KR102477419B1 - Cobalt-based Single-atom Dehydrogenation Catalysts Having Improved Thermal Stability and Method for Producing Corresponding Olefins from Paraffins Using the Same - Google Patents

Abstract

In the present disclosure, after pretreatment of silica through heat treatment and high-temperature water-based reaction, a dehydrogenation catalyst carrying monoatomic cobalt using this as a support and a method for preparing the same, and paraffin in the presence of the dehydrogenation catalyst, specifically hard A method of dehydrogenating paraffins to produce the corresponding olefins is described.

Description

Cobalt-based Single-atom Dehydrogenation Catalysts Having Improved Thermal Stability and Method for Producing Corresponding Olefins from Paraffins Using the Same}

The present disclosure relates to a cobalt-based monoatomic dehydrogenation catalyst with improved thermal durability and a method for producing a corresponding olefin from paraffin using the same. More specifically, the present disclosure provides a dehydrogenation catalyst carrying monoatomic cobalt as a support after pretreatment of silica through heat treatment and high-temperature water-based reaction, a method for preparing the same, and paraffin in the presence of the dehydrogenation catalyst , Specifically, it relates to a method for producing olefins corresponding thereto by dehydrogenation of light paraffins.

Recently, a catalyst technology using an active metal supported on a support has attracted attention. In particular, with the development of nanotechnology, research on supporting and utilizing a nano-sized active metal on a support is being actively conducted. However, nano-sized active metals have a wide size distribution and irregular morphological characteristics, so they are superior in activity compared to conventional catalysts. However, when used as catalysts, side reactions or catalyst deactivation rapidly progress This phenomenon is pointed out as a disadvantage.

On the other hand, in the case of a catalyst in which a metal is supported in a monoatomic size, the catalytic activity can be maximized by reducing the size of the metal active site to an atomic level of nanometer size or less. In particular, because it has an extremely simplified and ideal structure, it provides an advantage suitable for carrying out related research by simulating theoretical results obtained through computational science. In this regard, there is an example in which a transition metal, such as zinc (Zn) or cobalt (Co), is supported in a monoatomic form on a support such as silica and used as a catalyst for dehydrogenation of light paraffin.

In addition, when the active metal in monatomic form is supported, advantages such as minimization of cracking and suppression of coke formation during the reaction have been reported (e.g., ACS Catal. 2014, 4, 4, 1091-1098 ). However, in the above literature, in order to keep the concentration of the reactants low, a mixed gas (a mixed gas consisting of 3% propane as a reactant and argon (Ar) as the remaining component) is used to suppress by-products and paraffin It is difficult to apply in a practical commercial process, such as selectively converting to olefin corresponding thereto and reacting at a low temperature to increase the life of the catalyst.

Furthermore, in the case of a method for performing a dehydrogenation reaction of paraffin in the presence of a catalyst in which cobalt active metal is supported on a support in a monoatomic form, mutual aggregation of cobalt elements fixed on the support in the dehydrogenation reaction performed at a high temperature Alternatively, since a cobalt metal production reaction or the like occurs according to a reduction phenomenon, there is a limit to securing long-term reaction stability.

In order to suppress the above-described problems, a method for reducing aggregation of cobalt active metal on the surface of the support by introducing an alkali metal into the support has been reported (Korean Patent Publication No. 2020-0049209). However, there is a problem in that stability of the catalyst is lowered due to active metal aggregation caused by contraction behavior of the support due to continuous exposure to high temperatures during the dehydrogenation reaction. In addition, due to the effect of the alkali metal introduced during catalyst preparation, the volume of the silica support rapidly decreases during the dehydrogenation reaction, resulting in aggregation or sintering of metal ions due to the decrease in surface area. Moreover, when an alkali metal is used in the process of supporting a monoatomic active metal, it is difficult to synthesize a monoatomic catalyst on a commercial scale, such as requiring an expensive and complex process for synthesis. Therefore, there is a need for a simpler method for preparing a catalyst capable of maintaining a monoatomic form by suppressing aggregation of active metals over a long period of time even at high temperatures.

In one embodiment of the present disclosure, a monoatomic form of cobalt (Co)-supported catalyst capable of maintaining catalyst stability or long-term activity even when exposed to high temperatures, such as in the reaction of preparing olefins through dehydrogenation of paraffin, and its It is intended to provide a manufacturing method.

In another embodiment of the present disclosure, it is intended to provide a dehydrogenation process that has a high conversion rate of paraffin even for a high-concentration paraffin-containing feedstock and excellent selectivity for the corresponding olefin, suitable for commercialization.

According to the first aspect of the present disclosure,

As a method for producing a monoatomic cobalt-based catalyst,

a) Heat treatment of silica as a support under a temperature condition determined in the range of 600 to 870 ° C. to induce a contracted support and at the same time remove hydroxyl groups on the surface, and then perform a pretreatment including performing a high-temperature water-based reaction on silica selectively activating hydroxyl groups to form pretreated silica;

b) preparing the pretreated silica-containing aqueous dispersion;

c) preparing a pH-adjusted aqueous dispersion of pretreated silica by adding a base component to the aqueous dispersion of pretreated silica to adjust the pH to at least 10;

d) separately, preparing an aqueous solution of a cobalt precursor having an oxidation value of 3+ and adding a basic component to prepare a pH-adjusted aqueous solution of a cobalt precursor;

e) combining the pH-adjusted aqueous dispersion of the pretreated silica and the pH-adjusted aqueous cobalt precursor solution to prepare an aqueous dispersion in which at least some of the cobalt ions having an oxidation value of 3+ are adsorbed on the surface of the pretreated silica step;

f) removing cobalt ions not adsorbed on the surface of the pretreated silica; and

g) heat-treating the silica adsorbed with cobalt ions obtained from step f);

including,

Here, in the cobalt-based catalyst, cobalt having an oxidation value of 2+ exists in the form of an isolated single atom on the pretreated silica, and cobalt having an oxidation value of 2+ is tetrahedral in a three-membered hydroxyl ring present on the surface of the pretreated silica. A method of coordinating and forming a structure is provided.

According to a second aspect of the present disclosure,

providing a feedstock containing paraffin;

Performing a dehydrogenation reaction on the feedstock under conditions of a temperature of 500 to 700 ° C. and a pressure of 0.3 to 2 bar in the presence of a catalyst prepared according to the above method; and

recovering olefins corresponding to the light paraffins from the dehydrogenation reaction products;

A method for producing olefins from paraffins containing is provided.

A dehydrogenation catalyst according to an embodiment according to the present disclosure is a type in which monoatomic cobalt is supported on a silica support pretreated by performing heat treatment and selective hydroxyl group activation, and paraffin, particularly hard paraffin, is used. Even when exposed to a high temperature (eg, about 500 ° C. or more) during the dehydrogenation reaction of Aggregation or sintering can be effectively suppressed. Therefore, even when exposed to high temperatures for a long time during the dehydrogenation reaction or in contact with hydrogen generated from the dehydrogenation reaction, the catalyst is effectively suppressed from deformation or denaturation, so that the catalyst activity can be maintained for a long period of time.

