STABLE CATALYST FOR CARBON DIOXIDE TO METHANOL CONVERSION AND PROCESS OF CONVERSION THEREOF

Abstract

The present disclosure is directed to a catalyst for carbon dioxide to methanol conversion comprising: 1-10 wt % of Nickel; 5-15 wt % of Zinc; and 80-95 wt % of metal oxide, wherein the wt % is based on the total weight of the catalyst. The present disclosure also provides a method for preparation of a catalyst for carbon dioxide to methanol conversion comprising: i) dissolving 1-10 wt % nickel precursor and 5-15 wt % zinc precursor in a solvent to obtain a first mixture; ii) adding 80-95 wt % metal oxide in the first mixture as obtained in step (a) to obtain a second mixture; iii) evaporating the solvent from the second mixture as obtained in step (b), drying and calcining in air at a temperature in the range of 350? C. to 500? C. for a period in the range of 2 hr to 4 hrs to obtain calcined mixture; and iv) reducing the calcined mixture as obtained in step (c) under hydrogen atmosphere at a temperature in the range of 500? C. to 700? ? C. for a period in the range of 1 hr to 3 hrs to obtain the catalyst. The disclosure also provides a low pressure process for conversion of carbon dioxide to methanol.

Claims

1. A catalyst for carbon dioxide to methanol conversion comprising: a) 1-10 wt % of a Nickel metal of the total weight of the catalyst; b) 5-15 wt % of a Zinc metal of the total weight of the catalyst; and c) 80-95 wt % of a metal oxide of the total weight of the catalyst.

2. The catalyst as claimed in claim 1, wherein the metal oxide is selected from a group consisting of titania, zinc oxide, alumina or combinations thereof.

3. A method for preparation of a catalyst for carbon dioxide to methanol conversion comprising the steps of: i) dissolving 1-10 wt % nickel precursor and 5-15 wt % zinc precursor in a solvent to obtain a first mixture; ii) adding 80-95 wt % metal oxide in the first mixture as obtained in step (a) to obtain a second mixture; iii) evaporating the solvent from the second mixture as obtained in step (b), drying and calcining in air at a temperature in the range of 350? C. to 500? C. for a period in the range of 2 hr to 4 hrs to obtain calcined mixture; and iv) reducing the calcined mixture as obtained in step (c) under hydrogen atmosphere at a temperature in the range of 500? ? C. to 700? C. for a period in the range of 1 hr to 3 hrs to obtain the catalyst.

4. The method as claimed in claim 3, wherein the solvent is selected from a group consisting of water, ethanol, methanol and combination thereof.

5. The method as claimed in claim 3, wherein the nickel precursor is selected from a group consisting of nickel nitrate, nickel sulfate, nickel chloride, their hydrates, or combinations thereof.

6. The method as claimed in claim 3, wherein the zinc precursor is selected from a group consisting of zinc nitrate, zinc sulfate, zinc chloride, their hydrates, or combinations thereof.

7. The method as claimed in claim 3, wherein the air and hydrogen have a flow rate in the range of 20-25 ml/min.

8. A method of carbon dioxide to methanol conversion using the catalyst as claimed in claim 1 comprising the steps of: i. contacting carbon dioxide with the catalyst as claimed in claim 1 under atmosphere of hydrogen and nitrogen at a temperature in the range of 200-300? C. for a period in the range of 1 to 5 hrs with a pressure in the range of 2 to 40 bars to obtain methanol.

9. The method as claimed in claim 8, wherein the atmosphere of hydrogen and nitrogen have a flow rate in a range of 10 mL/min to 500 mL/min and gas hourly space velocity (GHSV) in the range of 1000 h.sup.?1 to 15000 h.sup.?1.

10. The method as claimed in claim 8, wherein the carbon dioxide to hydrogen ratio is 1:3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 provides high resolution transmission electron micrographs (HR-TEM) of the catalysts reduced at 550? C. (a is for 5 nm and b is for 50 nm), 600? C. (c is for 5 nm and d is for 50 nm) and 650? ? C. (e is for 5 nm and f is for 50 nm).

