Iron based catalyst for co2 hydrogenation

Abstract

A novel multifunctional iron catalyst composition suitable for the conversion of CO2 to sustainable aviation fuel. The iron catalyst is doped with copper and potassium. Also provided is a method of activating said iron catalyst composition. The process comprises exposing the iron catalyst composition to a chemical agent and heat. A method is also provided for facilitating a CO2 hydrogenation reaction suitable for the conversion of CO2 to sustainable aviation fuel. Hydrogen and carbon dioxide are provided at a mole ratio of from 0.1-9 to a reaction catalyzed by the present iron catalyst, and C8-C18 hydrocarbons are recovered as products of the reaction.

Description

IRON BASED CATALYST FOR CO2 HYDROGENATIONCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial No. 63 / 639,246 filed April 26, 2024, the complete disclosure of which is incorporated herein by reference in its entirety.BACKGROUND

[0002] The emission of huge amounts of CO2 to the atmosphere (33 BT in 2021) has caused global warming and sea level rise. Therefore, increasing attention is being paid to the conversion of CO2 to liquid transportation fuels through Fischer-Tropsch synthesis (FTS) technology. FTS technology is well-established as a viable carbon utilization technology to reduce carbon emission with the goal of achieving net zero carbon emissions by 2050.

[0003] Jet fuel is a kind of liquid transportation fuel, containing Cs-Cis hydrocarbons. Global jet fuel consumption is expected to increase at a faster rate than any other liquid transportation fuel through 2050. In the USA alone, jet fuel consumption was 18.3 billion gallons (BG) in 2018. Despite falling to 13.8 BG in 2021, due to the global pandemic, it is estimated to increase at 1.1% every year till 2040. Therefore, the increase in jet fuel consumption requires additional technologies to make up for the energy difference while also reducing carbon emissions. The conversion of waste CO2 to jet fuel is apparently one of the most effective and practical ways to reuse carbon and close the energy gap in the next three decades.

[0004] The hydrocarbon fuels produced via CO2 hydrogenation can be carbon neutral. It is foreseen that as carbon capture technology matures, including the capture of CO2 from power plants and air, the conversion of CO2 to aviation fuel technology will become increasingly important. This is especially true as fossil fuel will continue to be dominant before 2050. Moreover, this conversion will become increasingly attractive as green hydrogen technology matures (cost will be dropped to 1 $Zkg) and become more affordable. Companies such as power plants, steel plants, cement factories, coal companies, Biomass companies, FedEx, airlines, ground transportation, which are primarily responsible for CO2 emission, stand to benefit from this potential fuel source. Thus, the conversion of CO2 into fuel presents significant economic and environmentalbenefits. Moreover, if adopted by industrial plants, it offers substantial fossil energy savings.

[0005] Extensive conversion of CO2 to liquid fuels, including jet fuels, via FTS has been performed. US-DOE and industrial sectors along with national industrial parties have invested billions of dollars over many decades to develop FTS technology, many coal to liquid (CTL), gas to liquid (GTL) and biomass to liquid (BTL) pilot plants and commercial plants have been commissioned in the USA and in other places in the world in the past decades. These existing CTL, GTL and BTL technologies and infrastructures are mature, and fully or partly support the catalytic CO2 hydrogenation process. Various fuels or chemicals produced from catalytic CO2 conversion are of ultra clean characteristics, and they can be used in various vehicles (trucks, airplanes and ships), as such carbon is recycled, and carbon emission is reduced. Furthermore, unstable oil prices provide additional incentive to commercialize CO2 to SAF technology.

[0006] Iron based catalysts have been widely used for CO2 hydrogenation because of the availability of iron, its low cost and good activity for the reaction. Iron catalysts are known to catalyze CO2 hydrogenation through two steps, which can involve CO2 to CO through a reverse water gas shift (RWGS) reaction followed by the conversion of syngas (CO and H2 mixture) to hydrocarbons via a FTS reaction. However, there are two serious challenges related to using iron catalysts for CO2 hydrogenation. Specifically, iron-based catalysts show low activity, limited by their thermal equilibrium conversion (~ 28% at 300°C) and low selectivity to jet-fuel range hydrocarbons Cs-Cis (~42%) limited by the Anderson Schulz Flory (ASF) distribution. Many studies have been carried out to resolve these problems by developing various catalysts such as supported and precipitated iron, cobalt, and nickel catalysts. Those studies mainly focused on the catalyst preparation using different techniques and formulations, for example the preparation of FeMnK catalyst by OCM (organic combustion method), and formulation as Fe-molecular sieve and FeCo bimetallic carbide catalysts.

[0007] On the contrary there are only a few studies which systematically investigated methods / approaches for activating iron catalysts and optimizing the process conditions for CO2 hydrogenation. This is likely associated with a misunderstanding that CO2 hydrogenation on iron catalyst is similar to CO hydrogenation via FTS, in which activation by CO and process optimization have been well established. CO2 hydrogenation on an Fe catalyst is very different from CO hydrogenation for both theactivation scheme and process conditions, which can significantly affect Fe catalyst activity and selectivity to jet fuel range hydrocarbons.

