Gold-containing catalyst for removal of hydrogen from oxygen-rich streams

Abstract

A method for removing hydrogen from an oxygen stream includes electrolyzing water in an electrolytic cell to produce a hydrogen-rich stream and an oxygen-rich stream. The oxygen-rich stream comprises hydrogen. The method further includes feeding the oxygen-rich stream to a reactor having a gold-containing catalyst, and contacting the oxygen-rich stream with the gold-containing catalyst in the reactor. The gold-containing catalyst comprises gold and a second metal on an oxide support, and the oxygen partial pressure of the oxygen-rich stream in the reactor is greater than 1 bar.

Description

[0001] The present disclosure relates to removing hydrogen from oxygen-rich streams. More particularly, the present disclosure relates to gold-containing catalyst compositions and methods of preparing gold-containing catalyst compositions for removing hydrogen from oxygen-rich streams. Background Art

[0002] As the transition from fossil-based energy carriers to low-carbon energy solutions continues to progress, there is a demand for alternative non-fossil-based energy sources. One such low-carbon energy carrier is hydrogen. Hydrogen can be produced by thermochemical conversion (e.g., from biogas or natural gas) or by electrolysis, which decomposes water into hydrogen and oxygen. Hydrogen produced via electrolysis using green electricity as an energy source is particularly interesting because this hydrogen (also known as green hydrogen) has the lowest greenhouse gas emissions compared to other technologies for producing hydrogen. The electrolysis of water to form hydrogen and oxygen occurs in an electrolyzer having an anode and a cathode separated by an electrolyte. At the anode, water reacts to form oxygen (O2) and hydrogen ions (H + ). H + The ions move through the electrolyte to the cathode side of the electrolyzer to form hydrogen gas (H2). The electrolyzer outputs a stream of H2 that is further processed to remove contaminating amounts of oxygen and water before use.

[0003] In addition to the H2 gas stream, the electrolyzer also outputs a stream rich in O2. The stream rich in O2 can also be used for various purposes. In order to achieve safe storage, safe transportation and optimal use, it is necessary to further process the stream rich in O2 to remove the water and H2 gas of the contamination amount. In addition, it is believed that H2 plays a role as a greenhouse gas. Therefore, before use and / or release into the environment, regulatory agencies may need to remove H2 from certain gas streams (such as streams rich in O2). A technology for removing H2 gas from streams rich in O2 is catalytic oxidation, in which hydrogen reacts with excess oxygen in a catalytic converter to generate water. The water is then removed downstream in a separate unit. For example, in the deoxygenation of the H2 gas stream, a catalyst based on palladium (Pd) and platinum (Pt) is used. In Hanson et al., the reaction between H2 and O2 on a supported platinum catalyst was evaluated. (Hanson et al., The Reaction between H2 and O2 over Supported Platinum Catalysts, Journal of Catalysis, 53, pp. 56-67). However, these catalysts are not suitable for removing H2 from oxygen-rich streams. It was found that in an oxygen-rich environment, at elevated pressures and temperatures below 100 degrees Celsius (°C), these catalysts exhibited much lower activity than expected when compared to the same reaction in an oxygen-depleted environment. Therefore, it would be advantageous to develop catalysts with the desired activity and stability for removing H2 from O2-rich streams at low temperatures. Summary of the Invention

[0004] In one embodiment, a method for removing hydrogen from an oxygen stream comprises electrolyzing water in an electrolyzer to generate a hydrogen-enriched stream and an oxygen-enriched stream. The oxygen-enriched stream comprises hydrogen. The method further comprises feeding the oxygen-enriched stream to a reactor having a gold-containing catalyst, and contacting the oxygen-enriched stream with the gold-containing catalyst in the reactor. The gold-containing catalyst comprises gold and a second metal on an oxide support, and the oxygen-enriched stream in the reactor has an oxygen partial pressure greater than 1 bar.

[0005] Additional features and advantages of the exemplary embodiments of the present disclosure will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of such exemplary embodiments. The features and advantages of such embodiments may be realized and obtained by the instruments and combinations particularly pointed out in the appended claims. These and other features will become more apparent from the following description and the appended claims, or may be learned by practice of such exemplary embodiments set forth below. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Advantages of the present disclosure will become apparent upon reading the following detailed description and referring to the accompanying drawings, in which:

[0007] Figure 1 is a block diagram of a system having an electrolyzer and a hydrogen removal reactor according to an embodiment of the present disclosure, wherein the hydrogen removal reactor includes a catalyst for removing hydrogen (H 2 ) from an oxygen (O 2 )-rich stream generated in the electrolyzer; and

[0008] Figure 2 is prepared according to an embodiment of the present disclosure for use from Figure 1 Flowchart of a method for removing H2 from an O2-rich stream generated in a system using a bimetallic catalyst. DETAILED DESCRIPTION

[0009] One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the currently disclosed technology. In addition, in order to provide a concise description of these embodiments, not all features of an actual specific implementation may be described in the specification. It should be understood that in the development of any such actual specific implementation, as in any engineering or design project, many specific implementation-specific decisions will be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which may vary from one specific implementation to another. In addition, it should be understood that such development efforts may be complex and time-consuming, but are still routine tasks of design, production, and manufacturing for those of ordinary skill in the art who benefit from this disclosure.

[0010] When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that additional elements may be present in addition to the listed elements. Furthermore, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0011] As used herein, the terms "approximately," "about," and "substantially" refer to an amount that is close to a specified amount but still performs a desired function or achieves a desired result. For example, the terms "approximately," "about," and "substantially" may refer to an amount that is less than 10% of the stated amount, less than 5% of the stated amount, less than 1% of the stated amount, less than 0.1% of the stated amount, and less than 0.01% of the stated amount.

[0012] Energy conversion creates opportunities for alternative fuel and energy solutions that significantly reduce or eliminate carbon dioxide (CO2) emissions compared to traditional fossil-based fuels. An attractive alternative energy solution is hydrogen, partly due to its high energy density and zero CO2 emissions. Depending on the source of the hydrogen, there are various types of hydrogen (e.g., gray hydrogen, blue hydrogen, green hydrogen, etc.). For example, hydrogen produced by thermochemical conversion of natural gas is called gray hydrogen. Blue hydrogen is also produced by thermochemical conversion of natural gas. However, the difference between gray hydrogen and blue hydrogen is that in blue hydrogen, CO2 is captured and stored underground. Green hydrogen is generated from renewable sources and has the lowest CO2 emissions compared to gray hydrogen and blue hydrogen.

[0013] Green hydrogen can be produced by splitting water (H2O) via electrolysis. In electrolysis, water is electronically split into hydrogen (H2) and oxygen (O2) to generate an H2-rich output steam and an O2-rich output stream. The H2-rich output stream has contaminating amounts of O2 and water. Similarly, the O2-rich output stream has contaminating amounts of H2 and water. These contaminants are removed from the output stream before use. There are several precious metal-based catalysts for removing O2 and H2 from various streams. For example, catalysts based on palladium (Pd) and / or platinum (Pt) are used to catalyze reactions for removing O2 and H2. Typically, these catalysts are used to remove O2 from an H2-rich output stream, selectively remove H2 from a hydrocarbon stream or from a carbon monoxide (CO) stream, and remove H2 accumulation in the cell. For these applications, typical reaction conditions in these catalytic processes can be an inlet temperature of less than about 100 degrees Celsius (°C). Furthermore, these applications are typically performed at relatively low oxygen partial pressures (e.g., O2 partial pressures less than about 0.2 bar, as is the case with air). However, the O2 partial pressure in the O2-rich output stream generated by the electrolysis of water is typically in the range of about 1 bar to about 5 bar, or higher. It has been found that noble metal-based catalysts, such as Pd, Pt, or Pd / Pt-based catalysts, commonly used in catalytic reactions between hydrogen and oxygen, exhibit undesirable performance at temperatures below 160°C, particularly below 100°C, and at O2 partial pressures above 1 bar (e.g., 5 bar). That is, these noble metal-based catalysts have poor activity and stability and are oxidized in O2-rich environments.

