrier. Preferably, the interface layer is a metal oxide. Examples of the metal oxide include γ-Al.₂O₃, SiO₂, ZrO₂, TiO₂, Tungsten oxide, magnesium oxide, vanadium oxide, chromium oxide, manganese oxide, iron oxide, nickel oxide, cobalt oxide, copper oxide, zinc oxide, molybdenum oxide, tin oxide, calcium oxide, aluminum oxide, lanthanum series oxide (1 type) Or multiple types), zeolite (s), and combinations thereof, but are not limited thereto. The interface layer 104 can serve as a catalytically active layer without additional catalytically active material deposited on it. However, the interface layer 104 is usually used in combination with the catalytically active layer 106. The interface layer can also be made from two or more compositionally different sublayers. The interface layer has a thickness of less than half the average pore size of the porous carrier. Preferably, the thickness of the interface layer is from about 0.5 μm to about 100 μm, more preferably from about 1 to about 50 μm. The interface layer can be crystalline or amorphous and preferably has a BET surface area of at least 1 m2 / g.

The catalytically active layer 106 (if present) can be deposited on the interface layer 104. Alternatively, the catalytically active material can be deposited simultaneously with the interface layer. The catalytically active layer (if present) is typically closely dispersed over the interface layer. To "place" or "deposit" the catalytically active layer on the interface layer means that the microscopic catalytically active particles are: on the surface of the carrier layer (ie, the interface layer), in the gaps in the carrier layer, and in the carrier layer. Includes the conventional understanding that it is dispersed in the open pores in. As catalytically active layers: catalytic metals such as noble metals, transition metals and combinations thereof; metal oxides such as alkali elements, alkaline earth elements, boron, gallium, germanium, arsenic, selenium, tellurium, tarium, lead, bismuth , Polonium, magnesium, titanium, vanadium, chromium, manganese, iron, nickel, cobalt, copper, zinc, zirconium, molybdenum, tin, calcium, aluminum, silicon, oxides of lanthanum series elements (s), and Combinations thereof; composite materials; zeolites (s); nitrides; carbides; sulfides; halides; phosphates; and combinations of any of the above are included, but not limited to.

Preferably, the catalyst (including the porous carrier, buffer layer, interface layer and catalytically active layer, if any) is sized to fit in the reaction chamber. The catalyst preferably has continuous porosity such that molecules can diffuse in the catalyst. In this preferred embodiment, the catalyst can be placed in the reaction chamber so that the gas flows substantially into the catalyst rather than around it. In a preferred embodiment, the cross-sectional area of the catalyst occupies at least 80%, more preferably at least 95% of the cross-sectional area of the reaction chamber. In a preferred embodiment, the catalytically active material is dispersed on the surface of the entire catalyst so that the reactants passing through the catalyst can react anywhere along the passageway in the catalyst; it is unused inside the pellet. This is a significant advantage over pellet-type catalysts, where space or space where the catalyst is not effectively utilized exists in large volumes. In addition, the catalyst of the present invention is superior to the powder because the filled powder can cause a severe pressure drop.

The catalysts of the present invention can also be characterized by the properties they exhibit. Factors that can affect these properties by conditioning are: Porous carrier, buffer layer, interface layer, and catalytically active layer selection; stepwise change in coefficient of thermal expansion, crystallinity, metal / carrier Included are interactions, deposition methods, and other factors that are apparent from the description in the present invention. The use of buffer layers in combination with routine tests using these factors can be used to produce catalysts that catalyze various chemical reactions. Preferred embodiments of the catalysts of the present invention have the following properties: (1) Adhesion-After 3 thermal cycles in air, the catalyst is 2% (area basis) as observed by SEM (scanning electron microscope) analysis. ) Indicates flaking; (2) Indicates one or more oxidation resistance. Heating at 580 ° C for 2500 minutes in air increases the weight of the catalyst by less than 5%, more preferably less than 3%; even more preferably, heating at 750 ° C for 1500 minutes in air 0.5%. Increases by less than. Weight gain is measured by thermogravimetric analysis (TGA). Each thermal cycle consists of heating in air at a heating rate of 10 ° C / min from room temperature to 600 ° C, holding at 600 ° C for 3000 minutes, and cooling at a rate of 10 ° C / min. The catalyst is preferably about 0.5 m as measured by BET.²Over / g, more preferably about 2.0m²It has a surface area of more than / g.

