CO2 HYDROGENATION TO OXYGENATES USING PLASMA CATALYSIS

Abstract

An apparatus for forming C1 to C5 alcohol, carboxylic acid, or mixture thereof from carbon dioxide and hydrogen is described. The apparatus comprises: a dielectric barrier discharge, DBD, device arranged to generate a plasma; and a passageway having an inlet for the carbon dioxide and the hydrogen and an outlet for the C1 to C5 alcohol, carboxylic acid, or mixture thereof and including therein a catalyst comprising nickel and/or cobalt and/or copper on a support. The passageway extends, at least in part, through the DBD device wherein, in use, the carbon dioxide is exposed to the catalyst in the presence of the hydrogen in the generated plasma, thereby forming the C1 to C5 alcohol, carboxylic acid, or mixture thereof from at least some of the carbon dioxide and the hydrogen. The DBD devices comprises a water electrode. A method and a catalyst are also described.

Claims

1. An apparatus for forming C1 to C5 alcohol, carboxylic acid, or mixture thereof from carbon dioxide and hydrogen, the apparatus comprising: a dielectric barrier discharge, DBD, device arranged to generate a plasma; and a passageway including an inlet for the carbon dioxide and the hydrogen and an outlet for the C1 to C5 alcohol, carboxylic acid, or mixture thereof and having a catalyst comprising at least one of nickel, cobalt, or copper on a support therein, wherein the passageway extends, at least in part, through the DBD device wherein, in use, the carbon dioxide is exposed to the catalyst in the presence of the hydrogen in the generated plasma, thereby forming the C1 to C5 alcohol, carboxylic acid, or mixture thereof from at least some of the carbon dioxide and the hydrogen and wherein the DBD device comprises a water electrode.

2. The apparatus according to claim 1, wherein the catalyst comprises at least one of nickel, cobalt, or copper in a range from 1 to 20 wt. % by weight of the support.

3. The apparatus according to claim 1, wherein the catalyst comprises at least one of metallic nickel, metallic cobalt, or metallic copper.

4. The apparatus according to claim 3, wherein the catalyst comprises bimetallic nickel-cobalt or copper.

5. The apparatus according to claim 4, wherein the catalyst comprises at least one of 10 wt. % bimetallic nickel-cobalt alloy, or 10 wt. % copper based on the weight of the support .

6. The apparatus according to claim 1, wherein the support includes SiO.sub.2 (fumed and mesoporous), TiO.sub.2, Al.sub.2O.sub.3, CeO.sub.2, ZrO.sub.2, ZnO, Cr.sub.2O.sub.3, carbon nanotubes, Ga.sub.2O.sub.3, In.sub.2O.sub.3 and ZSM-5.

7. A method of forming C1 to C5 alcohol, carboxylic acid, or mixture thereof from carbon dioxide and hydrogen, the method comprising: generating a plasma using a dielectric barrier discharge, DBD device; and exposing the carbon dioxide in the presence of hydrogen to a catalyst comprising at least one of copper, nickel, or cobalt on a support in the generated plasma, thereby forming the C1 to C5 alcohol, carboxylic acid, or mixture thereof from at least some of the carbon dioxide; and wherein the DBD device comprises a water electrode.

8. The method according to claim 7, wherein exposing the carbon dioxide to the catalyst in the presence of hydrogen in the generated plasma comprises exposing the carbon dioxide to the catalyst in the presence of hydrogen in the generated plasma at approximately ambient temperature .

9. The method according to claim 7, wherein exposing the carbon dioxide to the catalyst in the presence of hydrogen in the generated plasma comprises exposing the carbon dioxide to the catalyst in the presence of hydrogen in the generated plasma at approximately ambient pressure.

10. The method according to claim 7, wherein generating the plasma using the DBD device comprises generating a stable plasma in a time in a range of from 1 to 60 minutes.

11. The method according to claim 7, wherein the method comprises activating the catalyst using, at least in part, the generated plasma by supplying a specific energy input in a range of 5 to 100 kJ/L.

12. The method according to claim 7, wherein the C1 to C5 alcohol, carboxylic acid, or mixture thereof is selected from a group consisting of: methanol, ethanol, propane, methanoic acid and ethanoic acid.

13. The method according to claim 12, having a selectivity of methanol of at least 30%.

14. The method according to claim 7, wherein carbon dioxide and hydrogen are provided in a molar ratio of from 1:2 to 1:4.