[0014] For example, the effect of oxygen partial pressure on the catalytic performance of a Pd catalyst with 0.5 wt% Pd is illustrated in Table 1. This catalyst represents a prior art noble metal based catalyst and is therefore considered a comparative sample, and its preparation is provided in Example 3 below. In Example 1, at an O2 partial pressure of 5 bar, 10,000 h-1 At an hourly gas space velocity of 1000 ppmv (i.e., 5 mbar), a Pd catalyst was contacted with a gas stream simulating electrolyzer O2 exhaust gas having an H2 concentration of 1000 parts per million by volume (ppmv) (i.e., 5 mbar) at a temperature of 115°C. For comparison, in Example 2, the Pd catalyst was contacted with a gas stream having the same 1000 ppmv H2 concentration, in which the majority of the O2 was replaced by nitrogen (N2) gas to reduce the O2 partial pressure from 5 bar to 0.25 bar. The H2 concentration in the outlet gas was measured and is shown in Table 1 below.

[0015] Table 1. Hydrogen removal activity of Pd catalysts in oxygen-containing gas streams

[0016] Example 1 Example 2 <![CDATA[Partial pressure of O2 (bar)]]> 5 0.25 <![CDATA[Concentration of H2 at the outlet (ppmv)]]> 600 40 Conversion Rate % 40 96

[0017] As shown in Table 1, the performance of the Pd catalyst is undesirable when the partial pressure of O2 is high (e.g., 5 bar) compared to when the partial pressure of O2 is low (e.g., 0.25 bar), based on a 40% conversion of H2. Without being bound by theory, it is believed that the reduction in the catalytic performance of the Pd catalyst in the presence of a gas rich in O2 is partly due to the oxidizing environment created by the O2 gas at a high (e.g., 5 bar) O2 partial pressure. Due to this high oxygen partial pressure, the reactive sites at the Pd nanoparticles present in the catalyst become oxidized, thereby hindering the reaction with hydrogen. In order to achieve the necessary activity for high conversion at the gas hourly space velocity required for the catalyst, it is necessary to reactivate the oxidized Pd catalyst by reduction at regular intervals in an oxygen-free environment, which regular intervals can be in the range of several hours to several months according to standard conditions and the mode of operation of the reactor. This operation is undesirable.

[0018] Another technique used to improve catalyst performance to achieve high conversion for a given gas hourly space velocity is to increase the reaction temperature. However, in an O2-rich environment and at O2 partial pressures above 1 bar, increasing the reaction temperature is suboptimal and complicated because it can introduce safety issues and affect equipment metallurgy due to reactions on equipment surfaces in contact with the O2-rich gas.

[0019] In addition, the presence of water vapor in the O2-rich electrolyzer off-gas adds additional complexity and also affects catalyst performance. For example, the O2-rich electrolyzer off-gas can have a dew point close to the temperature of the electrolyzer used for electrolysis of water, which is about 57°C and corresponds to about 0.17 bar. In addition, unlike the H2-rich electrolyzer off-gas, which promotes the self-activation of the precious metal catalyst by self-reduction, as discussed above, the O2-rich electrolyzer off-gas promotes oxidation. Therefore, when precious metal catalysts are used to process O2-rich streams, they become oxidized and the catalyst performance and stability are reduced compared to the reduced precious metal catalysts. However, as discussed in further detail below, it has been surprisingly found that by incorporating gold (Au) into the catalyst, the catalytic performance and stability of the precious metal catalysts are improved when used to remove hydrogen from O2-rich streams.

[0020] In view of the above, Figure 11 is a block diagram of a system 10 that can be used in a method for generating an oxygen-rich stream having a contaminant level of H2 and removing H2 from the oxygen-rich stream. As discussed in detail below, the system 10 uses a catalyst of the present disclosure to remove H2 from an oxygen-rich stream and includes an electrolyzer 14 and a hydrogen removal reactor 16. In the illustrated embodiment, the electrolyzer 14 receives a water (H2O) stream 20 through an inlet 24 and electrochemically decomposes the water in the H2O stream 20 into a hydrogen (H2)-rich stream 28 and an oxygen (O2)-rich stream 30. The electrolyzer 14 includes a first outlet 32 for outputting the H2-rich stream 28 and a second outlet 36 for outputting the O2-rich stream 30. Decomposing water via electrolysis is a method well known in the art and will not be described in detail. As discussed above, the O2-rich stream (such as the O2-rich stream 30) generated by the electrolysis of water has a contaminant amount of H2. Therefore, the contaminant amount of H2 in the O2-rich stream 30 is removed before use. Thus, as shown in the illustrated embodiment, an O2-rich stream 30 is fed to the reactor 16 via a reactor inlet 38. The reactor 16 includes one or more catalyst beds 40 having a gold-containing hydrogen removal catalyst 42. In the reactor 16, the O2-rich stream 30 contacts the catalyst 42 and removes contaminating amounts of H2, thereby generating a treated O2-rich stream 46 that is substantially free of H2 (e.g., containing less than about 50 ppmv, preferably less than 10 ppmv of H2). Thus, the treated O2-rich stream 46 can have between about 95% and 100% less hydrogen than the O2-rich stream 30. The treated O2-rich stream 46 can be released from the reactor 16 via a reactor outlet 50 and further processed in subsequent downstream processes. Depending on the intended use of the treated O2-rich stream 46, subsequent processes can remove water vapor from the stream 46. Between the second outlet 36 and the reactor inlet 38, elements such as heating elements, compressor elements, drying elements, contaminant removal elements, and combinations thereof can be added.

[0021] An integral part of the system disclosed herein is the electrolyzer 14. It is well known to those skilled in the art that there are various technologies and configurations for the electrolysis of water. There are three main water electrolysis technologies currently used on a commercial scale, and include 1.) alkaline water electrolysis (AEL), 2.) polymer electrolyte membranes (PEMEL), and 3.) solid oxide electrolytes (SOEL). In all of these technologies, gas crossover (e.g., H2 flows to the O2 side, and vice versa) is observed by the membrane separating the cathode from the anode compartment. As a result, the hydrogen formed on the cathode side leaks into the oxygen generated in the anode, and therefore it is necessary to remove the contaminating gas (e.g., H2 or O2) from the corresponding gas downstream of the electrolyzer 14.

[0022] In the reactor 16, a gold-containing hydrogen removal catalyst 42 removes H from the O2-rich stream 30. Surprisingly, it has been found that the gold-containing hydrogen removal catalyst 42 has improved activity and performance compared to a noble metal hydrogen removal catalyst that does not contain gold at an O2 partial pressure in the range of greater than about 1 bar. The reactor 16 may comprise a fixed bed reactor, a fluidized bed reactor, or one or more of the two. In one embodiment, the catalyst bed 42 is a stacked bed. In a preferred embodiment, the catalyst bed 42 has a packed catalyst bed configuration, whereby the catalyst is fixed inside the reactor 16. The packed catalyst bed configuration can be non-cooled (e.g., an adiabatic reactor), cooled (e.g., to promote isothermal behavior), or both. Since the reaction between H2 and O2 is exothermic, a non-cooled catalyst bed configuration in which heat is not removed from the catalyst bed causes the temperature of the O2-rich stream 30 in the reactor 16 to increase as the reaction propagates through the length of the catalyst bed 40. Ultimately, the O2-rich stream 30 in the reactor 16 reaches a final adiabatic temperature increase. However, in a cooled catalyst bed configuration, heat is continuously removed over the entire length of the catalyst bed 40. Therefore, the temperature of the O2-rich stream 30 can be maintained at or near the temperature of the reactor inlet 38 and will not reach an adiabatic temperature rise. In an embodiment in which the catalyst bed 40 is a cooled catalyst bed configuration, the bed 40 can be a multi-tube packed bed having a catalyst 42 filled in tubes surrounded by a heat exchange medium. The heat exchange medium can be water, steam, oil, molten salt or any other suitable heat exchange medium and a combination thereof. The catalyst bed 42 of the present disclosure can be arranged in a variety of ways. For example, the catalyst bed 42 can have a single catalyst (e.g., catalyst 42) that fills most of the internal volume of the reactor 16. The catalyst 42 can be supported by a grid that keeps the catalyst 42 within the reactor 16 while allowing the treated O2-rich stream 46 to flow through the catalyst bed 40 and leave the reactor 16. In a preferred embodiment, between the grid and the catalyst bed 40, a support bed is made of an inert material having grains of larger size than the catalyst 42 (e.g., spherical support bed grains, which typically have a diameter of about 1 millimeter (mm) to 20 mm, depending on the catalyst grain size). Such a support bed helps to prevent the grid from being blocked by relatively small catalyst grains (e.g., grains having a diameter of about 0.5 mm to 4 mm). In another embodiment, the catalyst bed 40 is covered with a guard bed that is designed so that it will capture contaminants present in the O2-rich stream 30 that could potentially damage (e.g., poison) the catalyst 42. As an example, the oxygen stream from an alkaline electrolyzer can carry a small amount of aqueous aerosol containing high levels of potassium hydroxide (KOH).A guard bed with high pore volume and / or acidic properties can help capture such aerosols while neutralizing and absorbing the alkaline KOH. Typical examples of such guard beds are activated alumina, silica, and / or silica gel. Such guard beds also help buffer the relative humidity of the O2-rich stream 30. In situations where the relative humidity becomes high and reaches concentrations approaching 100%, such guard beds may temporarily absorb water vapor during those extreme conditions.

