United States Patent: 8986511

Carbon Dioxide - - as we might conveniently harvest as a byproduct arising from our economically essential use of Coal in the generation of abundant, affordable and reliable electric power - - can be seen and treated as a valuable raw material resource.

Carbon Dioxide holds the potential to help free the United States of America from it's economic enslavement to the foreign and in some cases dangerous nations of OPEC, and to enable the creation of new industries, and more jobs, in United States Coal Country.

As we reported some years ago, in:

Pittsburgh USDOE Converts CO2 to Methane & Methanol | Research & Development | News; concerning the American Chemical Society article: "Visible Light Photoreduction of CO2; November, 2009; American Chemical Society; Congjun Wang, et. al.; National Energy Technology Laboratory, USDOE, Pittsburgh, PA; Abstract: A series of ... Titanium Dioxide (catalysts) have been synthesized, characterized, and tested for the photocatalytic reduction of CO2 in the presence of H2O. Our results show that these ... materials are capable of catalyzing the photoreduction of CO2 using visible light illumination ... . (Various treatments of the catalyst) have also been investigated. The ... analysis shows that the primary reaction product is CH4, with CH3OH, H2, and CO observed as secondary products";

the United States Department of Energy's Pittsburgh, PA, National Energy Technology Laboratory, which also has facilities in Morgantown, WV, has been at work developing "artificial photosynthesis" catalytic technologies that enable, in processes driven and powered by nothing but simple sunlight, the manufacture of chemical fuel products like substitute natural gas Methane, "CH4", and fuel alcohol Methanol, "CH3OH", from nothing as raw materials but water, "H2O", and, as harvested from whatever convenient source, Carbon Dioxide, "CO2".

In passing, we'll note, that, as seen in our report of:

ExxonMobil Coal to Methanol to Gasoline | Research & Development | News; concerning both: 

"United States Patent 4,348,486 - Production of Methanol via Catalytic Coal Gasification; 1982; Assignee: Exxon Research and Engineering Company, NJ; Claims: A process for the production of methanol from a carbonaceous feed material (by)gasifying said carbonaceous feed material with steam ... and added hydrogen and carbon monoxide (and) wherein said carbonaceous feed material comprises coal"; and:

"United States Patent 4,035,430 - Conversion of Methanol to Gasoline; 1977; Assignee: Mobil Oil Corporation, NY;

Claims:  (A) method for converting methanol to gasoline boiling products in a plurality of sequentially arranged catalyst beds ... . This invention relates to the method and system for converting methanol to gasoline";

Methanol - - once we've made it from one or the other of our precious domestic United States of America natural resources, whether Coal or Carbon Dioxide - - can be directly and efficiently converted into something we should all have an interest in: non-OPEC, all-USA gasoline.

And, further, as seen for one out of now many examples in our report of:

Honda USA 2014 Solar CO2 to Methane | Research & Development | News; concerning: "United States Patent 8,840,772 - Solar Fuel Cell; 2014; Inventor: Ting He, Dublin, Ohio; Assignee: Honda Motor Company, Ltd., Tokyo, Japan; Abstract: The present teachings are directed to a method of converting water and a carbon-containing compound, such as CO2, into a hydrocarbon through a process of absorbing sunlight on a light-absorbing component to photoelectrochemically oxidize water and reacting the products from that water oxidation reaction over a catalyst with the carbon-containing compound to produce the desired hydrocarbon compound";

such solar-powered artificial photosynthesis technologies, wherein Carbon Dioxide and water are converted into hydrocarbon fuels, are becoming, although we haven't been publicly informed about any of them, fairly commonplace. 

And, herein we see that, quite recently, We The People of the United States or America, through our employees working in one of the traditional hearts of United States Coal Country, at the United States Department of Energy's Pittsburgh, PA, National Energy Technology Laboratory, have come to own technology that, powered by nothing more than sunlight, uses and consumes only Carbon Dioxide and Water as the key, basic raw materials, and synthesizes, as end products, substitute and fracking-free natural gas Methane, and fuel alcohol Methanol. 