[0008] In view of the foregoing, the industry would be greatly served by a novel, multifunctional catalyst composition, activation scheme, and hydrogenation process for the efficient conversion of CO2 into a sustainable aviation fuel.SUMMARY

[0009] Against this backdrop, the present invention was developed. In one embodiment, a novel multifunctional doped iron catalyst composition is provided which is suitable for the conversion of CO2 to sustainable aviation fuel. The iron catalyst is doped with copper and potassium.

[0010] In one embodiment, a method of activating the iron catalyst composition is provided. The process comprises exposing the iron catalyst composition to a chemical agent comprising hydrogen and heat.

[0011] According to another embodiment, a method is provided for facilitating a CO2 hydrogenation reaction suitable for the conversion of CO2 to a sustainable aviation fuel. Hydrogen and carbon dioxide are provided at a mole ratio of from 0.1-9 to a reactor containing the present iron catalyst. Cs-Cis hydrocarbons are recovered as products of the reaction.

[0012] Among other factors, the present catalyst permits high conversion and selectivity of waste CO2 to sustainable aviation fuel (SAF). The hydrocarbon fuels produced can be a carbon neutral fuel. The catalyst is useful in enhancing carbon capture technology, including the capture of CO2 from a power plant and air. The use of the present catalyst and processes offer significant economic and environmental benefits if adopted in industrial plants such as power plants, steel plants, cement factories, and coal companies, as well as by biomass companies, airlines and ground transportation companies, all responsible for CO2 emissions.BRIEF DESCRIPTION OF THE FIGURES

[0013] FIG. 1 depicts Isotherm plots for prepared iron catalysts.

[0014] FIG. 2 depicts H2-TPR profiles for prepared iron catalysts.

[0015] FIG. 3A depicts the effect of a H2 / CO2 ratio on activity of a 100Fe40Zn / 13Cu / 4K in 1L-CSTR.

[0016] FIG. 3B depicts the effect of a H2 / CO2 ratio on hydrocarbon selectivity of a 100Fe40Zn / 13Cu / 4K in 1L-CSTR.

[0017] FIG. 4 depicts hydrocarbon distribution over 100Fe / 40Zn / 13Cu / 4K catalyst.

[0018] FIG. 5 depicts variation of conversion with time and temperature over a 100Fe / 40Zn / 2Cu / 6K catalyst in a micro fixed bed reactor.

[0019] FIG. 6 depicts variation of product selectivity with time and temperature over a 100Fe / 40Zn / 2Cu / 6K catalyst in a micro fixed bed reactor.

[0020] FIG. 7 depicts variation of olefin / paraffin ratio with time and temperature over a 100Fe / 40Zn / 2Cu / 6K catalyst in a micro fixed bed reactor.

[0021] FIG. 8 depicts oil hydrocarbon distribution over a 100Fe / 40Zn / 2Cu / 6K catalyst in a micro fixed bed reactor.

[0022] FIG. 9 depicts wax hydrocarbon distribution over a 100Fe / 40Zn / 2Cu / 6K catalyst in a micro fixed bed reactor.

[0023] FIG. 10 depicts overall hydrocarbon distribution over a 100Fe / 40Zn / 2Cu / 6K catalyst.

[0024] FIG. 11 A depicts the effect of time and temperature on activity for a 100Fe / 40Zn / 3Cu / 5K catalyst in a micro fixed bed reactor.

[0025] FIG. 1 IB depicts the effect of time and temperature on hydrocarbon selectivity for a 100Fe / 40Zn / 3Cu / 5K catalyst in a micro fixed bed reactor.

[0026] FIG. 12 depicts hydrocarbon distribution of oil product over a 100Fe / 40Zn / 3Cu / 5K catalyst.DETAILED DESCRIPTION

[0027] Before the doped iron catalysts and processes for activating and using the catalyst are disclosed and described, it is to be understood that this disclosure is not limited to the particular structures, process steps, or materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting. It must be noted that, as used in this specification, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a step" may include multiple steps, reference to "producing" or "products" of a reaction or treatment should not be taken to be all of the products of a reaction / treatment, and reference to "treating" may include reference to one or more ofsuch treatment steps. As such, the step of treating can include multiple or repeated treatment of similar materials / streams to produce identified treatment products.

[0028] Numerical values with "about" include typical experimental variances. As used herein, the term "about" means within a statistically meaningful range of a value, such as a stated particle size, concentration range, time frame, molecular weight, temperature, or pH. Such a range can be within an order of magnitude, typically within 10%, and more typically within 5% of the indicated value or range. Sometimes, such a range can be within the experimental error typical of standard methods used for the measurement and / or determination of a given value or range. The allowable variation encompassed by the term "about" will depend upon the particular system under study, and can be readily appreciated by one of ordinary skill in the art. Whenever a range is recited within this application, every whole number integer within the range is also contemplated as an embodiment of the invention.

[0029] The present application relates to an iron catalyst doped with copper and potassium. The iron catalyst is generally FeZn.

[0030] In one embodiment, the catalyst components comprise FeZnCuK. The catalyst components and compositions can be in the range of lOOFe, l-100Zn, l-30Cu, and 1-10 K (atom percentage).

