CN112774709A - Supported catalyst and preparation method and application thereof - Google Patents
Supported catalyst and preparation method and application thereof Download PDFInfo
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- CN112774709A CN112774709A CN201911095716.3A CN201911095716A CN112774709A CN 112774709 A CN112774709 A CN 112774709A CN 201911095716 A CN201911095716 A CN 201911095716A CN 112774709 A CN112774709 A CN 112774709A
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Abstract
The application discloses a supported catalyst, which comprises a carrier g-C3N4And an active metal element supported on a carrier, the metal being monoatomic in dispersion. The application also relates to the use of the supported catalyst for the preparation of oxygenates including methanol from methane and to a process for the preparation of oxygenates including methanol from methane using the supported catalyst. The supported catalyst provided by the application can maximally exert the catalytic effect of metal atoms. The method provided by the application enables methane to be activated at low temperature to prepare the oxygen-containing compound containing methanol in one step, the reaction temperature is low, and the selectivity of the oxygen-containing compound containing methanol is high.
Description
Technical Field
The application belongs to the field of methanol preparation from methane, and particularly relates to a supported catalyst, a preparation method of the supported catalyst, and a method for preparing an oxygen-containing compound containing methanol from methane by using the supported catalyst, in particular to a method for preparing the oxygen-containing compound containing methanol from methane by a low-temperature activation one-step method.
Background
Methanol, one of the basic raw materials for current industrial application, has been greatly developed whether being used as a traditional organic chemical raw material for preparing higher-value olefins or being used as a fuel cell and some product additives in the field of emerging energy substitutes.
At present, the domestic method for preparing methanol is mainly an indirect conversion method of coal or natural gas, and firstly, the coal or natural gas is converted into synthesis gas (H)2+ CO) and then via Fischer-Tropsch synthesis to methanol. The indirect conversion method has the defects of high reaction temperature (800 ℃) and complex reaction process flow.
Methanol can also be converted from methane, which is the main component of natural gas. In this process, the choice of catalyst is critical. In recent years, the research on catalysts has been mainly focused on noble metal and transition metal supported catalysts. The catalyst of noble metals such as gold-palladium alloy can activate methane at lower temperature, and has higher methanol selectivity, but the noble metals such as gold-palladium alloy have high cost and poor economical practicability.
Disclosure of Invention
Therefore, there is a need to develop new efficient catalysts with economical and high methane conversion. To this end, according to one aspect of the present application, there is provided a supported catalyst comprising a metal element and a support g-C3N4Wherein the metal is monoatomic; the supported catalyst is used for preparing the oxygenated compounds containing the methanol by one step through low-temperature activation of the methane, and has high selectivity>90％)。
In a preferred embodiment of the supported catalyst per se, the supported catalyst comprises a carrier and an active component supported on the carrier;
wherein the carrier is g-C3N4；
The active component comprises an active metal element, and the metal is in a monoatomic dispersion. Optionally, the metal element is at least one selected from Rh, Cu, Fe, and Co.
Optionally, the metal element is selected from one of Rh, Cu, Fe, and Co.
Optionally, the metal element in the supported catalyst is g-C relative to the support3N4The loading amount of (A) is 0.1-1 wt.%.
Optionally, the metal element in the supported catalyst is g-C relative to the support3N4The loading of (b) is most preferably 0.25 to 0.75 wt.%.
Optionally, the metal element in the supported catalyst is g-C relative to the support3N4The loading amount of (A) is 0.1-0.75 wt.%.
Optionally, the metal element in the supported catalyst is g-C relative to the support3N4Is selected from 0.25 wt.%, 0.5 wt.% or 1 wt.%; the lower limit is selected from 0.1 wt.%, 0.25 wt.%, or 0.5 wt.%.
Optionally, the supported catalyst has a layered structure.
In another aspect of the present application, there is provided a method for preparing the supported catalyst, which comprises:
will contain g-C3N4And roasting the raw material of the metal precursor I to obtain the supported catalyst.
Optionally, the metal precursor is selected from at least one of soluble metal salts.
Optionally, the metal source comprises at least one of a chloride of a metal, a nitrate of a metal, a sulfate of a metal.