Comment follows excerpts from the initial link in this dispatch to:

"United States Patent 8,986,511 - Visible Light Photoreduction of CO2 Using Heterostructured Catalysts

Visible light photoreduction of CO2 using heterostructured catalysts - U.S. Department of Energy

Patent US8986511 - Visible light photoreduction of CO2 using heterostructured catalysts - Google Patents

March 24, 2015

Inventors: Christopher Matranga, et. al., Pittsburgh and Bethel Park, PA

Assignee: The United States Department of Energy, Washington, DC

Abstract: The method provides for use of sensitized photocatalyst for the photocatalytic reduction of CO2 under visible light illumination. The photosensitized catalyst is comprised of a wide band gap semiconductor material, a transition metal co-catalyst, and a semiconductor sensitizer. The semiconductor sensitizer is photoexcited by visible light and forms a Type II band alignment with the wide band gap semiconductor material. The wide band gap semiconductor material and the semiconductor sensitizer may be a plurality of particles, and the particle diameters may be selected to accomplish desired band widths and optimize charge injection under visible light illumination by utilizing quantum size effects.

In a particular embodiment, CO2 is reduced under visible light illumination using a CdSe/Pt/TiO2(Cadmium/Selenium/Platinum/Titanium Dioxide) sensitized photocatalyst with H2O as a hydrogen source.

Government Interests: The United States Government has rights in this invention pursuant to the employer-employee relationship of the Government to the inventors as U.S. Department of Energy employees and site-support contractors at the National Energy Technology Laboratory.

(At this point in issued United States Patents, pertinent related prior art patents are cited by the inventors. Among those catalogued by our subject, "United States Patent 8,986,511 - Visible Light Photoreduction of CO2 Using Heterostructured Catalysts", is that seen in our report of:

Texaco Recycles CO2 to Methanol & Methane | Research & Development | News; concerning: "United States Patent 4,523,981 - Means and Method for Reducing Carbon Dioxide to Provide a Product; 1985;

Inventor: Peter Ang, et. al., IL; Assignee: Texaco, Incorporated, NY; Abstract: A process for reducing carbon dioxide to at least one useful product includes two redox couple electrolyte solutions separated by a first membrane having photosensitizers. The carbon dioxide to be reduced is separated from one of the redox couple electrolyte solutions by another membrane having a catalyst. Water provides hydrogen ions which participate in the reduction of carbon dioxide via a separator. In the operation both membranes are illuminated and produce excited solar sensitizers which cause electron transfer from a first redox solution to the second redox solution and then to the carbon dioxide to react with the hydrogen ions, reducing the carbon dioxide to provide at least one product. A process for reducing carbon dioxide to at least one useful product ... (including) ... methanol (and/or) methane".

Others, related, about which we have and haven't yet reported are also cited. And, it is enlightening, we think, to see both how many technologies for, in essence, the productive utilization of Carbon Dioxide have been developed, and, how long those technologies have been available, but haven't been, really, publicly disclosed to or discussed among the United States citizens who would benefit in many ways from the implementation of them.)

Claims: A method of photocatalytically reducing CO2 in the presence of water comprising: producing a sensitized photocatalyst comprised of: a wide band gap semiconductor material, where the valence band of the wide band gap semiconductor material has a more positive potential than the redox potential of H2O, a semiconductor sensitizer loaded on a surface of the wide band gap semiconductor material, where the semiconductor sensitizer comprises a binary semiconductor, where the binary semiconductor is InP, GaAs, PbS, PbSe, ZnTe, CdS, CdSe, or CdTe, (Indium Phosphide, Gallium Arsenide, Lead Sulfide, Lead Selenide, Zinc Telluride, Cadmium Sulfide, etc.) such that the binary semiconductor has a band gap such that visible light produces photoexcitation in the binary semiconductor, and where the valence band of the wide band gap semiconductor material has a more positive potential than the redox potential of H2O, and where the binary semiconductor has a band gap such that the binary semiconductor and the wide band gap semiconductor material form a heterojunction at an interface between the binary semiconductor and the wide band gap semiconductor material, where the heterojunction has a type II band alignment, and where the conduction band of the binary semiconductor has a more negative potential than the conduction band of the wide band gap semiconductor material, a co-catalyst loaded on the wide band gap semiconductor material, where the co-catalyst is comprised of a transition metal; and exposing the sensitized photocatalyst to CO2 and H2O, and exposing the sensitized photocatalyst to a visible light illumination, such that some portion of the CO2 is photocatalytically reduced and such that product molecules are produced. 