15. A catalyst comprising at least one of nickel, cobalt, or copper on a support.

16. The apparatus according to claim 5, wherein the catalyst comprises metallic nickel in a range from 1 to 9 wt.% and comprises metallic cobalt in a range from 9 wt.% to 1 wt.%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

[0100] FIG. 1A shows a schematic diagram of the water-cooled DBD system; FIG. 1A shows a detailed structure of the DBD plasma-catalytic reactor using a water electrode;

[0101] FIG. 2 shows XRD profiles of reduced Ni/ZSM-5 catalysts (a) Ni/ZSM-5(25)-Re, (b) Ni/ZSM-5(38)-Re, (c) Ni/ZSM-5(50)-Re, (d) Ni/ZSM-5(80)-Re and (e) Ni/ZSM-5(200)-Re;

[0102] FIG. 3 shows an evaluation of catalyst activities for CO.sub.2 hydrogenation. (A) Effect of catalysts on the conversion of CO.sub.2 and hydrogen at an SEI of 40 kJ/L. The selectivity (B), yield (C) of major carbon containing products (CO, CH.sub.4 and MeOH);

[0103] FIGS. 4A and B show a comparison of XRD patterns of calcined, reduced and spent samples of Ni/ZSM-5(50) catalysts;

[0104] FIG. 5 shows the XRD patterns of (a) calcined and (b) reduced samples of Ni/Co catalysts on an alumina support;

[0105] FIG. 6 shows the effect of different catalysts on CO.sub.2 hydrogenation at an SEI of 20 kJ/L (A) conversion of CO.sub.2 and hydrogen; (B) selectivity of gaseous products; (C) product distribution (selectivity) and (D) yield of alcohol (MeOH + EtOH) and acetic acid (AcA);

[0106] FIG. 7 shows the XRD patterns of (A) Cu/TiO.sub.2 (Cu/Ti), (B) Cu/Al.sub.2O.sub.3 (Cu/Al), (C) Cu/SiO.sub.2 (Cu/Si) and (D) Cu/CeO.sub.2 (Cu/Ce) catalysts; and

[0107] FIG. 8 shows the effect of different Cu-based catalysts on CO.sub.2 hydrogenation (A) conversion of CO.sub.2 and hydrogen; (B) selectivity of gaseous products and total gas selectivity; (C) selectivity of liquid products and (D) yield of major products and the ratio of CO/CH.sub.4.

EXAMPLES

[0108] The experiments were conducted in a coaxial DBD reactor with a special and novel electrode design, as shown in FIGS. 1A and 1B. Compared to traditional DBD reactors using metal as a ground electrode, this reactor used circulating water as both a ground electrode and cooling of the reactor. A cooling circulation bath (Grant LT Ecocool 150) was used to control the temperature of the discharge at 20° C. for Ni/ZSM-5 (35° C. for Ni—Co alloy and Cu-based catalysts). The length of the discharge region was 50 mm and the discharge gap was 1 mm (2 mm for Cu-based catalysts). The DBD reactor was connected to an AC high voltage power supply with a peak voltage of up to 30 kV. The DBD discharge power maintained at 20 W for Ni/ZSM-5 (10 W for Ni—Co alloy and 25 W for Cu-based catalysts), and the frequency was fixed at 9.2 kHz. CO.sub.2 and H.sub.2 were used as reactants at a total flow rate of 30 mL/min and a CO.sub.2/H.sub.2 molar ratio of 1:4 for Ni/ZSM-5 (1:3 for Ni—Co alloy and Cu-based catalysts). Catalyst was fully packed in the discharge area and 500 mg of catalyst was used for each testing.

[0109] The applied voltage of the DBD was measured by a high-voltage probe (TESTEC, HVP-15HF), while the current was recorded by a current monitor (Bergoz, CT-E0.5). The voltage on the external capacitor was used to measure the charge formed in the DBD. All the electrical signals were sampled by a four-channel digital oscilloscope (Tektronix, MDO 3024). A homemade system was used to monitor and control the discharge power of the DBD in real-time. The gas temperature in the discharge area near the catalyst bed was measured using a fiber optical thermometer (Omega, FOB102).

[0110] The gaseous products were analyzed using a gas chromatograph (Shimadzu GC-2014) equipped with a thermal conductivity detector (TCD) and a flame ionized detector (FID). A water/ice mixture bath was placed at the exit of the DBD reactor to condense liquid products. The oxygenates were qualitatively analyzed using a gas chromatography-mass spectrometer (GC-MS, Agilent GC 7820A and Agilent MSD 5973) and quantitatively analyzed using a gas chromatograph (Agilent 7820) equipped with a FID with a DB-WAX column. The change of the gas volume before and after the reaction was measured using a soap-film flow meter. Sampling and measurements started after running the reaction for 1 h and lasted for 3 h (3.5 h for Cu-based catalysts). Each measurement was repeated three times, and the measurement error was less than 4%.