In particular, in the case of a silica-based cobalt metal catalyst to secure thermal stability using the introduction of an existing alkali metal, the volume of the silica support during the dehydrogenation reaction is rapidly reduced due to the influence of the alkali metal introduced into the silica, There is a limit to prolonging the catalytic activity for a long period of time due to the occurrence of aggregation or sintering of metal ions due to a decrease in surface area. However, in one embodiment, volumetric shrinkage of silica itself can be suppressed by heat treatment before the reaction of performing heat treatment and selective hydroxyl group activation (water-based high temperature treatment) instead of introduction of alkali metal ions, and also the hydroxyl group is lost by heat treatment. By reassembling the surface active groups in such a way that a selective hydroxyl group activation step is performed later, the active metal ion can be effectively supported. Furthermore, catalysts according to embodiments of the present disclosure are particularly advantageous for commercialization because they can exhibit good conversion and olefin selectivity even for feedstocks containing high paraffin content in dehydrogenation reactions.

1 shows dehydration using a cobalt-based monoatomic catalyst prepared using a pretreated silica support (Preparation Example 1) and a cobalt-based monoatomic catalyst prepared using a silica support without pretreatment (Comparative Preparation Example 1), respectively. It is a graph showing the conversion rate and selectivity over time during the digestion reaction,
2 is a SEM photograph showing changes before and after the dehydrogenation reaction of a monoatomic Co catalyst prepared using silica particles without pretreatment, silica particles subjected to only heat treatment during pretreatment, and silica particles subjected to heat treatment-hydroxyl group activation as supports, respectively; and
3 is a graph showing the results of EXAFS Wavelet Transform analysis of the monoatomic cobalt catalyst before and after the dehydrogenation reaction.

The present invention can all be achieved by the following description. The following description should be understood as describing preferred embodiments of the present invention, but the present invention is not necessarily limited thereto. In addition, it should be understood that the accompanying drawings are for illustrative purposes only, and the present invention is not limited thereto.

Terms used in this specification may be defined as follows.

A “heterogeneous catalyst” may refer to a catalyst that is present in a different phase from the reactants during a catalytic reaction, for example, a catalyst that does not dissolve in a reaction medium. In the case of a heterogeneous catalyst, in order for a reaction to occur, at least one reactant needs to be diffused and adsorbed on the surface of the heterogeneous catalyst, and after the reaction, a product needs to be desorbed from the surface of the heterogeneous catalyst.

"Support" may mean a material with a high specific surface area (typically a solid material) to which a catalytically active component is attached, and may or may not participate in a catalytic reaction.

The terms "crystalline" or "crystalline" can typically refer to any solid-state material in which atoms are arranged to have a lattice structure (eg, three-dimensional order), whereas "amorphous" can mean any solid material that does not have such a lattice structure, generally by X-ray diffraction analysis (XRD), nuclear magnetic resonance analysis (NMR), differential scanning calorimetry (DSC) or a combination thereof can be specified.

"Hard paraffin" may mean paraffin having 2 to 5 carbon atoms, more specifically, paraffin having 3 to 4 carbon atoms, and specifically ethane, propane, n-butane, isobutane, pentane, and the like may be exemplified. In addition, "the olefin corresponding thereto" may mean an olefin having the same number of carbon atoms from which hydrogen molecules are removed from light paraffin in the feedstock for the dehydrogenation reaction.

"Silica" may refer to a material having a tetrahedral structure formed by bonding one silicon atom to four oxygen atoms.

"Porous silica" may refer to a three-dimensional network silica having porosity, and may be composed of an aggregate of primary silica particles.

"Heat treatment" is contemplated as intentionally raising the temperature of an entire object or a portion thereof, which may entail chemical or additional physical treatment, if necessary, to achieve certain desired structures and physical properties (or changes). .

The expression “substantially free” means that a specific component is not intentionally incorporated, but it can be understood to include the case where the component exists in the form of an impurity.

It can be understood that the expressions "on" and "above" are used to refer to the concept of relative position. Therefore, not only when other components or layers are directly present in the mentioned layers, other layers (intermediate layers) or components may be interposed or present therebetween. Similarly, the expressions “under”, “under” and “below” and “between” may also be understood as relative concepts of position. In addition, the expression “sequentially” may also be understood as a relative positional concept.

In the present specification, when a specific numerical range is described, it can be considered that any value within the range and any subcombination of two arbitrary values within the range as the lower limit and the upper limit, respectively, are described. For example, in the case of "1 to 5", it can be understood that each value of 1, 2, 3, 4 and 5 is described as well as any subcombination.

In this specification, when it is said that a certain component is "included", it means that it may further include other components and / or steps unless otherwise stated.

According to one embodiment of the present disclosure, it is suitable for converting a feedstock containing high concentration of paraffins (specifically, light paraffins) into olefins corresponding thereto with good conversion and selectivity, even when exposed to high temperatures for a long period of time during dehydrogenation reaction. A monoatomic cobalt-based catalyst exhibiting good thermal stability, specifically a heterogeneous catalyst in which monoatomic cobalt is supported as an active metal on a silica support is provided.

In the case of a cobalt-based catalyst in the form of a single atom according to one embodiment. It is possible to carry cobalt in the form of a monoatomic active metal without additionally or separately introducing a heterogeneous metal (eg, an alkali metal) in a manner that selectively activates a hydroxyl group on a silica, specifically, a silica support, as well as dehydration. Silica, which can secure thermal durability and long-term activity by suppressing volumetric shrinkage during the digestion reaction, is used as a support.

Pre-treatment of silica support

According to one embodiment, in order to provide the above-described properties of the silica support, a pretreatment step including heat treatment and high-temperature water treatment (hydroxyl group activation) may be performed on the silica (initial silica).

According to an exemplary embodiment, the initial silica provided prior to the pretreatment step is not limited to a specific type, but it may be advantageous to use high-purity silica having as little impurity content as possible. According to a specific embodiment, the initial silica may be amorphous silica, specifically, amorphous porous silica, for example, fumed silica, precipitated silica, and the like.

According to an exemplary embodiment, the initial silica (silica before pretreatment) may be in the form of particles, wherein the particle size (diameter) is, for example, about 0.5 to 5000 μm, specifically about 10 to 1000 μm, more specifically about It may range from 400 to 800 μm. However, the aforementioned particle size range can be understood as an example.

According to an exemplary embodiment, the specific surface area (BET specific surface area) of the initial silica is, for example, at least about 100 m / g, specifically about 200 to 1500 m / g, more specifically about 300 to 1000 m / g. can Further, the pore volume of the initial silica may be, for example, in the range of about 0.1 to 10 cm 3 /g, specifically about 0.3 to 5 cm 3 /g, and more specifically about 0.5 to 3 cm 3 /g. In addition, the pore size (average diameter) of the initial silica may be, for example, about 0.5 to 200 nm, specifically about 1 to 100 nm, and more specifically about 3 to 30 nm. It should be understood that the above numerical ranges are stated for illustrative purposes.

Further, according to an exemplary embodiment, the surface hydroxyl group concentration of the initial silica may range, for example, from about 3 to 5 mmol/cc, specifically from about 3.2 to 4.8 mmol/cc, and more specifically from about 3.5 to 4.5 mmol/cc. can

According to one embodiment, a step of shrinking the volume of the initial silica by heat treatment (first heat treatment) is first performed during the pretreatment process. This heat treatment step can compensate for the fact that silica used as a support in a conventional cobalt monoatomic catalyst, for example, amorphous silica, shows weakness at high temperatures.

According to one embodiment, the initial silica is heat treated or calcined at a high temperature, for example, about 600 to 870 ° C, specifically about 650 to 850 ° C, more specifically about 700 to 800 ° C. In this regard, when the heat treatment temperature is too low, it is difficult to induce desired volumetric shrinkage, whereas when it is too high, it is not easy to recover (or activate) hydroxyl groups in a subsequent step (high-temperature water treatment) due to excessive shrinkage. Therefore, it is advantageous to set in the above heat treatment temperature range.