The method ... where the co-catalyst is selected based on the composition of the product molecules. 

(Concerning the above claim, it is now possible, we now have the knowledge in other words, to select an hydrocarbon product we wish to make from CO2 and H2O, in a process powered by sunlight, and, to then select/design a catalyst system that will lead to the synthesis of that specific hydrocarbon.)

The method ... where the co-catalyst is Pt and the product molecules are hydrocarbons (or) where the co-catalyst is Fe and the product molecules are diatomic hydrogen.

(This is, in one aspect, also a technology that enables the solar-powered extraction of elemental, molecular Hydrogen from Water. Such Hydrogen would have uses in other, separate, processes for the conversion of both Carbon Dioxide and Coal into liquid and gaseous hydrocarbons. We're reported on many of those processes previously, but won't cite any of our past reports here. Of far, far more importance, we think, is the fact that both Carbon Dioxide and Water can be converted, in one aspect of the technology being disclosed, into hydrocarbons; and, that's where we want to keep our focus herein.)

The method ... where the where the wide band gap semiconductor material is TiO2 or ZnO (and) where the co-catalyst is Pt, the binary semiconductor is CdSe, and the product molecules are hydrocarbons. 

The method ...where the co-catalyst is Fe, the binary semiconductor is CdSe, and the product molecules are H2. 

The method ... where the wide band gap semiconductor material is TiO2, the co-catalyst is Pt, the binary semiconductor is CdSe, and the product molecules are hydrocarbons. 

The method ... where the wide band gap semiconductor material is comprised of a plurality of semiconductor particles, and where the co-catalyst is comprised of a plurality of co-catalyst particles, and where the co-catalyst is loaded on the wide band gap semiconductor when at least one of the co-catalyst particles is loaded on at least one of the semiconductor particles to form a catalyzed particle, and where the semiconductor sensitizer is comprised of a plurality of sensitizing particles, and where the semiconductor sensitizer contacts the wide band gap semiconductor material when at least one of the sensitizing particles contacts the catalyzed particle. 

The method ... where charge injection occurs from the semiconductor sensitizer to the wide band gap semiconductor material when the sensitized photocatalyst is exposed to the visible light illumination, and where the at least one of the sensitizing particles has a sensitizing particle diameter and the sensitizing particle diameter is selected based on a desired rate of charge injection, and where the at least one of the semiconductor particles has a semiconductor particle diameter and the semiconductor particle diameter is selected based on a desired rate of charge injection. 

The method ... where the at least one of the sensitizing particles has (sizes as specified and described).

Background and Field: One or more embodiments of the present invention relate to a sensitized photocatalyst for the photocatalytic reduction of CO2 under visible light illumination. The photosensitized catalyst is comprised of a wide band gap semiconductor material, a transition metal co-catalyst, and a semiconductor sensitizer. The semiconductor sensitizer and the wide band gap semiconductor material form a Type II band alignment, and the semiconductor sensitizer has a band gap such that visible light illumination produces photoexcitation in the semiconductor sensitizer. The wide band gap semiconductor material and the semiconductor sensitizer may be a plurality of particles, and the particle diameters may be selected to accomplish desired band widths and optimize charge injection under visible light illumination by utilizing quantum size effects. 