Example 1: Ni/ZSM-5

Catalyst Preparation

[0111] Hierarchical ZSM-5 nanocrystals with different Si/Al ratios were prepared as follows: sodium aluminate was dissolved in tetrapropylammonium hydroxide, together with deionized water and sodium hydroxide, TEOS were added to this solution. The volumes of these precursor solutions were determined by the certain ratios of Si/Al. The suspension obtained was maintained under mechanical agitation for 2 h. The mixture was heated at 140° C. and kept at this temperature for 72 h in hydrothermal vessel. The obtained solid by centrifugation was washed with deionized water and then dried at 60° C. for 12 h. The sample was then calcined at 550° C. for 5 h.

[0112] Then, nickel based ZSM-5 catalysts were prepared by wet impregnation using nickel nitrate. Various amounts of nickel nitrate hexahydrate, depending on the quantity of nickel required on the catalyst, were added to deionized water. This solution was then added into the support, and then stirred and dried at 105° C. This was followed by calcination in are at 450° C. for 2 h with a heating rate of 10° C./min.

Characterization

[0113] N.sub.2 adsorption-desorption measurements were carried out using an Autosorb IQ-C system at 77 K after outgassing the sample under vacuum at 573 K for 10 h. The specific surface area is calculated with BET method. X-ray diffraction (XRD) patterns of the calcined and reduced samples were recorded on a PANalytical XPert Pro powder diffractometer (45 kV and 40 mA) using Cu Kα radiation source (λ=1.5405 Å) in the 2θ range from 5° to 80°.

Physical Properties of the Hierarchical Ni/ZSM-5 Zeolites

[0114] The XRD diffraction patterns of as-prepared reduced Ni/ZSM-5 catalysts at 10% nickel loading are shown in FIG. 2. The peaks at 2θ value at 7.9°, 8.8°, 22.9°, 23.8° and 24.3° exhibit the characteristic MFI-type zeolite formation. This indicated that the crystalline structure of the ZSM-5 remained constant after 10% nickel loading. Additionally, all the reduced Ni/ZSM-5 catalysts showed XRD reflections at 44.50° (111) and 51.85° (200) corresponding to metallic Ni.

[0115] The physical properties of the as-prepared reduced Ni/ZSM-5 catalysts at 10% nickel loading are summarized in Table 1. All the reduced Ni/ZSM-5 catalysts contain similar surface area (S.sub.BET from 224 to 266 m.sup.2/g). The Ni/ZSM-5(50)-Re catalyst has the largest mesoporous volume (V.sub.meso = 0.1538 cm.sup.3/g). The N.sub.2 adsorption-desorption isotherms at 77 K for as-prepared reduced 10Ni/ZSM-5 catalysts with different Si/Al ratios are shown in FIG. 3A. All catalysts exhibit a type-IV isotherm with H.sub.2 hysteresis loops, suggesting the mesoporous structures. Clearly, the Ni/ZSM-5(50)-Re catalyst has the largest hysteresis loop, agreeing with its larger degree of mesopores than others. FIG. 3B depicts the BJH pore size distributions of reduced Ni/ZSM-5 catalysts with different Si/Al ratios. All the catalysts except the 10Ni/ZSM-5(38)-Re display relatively sharp distribution of mesopores at 5~10 nm diameter.

TABLE-US-00001 Physical properties reduced Ni/ZSM-5 catalysts..sup.a Samples S.sub.BET (m.sup.2/g) S.sub.micro (m.sup.2/g) S.sub.meso (m.sup.2/g) V.sub.total (cm.sup.3/g) V.sub.micro (cm.sup.3/g) V.sub.meso (cm.sup.3/g) Ni/ZSM-5(25)-Re 247 142 105 0.2089 0.071 0.1379 Ni/ZSM-5(38)-Re 243 186 57 0.1762 0.096 0.0802 Ni/ZSM-5(50)-Re 265 186 79 0.2548 0.101 0.1538 Ni/ZSM-5(80)-Re 224 115 109 0.1938 0.058 0.1358 Ni/ZSM-5(200)-Re 266 156 110 0.2229 0.08 0.1429 .sup.a Measured by N.sub.2 porosimetry.

