Patent Application
20250137150
This invention generally relates to catalysts and methods of use for the conversion of carbon dioxide into carbon-containing products (e.g., carbon monoxide, alcohols, ethers, and other hydrocarbon products). The invention also relates to multi-metal (including bimetallic) oxide compositions and their use in converting carbon dioxide into carbon-containing products.
There continues to be a keen interest in using carbon dioxide (CO2) as a source for the production of commodity chemicals and fuels, particularly as carbon dioxide is a growing atmospheric waste product contributing to climate change. Such methods have the potential to significantly reduce reliance on fossil fuels and reduce carbon dioxide emissions, which is an important step towards a carbon-neutral future. However, efforts in the conversion of carbon dioxide have been largely hindered by low production capacity, efficiency and difficulty in producing higher-order multi-carbon compounds. Production of higher carbon number (>C2) compounds from carbon dioxide would be particularly advantageous considering their utility in the production and processing of a wide range of commodities, such as plastics, polymers (e.g., polyolefins), lubricants, and detergents. There would be a further advantage in a method that could convert carbon dioxide to either precursors of chemicals or such commodity chemicals themselves at mild or ambient operating conditions to minimize operating costs and function in a further environmentally friendly manner.
In one aspect, the present disclosure is directed to porous multi-metal oxide compositions useful in the conversion of carbon dioxide to one or more carbon-containing products. The porosity, which includes micropores, mesopores, or a combination thereof, provides substantially higher surface areas for the compositions and also results in a greater selectivity in the capture and higher conversion of carbon dioxide as a result of pore confinement and surface interactions. The metal oxides can also be selected to tune the activity of the composition to promote the production of one or more specific products from carbon dioxide. Moreover, by virtue of the special synthetic method and/or dopants that may be included, the compositions described herein preferably contain defect sites corresponding to oxygen vacant sites. These defect sites increase the activity of the compositions to make them substantially more capable and efficient than metal oxide compositions of the art. The compositions described herein are further advantageous by being highly robust under high temperature conditions. The compositions described herein are further advantageous by being scalable and recyclable. The compositions described herein can also advantageously be fine-tuned to produce specific types of products.
More particularly, the porous multi-metal oxide compositions contain at least two metal elements interconnected with oxygen (oxide, i.e., O2′) atoms, wherein the at least two metal elements are selected from at least one transition metal element and at least one other element selected from transition metal elements, lanthanide elements, alkaline earth elements, and main group metal elements. The porosity of the composition is characterized by the presence of micropores and/or mesopores, typically in the absence of macropores. In some embodiments, the pores have a minimum size of precisely or about 0.5, 0.6, 0.7, 0.8, 0.9, or 1 nm and maximum size of precisely or about 2, 5, 8, or 10 nm. In embodiments, the composition contains defect sites corresponding to oxygen vacant sites (typically, where an alkaline earth metal functions as a dopant to replace a portion of a trivalent metal, such as a lanthanide metal). In some embodiments, the at least one transition metal element is selected from one or more of Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag, Pd, Pt, and Zn, or one or more of Cr, Mn, Fe, Co, Ni, Cu, and Zn, or more particularly selected from Cu, Ni, Mn, and/or Fe. In separate or further embodiments, the at least one other element (i.e., in addition to the at least one transition metal element) includes at least one lanthanide element, such as one or more of La, Ce, Pr, Nd, and Sm. In particular embodiments, the composition has the following formula: Ma2-xMbxMcO4 (1), wherein Ma is selected from one or more lanthanide elements; Mb is selected from one or more alkaline earth elements; Mc is selected from one or more first-row transition metal elements; and x is a value between 0 and 2, expressed as 0≤x≤2. In some embodiments of Formula (1), 0<x<2. In separate or further embodiments of Formula (1), Ma is selected from one or more of La, Ce, Pr, Nd, and Sm. In separate or further embodiments of Formula (1), Mc is selected from one or more of Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag, Pd, Pt, and Zn, or one or more of Cr, Mn, Fe, Co, Ni, Cu, and Zn, or more particularly, Cu, Ni, Mn, and/or Fe. In separate or further embodiments of Formula (1), the composition has the following formula: La2-xMbxCuO4 (1a), wherein 0≤x≤0.5.
In another aspect, the present disclosure is directed to a method for producing the porous multi-metal oxide composition described above. The method includes: (i) impregnating a sacrificial mesoporous template (i.e., “template”) with a solution containing an organic acid and at least two metal salts comprising: (a) a first metal salt containing at least one transition metal element and (b) a second metal salt containing at least one other metal element selected from transition metal elements, lanthanide elements, alkaline earth elements, and main group metal elements; (ii) calcining the impregnated sacrificial mesoporous template at a temperature of 400-1000° C. (or more particularly, 500-800° C.); and (iii) removing the sacrificial mesoporous template. In typical embodiments, the template has a metal oxide composition, such as a silicon oxide (SiO2) or silicate composition. In some embodiments, the template is removed by etching with an alkaline (e.g., alkali hydroxide) solution, particularly in the case of the template having a metal oxide (or SiO2 composition). In other embodiments, the template is removed by dissolving it in a solvent. In other embodiments, the template is removed by pyrolysis or vaporization.
In another aspect, the present disclosure is directed to a method for converting carbon dioxide to one or more carbon-containing products by use of the above-described porous multi-metal oxide composition (porous catalyst). The carbon-containing product may be selected from, for example, carbon monoxide, methane, or other hydrocarbons e.g., alkenes, alkanes, alcohols, ketones, ethers, aldehydes, and carboxylic acids. The porous catalyst used in the method is advantageously highly active, coke resistant, and stable. In some embodiments, the porous catalyst is contained in a packed-bed reactor or electrochemical cell, fixed to the cathode.
In a first embodiment, carbon dioxide gas (either alone or in admixture with one or more other gases) is directly contacted with the porous multi-metal oxide composition (i.e., “catalyst”) described above at a temperature of 25-1000° C. (or more particularly, 100-1000° C.) at ambient or elevated pressure (e.g., 1-200 bar), while the porous multi-metal oxide catalyst is disposed on an electrically charged cathode, to result in reductive conversion of the carbon dioxide to the one or more carbon-containing products. In a second embodiment, carbon dioxide gas is contacted with a solution in which the carbon dioxide is solubilized, e.g., converted to an ion, such as a carbonate or bicarbonate ion, and simultaneously or subsequently contacting the solution with the porous multi-metal oxide catalyst described above while the porous multi-metal oxide catalyst is disposed on an electrically charged cathode to result in conversion of the solubilized form of carbon dioxide to the one or more carbon-containing products. The solution may be contacted with the catalyst at ambient (room) temperature or at an elevated temperature, at ambient or elevated pressure, as provided above, to produce the carbon-containing product(s).