Optionally, the metal precursor is selected from at least one of soluble salts of Rh, soluble salts of Cu, soluble salts of Fe, and soluble salts of Co.
Alternatively, the soluble salt of Rh is selected from RhCl3、Rh(NO3)3At least one of;
optionally, the soluble salt of Cu is selected from CuCl2、Cu(NO3)2、CuSO4At least one of (1).
Optionally, the soluble salt of Fe is selected from FeCl3、Fe(NO3)3、FeSO4At least one of (1).
Optionally, the soluble salt of Co is selected from CoCl2、Co(NO3)2、CoSO4At least one of (1).
Alternatively, the g-C3N4The obtaining method comprises the following steps: thermally condensing a precursor containing carbon and nitrogen to prepare the g-C3N4。
Optionally, the carbon-and nitrogen-containing precursor is selected from at least one of melamine, thiourea, dicyanodiamine, urea;
the heat condensation temperature is 500-650 ℃, and the time is 2-6 h.
Alternatively, the g-C3N4The obtaining method comprises the following steps: roasting II a precursor containing carbon and nitrogen, and then cooling, washing, drying and grinding to obtain the g-C3N4。
As a specific embodiment thereof, said g-C3N4The obtaining method comprises the following steps: directly heating and roasting the precursor in static air, and then cooling, washing, drying and grinding to obtain the g-C3N4And (3) a carrier.
Alternatively, the g-C3N4The roasting temperature of the roasting II is 500-650 ℃ and the roasting time is 2-6 h during the preparation of the carrier.
Optionally, the upper temperature limit of roasting II is selected from 550 ℃, 600 ℃ or 650 ℃; the lower limit is selected from 500 deg.C, 550 deg.C or 600 deg.C.
Optionally, the upper time limit of the roasting II is selected from 3h, 4h, 5h or 6 h; the lower limit is selected from 2h, 3h, 4h or 5 h.
Optionally, the drying conditions are: the drying temperature is 90-150 ℃, and the drying time is 6-24 h.
As a specific embodiment, g-C in the catalyst3N4The specific preparation method of the carrier comprises the following steps: taking a certain amount of melamine, urea, thiourea or dicyanodiamide as a precursor, placing the precursor in a ceramic crucible, heating to 500-650 ℃ in a muffle furnace, and roasting for 2-6 h. To be naturally cooledCooling to room temperature, adding deionized water, washing, filtering, drying, and grinding to obtain g-C3N4And (3) a carrier.
Optionally, the roasting conditions are: the temperature of the roasting I is 200-500 ℃;
the roasting time I is 1-3 h;
and the atmosphere of the roasting I is an inert atmosphere.
Optionally, the upper temperature limit of the roasting I is selected from 250 ℃, 300 ℃, 350 ℃, 400 ℃ or 500 ℃; the lower limit is selected from 200 deg.C, 250 deg.C, 300 deg.C, 350 deg.C or 400 deg.C.
Optionally, the upper time limit of the roasting I is selected from 1.5h, 2h, 2.5h or 3 h; the lower limit is selected from 1h, 1.5h, 2h or 2.5 h.
Optionally, the inert atmosphere is selected from at least one of nitrogen and inert gas.
Optionally, the inert gas is selected from at least one of nitrogen and argon.
Optionally, the preparation method of the supported catalyst comprises:
soaking the solution containing the metal precursor in the same volume C3N4Drying and roasting to obtain the supported catalyst.
Optionally, the concentration of the solution containing the metal precursor is 0.2-50 mg/ml.
Optionally, the upper concentration limit of the solution containing the metal precursor is selected from 0.25mg/ml, 0.625mg/ml, 1.25mg/ml, 1.875mg/ml, or 2 mg/ml; the lower limit is selected from 0.2mg/ml, 0.25mg/ml, 0.625mg/ml, 1.25mg/ml or 1.875 mg/ml.
Optionally, the solvent of the solution containing the metal precursor comprises water.
Optionally, the drying conditions in the preparation method of the supported catalyst are as follows: the drying temperature is 40-100 ℃, and the drying time is 6-12 h.