[0045] FIG. 2 provides the x-ray diffraction patterns of: [0046] (a) acatalyst reduced at 550? C., and b-catalyst when used in CO.sub.2 conversion process; (b) a-catalyst reduced at 600? C., and bcatalyst when used in CO.sub.2 conversion process; (c) acatalyst reduced at 650? C., and bcatalyst when used in CO.sub.2 conversion process, wherein the catalyst is as per an exemplary embodiment of the present disclosure. Standard simulated patterns of NiZn alloy and ZnO are given for comparison.

[0047] FIG. 3 compared the methanol space time yield as a function of amount of methanol generated per gm of a catalyst per hour in the process of conversion of carbon dioxide to methanol with reduction performed at pressures ranging from 2.5 bars to 25 bars where the catalyst is: [0048] a) 2% Ni-8% Zn supported by TiO.sub.2 reduced at 550? ? C.; [0049] b) 2% Ni-8% Zn supported by TiO.sub.2 reduced at 600? C.; and [0050] c) 2% Ni-8% Zn supported by TiO.sub.2 reduced at 650? C.

[0051] FIG. 4 shows selectivity of the catalysts at 2.2, 20 and 40 bar.

[0052] FIG. 5 shows the in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) spectra of catalyst surface of 2% Ni-8% Zn supported by TiO.sub.2 and reduced at 650? C. while passing only CO.sub.2 (5 ml/min) over it at atmospheric pressure.

[0053] FIG. 6 depicts the durability of a catalyst reduced at 550? C. in generating methanol per gm of the catalyst over a period of 36 h under varying pressure and temperature conditions.

DETAILED DESCRIPTION OF THE INVENTION

[0054] The present disclosure provides an efficient catalyst for capture and conversion of carbon dioxide to methanol for suitable industrial applications. The disclosure also provides a process for conversion of carbon dioxide to methanol at low pressures employing the catalyst.

[0055] The present disclosure provides a stable catalyst for carbon dioxide to methanol conversion comprising: [0056] a) 1-10 wt % of a Nickel metal of the total weight of the catalyst; [0057] b) 5-15 wt % of a Zinc metal of the total weight of the catalyst; and [0058] c) 80-95 wt % of a metal oxide of the total weight of the catalyst.

[0059] The metal oxide is selected from a group consisting of titania, zinc oxide, alumina and combination thereof.

[0060] The catalyst is an intermetallic catalyst comprising metals including nickel and zinc. The metals are supported on a metal oxide preferably titania. Thus, the catalyst comprises nickel and zinc alloy supported on titania. The catalyst comprises an interface of nickel and zinc alloy with zinc oxide and titania.

[0061] The present invention provides a method for preparation of a catalyst for carbon dioxide to methanol conversion comprising: [0062] i) dissolving 1-10 wt % nickel precursor and 5-15 wt % zinc precursor in a solvent to obtain a first mixture; [0063] ii) adding 80-95 wt % metal oxide in the first mixture as obtained in step (a) to obtain a second mixture; [0064] iii) evaporating the solvent from the second mixture as obtained in step (b), drying and calcining in air at a temperature in the range of 350? ? C. to 500? C. for a period in the range of 2 hr to 4 hrs to obtain calcined mixture; and [0065] iv) reducing the calcined mixture as obtained in step (c) under hydrogen atmosphere at a temperature in the range of 500? ? C. to 700? C. for a period in the range of 1 hr to 3 hrs to obtain the catalyst.

[0066] The solvent may be any well-known solvent in the art capable of dissolving the nickel precursor, zinc precursor and titania, including but not limited to, water, ethanol, methanol and the like.

[0067] The solvent is selected from a group consisting of water, ethanol, methanol and combination thereof. Preferably, the solvent is water.

[0068] The nickel precursor is selected from a group consisting of nickel nitrate, nickel sulfate, nickel chloride, their hydrates, or combinations thereof.

[0069] The zinc precursor is selected from a group consisting of zinc nitrate, zinc sulfate, zinc chloride, their hydrates, or combinations thereof.