In a first aspect, the present disclosure is directed to a porous multi-metal oxide composition (i.e., “oxide composition”) useful, inter alia, in the conversion of carbon dioxide to one or more carbon-containing products. The multi-metal oxide composition contains at least two metal elements interconnected with oxygen atoms, wherein the at least two metal elements are selected from at least one (e.g., one, two, or more) transition metal element and at least one (e.g., one, two, or more) other element selected from transition metal elements, lanthanide elements, alkaline earth elements, and main group metal elements. Notably, the term “metal oxide,” as used herein, is meant to include metal oxide compositions that may include anions in addition to the oxide anion (O2′), and thus, the metal oxide compositions may include such compositions as metal oxide-hydroxides, oxide-halides, oxide-carbonates, oxide-sulfates, oxide-hydroxide-halides, oxide-hydroxide-carbonates, and oxide-carbonate-halides. In some embodiments, the metal oxide may exclude any of the above types of oxide compositions, or the metal oxide may exclusively contain the oxide anion or exclusively contain oxide and hydroxide anions.
The term “transition metal” refers to elements in Groups 3-12 of the Periodic Table of the Elements, and includes first row, second row, and third row transition elements. Typically, the one or more transition elements in the oxide composition are selected from first row transition metals (e.g., Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and early second row transition metals (e.g., Y, Zr, Nb, and Hf). In some embodiments, noble metals are included or excluded. In some embodiments, the at least one transition metal element is selected from one or more of Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag, Pd, Pt, and Zn, or one or more of Cr, Mn, Fe, Co, Ni, Cu, and Zn, or more particularly, from Cu, Ni, Mn, and/or Fe. In some embodiments, the oxide composition contains at least Cu or at least Fe or at least both of these elements. In some embodiments, any one or more of the above transition metal elements is excluded from the oxide composition.
The term “lanthanide” refers to those elements having an atomic number of 57-71. The lanthanide elements are listed as follows: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The lanthanide elements are typically in a trivalent state in their oxide compositions. In some embodiments, the oxide composition contains at least one lanthanide element selected from one or more of the above listed lanthanides, or more particularly, selected from one or more of La, Ce, Pr, Nd, and Sm. In some embodiments, any one or more of the above lanthanide elements is excluded from the oxide composition.
The term “alkaline earth elements” refers to elements of Group 2 of the Periodic Table. Some examples include Mg, Ca, Sr, and Ba. In some embodiments, the oxide composition includes at least one alkaline earth element, or more particularly, at least one of Ca and/or Sr.
The term “main group elements,” as used herein, refers to elements of Group 1 (except hydrogen), Group 2, and Groups 13-15 of the Periodic Table. Some examples include Li, Mg, Ca, Na, K, Sr, Cs, B, Al, Ga, In, Si, Ge, Sn, As, Sb, and Bi, or more particularly, B, Al, Ga, In, Si, Ge, Sn, As, Sb, and Bi. In some embodiments, the oxide composition includes at least one main group element selected from any of those provided above.
In a first set of embodiments, the oxide composition includes precisely or at least one or two transition metal elements selected from any of those provided above (or at least one or two selected from Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag, Pd, Pt, and Zn or at least one or two selected from Cr, Mn, Fe, Co, Ni, Cu, and Zn, or more particularly, Cu, Ni, Mn, and/or Fe, or more particularly Cu and/or Fe), which may be in the absence or presence of one or more lanthanide elements, absence or presence of one or more alkaline earth elements, and absence or presence of one or more main group elements. Some examples of oxide compositions containing one transition metal element includes LiMnO2, LiCoO2, and LiMn2O4. Some examples of oxide compositions containing two transition metal elements include CuFeO2, and Sr2FeMoO6,
In a second set of embodiments, the oxide composition includes precisely or at least one or two transition metal elements selected from any of those provided above (or at least one or two selected from Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag, Pd, Pt, and Zn, or one or two selected from Cr, Mn, Fe, Co, Ni, Cu, and Zn, or more particularly, Cu, Ni, Mn, and/or Fe), and precisely or at least one or two lanthanide elements selected from any of those provided above (or selected from one or more of La, Ce, Pr, Nd, and Sm), which may be in the absence or presence of one or more alkaline earth elements, and absence or presence of one or more main group elements. Some examples of oxide compositions containing at least one transition metal element and/or at least one lanthanide element include La2CuO4, LaCoO3, LaMn0.5Ni0.5O3, LaNiO3, LaCrO3, La2-xSrxCuO4, (La2-v-xNdv)SrxCuO4, Ce2CuO4, Nd2-vCevCuO4, LaFeO3, LaCa0.5Co0.5O3-δ and La2-xSrxFeO3, wherein 0≤x≤2, 0<x<2, 0≤x≤0.5, 0<x≤0.5, or 0<x<0.5, and wherein v may independently be within any of the foregoing ranges in which the variable x is substituted with v.
In a third set of embodiments, the oxide composition includes precisely or at least one or two transition metal elements selected from any of those provided above (or at least one or two selected from Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag, Pd, Pt, and Zn, or at least one or two selected from Cr, Mn, Fe, Co, Ni, Cu, and Zn, or more particularly, Cu, Ni, Mn, and/or Fe), and precisely or at least one or two alkaline earth elements selected from any of those provided above (or selected from one or more of Ca, Sr, and Ba), which may be in the absence or presence of one or more lanthanide elements, and absence or presence of one or more main group elements. Some examples of oxide compositions containing at least one transition metal element and at least one alkaline earth element include SrFeO4, CaFeO4, BaFeO4, SrFe12O19, BaFe12O19, SrCuO2, CaTiO3, Ca2-xSrxTiO3, CaNbO3, La0.5Ca0.5MnO3, LaCa0.5Co0.5O3-a, Ba0.5Sr0.5Co0.8Fe0.2O3-a and Ca2-xSrxNbO3.
In a fourth set of embodiments, the oxide composition includes precisely or at least one or two transition metal elements selected from any of those provided above (or at least one or two selected from Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag, Pd, Pt, and Zn, or at least one or two selected from Cr, Mn, Fe, Co, Ni, Cu, and Zn, or more particularly, Cu, Ni, Mn, and/or Fe), and precisely or at least one or two main group elements selected from any of those provided above, which may be in the absence or presence of one or more lanthanide elements, and absence or presence of one or more alkaline earth elements. Some examples of oxide compositions containing at least one transition metal element and at least one main group element include Al2CuO4 and Fe(AlO2)2.