According to exemplary embodiments, the heat treatment of silica may be performed for, for example, about 3 to 12 hours, specifically about 4 to 11 hours, and more specifically about 5 to 10 hours. Also, the heat treatment may be performed under an oxygen-containing atmosphere, for example, an air atmosphere. The temperature increase rate during the heat treatment process is, for example, about 1 to 20 ° C / min, specifically about 2 to 10 ° C / min, more specifically about 4 to 7 ° C / min. can be understood as

During the above heat treatment process, silica, specifically amorphous silica, is crystallized as it is exposed to high temperatures, and in the process, water molecules are removed, resulting in volume contraction. As an example, the heat-treated silica is reduced by, for example, about 75% or less, specifically about 5 to 70%, more specifically about 10 to 60%, and particularly about 20 to 50%, compared to silica before pretreatment (initial). volume (i.e., contracted).

However, since the heat treatment step converts all of the hydroxyl groups on the surface as well as inside the silica (specifically, amorphous silica) into silicon oxide, even hydroxyl functional groups providing a site for fixing cobalt, an active metal, are removed. Specifically, since the surface hydroxyl group is lost by high temperature on the surface of the heat-treated silica, the cobalt precursor cannot be effectively adsorbed or fixed to the surface of the silica support by electrostatic interaction, as will be described later. As such, as a result of performing the preemptive heat treatment step on the silica support during the catalyst preparation process, the volumetric shrinkage of the catalyst caused by the dehydrogenation reaction can be suppressed to some extent, while the active metal cobalt is supported in the form of a single atom. function deteriorates. Illustratively, the surface hydroxyl group concentration of the silica after heat treatment may be, for example, less than about 0.2 mmol/cc, specifically less than about 1.5 mmol/cc, and more specifically less than about 1 mmol/cc.

Considering this, in one embodiment, a high-temperature water-based treatment is performed in order to selectively activate surface hydroxyl groups (ie, hydroxylation function) present on silica subjected to a volume shrinkage process by heat treatment. The high-temperature aqueous treatment forms free hydroxyl groups on the surface of the silica, thereby effectively adsorbing or immobilizing cobalt metal ions as will be described later. Although the present disclosure is not bound by any particular theory, the reason for performing the high-temperature water-based treatment can be explained as follows.

On the surface of ordinary silica (initial silica), hydroxyl groups and free hydroxyl groups by hydrogen bonding exist together. However, when hydroxyl groups on the silica surface are removed by the aforementioned heat treatment and then hydroxyl groups on the surface are activated by performing a high-temperature water-based treatment, a large amount of free hydroxyl groups may be generated. Since the free hydroxyl groups thus produced can fix cobalt ions, they are suitable for forming a three-membered hydroxyl ring tetrahedral structure with cobalt atoms.

In addition, the free hydroxyl groups present on the initial silica surface may aggregate cobalt ions subsequently supported as the distance approaches due to contraction of the support due to exposure to high temperature. However, after heat treatment and high-temperature water treatment, each free hydroxyl group can be maintained at a certain distance from the cobalt ions without contraction of the silica support. Furthermore, as heat treatment performed prior to high-temperature water treatment removes weak hydroxyl groups due to hydrogen bonding other than free hydroxyl groups that already exist on the silica surface, additional thermal stability can be secured.

According to an exemplary embodiment, the silica support is, for example, at least about 0.8% by weight, specifically about 1% by weight, based on the pretreated silica support, by free hydroxyl groups generated through the above-described pretreatment (specifically, high temperature water treatment). %, more specifically from 1 to 2% by weight, particularly specifically from about 1.2 to 1.5% by weight of cobalt ions.

According to an exemplary embodiment, the high-temperature water-based treatment is performed by dispersing the previously heat-treated silica in an aqueous medium to prepare a silica-aqueous dispersion, and then, for example, about 70 to 150 ° C., specifically about 90 to 130 ° C., more specifically It may involve a boiling process under a temperature condition of about 95 to 110 ° C., for example, about 0.5 to 12 hours, specifically about 1 to 10 hours, and more specifically about 3 to 8 hours.

At this time, the aqueous medium used to prepare the dispersion (dispersion) of silica for high-temperature aqueous reaction (specifically, heat-treated silica) may be water, specifically distilled water, and the silica in the heat-treated silica-aqueous dispersion The content may range, for example, from about 1 to 30% by weight, specifically from about 3 to 20% by weight, more specifically from about 5 to 10% by weight.

On the other hand, the volume of silica heat-treated through high-temperature water treatment may increase (ie, volume expansion), for example, about 5 to 50%, specifically about 10 to 30%, more specifically about 10 to 30% compared to heat-treated silica 15 to 25% increased volume. In addition, the particle size (diameter) of the silica after the high-temperature water treatment may range, for example, from about 0.3 to 4000 μm, specifically from about 5 to 900 μm, and more specifically from about 300 to 700 μm. As much as it depends on the size, etc., it can be understood for illustrative purposes.

According to an exemplary embodiment, the hydroxyl group (ie, activated hydroxyl group) generated through the above-described high-temperature water treatment has excellent thermal durability compared to the hydroxyl group present on the surface of the initial silica, and also a three-membered hydroxyl ring that fixes cobalt. Since the tetrahedral structure is stably maintained, it is possible to effectively suppress the phenomenon of aggregation of cobalt in the form of a single atom, which is an active metal, during the dehydrogenation reaction. Furthermore, as the stability of the tetrahedral structure increases, the effect of hydrogen generated during the reaction decreases, and the reduction resistance of cobalt increases, which can contribute to suppressing the rapid decrease in activity during the dehydrogenation reaction. . On the other hand, according to an exemplary embodiment, the amount of surface hydroxyl groups reduced through the previous heat treatment can be restored to the initial level through the high-temperature water treatment, for example, about 3 to 5 mmol / cc, specifically about 3.2 to 4.8 mmol/cc, more specifically from about 3.5 to 4.5 mmol/cc, but this can be understood as an example.

Although the present disclosure is not bound by a particular theory, the total amount (concentration) of hydroxyl groups present on the silica surface after the high-temperature water treatment (reaction) can be recovered to a level similar to the initial state, but the thermal stability of the silica is secured. As a result, the shrinkage of the silica support is suppressed, and at the same time, a high proportion of free hydroxyl groups suitable for loading (or fixing) of monoatomic cobalt ions exist, while monoatomic cobalt ions are not supported, such as hydroxyl groups by hydrogen bonding. It is judged that the amount of hydroxyl groups that are not suitable for processing is reduced.

According to one embodiment, the silica that has undergone the pretreatment step may exhibit a characteristic of reducing at least one of the specific surface area, pore volume, and pore size, and a significant volume reduction (shrinkage) occurs first through high-temperature heat treatment of the silica, followed by subsequent This is because it is not completely restored to the initial (before pre-treatment) state even when the high-temperature water-based treatment is performed.

After the high-temperature water-based treatment, the pretreated silica is separated from the dispersion using a conventional separation and/or purification means (for example, at least one selected from filtration, stilling, washing, etc.), and using this, the cobalt support described later can be used as a support for Alternatively, the pretreated silica-containing aqueous dispersion may be used as it is and used for cobalt support without a separate separation process.