[0023] In an alternative embodiment, two or more different catalyst materials with different compositions are loaded in the bed, stacked one upon another. For example, catalyst bed 40 can have a first bed and a second bed, and this first bed has the first catalyst (for example, catalyst 42) that fills its volume. This second bed has the second catalyst (for example, catalyst 42) that is different from the first catalyst that fills its volume. Such configuration can promote the optimization of catalyst performance. The first catalyst can be located in the upstream portion of catalyst bed 40, and in this upstream portion, compared with the downstream portion of catalyst bed 40, hydrogen concentration is still relatively high. The first catalyst is designed to have higher activity at low temperatures compared with the second catalyst. The second catalyst is placed in the downstream portion of catalyst bed 40, and compared with the first catalyst, the second catalyst is more robust to higher temperatures and has better performance at very low hydrogen concentrations.

[0024] The catalyst 42 disclosed herein is preferably shaped into grains of sufficient size and intergranular porosity to generate a catalyst bed (e.g., catalyst bed 40) with a low pressure drop. The preferred shape of these catalysts is particles of uniform / regular shape. The catalyst particles can be pellets and / or extrudates. As non-limiting examples, the pellets and / or extrudates can be spherical, multi-lobed, rod-shaped, cylindrical, hollow, porous, and combinations thereof. Although irregularly shaped catalyst grains are less preferred, they can also be used in the catalyst bed 40. For fixed bed applications, the diameter of the catalyst grains can be in the range of about 0.5 mm to about 4 mm. For extrudates and pellets in which the length is significantly longer than the diameter, the length can be in the range of about 1 mm to about 10 mm. In fluidized bed applications, the catalyst grains can have a grain size distribution such that at least 60% of the catalyst particles have a particle size less than about 200 microns and no more than about 40% of the catalyst particles have a diameter less than about 40 microns.

[0025] In an alternative to a catalyst bed filled with grains, catalyst 42 can be shaped into a catalytically active structured body, wherein the structured body is optimized to minimize pressure drop and maximize the accessibility of catalyst 42. As a non-limiting example, the structured body of catalyst 42 can be a honeycomb, a monolith, a corrugated foil or a foam. Such a structure has a large number of small repeating elements, such as walls, foils and pillars. Both these elements and the cavities between them have a size of about 0.2mm-4mm. The catalytically active structured body of catalyst 42 has a size much larger than the repeating elements they contain, and can be in the range of about 5mm to about 600mm. The catalytically active material of catalyst 42, which is a combination of gold (Au), a second metal and an oxide carrier, can be a part of the structure of the structured body, or can be present on the structured body as a coating. In the latter case, the coating can have a thickness between about 0.05mm and about 1mm.

[0026] As discussed above, catalyst 42 contains Au mixed with another metal (i.e., a second metal) on an oxide support. The second metal can be selected from Group VIIIB and / or Group IB metals of the periodic table, with all metals having hydrogen activation function being preferred. As non-limiting examples, the second metal can be selected from nickel (Ni), cobalt (Co), copper (Cu), iridium (Ir), platinum (Pt), rhenium (Re), palladium (Pd), rhodium (Rh), and combinations thereof. Most preferably, noble metals such as Pd, Pt, and Rh, which are considered to be more susceptible to high oxygen partial pressures, are preferred. In addition to the second metal, the catalyst can also contain a third metal or more additional metals.

[0027] The catalyst disclosed herein comprises Au in combination with another metal (i.e., a second metal) on an oxide support, wherein Au is present in an amount of at least 0.01 wt % based on the total weight of the catalyst, and the second metal is present in an amount of at least 0.005 wt %. As will be appreciated by those skilled in the art, the activity and long-term performance of the catalyst are directly related to the metal loading. At low metal loadings of the catalysts disclosed herein (e.g., catalyst 42), activity and long-term performance tend to be linearly correlated with metal loading over a wide range. Catalysts with very low loadings typically require very large reactor sizes to achieve maximum conversion. At very high metal loadings (e.g., >5 wt %), the linear correlation between activity and long-term performance and metal loading may be weakened due to excessive capacity, diffusion limitations, and / or larger particle size of the precious metal. Optimizing the metal loading of the catalyst strongly depends on the desired process configuration and conditions.

[0028] X-ray fluorescence (XRF) is used to determine the metal loading on the catalyst disclosed herein. However, as will be appreciated by those skilled in the art, other techniques may also be used to measure the amount of metal on the catalyst. For example, the catalyst metal loading may also be measured using inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectroscopy (AAS). These measurement techniques may also be used to determine the level of pollutants on the catalyst. For the XRF method, wave dispersive X-ray fluorescence (WDXRF) spectroscopy was applied. The sample was ground using a disc grinder (Herzog HSM 100P) at 1420 rpm for 1 minute to about d 50 10 micrometers to 20 micrometers (μm) grain size (d 90 The sample was then mixed with a polyethylene wax binder (Ceridust 3620 from TER Chemicals) at a ratio of 80 wt% sample to 20 wt% binder and pressed into an alumina cup (40 mm) for 5 seconds at 200 kN to form a pill using a Herzog HTP40 press. The pill was then measured using a standard-free Full Analysis Vac method using WDXRF spectroscopy (S8 Tiger 3 kW from Bruker AXS). Results were analyzed using Eval 2 of SpectraPlus software (V2.5.500 from Bruker AXS) and matrix correction was applied. For this matrix correction, the support material, in this case aluminum oxide (Al2O3), titanium dioxide (TiO2) or silicon dioxide (SiO2), was defined as the matrix of the sample to avoid excessive presentation of heavy elements to light element support materials.

[0029] The XRF method was used to calculate both the metal loading and contamination levels in wt% using the following definitions:

[0030] Metal loading [wt%] = weight of precious metal [g] / weight of total catalyst [g]

[0031] Contamination level [wt%] = weight of contaminating element [g] / weight of total catalyst [g]

[0032] Based on this method, the total metal loading can also be calculated using the following definition:

[0033] Total metal loading [wt%] = metal loading [wt%] + second metal loading [wt%]

[0034] Where any additional Group VIIIB or IB metal is present, its corresponding metal loading will be added to the total metal loading.