In particular embodiments, the oxide composition has a composition of the following formula:
Ma2-xMbxMcO4 (1)
In Formula (1), Ma is precisely or at least one or two lanthanide elements selected from any of those provided above, or more particularly selected from one, two, or more of La, Ce, Pr, Nd, and Sm (or precisely or at least one or two alkaline earth elements); Mb is precisely or at least one or two alkaline earth elements selected from any of those provided above, or more particularly selected from one, two, or more of Ca, Sr, and Ba (or precisely or at least one or two transition metal elements, such as any of those provided above); and Mc is precisely or at least one or two transition metal elements selected from any of those provided above, or more particularly selected from one, two, or more of first-row transition metal elements, or more particularly selected from one, two, or more of Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag, Pd, Pt, and Zn, or more particularly selected from one, two, or more of Cr, Mn, Fe, Co, Ni, Cu, and Zn, or more particularly selected from Cu, Ni, Mn, and/or Fe. In the case where Ma is an alkaline earth element and Mb is an alkaline earth element, it is understood that Ma and Mb are different alkaline earth elements. Similarly, in the case where Mb is a transition metal element and Mc is a transition metal element, it is understood that Mb and Mc are different transition metal elements.
The variable x in Formula (1) is a value between 0 and 2, expressed as 0≤x≤2. In different embodiments, the variable x may be 0 or precisely or about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, and 2, or any range bounded by any two of the foregoing values, wherein the minimum and maximum bounds may be included or excluded from the range, e.g., 0<x<2, 0<x<2, 0<x<2, 0<x<2, 0.01<x<2, 0.01<x<2, 0.01<x<2, 0.01<x<2, 0.1<x<2, 0.1<x<2, 0.1<x<2, 0.1<x<2, 0<x<1, 0<x<1, 0<x<1, 0<x<1, 0.01<x<1, 0.01<x<1, 0.01<x<1, 0.01<x<1, 0.1<x<1, 0.1<x<1, 0.1<x<1, 0.1<x<1, 0<x<0.5, 0<x<0.5, 0<x<0.5, 0<x<0.5, 0.01<x<0.5, 0.01<x<0.5, 0.01<x<0.5, 0.01<x<0.5, 0.1<x<0.5, 0.1<x<0.5, 0.1<x<0.5, 0.1<x<0.5, 0<x<0.4, 0<x<0.4, x 0.4, 0<x<0.4, 0.01<x<0.4, 0.01 x<0.4, 0.01<x<0.4, 0.01<x<0.4, 0.1<x<0.4, 0.1<x<0.4, 0.1<x<0.4, 0.1<x<0.4, 0<x<0.3, 0<x<0.3, 0<x<0.3, 0<x<0.3, 0.01<x<0.3, 0.01<x<0.3, 0.01<x<0.3, 0.01<x<0.3, 0.1<x<0.3, 0.1<x<0.3, 0.1<x<0.3, and 0.1<x<0.3.
When variable x in Formula (1) is 0, Formula (1) reduces to the following sub-formula:
Ma2McO4 (1a)
Some examples of specific compositions within the scope of Formula (1a) include La2CuO4, Ce2CuO4, La1.8Ce0.2CuO4, La1.6Ce0.4CuO4, LaCeCuO4, La1.8Nd0.2CuO4, La1.6Nd0.4CuO4, LaNdCuO4, Nd1.8Ce0.2CuO4, Nd1.6Ce0.4CuO4, and NdCeCuO4.
When variable x in Formula (1) is 2, Formula (1) reduces to the following sub-formula:
Mb2McO4 (1b)
Some examples of specific compositions within the scope of Formula (1b) include SrFeO4, CaFeO4, and BaFeO4.
When variable x in Formula (1) is greater than 0 and less than 2, Formula (1) includes at least one alkaline earth element (Mb) in addition to the one or more lanthanide elements (Ma) and the one or more first-row transition metal elements (Mc). Some specific examples of such compositions include La1.8Sr0.2CuO4, La1.8Ce0.2Sr0.2CuO4, La1.6Ce0.4Sr0.2CuO4, LaCeSr0.2CuO4, La1.8Nd0.2Sr0.2CuO4, La1.6Nd0.4Sr0.2CuO4, LaNdSr0.2CuO4, Nd1.8Ce0.2Sr0.2CuO4, Nd1.6Ce0.4Sr0.2CuO4, NdCeSr0.2CuO4, La1.8Ca0.2CuO4, La1.8Ce0.2Ca0.2CuO4, La1.6Ce0.4Ca0.2CuO4, LaCeCa0.2CuO4, La1.8Nd0.2Ca0.2CuO4, La1.6Nd0.4Ca0.2CuO4, LaNdCa0.2CuO4, La1.8Ba0.2CuO4, La1.8Ce0.2Ba0.2CuO4, La1.6Ce0.4Ba0.2CuO4, LaCeBa0.2CuO4, La1.8Nd0.2Ba0.2CuO4, La1.6Nd0.4Ba0.2CuO4, and LaNdBa0.2CuO4.
In some embodiments, the oxide composition has the following formula:
La2-xMbxCuO4 (1c)
In Formula (1c), Mb is precisely or at least one or two alkaline earth elements selected from any of those provided above, or more particularly selected from one, two, or more of Ca, Sr, and Ba; and the variable x is any of the variables or within any of the ranges provided above. In particular embodiments, 0≤x≤1, 0<x≤1, 0≤x<1, 0<x<1, 0≤x≤0.5, 0<x≤0.5, 0≤x<0.5, or 0<x<0.5. Several examples of x within the scope of Formula (1c) have been provided above, all of which may apply in Formula (1c).
The porous multi-metal oxide composition may have a number of other possible formulas than those described above. These include, for example, MaMbO3, MaMa′O3, MbMb′O3, MaMa′MbO3, MaMa′MbMb′O3, MbMb′MaO3, MaMbO2, Ma2-xMbxO4, or MaMa′Mb2O5+δ, wherein Ma, Mb, and x are in accordance with any of the definitions or values provided above. The variable Ma′ indicates another instance of Ma, whether Ma is a lanthanide or alkaline earth element. Thus, if Ma is selected as a lanthanide element, Ma′ is a different lanthanide element, or Ma′ is an alkaline earth element. Similarly, if Ma is selected as an alkaline earth element, Ma′ is a different alkaline earth element, or Ma′ is a lanthanide element. The variable Mb′ indicates another instance of Mb, whether Mb is an alkaline earth element or transition metal. Thus, if Mb is selected as an alkaline earth element, Mb′ is a different alkaline earth element, or Mb′ is a transition metal element. Similarly, if Mb is selected as a transition metal element, Mb′ is a different transition metal element, or Mb′ is an alkaline earth element. The variable δ is a fudge factor that may be 0 or an integer or non-integer within the range of −1 to +1.