[0070] The present invention provides a method of carbon dioxide to methanol conversion comprising: [0071] (A) contacting carbon dioxide with the catalyst as claimed in claim 1 under atmosphere of hydrogen and nitrogen at a temperature in the range of 200-300? C. for a period in the range of 1 to 5 hrs with a pressure in the range of 2 to 40 bars to obtain methanol.

[0072] The carbon dioxide is contacted with the catalyst at a temperature in the range of 200-300?C, preferably at 250?C for a period in the range of 1 to 5 hrs, preferably for 2-3 hrs with a pressure in the range of 2 to 40 bars.

[0073] The atmosphere of hydrogen and nitrogen have a flow rate in a range of 10 ml/min to 500 mL/min, preferably 50 mL/min 500 mL/min, more preferably 100 mL/min.

[0074] The atmosphere of hydrogen and nitrogen may have a gas hourly space velocity (GHSV) of 1000 h.sup.?1 to 15000 h.sup.?1, preferably 9000 h.sup.?1.

[0075] The carbon dioxide to hydrogen ratio is 1:3.

[0076] The present disclosure provides a low pressure process for conversion of carbon dioxide to methanol, the process comprising the step of contacting carbon dioxide with a catalyst comprising NiZn supported on metal oxide under an atmosphere of hydrogen and nitrogen.

[0077] The process is performed on a fixed or moving bed reactor.

[0078] The process has yield methanol in a range of 0.005 g/g of catalyst/hour to 0.030 g/g of catalyst/hour, preferably in a range of 0.015 g/g of catalyst/hour to 0.020 g/g of catalyst/hour.

[0079] The process is combined with another process that employs methanol and generates carbon dioxide to give a cyclic process.

[0080] The catalyst comprises NiZn bimetals supported on TiO.sub.2 support prepared by wet impregnation.

[0081] The catalyst comprises alloy of NiZn or bimetallic system of Ni and Zn especially with ZnO with rich regions in the close proximity as the active catalyst wherein said alloy of NiZn or bimetallic system of Ni and Zn is optionally or specifically supported on a support.

[0082] Carbon dioxide is obtained through any suitable source such as from atmosphere, carbon dioxide obtained as by product from industrial sources such as power plants, and the like. The carbon dioxide is captured from the atmosphere by the catalyst.

[0083] The source of hydrogen includes a variety of sources such as hydrogen obtained from splitting of water, atmosphere, and the like.

[0084] Methanol produced by the above process is employed as an alternative environment friendly fuel. It may be used in the manufacture of chemicals including dimethyl ether, hydrogen, acetic acid, styrene, or formaldehyde which may be further employed in adhesives, construction materials, resins and the like.

[0085] The present invention (catalyst and process) is not limited to methanol production only, but also include other oxygenated products formation such as higher alcohols having carbon atoms up to 10 (C1-C10, e.g. ethanol, propanol, butanol, pentanol, hexanol, etc.), aldehydes (formaldehyde, etc.), acid (e.g. acetic acid, formic acid, etc), ether (DMEdimethyl ether, etc.) and so on, based on substrate/reagents keeping CO.sub.2 and catalyst the same as mentioned above.

[0086] Nickel and zinc surfaces are generally active for CO.sub.2 and hydrogen activation. However, individually these elements either have no activity for the reduction or cause methanation of carbon dioxide. The catalyst is capable of capturing carbon dioxide from atmosphere. The components of the catalyst synergistically enable the conversion of carbon dioxide to methanol at low pressures. Conventionally intermetallic NiZn catalysts employed in conversion of carbon dioxide would yield methane, but the synergism of the titania and the metals minimize methane from coming out of the catalyst system, driving the formation of methanol with more selectivity.

[0087] The catalyst of the present disclosure does not require high pressures of 50-100 bars for the reduction of carbon dioxide and performs efficient reduction with good yields at low pressures including 2-40 bars. Methanol formation in low concentration is also observed even at 2 bars. The reduction in pressures decreases the manufacturing costs of methanol from carbon dioxide.