[0035] The molar ratio between gold and the second metal is calculated using the following definitions:

[0036] Au / second metal molar ratio = (Au metal loading / second metal metal loading) * (MW second metal / 197)

[0037] A particular aspect of the catalyst disclosed herein is the ratio between Au and the second metal. Surprisingly, it was found that when used to remove hydrogen under high oxygen partial pressure, a higher Au content relative to the second metal resulted in a higher stability of the catalyst. The disclosed catalyst has a molar ratio of Au to the second metal of at least about 0.1. Below this level, the stabilizing effect of Au becomes limited, resulting in suboptimal performance of the catalyst. However, the more Au loaded on the catalyst, the more the second metal benefits from the stabilizing effect of Au. The positive stabilizing effect of the Au loading on the second metal can begin to level off at a molar ratio higher than 10. In commercial practice, catalyst performance can be optimized by limiting the molar ratio of Au to the second metal to approximately 1 to 5, so that the benefit of the cost of additional Au is optimized instead. Then, a more cost-effective and significant effect can be achieved by adding more second metal.

[0038] Another aspect of the catalysts disclosed herein is a support based on a material having oxidizing properties. This includes well-known catalyst supports such as alumina, silica, silica-alumina, titania, zirconium oxide, and mixtures thereof. Other less commonly used oxide supports may be used, such as, but not limited to, magnesium oxide, calcium oxide, chromium oxide, ceria, lanthanum oxide, manganese oxide, zinc oxide, tin oxide, and combinations thereof. Oxide supports may also include materials known to form an oxidizing outer surface when exposed to an oxygen atmosphere, such as metals, metal alloys, metal carbides, metal oxycarbides, metal nitrides, metal oxynitrides, and metal sulfides. As an example, it is well known in the art that silicon carbide forms a silicon dioxide layer several nanometers thick upon exposure to oxygen, and as a result, will have surface properties similar to, if not identical to, those of silicon dioxide. Oxide supports may also include materials that are mixtures between metal oxides and non-metal oxides. Examples of such supports include phosphates, borates, and sulfates. An example of such a material is aluminum phosphate.

[0039] The oxide support has a thickness greater than about 10 m2 / g (m 2 For example, the oxide support has a surface area greater than about 20 m 2 / g, more preferably greater than about 100m 2 / g, and most preferably greater than 200m 2 / g of high specific area. The water pore volume or specific pore volume of the support is in the range of 0.30 cubic centimeters / gram (cc / g) to 1.00 cc / g. Preferably, the pore volume is in the range of 0.50 cc / g to 0.80 cc / g. The porosity of the support structure is in the range of about 40 volume percent (vol.%) to 90 vol.%, and preferably in the range of about 50 vol.% and 80 vol.%. Porosity is defined as the fraction of the volume of pores in the support structure to the total volume of the support structure. The average pore size within the support structure depends on the support material, specific surface area and porosity, and is typically between about 2 nanometers (nm) and 50 nm. The support structure can be such that it has a bimodal pore size distribution. Therefore, there are also pores in the range of about 50 nm to 500 nm. The surface area of the catalyst support disclosed herein is determined by gas physical adsorption using the BET method ASTM D 3663. The porosity, specific pore volume and pore size distribution of the support are determined by mercury intrusion porosimetry, ASTM test method D 4284. The pore size distribution of the support can be measured by any suitable measuring instrument using a contact angle of 140° at 25°C with a mercury surface tension of 474 dynes / cm.

[0040] The catalyst of the present disclosure can have Au metal and the second metal across the catalyst grains or repeating elements of the structured main catalyst (e.g., pellets) of catalytic activity. In certain embodiments, the catalyst can also have a specific metal distribution, which is eggshell, yolk or egg white. For eggshell distribution, the local metal concentration is the highest at or near the outer surface of the catalyst structure, and the catalyst structure is a grain (e.g., sphere, extrudate or pellet), a structured main body (e.g., monolith or foam) or a carrier coating on such a structured main body. In the egg yolk distribution, the metal is present in the middle of the catalyst structure, and in the case of the egg white distribution, the metal concentration reaches a peak somewhere between the middle and the outer surface of the catalyst structure. Those skilled in the art will recognize that the preparation parameters that lead to this metal distribution, such as by selecting a metal precursor, changing the pH of the metal precursor solution, buffering the pH of the metal precursor solution and / or adding an adsorption modifier to the metal precursor solution, will improve or weaken the adsorption tendency of the metal precursor to the support structure. Preferably, the Au metal and the second metal have a similar distribution throughout the support structure. Although in some cases, the distribution of each metal may be different. As a result, the local ratio between Au and the second metal can vary within the catalyst structure.

[0041] As discussed above and in further detail below, the disclosed catalysts are used for selective hydrogen removal at low inlet temperatures (e.g., preferably less than 160° C., more preferably less than 100° C.) from O2-rich streams having an O2 partial pressure greater than or equal to about 1 bar (such as those O2-rich streams generated by the electrolysis of water). By using the catalysts of the present disclosure for removing H2 from O2-rich streams, the problems associated with using precious metal catalysts in oxidizing environments at low temperatures and high O2 partial pressures can be alleviated, and O2 that is substantially free of H2 can be obtained. As will be understood, the catalysts of the present disclosure are described in the context of a method for removing hydrogen from an O2-rich stream generated in an electrolyzer. However, the catalysts disclosed herein can be used in other processes for removing H2 from O2-rich streams (e.g., certain gas streams output by nuclear power plants) and in system configurations that generate H2-containing O2-rich streams. In addition, the process conditions can vary without departing from the scope of the present disclosure. For example, the catalysts disclosed herein can be used when process conditions include low inlet temperature (as low as 60°C or even ambient temperature), high catalyst bed temperature (250°C, or even up to 350°C), and high relative humidity of water vapor (up to 90%, or even 95%).

[0042] In view of the above, Figure 21 is a flow chart of a method 100 for preparing a bimetallic catalyst of the present disclosure. Method 100 includes preparing a metal salt impregnation solution (block 102). The metal salt impregnation solution can be prepared by any suitable technique. For example, the metal salt can be dissolved in a desired volume of a solvent (e.g., water). The metal salt used to prepare the impregnation solution includes, but is not limited to, noble metal salts of metals from Groups VIIIB and IB of the Periodic Table of Elements, such as palladium salts and gold salts. As a non-limiting example, the palladium precursor used in the preparation of the impregnation solution for the palladium and gold catalyst is selected from the group consisting of i) palladium salts, consisting of palladium nitrate, palladium halide, chloropalladate, bromopalladate, palladium acetate and palladium sulfate, or ii) chelated palladium complexes, consisting of palladium ammonia complexes, palladium (poly) amine complexes (such as ethylenediamine and diethylenetriamine), palladium (poly) carboxylic acid complexes (such as citric acid, gluconic acid), palladium complexes combining carboxyl and amine groups (such as EDTA and NTA), palladium amino acid complexes, palladium phosphine complexes, and the gold salt used to prepare the impregnation solution is selected from the group consisting of gold salts, consisting of gold nitrate, gold halide, chloroauric acid, chloroaurate, sodium bromoaurate, bromoaurate, dicyanurate, hydroxygold (III) complex, gold acetate and gold sulfate. Preferred palladium salts are palladium halide, tetrachloropalladate or palladium nitrate, and preferred gold salts are gold halide or chloroaurate. In certain embodiments, the impregnation solution is a colloidal solution of nanometer-sized particles containing a mixture of palladium and gold (as salt or as metal). In certain embodiments, when an organic solvent is used, the precursor can be an organopalladium and organogold compound. The solvent used to dissolve the noble metal precursor is water, alcohol, ketone, hydrocarbon or other volatile solvent, and a combination thereof. In a preferred embodiment, the solvent is water. Other components can be added to the solvent to adjust the pH, promote absorption of the porous support, adjust the viscosity of the solvent, and / or control the interaction between the precursor and the support.

[0043] The amount of solvent used to dissolve the precious metal salt is preferably such that it is equal to the pore volume of the support. The relative amounts of palladium and gold salts in the impregnation solution are such that the catalyst of the present disclosure has approximately 0.005 wt% and 0.5 wt% palladium and approximately 0.01 wt% to 2 wt% gold. Catalysts having other metals can be prepared using similar precursors and by similar methods.

