Metal organic framework derived nanocomposite catalyst for synthesis gas production

Abstract

A method for photothermal synthesis gas production. The method comprises feeding methane and carbon dioxide into a photothermal reactor, the photothermal reactor comprising a catalyst. The catalyst comprises a metal organic framework (MOF) derived nanocomposite oxide catalyst, the MOF derived nanocomposite oxide catalyst being grown on titanium dioxide (TiO.sub.2) quantum dots.

Claims

1. A method for photothermal synthesis gas production, the method comprising the steps of: feeding methane and carbon dioxide into a photothermal reactor, the photothermal reactor comprising a catalyst; reforming the methane and carbon dioxide to produce carbon monoxide and hydrogen; wherein the catalyst comprises a metal organic framework (MOF) derived nanocomposite oxide catalyst, wherein the oxide is three-dimensional (3D) cobalt oxide dodecahedral crystals, and wherein the catalyst comprises exfoliated graphitic carbon nitride, the MOF derived nanocomposite oxide catalyst being grown on titanium dioxide (TiO.sub.2) quantum dots.

2. The method as claimed in claim 1, wherein the MOF is ZIF-67.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The manner in which the above-recited features of the present invention is understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present disclosure and are therefore not to be considered limiting of its scope, for the present disclosure may admit to other equally effective embodiments.

(2) FIG. 1a shows a method of synthesizing MOF derived cobalt oxide according to an embodiment of the present disclosure;

(3) FIG. 1b shows a method of synthesizing MOF derived nanocomposite cobalt oxide catalyst according to an embodiment of the present disclosure;

(4) FIG. 1c shows a method of synthesizing MOF derived nanocomposite cobalt oxide catalyst according to an embodiment of the present disclosure;

(5) FIG. 2 shows a photoreactor according to an embodiment of the present disclosure;

(6) FIG. 3 shows x-ray diffraction analysis of g-C.sub.3N.sub.4, ZIF-67, MOF-derived Co.sub.3O.sub.4 and their Co.sub.3O.sub.4-based composites, according to an embodiment of the present disclosure;

(7) FIGS. 4a and 4b show the performance of pure g-C.sub.3N.sub.4 and various Co.sub.3O.sub.4 (1 to 5 wt. %) loaded g-C.sub.3N.sub.4 samples at different reaction times, according to an embodiment of the present disclosure;

(8) FIGS. 5a and 5b show the performance of pure TiO.sub.2 and various Co.sub.3O.sub.4 (1 to 5 wt. %) loaded TiO.sub.2 samples at different reaction times according to an embodiment of the present disclosure;

(9) FIGS. 6a and 6b show the effect of temperature (25 to 200 C.) on the conversion of CO.sub.2 with CH.sub.4 to produce H.sub.2 and CO according to an embodiment of the present disclosure; and

(10) FIGS. 7a and 7b show the effect of temperature (25 to 200 C.) on the conversion of CO.sub.2 with CH.sub.4 to produce H.sub.2 and CO, according to an embodiment of the present disclosure.

(11) The foregoing and other objects, features and advantages of the present invention, as well as the invention itself, will be more fully understood from the following description of preferred embodiments, when read together with the accompanying drawings.

DETAILED DESCRIPTION

(12) The present disclosure relates to the field of photothermal synthesis gas production, and more particularly to photothermal synthesis gas production using MOF derived nanocomposite oxide catalyst being grown on titanium dioxide (TiO.sub.2).

(13) The principles of the present invention and their advantages are best understood by referring to FIG. 1a to FIG. 7b. In the following detailed description of illustrative or exemplary embodiments of the disclosure, specific embodiments in which the disclosure may be practiced are described in sufficient detail to enable those skilled in the art to practice the disclosed embodiments. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims and equivalents thereof. References within the specification to one embodiment, an embodiment, embodiments, or one or more embodiments are intended to indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure.

(14) FIG. 1a shows a method of synthesizing MOF derived cobalt oxide according to an embodiment of the present disclosure.