Further, the present invention comprises passing at least one reactant through a reaction chamber containing the catalyst of the present invention, converting the at least one reactant into at least one product, and producing the product from the reaction chamber. Provided is a catalytic method including a step of taking out an object. In a preferred embodiment, the catalytic method is carried out in an apparatus having microchannels. Factors related to suitable microchannel devices and various methods include, for example, US Pat. Nos. 5,611,214, 5,811,062, 5,534,328 and US Patent Applications 08 / 883,643, 08 / 938,228, 09 / 375,610. No., 09 / 123,779, US Patent Application No. 09 / 492,246 (agent reference number E-1666B-CIP), 09 / 375,614 (filed August 17, 1999) and 09 / 265,227 (1999) (Applied on March 8, 2014). The above patents and patent applications are incorporated herein by reference as if they were fully reproduced below. In another preferred embodiment, the catalyst is a monolith, i.e. a single adjacent porous catalyst piece, or a number stacked together that can be easily inserted into and removed from the reaction chamber. Adjacent pieces (not filled powder beds or pellets or coatings on microchannel walls). A piece or stack of catalyst pieces preferably has a width of 0.1 mm to about 2 cm, preferably less than 1 cm thick, more preferably about 1 mm to about 3 mm. The catalysts of the present invention have many advantages over catalytic methods: for example, chemical stability, stability against repeated thermal cycles, thermal stability, efficient loading / unloading of catalysts, fast heat transfer and mass transfer. , And the maintenance of desired catalytic activity can be provided.

The metal surface in the microchannel device can be coated with either or both of a buffer layer and an interface layer. It can be done by vapor deposition, preferably using any of the methods described herein. Preferred coating materials are titanium and 5% -10% SiO₂/ Al₂O₃including. The inner surface of the reaction chamber and heat exchanger and other surfaces of the microchannel device can be coated. In some embodiments, the walls of the reaction chamber are coated with any buffer layer, interfacial layer, and catalytically active material, typically in combination with the catalytically active material and interfacial layer to create a supported catalyst. Can be done. The coating can also be applied to metal walls in tubes and pipes that form connections to or within microchannel devices.

The catalytic methods of the present invention include: acetylation, addition reaction, alkylation, dealkylation, hydrogenation dealkylation, reductive alkylation, amination, aromaticization, allylation, self-thermal modification, carbonylation. , Decarbonylation, reductive carbonylation, carboxylation, reductive carboxylation, reductive coupling, condensation, decomposition, hydrogenation, cyclization, cyclo oligomerization, dehalogenation, dimerization, epoxidation, ester Conversion, exchange, Fisher Tropsch, hydrogenation, hydrohalogenation, homologation, hydration, dehydration, hydrogenation, dehydrogenation, hydrocarboxylation, hydroformylation, hydrocracking, hydrometallation , Hydrosilylation, hydrolysis, hydrogenation, hydrodesulfurization / hydrogenation denitrification (HDS / HDN), isomerization, methanol synthesis, methylation, demethylation, metathesis, nitrate, oxidation, partial oxidation, polymerization, These include reduction, steam reforming and carbon dioxide reforming, sulfonated, telomerization, ester exchange reactions, trimerization, aqueous gas conversion (WGS), and reverse aqueous gas conversion (RWGS).