[0031] In all of the foregoing catalysts, the Cu component can be present in an amount where its atomic ratio value in the catalyst is 1-30. In all of the foregoing catalysts, the K component of the catalyst can be present in an amount where its atomic ratio value in the catalyst ranges from 1 to 10, and in another embodiment from 4 to 6. In one embodiment, the atomic ratio value of K is about 4. In one embodiment, the atomic ratio value of K is about 5 in all of the foregoing catalysts.

[0032] The catalysts can be prepared by a co-precipitation method. An iron precursor compound can be combined with a zinc precursor compound and a precipitant agent in an aqueous solution. Such compounds and agents are well known in the industry and are available. The amount of each compound added can be controlled to achieve desired amounts in the final iron catalyst.

[0033] For example, to prepare an FeZn iron catalyst precursor, prior to doping, a solution of iron (III) nitrate nonahydrate and tetraethyl ortho silicate can be prepared with ammonia as the precipitant agent. The precipitation can be carried out at a suitable temperature and pH, for example 70-80°C and a pH of 7-10. The resulting slurry containing the precipitate can then be filtered. The precipitate solid can then be washed,generally several times, and generally with deionized water. The catalyst product is then dried.

[0034] The final iron catalyst, FeZnCuK, can then be obtained by impregnating the FeZn precursor with the desired amount of K and Cu, e.g., by a potassium nitrate aqueous solution and a copper nitrate solution. Any suitable potassium and copper salt solution can be used. After the copper and potassium promoters have been added, the catalyst is dried. Once dried, the catalyst is calcined.

[0035] The iron doped catalysts was sieved to 30-170 mesh.

[0036] The iron catalyst was diluted with 46 grit SiC at a weight ratio of 1 :2-4, in case a fixed bed is used.

[0037] In case a continuous slurry stirred tank (CSTR) is used, 300 g C30 was used as slurry medium.

[0038] In case a IL continuous slurry stirred tank (CSTR) was used, the rotate speed of the stirrer was 500 + rpm.

[0039] The iron doped catalysts can then be activated by exposing the iron catalyst to an appropriate gaseous chemical agent comprising hydrogen. The chemical agent can just be hydrogen, or a mix of gases. In one embodiment, a mix of hydrogen and carbon monoxide is used. In another embodiment, a mix of hydrogen and nitrogen is used. Upon exposure, the iron catalyst is heated for a suitable length of time and at an appropriate temperature, e.g., 280°C for 20-24 hours. In has been found that the exposure and activation of the catalyst in the presence of hydrogen is quite effective.

[0040] Once activated, the iron doped catalyst can be employed as the catalyst in a CO2 hydrogenation reaction.

[0041] In the reaction, hydrogen and carbon dioxide is provided to a reactor containing the doped iron catalyst. The hydrogen to carbon dioxide mol ratio can be any suitable ratio. In one embodiment, the ratio ranges from 0.1 to 9. Once the reaction is complete, hydrocarbons in the Cs-Cis range can be recovered. Such hydrocarbons are suitable for preparation of jet fuels. The hydrocarbons in the Cs-Cis range are provided in enhanced amounts due to the use of the present iron doped catalysts.

[0042] The following examples are given to illustrate the preparation, activation, and use of the present iron catalysts in preparing aviation fuels. The scope of the present invention is not to be limited by the following examples in any way.Catalyst Preparation, Testing, and Activation Example 1

[0043] Catalysts were prepared using a co-precipitation method. Ammonia was used as a precipitant agent. A solution of iron (III) nitrate nonahydrate and zinc nitrite with an appropriate amount were used as catalyst precursors. The precipitation was carried out at 70-80°C and a pH of ca. 7-10. The obtained slurry was filtered and the solid was washed several times with deionized water and then dried at 120°C overnight. The final FeZnCuK iron catalyst was obtained by impregnating FeZn precursor with the desired amount of K nitrate aqueous solution (1-10%) and Cu nitrate solution (1-30%). After the specific amount of promoters were added, the catalyst was further dried at 120°C overnight and finally calcinated at 350°C in air for 4 h.

[0044] Five FeZn catalysts i.e., 100 Fe / 40Zn, 100 Fe / 40Zn / 13Cu / 4K, 100 Fe / 40Zn / 25Cu / 4K, 100Fe / 5Zn / 2Cu / 3K and 100 Fe / 5Zn / 2Cu / 6K (atomic ratio) were prepared.

[0045] BET (Brunauer, Emmett, and Teller) and BJH (Barrett, Joyner, and Halenda) measurements for the catalysts were conducted to determine the surface area, pore volume and pore diameter with different catalyst compositions (i.e., copper loading). These measurements were conducted using a Micromeritics 3 flex surface characterization system. Prior to the measurement, the samples were slowly ramped to 160°C and evacuated overnight to approximately 50 mTorr.

[0046] Temperature programmed reduction (TPR) profiles were recorded using a Zeton- Altamira AMI-200 unit with a TCD detector. The samples were first ramped to 350°C in pure Ar to drive off any residual water from the sample, prior to cooling to room temperature to begin the TPR. The tests were performed using a 10% Fb / Ar mixture, referenced to Ar at a flow rate of 30 cm3 / min. The samples were heated to 950°C at a ramp rate of 10°C per min.

[0047] Testing of three of the FeZn catalysts was conducted in a 1-L continuous stir tank reactor (CSTR).