Wide band gap semiconductor materials are used as photocatalysts for degrading dilute pollutants in air and water as well as for converting CO2 and H2O gases to valuable products such as hydrocarbons and H2 through oxidation and reductions (redox) reactions.

A particular interest is the photocatalytic reduction of CO2 for the production of hydrocarbons and other valuable products using inexpensive and abundant semiconductors such as TiO2 and ZnO.

Such processes provide a potential means to reduce atmospheric CO2, as well as providing an attractive alternative to purely chemical means of converting CO2 to hydrocarbons.

However, a fundamental difficulty in the widespread use of many semiconductors such as TiO2 and ZnO is the requirement for ultraviolet light to drive photoexcitation.

Because ultraviolet light constitutes a relatively small fraction of the solar spectrum, use of these materials for photocatalytic reduction of CO2 has generally required illumination by an artificial UV light source in order to generate sufficient redox capacity. This is a parasitic load to the system as a whole, and negatively impacts the efficiency of the process. As a result, shifting the optical response of these inexpensive and abundant semiconductor materials to provide for photoexcitation in the visible spectral range while preserving the ability to facilitate specific redox reactions is the subject of significant effort. In particular, providing a methodology by which wide band gap semiconductor materials could be effectively utilized for the photocatalytic reduction of CO2 as a response to visible light illumination would be of enormous benefit. 

It would be advantageous to provide a sensitized semiconductor for the photocatalytic reduction of CO2 under visible light illumination, in order to provide a potential means to reduce atmospheric CO2 as well as provide a mechanism for converting CO2 to hydrocarbons through more efficient use of the solar spectrum. 

The use of dye sensitized platinized TiO2 has also been reported for the photocatalytic reduction of CO2 under illumination from a daylight lamp. ... Methane production is reported under illumination by the daylight lamp, however daylight lamps provide illumination in both the UV and visible spectrum, and it is unclear whether the CO2 reduction for the production of methane reported results from UV or visible light irradiation. Additionally, dyes are known to degrade under UV light, and sensitizer-semiconductor systems such as solar cells which incorporate dyes for use under a typical solar spectrum typically include UV barriers to prolong service life. It would be advantageous to provide a methodology whereby a sensitized wide band gap semiconductor could rely solely on visible light for the photocatalytic reduction of CO2 without possible reliance on included UV wavelengths and direct photoactivation of the semiconductor material, so that the sensitized semiconductor could definitively utilize the greater fraction of the solar spectrum represented by the visible light. It would be further advantageous if the sensitized semiconductor could tolerate the presence of UV light in the utilized spectrum without reliance on UV barriers for prolonged service life.

Photocatalytic conversion of CO2 and H2O to hydrocarbons has been reported using nitrogen-doped TiO2 exposed to outdoor sunlight. See Varghese, et al., "High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels", Nano. Lett. Vol. 9, No. 2 (2009).

(The full text of the above-cited reference is accessible via the link to it included in our report of:

Penn State Solar CO2 + H2O = Methane | Research & Development | News.)

In these materials, the dopants are located in the lattice of the semiconductor material interstitially and/or substitutionally, in order to produce a doped semiconductor material which directly responds to visible light illumination. It would be advantageous to eliminate the interstitial and/or substitutional doping requirement and provide a sensitized semiconductor for the photocatalytic reduction of CO2 under visible light, in order to simplify synthesis and take advantage of characteristics such as impact ionization which may arise. 

Doped semiconductor materials have also been utilized to produce composite semiconductor materials providing for oxidation and reduction reactions under visible light. See e.g., U.S. Pat. No. 7,169,733, issued to Wang et al, issued Jan. 30, 2007. Wang produces a composite material from two doped materials, both of which photoactivate under visible light activation. In this manner, the composite material is able to provide both a hole with high oxidation potential and an electron with high reducing potential. However, the composite material relies on doping as discussed above to provide visible light excitation of both materials involved, and does not rely on a sensitizer for the injection of electrons into a wide band gap semiconductor material. 