In a preferred embodiment of the supported catalyst of the present application, wherein the supported catalyst is prepared by a process comprising the steps of:
1) preparation of g-C3N4Carrier: by reacting g-C3N4The precursor of the carrier is subjected to the steps of roasting, cooling, washing, drying and grinding to obtain g-C3N4A carrier, a carrier and a water-soluble polymer,
2) preparation of a catalyst comprising a metal and g-C3N4Supported catalyst: isovolumetrically impregnating the g-C obtained in step 1) with a solution of a metal precursor3N4Drying and grinding the carrier, and roasting at 200-600 ℃, preferably 200-500 ℃, more preferably 250-400 ℃ for 1-3 h, preferably 2-3 h to obtain the carrier containing metal and g-C3N4A supported catalyst.
In a more preferred embodiment of the supported catalyst herein, g-C3N4The precursor of the carrier is selected from one of melamine, thiourea, dicyanodiamine and urea.
In a preferred embodiment of the supported catalyst herein, the process for preparing the supported catalyst comprises the steps of:
1) preparation of g-C3N4Carrier: g-C3N4The g-C is obtained by directly heating and roasting a precursor in static air for thermal condensation, and then cooling, washing, drying and grinding the precursor3N4A carrier, a carrier and a water-soluble polymer,
2) preparation of a catalyst comprising a metal and g-C3N4Supported catalyst: isovolumetrically impregnating the g-C with a solution of a metal precursor3N4The carrier is dried, ground and roasted to obtain the catalyst containing the metal and g-C3N4A supported catalyst.
In a more preferred embodiment of the supported catalyst of the present application, the drying temperature in step 1) and step 2) is 40 to 120 ℃, preferably 40 to 100 ℃, and more preferably 50 to 100 ℃. In this embodiment, the drying temperature in step 1) and step 2) may be the same or different, for example, the drying temperature in step 1) may be 100 ℃ and the drying temperature in step 2) may be 60 ℃.
In a more preferred embodiment of the supported catalyst of the present application, the drying time in step 1) and step 2) is 6 to 12 hours, preferably 8 to 12 hours. In this embodiment, the drying time and temperature in step 1) and step 2) may be the same or different, for example, the drying time in step 1) may be at 100 ℃ for 12 hours, and the drying temperature in step 2) may be at 60 ℃ for 12 hours.
In a more preferred embodiment of the supported catalyst of the present application, the calcination temperature of the catalyst in step 2) is 200 to 600 ℃, preferably 200 to 500 ℃, more preferably 250 to 400 ℃, the calcination time is 1 to 3 hours, preferably 2 to 3 hours, and the calcination atmosphere is an inert gas, such as argon.
According to another aspect of the present application there is provided the use of a supported catalyst of the present application for the production of oxygenates including methanol from methane.
In still another aspect of the present application, a method for preparing an oxygen-containing compound including methanol in one step from methane is provided, which is characterized in that a feed gas containing methane is introduced into a reactor containing an oxidant and a catalyst, and reacted to obtain the oxygen-containing compound including methanol;
wherein the catalyst is selected from at least one of the supported catalysts and the supported catalysts prepared by the method;
the oxygenates include methanol and methyl hydroperoxide.
Optionally, a solvent, a catalyst, and an oxidant are included in the reactor;
wherein the oxidizing agent comprises hydrogen peroxide;
the container is an intermittent high-pressure reaction kettle.
Optionally, the oxidizing agent is a hydrogen peroxide solution with a mass concentration of 0.1% -30%.
Optionally, the ratio of the catalyst to the solvent is 10-200 mg: 5-200 mL, preferably 20-150 mg: 10-150 mL, and more preferably 30-100 mg: 10-100 mL.
Optionally, the amount of the oxidant added is 5-50 ml.
Optionally, the solvent comprises water.
Optionally, the temperature of the reaction is 25-50 ℃;
the reaction time is 0.5-12 h;
the reaction pressure is 0.5-5 MPa.
Optionally, the upper temperature limit of the reaction is selected from 30 ℃, 35 ℃, 40 ℃, 45 ℃ or 50 ℃; the lower limit is selected from 25 deg.C, 30 deg.C, 35 deg.C, 40 deg.C or 45 deg.C.