[0048] The FeZnCuK catalysts with and without Cu and K promoters were activated in a CSTR in-situ under syngas environment (H2 / CO = 1) at 280°C for 20-24 h before starting the CO2 hydrogenation reaction. The catalyst was tested at standard reaction conditions: 270-300°C, 2.0 MPa, H2 / CO2 = 3 and 3 NL / gcat / h.

[0049] The FeZnCuK was also tested in a micro-fixed bed reactor (FBR). In such case, 3 g of FeZnCuK catalyst was used, diluted by 6 g of SiC. The catalyst was loaded to theFBR. The catalyst was activated in H2 at 300-450 °C or in syngas at 230-280 °C and tested under the same conditions as it was tested in the CSTR reactor.

[0050] The BET surface area of FeZn without and with CuK promoter varied between 70-120 m2 / g. The three catalysts have a type IV isotherm (FIG. 1), typical for mesoporous materials, and type Hl hysteresis loop which is usually associated with well- defined cylindrical-like pore channels or agglomerates of approximately uniform spheres.

[0051] TPR-H2 profiles for the three catalysts 100Fe / 40Zn, 100Fe / 40Zn / 13Cu / 4K and 100Fe / 40Zn / 25Cu / 4K are shown in FIG. 2. 100Fe / 40Zn is characterized by two reduction steps. The first one is the reduction from hematite (Fe2O3) to magnetite (FeaCh) and occurs from 200 to 350°C, whereas the second step is the reduction of magnetite to metallic iron involving some intermediates (i.e., FeO) and occurs from 350 to 950 °C. The addition of copper shifts the reduction profile to a lower temperature. In particular, the maximum of the first peak (associated to the reduction from Fe2O3 to FesC ) shifts from 300°C to 220°C when 13Cu is added, and it further decreases to 180°C for the samples with 25Cu. Finally, the reduction to metallic iron is completed at 800°C for the sample 100Fe / 40Zn / 25Cu / 4K, whereas temperatures higher than 900°C are required for the sample without copper.

[0052] As part of the investigation of the potassium effect on the iron catalyst during CO2 hydrogenation, the performances of 100Fe / 5Zn / 2Cu / 3K (3K) and 100Fe / 5Zn / 2Cu / 6K (6K) catalysts (45-90 mesh) were studied in a IL CSTR. In addition to the effect of potassium, the role of the calcination step prior to the activation was also investigated for the 3K catalyst. The results of three test-runs over the 3K and 6K catalysts are summarized in Table 1. Apparently, the 3K catalyst after calcination at 350°C had better performance than the catalyst without calcination. CO2 conversion on the calcinated 3K catalyst was increased from 21.4 to 26.5% at 270 °C, meanwhile, the CO selectivity and CH4 selectivity decreased dramatically from 26.4% to 12.9% and 31.3 to 22.6%, accompanied by an increase in Cs+selectivity from 27.5 to 34.8%. The difference is reduced at 300 °C, probably due to the deactivation of the catalyst. When the K loading increased to 6%, the performance of the FeZn catalyst was continuously improved. The CO2 conversion and Cs+selectivity of the 6K catalyst were further increased to 30.5% and 41.5% respectively, whereas CO selectivity and CH4 selectivity were further reduced to 9.5 and 20.7%, respectively. The results suggest a strong impact of K loading on the CO2 hydrogenation reaction of the Fe catalyst.

[0053] Furthermore, Table 1 shows high olefin content on the FeZnCuK catalyst (50- 79%, or C2-C4 olefin / paraffin ratio fall in the range of 1-4).Table 1. Results of CO2 hydrogenation reaction on FeZnCuK catalysts in 1L-CSTR.Time Reactio: Conversion, % CO Selectivity (C atom), % Olefin / ParafiBn h °C H2CO2Sel.% C2-C4C5+C2C3C4100Fe / 5Zn / 3K / 2Cu In-situ calcination in CSTR @ 295 °C21.5 270 22.6 21.4 26.4 31.3 41.2 27.5 1.8 2.3 3.326.5 300 30.8 30.0 18.2 22.0 37.1 40.9 1.3 3.0 4.1100Fe / 5Zn / 3K / 2Cu (calcination @ 350 °C for 4 h in Air)5 270 28.8 26.5 12.9 22.6 42.6 34.8 1.4 2.8 3.520 300 20.7 28.3 18.4 24.8 37.6 37.6 1.1 2.7 3.7100Fe / 5Zn / 6K / 2Cu (calcination @ 350 °C for 4 h in Air)5.3 270 22.6 30.5 9.5 20.7 37.8 41.5 0.9 2.7 3.325.5 300 32.2 30.8 15.5 26.6 36.5 36.9 0.8 2.4 3.4Activation, CO / H2 =1 at 280°C for 16 h. Reaction: 2 MPa, 3 NL / g-cat / h, and H2 / CO2 = 3

