Patent Publication Number: US-2021171343-A1

Title: Two-step thermochemical reactor

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application 62/946,006, filed Dec. 10, 2019 titled “Two-Step Thermochemical Reactor,” the entirety of the disclosure of which is hereby incorporated by this reference. 
    
    
     TECHNICAL FIELD 
     Aspects of this document relate generally to thermochemical reactors. 
     BACKGROUND 
     Thermochemical reactors can provide an effective means for water splitting and carbon dioxide splitting. These reactors are able to produce energized chemicals (e.g. H 2  and CO), which can subsequently be used in other chemical reactions (e.g. reductants, fuels etc.) or from which other chemicals can be made (e.g. hydrocarbon fuels, etc.). These reactors employ thermochemical cycles, which combine heat sources with chemical reactions to split bonds and generate a desired product stream. 
     In order for thermochemical reactors to be economically competitive with other competing technologies, they must be efficient while remaining sufficiently inexpensive to manufacture and operate. In water splitting, the main competing technologies are steam-methane reforming (which is not renewable) and electrolysis. The advantages thermochemical reactors may provide over electrolysis are a potentially much lower capital cost and improved robustness to impurities in the feedstock water. In CO2 splitting, thermochemical reactors are the most advanced technology, and have found application in CO2 re-utilization. 
     One of the ways that the operating expense of thermochemical reactors is kept down is through the use of renewable energy to provide the necessary heat. In some cases, conventional thermochemical reactors have harnessed direct, concentrated solar flux to provide the needed heat for splitting. However, such implementations are accompanied by a number of difficulties. Like other solar technologies, the use of concentrated solar flux is subject to the availability of direct exposure to sunlight, making production subject to a number of factors including weather conditions and the time of day. Furthermore, since thermochemical reactors need to carry out various steps at different temperatures, efficient use of concentrated solar flux requires the use of multiple chambers and moving reactive materials (e.g. metal oxide particles, etc.) rather than repeatedly cooling down the solar heated chamber. The incorporation of moving parts increases the cost of conventional thermochemical reactors, as well as the cost of maintenance. 
     SUMMARY 
     According to one aspect, a thermochemical reactor includes a housing having a thermal insulation, and a reactor cavity formed within, and surrounded by, the thermal insulation. The reactor cavity includes a plurality of unit cells, each unit cell of the plurality of unit cells having an electric heat source that is an incandescent heat lamp capable of reaching a first temperature of greater than 1600° C., and a reactive material including cerium oxide. The reactor also includes a feedstock inlet in fluid communication with the reactor cavity and coupled to a feedstock gas source supplying a feedstock gas, and a product outlet in fluid communication with the reactor cavity. The thermochemical reactor also includes a reducing configuration and a splitting configuration. The reducing configuration includes the inlet being closed and the electric heat source of each of the at least one unit cell being driven to thermally reduce the reactive material at the first temperature, releasing oxygen from the reactive material into the reactor cavity. The splitting configuration includes the reactive material of each of the at least one unit cell being maintained at a second temperature by the electric heat source, the second temperature lower than the first temperature, the feedstock inlet being open and introducing feedstock gas into the reactor cavity to react with and reoxidize the reactive material, the feedstock gas splitting into a product gas received from the reactor cavity through the product outlet, the product outlet being open. The feedstock gas includes at least one of steam and carbon dioxide, and wherein the product gas comprises at least one of hydrogen and carbon monoxide. 
     Particular embodiments may comprise one or more of the following features. For each unit cell in the plurality of unit cells, the reactive material may encircle the electric heat element. The reducing configuration may further include the reactor cavity being evacuated and maintained at a pressure that may be at least two orders of magnitude below atmospheric pressure to remove at least the oxygen released by the reactive material from the reactor cavity. For each of the plurality of unit cells, the reactive material may be stationary with respect to the electric heat source. 
