Patent Application
20080045398
The above and related objects, features and advantages of the present invention will be more fully understood by reference to the following, detailed description of the preferred, albeit illustrative, embodiments of the present invention when taken in conjunction with the accompanying figures, wherein:
It has now been found that the above and related objects of the present invention are obtained in the form of a ceramic catalyst having interconnecting pores partially stuffed with amorphous and/or crystalline nano-particles comprising one or more noble metals on the surface of the interconnecting pores.
One embodiment of the present invention is a ceramic catalyst for use at a high temperature comprising a porous ceramic/silica glass substrate having substantially interconnecting pores with an average pore size of approximately 2 microns or less and particles comprising one or more noble metals on the surface of the substantially interconnecting pores. Preferably, the catalyst can operate at the temperature of 200° C. or more, 250° C. or more, 300° C. or more, or 350° C. or more. The particles may be amorphous and/or crystalline nano-particles. The noble metals may preferably comprise silver, gold, rhodium and/or palladium. The porous ceramic/silica can be made by many methods including: phase-separated leached glass; and silica gel, made by solution chemistry or plasma precipitation.
The porous ceramic/silica substrate has an average pore size preferably of approximately 2 microns or less, preferably of approximately 1 micron or less, preferably of approximately 0.5 microns or less, preferably of approximately 0.3 microns or less, preferably of approximately 0.2 microns or less, preferably of approximately 100 nanometers or less, preferably of approximately 50 nanometers or less, or between 50 nanometers and 150 nanometers.
The size of the porous ceramic/silica glass substrate is preferably 40 mesh (0.420 mm) or less, preferably between 40 mesh (0.420 mm) and 100 mesh (0.149 mm), preferably between 100 mesh (0.149 mm) and 200 mesh (0.074 mm), preferably between 200 mesh (0.074 mm) and 325 mesh (0.044 mm), or preferably less than 325 mesh (0.044 mm).
The average size of each of the noble metal particles is preferably 1.0 micron or less, preferably 0.5 microns or less, preferably 200 nanometers or less, preferably 100 nanometers or less, or preferably 50 nanometers or less.
The concentration of noble metals in the catalyst is given in Table A below, which relates molar concentrations of noble metals in aqueous solution to weight % of noble metal(s) per gram of porous glass. Preferably, there may be at least 1 weight % of noble metal(s) or more, preferably at least 2 weight %, or preferably at least 5 weight % in the ceramic catalyst.
The concentration of the noble metals in the substantially interconnecting pores is equivalent to preferably 0.1 molar solution or greater, preferably 0.2 molar solution or greater, preferably 0.5 molar solution or greater, preferably 1.0 molar solution or greater, or preferably 1.5 molar solution or greater.
The concentration of a non-noble metal is smaller than the concentration of the noble metal in the substantially interconnecting pores in the catalyst, wherein the non-noble metal may be iron, tin, nickel, chromium, cobalt, zinc, or manganese, which may catalyze undesirable reaction. The concentration of the non-noble metal in the substantially interconnecting pores in the catalyst is preferably less than approximately 10% of the concentration of the noble metals in the substantially interconnecting pores, or more preferably less than approximately 1% of the concentration of the noble metals in the substantially interconnecting pores.
In another embodiment of the present invention, the noble metal particles are coated with a different noble metal. In this embodiment, the first noble metal may preferably be silver and the second noble metal may preferably be gold, rhodium, and/or palladium.
Yet another embodiment of the present invention is a noble metal alkali borosilicate glass with the following composition range in mole percent: 48-64 SiO2, 28-42 B2O3, 4-9 R2O, 0-3 Al2O3, and 1-4 MxOy, wherein R refers to one or more alkali metals, M refers one or more noble metals, x varies between approximately 1 and approximately 2, and y varies between approximately 1 and approximately 2. The alkali metals R may be one or more of the following alkali metals: lithium, sodium, potassium, rubidium and cesium. The noble metals M may preferably comprise one or more of the following noble metals: silver, rhodium, and/or palladium. In the case where M is silver, x is approximately 2 and y is approximately 1. In the case where M is rhodium, x and y are approximately 1 and 2, respectively. In the case where M is palladium, x and y are approximately 1.