[0054] The test runs over 100Fe / 40Zn and 100Fe / 40Zn / 13Cu / 4K (atomic ratio) were carried out previously in a IL CSTR over a wide range of conditions (FIGS. 3A and 3B). Herein, the hydrocarbon distributions of the Cu and K doubly promoted FeZn catalyst were analyzed in detail. The raw hydrocarbon distribution results from the GC analysis of the oil fraction is summarized in FIG. 4. It is observed that the hydrocarbon distribution of the oil fraction falls in the carbon range of C5-C32. Interestingly, the distribution shifts to heavier hydrocarbons when the H2 / CO2 ratio is decreased from 3 to 0.33 (FIGS. 3A and 3B). In FIG. 4, the first peak is centered at Cs-Cio, whereas the second peak, centered between C25-C32, is due to the effluent of the C30 oil slurry medium. Therefore, by subtracting the amounts of the components C25-C32 in the second peak and considering the overall hydrocarbon selectivity results based on the GC gas phase analysis, the selectivity of jet fuel range hydrocarbons (Cs-Cis) of the iron catalysts were calculated. The overall selectivity of the hydrocarbons formed, the jet fuel hydrocarbon selectivity, and activity for 100Fe / 40Zn and 100Fe / 40Zn / 13Cu / 4K under different reaction conditions (H2 / CO2 = 0.33-3) are summarized in Table 2 below and compared with the two best results from literature over Fe based catalysts.

[0055] Table 2 shows that adding 13%Cu and 4%K to the FeZn catalyst remarkably increased catalyst activity from 11.6% to 21.3% and C5+ selectivity from 4.4 to 58.7%.More interestingly, the C5+ selectivity and the selectivity to the jet fuel hydrocarbons over the Cu and K promoted FeZn catalyst were increased significantly with decreasing H2 / CO2 ratio. For example, Cs+selectivity increases from 58.7 to 90.3% and the jet fuel hydrocarbon selectivity for Cs-Cis was increased from 47 to 73.8% when the H2 / CO2 ratio is decreased from 3 to 0.33. The jet fuel Cs-Cis selectivity was 61-73.5% when the H2 / CO2 ratio was equal or less than 1. These selectivity values obtained on the FeZnCuK catalyst are comparable to the literature values (Y ao et al. and Wei et al).Table 2. Catalytic performance of FeZn and FeZnCuK catalysts.„ , CO2CO HC Selectivity (C atom), %Catalyst H2 / CO2} v'Conversion, % selectivity, % C2-C4C5+C8-Ci6100Fe40Zn(a)3 11.6 30.8 57.4 38.1 4.43 21.3 20.3 13.7 27.7 58.7 47.0,a, 2 22.6 15.3 8.9 23.1 67.9 47.0100Fe40 Znl3Cu4K(a)1 16.7 14.9 7.4 13.8 78.7 60.90.33 13.8 16.0 5.5 4.2 90.3 73.8Best results from literature(b,c)Fe-Mn-K 3.0 38.2 5.6 10.4 27.7 61.9 47.8Na-Fe3O4 / HZSM-5 1.0 22.0 20.1 4.0 16.6 79.4 C5-Cn>98% a) 270°C, 2 MPa, 3 NL / g-cat / h b) B. Yao, T.Xiao, O. Makgae, et al., Nature Comm., 2020, 11:6395 (300°C, 1 MPa, 2.4 NL / g-cat / h) c) J. Wei, Q. Ge, R. Yao, Nature Comm., 2017, 8:15174 (320°C, 3 MPa, 4 NL / g- cat / h)

[0056] The hydrocarbon distribution of 100Fe40Znl3Cu4K catalyst obtained in wide range of reaction conditions was studied. The selectivity of jet fuel (Cs-Cis) 61-73.8% and CO2 conversion of 14-23% were obtained when H2 / CO2 ratios in 0.33-1.0 were applied.

[0057] More than 80% C5+ hydrocarbons was achieved when change the H2 / CO2 ratio changed from 9.0 to 0.1 (FIGS. 3 A and 3B)Example 2

[0058] FeZnCuK catalysts were prepared using a co-precipitation method. Ammonia was used as a precipitant agent. A solution of iron nitrate nonahydrate and iron sulfide and hexahydrate zinc nitrate an appropriate amounts ratio were used as catalystprecursors. The precipitation was carried out at 70-80°C and a pH of ca. 7-10. The obtained slurry was filtered and the solid was washed several times with deionized water and then dried at 110°C overnight. The final FeZnCuK was obtained by impregnating the FeZn precursor with the desired amount of K nitrate aqueous solution. After the specific amount of potassium was added, the catalyst was further dried at 110°C overnight and finally calcinated at 350°C in air for 4 hours.

[0059] FeZnCuK catalysts (100 Fe / 40Zn / 2Cu / 6K) was prepared in this period.

[0060] BET (Brunauer, Emmett, and Teller) and BJH (Barrett, Joyner, and Halenda) measurements for the catalysts were conducted to determine the surface area, pore volume and pore diameter with different catalyst composition. These measurements were conducted using a Micromeritics 3 flex surface characterization system. Prior to the measurement, the samples were slowly ramped to 160°C and evacuated overnight to approximately 50 mTorr.

[0061] Temperature programmed reduction (Fb-TPR) profiles were recorded using a Zeton- Altamira AMI-200 unit with a TCD detector. The samples were first ramped to 350°C in pure Ar to drive off any residual water from the sample, prior to cooling to room temperature to begin the TPR. The tests were performed using a 10%H2 / Ar mixture referenced to Ar at a flow rate of 30 cm3 / min. The samples were heated to 950°C at a ramp rate of 10°C per min.