     According to another aspect of the disclosure, a thermochemical reactor includes a housing comprising a thermal insulation, and a reactor cavity formed within, and surrounded by, the thermal insulation. The reactor cavity includes at least one unit cell, each unit cell of the at least one unit cell including an electric heat source capable of reaching a first temperature, and a reactive material. The reactor also includes a feedstock inlet in fluid communication with the reactor cavity and coupled to a feedstock gas source supplying a feedstock gas, and a product outlet in fluid communication with the reactor cavity. The thermochemical reactor also includes a reducing configuration and a splitting configuration. The reducing configuration includes the inlet being closed and the electric heat source of each of the at least one unit cell being driven to thermally reduce the reactive material at the first temperature, releasing oxygen from the reactive material into the reactor cavity. The splitting configuration includes the reactive material of each of the at least one unit cell being maintained at a second temperature by the electric heat source, the second temperature lower than the first temperature, the feedstock inlet being open and introducing feedstock gas into the reactor cavity to react with and reoxidize the reactive material, the feedstock gas splitting into a product gas received from the reactor cavity through the product outlet, the product outlet being open. 
     Particular embodiments may comprise one or more of the following features. The reactive material may include a metal oxide. The metal oxide may be cerium oxide. The feedstock gas may include at least one of steam and carbon dioxide, and the product gas may include at least one of hydrogen and carbon monoxide. The electric heat source may be an incandescent heat lamp. The first temperature may be above 1600° C. At least one of the product gas and the oxygen is removed from the reactor cavity using a sweep gas. The reducing configuration further comprises the reactor cavity being evacuated and maintained at a pressure at least two orders of magnitude below atmospheric pressure to remove at least the oxygen released by the reactive material from the reactor cavity. 
     According to yet another aspect of the disclosure, a method for a thermochemical reactor cycle includes heating a reactive material to a first temperature with an electric heat source to thermally reduce the reactive material and release oxygen. The reactive material and the electric heat source are enclosed within a reactor cavity formed within, and surrounded by, thermal insulation. The method also includes removing the released oxygen from the reactor cavity, and cooling the reactive material to a second temperature maintained by the electric heat source, the second temperature being lower than the first temperature. The method includes reoxidizing the reactive material by introducing a feedstock gas into the reactor cavity, the feedstock gas reacting with the reactive material and splitting into a product gas, and removing the product gas from the reactor cavity. The reactive material is stationary with respect to the electric heat source. The feedstock gas includes at least one of steam and carbon dioxide, and the product gas includes at least one of hydrogen and carbon monoxide. 
     Particular embodiments may comprise one or more of the following features. The electric heat source may be an incandescent heat lamp. The first temperature may be above 1600° C. The method may further include removing at least one of the product gas and the oxygen from the reactor cavity using a sweep gas. Removing the released oxygen from the reactor cavity may include evacuating the reactor cavity, removing the oxygen while maintaining the reactor cavity at a pressure at least two orders of magnitude below atmospheric pressure. The reactive material may encircle the electric heat element. 
     Aspects and applications of the disclosure presented here are described below in the drawings and detailed description. Unless specifically noted, it is intended that the words and phrases in the specification and the claims be given their plain, ordinary, and accustomed meaning to those of ordinary skill in the applicable arts. The inventors are fully aware that they can be their own lexicographers if desired. The inventors expressly elect, as their own lexicographers, to use only the plain and ordinary meaning of terms in the specification and claims unless they clearly state otherwise and then further, expressly set forth the “special” definition of that term and explain how it differs from the plain and ordinary meaning. Absent such clear statements of intent to apply a “special” definition, it is the inventors&#39; intent and desire that the simple, plain and ordinary meaning to the terms be applied to the interpretation of the specification and claims. 