Yet another embodiment of the present invention is a noble metal alkali borosilicate glass with the following composition range in mole percent: 49.5-59 SiO2, 33-37 B2O3, 5-8 R2O, 0-2 Al2O3, and 1.5-2.5 MxOy, wherein R refers to one or more alkali metals, M refers one or more noble metals, x varies between approximately 1 and approximately 2, and y varies between approximately 1 and approximately 2. The alkali metals R may be one or more of the following alkali metals: lithium, sodium, potassium, rubidium and cesium. The noble metals M may preferably comprise one or more of the following noble metals: silver, rhodium, and/or palladium. In the case where M is silver, x is approximately 2 and y is approximately 1.
The present invention is also directed to a ceramic catalyst comprising a borosilicate glass substrate having substantially interconnecting pores with an average pore size of approximately 1 micron or less, and particles comprising one or more noble metals on the surface of the substantially interconnecting pores. The particles in the catalyst may comprise colloids, or nanocrystals, or a combination of colloids and nanocrystals. The one or more noble metals in the catalyst may comprise silver, gold, rhodium, or palladium. Alternatively, the one or more noble metals may comprise silver and gold. Alternatively, the one or more noble metals may comprise silver and the particles may be coated with a layer of a second noble metal on a surface of the particles, wherein the second noble metal is gold, rhodium, or palladium. The average pore size is preferably approximately 0.5 microns or less, preferably approximately 0.3 microns or less, or preferably approximately 0.2 microns or less.
The present invention is also directed to a noble metal alkali borosilicate glass composition comprising approximately 48-64 mole % SiO2, 28-42 mole % B2O3, 4-9 mole % R2O, 0-3 mole % Al2O3, and 1-4 mole % MxOy, wherein R is one or more alkali metals, M is one or more noble metals, x varies between approximately 1 and approximately 2, and y varies between approximately 1 and approximately 5. M may comprise gold, silver or rhodium. Alternatively, M may comprise gold and silver, x is approximately 2 and y is approximately 1.
The present invention is also directed to a noble metal alkali borosilicate glass composition comprising approximately 49.5-59 mole % SiO2, 33-37 mole % B2O3, 5-8 mole % R2O, 0-2 mole % Al2O3, and 1.5-2.5 mole % MxOy wherein R is one or more alkali metals, M is one or more noble metals, x varies between approximately 1 and approximately 2 and y varies between approximately 1 and approximately 5. M may comprise gold, silver, rhodium, or palladium. Alternatively, M comprises gold and silver, x is approximately 2 and y is approximately 1. Alternatively, M comprises rhodium and x and y are approximately 1.
The present invention is also directed to a noble metal alkali borosilicate glass composition comprising approximately 56 mole % SiO2, 36 mole % B2O3, 3 mole % Na2O, 3 mole % K2O, 2 mole % Ag2O.
Yet another embodiment of the present invention is a method of manufacturing a ceramic catalyst comprising the following steps:
In one embodiment of this method of manufacturing a ceramic catalyst, the noble metal may be silver. The raw materials may be silver nitrate and/or silver chloride. The method of reducing the noble metal(s) may also comprise the step of exposing the glass to UV light. The method may also include the step of grinding and sieving the glass prior to leaching.
Yet another embodiment of the present invention comprises a method of making a ceramic catalyst using the following steps:
Yet another embodiment of the present invention comprises a method of making a ceramic catalyst using the following steps:
One embodiment of the present invention is to make a ceramic catalyst comprising a porous silica glass substrate (PG) having substantially interconnecting pores with an average pore size of approximately 2 microns or less, and particles including one or more noble metals on the surface of the substantially interconnecting pores. Particles of noble metals, which may be amorphous and/or crystalline nano-particles, are deposited in the PG. The noble metals may preferably include gold, silver, rhodium and/or palladium. The deposition occurs by introducing a solution of soluble noble metal salts whose concentration of noble metals is given in the Table 1.
The noble metal(s) may be precipitated by the following steps:
a) evaporating the water; and
b) adding chemical that causes precipitation.
The noble metal(s) may be reduced by irradiating with UV light. Other known techniques of reducing the noble metal(s) include addition of a reducing agent such as a soluble compound of Fe+2. Alternatively, another non-noble metal with multiple oxidation states in one of its lower oxidation state may be used. Non-noble metals that may be used as a reducing agents include iron, tin, chromium, and manganese. Another alternative for the reducing agent is a solution containing NaBH4 (as used in Example 2 below). Upon reduction of the noble metal(s), the catalyst will turn black as the amorphous and/or crystalline nano-particles become metallic and attach to PG.
