Patent Description:
Precious metals have excellent catalytic properties and are prominent in the catalysis field. However, precious metals, such as palladium, platinum, gold, ruthenium, and iridium, have limited available reserves and high prices, so the large-scale use of precious metals for industrial catalysis is not a long-term solution. In light of these problems, attention has been focused on developing and utilizing transition metals with multiple valence states.

As one of the transition metals, cobalt itself has specific catalytic properties, which is abundant in reserves and low in price compared to precious metals. Cobalt-based catalysts in practice mostly use oxides, sulfides, and borides of cobalt, which are comparable to precious metals in catalytic ability in some reactions.

Cobalt-based catalysts are usually supported catalysts, which are prone to losing active components during the use process, resulting in gradual deactivation of the catalysts, causing difficulties in product separation and purification, and increasing operational steps and production costs of the whole process of a catalytic reaction. <CIT> and <CIT> disclose cobalt catalysts and their preparation.

In order to solve the above technical problems, the present application provides a cobalt catalyst and a preparation method thereof. The catalytically active substance is grown on the surface of a cobalt-based substrate material, which improves the binding force of the active substance on carrier, extends the service life of catalyst, and reduces the loss of active components.

To achieve the above purpose, the technical solution used in the present application is as follows:
In one aspect of the present application, a cobalt catalyst is provided. The cobalt catalyst includes a carrier and a catalytically active substance.

The carrier is a cobalt-based substrate material.

The catalytically active substance is grown on the surface of the carrier.

The morphology of the catalytically active substance is hydrangea-like nanospheres.

The catalytically active material uses the carrier as a cobalt source and is grown on the surface of the carrier autogenously.

The cobalt-based substrate material is at least one selected from the group consisting of a cobalt foam, a cobalt sheet, a cobalt foil, and a cobalt wire.

Optionally, the diameter of each nanosphere is <NUM>-<NUM>.

Optionally, the thickness of the sheet layer on the surface of the nanospheres is <NUM>-<NUM>.

The catalytically active substance is cobalt oxyhydroxide.

In another aspect of the present application, a preparation method of the cobalt catalyst is provided. The method at least includes:.

Specifically, step a includes: drying the sulfur source at a preset temperature in the protective gas atmosphere with a preset flow rate for a certain time.

Specifically, the preset temperature is <NUM>-<NUM>.

The protective gas is at least one of nitrogen, argon, and helium.

The flow rate of the protective gas is <NUM>/min-<NUM>/min.

Preferably, the sulfur source is dried at <NUM> for a certain time in a <NUM>/min nitrogen atmosphere to remove the contained moisture.

In the present application, there is no special limitation on the drying time of the selected sulfur source. In order to prepare monolithic hydrangea-like cobalt oxyhydroxide nanosphere catalysts with excellent performance and high purity, preferably, the drying time is <NUM>-<NUM>.

Specifically, in step b, the washing solution is at least one selected from the group consisting of anhydrous ethanol and acetone.

The washing is performed by ultrasonic cleaning for <NUM>-<NUM>.

The drying is carried out at <NUM>-<NUM> for <NUM>-<NUM>.

Preferably, step b includes: immerging the carrier in anhydrous ethanol, performing an ultrasonic cleaning for <NUM>, and drying at <NUM> for <NUM>.

In order to successfully prepare a monolithic catalyst, the carrier should be the cobalt-based material, and preferably, the carrier is a cobalt foam, a cobalt sheet, a cobalt foil, etc. that can play a support role themselves.

Specifically, step S100 uses a heating furnace as the reaction device. In this step, the precursor is obtained through a sulfidation process. The heating furnace is preferably a tube furnace internally provided with a quartz tube or a corundum tube for the convenience of introducing the protective gas. The protective gas is preferably one or more of nitrogen, argon, and helium. The flow rate of the protective gas should not be too large, preferably <NUM>/min-<NUM>/min. This flow rate can prevent the dry sulfur source powder from being blown away directly and prevent the ablation of the product, thus improving the quality of the product and enhancing the mechanical and chemical properties of the product.

Specifically, the upper limit of the flow rate of the protective gas is independently selected from <NUM>/min, <NUM>/min, <NUM>/min, <NUM>/min, and <NUM>/min; the lower limit of the flow rate of the protective gas is independently selected from <NUM>/min, <NUM>/min, <NUM>/min, <NUM>/min, and <NUM>/min.

Optionally, in step S100, the mass ratio of the sulfur source to the carrier is (<NUM>-<NUM>):<NUM>.

Preferably, the sulfur source is at least one of sublimed sulfur, sodium sulfide, and thiourea.