The porous multi-metal oxide composition contains micropores, mesopores, or a combination thereof. The pores permit the carbon dioxide to selectively enter the oxide composition (catalyst) and get converted into carbon-containing products. The pores also provide the oxide composition with a very high surface area, which improves the efficiency of the carbon dioxide conversion. When the composition is employed as a carbon conversion catalyst, the oxide composition preferably does not contain macropores (i.e., pore sizes greater than 50 nm or 100 nm) since such a pore size would permit entry of any gaseous species with no selectivity. However, the presence of macropores may be acceptable or even beneficial in other applications, such as in photovoltaic or battery devices.
As well known, micropores correspond to a pore size having a diameter of up to or less than 2 nm. The micropores may have a size of precisely or about, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, or 2 nm, or a micropore size within a range bounded by any two of these values, such as, for example, 0.1-2 nm, 0.2-2 nm, 0.5-2 nm, 1-2 nm, 0.1-1.5 nm, 0.2-1.5 nm, 0.5-1.5 nm, 1-1.5 nm, 0.1-1 nm, 0.2-1 nm, or 0.5-1 nm.
As also well known, mesopores correspond to a pore size having a diameter of at least or above 2 nm and up to 50 nm. The mesopores may have a size of precisely or about, for example, 2, 2.2, 2.5, 3, 5, 8, 10, 12, 15, 20, 30, 40, or 50 nm, or a mesopore size within a range bounded by any two of these values, such as, for example, 2-50 nm, 2-40 nm, 2-30 nm, 2-20 nm, 2-10 nm, 2-8 nm, 2-5 nm, 2-4 nm, 2.5-50 nm, 2.5-40 nm, 2.5-30 nm, 2.5-20 nm, 2.5-10 nm, 2.5-8 nm, 2.5-5 nm, 2-4 nm, 3-50 nm, 3-40 nm, 3-30 nm, 3-20 nm, 3-10 nm, 3-8 nm, 3-5 nm, 3-4 nm, 5-50 nm, 5-40 nm, 5-30 nm, 5-20 nm, 5-10 nm, or 5-8 nm.
In some embodiments, the total (i.e., 100%) of the pore volume in the oxide composition is attributed to micropores, which may correspond to any of the foregoing micropore size ranges. In the latter case, mesopores and macropores are necessarily excluded. In other embodiments, the total (i.e., 100%) of the pore volume in the oxide composition is attributed to mesopores, which may correspond to any of the foregoing mesopore size ranges. In the latter case, micropores and macropores are necessarily excluded. In other embodiments, the oxide composition includes a combination of micropores and mesopores, in which case macropores may or may not be present. When a combination of micropores and mesopores is present in the oxide composition, the micropores and mesopores may each have a size independently selected from any of the exemplary values or ranges for micropore and mesopore sizes, respectively, provided above. Moreover, if the pore volume attributed to mesopores is designated as x % and macropores are not present, then the pore volume attributed to micropores is (100-x)%, wherein x is a value greater than 0 and less than 100, e.g., 2, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 95, or 98%, or a value within a range bounded by any two of the foregoing values. In the event that macropores are present and their pore volume is designated as y %, then the pore volume attributed to micropores is (100-x-y)%, wherein y % is typically up to or less than 1, 2, 5, 10, 20, 30, 40, or 50%, or within a range bounded by any two of these values. Moreover, the pore size distribution may be monomodal, bimodal, or higher modal, with each mode having a peak pore size independently selected from any of the values of micropore and mesopore sizes provided above.
In some embodiments, the oxide composition contains defect sites corresponding to oxygen vacant sites. These defect sites increase the activity of the compositions to make them substantially more capable and efficient than metal oxide compositions of the art. In some embodiments, the defect sites arise from the substitution of a trivalent atom (e.g., a lanthanide atom) with a divalent alkaline earth metal, which results in a bonding vacancy due to the lower bonding capacity of an alkaline earth metal compared to a lanthanide.
In another aspect, the present disclosure is directed to a method of producing any of the porous multi-metal oxide compositions described above. The method can be used to produce particles of the oxide composition or a monolithic film or membrane of the oxide composition. In some embodiments, particularly where the oxide composition includes at least one lanthanide and at least one transition metal, the surface of the particles or membrane possesses a decreased transition metal (e.g., copper and/or iron) content and a higher lanthanide (e.g., La or Ce) content compared to an inner or core portion of the particles or membrane.
In a first step of the method, a sacrificial mesoporous template (i.e., “template”) is impregnated with a solution containing an organic acid and at least two metal salts containing: (a) a first metal salt containing at least one transition metal element and (b) a second metal salt containing at least one other metal element selected from transition metal elements, lanthanide elements, alkaline earth elements, and main group elements. The transition metal elements, lanthanide elements, alkaline elements, and/or main group elements in the first and second metal salts can be selected from any of those provided earlier above to result in a desired metal oxide composition, such as any of those described earlier above. The metal salt is composed of the metal ion in association with a suitable anion which confers solubility of the metal salt in the solution. The anion may be, for example, nitrate (NO3−), halide (e.g., chloride or bromide), hydroxide (OH−), a complexing ligand, such as a phenanthroline, ethylenediamine, or oxalate, or a combination of any two or more of these types of anions.
The sacrificial mesoporous template may be any mesoporous material that resists decomposition at temperatures of at least 500° C. and which can be subsequently removed after exposure to a heat treatment at a temperature of at least 500° C. or with a solvent such as an aqueous base or acid. In some embodiments, the sacrificial mesoporous template has a metal oxide composition, which is typically but not necessarily a single-metal oxide, such as SiO2, TiO2, Al2O3, ZrO2, Fe2O3, and CrO3. Mesoporous metal oxides are well known in the art, such as described in Y. Peng et al., Chemistry of Materials, 34(15), 7042-7057, 2022, the contents of which are herein incorporated by reference. The sacrificial mesoporous template may alternatively be an aluminosilicate (e.g., a zeolite), MCM-type silicate, or an organic-inorganic hybrid material. Such materials are well known in the art, such as described in N. Pal et al., Advances in Colloid and Interface Science, 189-190, 21-41, March 2013, the contents of which are herein incorporated by reference. The sacrificial mesoporous template possesses mesopores, such as any of the sizes or ranges thereof provided above, typically in the absence of micropores and macropores. The sacrificial mesoporous template may be in the form of particles or a monolith, the latter of which may be used to produce a membrane or film of the oxide composition.