[0116] On the spent Ni/ZSM-5(50)-spent catalysts, as shown in FIGS. 4A and 4B, the intensity of the peaks associated with Ni(111) and Ni(200) show unchanged. No NiO at 2θ value at 43.5° was observed on the reduced Ni/ZSM-5(50)-Re and spent Ni/ZSM-5(50)-spent catalysts.

Example 2: Bimetallic Ni-Co Alloy Catalysts on an Alumina Support

[0117] Catalysts comprising nickel and/or cobalt on an alumina support were prepared as follows:

[0118] 10 wt.% nickel (10Ni), 7 wt.% nickel and 3 wt.% cobalt (7Ni3Co), 5 wt.% nickel and 5 wt.% cobalt (5Ni5Co), 3 wt.% nickel and 7 wt.% cobalt (3Ni7Co) and 10 wt.% cobalt (10Co)

[0119] Bimetallic xNi-(10-x) Co/Al.sub.2O.sub.3 (x = 10, 7, 5, 3 and 0 wt %) alloy catalysts were prepared by ultrasonic incipient-wetness impregnation using nitrate salts (Alfa Aesar, 99.5%) as the metal precursor. Initially, a certain amount (3 g) of catalyst support (Al.sub.2O.sub.3) was added into the solution of nitrate salts. The slurry was continuously ultrasonic treated at 60° C. for 2 h, after which it was aged at room temperature overnight. The samples were then dried at 110° C. for 5 h and calcined at 500° C. for 5 h. The catalysts were then sieved to 40-60 meshes and reduced by a mixture of Ar/H.sub.2 (50 mL/min; Ar/H.sub.2 volume ratio 3:2) at 550° C. for 5 h before the plasma reaction. The calcined catalysts are labelled as Ni.sub.xCo.sub.10-x-c (x = 10, 7, 5, 3 and 0), while the pristine catalysts (reduced samples) are labelled as Ni.sub.xCo.sub.10-x (x = 10, 7, 5, 3 and 0) in following content. Otherwise, the spent catalysts are assigned to Ni.sub.xCo.sub.10-x-s (x = 10, 7, 5, 3 and 0).

Characterization

[0120] N.sub.2 adsorption-desorption measurements were carried out using an Autosorb IQ-C system at 77 K after outgassing the sample under vacuum at 573 K for 10 h. The specific surface area is calculated with BET method. X-ray diffraction (XRD) patterns of the calcined and reduced samples were recorded on a PANalytical XPert Pro powder diffractometer (45 kV and 40 mA) using Cu Kα radiation source (λ=1.5405 Å) in the 2θ range from 5° to 80°.

TABLE-US-00002 Physical properties of the pristine catalysts Samples Surface area (m.sup.2/g) Total pore volume (cm.sup.3/g) Average pore diameter (Å) Al.sub.2O.sub.3 221 0.43 77.5 10Ni 210 0.39 74.1 7Ni3Co 159 0.32 79.7 5Ni5Co 181 0.35 77.8 3Ni7Co 166 0.32 78.2 10Co 218 0.39 71.1

[0121] FIG. 5 shows the XRD patterns of the calcined samples and the reduced samples. The major diffraction peaks at 2θ= 37.6°, 45.9° and 67.0° can correspond to the cubic structure of crystalline γ-Al.sub.2O.sub.3 (JCPDS 00-010-0425) both in FIG. 5(a). The characteristic diffraction peaks centred at 2θ= 37.3°, 43.3°, 62.9°, and 75.4° could be attributed to the (111), (200), (220), and (311) lattice planes of NiO (JCPDS #78-0643). Meanwhile, the peaks located at 2θ= 19.0°, 31.3°, 36.9°, 44.8°, 55.7°, 59.4°, and 65.3° could well match with the (111), (220), (311), (400), (422), (511), and (440) lattice planes of Co.sub.3O.sub.4 (JCPDS #76-1802) respectively. Furthermore, there is a shift of the diffraction peak (around 37°) of the bimetallic Ni—Co oxides, especially in 7Ni3Co and 5Ni5Co, suggesting the formation of NiCo.sub.2O.sub.4 (JCPDS #20-0781) spinel, which demonstrates the formation of Ni—Co alloy after reduction. FIG. 5(b) The peaks of all samples match well with the standard peaks of Ni (JCPDS 04-0850) and Co (JCPDS 01-1255). There are no obvious characteristic peaks of Co.sub.3O.sub.4 and NiO, suggesting a relative complete thermal-reduction of the samples.