Specifically, the upper limit of the mass ratio of the sulfur source to the carrier is independently selected from <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM>; the lower limit of the mass ratio of the sulfur source to the carrier is independently selected from <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, and <NUM>:<NUM>.

Optionally, in step S100, the temperature of the reaction under heating is <NUM>-<NUM>, and the reaction time is <NUM>-<NUM>.

To ensure product quality, the heating rate should not be too fast. Preferably, the heating rate of the reaction under heating is <NUM>/min-<NUM>/min.

Specifically, the upper limit of the temperature of the reaction under heating is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>; the lower limit of the temperature of the reaction under heating is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Specifically, the upper limit of the reaction time is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>; and the lower limit of the reaction time is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Specifically, the upper limit of the heating rate is independently selected from <NUM>/min, <NUM>/min, <NUM>/min, <NUM>/min, and <NUM>/min; the lower limit of the heating rate is independently selected from <NUM>/min, <NUM>/min, <NUM>/min, <NUM>/min, and <NUM>/min.

Optionally, step S200 includes:
Subjecting the precursor as an anode in the electrolyte for electrical activation, then washing and drying to obtain the cobalt catalyst.

Specifically, the precursor is used as the anode, together with a cathode and a reference electrode, to form a three-electrode electrolytic cell, activated electrically in the electrolyte, and washed and dried to obtain the cobalt catalyst.

Optionally, the cathode is at least one of a graphite rod, a platinum wire, a platinum mesh, and a platinum sheet.

The reference electrode is any one of a mercury/mercuric oxide electrode, a saturated calomel electrode, and a silver/silver chloride electrode.

The electrolyte is at least one of a potassium hydroxide solution and a sodium hydroxide solution.

The concentration of the electrolyte is <NUM>-<NUM>.

Preferably, step S200 includes: subjecting the precursor as the anode, the graphite rod as the cathode, and the mercury/mercuric oxide electrode as the reference electrode to form the three-electrode electrolytic cell, conducting the electrical activation in the electrolyte with a concentration of <NUM>, then washing and drying to obtain the monolithic hydrangea-like cobalt oxyhydroxide nanosphere catalyst.

Specifically, the upper limit of the concentration of the electrolyte is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>; the lower limit of the concentration of the electrolyte is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

In step S200, the methods for performing the electrical activation include cyclic voltammetry, linear voltammetry, the constant current method, the chronopotentiometry method, and other methods capable of applying positive potential to oxidize and transform the cobalt sulfide precursor into cobalt oxyhydroxide. In order to ensure the catalytic performance and stability of the product, the electrical activation should not be performed at a too high speed and too long or short time.

Preferably, the cyclic voltammetry or the linear voltammetry is used. Preferably, the parameters of the electrical activation include a potential window of -<NUM> V vs. RHE-<NUM> V vs. RHE and an activation time of <NUM>-<NUM>.

Specifically, the upper limit of the window potential is independently selected from <NUM> V vs. RHE, <NUM> V vs. RHE, <NUM> V vs. RHE, <NUM> V vs. RHE, and <NUM> V vs. RHE; the lower limit of the window potential is independently selected from -<NUM> V vs. RHE, -<NUM> V vs. RHE, -<NUM> V vs. RHE, <NUM> V vs. RHE, and <NUM> V vs. RHE.

Specifically, the upper limit of the activation time is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>; the lower limit of the activation time is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Preferably, the conditions of performing the electrical activation with the constant current method include: setting a current density of <NUM> mA/cm<NUM>-<NUM> mA/cm<NUM>, inputting the constant current for activation until the potential is stable, activating for <NUM>-<NUM>.

Specifically, the upper limit of the current density is independently selected from <NUM> mA/cm<NUM>, <NUM> mA/cm<NUM>, <NUM> mA/cm<NUM>, <NUM> mA/cm<NUM>, and <NUM> mA/cm<NUM>; the lower limit of the current density is independently selected from <NUM> mA/cm<NUM>, <NUM> mA/cm<NUM>, <NUM> mA/cm<NUM>, <NUM> mA/cm<NUM>, and <NUM> mA/cm<NUM>.

Preferably, the conditions of performing the electrical activation with the chronopotentiometry method include: maintaining the current input for <NUM>-<NUM> within the potential range of <NUM> V-<NUM> V (relative to a reversible hydrogen electrode).

Specifically, the upper limit of the potential range is independently selected from <NUM> V, <NUM> V, <NUM> V, <NUM> V, and <NUM> V; and the lower limit of the potential range is independently selected from <NUM> V, <NUM> V, <NUM> V, <NUM> V, and <NUM> V.