The solution used in the impregnating step contains, at minimum, the metal salt, organic acid, and a solvent. The organic acid may be any of the known organic acids, such as citric acid, oxalic acid, acetic acid, propanoic acid, butyric acid, or tartaric acid. The solvent is typically hydrophilic, such as water, an alcohol (e.g., ethanol, methanol, or isopropyl alcohol), acetone, or acetonitrile, or a combination of any of these. The solvent typically has a boiling point less than 100° C. to make solvent removal easier.
The resulting impregnated sacrificial mesoporous template is typically subjected to conditions in which the solvent is removed, before it is subjected to a calcination step. The solvent removal step may entail subjecting the impregnated sacrificial mesoporous template to an elevated temperature (e.g., at least 50° C., 80° C., 100° C., or 120° C., or a range therein) for a suitable period of time (e.g., at least 4, 6, 8, 12, 24, or 36 hours) to remove all solvent.
In a second step of the method, the impregnated sacrificial mesoporous template is subjected to a temperature of 500-1000° C. to calcine the metal salts and convert them to metal oxides, which may be any of the porous multi-metal oxide compositions described earlier above. In different embodiments, and depending on the nature of the metal salts and mesoporous template, the calcination temperature may be precisely or about, for example, 500° C., 550° C., 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., or 1000° C., or a temperature within a range bounded by any two of the foregoing values. From room temperature (about 20° C. or 25° C.) or from the solvent removal temperature, the mesoporous template may be suddenly or gradually raised to the calcination temperature. A gradual rise in temperature may correspond to a temperature ramp rate of, for example, 1, 2, 3, 4, 5, or 10° C. per hour or a ramp rate within a range therein.
In a third step of the method, the sacrificial mesoporous template is removed, thus freeing the porous multi-metal oxide composition from the template. Depending on the composition of the template, various means may be available for removing it. The term “removed” or “removing,” as used herein, may refer to a complete or partial removal. A complete removal means that no residue of the template or a decomposition product (e.g., carbonaceous or non-carbonaceous) of the template remains after the removal process. A partial removal means that a residue of the template or a decomposition product of the template remains bound to the oxide composition. In some embodiments, the template is removed by etching with an alkaline (e.g., alkali hydroxide, such as NaOH or KOH, or alkali alkoxide) solution, particularly in the case of the template having a metal oxide composition. In other embodiments, the template is removed by dissolving it in a solvent. In other embodiments, the template is removed by pyrolysis or vaporization. A combination of these methods may also be used to remove the template.
In another aspect, the present disclosure is directed to methods for reductively converting carbon dioxide to one or more carbon-containing products by use of the above-described oxide composition (i.e., “catalyst”). The carbon-containing products typically result from several electron/proton transfer processes facilitated by the catalyst. The carbon-containing product may be selected from one or more of, for example, carbon monoxide, hydrocarbons (e.g., alkenes or alkanes), alcohols, ketones, ethers, aldehydes, and carboxylic acids. The hydrocarbons may include one or more of, for example, methane, ethane, propane, butane, isobutane, ethylene, propylene, 2-methylpropene, 2-butylene, and aromatics (e.g., benzene, toluene, and/or xylenes). The alcohols may include one or more of, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol. The ketones may include one or more of, for example, acetone (2-propanone), butanone (methyl ethyl ketone), 2-pentanone, 3-pentanone, 2,3-butanedione (diacetyl), 2,4-pentanedione, and acetic anhydride. The ethers may include one or more of, for example, dimethyl ether, diethyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, methyl butyl ether, dipropyl ether, and dibutyl ether. The aldehydes may include one or more of, for example, formaldehyde, glyoxal, acetaldehyde, propionaldehyde, butyraldehyde, malondialdehyde, and succinaldehyde. In some embodiments, any one or more of the foregoing classes or specific types of products may be excluded.
The carbon dioxide being converted may be produced by any known source of carbon dioxide. The source of carbon dioxide may be, for example, ambient air, a combustion source (e.g., from burning of fossil fuels in an engine or generator), natural gas emission (natural gas combined cycle), commercial biomass fermenter (e.g., ethanol fermentation), flue gas, or commercial carbon dioxide-methane separation process for gas wells or agricultural bio residues, i.e., animal manure. In some embodiments, the source of the carbon dioxide gas is a waste or emission stream from an industrial or combustion process, wherein the gaseous source may be directly contacted with the catalyst without an intermediate processing step, or the gaseous source is first treated by an intermediate processing step, such as by removing one or more gaseous contaminants (e.g., soot, NOx gases, amines, or CO) before contacting the catalyst.
In a first embodiment, carbon dioxide gas (either alone or in admixture with one or more other gases) is directly contacted with the porous multi-metal oxide composition (i.e., “catalyst”) described above at a temperature of 25-1000° C., while the porous multi-metal oxide catalyst is disposed on an electrically charged cathode, to result in reductive conversion of the carbon dioxide to the one or more carbon-containing products. The temperature may be precisely or about, for example, 25° C., 50° C., 100° C., 150° C., 200° C., 250° C., 300° C., 350° C., 400° C., 450° C., 500° C., 550° C., 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., or 1000° C., or a temperature within a range bounded by any two of the foregoing values. The input gas stream may or may not be heated before contacting the catalyst. If heated, the input gas stream may be heated to any of the temperatures provided above. The catalyst described herein may, alternatively or in addition to converting carbon dioxide, reductively convert known noxious or polluting gases (e.g., NOx or SOx) to less harmful (reduced) substances using the same conditions described above. In some embodiments, the carbon dioxide is in admixture with a small amount (e.g., 1-5 vol %) of hydrogen gas to facilitate the reduction process. The method is typically conducted at ambient pressure (about 1 atm) but may be conducted at an elevated pressure (i.e., above 1 atm, or 2, 5, 10, 15, 20, or 25 atm, or within a range therebetween).