(15) A co-precipitation technique is used to create the cobalt-based ZIF-67 MOF. First, 75 mL of methanol 112 is used to dissolve 5.46 g of Cobalt (II) nitrate hexahydrate (Co(NO.sub.3).sup.2.Math.6H.sub.2O) 103, which is then stirred magnetically for 30 minutes.

(16) Next, another 75 mL of methanol 112 is used to dissolve 6.16 g of 2-methylimidazole 101. After adding the 2-methylimidazole combination to the cobalt mixture dropwise 105, the mixture was vigorously stirred with a magnetic stirrer for a further six hours at room temperature. ZIF-67 MOF crystals 109 were obtained by drying 107 the purple suspension in an oven at 80 C. for an entire night following three rounds of methanol washing.

(17) The ZIF-67 MOF 109 then undergoes thermal treatment 111 to become Co.sub.3O.sub.4 114. To produce the final product of Co.sub.3O.sub.4 114 powders, ZIF-67 crystals are first placed in a crucible and then calcined for 4 hours at 350 C. in a muffle furnace.

(18) FIG. 1b shows a method of synthesizing MOF derived nanocomposite cobalt oxide catalyst according to an embodiment of the present disclosure.

(19) Graphitic carbon nitride 104 is produced using a melamine 100 precursor. The melamine 100 precursor is thermally decomposed 102 at 500 C. for 2 hours to arrive at graphitic carbon nitride 104.

(20) In embodiments, the graphitic carbon nitride is two dimensional graphitic carbon nitride nanosheets (2D g-C.sub.3N.sub.4).

(21) For the synthesis of exfoliated graphitic carbon nitride (ECN) 110, a mixture of melamine and urea 106 is used. Melamine and urea 106 in equal amounts are mixed and placed in a ceramic crucible before being heated 108 to 550 C. for the duration of 2 hours.

(22) The gas produced by the decomposition of urea is used to exfoliate graphitic carbon nitride layers and produce defective graphitic carbon nitride with oxygen vacancies. The product obtained is grinded to a fine powder and is given the name exfoliated graphitic carbon nitride (ECN) 110.

(23) It has been found that synthesizing exfoliated 2D nanosheets of graphitic carbon nitrides with the use of the method using melamine/urea with controlled thermal decomposition conditions results in a larger surface area and higher charge separation efficiency.

(24) The Co.sub.3O.sub.4/g-C.sub.3N.sub.4 composites 122 were synthesized using a self-assembly approach. For this purpose, Co.sub.3O.sub.4 114 and g-C.sub.3N.sub.4 104 were used as discussed previously. First, g-C.sub.3N.sub.4 104 of specific quantity (0.2 to 1 g) was dispersed in methanol 112 (5 to 20 mL) and stirred 148 for a specific time (1 to 4 hours) to get good dispersion in suspension 116. In the next step, specific amount of Co.sub.3O.sub.4 114 (1 to 10 wt. %) is dispersed in methanol and is added 118 to the above suspension 116 under stirring and the solution was stirred for another 4 hours in addition to ultrasonic to get well-dispersed Co.sub.3O.sub.4-loaded g-C.sub.3N.sub.4. The solution was finally dried 120 in an oven at 100 C. overnight to get a Co.sub.3O.sub.3/g-C.sub.3N.sub.4 composite 122.

(25) In embodiments, the Co.sub.3O.sub.3/g-C.sub.3N.sub.4 composite is a binary composite.

(26) FIG. 1c shows a method of synthesizing MOF derived nanocomposite cobalt oxide catalyst according to an embodiment of the present disclosure.

(27) The Co.sub.3O.sub.4/TiO.sub.2 composites 123 are synthesized using a self-assembly approach. For this purpose, titanium dioxide (TiO.sub.2) 115 is used, which is synthesized using the sol-gel method. The sol-gel method results in TiO.sub.2 quantum dots. First, TiO.sub.2 115 of specific quantity (0.2 to 1 g) is dispersed in methanol 112 (5 to 20 mL) and stirred 117 for a specific time (1 to 4 hours) to get good dispersion.