     The inventors are also aware of the normal precepts of English grammar. Thus, if a noun, term, or phrase is intended to be further characterized, specified, or narrowed in some way, then such noun, term, or phrase will expressly include additional adjectives, descriptive terms, or other modifiers in accordance with the normal precepts of English grammar. Absent the use of such adjectives, descriptive terms, or modifiers, it is the intent that such nouns, terms, or phrases be given their plain, and ordinary English meaning to those skilled in the applicable arts as set forth above. 
     Further, the inventors are fully informed of the standards and application of the special provisions of 35 U.S.C. § 112(f). Thus, the use of the words “function,” “means” or “step” in the Detailed Description or Description of the Drawings or claims is not intended to somehow indicate a desire to invoke the special provisions of 35 U.S.C. § 112(f), to define the invention. To the contrary, if the provisions of 35 U.S.C. § 112(f) are sought to be invoked to define the inventions, the claims will specifically and expressly state the exact phrases “means for” or “step for”, and will also recite the word “function” (i.e., will state “means for performing the function of [insert function]”), without also reciting in such phrases any structure, material or act in support of the function. Thus, even when the claims recite a “means for performing the function of . . . ” or “step for performing the function of . . . ,” if the claims also recite any structure, material or acts in support of that means or step, or that perform the recited function, then it is the clear intention of the inventors not to invoke the provisions of 35 U.S.C. § 112(f). Moreover, even if the provisions of 35 U. S.C. § 112(f) are invoked to define the claimed aspects, it is intended that these aspects not be limited only to the specific structure, material or acts that are described in the preferred embodiments, but in addition, include any and all structures, materials or acts that perform the claimed function as described in alternative embodiments or forms of the disclosure, or that are well known present or later-developed, equivalent structures, material or acts for performing the claimed function. 
     The foregoing and other aspects, features, and advantages will be apparent to those artisans of ordinary skill in the art from the DESCRIPTION and DRAWINGS, and from the CLAIMS. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will hereinafter be described in conjunction with the appended drawings, where like designations denote like elements, and: 
         FIGS. 1A and 1B  are internal schematic views of a two-step thermochemical reactor in reducing and splitting configurations, respectively; and 
         FIG. 2  is an internal schematic view of another embodiment of a two-step thermochemical reactor in a reducing configuration. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure, its aspects and implementations, are not limited to the specific material types, components, methods, or other examples disclosed herein. Many additional material types, components, methods, and procedures known in the art are contemplated for use with particular implementations from this disclosure. Accordingly, for example, although particular implementations are disclosed, such implementations and implementing components may comprise any components, models, types, materials, versions, quantities, and/or the like as is known in the art for such systems and implementing components, consistent with the intended operation. 
     The word “exemplary,” “example,” or various forms thereof are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” or as an “example” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Furthermore, examples are provided solely for purposes of clarity and understanding and are not meant to limit or restrict the disclosed subject matter or relevant portions of this disclosure in any manner. It is to be appreciated that a myriad of additional or alternate examples of varying scope could have been presented, but have been omitted for purposes of brevity. 
     While this disclosure includes a number of embodiments in many different forms, there is shown in the drawings and will herein be described in detail particular embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the disclosed methods and systems, and is not intended to limit the broad aspect of the disclosed concepts to the embodiments illustrated. 
     Thermochemical reactors can provide an effective means for water splitting and carbon dioxide splitting. These reactors are able to produce energized chemicals (e.g. H 2  and CO), which can subsequently be used in other chemical reactions (e.g. reductants, fuels etc.) or from which other chemicals can be made (e.g. hydrocarbon fuels, etc.). These reactors employ thermochemical cycles, which combine heat sources with chemical reactions to split bonds and generate a desired product stream. 
     In order for thermochemical reactors to be economically competitive with other competing technologies, they must be efficient while remaining sufficiently inexpensive to manufacture and operate. In water splitting, the main competing technologies are steam-methane reforming (which is not renewable) and electrolysis. The advantages thermochemical reactors may provide over electrolysis are a potentially much lower capital cost and improved robustness to impurities in the feedstock water. In CO 2  splitting, thermochemical reactors are the most advanced technology, and have found application in CO 2  re-utilization. 