Cobalt in monatomic form supported on a pretreated silica support

According to one embodiment, pretreated silica is dispersed in an aqueous medium to prepare a pretreated silica-containing aqueous dispersion. At this time, as described above, the aqueous medium may be water, specifically distilled water, and the content of the pretreated silica in the pretreated silica-containing aqueous dispersion is, for example, about 1 to 30% by weight, specifically about 3 to 20% by weight. weight percent more specifically in the range of about 5 to 10 weight percent.

Then, a base component may be added to the pretreated silica-containing aqueous dispersion to prepare a pH-adjusted aqueous dispersion of pretreated silica. At this time, the pH of the aqueous dispersion may be adjusted to, for example, at least about 10, specifically at least about 11, and more specifically in the range of about 10.5 to 11.5. The reason for increasing the pH of the dispersion is to deprotonate the silica surface, specifically by removing hydrogen ions (H ⁺ ) from silanol groups (Si-OH) present on the surface of the pretreated silica (i.e., hydrogen from hydroxyl groups). ions can be removed) so that they have a negative charge. That is, since the ion is not adsorbed at the zero charge point of silica and the hydroxyl group is maintained, negative charge can be displayed by deprotonating the silica surface through pH adjustment.

As a result, the hydroxyl anion on the surface of the deprotonated silica and the hydroxyl group present on the silica surface, specifically the 3-membered hydroxyl group, form three hydroxyl anions in the basic aqueous medium, which in the subsequent process have an electrostatic interaction (i.e., It is possible to provide a site where cobalt is fixed or grafted in the form of a single atom by electrostatic adsorption (ie, selective activation of a hydroxyl group). This fixation mechanism is different from a passive method in which an alkali metal is interposed between the cobalt ions to provide a site where the cobalt ions are fixed in a monoatomic form. In particular, it is noteworthy in that it effectively suppresses the accelerated shrinkage of the silica support itself during the dehydrogenation reaction resulting from the use of an alkali metal.

According to an exemplary embodiment, the base component may be, for example, at least one selected from sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc., specifically an ammonium-containing base, more specifically ammonium hydroxide (aqueous ammonia) Use At this time, it is advantageous to use a type that does not cause precipitation when combined or mixed with an aqueous solution of a cobalt precursor as the base to be added.

According to one embodiment of the present disclosure, separately from the step of preparing an aqueous dispersion of pH-adjusted base-treated silica, an aqueous solution of cobalt precursor is prepared, and a pH-adjusted aqueous cobalt precursor solution is prepared by adding a base component. steps may be performed.

In this regard, the cobalt precursor may be a precursor containing a cobalt (Co(III)) complex ion having an oxidation value of 3+, for example, Co(NH ₃ ) ₆ Cl ₃ is directly used, or Co After treating at least one cobalt compound (precursor) selected from (NO ₃ ) ₂ , CoCl ₂ , Co(acac) ₃ and the like with ammonia water, a precursor containing cobalt complex ions may be obtained through filtration. However, it may be advantageous to use Co(NH ₃ ) ₆ Cl ₃ as a precursor, which can minimize manufacturing steps for smooth formation of a cobalt monoatomic catalyst.

In an exemplary embodiment, the concentration of the cobalt precursor in the aqueous precursor solution may range, for example, from about 0.1 to 20% by weight, specifically from about 0.5 to 10% by weight, and more specifically from about 1 to 5% by weight.

In addition, the pH of the cobalt precursor solution can be adjusted by adding a base component, which is also in a state where the silica surface is deprotonated (i.e., negatively charged) when combined with an aqueous dispersion of pH-adjusted pretreated silica during a subsequent step. The cobalt ion (Co ³⁺ ) of the precursor having a positive charge can be fixed on the silica surface in an electrostatic adsorption manner by stably maintaining the modified state) to have a positive charge. At this time, the base component may be selected from at least one of the types previously used in the preparation of the aqueous dispersion of pretreated silica, and in this case, the same base component or base compound may be used, but in some cases, different base components may be used. have. However, as the base to be added, it is preferable to use a kind that does not cause precipitation when mixed with the aqueous solution of the cobalt precursor as described above. In addition, according to an exemplary embodiment, the pH of the aqueous cobalt precursor solution may be adjusted to, for example, at least about 10, specifically at least about 11, and more specifically in the range of about 10.5 to 11.5 through the addition of a base.

As described above, once the aqueous solution of the pH adjusted Co(III) precursor has been prepared, a step of combining it with the aqueous dispersion of the pH adjusted pretreated silica is performed. At this time, the mixing ratio of the pH-adjusted aqueous cobalt precursor solution and the aqueous dispersion of the pH-adjusted pretreated silica is the amount of cobalt ions in the aqueous cobalt precursor solution fixed in a monoatomic form (specifically, a monoatomic form of a single layer) on the surface of the pretreated silica. can be determined taking into account In this regard, cobalt ions can be supported in the form of a single atom by up to about 2 to 3% by weight on the surface of the pretreated silica, but in practice, as all of the cobalt precursors used cannot be fixed on the surface of the pretreated silica, an excess amount compared to the theoretical amount of cobalt (Co(III)) precursor. In an exemplary embodiment, the cobalt precursor is, for example, at least about 1% by weight, specifically about 1 to 20% by weight, more specifically about 2 to 10% by weight, particularly specifically about The mixing ratio of the aqueous dispersion of the aqueous cobalt precursor solution and the pretreated silica may be adjusted to be in the range of 3 to 8% by weight.

According to an exemplary embodiment, the combination of the two aqueous fluids (aqueous silica-dispersion and aqueous cobalt precursor solution) can be performed under stirring, such that the stirring speed is, for example, about 200 to 500 rpm, specifically about 250 rpm. to 400 rpm, and the stirring time may be, for example, at least about 3 minutes, specifically at least about 5 minutes, more specifically about 5 to 10 minutes, but is not necessarily limited to the above conditions. . In addition, the temperature at the time of combination is not particularly limited, but may be set to, for example, about 10 to 40°C, specifically about 20 to 30°C, and more specifically, room temperature.

Then, from the aqueous dispersion of silica to which the cobalt precursor has been adsorbed, the cobalt not fixed to the silica surface in monoatomic form is removed as completely as possible. This is to be distinguished from the impregnation-type supporting method, and is to remove and leave only cobalt (or Co ³⁺ ) fixed in a monoatomic form by electrical interaction on the surface of the silica. If, as in the conventional impregnation method, when the cobalt precursor is attached to the silica surface in a bulk state, phenomena such as reduction and aggregation may occur during the dehydrogenation reaction to decrease activity.

Considering the foregoing, the solid content (pretreated silica to which the cobalt precursor is adsorbed (immobilized)) in the combined dispersion may be separated by conventional solid-liquid separation processes such as settling and filtering. If necessary, water, specifically distilled water is added to the separated solids to perform stirring, and the process of separating the solids can be repeated. In addition, the separated solid content may be washed with water, specifically distilled water, at least once, specifically, multiple times, so that the cobalt precursor remaining without being adsorbed may be removed as thoroughly as possible. Thereafter, a step of drying the obtained solid content may be performed, and the drying temperature is not particularly limited, but may be set to, for example, about 10 to 40 ° C, specifically about 20 to 30 ° C, and more specifically, room temperature. have. At this time, the oxidation state of cobalt ions is still maintained at +3.