It would be advantageous to provide a method whereby the photoreduction of CO2 under visible light illumination could be accomplished using an abundant and inexpensive wide band gap semiconductor material, such as TiO.sub.2 or ZnO. It would further be advantageous if visible light response was provided via electron injection from a sensitizing material responsive to visible light, in order to avoid doping requirements or other mechanisms designed to drive the wide band gap semiconductor itself into visible light photoresponse. It would be further advantageous to provide for the photoreduction of CO2 in a manner that avoid sensitization using dyes, so that sensitizer degradation from the UV fraction of the solar spectrum can be avoided, and so that impact ionization and higher conversion efficiencies can potentially be realized. 

Accordingly, it is an object of this disclosure to provide a method of photocatalytically reducing CO2 under visible light excitation in the presence of hydrogen from a hydrogen source utilizing a sensitized photocatalyst comprised of a wide band gap semiconductor, a transition metal co-catalyst, and a semiconductor sensitizer. 

It is a further object of this disclosure to photocatalytically reduce CO2 under visible light excitation in the presence of hydrogen from a hydrogen source in order to produce product molecules such as hydrocarbons, H2, and others. 

It is a further object of this disclosure to control the composition of the product molecules based on the transition metal co-catalyst. 

It is a further object of this disclosure to provide a method of photocatalytically reducing CO2 utilizing a sensitized photocatalyst comprised of particles of the wide band gap semiconductor, the transition metal co-catalyst, and the semiconductor sensitizer, in order to optimize charge injection and band alignments under visible light illumination. 

It is a further object of this disclosure to provide a method of photocatalytically reducing CO2 under visible light illumination utilizing a sensitized photocatalyst in a CO2 and H2O environment. 

One or more embodiments of the present invention relates to a method for photocatalytically reducing CO2 in the presence of hydrogen using a sensitized photocatalyst. 

(Again, plain old water, H2O, serves as the source of the needed "hydrogen".)

The band gap of the semiconductor sensitizer and/or the wide band gap semiconductor material may be altered to form more advantageous Type II band alignments and photoexcitation under visible light using the quantum size effect. In a particular embodiment, the semiconductor sensitizer has diameter less than 50 nm and the wide band gap semiconductor material has a diameter less than 100 nm. In certain embodiments, the semiconductor sensitizer, the wide band gap semiconductor material, and the transition metal co-catalyst may be a plurality of particles, where individual particles in each plurality combine to produce the sensitized photocatalyst. 

The method may be utilized to produce product molecules following the photocatalytic reduction of CO2 with visible light illumination. In a particular embodiment, the product molecules are comprised of hydrocarbons, such as CH4 (Methane), CH3OH (Methanol), and others. The method may be utilized for production of additional product molecules, such as CO and H2".

--------------------------------- 

Note, in addition to making substitute natural gas Methane and fuel alcohol Methanol out of Carbon Dioxide, as harvested from whatever handy source, and Water, in a process powered by solar light energy, this United States Department of Energy artificial photosynthesis technology can also convert CO2 and H2O into Carbon Monoxide, "CO", and Hydrogen, "H2", which, together, comprise a hydrocarbon synthesis gas, or syngas, that, as seen in:

Bayer Improves Fischer-Tropsch Hydrocarbon Synthesis | Research & Development | News; concerning: "United States Patent 8,557,880 - Multi-stage Adiabatic Method for Performing the Fischer-Tropsch Synthesis; 2013; Inventors: Ralph Schellen, et. al., Germany and Texas; Assignee: Bayer Intellectual Property GmbH, Germany; Abstract: The present invention relates to a multistage adiabatic process for performing the Fischer-Tropsch synthesis at low temperatures, in which the synthesis is performed in 5 to 40 series-connected reaction zones under adiabatic conditions. Claims: Process for preparing liquid hydrocarbons from the process gases carbon monoxide and hydrogen";

can, in technologies that are being made increasingly sophisticated, effective and efficient, be catalytically, chemically condensed into a full range of hydrocarbon fuels and chemicals. Moreover, as seen for just one example in our report of:

USDOE Hires Nevada to Photo-Convert CO2 into Fuels | Research & Development | News; concerning: "United States Patent 8,709,304 - Hydrothermal Synthesis of Nanocubes of Sillenite Type Compounds for Photovoltaic Applications and Solar Energy Conversion of Carbon Dioxide to Fuels; 2014; Inventors: Vaidyanathan Subramanian and Sankaran Murugesan, NV and TX; Assignee: Board of Regents of the Nevada System of Higher Education, on behalf of the University of Nevada; Abstract: The present invention relates to formation of nanocubes of sillenite type compounds (as described) useful in solar energy conversion, environmental remediation, and/or energy storage, for example. ... Government Interests: This invention was made with government support under Grant Number DE-EE0000272, awarded by the U.S. Department of Energy; the United States federal government, therefore, has certain rights in the invention. Background and Field: The present invention relates to formation of nanostructures of sillenite type compounds, such as bismuth titanate nanocubes, via a hydrothermal synthesis process, with the resulting compounds being useful in photovoltaic applications and solar energy conversion for fuel production, for example. (Extensively) studied and used as photocatalysts to harvest solar energy are nanoparticles of titanium dioxide (TiO2). TiO2 nanoparticles have shown very good stability over a wide pH range and are compatible with other materials, environmentally friendly, inexpensive, and non-toxic. However, interfacial grain boundaries in films prepared from TiO2 nanoparticles have been known to contribute to reducing charge transport by functioning as recombination centers. Recently, the synthesis of TiO2 specifically in the form of hollow nanotubes by anodization of a titanium foil has been demonstrated ... . Such nanotubes are generally produced by anodic oxidation in various electrolytes. Notably, the absence of grain boundaries in the resulting nanotubes favors efficient transport of photogenerated electrons. And since the TiO2 nanotubes are electrically well connected and anchored firmly on an underlying titanium substrate as a raw material for preparing sillenite type compounds, the material is desirable in energy conversion (photovoltaics), environmental remediation (photodegradation), or solar fuel production (CO2 conversion to value added hydrocarbon chemicals such as alcohols, acids, and ethers), for example. (It) would be beneficial to provide a simple synthesis process for preparing nanostructures of sillenite type compounds, including Bi12TiO20 nanotubes, from corresponding oxides, e.g., TiO2, which overcomes the (known) drawbacks (of establised art), with the resulting compounds being desirable for use in photovoltaic applications and for solar energy conversion CO2 to fuels, for example";

the process of our subject, "United States Patent 8,986,511 - Visible Light Photoreduction of CO2 Using Heterostructured Catalysts", is, clearly, just one component of what is a complete technological system "for solar energy conversion CO2 to fuels" that has been, and is being, developed by our United States Department of Energy and their contractors.

The implications for the entire United States of America, and, especially, for United States Coal Country, in terms of jobs, economy and security, should, we would think, be obvious. Those genuinely concerned about the conjectured environmental effects of rising amounts of CO2 in the atmosphere should be able to find at least certain aspects of this technology worthy of promotion, as well.

In sum, nearly all United States citizens could find some benefit in this technology for utilizing Carbon Dioxide as a raw material, in a solar-powered process that generates as products hydrocarbon fuels and chemicals, hydrocarbons that we might otherwise have to import from OPEC or put our environment at risk by drilling into and fracking the abyssal, radioactive shale beds to extract.

And, all United States citizens actually own the technology embodied in and disclosed by our subject, "United States Patent 8,986,511 - Visible Light Photoreduction of CO2 Using Heterostructured Catalysts".

Isn't it time all United States citizens began demanding of their employees - their federal government elected office holders - that they be told all about it?


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