(28) In the next step, a specific amount of Co.sub.3O.sub.4 114 (1 to 10 wt. %) dispersed in methanol is added to the above suspension under stirring 119 and the solution is then stirred for another 4 hours in addition to ultrasonic application to get well-dispersed Co.sub.3O.sub.4-loaded TiO.sub.2. The solution is finally dried 121 in an oven at 100 C. overnight to get a Co.sub.3O.sub.4/TiO.sub.2 composite 123.

(29) In embodiments, the Co.sub.3O.sub.4/TiO.sub.2 composite is a binary composite.

(30) In embodiments, Co3O4/0D TiO2 binary composite is synthesized using an in-situ growing method of ZIF-derived 3D Co3O4 over titania (TiO.sub.2) quantum dots. This method is termed a solvothermal synthesis method and is designed to achieve easy morphological regulation of MOF derivatives in the final binary composites.

(31) In embodiments, the method of synthesizing MOF derived nanocomposite cobalt oxide catalyst is a method of synthesizing MOF derived nanocomposite cobalt oxide catalyst, wherein the composite is a ternary composite. In embodiments, the ternary composite comprises titanium dioxide, cobalt oxide, and graphitic carbon nitride.

(32) In embodiments, The ternary oxides/nitrides composites of three dimensional cobalt oxide coupled with two dimensional exfoliated graphitic carbon nitride and titanium dioxide nano dots (3DCo.sub.3O.sub.4/2D E-gC.sub.3N.sub.4/0D TiO.sub.2) with hierarchical nanotexture were synthesized using an ultrasonic approach with good interface interaction, Schottky formation, maximum band structure position and good stability under photothermal conditions at low-temperature range.

(33) The ultrasonic approach may comprise a combination of the steps of FIG. 1b and FIG. 1c. The ultrasonic approach for synthesizing the ternary composite may comprise dispersing TiO.sub.2 of specific quantity (0.2 to 1 g) in methanol (5 to 20 mL) and stirring for a specific time (1 to 4 hours) to get good dispersion. The method may also comprise dispersing g-C.sub.3N.sub.4 of specific quantity (0.2 to 1 g) in methanol (5 to 20 mL) and stirring for a specific time (1 to 4 hours) to get good dispersion in suspension. The method may also comprise mixing the g-C.sub.3N.sub.4 dispersion with the TiO.sub.2 dispersion. The method may comprise mixing Co.sub.3O.sub.4 with methanol and adding it to the g-C.sub.3N.sub.4 TiO.sub.2 mixture. In embodiments, the Co.sub.3O.sub.4 mixed with methanol is added to either the g-C.sub.3N.sub.4 dispersion or the TiO.sub.2 dispersion first, and then mixed. The method may then comprise drying the final mixture to arrive at the ternary composite.

(34) It has been found that the ternary composite exhibits a higher oxidation potential.

(35) FIG. 2 shows a photoreactor according to an embodiment of the present disclosure.

(36) A continuous flow stainless steel fixed bed photothermal reactor 300 is used to carry out the photocatalytic, thermochemical and photothermal driven CO.sub.2 reforming of methane (CH.sub.4) reaction. The reactor comprises a main reactor chamber 307, a glass window 305 to pass the light and a heating jacket 309 to control the reactor temperature. The catalyst 350 is placed inside the reactor's bottom surface with a loading amount of 150 mg and it can be varied from 50 to 250 mg. The feed mixture 311 comprises CO.sub.2 and CH.sub.4 with a feed ratio of 1:1. The gas 311 is flowed through the reactor at a flow rate of 15 mL/min and is kept constant in at steady state.

(37) In embodiments, depending on the size of the photoreactor, the flowrates and quantities of catalyst may be different as required by the scale.

(38) In embodiments, the temperature of the reactor is greater than 25 C. In embodiments, the temperature of the reactor is greater than 100 C. In embodiments, the temperature of the reactor is greater than 150 C.

(39) Transmitted light 303 passes into the photoreactor to initiate the reaction process.

(40) Typically, some light 301 is reflected off the reactor surface. The intensity of the sunlight is typically in the region of 100 mW/cm.sup.2.

EXPERIMENTS

(41) The photothermal reactor of FIG. 2 was used to conduct experiments on the efficacy of the catalysts.