As a subsequent step, silica on which cobalt ions are adsorbed (fixed) is converted into a dehydrogenation catalyst by heat treatment (second heat treatment). At this time, the heat treatment may be performed in an oxygen-containing atmosphere, for example, about 250 to 1000 ° C, specifically about 270 to 800 ° C, more specifically about 280 to 600 ° C, particularly specifically about 290 to 400 ° C range. You can set the heat treatment temperature in In this specific embodiment, cobalt having an oxidation value of 3+ adsorbed on the silica is converted to cobalt having an oxidation value of 2+ by heat-treating the silica on which cobalt is adsorbed (fixed). In addition, the temperature increase rate in the heat treatment process is, for example, about 1 to 20 °C / min, specifically about 1.5 to 10 ° C / min, more specifically, it is possible to adjust within the range of 2 to 7 ° C / min.

However, optionally, an additional drying step may be performed prior to the heat treatment step in an oxygen-containing atmosphere, wherein the additional drying temperature may be, for example, in the range of about 50 to 150 °C, specifically about 120 to 150 °C. have. During the drying process at a relatively high temperature, at least a portion of cobalt present with an oxidation value of 3+ may be partially reduced to cobalt with an oxidation value of 2+ in advance, and the remaining cobalt may have a oxidation value of 2+ through heat treatment. can be converted

Although the present invention is not bound by any particular theory, the reason why the oxidation number of cobalt is maintained at 2+ after heat treatment can be explained as follows.

When cobalt is 3+, it occupies 6 electrons in the outermost orbital, so only an octahedral shape with 6 bonds is possible. On the other hand, in the case of 2+, since there are 7 electrons in the outermost orbital, a tetrahedral is mainly formed, but an octahedral is also possible as in the case of CoO. In the case of this specific example, since it must be structurally combined with a 3-membered hydroxyl group, it can be considered to be changed to 2+ to form a tetrahedral structure. On the other hand, in order to exist as 3+ again, it is necessary to form an octahedron in harmony with the surroundings. Since silicon (Si) is an element that does not have a structure other than a tetrahedron, it is judged that it does not conform to the surrounding environment and does not convert to 3+ cobalt. do. In addition, since inactivation is when the connection (communication) with Si is cut and aggregated into Co metal alone, it is determined that Co ₃ O ₄ containing 3+ cobalt can be formed when an oxide is formed in contact with oxygen. .

In addition, the heat treatment time is not particularly limited as long as it is a time sufficient for converting 3+ cobalt to 2+ cobalt, and is, for example, about 2 to 12 hours, specifically about 2.5 to 8 hours, more specifically about 2+ hours. It may range from 3 to 4 hours.

Cobalt with an oxidation value of 2+ converted by heating to a predetermined temperature or higher in the heat treatment step is not converted back to cobalt with an oxidation value of 3+ even if the heat treatment is continued in an oxygen-containing (or oxidizing) atmosphere (or a calcination atmosphere). This is because the tetrahedral structure must be maintained as a single atom. Moreover, even when the catalyst is applied to a dehydrogenation reaction operated at a predetermined temperature or higher, this oxidation state does not change, indicating that the catalyst according to the present embodiment has resistance to reduction.

According to this specific embodiment, the negatively charged SiO ⁻ present on the surface of the pretreated silica and the cobalt ion having an oxidation value of 2+ can be bonded in the form of isolated single atoms by electrostatic interaction or adsorption. Cobalt in this monoatomic form is coordinated by forming a tetrahedral structure in a three-membered hydroxyl ring by three hydroxyl groups present on the surface of silica.

As in one embodiment, when the silica support is subjected to heat treatment and high-temperature aqueous treatment prior to carrying cobalt, the advantages differentiated from the conventional alkali metal technology are as follows:

That is, when an alkali metal is introduced in order to supplement or secure thermal durability, a phenomenon in which the volume of the silica support itself decreases by about 30% or more occurs during the reaction by promoting volumetric shrinkage. On the other hand, in the present embodiment, in order to suppress the volumetric shrinkage of silica during the dehydrogenation reaction, heat treatment is performed before supporting the active metal, that is, cobalt (Co) in the form of a single atom to preemptively perform possible volumetric shrinkage, thereby causing in the reaction process. shrinkage of the supporting body can be suppressed.

In addition, if a trace amount of an alkali metal is unavoidably contained as an impurity in the catalyst (for example, based on the catalyst, for example, less than about 0.001% by weight), it can be tolerated, but in the conventional method for producing a monoatomic cobalt catalyst As in the case of intentionally introducing an alkali metal to provide a supported site for cobalt, it can be excluded. From this point of view, the dehydrogenation catalyst according to certain embodiments is substantially free of alkali metals.

Therefore, the monoatomic cobalt catalyst according to one embodiment can suppress cobalt aggregation due to volumetric shrinkage without introducing additional metal ions, and also introduces a large amount of free hydroxyl groups having thermal durability, so that cobalt ions are isolated. It can be maintained in monoatomic form. As a result, the activity maintenance and long-term durability of the dehydrogenation catalyst itself can be secured.

According to an exemplary embodiment, the content (supported amount) of cobalt in the dehydrogenation catalyst may be, for example, at least about 1% by weight, specifically at least about 1.1 to 3% by weight, particularly specifically about 1.2 to 2% by weight. have. The above-mentioned supported amount may vary somewhat depending on the type of silica, but as described above, the amount of cobalt that may exist in the form of a single atom is typically up to about 2 to 3% by weight, so it may be determined in consideration of this.

dehydrogenation reaction

According to another embodiment of the present disclosure, paraffin, specifically, light paraffin (more specifically, light paraffin having 2 to 5 carbon atoms) is dehydrogenated using the above-described monoatomic cobalt-based catalyst to obtain an olefin corresponding thereto A process for converting to is provided. In particular, it may contain propane as hard paraffin. In this regard, the feedstock may be provided in the gas phase.

At this time, it should be noted that when the above-described catalyst is applied, good conversion rate and selectivity can be achieved even when a feedstock having a high paraffin content is used. Illustratively, the paraffin content in the feedstock may range, for example, from at least about 50 vol%, specifically at least about 70 vol%, more specifically at least about 80 vol%, and even greater than about 99 vol%. level may be. This is different from experiments on conventional monoatomic catalysts (eg, Zn catalysts) in which dehydrogenation is performed on feedstocks containing up to about 20% by volume of paraffins.

In the dehydrogenation reaction according to an exemplary embodiment, the reaction temperature may be, for example, about 500 to 700 ° C, specifically about 550 to 650 ° C, more specifically about 570 to 620 ° C, and the reaction pressure is , For example, it may be adjusted in the range of about 0.3 to 2 bar, specifically about 0.4 to 1.5 bar, and more specifically about 0.5 to 1 bar. In addition, the gaseous space velocity (GHSV) in the standard state is, for example, about 100 to 2000 hr ^-1 , specifically about 200 to 1500 hr ^-1 , more specifically about 300 to 1000 hr ^-1 Can be set within the range have. The above-described dehydrogenation reaction conditions can be changed in consideration of the type of paraffin in the feedstock, the supported amount and ratio of the active metal and alkali metal in the catalyst, and the like.

According to an exemplary embodiment, each of the conversion rate and selectivity in the dehydrogenation reaction step is, for example, at least about 30% (specifically at least about 40%) and at least about 70% (specifically at least about 80%) level. can be

The present invention can be more clearly understood by the following examples, which are only for illustrative purposes of the present invention and are not intended to limit the scope of the present invention.