[0044] After preparing the impregnation solution according to the actions of block 102, method 100 includes impregnating a support (support / carrier) with the impregnation solution to form an impregnated support (block 106). For example, the impregnation solution can be sprayed onto the support at ambient temperature in a manner such that the pores of the support are filled with the impregnation solution. However, any other suitable impregnation technique can be used to completely impregnate the pore structure of the support, such as, for example, incipient wetness impregnation, immersion impregnation, and wet impregnation. In one embodiment, only a portion of the support pore volume becomes impregnated with the impregnation solution. In this specific embodiment, to achieve uniform distribution on the support, the solution is sprayed as a fine spray while the support is tumbled in a rotating drum.

[0045] After the support is impregnated according to block 106, the precious metal in the impregnated support is reduced to form a reduced metal-impregnated support (block 108). Reduction is accomplished, for example, by treating the impregnated support with a solution having a reducing agent. The reducing agent can be any suitable reducing agent, such as, for example, hydrazine (N2H4), formic acid, a formate salt, formaldehyde, acetaldehyde, and sodium borohydride. The added volume of the reducing agent solution is at least 80% compared to the pore volume. If the added volume is significantly greater than the pore volume, the excess reducing agent solution is decanted after the reduction is complete.

[0046] In a specific embodiment, the reducing agent may have been added to the impregnation solution, whereby the reduction is accomplished by increasing the temperature after impregnation of the combined solution.

[0047] The method 100 further includes drying the reduced metal-impregnated support to form a first dried impregnated support (block 120). For example, the impregnated support is dried in a stream of air for 5 to 30 minutes, wherein the temperature of the air is between about 80° C. and about 175° C. After the drying step according to the actions of block 120, the remaining solvent on the support is less than about 5 wt % compared to the weight of the support.

[0048] In certain embodiments, the reduced metal-impregnated support may be equilibrated prior to decanting and drying to ensure that the porous support / carrier absorbs the remaining amount of impregnation solution and / or added reducing agent solution and to allow reduction of the impregnated metal to proceed to a maximum extent. That is, the support / carrier and impregnation solution are tumbled together for a sufficient time to allow equilibrium to occur so that the support is no longer able to absorb (absorb) the impregnation solution and / or reducing agent solution, and sufficient time is allowed for proper reduction of the metal precursor to produce the reduced metal. To achieve a more rapid degree of reduction, the temperature of the reduced metal-impregnated support may be increased.

[0049] In an optional step, after drying according to block 120, the first dried impregnated support can undergo a washing step to form a washed impregnated support (block 124). For example, the first dried impregnated support is washed with a volume of a washing fluid (e.g., deionized water or a solution containing non-halogen ions) to remove contaminants such as, but not limited to, sodium, potassium, chloride, bromide, or any other element that may undesirably affect the performance of the catalyst. To promote washing of the internal pores of the porous support, the volume of water in the first washing step should be greater than the pore volume of the first dried impregnated support. The volume of washing fluid added during subsequent washing steps can be approximately equal to the volume of the support. After the first or subsequent addition of the washing fluid, the impregnated support is left with the washing fluid for a few minutes to allow the contaminants to diffuse out of the porous support. After each washing step, excess washing fluid can be removed by decantation. The washing is repeated until the washed impregnated support is substantially free of contaminants. The level of contaminants on the catalyst is assessed using X-ray fluorescence (XRF). However, inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectroscopy (AAS) can also be used to determine the level of contaminants on the catalyst.

[0050] Method 100 also includes drying the washed impregnated support to form a second dried impregnated support (box 126), and optionally, heating the second dried impregnated support to form a catalyst (box 130). For example, the washed impregnated support is dried in air at a temperature between about 100°C and about 175°C for 4 to 8 hours. After drying the washed impregnated support, the residual solvent on the second dried impregnated support is less than about 5 wt% compared to the weight of the support. After the drying step of box 126, the second dried impregnated support can optionally be subjected to a single heat treatment or a series of heat treatments. During such heat treatment, the catalyst is heated at a temperature in the range of about 250°C and 600°C for 10 minutes to 2 hours. The heat treatment can be carried out in air or inert gas or both. The heat treatment is used to remove non-ash-producing substances (such as residual nitrates, carbonates or other carbon or nitrogen-containing molecules) from the catalyst.

[0051] In embodiments where the dried impregnated support is heat treated according to the actions of block 130, it is preferred that at least one heat treatment be conducted in a reducing atmosphere, preferably a hydrogen-containing atmosphere. Preferably, the at least one heat treatment (e.g., a reducing heat treatment) is conducted after the oxidative or inert heat treatment, or in certain embodiments, as a replacement for the oxidative or inert heat treatment. If the other components in the hydrogen-containing gas used in the at least one heat treatment have inert properties (such as argon, nitrogen, and helium that would be present in the hydrogen-containing gas), the concentration of hydrogen can be lower (e.g., less than 95% compared to a hydrogen-containing gas without components having inert properties) and still achieve the desired reduction effect. To allow for appropriate kinetics, it is preferred that the hydrogen concentration in the hydrogen-containing gas exceed 1% by volume. During the at least one heat treatment, the catalyst is heated at a temperature in the range of approximately 250° C. and 400° C. for between 10 minutes and 2 hours.

[0052] The reductive heat treatment can be performed in a separate apparatus from the oxidative heat treatment, although it is preferred to use separate apparatus for the oxidative and reductive heat treatments. In a preferred embodiment, the reductive heat treatment is performed in the same reactor apparatus as the reactor apparatus in which the actual catalytic removal reaction will occur. Such a reductive heat treatment can also be performed to regenerate or restore the spent catalyst. This can be performed external to the reactor apparatus in which the actual catalytic removal reaction will occur, or internally.

[0053] As will be appreciated, the manner in which the catalyst is prepared affects its properties, such as, for example, the particle size of the metal particles within the support. Such particle size may affect the performance of the catalyst. The size of the metal particles present within the internal pore volume of the oxide support of the disclosed catalyst may be in the nanometer range. This is highly desirable because Au and the second metal are very expensive. Therefore, it is important to maximize the catalytic performance per unit mass of the precious metal. This is achieved by nanometer-sized metal alloy particles (i.e., Au and second metal alloy particles). However, when the particle size of most metal alloy particles becomes very small (e.g., below 4 nm), the chemical properties of the surfaces of these metal alloys may change dramatically and may result in completely different catalytic behavior. Therefore, when entering very small particles, the catalytic performance per unit mass of the precious metal may decrease dramatically. As will be appreciated by those skilled in the art, this requires optimization to maximize the catalytic activity.

[0054] The particle size of metal nanoparticles can be measured using any suitable technology known in the art. As a non-limiting example, the particle size of metal nanoparticles can be measured using transmission electron microscopy, x-ray photoelectron microscopy (XPS) and chemical adsorption. As will be appreciated by those skilled in the art, the particle size of metal particles can vary according to measurement techniques. For example, when using CO chemical adsorption, the metal particle size of catalyst disclosed herein shows an average particle size of 16nm. However, for example, when using transmission electron microscopy, the particle size of the metal particles of catalyst disclosed herein shows that most metal particles have a diameter less than 50nm, wherein most particles have a diameter between 2nm and 27nm, and wherein the average particle size is 6.5nm.

[0055] As will be appreciated by those skilled in the art, the surface composition of the metal particles on the catalyst determines its catalytic properties. Such surface composition may be significantly different from the bulk composition of the metal particles, and therefore, activity is not necessarily determined by the bulk composition of the metal particles. The metal distribution within each metal particle, and in particular its surface composition, may strongly depend on the conditions during the preparation of the catalyst and / or the pretreatment of the catalyst. In addition, the metal distribution and / or surface composition of the catalyst may change during use in the system process. By changing the system operating conditions so that the surface composition changes, the catalyst activity can be improved or weakened.

[0056] Testing the catalytic activity of the catalyst composition

[0057] Example 1 - Invention

[0058] This Example 1 describes the preparation of Catalyst 1, which is representative of the catalysts of the present invention.