Specifically, the upper limit of the activation time is selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>; the lower limit of the activation time is selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

The activated catalyst surface carries a small amount of electrolyte. In order to remove the electrolyte, a washing operation is needed. Preferably, the washing method includes: washing the catalyst with deionized water <NUM> to <NUM> times. After washing, the catalyst is dried to prolong the service life of the catalyst.

Optionally, the drying is conducted at <NUM>-<NUM> for <NUM>-<NUM>.

Specifically, the upper limit of the drying temperature is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>; the lower limit of the drying temperature is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Specifically, the upper limit of the drying time is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>; the lower limit of the drying time is independently selected from <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

The advantages of the present application are as follows:.

<NUM>, power supply; <NUM>, anode; <NUM>, cathode; <NUM>, electrolyte; <NUM>, gas guide tube; <NUM>, measuring cylinder; <NUM>, water tank; <NUM>, water.

The present application is further described below in conjunction with the accompanying drawings and specific embodiments.

The experimental methods used in the following embodiments are conventional methods unless otherwise specified. The reagents, materials, etc. used in the following embodiments are commercially available unless otherwise specified. The instruments used in the following embodiments imply the parameters recommended by the manufacturers unless otherwise specified.

The instruments and parameters used in sample analysis in the embodiments are as follows:
SEM analysis was performed using a HITACHI S-<NUM> scanning electron microscope at <NUM> kV.

EDX analysis was performed using the HITACHI S-<NUM> scanning electron microscope at <NUM> kV.

TEM analysis was performed using an FEI F20 transmission electron microscope at <NUM> kV.

Selected area electron diffraction analysis was performed using the FEI F20 transmission electron microscope at <NUM> kV.

Compared to Embodiment <NUM>, the mass of the carrier used in Embodiment <NUM> was changed, and the rest of the preparation conditions remained unchanged. As the mass of the carrier increases, the number of cobalt oxyhydroxide nanospheres in the final catalyst decreases.

Compared to Embodiment <NUM>, the mass of the sulfur source used in Embodiment <NUM> was changed, and the rest of the preparation conditions remained unchanged. As the mass of the sulfur source decreases, the number of cobalt oxyhydroxide nanospheres in the final catalyst decreases.

Sample <NUM>-sample <NUM> were subjected to SEM, EDX, and TEM tests.

<FIG> are scanning electron microscope images of sample <NUM>. It can be seen that the microstructure of the catalyst is in the morphology of hydrangea-like nanospheres and the surface of the nanospheres is a three-dimensional structure assembled by nano-sheets, which has good mechanical properties.

<FIG> are EDX graphs showing the elemental distribution of sample <NUM>. It can be seen that cobalt element and oxygen element are uniformly distributed.

<FIG> are transmission electron microscope images of sample <NUM>. It can be seen that the surface of the nanospheres of the catalyst is a three-dimensional structure assembled by nano-sheets, and the characterization result is consistent with that of the scanning electron microscope image.

<FIG> is a selected area electron diffraction pattern of sample <NUM>. It can be seen that the electron diffraction rings correspond to the (<NUM><NUM><NUM>), (<NUM><NUM><NUM>), (<NUM><NUM><NUM>), and (<NUM><NUM><NUM>) facets of the cobalt oxyhydroxide standard card <NUM>-<NUM>, which confirms that the catalyst phase is cobalt oxyhydroxide.

The SEM images, the elemental distribution graphs, and the TEM images of sample <NUM>-sample <NUM> are similar to those of sample <NUM>, with the only differences in the number and size of nanospheres.

The selected area electron diffraction patterns of sample <NUM>-sample <NUM> are consistent with that of sample <NUM>, which confirms that all the catalyst phases are cobalt oxyhydroxide.

Working electrode preparation: Sample <NUM>-sample <NUM> and pure cobalt foams were respectively fixed by stainless steel electrode clamps to prepare working electrodes.

Counter electrode: Graphite rod was configured as a counter electrode.

Three-electrode electrolytic cell: The working electrode was configured as an anode, the counter electrode was configured as a cathode, and the mercury/mercuric oxide electrode was configured as a reference electrode to be fixed in a Teflon plug and fixed in a <NUM> reaction cell.

Two-electrode symmetric electrolytic cell: The cathode and the anode were two identical working electrodes, and the reactor volume was <NUM> or more.