     One of the ways that the operating expense of thermochemical reactors is kept down is through the use of renewable energy to provide the necessary heat. In some cases, conventional thermochemical reactors have harnessed direct, concentrated solar flux to provide the needed heat for splitting. However, such implementations are accompanied by a number of difficulties. Like other solar technologies, the use of concentrated solar flux is subject to the availability of direct exposure to sunlight, making production subject to a number of factors including weather conditions and the time of day. Furthermore, since thermochemical reactors need to carry out various steps at different temperatures, efficient use of concentrated solar flux requires the use of multiple chambers and moving reactive materials (e.g. metal oxide particles, etc.) rather than repeatedly cooling down the solar heated chamber. The incorporation of moving parts increases the cost of conventional thermochemical reactors, as well as the cost of maintenance. 
     Contemplated herein is an electrically powered two-step thermochemical reactor for water and CO 2  splitting. Unlike conventional thermochemical reactors, the reactors and methods contemplated herein are able to harness electrical heating in an economical way. Expense of operation and manufacture are kept down through the use of a modular design, inexpensive materials, and adaptability to work in conjunction with various renewable energy sources. 
     Compared to existing thermochemical reactor designs, the reactors contemplated herein are able to operate at higher temperatures with greater efficiency. The temperatures used for thermal reduction in conventional reactors that use concentrated solar flux are limited due to the unavoidable radiation losses through the reactor aperture. Operating at 1700° C., for example, would be extremely inefficient and not economically practical in a conventional thermochemical reactor. According to various embodiments, the reactors contemplated herein are able to thermally reduce a reactive material at temperatures exceeding 1700° C. The use of electric heating lamps means the reactor can afford to go to temperatures that are practically unobtainable with concentrated solar, and even if they could be reached, the losses through the aperture would be massive. These higher temperatures mean the reactor contemplated herein can provide a greater power density and higher efficiency than conventional reactors. 
     According to various embodiments, the reactor contemplated herein is able to outperform conventional reactors, and can do so without having any moving parts. The simple design and lack of moving parts results in a robust reactor that is compact, which further reduces unit cost and heat losses. The lack of moving parts also greatly reduces the cost of operation and maintenance, while increasing the lifespan of the reactor. Additionally, the thermochemical reactors contemplated herein are agnostic with respect to the source of electrical power, and are not reliant on the availability of direct solar flux. 
     An additional advantage provided by the lack of moving parts is that the contemplated thermochemical reactor may be implemented in a wide range of sizes, including sizes much smaller than possible with conventional reactor designs (e.g. handheld size, desktop sized, etc.). Additionally, the contemplated reactor is able to operate in a wider range of circumstances than conventional reactors. For example, the contemplated thermochemical reactor is able to operate using impure input water (e.g. ocean water, ground well water, etc.) which is subsequently turned into steam. Some embodiments of the contemplated reactor may be configured to be very rugged and easily adapted for use in less than ideal conditions. 
     The thermochemical reactor contemplated herein is less expensive when compared to conventional thermochemical reactors. In comparison with an electrolyzer, which may make more efficient use of electricity, the contemplated reactor is vastly less expensive. As the cost of electricity coming from renewable sources continues to drop, the advantage of the electrolyzer&#39;s efficient use of electricity will diminish even further. 
     Another advantage the thermochemical reactors contemplated herein have over conventional thermochemical reactors includes being compatible with a wider range of reactive materials. While the following discussion of various embodiments will be focused on using a metal oxide as the reactive material, specifically cerium, it should be noted that other metal oxides, such as iron oxide and zinc oxide, and many other oxides and reactive materials may be substituted. Those skilled in the art will recognize that changing the reactive material may also open up applications for the thermal reduction of feedstocks other than water and carbon dioxide, resulting in different products. 