Optionally, the upper pressure limit of the reaction is selected from 1MPa, 2MPa, 3MPa, 4MPa, or 5 MPa; the lower limit is selected from 0.5MPa, 1MPa, 2MPa, 3MPa or 4 MPa.
As a specific embodiment, the method for preparing the oxygenated compounds including methanol by methane in one step comprises the following steps: introducing methane into a batch high-pressure reaction kettle filled with a catalyst, water and a hydrogen peroxide solution with the mass concentration of 0.1-30% for reaction.
As a specific embodiment, the method for preparing the oxygenated compounds including methanol by methane in one step comprises the following steps:
methane (CH)4) Introducing the mixture into a batch high-pressure reaction kettle containing the catalyst, water and a hydrogen peroxide solution with the mass concentration of 0.1-30% to react at the temperature of 25-65 ℃ for 0.5-12 h and under the pressure of 0.5-5 MPa; obtaining a mixed aqueous solution of the product methanol and methyl hydroperoxide;
preferably, the reaction temperature is 25-60 ℃, and more preferably 25-50 ℃;
in a preferred embodiment of the present methane production oxygenate process including methanol, wherein the process is a one-step process.
In a preferred embodiment of the present methane production oxygenate process including methanol, the reaction is carried out in the presence of an oxidant, hydrogen peroxide solution. The mass concentration of the hydrogen peroxide solution may be 0.1 to 30 wt.%.
In a more preferred embodiment of the present methane production oxygenate process including methanol, the process comprises: raw material gas CH4Introducing into a reactor containing a catalyst as described herein, adding a hydrogen peroxide solution, addingHeating to 25-50 ℃ and starting to react for 0.5-12 h. Preferably, the feed gas CH4Is high-purity CH4. Also preferably, the concentration of the hydrogen peroxide solution is 0.1% to 30%.
In a further preferred embodiment of the process for methane production of oxygenates including methanol according to the present application, the reactor containing the catalyst also contains water.
In the application, the method is a method for preparing oxygen-containing compounds including methanol by methane low-temperature activation in one step, water is used as a reaction solvent, and high-purity CH is used4The gas is used as a raw material gas, the hydrogen peroxide solution is used as an oxidant, the reaction is carried out for 0.5-12 h at the temperature of 25-50 ℃ under the action of a catalyst, the mixed aqueous solution of the methanol and the methyl hydrogen peroxide can be prepared, the solution is further heated and reacted at the temperature of 90-250 ℃, and the methyl hydrogen peroxide can be completely converted into the methanol.
In a preferred embodiment of the present methane production oxygenate process comprising methanol, wherein the selectivity of the oxygenate comprising methanol is > 90%, preferably 90-100%, more preferably 95-100%.
In the present application, the TOF value of the catalyst is 0.2 to 3.5, preferably 0.3 to 3.0, more preferably 0.4 to 2.5.
In the present application, the term "support" is understood to mean a substance which interacts with the metal and has a co-catalytic effect, and is not understood to mean a substance which merely has the effect of supporting the active component.
In this application "g-C3N4"refers to graphite-like phase carbon nitride.
The beneficial effects that this application produced include:
1) the main active component of the supported catalyst provided by the application is metal single atom, so that the catalytic effect of the metal atom can be exerted to the maximum, and meanwhile, the metal atom and the carrier interact with each other, so that the metal atom is prevented from being agglomerated to reduce the catalytic performance.
2) The method provided by the application can activate methane at low temperature to prepare methanol in one step, and compared with the existing method for preparing methanol from methane, the method provided by the application is simple and feasible, and is suitable for large-scale production; in addition, the method can directly convert methane into methanol in one step, and has high selectivity (> 90%) of the oxygen-containing compounds.
3) The method provided by the application enables methane to be activated at low temperature to prepare methanol in one step, and compared with the traditional method for preparing oxygen-containing compounds by directly converting methane in one step, the method provided by the application has low reaction temperature, and even can activate methane at room temperature to react.
Drawings
FIG. 1 shows pure g-C prepared according to the procedure of example 13N4X-ray powder diffraction pattern of support and supported catalysts M/g-C supporting different metals prepared according to examples 2 and 9-11 of the present application3N4-350X-ray powder diffraction pattern.