[0059] The impregnation solution was prepared by dissolving a certain amount of sodium tetrachloropalladate (Na2PdCl4) and chloroauric acid (HAuCl4) in a volume of water equal to the water pore volume of the alumina support so that the concentration of the solution would produce approximately 0.1 wt% Pd and 0.05 wt% Au on the final catalyst. The impregnation solution was sprayed onto the alumina support at ambient temperature. The alumina support was a spherical 2.5 mm diameter alumina support with a diameter of approximately 210 m 2 / g BET surface area and a pore volume of approximately 0.78 ml / g. The impregnated alumina support is treated with a volume of a 2.3 wt% hydrazine (N2H4) solution to reduce the Pd and Au in the impregnated alumina support. The volume of the hydrazine solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support and hydrazine solution are tumbled together for 10 minutes to allow equilibrium and ensure that the support absorbs the maximum amount of hydrazine and completes the reduction reaction. The resulting support is then dried in air at 150°C for 45 minutes to form a first dried impregnated support. The first dried impregnated support is washed in a stepwise manner with a volume of distilled or deionized water until the resulting wash water is substantially free of chloride. The volume of distilled or deionized water is approximately equal to the volume of the first dried impregnated support. Excess wash water is decanted, and the washed impregnated support is then dried at 120°C for approximately 6 hours to form a second dried impregnated support. The second dried impregnated support used contained 0.102 wt% Pd and 0.050 wt% Au and 0.009 wt% chloride as measured by XRF.The second dried impregnated support was heated at 300°C in a hydrogen atmosphere for approximately 1 hour to form the catalyst of the present invention.

[0060] Example 2-Comparison

[0061] This Example 2 describes the preparation of Catalyst 2 which is representative of a comparative catalyst.

[0062] The impregnation solution was prepared by dissolving an amount of palladium nitrate (Pd(NO3)2) in a volume of water equal to the water pore volume of the alumina support to produce approximately 0.1 wt% Pd on the final catalyst. The impregnation solution was sprayed onto the alumina support at ambient temperature. The alumina support was a spherical 2.5 mm diameter alumina support having a diameter of approximately 210 m 2 / g BET surface area and has a pore volume of approximately 0.78 milliliters per gram (ml / g), which corresponds to a porosity of 75%. After impregnation, the impregnated alumina support was conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours to form a dried catalyst. The dried catalyst was calcined at 450°C for 3 hours and then treated with a certain volume of 2.3 wt% hydrazine (N2H4) solution to reduce the Pd in the impregnated alumina support. The volume of hydrazine solution was approximately equal to the pore volume of the alumina support. After reduction, the resulting support was pre-dried at 150°C for 45 minutes and then dried at 120°C for 6 hours to form a dried impregnated support. The dried impregnated support was heated at 300°C in a hydrogen atmosphere for about 1 hour to form the catalyst of the present invention.

[0063] Example 3-Comparison

[0064] This Example 3 describes the preparation of Catalyst 3 which is representative of a comparative catalyst.

[0065] The impregnation solution was prepared by dissolving an amount of palladium nitrate (Pd(NO3)2) in a volume of water equal to the water pore volume of the alumina support to produce approximately 0.5 wt% Pd on the final catalyst. The impregnation solution was sprayed onto the alumina support at ambient temperature. The alumina support was a spherical 2.5 mm diameter alumina support having a diameter of approximately 210 m 2 / g BET surface area and has a pore volume of approximately 0.78 milliliters per gram (ml / g), which corresponds to a porosity of 75%. After impregnation, the impregnated alumina support was conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours to form a dried catalyst. The dried catalyst was calcined at 450°C for 3 hours and then treated with a certain volume of 2.3 wt% hydrazine (N2H4) solution to reduce the Pd in the impregnated alumina support. The volume of hydrazine solution was approximately equal to the pore volume of the alumina support. After reduction, the resulting support was pre-dried at 150°C for 45 minutes and then dried at 120°C for 6 hours to form a dried impregnated support. The dried impregnated support was heated at 300°C in a hydrogen atmosphere for about 1 hour to form the catalyst of the present invention.

[0066] Example 4-Comparison

[0067] This Example 4 describes the preparation of Catalyst 4 which is representative of a comparative catalyst.

[0068] The impregnation solution was prepared by dissolving an amount of palladium nitrate (Pd(NO3)2) and platinum nitrate (Pt(NO3)2) in a volume of water equal to the water pore volume of the alumina support to produce approximately 0.1 wt% Pd and approximately 0.05 wt% Pt on the final catalyst. The impregnation solution was sprayed onto the alumina support at ambient temperature. The alumina support was a spherical 2.5 mm diameter alumina support having a diameter of approximately 210 m. 2 / g BET surface area and has a pore volume of approximately 0.78 milliliters per gram (ml / g), which corresponds to a porosity of 75%. After impregnation, the impregnated alumina support was conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours to form a dried catalyst. The dried catalyst was calcined at 450°C for 3 hours and then treated with a certain volume of 2.3 wt% hydrazine (N2H4) solution to reduce the Pd and Pt in the impregnated alumina support. The volume of hydrazine solution was approximately equal to the pore volume of the alumina support. After reduction, the resulting support was pre-dried at 150°C for 45 minutes and then dried at 120°C for 6 hours to form a dried impregnated support. The dried impregnated support was heated at 300°C in a hydrogen atmosphere for about 1 hour to form the catalyst of the present invention.

[0069] Example 5-Comparison

[0070] This Example 5 describes the preparation of Catalyst 5 which is representative of a comparative catalyst.

[0071] The impregnation solution was prepared by dissolving an amount of palladium nitrate (Pd(NO3)2) and silver nitrate (AgNO3) in a volume of water equal to the water pore volume of the alumina support to produce approximately 0.1 wt% Pd and approximately 0.05 wt% Ag on the final catalyst. The impregnation solution was sprayed onto the alumina support at ambient temperature. The alumina support was a spherical 2.5 mm diameter alumina support having a diameter of approximately 210 m. 2 / g BET surface area and has a pore volume of approximately 0.78 milliliters per gram (ml / g), which corresponds to a porosity of 75%. After impregnation, the impregnated alumina support was conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours to form a dried catalyst. The dried catalyst was calcined at 450°C for 3 hours and then treated with a certain volume of 2.3 wt% hydrazine (N2H4) solution to reduce the Pd and Ag in the impregnated alumina support. The volume of hydrazine solution was approximately equal to the pore volume of the alumina support. After reduction, the resulting support was pre-dried at 150°C for 45 minutes and then dried at 120°C for 6 hours to form a dried impregnated support. The dried impregnated support was heated at 300°C in a hydrogen atmosphere for about 1 hour to form the catalyst of the present invention.

[0072] Example 6-Comparison

[0073] This Example 6 describes the preparation of Catalyst 7 as a representative comparative catalyst containing only Pt.

[0074] The impregnation solution was prepared by dissolving an amount of platinum nitrate (Pt(NO3)2) in a volume of water equal to the water pore volume of the alumina support to produce approximately 0.3 wt% Pt on the final catalyst. The impregnation solution was sprayed onto the alumina support at ambient temperature. The alumina support was a spherical 2.5 mm diameter alumina support having a diameter of approximately 210 m 2 / g BET surface area and has a pore volume of approximately 0.78 milliliters per gram (ml / g), which corresponds to a porosity of 75%. After impregnation, the impregnated alumina support was conditioned for 5 minutes, pre-dried at 150°C for 20 minutes, and then dried at 120°C for 6 hours to form a dried catalyst. The dried catalyst was calcined at 450°C for 3 hours and then treated with a certain volume of 2.3 wt% hydrazine (N2H4) solution to reduce the Pt in the impregnated alumina support. The volume of hydrazine solution was approximately equal to the pore volume of the alumina support. After reduction, the resulting support was pre-dried at 150°C for 45 minutes and then dried at 120°C for 6 hours to form a dried impregnated support. The dried impregnated support was heated at 300°C in a hydrogen atmosphere for about 1 hour to form the catalyst of the present invention.

[0075] Example 7-Comparison

[0076] This Example 7 describes the preparation of Catalyst 7 as a representative comparative catalyst containing only Au.