The analysis equipment and analysis method used in this Example are as follows.

- EXAFS

^In order to identify the cobalt single atom of the cobalt single atom catalyst and analyze the change in the surrounding environment of the cobalt single atom, Co K-edge (7.709 keV) X-ray absorption spectroscopy (XAFS) was measured. The gas was adjusted so that the absorption rate of I ₀ was 15% and the absorption rate of It+Ir was 85%, and the monochromator was detuned to 70%. All samples except for the reference (0.1 mm) were measured in transmission mode after flattening by filling a 2 mm slit with powder. Wavelet transformation was performed with η=8 and σ=1 using the Morlet mother wavelet in the range of k = 2-11 Å ^-1 , R = 1-4 Å with the HAMA-Fortran program.

- Calculate conversion rate and selectivity

Conversion and selectivity of propane were calculated according to Equations 1 and 2 below.

[Equation 1]

[Equation 2]

Preparation Example 1

Among commercially available silica (Fuji's product name Q6), one having an average particle size of 500 μm or more, a specific surface area of 450 m 2 / g or more, and a pore volume of 0.8 cm 3 / g or more was selected and used. After heat treatment for a period of time, it was cooled to obtain heat treated silica. Then, 10 g of the heat-treated silica was dispersed in 100 mL of distilled water, boiled at 100° C. for 2 hours, cooled, and filtered to obtain pre-treated silica particles. Hereinafter, silica subjected to heat treatment and high-temperature water treatment is referred to as "silica after pretreatment".

After pretreatment, 10 g of silica was prepared by dispersing in 100 mL of distilled water, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH of the dispersion to 11 to prepare an aqueous dispersion of silica after pretreatment with the pH adjusted.

Separately, 0.5 g of a cobalt precursor (Co(NH ₃ ) ₆ Cl ₃ ) was dissolved in 50 mL of distilled water in a beaker, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH to 11. An aqueous conditioned cobalt precursor solution was prepared.

Then, an aqueous solution of the pH-adjusted cobalt precursor was added to the aqueous dispersion of silica after pH-adjusted pretreatment and stirred at room temperature for 1 hour. After completion of stirring, the dispersion was filtered and washed several times with distilled water.

The filtered sample was dried at room temperature, dried at 120 ° C. for 6 hours, heated up to 300 ° C. at a heating rate of 2 ° C. per minute, and then heat-treated in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Comparative Preparation Example 1

Among commercially available silica (Fuji's product name Q6), one with an average particle size of 500 μm or more was selected and used, and 10 g of silica was prepared by dispersing in 100 mL of distilled water, and 28% by weight of ammonia water (Sigma-Aldrich) was added. A pH-adjusted aqueous dispersion of silica was prepared by adjusting the pH of the dispersion to 11.

Separately, 0.5 g of cobalt precursor (Co(NH ₃ ) ₆ Cl ₃ ) was dissolved in 50 mL of distilled water in a beaker, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH to 11 to adjust the pH. An aqueous cobalt precursor solution was prepared.

Then, the pH-adjusted aqueous cobalt precursor solution was added to the pH-adjusted silica dispersion and stirred at room temperature for 1 hour. After completion of stirring, the dispersion was filtered and washed several times with distilled water.

The filtered sample was dried at room temperature, dried at 120 ° C. for 6 hours, heated up to 300 ° C. at a heating rate of 2 ° C. per minute, and then heat-treated in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Preparation Example 2

Among commercially available silica (Fuji's product name Q6), one having an average particle size of 500 μm or more, a specific surface area of 450 m 2 / g or more, and a pore volume of 0.8 cm 3 / g or more was selected and used, and was heated at 600 ° C for 6 hours. After treatment, it was cooled to obtain heat-treated silica. Then, 10 g of the heat-treated silica was dispersed in 100 mL of distilled water, boiled at 100° C. for 2 hours, cooled, and filtered to obtain silica particles. At this time, silica that has undergone heat treatment and high-temperature water treatment is referred to as "silica after pretreatment".

After pretreatment, 10 g of silica was prepared by dispersing in 100 mL of distilled water, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH of the dispersion to 11 to prepare an aqueous dispersion of silica after heat treatment with the pH adjusted.

Separately, 0.5 g of a cobalt precursor (Co(NH ₃ ) ₆ Cl ₃ ) was dissolved in 50 mL of distilled water in a beaker, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH to 11. An aqueous conditioned cobalt precursor solution was prepared.

Then, an aqueous solution of the pH-adjusted cobalt precursor was added to the aqueous dispersion of silica after a pH-adjusted heat treatment and stirred at room temperature for 1 hour. After completion of stirring, the dispersion was filtered and washed several times with distilled water.

The filtered sample was dried at room temperature, dried at 120 ° C. for 6 hours, heated up to 300 ° C. at a heating rate of 2 ° C. per minute, and then heat-treated in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Preparation Example 3

Among commercially available silica (Fuji's product name Q6), one having an average particle size of 500 μm or more, a specific surface area of 450 m 2 / g or more, and a pore volume of 0.8 cm 3 / g or more was selected and used for 6 hours at 700 ° C. in an air atmosphere. After heat treatment, it was cooled to obtain heat-treated silica. Then, 10 g of the heat-treated silica was dispersed in 100 mL of distilled water, boiled at 100° C. for 2 hours, cooled, and filtered to obtain pre-treated silica particles. Hereinafter, the silica treated with heat treatment and high-temperature water system is referred to as "silica after pretreatment".

After pretreatment, 10 g of silica was prepared by dispersing in 100 mL of distilled water, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH of the dispersion to 11 to prepare an aqueous dispersion of silica after pretreatment with the pH adjusted.

Separately, 0.5 g of a cobalt precursor (Co(NH ₃ ) ₆ Cl ₃ ) was dissolved in 50 mL of distilled water in a beaker, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH to 11. An aqueous conditioned cobalt precursor solution was prepared.

Then, an aqueous solution of the pH-adjusted cobalt precursor was added to the aqueous dispersion of silica after pH-adjusted pretreatment and stirred at room temperature for 1 hour. After completion of stirring, the dispersion was filtered and washed several times with distilled water.

The filtered sample was dried at room temperature, dried at 120 ° C. for 6 hours, heated up to 300 ° C. at a heating rate of 2 ° C. per minute, and then heat-treated in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Production Example 4

Of commercially available silica (Fuji's product name Q6), one having an average particle size of 500 μm or more, a specific surface area of 450 m 2 / g or more, and a pore volume of 0.8 cm 3 / g or more was selected and used. After treatment for an hour, it was cooled to obtain heat-treated silica. Then, 10 g of the heat-treated silica was dispersed in 100 mL of distilled water, boiled at 100° C. for 2 hours, cooled, and filtered to obtain pre-treated silica particles. Hereinafter, the silica treated with heat treatment and high-temperature water system is referred to as "silica after pretreatment".

After pretreatment, 10 g of silica was prepared by dispersing in 100 mL of distilled water, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH of the dispersion to 11 to prepare an aqueous dispersion of silica after pretreatment with the pH adjusted.

Separately, 0.5 g of a cobalt precursor (Co(NH ₃ ) ₆ Cl ₃ ) was dissolved in 50 mL of distilled water in a beaker, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH to 11. An aqueous conditioned cobalt precursor solution was prepared.

Then, an aqueous solution of the pH-adjusted cobalt precursor was added to the aqueous dispersion of silica after pH-adjusted pretreatment and stirred at room temperature for 1 hour. After completion of stirring, the dispersion was filtered and washed several times with distilled water.