FIGS. 2a-2b are high resolution TEM and spherical aberration SEM images of the catalyst prepared in example 2 of the present application.
FIG. 3 shows the results of nuclear magnetic measurements of the catalyst prepared according to example 2 of the present application in the low temperature conversion of methane.
Detailed Description
The present application will be described in detail with reference to examples, but the present application is not limited to these examples.
Unless otherwise specified, the raw materials, equipment and detection equipment used in the examples of the present application are all conventional raw materials, equipment and detection equipment in the art purchased from commercial sources; unless otherwise specified, the experimental conditions in the present application are all normal temperature and normal pressure.
In the present application, the selectivity of the product methanol and methyl hydroperoxide mixed aqueous solution and the TOF value of the catalyst were determined as follows: the liquid phase, i.e., a mixed aqueous solution of the products methanol and methyl hydroperoxide, was analyzed by Nuclear Magnetic Resonance (NMR), and the selectivity of the liquid phase oxygenates (methanol and methyl hydroperoxide) and the TOF value of the catalyst were calculated according to the following formulas.
Selectivity S of liquid phase oxygen-containing compoundOxygenateAnd (3) calculating:
SOxygenate＝{[Oxygenate]/([CH4]in-[CH4]out)}×100％
wherein: [Oxygenate]Is the total molar amount of liquid-phase oxygenates (methanol and methyl hydroperoxide) [ CH ]4]inIs filled with CH4Molar amount of [ CH ]4]outIs the molar amount of remaining methane.
The TOF values of the catalysts were calculated as follows:
TOF＝[Oxygenate]/[Active sites]/time
wherein: [ Oxygenate ] is the total molar amount of liquid phase oxygenates (methanol and methyl hydroperoxide), [ Active sites ] is the molar amount of Active sites on the catalyst, and time is the reaction time.
Examples the catalyst loading is the loading of the metal element relative to the support.
Main raw materials and apparatus
X-ray diffractometer (XRD), model X' pert Pro-1, available from PANALYtic, the Netherlands. Transmission Electron Microscope (TEM), model JEM-2100F, available from JEOL (JEOL) of Japan Electron Co.
A batch type high pressure reactor, model NSC, is typically fast-open and is purchased from Anhui Ke power mechanical science and technology, Inc.
A spherical aberration corrected transmission electron microscope, model JEM-ARM200F, available from Beijing Korsar, Inc. of Jie Ou, Japan.
Gas chromatography, model HP6890CIP chromatograph, available from agilent technologies, ltd. .
Nuclear magnetic resonance apparatus (NMR), model AVANCE III 400MHz, available from Brukbyebergin, Switzerland.
Example 1
g-C3N4Preparation of the support
Putting 10g of melamine into a ceramic crucible, putting the ceramic crucible into a muffle furnace, heating to 550 ℃, keeping for 4h, naturally cooling to room temperature, adding deionized water, stirring for half an hour, filtering, repeatedly washing for 5 times, drying at 100 ℃ for 12h, and then grinding to obtain the required g-C3N4And (3) a carrier.
Example 2
The loading was 0.5 wt.% Rh/g-C3N4Preparation of-350 catalyst
0.5g of g-C prepared in example 13N4The carrier was placed in a beaker and 0.25mL of RhCl at a concentration of 10mg/mL was taken3Aqueous solution, diluted by adding 1.75ml of deionized water and added dropwise to g-C3N4Stirring the carrier until the sample is in a viscous liquid drop shape, and stopping stirring. After standing for 12 hours, the mixture was dried in a 60 ℃ drying oven for 12 hours. Grinding the dried catalyst into powder, and roasting the powder at 350 ℃ for 2 hours in Ar atmosphere to obtain 0.5 wt.% Rh/g-C3N4-350 catalyst.
Example 3
The loading was 0.5 wt.% Rh/g-C3N4Preparation of-200 catalyst
The specific operation is the same as in example 2, except that the calcination temperature is 200 ℃ to obtain 0.5 wt.% Rh/g-C3N4-200 catalyst.
Example 4
The loading was 0.5 wt.% Rh/g-C3N4Preparation of the-500 catalyst
The specific operation was the same as in example 2, except that the calcination temperature was 500 ℃ to obtain 0.5 wt.% Rh/g-C3N4-500 catalyst.