Performance

[0122] Compared to the plasma reaction without a catalyst, the combination of DBD with these catalysts enhances the conversion of CO.sub.2 and H.sub.2.

[0123] It was found that 7Ni3Co shows the highest CO.sub.2 conversion of 24% with CO.sub.2. It was also found that the bimetallic Ni—Co alloy catalysts generate less CO and CH.sub.4 and produce more liquid chemicals (FIG. 6A), suggesting that the existence of Ni—Co alloy would inhibit the production of CO.

[0124] FIG. 6C shows the distribution of main products, including gaseous products (CO and CH.sub.4) and major liquid products (methanol (MeOH), ethanol (EtOH) and acetic acid (AcA)).

[0125] 7Ni3Co exhibits the highest methanol selectivity of 45.4%.

[0126] 7Ni3Co shows the highest alcohol (methanol + ethanol) yield of 11% (FIG. 6D). The yield of acetic acid is 0.8% using 7Ni3Co. 5Ni5Co shows the highest yield of acetic acid (1.3%).

[0127] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0128] All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive.

[0129] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0130] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Example 3: Cu-Based Catalysts with Different Supports

[0131] Catalysts comprising copper on a series of supports, including Al.sub.2O.sub.3, TiO.sub.2, CeO.sub.2, SiO.sub.2 (mesoporous), were prepared as follows: 10 wt.% Cu/Al.sub.2O.sub.3 (Cu/Al), 10 wt.% Cu/TiO.sub.2 (Cu/Ti), 10 wt.% Cu/CeO.sub.2 (Cu/Ce), 10 wt.% Cu/SiO.sub.2 (Cu/Si).

[0132] Cu-based catalysts using different supports were prepared by an ultrasonic incipient-wetness impregnation. Desired amount of copper nitrate (Alfa Aesar, 99.5%) was dissolved in deionized water, and the obtained solution was vigorously stirred at room temperature for 15 min. After that, a certain amount (3 g) of catalyst supports (Al.sub.2O.sub.3, TiO.sub.2, CeO.sub.2, or mesoporous SiO.sub.2) was added into this precursor solution. The slurry was continuously ultrasonic treated at 60° C. for 2 h, followed by aging overnight at room temperature. The samples were then dried at 110° C. for 5 h and calcined at 500° C. for 5 h. The catalysts were then sieved to 40-60 meshes and reduced by Ar/H.sub.2 mixed gas (50 mL/min; Ar/H.sub.2 = 3:2) at 550° C. for 5 h before the plasma reaction.

Physical Properties of the Cu-Based Catalysts

[0133] The XRD diffraction patterns of as-prepared reduced Cu-based catalysts at 10% copper loading are shown in FIG. 7. The peaks in all XRD patterns at 2θ value at 43.6°, 50.8° and 74.4° exhibit the formation of metallic copper (JCPDS#04-0836). Weak peaks of CuO (JCPDS#45-0937) could be found on both TiO.sub.2 (FIG. 7(A)) and SiO.sub.2 (FIG. 7(C)). Further, typical diffraction peaks in FIG. 7(a) indicate the presence of both anatase (JCPDS#21-1272) and rutile (JCPDS#21-1276) phases of TiO.sub.2. The XRD pattern of γ-Al.sub.2O.sub.3 (JCPDS#00-010-0425) could be observed in FIG. 7(B), and the XRD pattern of Cu/Ce (FIG. 7(D)) shows a typical diffraction pattern of cubic fluorite-type CeO.sub.2 (JCPDS#34-0394).

Performance

[0134] FIG. 8(A) shows the presence of Cu/Al.sub.2O.sub.3, Cu/Ce.sub.2O.sub.3 and Cu/SiO.sub.2 enhances the conversion of CO.sub.2 and H.sub.2 compared to the plasma CO.sub.2 hydrogenation without a catalyst. Cu/SiO.sub.2 shows the highest CO.sub.2 conversion of 56.4%.

[0135] Compared with other catalysts, the Cu/SiO.sub.2 catalyst shows significantly lower selectivity of CO and CH.sub.4, suggesting that Cu/SiO.sub.2 inhibits the production of CO and CH.sub.4.

[0136] FIG. 8(C) shows the combination of DBD with Cu-based catalysts significantly enhances the selectivity of methanol and ethanol. The Cu/SiO.sub.2 catalyst shows the highest methanol selectivity of 61.5% and with an ethanol selectivity of 0.7%.

[0137] The highest methanol yield of 35% is achieved using Cu/SiO.sub.2 in the plasma CO.sub.2 hydrogenation process.