       FIGS. 1A and 1B  show internal schematic views of a non-limiting example of a thermochemical reactor  100  with a two-step cycle for water or carbon dioxide splitting. Specifically,  FIG. 1A  shows a thermochemical reactor  100  in a reducing configuration  122 , and  FIG. 1B  shows the reactor  100  in a splitting configuration  132 . These configurations will be discussed in greater detail below. 
     As shown, the reactor  100  comprises a housing  102  comprising a thermal insulation  104 . The reactor  100  has a modular design, consisting of one or more unit cells  108  within a reactor cavity  106  inside the housing  102 . According to various embodiments, the reactor cavity  106  is formed within, and surrounded by, the thermal insulation  104 . Each unit cell  108  comprises an electric heat source  110  and a reactive material  114  that will be reduced and reoxidized repeatedly in the thermochemical cycle. According to various embodiments, the reactor  100  also comprises a feedstock inlet  118  and at least one product outlet  120 , all in fluid communication with the reactor cavity  106 . The feedstock inlet  118  is also in fluid communication with a feedstock gas source  136 , as will be discussed below, with respect to  FIG. 1B . 
     Not shown in  FIG. 1  are auxiliary components which may include, but are not limited to, additional feedstock sources, sweep gases, vacuum systems, gas preheating systems, heat recovery systems and mechanisms, product separation systems, process control systems, electrical power sources, and the like. 
     The housing  102  is thermally insulated, improving the energy efficiency of the reactor  100 . In some embodiments, the thermal insulation  104  may comprise insulating materials. In other embodiments, the housing  102  may make use of evacuated, insulating walls. In still other embodiments, the housing  102  may be insulated using any other method known in the art. In some embodiments, the housing  102  may be vacuum tight, while in others the housing  102  may be configured to seal sufficiently to maintain a desired pressure/oxygen partial pressure, which in many embodiments is much lower than atmospheric pressures. 
     Advantageous over conventional thermochemical reactors heated with concentrated solar flux, the reactor cavity  106  of the reactor  100  does not have an aperture to let in solar flux. Losses through an aperture are difficult to mitigate; that difficulty rapidly increases with temperature. In the contemplated reactor  100 , heat loss may be reduced with use of additional or more efficient thermal insulation  104 . Not having to deal with losses through an aperture allows the reactor  100  to operate at temperatures practically impossible to employ with concentrated solar flux in conventional reactors. 
     As shown, each unit cell  108  comprises a reactive material  114 . According to various embodiments, the reactive material  114  is a metal oxide  116 . Advantageous over conventional thermochemical reactors, the reactor  100  contemplated herein is able to operate with a wide range of reactive MOx materials. As a specific, non-limiting example, in one embodiment the reactive material  114  is cerium oxide. It is important to note that while the following discussion will be in the context of embodiments of the reactor  100  making use of the cerium(IV) oxide-cerium(III) oxide thermochemical cycle, other embodiments may be adapted for use with other metal oxides  116  or other reactive material  114  including, but not limited to, iron oxide and zinc oxide. 
     Each unit cell  108  also comprises an electric heat source  110 . Using electric input enables a simple design that is agnostic to the source of power, making it compatible with numerous renewable sources of electricity including, but not limited to, solar, hydroelectric, wind powered, thermoelectric, and the like. According to various embodiments, this electric heat source  110  is a heat lamp, which transfers energy to the reactive material  114  and reactor cavity  106  through electromagnetic radiation. Conventional electric heat lamps able to reach temperatures over 1450° C., the threshold for this thermochemical cycle, tend to be expensive and very slow. Carrying out the thermochemical cycle within a single reactor cavity  106  and eliminating the need for moving parts means the temperature will need to cycle within that cavity  106 . A slow heater will reduce the overall efficiency of the reactor  100 . Conventional incandescent heat lamps are able to ramp up and down in temperature very quickly, but have difficulty reaching the desired temperature range. 