Example 5
The loading was 0.1 wt.% Rh/g-C3N4Preparation of-350 catalyst
The procedure is as in example 2, except that the addition of the RhCl precursor is varied3The amount of solution and the amount of deionized water added. Specifically, 0.05mL of RhCl with a concentration of 10mg/mL was taken3The solution was diluted by adding 1.95ml of deionized water to give 0.1 wt.% Rh/g-C3N4-350 catalyst.
Example 6
Loading of 0.25 wt.% Rh/g-C3N4Preparation of-350 catalyst
The procedure is as in example 2, except that the addition of the RhCl precursor is varied3The amount of solution and the amount of deionized water added. Specifically, 0.125mL of RhCl with a concentration of 10mg/mL was taken3The solution was diluted with 1.875ml of deionized waterRelease, 0.25 wt.% Rh/g-C was obtained3N4-350 catalyst.
Example 7
The loading was 0.75 wt.% Rh/g-C3N4Preparation of-350 catalyst
The procedure is as in example 2, except that the addition of the RhCl precursor is varied3The amount of solution and the amount of deionized water added. Specifically, 0.375mL of RhCl with a concentration of 10mg/mL was taken3The solution was diluted by adding 1.625ml deionized water to give 0.75 wt.% Rh/g-C3N4-350 catalyst.
Example 8
The loading was 1 wt.% Rh/g-C3N4Preparation of-350 catalyst
The procedure is as in example 2, except that the addition of the RhCl precursor is varied3The amount of solution and the amount of deionized water added. Specifically, 0.5mL of RhCl with a concentration of 10mg/mL was taken3The solution was diluted with 1.5ml of deionized water to give 1 wt.% Rh/g-C3N4-350 catalyst.
Example 9
A loading of 0.5 wt.% Cu/g-C3N4Preparation of-350 catalyst
The specific operation was the same as example 2, except that the precursor metal solution was changed, specifically, 0.25mL of Cu (NO) was used at a concentration of 10mg/mL3)2Solution to give 0.5 wt.% Cu/g-C3N4-350 catalyst.
Example 10
The loading was 0.5 wt.% Fe/g-C3N4Preparation of-350 catalyst
The specific operation was the same as example 2, except that the precursor metal solution was changed, specifically, 0.25mL of Fe (NO) with a concentration of 10mg/mL was used3)3Solution to give 0.5 wt.% Fe/g-C3N4-350 catalyst.
Example 11
The loading was 0.5 wt.% Co/g-C3N4Preparation of-350 catalyst
The specific operation was the same as in example 2,except that the precursor metal solution was changed, specifically, 0.25mL of Co (NO) with a concentration of 10mg/mL was taken3)2Solution to give 0.5 wt.% Co/g-C3N4-350 catalyst.
Example 12
The catalysts prepared in examples 1-2 and 9-11 were structurally characterized using XRD powder diffraction measurements, typical results of which are shown in figure 1. Wherein, Fe/C in figure 13N4、Rh/C3N4、Co/C3N4、Cu/C3N4、C3N4Corresponding to the samples of the pure carrier and the loaded Fe, Rh, Co and Cu respectively, the structure of the catalyst is not obviously changed after the metal elements are introduced.
The test results of the other examples were similar to those described above, and the catalyst support structure remained unchanged after the metal was supported.
Morphology characterization of the catalysts of examples 1-2 and 9-11 was performed using TEM and spherical aberration corrected transmission electron microscopy, typical morphology testing was performed on the catalyst prepared as in example 2, and the results are shown in FIG. 2. FIG. 2 shows 0.5 wt.% Rh/g-C prepared in example 23N4The-350 catalyst still maintains a layered structure, in which Rh is mainly present in the form of a single atom.
The test results of the other examples were similar to those described above, and a monoatomic dispersion catalyst was obtained.