[0062] Temperature programmed desorption (CO2-TPD) was recorded using a Zeton- Altamira AMI-200 unit with a TCD detector. The samples were firstly reduced at 350°C for 10 h in 33% H2 in Ar, followed by cooling down at 100°C in H2 flowing, then the feed was switched to argon for preventing the adsorption of weakly bonded species, and finally TPD was carried out until 350°C.

[0063] The 100Fe40Zn2Cu6K catalysts were examined in a down flow micro-fixed reactor with a dimension of 1cm I.D. and 60 cm of length. The system is equipped with four mass flow controllers which provide four separate flows at the desired rate for CO2, H2, N2 and CO, respectively. The gases were premixed in a small vessel before entering the reactor. Carbon monoxide, if needed, was passed through a vessel containing lead oxide-alumina to remove traces of iron carbonyl. The mixed gases entered the fixed bed reactor and pass through the catalyst bed that is centered in the reactor. The Fe catalyst was diluted with 46 grids of SiC (catalyst: SiC = 1:2 (mass ratio)) and loaded in the fixed bed reactor. The particles size of the FeZn catalyst was 30-170 mesh.

[0064] This FeZnCuK catalyst can be activated in-situ under H2 / N2 (1 / 1- 1 / 4) environment at 300-450 °C before starting a CO2 hydrogenation reaction. The catalyst was tested at reaction conditions: 270-310°C, 1.5 MPa, H2 / CO2 = 3 and 2-3 NL / g-cat / h.

[0065] The surface area of the 100Fe40Zn2Cu6K catalyst was 95 m2 / g.

[0066] H2-TPR profiles for catalysts with different zinc loading are referred to in FIG. 2. The zinc loading does not influence the first reduction peak (Fe2O3 — FesC ), whereas the second peak (FesC — > Fe) is shifted to a lower temperature for the catalyst with 40Zn loading.

[0067] Hydrogen chemisorption followed by TPD were carried out for 100 Fe and 100Fe / 40Zn / 12Cu / 4K. The pinole of hydrogen desorbed during TPD were 21.4 and 13.7 for lOOFe and 100Fe / 40Zn / 13Cu / 4K, respectively. The lower H2 adsorption capability for the promoted catalyst is due to the addition of potassium (electron donor) which apparently inhibits the H2 adsorption, consequently improving the formation of olefins and long chain hydrocarbons during FTS or CO2 hydrogenation.

[0068] An investigation of the potassium effect on CO2 hydrogenation over several ironzinc catalysts was performed in FBR after the catalysts were pretreated using syngas at 280°C. CO2 conversion over six FeZn catalysts was 21-30% at 270-300°C. Thus, the CO2 conversion value is close to or below the CO2 thermodynamic equilibrium conversion at the corresponding temperature.

[0069] The 100Fe / 40Zn / 2Cu / 6K catalyst was activated in a H2 / N2 (1:4) gas mixture.

[0070] The 100Fe / 40Zn / 2Cu / 6K catalyst was activated in H2 at 420°C for 6 h.

[0071] The CO2 hydrogenation performance of 100Fe / 40Zn / 2Cu / 6K catalyst is summarized in Table 3 and FIGS. 4-6. The catalyst was first tested at 270°C for 24 h, then the temperature was gradually increased to 290°C and tested at this condition for another 24 hours. The run was continued at a higher temperature of 300°C for 5 days followed by testing under further elevated temperature of 310°C for another 5 days before the shut-down. The total time on stream (ToS) was -290 h (FIG. 5). The other process conditions were 1.5 MPa, H2 / CO2 = 3, 2-2.5 NL / g-cat / h.

[0072] CO2 conversion is 24.4% at 270°C, it increases significantly to 35.5% as the temperature is raised to 290°C; the CO2 conversion is further increased to 41% when the temperature attains 300°C and above (Table 3 and FIG. 5). The large conversion span between 270 and 300°C achieved on this H2 / N2 activated Fe catalyst is significantly different from a narrow ranged CO2 conversion observed on the Fe catalyst activated by syngas. It is evident that the H2 / N2 activation is more effective than the syngas activation.The varied conversions achieved between 270°C and 300°C remarkably surpassed the CO2 hydrogenation equilibrium conversions at different temperatures (20-25% at 270- 300°C), this clearly indicates that the Fe catalyst broke the thermodynamic equilibrium limitation of the CO2 hydrogenation. The Fe catalyst exhibited 41.2% CO2 conversion at 300°C or above after 170 h.