EXAMPLES

[0088] Following examples are given as a way of illustration only and should not be construed to limit the scope of the present invention.

Details of the Chemicals Used

[0089] The following chemicals, gases and materials were used: [0090] nickel(II) nitrate hexahydrate (Ni(NO.sub.3).sub.2.Math.6H.sub.2O), 99.999%, Sigma-Aldrich); [0091] zinc(II) nitrate hexahydrate (Zn(NO.sub.3).sub.2.Math.6H.sub.2O, 98%, Sigma-Aldrich); [0092] CO.sub.2 (99.99%, EffecTech); [0093] H.sub.2 (99.998%, Sandesh Gases); and [0094] N2 (99.998%, Sandesh Gases).

Example 1: Synthesis of Intermetallic Catalyst [2% Ni-8% Zn/90% TiO.SUB.2 .Catalyst]

[0095] 2% Ni-8% Zn/90% TiO.sub.2 intermetallic catalyst was prepared by wet impregnation. Precursor salts, Nickel(II) nitrate hexahydrate (0.198 g) and Zinc(II) nitrate hexahydrate (0.7279 g) were dissolved in 30-40 ml of water and stirred with TiO.sub.2 (P25: titania which is a mixture of rutile and anatase titania) (1.5 g) for 2 hrs at a temperature range of 25-30? C. Water was removed by rotary evaporator, dried overnight (about 10 hrs) in oven at 100? C. and calcined in air in a U-Tube furnace at 450? C. for 3 hrs under air flow with rate of 20-25 ml/min for 3 hrs with ramping rate 3? C./min. The catalyst was then divided into three batches which were reduced at 550? C., 600? C., and 650? C. respectively for 2 hrs, in the presence of H.sub.2 with rate of 20-25 ml/min.

Example 2: Synthesis of Intermetallic Catalyst: [2% Ni-8% Zn/90% Al.SUB.2.O.SUB.3 .Catalyst]

[0096] 2% Ni-8% Zn/90% Al.sub.2O.sub.3 intermetallic catalyst was prepared by wet impregnation. Precursor salts, Nickel(II) nitrate hexahydrate (0.198 g) and Zinc(II) nitrate hexahydrate (0.7279 g) were dissolved in 30-40 ml of water and stirred with Al.sub.2O.sub.3 (1.5 g) for 2 hrs at a temperature range of 25-30? C. Water was removed by rotary evaporator, dried overnight (about 10 hrs) in oven at 100? C. and calcined in air in a U-Tube furnace at 450? C. for a period in the range of 3 hrs under air flow with rate of 20-25 ml/min for 3 hrs with ramping rate 3?C/min. the catalyst was then reduced at 550? ? C. for 2 hrs while passing H.sub.2 with rate of 20-25 ml/min.

Example 3: Characterization of Intermetallic Catalyst

[0097] High resolution transmission electron micrographs (HR-TEM) images were collected using an FEI HRTEM instrument at 300 kV. Samples were prepared by dispersing in ethanol and drop casting on a holey C Cu grid. This was dried overnight in air before analyzing.

[0098] FIG. 1 provides HR-TEM of the catalysts reduced at 550? C. (a is 5 nm resolution image and b is 50 nm resolution image), 600? C. (c is 5 nm resolution image and d is 50 nm resolution image) and 650? C. (e is 5 nm resolution image and f is 50 nm resolution image).

[0099] XRD patterns were recorded in a PANalyticalXPert Pro dual goniometer diffractometer with Ni as filter and Cu K? source operating at 40 kV and 30 mA with step size 0.0083? and time per step 91.44 s. X'celerator solid state detector was used for recording the data.

[0100] FIG. 2 provides the X-ray diffraction patterns of: (a) acatalyst reduced at 550? C., and b-catalyst when used in CO.sub.2 conversion process; (b) acatalyst reduced at 600? C., and bcatalyst when used in CO.sub.2 conversion process; and (c) acatalyst reduced at 650? ? C., and bcatalyst when used in CO.sub.2 conversion process.