The non-noble metal(s) may be removed by the following steps:
The present invention is also directed to a method of making a ceramic catalyst comprising the steps of:
The noble metal may comprise silver, and may be provided as silver nitrate or silver chloride. The method of making a ceramic catalyst may further comprise the step of exposing the glass to light between and/or during steps e. and/or f. The method may further comprise the step of grinding and sieving the glass prior to the leaching step.
The present invention is also directed to a method of making a ceramic catalyst, comprising the steps of providing raw materials for forming a noble metal alkali borosilicate glass; melting the raw materials at approximately 1200° C.-1500° C. to form a melt; stirring the melt; cooling the melt without phase separation; heat treating the melt for approximately 0.5-24 hours at approximately 500° C.-650° C. to cause phase separation into a silica rich phase and a silica poor phase, wherein the silica poor phase comprises a noble metal; cooling the phase separated melt to approximately room temperature, at which time the melt has become the glass; leaching the silica poor phase of the glass with a leaching agent to form substantially interconnecting pores in the glass so that at least a portion of the noble metal remains on a surface of the interconnecting pores, wherein the leaching agent is not a solvent for the noble metal; reducing the noble metal to a metallic state; and drying the porous glass containing the noble metal. The reducing step may comprise the step of exposing the glass to UV radiation, or the step of adding a reducing agent, wherein the reducing agent may be a non-noble metal. The above method of making a ceramic catalyst may further comprise the step of grinding and sieving the glass prior to the leaching step. The leaching agent used in the leaching step may comprise chloride and/or bromide.
The noble metal in the catalyst may comprise silver, in which case the raw materials for making the catalyst may comprise silver nitrate or silver chloride. In the case the noble metal comprises silver, the method of making a ceramic catalyst may further comprise the step of submerging the porous glass containing metallic silver particles in a solution comprising dissolved gold.
The present invention is also directed to a method of making an efficient high temperature ceramic catalyst, comprising the steps of providing a porous ceramic/silica glass substrate comprising substantially interconnecting pores with an average pore size of approximately 2 microns or less; depositing particles comprising one or more noble metals in the silica glass substrate; precipitating the one or more noble metals; and reducing the one or more noble metals. The first noble metal used in making a ceramic catalyst may be a material selected from the group consisting of silver, gold, rhodium and palladium. The depositing step may comprise the step of introducing a solution of soluble noble metal salts whose concentration of the first noble metal is larger than 0.1 molar solution.
The reducing step may comprise the step of adding a reducing agent, which may comprise a non-noble metal or sodium borohydride. The non-noble metal used as a reducing agent in the reducing step may be iron, tin, chromium, or manganese. Alternatively, the non-noble metal reducing agent may comprise a soluble compound of Fe+2. Alternatively, the non-noble metal used as a reducing agent is in a lower oxidation state among its multiple oxidation states. The reducing step may also comprise the step of turning the particles to metallic and attaching them to the porous ceramic/silica glass substrate, wherein the particles comprise amorphous and/or crystalline nano-particles. When a non-noble metal is used as a reducing agent, the method of making the catalyst may further comprise the step of washing away the non-noble metal until the concentration of the non-noble metal is smaller than the concentration of the one or more noble metals in the substantially interconnecting pores, preferably approximately less than 10% of the concentration of the one or more noble metals in the substantially interconnecting pores, or more preferably approximately less than 1% of the concentration of the one or more noble metals in the substantially interconnecting pores.
The one or more noble metals may comprise a first noble metal and a second noble metal, wherein the first and the second noble metals are different from each other (e.g., particles comprising the first noble metal being coated on its surface with the second noble metal). The first noble metal may be silver or gold. The second noble metal may be gold, rhodium or palladium.
The average pore size of the catalyst is preferably 1 micron or less, preferably 0.5 microns or less, preferably 0.3 microns or less, preferably 0.2 microns or less, preferably 100 nanometers or less, or preferably 50 nanometers or less.
The size of the porous ceramic/silica glass substrate is preferably 40 mesh (0.420 mm) or less, preferably between 40 mesh (0.420 mm) and 100 mesh (0.149 mm), preferably between 100 mesh (0.149 mm) and 200 mesh (0.074 mm), preferably between 200 mesh (0.074 mm) and 325 mesh (0.044 mm), or preferably less than 325 mesh (0.044 mm).