Example 13
Preparation of methanol from methane
Specifically, 50mg of 0.5 wt.% Rh/g-C prepared in example 2 was added3N4-350 catalyst to 10mL deionized water and 5mL 30 wt% H2O2And (3) solution. Then, adding 3MPa CH4The mixture is introduced into a reaction vessel, an electric heating furnace is used for heating the batch type high-pressure reaction kettle to the reaction temperature shown in the table 1, the heating rate is 5 ℃/min, and the mixture is magnetically stirred and reacts for 4 hours. After the reaction is finished, the temperature of the reaction kettle is reduced to below 10 ℃ by ice water. Analyzing the gas phase composition by gas chromatography, collecting the reaction liquid after filtering the catalyst, and analyzing by Nuclear Magnetic Resonance (NMR)The liquid phase and the liquid phase oxygenate (methanol and methyl hydroperoxide) selectivity and catalyst TOF values were calculated.
The results of NMR are shown in FIG. 3, from which it can be seen that the nuclear magnetism clearly detects methyl hydroperoxide and methanol in the product, respectively, and even dissolved methane in the solution.
TABLE 1 catalyst reaction Selectivity and TOF values for different reaction temperatures
| Sample (I) | Temperature (. degree.C.) | TOF(h-1) | SOxygenate(％) |
| 0.5wt.％Rh/g-C3N4-350 | 25 | 0.89 | 91 |
| 0.5wt.％Rh/g-C3N4-350 | 35 | 1.47 | 91 |
| 0.5wt.％Rh/g-C3N4-350 | 50 | 2.42 | 91 |
As shown in table 1, the reaction temperature is increased to facilitate methane activation, TOF of the catalyst is increased obviously due to the increase of the amount of liquid-phase oxygenates (methanol and methyl hydroperoxide) of the reaction product, and the selectivity of the liquid-phase oxygenates (methanol and methyl hydroperoxide) of the reaction product can be stabilized above 90% during the reaction at 50 ℃.
Example 14
Performance study of catalysts prepared at different calcination temperatures
Methanol was prepared from methane by reacting at 50 ℃ using the catalysts of examples 3 to 4, and other specific operations were carried out in the same manner as in example 13, and the results are shown in Table 2, and the results of example 13 shown in Table 1 at a reaction temperature of 50 ℃ are shown in Table 2 for comparison.
TABLE 2 0.5 wt.% Rh/g-C prepared at different calcination temperatures3N4Reaction selectivity and TOF value of
As can be seen from Table 2, when the catalyst calcination temperature is 200-500 ℃, both the TOF value of the catalyst and the selectivity of the liquid-phase oxygen-containing compounds (methanol and methyl hydroperoxide) are shown to be volcano-type, and the maximum value is reached at 350 ℃.
Example 15
Research on catalyst reaction performance of same metal in different loading amounts
Methanol was prepared from methane by reacting at 50 ℃ using the catalysts of examples 5 to 8, and other specific operations were carried out in the same manner as in example 13, and the results are shown in Table 3, and the results of example 13 shown in Table 1 at a reaction temperature of 50 ℃ are shown in Table 3 for comparison.
TABLE 3 reactivity of Rh catalysts with different loadings
| Catalyst and process for preparing same | SOxygenate(％) | TOF(h-1) |
| 0.1wt.％Rh/g-C3N4-350 (example 5) | 91 | 2.18 |
| 0.25wt.％Rh/g-C3N4-350 (example 6) | 91 | 2.26 |
| 0.5wt.％Rh/g-C3N4-350 (example 2) | 91 | 2.42 |
| 0.75wt.％Rh/g-C3N4-350 (example 7) | 79 | 1.92 |
| 1wt.％Rh/g-C3N4-350 (example 8) | 68 | 0.93 |
As can be seen from table 3, the selectivity of the product liquid phase oxygenates (methanol and methyl hydroperoxide) stabilized first and then gradually decreased with increasing loading, but the TOF of the catalyst increased first and then decreased. Taken together, the performance of the catalyst at loadings of 0.25 wt.%, 0.5 wt.% and 0.75 wt.% was superior, with the catalyst at a loading of 0.5 wt.% performing best.
Example 16
Performance Studies of catalysts supported on different metals
Methanol was prepared from methane by reacting at 50 ℃ using the catalysts of examples 9 to 11, and other specific operations were carried out in the same manner as in example 13, and the results are shown in Table 4, and the results of example 13 shown in Table 1 at a reaction temperature of 50 ℃ are shown in Table 4 for comparison.