[0101] HR-TEM shows the NiZn inter-metallic particles were available on the surface of TiO.sub.2 in all reduced samples and powder XRD analysis shows that dspacing also matched with those of NiZn. XRD analysis clearly shows the presence of NiZn intermetallics were formed at reduced temperatures around 43.30 (2?). Catalyst which was reduced at 550? C. showed ZnO impurities with peaks around 31.8 and 34.50 (2?), it may due to lesser reduction temperature as compared to other two samples which were reduced at 600? ? C. and 650? C. At 600? C., ZnO peak intensity reduced, at the same time titania phase started to change from anatase to rutile but did not change completely thus the catalyst has NiZn alloy on TiO.sub.2 with anatase-rutile mixture. Also, at 600? C., ZnO was absent and the presence of the new phase of Zn.sub.2Ti.sub.3O.sub.8 was confirmed from HRTEM and SAED patterns; HAADF imaging indicated an increase in particle size of NiZn particles to ?75 nm; and EDS mapping and line profile of a single NiZn particle clearly showed the Zn and Ti rich domains corroborating an interface with Zn.sub.2Ti.sub.3O.sub.8 phase. At 650? C., there was total reduction of ZnO peak and peaks related to NiZn alloy along with phase change of titania to rutile. Surprisingly, at 650? ? C., neither ZnO nor Zn.sub.2Ti.sub.3O.sub.8 was observed; Zn based oxides may have vaporized at the high temperature without forming the stable Zn titanate. Unexpectedly, the size of NiZn particles was smaller than NZT-600 but almost similar to NZT-550. From the elemental quantification by EDS analysis of all the samples, the Ni atomic fraction (%) was found to be in the range of 50-55, and the atomic fraction (%) of Zn varies between 45-50.

[0102] From HAADF and EDS mapping, it becomes clear that NiZn particles of size ?40 nm (particle size distribution) are well dispersed on the TiO.sub.2 surface. Interestingly, almost all the NiZn particles are in the close vicinity of ZnO particles, projecting a clear interface between NiZn and ZnO nanoparticles. Oxygen rich layer around NiZn particle could have formed due to atmospheric surface oxidation.

Example 4: Conversion of Carbon Dioxide to Methanol

[0103] 2% Ni-8% Zn/90% TiO.sub.2 catalyst synthesized in Example 1 was tested for the conversion of carbon dioxide to methanol. The CO.sub.2 reduction was performed at 250? C. with pressure varying from 2.2 20, and 40 bar employing catalysts: a) 2% Ni-8% Zn supported by TiO.sub.2 reduced at 550? C.; b) 2% Ni-8% Zn supported by TiO.sub.2 reduced at 600? C.; and c) 2% Ni-8% Zn supported by TiO.sub.2 reduced at 650? C. A downflow fixed bed reactor was loaded with 0.4 cc of the catalyst. CO.sub.2, N.sub.2 and H.sub.2 flow rates were controlled by mass flow controllers and the reactor was fitted with high pressure valves and connections. Ratio of the CO.sub.2 to hydrogen was controlled to 1:3 with total flow rate of 60 mL/min and GHSV of 9000 h.sup.?1. The catalyst was pretreated under H.sub.2 gas for 2 h at 250? C. and then switched to the reactant feed. The outlet of the reactor was connected to a series of bubblers with water and analyzed by HPLC. The gas separated was analyzed online by GC. The methanol space time yield as a function of amount of methanol generated per gm of the catalyst per hour for the different catalysts and process conditions is presented in Table 1.

TABLE-US-00001 TABLE 1 Methanol yield of 2% Ni-8% Zn/TiO.sub.2 and 4% Ni-8% Zn/TiO2 catalyst reduced at different temperature/pressure conditions Catalyst reduced Catalyst reduced Catalyst reduced 4% Ni-8% Zn/TiO2 at 550? C. at 600? C. at 650? C. Reduced at 550? C. Reaction (Methanol STY) (Methanol STY) (Methanol STY) Methanol STY) pressure g of g of g of g of (Bar)/T (? C.) methanol/g.sub.cat/h methanol/g.sub.cat/h methanol/g.sub.cat/h methanol/g.sub.cat/h 2.2/250 0.00229 0.00520 0.00120 0.000701 20/250 0.01512 0.01242 0.00606 0.004224 40/250 0.02128 0.01552 0.00829 0.005315 *STYspace time yield.