The average size of each of the noble metal particles in the catalyst is preferably 1 micron or less, preferably 0.5 microns or less, preferably 200 nanometers or less, preferably 100 nanometers or less, or preferably 50 nanometers or less.
The concentration of the first noble metal in the substantially interconnecting pores in the catalyst is equivalent to preferably 0.1 molar solution or greater, preferably 0.2 molar solution or greater, preferably 0.5 molar solution or greater, preferably 1.0 molar solution or greater, or preferably 1.5 molar solution or greater.
Yet another embodiment of the present invention is directed to a method of using the ceramic catalyst made in accordance with the present invention for producing and storing hydrogen for use in generating energy, which involves the following process:
The present invention generally relates to a ceramic catalyst, preferably a high-silica content glass, and a method of making the same. The present invention also generally relates to novel glass compositions and to glass articles, particularly suitable for forming or being converted to ceramic catalysts that can be used and operate at high temperatures, preferably up to approximately 200° C., preferably up to approximately 250° C., preferably up to approximately 300° C., or preferably up to approximately 350° C.
The efficiency of a catalyst depends on the surface area of noble metals. For a given weight of noble metal, the surface area is inversely proportional to the size of the noble metal particle. U.S. Pat. No. 7,185,396 discloses the use of gold particles of 5 microns (5,000 nm). Under the present invention, noble metal particles of 1 micron or less (1,000 nm or less) may be used.
In a preferred embodiment of the present invention, the ceramic catalyst is comprised of a ceramic substrate having substantially interconnecting pores, with amorphous and/or crystalline nano-particles of one or more noble metals on a surface of the interconnecting pores. The noble metals form particles that can either be amorphous or crystalline nano-particles, or a mixture of amorphous and crystalline nano-particles. The noble metals may comprise silver, gold, rhodium, or palladium. They comprise preferably silver and gold, wherein the silver particles are coated with a different noble metal, such as gold, rhodium, and/or palladium.
To achieve a satisfactory ceramic substrate having substantially interconnecting pores, it is preferred to choose a phase-separable composition, which, upon heat treatment at a particular temperature, separates into approximately equal volume fractions, and, when held at that temperature, develops a substantially interconnecting structure with a desirable pore size. While every pore does not need to be interconnected, a sufficient percentage of the pores needs to be interconnected to enable fluid, either gas and/or liquid phases, to flow or diffuse in, out of, or through them. The present invention utilizes the method of manufacturing a phase-separable borosilicate glass disclosed in Pedro M Buarque de Macedo's prior U.S. Pat. No. 4,319,905 discussed above, as modified by the teachings discussed herein. Preferred compositions of alkali borosilicate glass as the starting material for such a substrate as set forth in U.S. Pat. No. 4,319,905 include the following ranges of elements in mole % as set forth in Table 1 below:
In accordance with an embodiment of the present invention, an initial glass composition for the ceramic catalyst may be chosen to have the following characteristics:
The porous ceramic/silica glass substrate has an average pore size of approximately 2 microns or less, preferably of approximately 1 micron or less, preferably of approximately 0.5 microns or less, preferably of approximately 0.3 microns or less, preferably of approximately 0.2 microns or less, preferably of approximately 100 nanometers or less, preferably of approximately 50 nanometers or less, or most preferably between 150 and 50 nanometers.