(42) The following experiments were conducted: CO.sub.2 reforming with CH.sub.4 over Co.sub.3O.sub.4/g-C.sub.3N.sub.4 (Co.sub.3O.sub.4 loading: 1 to 5 wt. %) at 100 C. and with light; CO.sub.2 reforming with CH.sub.4 over 3% Co.sub.3O.sub.4/g-C.sub.3N.sub.4 at different temperatures from 25 to 200 C. and with light; CO.sub.2 reforming with CH.sub.4 over 3% Co.sub.3O.sub.4/g-C.sub.3N.sub.4 at different temperatures from 100 to 200 C. and without light; CO.sub.2 reforming with CH.sub.4 over Co.sub.3O.sub.4/TiO.sub.2 (Co.sub.3O.sub.4 loading: 1 to 5 wt. %) at 100 C. and with light; CO.sub.2 reforming with CH.sub.4 over 3% Co.sub.3O.sub.4/TiO.sub.2 at different temperatures from 25 to 200 C. and with light; and CO.sub.2 reforming with CH.sub.4 over 3% Co.sub.3O.sub.4/TiO.sub.2 at different temperatures from 100 to 200 C. and without light.

(43) FIG. 3 shows x-ray diffraction (XRD) analysis of g-C.sub.3N.sub.4, ZIF-67, MOF-derived Co.sub.3O.sub.4 and their Co.sub.3O.sub.4-based composites.

(44) The peaks observed at 2-theta (2) of 12.85 were related (100) crystal planes of g-C.sub.3N.sub.4, whereas, a strong peak at 20 of 27.47 reflects the (002) crystal plane of g-C.sub.3N.sub.4 having a typical aromatic ring with interlayers. The anatase phase of TiO.sub.2 is represented by the diffraction peaks in the XRD patterns of pure TiO.sub.2 that belong to the lattice plans of (101), (004), (200), (220), and (215). On the other hand, a different lattice design at (110) verifies the existence of a smaller-sized rutile phase of TiO.sub.2. The as-prepared ZIF-67 showed peaks at 10.36, 12.71, 14.68, 16.41, 17.96, 22.06, 24.47, 26.56 and 29.61 corresponding to (002), (112), (022), (013), (222), (114), (233), (134) and (044), respectively, with the highest peak at 7.33 showing the (011) plane. Co.sub.3O.sub.4 is successfully generated by thermally heating ZIF-67 at 350 C. for 4 hours, as evidenced by the characteristic peaks at 20=19.09, 31.3, 36.9, 45.0, 59.47, and 65.31. For the composite Co.sub.3O.sub.4/TiO.sub.2 and Co.sub.3O.sub.4/g-C.sub.3N.sub.4, all the peaks related to Co.sub.3O.sub.4, g-C.sub.3N.sub.4 and TiO.sub.2 were present, which confirms the successful synthesis of these composites.

(45) Field emission scanning electron microscopy (FESEM) was conducted to understand the dimensionality, morphology, and structure of the prepared samples. ZIF-67 exhibited uniform three-dimensional (3D) dodecahedral particles with smooth surfaces. The morphology of Co.sub.3O.sub.4 was similar to ZIF-67 with a 3D dodecahedron structure. However, Co.sub.3O.sub.4 surfaces were relatively rough without obvious edges when it was compared to ZIF-67. Uniform size and shape of TiO.sub.2 particles was also observed. The morphology of g-C.sub.3N.sub.4 had a 2D layered structure. When Co.sub.3O.sub.4 was added to g-C.sub.3N.sub.4, there was no change in morphology, however, Co.sub.3O.sub.4 was uniformly spread over the g-C.sub.3N surface to provide a heterojunction among the two materials. This shows that self-assembly is a promising approach to produce 3D/2D heterojunction composites.

(46) It was also seen that Co.sub.3O.sub.4 with large sizes and clear edges are distributed within the TiO.sub.2 particles. With high magnification a 3D Co.sub.3O.sub.4 dodecahedron structure can be observed. All these results further support the successful synthesis of single materials and binary composites with controlled structure and morphology.

(47) FIG. 4a shows the yield of H.sub.2 of pure g-C.sub.3N.sub.4 and various Co.sub.3O.sub.4 (1 to 5 wt. %) loaded g-C.sub.3N.sub.4 samples at different reaction times.