[0077] The impregnation solution was prepared by dissolving an amount of chloroauric acid (HAuCl4) in a volume of water equal to the water pore volume of the alumina support, such that the concentration of the solution resulted in approximately 0.1 wt% Au on the final catalyst. The impregnation solution was sprayed onto the alumina support at ambient temperature. The alumina support was a spherical 2.5 mm diameter alumina support having a diameter of approximately 210 m 2 / g BET surface area and having a pore volume of approximately 0.78 ml / g. The impregnated alumina support is treated with a volume of 54 wt% sodium formate solution to reduce the Au in the impregnated alumina support. The volume of the sodium formate solution is approximately equal to the pore volume of the alumina support. After reduction, the resulting support and sodium formate solution are tumbled together for 10 minutes to allow equilibrium and ensure that the support absorbs the maximum amount of sodium formate and completes the reduction reaction, and then the resulting support is dried in air at 150°C for 45 minutes to form a first dried impregnated support. The first dried impregnated support is washed in a stepwise manner with a volume of distilled or deionized water until the resulting wash water is substantially free of chloride. The volume of distilled or deionized water is approximately equal to the volume of the first dried impregnated support. Excess wash water is decanted, and the washed impregnated support is then dried at 120°C for approximately 6 hours to form a second dried impregnated support. The second dried impregnated support was heated in a hydrogen atmosphere at 300°C for about 1 hour to form the catalyst of the present invention.

[0078] Table 2 below provides the properties of the selective hydrogenation catalysts 1-7 of Examples 1-7 above.

[0079] Table 2. Properties of the Inventive and Comparative Hydrogen Removal Catalysts

[0080]

[0081] Example 8 - Performance Test

[0082] Example 8 describes performance testing conducted to characterize the hydrogen removal activity of the catalyst compositions of Examples 1-7.

[0083] Experimental conditions were chosen that were very similar to those used for hydrogen removal of O2-rich streams using a typical feed gas composition for electrolyzer O2 off-gas. For example, the laboratory reactor was filled with 15 ml of catalyst. An O2-rich feed with 1000 ppm H2 and 3.5% by volume of water vapor (equivalent to a partial pressure of 0.17 bar and a dew point of 57°C) was fed to the reactor at a rate that provided a GHSV of 2500 v / vh. The reactor was operated at an O2 partial pressure of 5 bar and at three different temperatures: 80°C, 120°C, and 160°C.

[0084] Table 3 illustrates the performance of catalysts 1-7 of Examples 1-7 as a function of temperature. As is clear from Table 3, when the catalyst of the present invention (Example 1) is used, the H2 concentration in the O2-rich gas stream is reduced from 1000 ppmv to less than about 10 ppmv at temperatures ranging between 80°C and 160°C. In contrast, O2-rich gas streams treated with catalysts without Au (e.g., Examples 3-6) and catalysts with Au alone (e.g., Example 7) have H2 concentrations of 400 ppmv or higher at 80°C. Even at 120°C, O2-rich gas streams treated with certain comparative catalysts (e.g., Examples 2, 4, 5, and 7) have H2 concentrations above 150 ppmv. Only after the reaction temperature is increased to 160°C do catalysts with Pd / Pt or high Pd loadings reduce the H2 concentration in the O2-rich gas stream to levels comparable to those of the Pd / Au catalyst of the present invention. Thus, Catalyst 1 of the present invention removes H₂ from an O₂-rich gas stream at temperatures below 120°C, resulting in an O₂-rich gas stream having an H₂ concentration of less than approximately 10 ppmv. It is clear from these examples that the addition of Au to Pd results in significantly improved performance. On the other hand, the very low conversion across the entire temperature range for EX 7 suggests that it is not Au itself that produces the activity. Without being bound by theory, it is believed that the addition of Au to the catalyst results in a more oxidation-resistant catalytic system.

[0085] Table 3 below shows the outlet hydrogen concentration (ppmv) at three different temperatures for each catalyst sample.

[0086] Table 3. Outlet hydrogen concentration of O2-enriched gas stream

[0087] Temperature (℃) EX 1 EX 2 EX 3 EX 4 EX 5 EX 6 EX 7 80 8 836 400 800 950 690 1010 120 0 790 27 170 430 60 950 160 0 560 18 6 22 2 870

[0088] Testing the catalyst composition for catalyst stability

[0089] Examples 9-20 - Invention

[0090] These examples describe the preparation of Catalysts 9-20, which are representative of catalysts of the present invention.

[0091] Catalysts 9-20 were prepared in the same manner. The metal precursor salts, their corresponding concentrations and supports were varied and are summarized in Table 4.

[0092] The impregnation solution is prepared by dissolving a certain amount of the second metal precursor and chloroauric acid (HAuCl4) as an Au precursor in a volume of water equal to the water pore volume of the oxide support so that the concentration of the solution after evaporation produces the desired metal concentration on the final catalyst. The precursor solution is sprayed onto the oxide support at ambient temperature. The impregnated oxide support is dried in air at 65°C for 15 minutes to form a first dried impregnated support. The dried impregnated support is treated with a certain volume of 20g / l ascorbic acid solution to reduce the metal in the impregnated support. The volume of ascorbic acid solution added is approximately equal to the pore volume of the oxide support. After this reduction step, the resulting support and ascorbic acid solution are tumbled together for 10 minutes to allow equilibrium and ensure that the support absorbs the maximum amount of ascorbic acid and completes the reduction reaction. The reduced resulting support is washed six times with a certain volume of deionized water. A volume of deionized water three times the volume of the first dried impregnated support was added, and the support and wash liquid were then tumbled together for 10 minutes for each wash. After each wash, the liquid was decanted. Following the washing step, the washed impregnated support was dried at 120° C. for approximately 6 hours to form a second dried impregnated support.

[0093] As discussed above, the metal precursors and oxide supports for Catalysts 9-20 are summarized below in Table 4. The alumina supports were spherical, 1.8 mm diameter alumina supports having approximately 210 m 2 / g BET surface area and has a pore volume of approximately 0.65 ml / g. The titania support is a 1.6 mm diameter trilobal extrudate containing anatase as the titania phase with a pore volume of approximately 45 m 2 / g BET surface area and has a pore volume of about 0.32 ml / g. The silica support is a 1.6 mm diameter spherical silica with a pore volume of about 300 m 2 / g of BET surface area and has a pore volume of approximately 0.85 ml / g.

[0094] Examples 21-23 - Comparative

[0095] These examples describe the preparation of Catalysts 21-23, which are representative of comparative catalysts.

[0096] Catalysts 21-23 were prepared in a manner similar to Catalysts 9-20. Catalysts 21-23 contained a single metal, and their compositions, corresponding metal precursors, and oxide supports are summarized in Table 3.

[0097] Example 24 - Performance Test

[0098] Example 24 describes performance testing conducted to characterize the stability of the catalyst components of Catalysts 9-23.

[0099] The experimental conditions chosen are highly similar to those used for hydrogen removal of O2-rich streams using a typical feed gas composition of electrolyser O2 off-gas. In order to determine the stability of the catalyst, each catalyst sample tested was subjected to a temperature typical of that in an adiabatic reactor, where the temperature rises significantly due to the exotherm of the reactor, which for these tests was 230°C. The laboratory reactor was filled with 1 ml of the corresponding catalyst sample. The catalyst samples were exposed to a pure oxygen flow at 4 bar absolute pressure at 230°C for 48 hours. Before and after this treatment, the activity of the catalyst samples was evaluated with an oxygen-rich feed having 5000 ppm of H2 and a flow rate providing a GHSV of 25000 v / vh. The reactor was operated at an O2 partial pressure of 1.4 bar and a temperature of 50°C. Based on the hydrogen conversion in the reactor, the first-order activity constant was determined according to the following formula:

[0100] k A [s -1 ]=H2 flow rate [mol / s / m 3 ]*LN(1 / (1–H2 conversion rate)) / H2 concentration [mol / m 3 ]

[0101] where k A [s -1 ] is the first-order activity constant of the catalyst, and the LN term is the natural logarithm, and its

[0102] The H2 conversion is defined by the following formula:

[0103] H2 conversion rate = (H2 inlet concentration [mol / m 3 ]-H2 outlet concentration [mol / m 3 ]) / H2 inlet concentration

[0104] [mol / m 3 ]).