The gas stream makes contact with the catalyst for any suitable gas-phase residence time at any of the gas ratios, pressures, or temperatures provided above. The residence time is typically within a range of 1 second to 24 hours, depending on the conditions employed. In some embodiments, the residence time may be longer, e.g., 30, 35, or 40 hours. In different embodiments, and depending on the conditions used, the residence time may be 1 second, 5 seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 12 hours, 18 hours, or 24 hours, or a residence time within a range bounded by any two of the foregoing values (e.g., 1 second to 24 hours, 1 second to 12 hours, 1 second to 6 hours, 1 second to 2 hours, 1 second to 1 hour, 1 second to 30 minutes, 1 second to 10 minutes, 1 second to 1 minute, 1-30 seconds, 1 minute to 24 hours, 1 minute to 12 hours, 1 minute to 6 hours, 1-40 hours, 1-30 hours, 6-40 hours, 6-30 hours, 6-24 hours, 10-40 hours, 10-30 hours, or 10-24 hours).
The method employs any suitable weight hourly space velocity (WHSV) of CO2, wherein it is known that the WHSV is at least in part determined by the feed content and gas-phase residence time. The WHSV is typically in a range of 0.2-3 h−1. In different embodiments, and dependent on the feed content, residence time, and other factors, the WHSV may be precisely or about, for example, 0.2h−1, 0.3h−1, 0.4h−1, 0.5h−1, 0.6h−1, 0.7h−1, 0.8h−1, 0.9h−1, 1h−1, 1.2h−1, 1.4h−1, 1.6h−1, 1.8h−1, 2h−1, 2.2h−1, 2.4h−1, 2.6h−1, 2.8h−1, or 3 h−1, or a WHSV within a range bound by any two of the foregoing values (e.g., 0.2-3h−1, 0.2-2.5h−1, 0.2-2h−1, 0.3-3h−1, 0.3-2.5h−1, 0.3-2h−1, 0.4-3h−1, 0.4-2.5h−1, 0.4-2h−1, 0.5-3h−1, 0.5-2.5h−1, 0.5-2h−1, 1-3h−1, 1-2.5h−1, or 1-2h−1).
In a second embodiment, carbon dioxide gas is contacted with a solution (typically an electrolyte solution) in which the carbon dioxide is made to be in a soluble form, typically by conversion of the carbon dioxide to an ionic form (e.g., a carbonate or bicarbonate ion) remaining soluble in the solution, and simultaneously or subsequently contacting the solution with the porous multi-metal oxide catalyst, as described above, while the porous multi-metal oxide catalyst is disposed on an electrically charged cathode. The carbon dioxide may be reacted with, for example, a base (e.g., an alkali hydroxide or amine) dissolved in the solution to produce a carbonate, bicarbonate, or carbamate ion that remains soluble in the solution while the solution is in contact with the catalyst which is disposed on an electrically charged cathode. The result is the reductive conversion of the carbon dioxide to the one or more carbon-containing products. The solution may be contacted with the catalyst at ambient (room) temperature or at an elevated temperature, as provided above, to produce the carbon-containing product(s). The solution may be contacted with the catalyst at room (ambient) temperature or at a slightly elevated temperature (e.g., 30, 40, 50, 60, 70, or 80° C., or within a range there between), depending on the boiling point of the solvent.
When contacting the gas or solution, the catalyst may be housed in any suitable reactor design in non-electrochemical reactors, such as a packed-bed reactor, pellet-bed reactor, trickle bed, bubble bed, stirred tank, microwave, plasma or a fluidized bed reactor. In some embodiments, the reactor has a 3D printed (e.g., into microchannels) or electrospun reactor design to better overcome pressure drop issues and improve the product distribution. Coating of the catalyst onto monoliths may also be advantageous in overcoming pressure drop issues. Electrospun reactors (e.g., containing electrospun polymetallic fibers) can also improve the metal distribution, which can improve product selectivity.
The process described above may produce hydrocarbons (e.g., paraffins or olefins) containing at least three or four carbon atoms. In some embodiments, at least 20 vol % of the hydrocarbons produced by the process contains at least three or four carbon atoms. In various embodiments, at least or greater than 20, 30, 40, 50, 60, 70, 80, 85, 90, or 95 vol % of the hydrocarbons (or more particularly, paraffins or olefins) produced by the method contains at least three or four carbon atoms. In further or separate embodiments, at least or greater than 1, 2, 5, 10, 15, 20, 30, 40, 50, 60, 70, or 80 vol % of the hydrocarbons (or more particularly, paraffins olefins) produced by the method contains at least five carbon atoms. In further or separate embodiments, at least or greater than 1, 2, 5, 10, 15, 20, 30, 40, or 50 vol % of the hydrocarbons (or more particularly, paraffins or olefins) produced by the method contains at least six, seven, eight or a higher number of carbon atoms. In some embodiments, the process produces one or more hydrocarbons (or more particularly, paraffins or olefins) containing up to 8, 10, 12, 15, 18, or 20 carbon atoms. Any of the minimum and maximum number of carbon atoms disclosed above may be combined to result in a range of carbon atoms (e.g., 4-20, 4-15, or 4-13 carbon atoms).
In some embodiments, hydrocarbons (or more particularly, paraffins and/or olefins) containing less than three or four carbon atoms are not produced or are produced in a minor amount, such as no more than or less than 20, 15, 10, 5, 2, or 1 vol %. In some embodiments, hydrocarbons (or more particularly, paraffins or olefins) containing precisely or less than three carbon atoms are not produced or are produced in a minor amount, such as no more than or less than 20, 15, 10, 5, 2, or 1 vol %. In some embodiments, hydrocarbons containing two carbon atoms (e.g., ethylene and/or ethane) are not produced or are produced in a minor amount, such as no more than or less than 20, 15, 10, 5, 2, or 1 vol %. In some embodiments, methane is not produced or is produced in a minor amount, such as no more than or less than 10, 5, 2, or 1 vol %. In some embodiments, aromatic molecules are not produced or are produced in a minor amount, such as no more than or less than 10, 5, 2, or 1 vol %. In some embodiments, oxygen-containing molecules (e.g., alcohols, ketones, aldehydes, ethers, and the like) are not produced or are produced in a minor amount, such as no more than or less than 10, 5, 2, or 1 vol %. In some embodiments, carbon monoxide (CO) is not produced or is produced in a minor amount, such as no more than or less than 10, 5, 2, or 1 vol %. In some embodiments, alkanes (i.e., methane and/or paraffins) are not produced or are produced in a minor amount, such as no more than or less than 50, 40, 30, 20, 10, 5, 2, or 1 vol %.
In some embodiments, at least a portion of the carbon-containing products produced by the method are olefins. For example, in some embodiments, at least or greater than 20, 30, 40, 50, 60, 70, 80, or 90 vol % (or 100 vol %) of the carbon-containing products produced by the method are olefins. In some embodiments, at least a portion of the carbon-containing products has an olefinic composition. For example, in some embodiments, at least or greater than 20, 30, 40, 50, 60, 70, 80, or 90 vol % (or 100 vol %) of the carbon-containing products has an olefinic composition.