[0104] Interestingly, the catalysts which are reduced at higher temperatures, viz., 550, 600 and 650? C., exhibited methanol formation at near ambient pressures (2.2 bar), but the catalysts reduced at lower temperatures (300 and 400? C.) did not show any methanol formation at near ambient pressures.

[0105] FIG. 3 shows the methanol space time yield for all three catalysts. Among these catalysts, 2% Ni-8% Zn supported by TiO.sub.2 and reduced at 550? C. exhibited most activity. It may due to more effective CO.sub.2 adsorption on its titania surface compared to other catalysts and appropriate NiZn particle size, and its interface with very small particles of ZnO.

[0106] FIG. 4 shows the selectivity of the catalysts at 2.2, 20 and 40 bar for methanol and methane which is the only by-product obtained. At near ambient pressure, selectivity is more for methane, but as pressure increases, NZT-550 shows more selectivity towards methanol.

[0107] FIG. 5 shows the in-situ infra-red spectra collected while passing only CO.sub.2 (5 ml/min) over reduced catalyst surface of 2% Ni-8% Zn supported by TiO.sub.2 and reduced at 650? C. at atmospheric pressure. The bands at 1367 cm.sup.?1 and 1577 cm.sup.?1 are assigned to symmetric and asymmetric vibrations of formate, respectively, and corresponding peaks of CH stretching of formate are present at 2887 cm.sup.?1 and 2971 cm-1, respectively. The bands at 2832 cm.sup.?1, 2930 cm.sup.?1 and 3412 cm.sup.?1 are ascribed to adsorbed methanolic species on the catalytic surface. The peaks at 1447 cm.sup.?1 and 1503 cm.sup.?1 are assigned to carbonate species.

[0108] The yield of methanol generated was compared for catalyst with different supports such as silica, alumina and indium oxide. Results are presented in Table 2. Thus, it is clear that not all supports generate methanol from carbon dioxide.

TABLE-US-00002 TABLE 2 Comparison of NiZn supported on different supports 2% Ni-8% 2% Ni-8% Zn/TiO.sub.2 2% Ni-8% Zn/TiO.sub.2 2% Ni-8% 2% Ni-8% Reaction (anatase) Zn/SiO.sub.2 (p-25)-Al.sub.2O.sub.3 Zn/Al.sub.2O.sub.3 Zn/In.sub.2O.sub.3 pressure g of g of g of g of g of (Bar)/T methanol/ methanol/ methanol/ methanol/ methanol/ (? C.) g.sub.cat/h g.sub.cat/h g.sub.cat/h g.sub.cat/h g.sub.cat/h 2.2/250 0.00049 0.00083 20/250 0.003903 0.003782 40/250 0.00549 0.005089

Example 5: Durability of the Catalyst

[0109] The durability for the catalyst reduced at 550? ? C. was studied for up to 36 hours under varying conditions. After placing the catalyst in the reactor, the temperature was set to 250? C. and the pressure was increased to 2.2 bars and the reaction was monitored for 12 h in the same condition. After 12 h the sample was collected and analyzed. Again, the pressure was increased to 20 bars and 40 bars in 12 h intervals and the collected sample was analyzed. The catalyst was found to be stable across all the conditions (FIG. 6).

[0110] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

Advantages of the Invention

[0111] The present disclosure provides a stable and efficient catalyst for conversion of carbon dioxide to methanol.

[0112] The present disclosure provides a facile and low pressure process for conversion of carbon dioxide to methanol.

[0113] The present disclosure provides a method of mitigating the effects of high atmospheric carbon dioxide to produce industrially useful methanol.