The method for producing the catalyst of the present invention includes a step of selecting the porous carrier 100, a step of depositing a buffer layer 102 on the porous carrier 100, and a step of depositing an interface layer 104 on the buffer layer 102. Optionally, the catalyst layer 106 can be deposited on the interface layer 104, or both the interface layer and the catalyst layer can be deposited simultaneously on the buffer layer 102.

Since the metal has a non-porous and smooth web surface, the deposition of the buffer layer may be hindered. One way to alleviate this problem is to roughen the metal surface by chemical etching. Roughening the metal foam by chemical etching with a mineral acid solution, such as 0.1M to 1M HCl, significantly improves the adhesion of the high surface area gamma-alumina-supported metal catalyst to the metal foam. The roughened web surface also exhibits improved resistance to spalling of the catalyst layer under thermal cycles. In a preferred embodiment using the metal foam as the porous carrier 100, the metal foam is etched before depositing the buffer layer 102. Etching is preferably carried out with an acid, such as HCl.

The deposition of the buffer layer 102 is preferably performed by, but not limited to, chemical vapor deposition, physical vapor deposition, or vapor deposition including a combination thereof. Surprisingly, it has been found that vapor deposition, typically performed at high temperatures, produces a polycrystalline or amorphous phase that favorably adheres the buffer layer to the surface of the porous carrier. The method is particularly convenient for adhering the metal oxide buffer layer to the metal porous carrier. Alternatively, the buffer layer 102 can be obtained by solution coating. For example, solution coating involves exposing the metal surface to water vapor to generate surface hydroxyls to functionalize the metal surface, then surface reacting and hydrolyzing the alkoxide to obtain a metal oxide coating. Have. This solution coating may be preferred as a lower cost method for depositing the buffer layer 102.

The interface layer 104 is preferably made by vapor deposition or solution deposition using precursors known in these techniques. Suitable precursors include organometallic compounds, halides, carbonyls, acetonates, acetates, metals, colloidal dispersions of metal oxides, nitrates, slurries and the like. For example, the porous alumina interface layer can be washed and coated with PQ alumina (Nyacol Products, Ashland, Mass.) Colloidal dispersion, then dried in vacuum overnight and fired at 500 ° C. for 2 hours. ..

The catalytically active material can be deposited by any suitable method. For example, the catalyst precursor can be deposited on colloidal metal oxide particles, slurry coated on a buffer coated porous carrier, then dried and reduced.

Example 1 Experiments have been carried out to prove certain advantages of the buffer layer of the present invention. Unetched stainless steel foam (Astromet, Ncinati, Ohio), vapor deposition, 1000 Å of TiO₂Covered with. Titanium isopropoxide (Strem Chemicals, New Burry Port, Massachusetts) was deposited at a pressure of 0.1 torr 100 at a temperature of 250 ° C to 800 ° C. At a deposition temperature of 600 ° C and a reactor pressure of 3 torr, a titanium coating with excellent adhesion to the foam was obtained.

According to SEM (scanning electron microscope) analysis, TiO₂It was found that the stainless steel foam-supported gamma-alumina with the above showed no spalling after several (3) thermal cycles from room temperature to 600 ° C. TiO₂In a control experiment using a stainless steel foam carrier coated with gamma-alumina without a buffer layer, severe flaking or spalling was observed under the same test conditions. Resistance to high temperature oxidation is shown in Figures 2a and 2b. As can be seen in Figure 2a, uncoated stainless steel foam oxidizes rapidly (indicated by weight gain, or thermogravimetric), while titanium coated stainless steel oxidizes relatively slowly. Will be done. As can be seen in Figure 2b, the uncoated nickel foam was oxidized, but under the same conditions, the titania-coated nickel foam was zero-oxidized (ie, undetectable levels of oxidation).

Conclusion Although the preferred embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many modifications and improvements can be made without departing from the present invention in a broader aspect of the present invention. Thus, the appended claims are intended to cover all changes and improvements within the true spirit and scope of the invention.