Examples have been set forth below for the purpose of illustration and to describe certain specific embodiments of the invention. However, the scope of this invention is not to be in any way limited by the examples set forth herein.
Three lanthanum cuprate compositions were synthesized and characterized: conventional (non-porous) La2CuO4, porous La1.8Sr0.2Cu, and porous La2CuO4. The varying synthetic methods altered the elemental composition, lattice oxygen content, and structure at the catalyst surface. These changes created unique electrochemical characteristics.
All materials were of analytical grade and obtained from a commercial source. Lanthanum nitrate, La(NO3)3·6H2O, strontium nitrate, Sr(NO3)2·3H2O, copper nitrate, Cu(NO3)2·3H2O, urea, citric acid, sodium hydroxide, and ethanol were used as received. Water was purified by an in-house osmotic system connected to a deionized filter system and generated at 18Ω.
La2CuO4 and La1.8Sr0.2CuO4 were synthesized via a solution combustion method. Briefly, 5 g of La(NO3)3·6H2O, 1.39 g of Cu(NO3)2·3H2O, and 2.31 g of urea were combined in 20 mL deionized water in a shallow glass dish and stirred at room temperature for 1 hour. The magnetic stirrer was removed, and the dish placed in a muffle furnace preheated to 300° C. where the contents were dried and combusted. After grinding in a mortar and pestle, the black powder was placed in a quartz boat and calcined in a tube furnace at 900° C., heated at 4° C. per minute from room temperature, and held for 10 hours.
As further discussed below, porous metal oxide catalysts were nano-casted on KIT-6, a mesoporous silica hard template. For example, La2CuO4 was incorporated into the KIT-6 structure using a wet impregnation method, as follows. 3 mol of citric acid were dissolved in 10 mL of ethanol. 4 mmol of La(NO3)3·6H2O and 2 mmol of Cu(NO3)2·3H2O were then added to the citric acid solution. 1 g of KIT-6 powder was stirred in 10 mL of water, and the metal-chelated citric acid solution was added and stirred overnight at room temperature. The solvent was removed via a roto-evaporator, and the resulting powder dried at 80° C. for 24 hours. The powder was ground with a mortar and pestle before being ramped at 4° C. per minute, for 4 hours, and calcined at 500° C. Impregnation was repeated twice; the second repetition used halved precursor amounts to achieve higher loadings. The final powder was calcined at 700° C. for 6 hours. The silica template was removed by etching with 2 M NaOH. In the etching process, the calcined template was mixed NaOH solution was stirred overnight, filtered, and washed with water. Etching was repeated three times. The final powder was washed with water and ethanol until neutral pH and then dried at 80° C.
Powder X-ray diffraction (XRD) data were recorded with a diffractometer operated at 45 kV and 40 mA with a scanning step of 0.02°. The diffraction patterns were recorded between 20° and 80°. Elemental analysis was conducted via an ICP-OES.
X-ray photoelectron spectroscopy (XPS) was performed with a commercial instrument using monochromatic, micro-focused Al Kα X-rays (1486.6 eV) with a variable spot size. Sample analyses were performed with a 400 m X-ray spot size to obtain maximum signal and the largest possible area for average surface composition. The instrument had a hemispherical electron energy analyzer equipped with a 128-channel detector system. Base pressure in the analysis chamber was typically 2×10-9 mbar or lower. Samples were mounted by dispersing powder onto double-sided tape fixed to clean glass sides. Areas were selected for analysis by viewing the samples with a digital optical camera at a magnification of 60-200×. Survey spectra (200 eV pass energy) were acquired for qualitative and quantitative analysis. High-resolution core level spectra (50 eV pass energy) were obtained for detailed chemical state analysis. Stable analysis conditions for spectra acquisition were maintained with the charge neutralization flood gun, which used a combination of low energy electrons and argon ions for optimum charge compensation. Typical pressure in the analysis chamber with the flood gun operating was 2×10−7 mbar. Data were collected and processed using a commercial software package. Peak fitting was performed using mixed Gaussian/Lorentzian peak shapes and a Shirley/Smart type background.
Nitrogen sorption measurements were made using a commercial device. The specific surface area and pore size distribution were calculated using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, respectively. The pore size distribution for the porous system was determined using the Density Functional Theory method to account for capillary condensation and non-homogenous pore distribution. Thermogravimetric analysis (TGA) was performed using a commercial device under a 25 mL/min flow of argon. The furnace temperature was raised from room temperature to 800° C. at 10° C. per minute.
Initial cyclic voltammetry measurements were performed with a standard three-electrode setup in an undivided glass cell. To prepare the cathode, a mixture of carbon powder and mineral oil was packed into a glass tube. Perovskite powder was deposited on the exposed paste. A commercial graphitic carbon rod and saturated Ag/AgCl were used as the anode and reference electrode, respectively. The electrochemical system was tested at ambient temperature and pressure in aqueous 0.5 M NaHCO3 saturated with either argon or CO2 gas. Potentials were cycled between 0 V and −1.2 V vs. Ag/AgCl for four scans using a commercial instrument at a scan rate of 20 and 40 mV/sec.
Gas aliquots were taken from the glass cell and injected into a gas chromatography-flame ionization detector (GC-FID) device equipped with a nickel catalyst and a stationary phase carbon-layer column for quantification. Identification of products were done by authentic gas samples to determine retention times, as well as injection into a mass spectrometer (MS) also equipped with a stationary phase carbon-layer.
Lanthanum cuprate-based perovskites were synthesized as electrocatalysts for the production of higher-order carbon products from CO2. XRD patterns, as shown in
XPS was used to analyze the surface characteristics of the perovskite materials. Details are provided in Table 1 (below) and
Initial nitrogen (N2) sorption isotherms indicate that neither La2CuO4 nor La1.8Sr0.2CuO4 contained pores. The strontium-containing perovskite exhibited a slightly higher surface area, as noted in Table 2 (below). Porous La2CuO4 and La1.8Sr0.2CuO4 was templated on a mesoporous KIT-6 substrate with a 50 Å average pore diameter and surface area of 930 m2/g. The porous sample showed a higher than ca. 40-fold increase in surface area compared to the non-porous systems, although it contained substantially less area than the hard template. Associated N2 sorption isotherms indicated a system with microporous and mesoporous characteristics. Mesopore formation was associated with the nano-casting process, while micropores were formed via wall etching during KIT-6 removal. The mesopore distribution included pores from 30 Å (3.0 nm) to over 80 Å (8.0 nm), with a mode width of 47.5 Å (4.75 nm). Micropore volume could not be accurately calculated due to instrument limitations of 7 Å (microporosity was at 7.86 Å and below). Rough estimates placed the width at approximately 5 Å, as also indicated by N2 sorption isotherms and DFT method pore size distribution.