     According to various embodiments, the electric heat source  110  may be a fast-cycling, high temperature incandescent heat lamp  112  comprising a filament housed in an envelope composed of refractory material. Able to ramp up and down in temperature, while also reaching temperatures as high as 1700° C., or higher, these incandescent heat lamps  112  result in shorter cycle times than existing reactor designs, leading to higher productivities per unit MO x , and higher power densities. Higher efficiency and power density are also obtained from the use of more effective heaters that can reach higher reaction temperatures within the reactor cavity  106 . 
     As shown, in some embodiments, the reactive material  114  encircles the electric heat source  110 , meaning the reactive material  114  is stationary with respect to at least the electric heat source  110 , and in many embodiments the reactor  100  as a whole. The ability to place the heat source inside the reactor cavity  106 , rather than utilizing an external heat source such as concentrated solar flux, permits a much greater degree of freedom in choosing a geometry or structure for the reactive material  114 . In the temperature ranges and reactions contemplated in the non-limiting example of cerium oxide discussed above, the CeO 2  reduction operates predominantly within a surface-controlled regime, meaning greater efficiencies can be achieved by increasing the exposed surface area. Conventional reactors often make use of powdered or particularized metal oxides to maximize surface area and facilitate the transit necessitated by the use of solar flux. At higher temperatures, sintering may become a problem, yet another reason conventional reactors are temperature (and thus, efficiency) limited. 
     According to various embodiments, the reactive material  114  of each unit cell  108  may be a solid structure having a surface area-maximizing geometry, such as being porous. Placing the heat source  110  within the reactive material  114  of each unit cell  108  permits a more efficient heating of the material  114 . Other embodiments may place the heater for each unit cell  108  in a different relative position, or may share heaters between more than one unit cell. 
     In some embodiments, the electric heat source  110  may be entirely contained within the reactor cavity  106 . In other embodiments, a portion of the electric heat source  110  may extend into, or even through, the thermal insulation  104  of the housing  102 . For example, as shown in the Figures, in some embodiments, the ends of the heater lamp may be more sensitive to heat than the middle part, and may be protected from damage by positioning the more sensitive ends in the thermal insulation  104 . In some embodiments, single ended heat sources  110  may be used, as is known in the art. 
     As mentioned above, according to various embodiments, the thermochemical reactor  100  comprises a reducing configuration  122 , shown in  FIG. 1A , and a splitting configuration  132 , shown in  FIG. 1B . These two configurations represent the two stages of the two-step thermochemical cycle contemplated herein. 
     As shown, the reducing configuration  122  comprises the feedstock inlet  118  being closed and the electric heat source  110  of each unit cell  108  being driven to thermally reduce the reactive material  114 , heating the material  114  to a first temperature  124 , releasing oxygen  128  from the reactive material  114  into the reactor cavity  106 . 
     Additionally, the splitting configuration  132  comprises the reactive material  114  of each unit cell  108  being maintained at a second temperature  134  by the electric heat source  110 . The second temperature  134  is lower than the first temperature  124 . Also, the feedstock inlet  118  is opened to introduce feedstock gas  138  into the reactor cavity  106  to react with and reoxidize the reactive material  114 . This results in the splitting of the feedstock gas  138  into a product gas  144 , which is received from the reactor cavity  106  through an open product outlet  120 . 
     The cycle contemplated herein may be broken down further. The first step of the contemplated two-step thermochemical cycle for water and/or carbon dioxide splitting begins with heating the reactive material  114  of the unit cells  108  to a first temperature  124 . See ‘circle 1’. This heat results in the thermal reduction of the reactive material  114 . In one embodiment, the first temperature may be at least 1500° C., in another embodiment, the first temperature may be at least 1600° C., and in still another embodiment, the first temperature may be at least 1700° C. In other embodiments, the first temperature may be higher than 1700° C. 