The ceramic catalyst will have an average particle size of approximately 40 mesh (0.420 mm) or less, preferably between 40 mesh (0.420 mm) and 100 mesh (0.149 mm), preferably between 100 mesh (0.149 mm) and 200 mesh (0.074 mm), or preferably between 200 mesh (0.074 mm) and 325 mesh (0.044 mm). Under the present invention, the ceramic catalyst is preferably manufactured from a glass composition comprising a noble metal alkali borosilicate glass, which simultaneously addresses problems associated with prior art ceramic catalysts. In accordance with an embodiment of the present invention, an initial glass composition for the ceramic catalyst may be chosen to have the following characteristics:
Another embodiment of the present invention has found a way of using the large surface areas available from the leached phase-separated glasses to become useful catalysts, by attaching monovalent (or divalent) noble metal with amorphous and/or crystalline nano-particles comprised of one or more noble metals. Prior art techniques of doping leached phase-separated glasses to add noble metal atoms on the interconnected surface areas are not practical or economically feasible to form amorphous and/or crystalline nano-particles comprised of one or more noble metals on the interconnected surface areas, as noted above. The present invention solves this problem by dissolving one or more noble metals in the molten glass at the beginning of the formation process and phase separation. This can be achieved by modifying the composition of the alkali borosilicate glass to include the following ranges of elements in mole % as set forth in Table 2 below:
In Table 2, R refers to one or more alkali metals, M refers one or more noble metals, and x and y are respectively selected based on the appropriate valence of the selected noble metals. Typically x varies between approximately 1 and approximately 2, and y varies between approximately 1 and approximately 5. Examples of alkali metals that can be used as R include lithium, sodium, potassium, rubidium, and cesium. In a preferred embodiment, sodium and/or potassium are used. Examples of noble metals that can be used as M include silver, rhodium, palladium, and iridium. In a preferred embodiment, silver is used, in which case x is approximately 2 and y is approximately 1. In another embodiment, rhodium may also be used in conjunction with or instead of silver, in which case x and y for the rhodium compound are approximately 1.
In one embodiment of the present invention, silver is chosen to be one of the noble metals used to form the majority of the weight and/or volume of the amorphous and/or crystalline nano-particles. A ceramic catalyst having amorphous and/or crystalline nano-particles including silver can be formed in accordance with an embodiment of the present invention by the following process:
By following this process, a ceramic catalyst having substantially interconnecting pores with a large surface area, and metallic amorphous and/or crystalline nano-particles of silver on the surface of the interconnecting pores is formed.
In yet another embodiment of the present invention, a layer of a second noble metal, such as gold, may be formed on the surface of a first noble metal, such as silver, which is sitting on the surface of the interconnecting pores of the ceramic catalyst.
An example of a ceramic catalyst in accordance with this embodiment of the present invention can be made as follows:
By following this process, a ceramic catalyst having substantially interconnecting pores with a large surface area, and amorphous and/or crystalline nano-particles including silver on the surface of the interconnecting pores is formed, with a second noble metal metallic layer of, for instance, gold, coating the surface of the silver particles.
Furthermore, the present invention provides a ceramic catalyst capable of operating at temperatures higher than 200° C. to detach the hydrogen atoms, which become hydrogen gas, from organothiol molecules as described in U.S. Pat. No. 7,186,396, the contents of which have been incorporated herein by reference in their entirety. The catalyst in U.S. Pat. No. 7,186,396 uses gold particles with the size of 5 microns. As the micrograph in
Accordingly, another embodiment of the present invention may be directed to a method of using the ceramic catalyst made in accordance with the present invention for producing and storing hydrogen for use in generating energy, which involves the following process:
This method addresses the problem of U.S. Pat. No. 7,185,396 noted above by providing an efficient catalyst to detach the hydrogen from the organothiol so that the hydrogen can be used to generate energy and to attach to the depleted organothiol molecules at the hydrogen source.
The following examples provide the details of exemplary processes and compositions for preparing the ceramic catalyst in accordance with the present invention.
Details of the process to prepare the ceramic catalyst:
Details of the process to prepare the ceramic catalyst:
Details of the process to prepare the ceramic catalyst:
Details of hydrogen production following the reaction of an organothiol with a ceramic catalyst substrate having amorphous and/or crystalline noble metal nano-particles are described as follows:
Thus, as a first test, it produced very successful results. The reaction can be further optimized by adjusting parameters such as reaction temperature, gas pressure, amount and type of noble metals in the catalyst, etc. Thus, this result shows that the catalyst made in accordance with the present invention can be used for the storing and producing hydrogen for use in generating energy.
Now that the preferred embodiments of the present invention have been shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. For example, the same procedure can be done with other noble metals, such as, rhodium nitrate which is also soluble. For high temperature applications rhodium may be the preferred noble metal, even though it is much more expensive than gold. Accordingly, the spirit and scope of the present invention is to be construed broadly and limited only by the appended claims and not by the foregoing specification.
This patent application is a continuation-in-part of co-pending U.S. patent application Ser. No. 11/504,953, filed on Aug. 16, 2006 and entitled “Ceramic Catalysts,” the entire content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11504953 | Aug 2006 | US |
| Child | 11893257 | US |