The electrochemical behavior of the perovskite materials was analyzed by cyclic voltammetry. All La2CuO4-based catalysts demonstrated enhanced electrochemical activity compared to a carbon black control under both argon- and CO2-saturated conditions. CVs for each catalyst are shown in
Changes in the system CVs under both argon and CO2 saturation indicate significant irreversibility in the electrochemical system. Increasingly positive reduction currents beyond −0.6 V vs. Ag/AgCl for the La2CuO4 (
Although argon is a relatively inert gas, significant electrochemical activity was observed for each of the perovskite catalysts under argon saturation. Porous La2CuO4 and La1.8Sr0.2CuO4 (
Although cathode catalyst materials are one of the most important factors in determining product identity and distribution, system selectivity is also dependent on the CO2 to proton ratio at the electrode surface and the associated kinetics. Additional parameters can directly impact the transportation and activity of relevant species and alter product formation.
Electrolytes serve to increase solvent conductivity and can play a key role in driving electrochemical cell efficiency and selectivity. Bicarbonate electrolytes, such as KHCO3, are commonly used in aqueous solutions for their ability to form an equilibrium with dissolved CO2 and supply the cathode with greater CO2 concentrations than gas diffusion alone (e.g., M. Dunwell et al., J. Am. Chem. Soc. 139(10), 3774-3783, 2017). The corresponding alkali metal cations also act as a local pH buffer. Increasing cation size is associated with decreased pH and increased CO2 concentration near the electrode surface (e.g., M. R. Singh et al., J. Am. Chem. Soc. 138(39), 13006-13012, 2016). Non-bicarbonate electrolytes, such as KCl and KOH, have also been used, with KOH showing a particular selectivity towards ethanol and ethylene. In all cases, the electrolyte concentration can alter product selectivity (e.g., Y. Hori et al., J. Chem. Soc. Faraday Trans. 1: Phys. Chem. Condens. Phases 85(8), 2309-2326, 1989).
Aqueous solvents are frequently used due to their inexpensive and nonvolatile nature, but CO2 solubility is minimal and H2 evolution prominent at ambient conditions (J. Li et al., J. Electrochem. Soc. 144(12), 4284, 1997). Acetonitrile is a common alternative to aqueous systems and can produce oxalic acid and CO when dry (W. Lv et al., J. Solid State Electrochem 17(11), 2789-2794, 2013). The addition of water provides a proton source, thus providing additional product formation and shifting peak potentials (e.g., Y. Tomita et al., J. Electrochem. Soc. 147(11), 4164, 2000). Protic solvents like methanol demonstrate high CO2 solubility and have been used to produce formic acid (S. Kaneco et al., Environ. Eng. Sci. 16(2), 131-137, 1999). Imidazolium-based ionic liquids are also employed as a non-volatile, stable solvent and electrolyte; the imidazole group acts as a co-catalyst in CO2RR, thereby decreasing energy barriers to extended reduction (e.g., L. Chen et al., ChemSusChem 9(11), 1271-1278, 2016).
Solvent and electrolyte choices directly impact the bulk and local system pH. Acidic solutions promote H2 evolution, while neutral pH is favored in most CO2RR cells (e.g., C. H. Lee et al., ACS Catal. 5(1), 465-469, 2015). A constant cell pH is essential for long-term industrial operation. CO2 electroreduction generates hydroxide species at the cathode that can be neutralized by weak acid electrolytes. Electrolyte identity, size, concentration, and system temperature are all known to impact this buffering action.
Tests on porous La1.8Sr0.2CuO4 and La2CuO4 were conducted at room temperature and pressure and show higher reduction rate and efficiency, especially for the porous La2CuO4 than non porous La2CuO4. For comparison, limited studies exist on the temperature dependence of CO2RR, with most work conducted under ambient temperature. Decreased reaction temperatures correspond with H2 evolution suppression, and non-aqueous solutions can take advantage of high CO2 solubility at sub-zero temperatures (e.g., A. Kudo et al., J. Electrochem. Soc. 140(6), 1541, 1993). Moderately high temperatures may provide improvements related to kinetics, current densities, and conductivity, although elevated temperatures are known to be severely limited by decreased CO2 solubility and corresponding H2 production.
Increased cell pressure is associated with improved CO2RR in both aqueous and non-aqueous systems (A. Kudo et al., Ibid.). The elevated pressure is also capable of altering metal electroreduction activity, increasing current densities, and increasing solution resistance (e.g., K. Hara et al., J. Electroanal. Chem. 391(1), 141-147, 1995). These changes are generally attributed to the increased concentration of CO2 in solution at above-ambient pressures (H. Hashiba et al., ACS Comb. Sci. 18(4), 203-208, 2016). Testing on porous La1.8Sr0.2CuO4 and porous La2CuO4 were conducted at ambient pressure and showed a marked increase in electrocatalytic reduction than non-porous La2CuO4, thus indicating pressure would likely increase CO2 reduction of the porous La1.8Sr0.2CuO4 and porous La2CuO4 systems in comparison.
Porous lanthanum cuprate mixed-metal oxide, La2CuO4, have herein been shown to function as exceptional CO2 electroreduction catalysts capable of producing multi-carbon products. Altered synthetic procedures resulted in the modification of surface characteristics, including surface area, pore structure, and elemental composition. The porous La2CuO4 system notably exhibited decreased copper and lattice oxygen content at the catalyst surface. In comparison with carbon black controls, all porous La2CuO4-based perovskites demonstrated improved CO2 electroreduction at ambient conditions. Differences in electrochemical activity can be attributed to the surface-level alterations in each catalyst surface such as lattice oxygen, defect sites, lanthanum-oxygen terminated surface and oxygen vacancies to allow stronger CO2 adsorption strength, and higher CO2 conversion sites.
While there have been shown and described what are at present considered the preferred embodiments of the invention, those skilled in the art may make various changes and modifications which remain within the scope of the invention defined by the appended claims.
The present application claims benefit of U.S. Provisional Application No. 63/545,998, filed on Oct. 27, 2023, all of the contents of which are incorporated herein by reference.
This invention was made with government support under Prime Contract No. DE-AC05-000R22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63545998 | Oct 2023 | US |