Table 4 comparison of the reaction performance of catalysts supported on different metals
| Catalyst and process for preparing same | SOxygenate(％) | TOF(h-1) |
| 0.5wt.％Rh/g-C3N4-350 (example 2) | 91 | 2.42 |
| 0.5wt.％Cu/g-C3N4-350 (example 9) | 100 | 0.36 |
| 0.5wt.％Fe/g-C3N4-350 (example 10) | 100 | 0.30 |
| 0.5wt.％Co/g-C3N4-350 (example 11) | 100 | 0.29 |
As can be seen from Table 4, like Rh-loaded g-C3N4The catalyst, Fe, Cu and Co loaded catalyst, has excellent catalytic effect in the one-step preparation of methanol by the low-temperature activation reaction of methane, and the reaction activities of three transition metals of Fe, Cu and Co are relatively close, and the selectivity of the liquid-phase oxygen-containing compound (methanol and methyl hydroperoxide) of the product is as high as 100%.
Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.
Claims (10)
1. A supported catalyst, characterized in that the supported catalyst comprises a carrier and an active component supported on the carrier;
wherein the carrier is g-C3N4，
The active component comprises an active metal element,
the metal elements are in monoatomic dispersion;
preferably, the metal element is at least one selected from Rh, Cu, Fe, and Co.
2. The supported catalyst of claim 1, wherein the metal element in the supported catalyst is g-C relative to the support3N4The loading amount of (A) is 0.1-1 wt.%.
3. The supported catalyst of any of claims 1-2, wherein the supported catalyst has a layered structure.
4. A process for the preparation of a supported catalyst according to any one of claims 1 to 3, characterized in that it comprises:
will contain the carrier g-C3N4And roasting the raw materials of the metal precursor to obtain a supported catalyst;
preferably, the metal precursor is selected from at least one of soluble metal salts;
more preferably, the metal salt comprises at least one of a chloride of a metal, a nitrate of a metal, a sulfate of a metal.
5. The process according to claim 4, wherein the carrier g-C is3N4The obtaining method comprises the following steps: thermally condensing a precursor containing carbon and nitrogen to prepare a carrier g-C3N4；
Preferably, the support g-C3N4The obtaining method comprises the following steps: roasting a precursor containing carbon and nitrogen, and then cooling, washing, drying and grinding to obtain the g-C3N4。
6. The method according to any one of claims 4 to 5, wherein the carbon-and nitrogen-containing precursor is selected from at least one of melamine, thiourea, dicyanodiamine, urea;
the heat condensation temperature is 500-650 ℃, and the time is 2-6 h.
7. The method according to any one of claims 4 to 6, wherein the conditions for the calcination are: the roasting temperature is 200-500 ℃;
preferably, the roasting time is 1-3 h;
preferably, the roasting atmosphere is an inert atmosphere, and preferably, the inert atmosphere is selected from at least one of nitrogen and inert gas.
8. The method according to any one of claims 4 to 7, wherein the method for preparing the supported catalyst comprises:
soaking the solution containing the metal precursor in g-C in equal volume3N4Drying and roasting to obtain the supported catalyst;
preferably, the concentration of the solution containing the metal precursor is 0.2-50 mg/ml.
9. A method for preparing oxygen-containing compounds including methanol by methane in one step is characterized in that raw material gas containing methane is introduced into a reactor containing an oxidant and a catalyst to react to obtain oxygen-containing compounds including methanol;
wherein the catalyst is selected from at least one of the supported catalyst of any one of claims 1 to 3, the supported catalyst prepared by the method of any one of claims 4 to 8;
the oxygenate including methanol also includes methyl hydroperoxide.
10. The method of claim 9, wherein the reactor comprises a solvent, a catalyst, and an oxidant;
wherein the oxidizing agent comprises hydrogen peroxide;
preferably, the vessel is a batch high pressure reactor;
preferably, the oxidant is hydrogen peroxide solution with the mass concentration of 0.1-30%;
preferably, the solvent comprises water;
preferably, the reaction temperature is 25-50 ℃;
preferably, the reaction time is 0.5-12 h;
preferably, the pressure of the reaction is 0.5-5 MPa.
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