[0073] The catalyst activity did not significantly increase at 310°C due to a simultaneous increase in temperature and space velocity (2 to 2.5 Nl / g-cat / h) between 170 and 290 h, at these conditions, the catalyst was stable during the test period.Table 3. CO2 hydrogenation performance over 100Fe / 40Zn / 2Cu / 6K catalystTime, h 47.5 96 263Temperature, °C 290 300 310Pressure, MPa 1.5 1.5 1.5SV, Nl / g-cat / h 2 2 2.5CO2Conversion, % 35.5 41.8 41.2HC distribution, C% Ci, % 14.74 12.76 13.41C2-C4, % 30.9 28.236 27.36C5+, % 54.36 59.004 59.23Oil+wax Distribution, wt% C8-Ci8 66.78 63.67 71.68C5-C11 38.37 62.32 61.98C12-C19 40.32 28.13 29.85C20+ 21.32 9.56 8.17JF(Cg-Ci8) in all hydrocarbons, wt% 36.30 37.57 42.45CO sei, % 7.59 7.08 9.62Catalyst loading 4.5g, particle size, 180-45 mesh, diluted by 9 g SiC, Activation, H2 / N2 = 4 and 420°C for 6 h, Reactions: 1.5 MPa, and H2 / CO2 =3.

[0074] A change in CO selectivity and CH4, C2-C4, and C5+ selectivities with time and temperature are summarized in Table 3 and FIG. 6. At 270°C, CO selectivity was 17.6%, it suddenly dropped to 7.6% when the reaction temperature increased to 290°C at 30 h. The CO selectivity did not change significantly with time up to 170 h at this temperature and at 300°C. After this point, CO selectivity increased to 9.6% with the increase in reaction temperature to 310°C. The starting temperature for the reaction of CO generated by RWGS with adsorbed hydrogen appear to be high, ~270°C, but the CO2 hydrogenation reaction rate has a remarkable increase after the temperature of 290°C. The change trend for CH4 selectivity is similar to that of CO selectivity. CH4 selectivitywas 22.2% at 270°C, it decreased to 14.7-12.8% when the temperature was increased to 290°C and above. The increase in temperature from 270°C to 310°C did not greatly alter C2-C4 selectivity during 290 h of testing, i.e. 27-29%, whereas C5+ selectivity was increased from 48% to 59% at the temperature range (Table 3 and FIG. 6).

[0075] Low olefins (C2-C4) contents of the FeZnCuK is 70-90%, corresponding to the Olefin / Paraffm ratio of 2-6.7 (FIG. 7) at 270-310°C.

[0076] Oil and wax products were formed during the CO2 hydrogenation over the 100Fe40Zn2Cu6K catalyst. The hydrocarbon distribution of the oil and wax products collected at different temperatures are shown in FIGS. 8 and 9, respectively. The oil hydrocarbon distribution covers C5 to C38 with a maximum at Cs-Cio; while the wax hydrocarbon distribution varies in a higher carbon range from C11 to C50 with a maximum at C12-C13. The increase in temperature shifted the hydrocarbon spectrum to lower carbons. Based on the oil and wax hydrocarbon distribution, the weight fractions of gasoline range hydrocarbons (C5-C11), jet fuel range hydrocarbons (Cs-Cis) and diesel range hydrocarbons (C12-C19) in the combined oil / wax products are obtained and summarized in Table 3. The weight fractions of gasoline, jet fuel, and diesel hydrocarbons at 290°C, 300°C, and 310°C change in the following ranges 38-62%, 64- 72%, and 28-40%, respectively. It appears that the maximum content of gasoline, jet fuel or diesel in the oil / wax product can be obtained at 300°C, 310°C and 290°C, respectively.

[0077] The jet fuel contents in all hydrocarbons produced at different temperatures are reported in Table 3. 36-42.5% of all hydrocarbons produced at 290 to 310°C over the iron catalyst are jet fuel hydrocarbons.

[0078] The FeZnCuK catalyst gave 36.3% jet fuel hydrocarbons at 290°C under H2 activation. Considering the increasing trend of the jet fuel fraction with the increase in temperature as shown in Table 3, the results likely imply that hydrogen activation remarkably increased activity of the iron catalyst.

[0079] The overall hydrocarbon distribution for the CO2 hydrogenation at different temperatures over 100 Fe / 40Zn2Cu / 6K catalyst is shown in FIG. 10. In all cases, the hydrocarbon distribution can be described by the Anderson-Schulz Flory (ASF) law, and double alpha type hydrocarbon distributions are observed. The bending carbon is at ca. C10. The result is essentially consistent with the typical hydrocarbon distribution on ironbased catalysts for the CO hydrogenation reaction (FTS). The double alpha distribution reflects a complicated chain growth mechanism during FTS over the Fe catalysts, which has been interpreted by double active sites, secondary reactions of olefins and longerresidence time of heavier hydrocarbons in the reactor. From FIG. 10, increasing temperature slightly shifts the product distribution to the left lower carbon numbers. The CO2 hydrogenation over 100Fe / 40Zn / 2Cu / 6K surpassed the limitation of the thermodynamic equilibrium of the reaction, during 290 h of testing, the FeZnCuK catalyst displayed 41%CCh conversion at 300 -310°C after the H2 / N2 activation was applied.Example 3

[0080] Another iron-zinc catalyst, i.e., FeZnCuK catalyst was prepared and investigated for the activation study and the optimization of key processed parameters for maximizing the selectivity to jet fuel ranged hydrocarbons. The iron catalyst were prepared by adding the desired amount of Cu and K nitrate solutions using incipient wet impregnation technique onto a 100Fe40Zn precursor, which was prepared by coprecipitation of Fe and Zn nitrate solution and ammonia solution at 70-80°C and pH 7-10. The catalyst had a final formulation of 100Fe40Zn3Cu5K