Under normal temperature and pressure conditions, the electrocatalytic performance was tested in the assembled two-electrode system at a controlled electrolytic cell voltage of <NUM> V with a potassium hydroxide (<NUM>) solution and a potassium hydroxide (<NUM>) solution containing <NUM> <NUM>,<NUM>-furandimethanol (BHMF), respectively.

The test apparatus is shown in <FIG>. An electrolytic cell is constructed to include the power supply <NUM>, the electrolyte <NUM>, the anode <NUM>, the cathode <NUM>, and a current loop. The electrolyte is placed in a sealed reactor. The gas produced by the cathode is introduced into a gas collection device through the gas guide tube <NUM>, and the gas volume is obtained by a drainage method. The gas collection device includes the measuring cylinder <NUM>, the measuring cylinder <NUM> is filled with water and inverted in the water tank <NUM> containing the water <NUM>, and the outlet of the gas guide tube is located in the measuring cylinder <NUM>. Only a lower voltage is required to drive the coupling reaction when the electrolyte is the potassium hydroxide (<NUM>) solution containing <NUM> BHMF.

The electrocatalytic oxidation of BHMF, with sample <NUM>-sample <NUM> as the anode catalyst, respectively, to prepare <NUM>,<NUM>-furandicarboxylic acid (FDCA) was conducted, which shows sample <NUM>-sample <NUM> have similar good catalytic effects. Typically, sample <NUM> is taken as an example for illustration.

Sample <NUM> was configured as the anode catalyst, and the test results are shown in <FIG>.

<FIG> shows that in the three-electrode system, the autogenously grown monolithic hydrangea-like cobalt oxyhydroxide nanosphere catalyst used as the anode catalyst performs better for water electrolysis and oxygen evolution than pure cobalt foams (that is, the potential required to achieve the same current density is lower, and the curve is closer to the Y axis). In the electrocatalytic oxidation of BHMF to prepare FDCA, a lower potential can drive the reaction, thus showing excellent performance.

<FIG> shows that in the three-electrode system, the autogenously grown monolithic hydrangea-like cobalt oxyhydroxide nanosphere catalyst also performs much better in water electrolysis and hydrogen production than pure cobalt foams as the cathode (that is, the potential required to achieve the same current density is lower, and the curve is closer to the Y axis). The addition of <NUM> BHMF to the electrolyte has no obvious effect on the hydrogen production performance (the curve has no obvious deviation and basically overlaps), indicating that the catalyst has high hydrogen evolution selectivity.

The sample hydrangea-like cobalt oxyhydroxide nanosphere catalyst prepared in Embodiment <NUM> was configured as the cathode catalyst and the anode catalyst simultaneously to assemble the two-electrode symmetric electrolytic cell. The electrocatalytic reactions were carried out in the electrolyte without BHMF and in the electrolyte with <NUM> BHMF, respectively. The results are shown in <FIG>. The electrocatalytic oxidation of BHMF to produce FDCA and the water electrolysis to produce hydrogen were simultaneously conducted, where the overpotential required is <NUM> mV lower than that of the water splitting alone (the curve is closer to the Y-axis). The results indicate that only a lower energy is required to oxidize BHMF to produce FDCA and reduce water to hydrogen and confirms that the catalyst of the present application has better catalytic performance.

The sample hydrangea-like cobalt oxyhydroxide nanosphere catalyst prepared in Embodiment <NUM> was configured as the cathode catalyst and the anode catalyst simultaneously to assemble the two-electrode symmetric electrolytic cell for the electrocatalytic oxidation of BHMF to prepare FDCA. The results are shown in <FIG>. The anode products include HMF, FDCA, HMFCA, FFCA, and DFF. The concentrations of HMF, HMFCA, FFCA, and DFF at the end of the reaction were extremely low compared to that of FDCA. The results indicate that the catalyst has high selectivity for FDCA, and the high FDCA selectivity not only ensures a high purity of the product but also results in a very high product yield. Meanwhile, the Faraday efficiency of FDCA is close to <NUM>%, with high energy utilization and almost no energy waste.

All other samples, used as anode catalyst, can achieve similar catalytic effects.

Claim 1:
A cobalt catalyst, comprising a carrier and a catalytically active substance; wherein
the carrier is a cobalt-based substrate material, the cobalt-based substrate material is at least one selected from the group consisting of a cobalt foam, a cobalt sheet, a cobalt foil, and a cobalt wire;
the catalytically active substance is grown on a surface of the carrier; characterized in that
the catalytically active substance is cobalt oxyhydroxide, a morphology of the catalytically active substance is hydrangea-like nanospheres, a surface of each of the hydrangea-like nanospheres is a three-dimensional structure assembled by nano-sheets.