[0105] By comparing the activity constants before and after high temperature treatment, an indication of stability can be obtained.

[0106] The stability ratio is defined as

[0107] Stability ratio = k A (after high temperature treatment) / k A (Before high temperature treatment)

[0108] A stability ratio below 1 indicates inactivation, a stability ratio of about 1 or even above 1 indicates high stability or even autoactivation.

[0109] Table 4 below illustrates the components of various catalysts among Catalysts 9-23 and the first order activity constants k of these components after long term exposure to 4 bar oxygen at 230°C. A and stability ratio.

[0110] Table 4. Properties of the Inventive Catalysts and Comparative Catalysts 9-23

[0111]

[0112] *TiO2-loaded, **SiO2-loaded

[0113] As shown in Table 4, the activity and stability ratios of catalysts 9-15 of the present invention are better than those of catalyst 21, indicating that the Pd-containing catalysts (e.g., catalysts 9-15) benefit from the addition of Au. Compared with the Pd-Au catalysts 9-15 of the present invention, the Pd-containing catalysts (e.g., catalysts 21 and 22) that do not contain Au have low stability ratios and low activity after high temperature treatment. When the activity and stability ratios of the Pt-Au catalysts 16 and 17 of the present invention are compared with the activity and stability ratios of catalyst 22, it becomes apparent that the Pt-containing catalysts also benefit from the addition of Au. Compared with the Pt-Au-catalysts 16 and 17 of the present invention, the Pt-containing catalysts (e.g., catalyst 22) that do not contain Au have low stability ratios and low activity after high temperature treatment. Similar to single metal catalysts having only Pd or Pt as active metals, catalysts having Au as the single active metal also have low stability ratios and low activity after high temperature treatment. For example, as shown in Table 4, the activity and stability ratios of catalysts 10 and 17 of the present invention are higher than the activity and stability ratios of catalyst 23 containing the same Au loading as catalysts 10 and 17 of the present invention. It is clear that for the application of removing H2 from an O2-rich stream, Pd, Pt, and Au alone are insufficient to achieve the activity and stability ratios observed in catalysts 9-20 of the present invention. Instead, the improved activity and stability ratios are the result of combining Au with another precious metal (i.e., a second metal).

[0114] Furthermore, as shown in Table 4, the catalyst stability of inventive catalysts 9-15 improved with increasing Au content and the molar ratio of Au to the second metal. Similarly, comparing inventive catalysts 16 and 17, improved stability was observed with increasing Au content and the molar ratio of Au to the second metal.

[0115] Furthermore, comparing the stabilities of inventive catalysts 13 and 20, it is apparent that at low Au and secondary metal loadings, the stability ratio is above 1, demonstrating the high stability of these catalysts. Furthermore, compared to comparative catalysts 21 and 22, which have total metal loadings of 0.1 wt% Pd and 0.1 wt% Pt, respectively, catalyst 20 exhibits higher stability at a lower metal loading of 0.03 wt%. It should be noted that the choice of Pd precursor used in catalyst preparation is not critical. For example, inventive catalysts 10 and 12 exhibit comparable activity and stability, as shown in Table 4.

[0116] The effects of different oxide supports on the activity and stability of the catalysts were also evaluated. As shown in Table 4, catalysts 9 and 11 of the present invention using alumina as the oxide support had similar activities to catalysts 18 and 19 of the present invention using titania and silica as the oxide supports, respectively. At the same metal loading for each of catalysts 9, 11, 18, and 19, all of these catalysts showed no activity within 8 seconds after the deactivation test at 230°C. -1 -15s -1 showed similar activity in the range of 45 m 2 / g to 300m 2 Without wishing to be bound by theory, the stabilization effect appears to be controlled by the presence of Au in the catalyst and, to a lesser extent, by the nature and characteristics of the oxide support.

[0117] The technical effect of using the catalysts disclosed herein for removing H2 from O2-rich gas streams, such as those generated in electrolyzers, is to provide effective and efficient H2 removal under oxidative conditions with high oxygen partial pressures at temperatures below 160°C, particularly below 100°C. The addition of Au to these catalysts mitigates oxidation of the catalysts and improves the H2 removal performance of the catalysts at O2 partial pressures above 1 bar, particularly at 5 bar or higher. Thus, it is the addition of Au in combination with the second metal that produces the desired H2 removal activity at low temperatures (e.g., below 160°C) under oxidative conditions (e.g., above 1 bar O2 partial pressure).

[0118] Without departing from the essence or essential features of the present disclosure, the present disclosure may be embodied in other specific forms. The described embodiments should be considered in all respects to be merely illustrative and not restrictive. Therefore, the scope of the present disclosure is indicated by the appended claims rather than by the foregoing description. All changes that fall within the equivalent meaning and scope of the claims will be included within the scope of the claims.

Claims

1. A method for removing hydrogen from an oxygen stream, comprising: electrolyzing water in an electrolyzer to produce a hydrogen-rich stream and an oxygen-rich stream, wherein the oxygen-rich stream comprises hydrogen; feeding the oxygen-rich stream to a reactor containing a gold-containing catalyst; as well as The oxygen-rich stream is contacted with the gold-containing catalyst in the reactor, wherein the gold-containing catalyst comprises gold and a second metal on an oxide support, wherein the oxygen partial pressure of the oxygen-rich stream in the reactor is greater than 1 bar.

2. The process according to claim 1, wherein the temperature at the inlet of the reactor is between 40 degrees Celsius (°C) and 160°C.

3. The method of claim 1 or 2, wherein greater than 95% of the hydrogen is removed from the oxygen stream.

4. The method according to any one of the preceding claims, wherein the second metal is selected from Group VIIIB and / or Group IB metals of the Periodic Table of the Elements.

5. The method of claim 4, wherein the second metal is palladium, platinum or rhodium.

6. The method of claim 5, wherein the second metal is present in an amount of at least 0.005 wt%, and wherein the gold is present in an amount of at least 0.01 wt%.

7. The method of claim 6, wherein the amount of the second metal is measured by X-ray fluorescence (XRF).

8. The method of any one of the preceding claims, wherein the molar ratio of gold to the second metal is at least 0.

1.

9. The method according to any one of the preceding claims, wherein the gold-containing catalyst has a porosity of between 40 volume percent (vol.%) and 90 vol.%, preferably between 50 vol.% and 80 vol.%.

10. The method of claim 9, wherein the porosity is measured by mercury intrusion porosimetry according to ASTM test method D 4284.

11. The process according to any one of the preceding claims, wherein the oxide support has a thickness greater than 10 m2 / g (m 2 / g) of specific surface area.

12. The method according to any one of the preceding claims, wherein the specific surface area is greater than 20 m 2 / g, preferably greater than 100m 2 / g, and most preferably 200m 2 / g.

13. The method according to claim 11 or 12, wherein the specific surface area is measured by gas physical adsorption according to the BET method ASTM D3663.

14. The method of any one of the preceding claims, wherein the gold is present in an amount of at least 0.01 weight percent (wt. %).

15. The method of claim 14, wherein the amount of gold is measured by XRF.

16. The process of any one of the preceding claims, wherein the oxide support is alumina, silica, silica-alumina, titania, zirconia, and combinations thereof.

17. A process according to any one of the preceding claims, wherein the total metal content of the gold-containing catalyst is between 0.03 wt% and 2.1 wt%.

18. The method of claim 17, wherein the total metal content is measured by XRF.

19. The method of any one of the preceding claims, wherein at least the gold or the second metal in the catalyst has an average particle size greater than 4 nanometers (nm).

20. The method of claim 19, wherein the average particle size is measured by CO chemisorption.

21. The method of claim 19, wherein the average particle size is measured by TEM.

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