[0081] The catalyst was tested in micro-fixed bed reactor, an iron catalyst with low Cu loading (i.e., 100 Fe / 40Zn / 3Cu / 5K) was examined. The catalyst was activated using the H2 / N2 gas mixture with mole ratio of 1 / 3 at 420°C for 6 h, the ramp rate was 2 °C / min. The iron catalyst was tested in a wide range of process conditions 270-310°C. H2 / CO2 = 3, GHSV of 2-3 NL / gcat / h, and 200 psig. The testing was performed for 360 h. The effect of reaction conditions and time on the catalyst activity and selectivity are summarized in Table 4 and FIGS. 11 A and 1 IB, whereas the hydrocarbon distribution of oil phase is shown in FIG. 12.Table 4. Catalytic performance of 100Fe / 40Zn / 3Cu / 5K catalystsTime, h 24.0 48.0 96.0 251.0Temperature, oC 270 290 300 310Pressure, MPa 205 205 205 205H2 / CO2ratio 3.0 3.0 3.0 3.0SV, Nl / g-cat / h 2.0 2.0 2.5 3.0CO2 Conversion, % 28.74 40.06 42.58 42.94HC distribution,C%Cb% 6.88 8.89 9.27 10.93C2-C4, % 26.94 30.60 28.89 30.04C5+, % 66.19 60.51 61.83 59.03Oil Distribution, wt%C5-Cn 67.43 63.69 71.56 73.47C8-C1886.07 71.95 74.26 76.18C12-Ci931.16 29.44 25.63 24.42C2(1.42 6.87 2.81 2.11Gasoline(C5-Cn) in all hydrocarbons, wt% 44.63 38.54 44.25 43.37JF (C8-Ci8) in all hydrocarbons, wt% 56.97 43.54 45.92 44.97Diesel (Ci2-Ci9) in all hydrocarbons, wt% 20.62 17.81 15.85 14.42CO sei, % 12.90 5.85 6.55 7.69

[0082] One aspect regarding the determination of optimal catalyst composition and activation that was found was that the H2 activation used in these experiments remarkably increased activity to 45% at 300 °C from the routine value of 25-30% for a 100Fe / 40Zn / 3Cu / 5K catalyst. These values exceed the thermodynamic equilibrium conversion of the CO2 hydrogenation at the conditions used. From FIG. 12, the jet fuel fraction in the oil phase is 68-77%, higher than that on 100Fe / 40Zn / 2Cu / 6K. The activity and jet fuel content from this FeZnCuK catalyst are superior or similar to the literature results.

[0083] The Fe catalyst compositions, formulations (l-100Zn, l-30Cu and 1-10 K), also the H2 activation and process addressed above are effective for producing jet fuel from CO2 hydrogenation.

[0084] As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of’ or “consistingessentially of’ is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of’ or “consists of’ is intended as a transition meaning the exclusion of all but the recited elements except for only minor traces of impurities.

[0085] As those skilled in the art will appreciate, numerous modifications and variations of the present invention are possible considering these teachings, and all such are contemplated hereby. For example, in addition to the embodiments described herein, the present invention contemplates and claims those inventions resulting from the combination of features of the invention cited herein and those of the cited prior art references which complement the features of the present invention. Similarly, it will be appreciated that any described material, feature, or article may be used in combination with any other material, feature, or article, and such combinations are considered within the scope of this invention.

[0086] All of the publications cited in this disclosure are incorporated by reference herein in their entireties for all purposes.

Claims

What is claimed is:

1. An iron catalyst comprised of FeZn, doped with copper and potassium.

2. The iron catalyst of claim 1, wherein the catalyst comprises FeZnCuK.

3. The iron catalyst of claims 1 -2, wherein the atomic ratio value of Zn in the catalyst ranges from 1 to 100.

4. The iron catalyst of claims 2-3, wherein the atomic ratio value of Cu in the catalyst is about 1-30.

5. The iron catalyst of claims 2-4, wherein the atomic ratio value of K in the catalyst ranges from 1 to 10.

6. The iron catalyst of claims 2-4, wherein the atomic ratio value of K in the catalyst is about 4 to 6, or about 5 or about 6.

7. A method of activating the iron catalyst of any of claims 1 -6, comprising: a) exposing the iron catalyst to a chemical agent comprising hydrogen; and b) further heating the exposed iron catalyst.

8. The method of claim 7, wherein the chemical agent is hydrogen.

9. The method of claim 7, wherein the chemical agent comprises a mix of hydrogen and carbon monoxide.

10. The method of claim 7, wherein the chemical agent comprises a mix of hydrogen and nitrogen.

11. A method of activation and testing the iron catalyst of any of claims 1 -7 is in a continuous stirred tank slurry reactor or in a micro-fixed bed reactor.

12. A method of facilitating a CO2 hydrogenation reaction comprising:a) providing hydrogen and carbon dioxide to a reactor containing the catalyst of any of the claims 1-6 and 11 at a mole ratio of from 0.1-9; and b) recovering products from the reaction.

13. The method of claim 12, wherein the temperature of the reaction is in the range of 270-320°C.

14. The method of claim 12, wherein the products recovered from the reaction comprise Cs-Cis hydrocarbons.

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