The filtered sample was dried at room temperature, dried at 120 ° C. for 6 hours, heated up to 300 ° C. at a heating rate of 2 ° C. per minute, and then heat-treated in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Comparative Preparation Example 2

Among commercially available silica (Fuji's product name Q6), one having an average particle size of 500 μm or more, a specific surface area of 450 m 2 / g or more, and a pore volume of 0.8 cm 3 / g or more was selected and used. After heat treatment for a period of time, it was cooled to obtain heat treated silica. Then, 10 g of the heat-treated silica was dispersed in 100 mL of distilled water, boiled at 100° C. for 2 hours, cooled, and filtered to obtain silica particles. Hereinafter, the silica treated with heat treatment and high-temperature water system is referred to as "silica after pretreatment".

After pretreatment, 10 g of silica was prepared by dispersing in 100 mL of distilled water, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH of the dispersion to 11 to prepare an aqueous dispersion of silica after pretreatment with the pH adjusted.

Separately, 0.5 g of cobalt precursor (Co(NH ₃ ) ₆ Cl ₃ ) was dissolved in 50 mL of distilled water in a beaker, and 28% by weight of ammonia water (Sigma-Aldrich) was added to adjust the pH to 11 to adjust the pH. An aqueous cobalt precursor solution was prepared.

Then, an aqueous solution of the pH-adjusted cobalt precursor was added to the aqueous dispersion of silica after pH-adjusted pretreatment and stirred at room temperature for 1 hour. After completion of stirring, the dispersion was filtered and washed several times with distilled water.

The filtered sample was dried at room temperature, dried at 120 ° C. for 6 hours, heated up to 300 ° C. at a heating rate of 2 ° C. per minute, and then heat-treated in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Cobalt contents in the catalysts prepared according to Preparation Examples 1 to 3 and Comparative Preparation Examples 1 to 3 are shown in Table 1 below.

compare
Preparation Example 1 Preparation Example 2 Preparation Example 3 Production Example 4 Preparation Example 1 Comparative Preparation Example 2 Co content (% by weight) 1.2 1.1 1.1 1.5 1.3 0.7

Comparing Preparation Examples 1 to 4 and Comparative Preparation Example 2 in the table above, it can be seen that the supported amount of cobalt is affected by the heat treatment temperature during the pretreatment step of silica. Specifically, in Comparative Preparation Example 2, the heat treatment temperature is too high, indicating that there is a limit to carrying an appropriate amount of monoatomic cobalt due to insufficient activation of the hydroxyl group even if a high-temperature water-based treatment is performed after the heat treatment.

Experimental Example 1

In this Experimental Example, a dehydrogenation reaction was performed to synthesize olefins from a reactant gas containing a high paraffin content in the presence of cobalt-based catalysts prepared according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 and 2, respectively.

The dehydrogenation reaction for catalyst evaluation was carried out using a 3/4 inch quartz tube reactor (the diameter of the catalyst loading zone is 3/4 inch, and the diameter of the tube excluding it is 1/4 inch). The flow rate of each gas was controlled using a mass flow controller, and the product gas passing through the reactor was analyzed through an online gas chromatography device (50 m, HP-Plot column).

6 cc of catalyst was weighed and supported in a reaction tube with quartz wool, and the temperature was raised from room temperature to 590 °C at a rate of 5 °C/min per minute while flowing N ₂ at a flow rate of 100 cc/min.

For the dehydrogenation reaction of paranfin, 99.5% propane (gas) was injected into the reactor at a rate of 20 cc/min as the reactant gas. The composition of the product gas passing through the reactor was analyzed using a flame ionization detector (FID).

- Conversion rate and selectivity evaluation

In dehydrogenation reaction using each of the cobalt-based monoatomic catalyst prepared using a pretreated silica support (Preparation Example 1) and the cobalt-based monoatomic catalyst prepared using a silica support without pretreatment (Comparative Preparation Example 1) Conversion and selectivity over time are shown in FIG. 1 .

According to the figure, as a result of the dehydrogenation reaction, in the case of the catalyst according to Preparation Example 1, the selectivity to the catalyst is similar to that of the catalyst according to Comparative Preparation Example 1, but the conversion rate is at a high level, which is means more than equal.

- SEM analysis

The changes before and after the dehydrogenation reaction were analyzed by SEM for a Co monoatomic catalyst (A) using silica particles without pretreatment as a support and a Co monoatomic catalyst (C) using silica particles after heat treatment and hydroxyl activation as a support. And the results are shown in Figure 2. In addition, the results of observing the change before and after the dehydrogenation reaction by separately preparing a Co monoatomic catalyst (B) prepared using silica particles subjected to only heat treatment are shown in FIG. 2 together.

According to the figure, it was confirmed that the particle size of the Co monoatomic catalyst (A) using untreated silica as a support was reduced by 10% or more due to shrinkage of the silica support after the dehydrogenation reaction. In addition, the Co monoatomic catalyst (B) using only heat-treated silica as a support exhibited a volume shrinkage of about 40% compared to the Co monoatomic catalyst using untreated silica as a support, but preemptively shrinked by heat treatment. The volume obtained did not significantly increase or decrease after the dehydrogenation reaction. However, cracks were formed on the surface of the catalyst during the dehydrogenation reaction, and the catalyst was partially damaged.

On the other hand, the particle size of the Co monoatomic catalyst (C) using silica subjected to high-temperature water treatment (hydroxyl group activation) as a support after heat treatment increased by about 20% compared to the Co monoatomic catalyst when only heat treatment was performed, but before and after the dehydrogenation reaction. It was observed that the size change of was not large, and the crushing of the particles due to the dehydrogenation reaction temperature was not observed.

According to the above results, in order to mitigate the volumetric shrinkage caused by heat during the dehydrogenation reaction of the Co catalyst using untreated silica as a support, when heat treatment is preemptively performed on the silica during the dehydrogenation reaction, the dehydrogenation reaction It is judged that the volumetric shrinkage of the heavy catalyst support can be suppressed. In addition, resistance to volume shrinkage is increased by supplementing the reduction in the loading rate of active metals in the catalyst due to the disappearance of hydroxyl groups on the surface of silica by heat treatment through a high-temperature water-based treatment (activation of hydroxyl groups), and at the same time, the optimal amount of activity Since the metal can be supported, it is believed that a catalyst having good thermal durability can be prepared.

- EXAFS Wavelet Transform Analysis

EXAFS Wavelet Transform analysis results for the cobalt-based catalysts prepared according to Example 1 and Comparative Preparation Example 2 are shown in FIG. 3 .

Referring to the figure, in the case of Co metal, a single pattern was confirmed at R = 2.2 Å, which is a characteristic that appears when Co metal exists as a Co-Co bond.

As for the pattern of Co ₃ O ₄ corresponding to normal Co oxide, Co-O in the first pattern (R = 1.5 Å) and Co-O-Co in the second pattern (R = 2.5 Å) are observed. In this regard, in bulky oxides, structures appear repeatedly from basic lattice units. At this time, since the number of second adjacent atoms (8, 12) is greater than the number of closest atoms (4, 6), the pattern intensity at a high R value is usually stronger than the first pattern intensity. . That is, in the case of the oxide, the second pattern is well developed because the structure of the unit cell is repeated because it exists as a crystal in the particle. Accordingly, it can be seen that the graph in which the second pattern is well developed exists in the form of cobalt oxide.