(48) It can be seen that the production of H.sub.2 is fairly consistent across the entire reaction time, evidenced by the steady increase in the total yield over time.

(49) The production of H.sub.2 was very small with pure g-C.sub.3N.sub.4 411 and there was no significant impact on the yield of H.sub.2 with 1% Co.sub.3O.sub.4 413 loading. However, when Co.sub.3O.sub.4 loading was increased to 3 wt. % 415 and 5 wt. % 417, a significant amount of H.sub.2 was produced.

(50) FIG. 4b shows the yield of carbon monoxide (CO) of pure g-C.sub.3N.sub.4 and various Co.sub.3O.sub.4 (1 to 5 wt. %) loaded g-C.sub.3N.sub.4 samples at different reaction times.

(51) The production of CO was very small with pure g-C.sub.3N.sub.4 411, however, CO yield was significantly increased with 1% Co.sub.3O.sub.4 413 loading. The highest yield of CO was obtained with 3 wt. % Co.sub.3O.sub.4 415 loading into g-C.sub.3N.sub.4. However, when Co.sub.3O.sub.4 loading was increased to 5 wt. % 417, the production of CO was decreased.

(52) The trends for CO and H.sub.2 production over Co.sub.3O.sub.4/g-C.sub.3N.sub.4 composites were different during CO.sub.2 reforming of CH.sub.4 reactions. The production of H.sub.2 was increased with Co.sub.3O.sub.4 loading, which shows it is beneficial to maximize hydrogen production. On the other hand, production of CO was decreased with higher Co.sub.3O.sub.4 loading, which was possibly due to the photocatalytic effect. The increasing Co.sub.3O.sub.4 may increase the charge recombination centres and also more active sites to active sides reactions. Overall, Co.sub.3O.sub.4/g-C.sub.3N.sub.4 composite was more selective to produce CO during dry reforming of methane reaction.

(53) FIG. 5a shows the yield of H.sub.2 of pure TiO.sub.2 and various Co.sub.3O.sub.4 (1 to 5 wt. %) loaded TiO.sub.2 samples at different reaction times.

(54) Again, it is clear that the production rate of H.sub.2 is fairly continuous over the entire reaction time.

(55) The production of H.sub.2 was lower with pure TiO.sub.2 511 and there was no significant impact on the yield of H.sub.2 with 1% Co.sub.3O.sub.4 513 loading. However, when Co.sub.3O.sub.4 loading was increased to 3 wt. % 515 and 5 wt. % 517, a significant amount of H.sub.2 was produced.

(56) In embodiments, the Co.sub.3O.sub.4 loading is between 3 wt. % and 5 wt. %.

(57) FIG. 5b shows the yield of CO of pure TiO.sub.2 and various Co.sub.3O.sub.4 (1 to 5 wt. %) loaded TiO.sub.2 samples at different reaction times.

(58) The production of CO was very small with pure TiO.sub.2 511; however, CO yield was significantly increased with 1% Co.sub.3O.sub.4 513 loading. The highest yield of CO was obtained with 3 wt. % Co.sub.3O.sub.4 515 loading into g-C.sub.3N.sub.4. However, when Co.sub.3O.sub.4 loading was increased to 5 wt. % 517, the production of CO was decreased.

(59) The trends for CO and H.sub.2 production over Co.sub.3O.sub.4/TiO.sub.2 composites were different during CO.sub.2 reforming of CH.sub.4 reactions. The production of H.sub.2 was increased with Co.sub.3O.sub.4 loading, which shows it is beneficial to maximize hydrogen production. On the other hand, production of CO was decreased with higher Co.sub.3O.sub.4 loading, which was possibly due to the photocatalytic effect. The increasing Co.sub.3O.sub.4 may increase the charge recombination centres and also more active sites to active site reactions. Overall, the Co.sub.3O.sub.4/TiO.sub.2 composite was more selective in producing CO during dry reforming of the methane reaction.