     According to various embodiments, this heating process may begin with an evacuated or partially evacuated reactor cavity  106 . The unit cells are heated to a high temperature within the housing. This removes some of the oxygen  128  from the reactive material  114 , typically at low oxygen partial pressure, relative to ambient. As a specific example, in one embodiment, the heating of the reactive material may introduce to the reactor cavity  106  a low oxygen partial pressure no greater than 100 Pa. The oxygen  128  freed from the reactive material  114  may continue to be removed from the reactor cavity  106  through an outlet (e.g. a product outlet  120 , etc.) as the internal pressure, or just the oxygen partial pressure in some embodiments, is maintained at a pressure  130  that is at least two orders of magnitude below atmospheric levels. In other embodiments, the pressure  130  may be at least three orders of magnitude below atmospheric pressure. See ‘circle 2’. The removal of the oxygen gas  128  from the reactor cavity  106  prepares the reactor  100  for the second step, which involves placing the reactor  100  in the splitting configuration  132 , shown in  FIG. 1B . In other embodiments, the oxygen  128  may be removed from the reactor cavity  106  using an inert sweep gas  150 , as shown in  FIG. 2 . In some embodiments, steam may be used as a sweep gas. For example, in one embodiment, a continuous stream of steam may serve, at high temperatures, as a reductant, and at lower temperatures, as an oxidizer, all the while moving the gaseous products of these reactions out of the reactor cavity. 
     Transitioning into the splitting configuration  132  requires a reduction in the energy sent to the electric heat sources  110 , allowing the reactive material  114  to cool down to the second temperature  134 . See ‘circle 3’. While this is being done, the inlets and outlets may be closed, preventing any gas exchange. According to various embodiments, the second temperature  134  may be roughly 1000° C. for cerium oxide. Those skilled in the art will recognize that the first and second temperatures may change, depending on the reactive material  114  being used. 
     Once the second temperature  130  has been achieved, and is being maintained by the electric heat sources  110 , a feedstock gas  138  is introduced to the reactor cavity  106  through the feedstock inlet  118 . See ‘circle 4’. The feedstock gas  138  reoxidizes the reactive material  114 . The feedstock gas  138  is introduced to the cavity  106  at a lower temperature and/or a higher pressure than exists in the cavity  106  when in the reducing configuration  122 , according to various embodiments. According to various embodiments, the feedstock gas  138  is at least one of steam  140  and carbon dioxide  142 , as shown. Other feedstock gases  138  may be used in other embodiments, with appropriate reactive materials  114 , as well as first and second temperatures. 
     The introduction of the feedstock gas  138  to the partially reduced reactive material  114  results in the removal of oxygen  128  from the feedstock  138 , effectively splitting it to yield hydrogen  146  and/or carbon monoxide  148 , as shown. In our specific, non-limiting example, this takes at least some of the partially reduced cerium oxide to back to cerium(IV) oxide, in preparation for the next cycle. 
     Finally, the results of the splitting are removed from the cavity  106  through a product outlet  120 . See ‘circle 5’. Again, in our non-limiting example of the application of water (i.e. steam) and carbon dioxide as feedstock gases  138  will result in a mixture of hydrogen  146  and carbon monoxide  148 , or syngas. Typically, there is also residual steam  140  and carbon dioxide  142  recovered through the product outlet  120 , as well. These gases may then be processed for further use, whether that be reuse in the reactor  100  or applied to another process. 
     Where the above examples, embodiments and implementations reference examples, it should be understood by those of ordinary skill in the art that other reactive materials, feedstock gases, and product gases could be intermixed or substituted with those provided. In places where the description above refers to particular embodiments of a two-step thermochemical reactor, it should be readily apparent that a number of modifications may be made without departing from the spirit thereof and that these embodiments and implementations may be applied to other reactor technologies as well. Accordingly, the disclosed subject matter is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the disclosure and the knowledge of one of ordinary skill in the art.