In this regard, the monoatomic cobalt catalyst exhibited a feature in which only a pattern at a low R value (R = 1.5 Å) was expressed very strongly.

Referring to FIG. 3, in the two cobalt catalysts (before reaction) prepared according to Preparation Example 1 and Comparative Preparation Example 2, the first pattern was well developed, but the second pattern was not confirmed. Increasing distance indicates that the structure is not developed. Considering these results, the state before the reaction in both samples suggests that Co exists in the form of a single atom.

Experimental Example 2

In this Experimental Example, a dehydrogenation reaction for preparing olefins from a reactant gas containing a high paraffin content was repeated a plurality of times using the cobalt-based catalyst prepared according to Preparation Example 1 and Comparative Preparation Example 2.

Specifically, the dehydrogenation reaction was performed in the same apparatus and initial reaction conditions as in Experimental Example 1. At this time, in the first dehydrogenation reaction, 99.5% propane (gas) as a reactant gas was injected into the reactor at a flow rate of 20 cc/min and maintained for 1 hour. After performing the dehydrogenation reaction for 1 hour, the inside of the reaction tube was purged while flowing N ₂ gas at 100 cc/min over 30 minutes. The composition of the product gas passing through the reactor was automatically collected at 15-minute intervals and analyzed with a flame ionization detector (FID). In the catalyst regeneration step, air (99.999%) was flowed at a flow rate of 100 cc/min to remove coke generated in the reaction step, and then N ₂ gas was flowed at a flow rate of 10 cc/min for another 30 minutes to cool the reaction tube. The inside was purged.

As described above, the four steps of reaction-purge-regeneration-purge were repeated, and the catalyst change after repeating the repeated reaction experiment 5 times was analyzed through EXAFS, and the results are shown in FIG. 3.

According to the figure, as a result of analysis after dehydrogenation using the catalysts according to Preparation Example 1 and Comparative Preparation Example 2, Preparation Example 1 showed almost the same phenomenon as before the reaction, but in Comparative Preparation Example 2, the second pattern after the reaction ( It can be seen that R = 2.5 Å) is relatively more developed than before the reaction. This indicates that the monoatomic form of Co was converted to an oxide form during the dehydrogenation reaction. Therefore, in the case of Preparation Example 1, the monoatomic state of Co before and after the reaction is maintained, whereas in the case of Comparative Preparation Example 2, the Co existence state before and after the reaction is different.

Simple modifications or changes of the present invention can be easily used by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (19)

As a method for producing a monoatomic cobalt-based catalyst for the dehydrogenation of paraffin,
a) Heat treatment of silica as a support under a temperature condition determined in the range of 600 to 870 ° C. to induce a contracted support and at the same time remove hydroxyl groups on the surface, and then perform a pretreatment including performing a high-temperature water-based reaction on silica selectively activating hydroxyl groups to form pretreated silica;
b) preparing an aqueous dispersion of the pretreated silica obtained in step a);
c) preparing a pH-adjusted aqueous dispersion of pretreated silica by adding a base component to the aqueous dispersion of pretreated silica to adjust the pH to at least 10;
d) separately, preparing an aqueous solution of a cobalt precursor having an oxidation value of 3+ and adding a basic component to prepare a pH-adjusted aqueous solution of a cobalt precursor;
e) combining the pH-adjusted aqueous dispersion of the pretreated silica and the pH-adjusted aqueous cobalt precursor solution to prepare an aqueous dispersion in which at least some of the cobalt ions having an oxidation value of 3+ are adsorbed on the surface of the pretreated silica step;
f) removing cobalt ions not adsorbed on the surface of the pretreated silica; and
g) heat-treating the silica adsorbed with cobalt ions obtained from step f);
including,
Here, in the cobalt-based catalyst, cobalt having an oxidation value of 2+ exists in the form of an isolated single atom on the pretreated silica, and cobalt having an oxidation value of 2+ is tetrahedral in a three-membered hydroxyl ring present on the surface of the pretreated silica. The way in which structure is formed and coordinated. The method of claim 1, wherein the silica exhibits a volume reduced by 75% or less compared to silica before pretreatment by heat treatment in step a), and exhibits a volume increased by 5 to 50% compared to silica heat treated by high-temperature water-based reaction How to. The method of claim 1, wherein the silica before pretreatment in step a) is amorphous silica. The method of claim 3, wherein the silica before pretreatment in step a) is in the form of particles and has a particle size ranging from 0.5 to 5000 μm. The method of claim 1, wherein in step a), the surface hydroxyl group concentration of the silica before heat treatment is in the range of 3 to 5 mmol/cc, and the surface hydroxyl group concentration of the silica after heat treatment is less than 0.2 mmol/cc, and
The method, characterized in that the surface hydroxyl group concentration of the silica after the high-temperature water-based reaction in step a) is in the range of 3 to 5 mmol / cc. 2. The method of claim 1, wherein the pretreated silica has a carrying capacity of at least 0.8% by weight of cobalt ions. The method of claim 1, wherein the high-temperature water-based treatment in step a) comprises preparing a heat-treated silica-aqueous dispersion by dispersing the heat-treated silica in an aqueous medium; and
Boiling the heat-treated silica-aqueous dispersion under a temperature condition of 70 to 150 ° C;
A method comprising a. 8. The method according to claim 7, characterized in that the content of silica in the heat-treated silica-aqueous dispersion ranges from 1 to 30% by weight. The method according to claim 1, characterized in that the particle size of the pretreated silica obtained from step a) ranges from 0.3 to 4000 μm. The method according to claim 1, characterized in that the concentration of the pretreated silica-containing aqueous dispersion prepared in step b) is in the range of 1 to 30% by weight. The method of claim 1, wherein the basic components used in each of step c) and step d) are the same as or different from each other and are at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and ammonium hydroxide. . The method of claim 1, wherein the cobalt precursor in step d) is a precursor containing a cobalt (Co(III)) complex ion having an oxidation value of 3+, and
The method, characterized in that the concentration of the cobalt precursor in the aqueous solution of the cobalt precursor ranges from 0.1 to 20% by weight. The method of claim 12, wherein Co(NH ₃ ) ₆ Cl ₃ is directly used as the cobalt precursor, or at least one cobalt compound selected from the group consisting of Co(NO ₃ ) ₂ , CoCl ₂ , and Co(acac) ₃ A method characterized by using a precursor containing cobalt complex ions obtained through filtration after treating with ammonia water. The method of claim 1, wherein the mixing ratio of the aqueous dispersion of the pH-adjusted cobalt precursor solution and the pH-adjusted pretreated silica in step e) is adjusted so that the cobalt precursor is at least 1% by weight based on the weight of the silica. Way. The method according to claim 1, wherein the heat treatment in step g) is performed in an oxygen-containing atmosphere and at a temperature of 250 to 1000 °C. 2. A method according to claim 1, characterized in that the content of cobalt in the catalyst is at least 1% by weight. 2. The method of claim 1, wherein the catalyst is free of alkali metals. providing a feedstock containing paraffin;
Performing a dehydrogenation reaction on the feedstock under conditions of a temperature of 500 to 700 ° C. and a pressure of 0.3 to 2 bar in the presence of a catalyst prepared according to any one of claims 1 to 17; and
recovering olefins corresponding to the paraffins from the dehydrogenation reaction products;
Method for producing olefins from paraffins comprising a. 19. The process of claim 18, wherein the paraffin content in the feedstock is at least 50% by volume.

Images