(60) FIG. 6a shows the production of H.sub.2 at different reaction temperatures with light and without light using 3% Co.sub.3O.sub.4/g-C.sub.3N.sub.4 composite catalyst. It was observed that the production of hydrogen was increased with the increase of temperature, and its yield was higher when both the light and the temperature were used through the photothermal process. This was evidently due to the higher stability of methane and its need for higher activation energy, which can be minimized using a hybrid system.

(61) There are seven bars represented in the chart for each time period, with the bars representing, from left to right: 25 C.+light; 100 C.+light; 150 C.+light; 200 C.+light; 100 C. (no light); 150 C. (no light); and 200 C. (no light) respectively.

(62) FIG. 6b shows the production of CO over 3% Co.sub.3O.sub.4/g-C.sub.3N.sub.4 composite at different temperatures and photothermal conditions. The sequence of conditions represented by the bars are in the same order and arrangement as that of FIG. 6a.

(63) Interestingly, it is observed that without light and using only thermal conditions, the yield of CO was very small, however, when both the light and the temperature were employed, the yield of CO was significantly increased. These results confirm that photothermal with the use of light and heat over Co.sub.3O.sub.4/g-C.sub.3N.sub.4 is a promising approach to convert CO.sub.2 and CH.sub.4 through dry reforming process to produce CO and H.sub.2.

(64) FIG. 7a shows the production of H.sub.2 at different reaction temperatures with light and without light using 3% Co.sub.3O.sub.4/TiO.sub.2. The sequence of conditions represented by the bars are in the same order and arrangement as that of FIG. 6a.

(65) It was observed that the production of hydrogen was increased with the increase of temperature, and its yield was higher when both the light and the temperature were used through the photothermal process. This was due to the higher stability of methane and it need higher activation energy, which can be minimized using a hybrid system.

(66) FIG. 7b shows the production of CO over 3% Co.sub.3O.sub.4/TiO.sub.2 composite at different temperatures and photothermal conditions. The sequence of conditions represented by the bars are in the same order and arrangement as that of FIG. 6a.

(67) Interestingly, it can be observed that without light and using only thermal conditions, the yield of CO was very small, however, when both the light and the temperature were employed, the yield of CO was significantly increased. These results confirm that photothermal with the use of light and heat over Co.sub.3O.sub.4/TiO.sub.2 is a promising approach to convert CO.sub.2 and CH.sub.4 through a dry reforming process to produce CO and H.sub.2.

(68) It has been found that both the Co.sub.3O.sub.4/g-C.sub.3N.sub.4 and Co.sub.3O.sub.4/TiO.sub.2 composites increased the production of H.sub.2 and CO, with a loading of about 3% CO.sub.3O.sub.4 yielding good results.

(69) 3D CO.sub.3O.sub.4 according to the present disclosure can be an efficient sensitizer, and can be used as a catalyst/cocatalyst with semiconductors to increase charge separation efficiency, electrical conductivity, and solar energy harvesting efficiency.

(70) Synthesizing TiO2 nanoparticles with the sol-gel method with suitable operating conditions has been found to be beneficial to adjusting surface area, light harvesting efficiency and charge separation productivity under solar energy irradiation.

(71) Furthermore, the highest yield of CO was obtained when the reaction temperature of 100 C. was used with the light energy. When the temperature was increased to 150 and 200 C., the production of CO was decreased. These results can be explained based on the adsorption-desorption process. Using a higher temperature of more than 100 C., there is possible desorption of reactants over the catalyst surface, which lowers the catalytic activity. When the reaction was conducted without light, there was very small amount of CO formation, which shows at lower temperatures, reaction with Co.sub.3O.sub.4/TiO.sub.2 composite is more dependent on the light energy than using heat energy. This can be further confirmed by the results of 200 C., in which the yield of CO was increased without light, the yield of CO was increased.

(72) It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. The disclosures and the description herein are intended to be illustrative and are not in any sense limiting the present disclosure, defined in scope by the following claims.

(73) Many changes, modifications, variations and other uses and applications of the present disclosure will become apparent to those skilled in the art after considering this specification and the accompanying drawings, which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications, which do not depart from the spirit and scope of the present disclosure, are deemed to be covered by the invention, which is to be limited only by the claims which follow.