KR20220000347A - Cobalt-based Single-atom Dehydrogenation Catalysts Having Improved Thermal Stability and Method for Producing Corresponding Olefins from Paraffins Using the Same - Google Patents

Abstract

The present disclosure describes a dehydrogenation catalyst in which monatomic cobalt is supported by using silica as a supporter after pretreatment of silica with heat treatment and a high-temperature aqueous reaction, a method for preparing the same, and a method of preparing a corresponding olefin obtained by dehydrogenating paraffin, specifically hard paraffin, in the presence of the dehydrogenation catalyst.

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 preparing a corresponding olefin from paraffin using the same. More specifically, the present disclosure relates to a dehydrogenation catalyst supported with monoatomic cobalt, a method for preparing the same, and paraffin in the presence of the dehydrogenation catalyst by pretreating silica through heat treatment and high temperature aqueous reaction, and then using it as a support. , specifically to a method for producing an olefin corresponding thereto by dehydrogenating light paraffin.

Recently, a catalyst technology using an active metal by supporting it on a support has been attracting attention. In particular, as nanotechnology develops, research on using a nano-sized active metal by supporting it on a support is being actively conducted. However, nano-sized active metals have a wide size distribution and irregular morphological characteristics, so despite their superior activity compared to conventional catalysts, when used as a catalyst, side reactions or catalyst deactivation proceed rapidly 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 monatomic size, catalyst activity can be maximized by reducing the size of the metal active site to an atomic level of nano size or less. In particular, since it has an extremely simplified and ideal structure, it provides an advantage suitable for conducting related research by simulating theoretical results obtained through computational science, etc. 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 hard paraffin.

In addition, advantages such as minimization of cracking and suppression of coke generation during the reaction have been reported (eg, ACS Catal. 2014, 4, 4, 1091-1098) when an active metal in a monoatomic form is supported (eg, ACS Catal. 2014, 4, 4, 1091-1098) ). However, in the literature and the like, in order to keep the concentration of the reactant low, a mixed gas (a mixed gas consisting of 3% propane as a reactant and argon (Ar) as an inert gas) is used to suppress paraffin while suppressing by-products. It is difficult to apply in practical commercial processes, such as selectively converting the olefin to the corresponding olefin and reacting it at a low temperature to increase the lifetime of the catalyst.

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

In order to suppress the above-mentioned problems, a method for reducing the aggregation of cobalt active metal on the surface of the support by introducing an alkali metal to the support has been reported (Korean Patent Publication No. 2020-0049209). However, there is a problem in that the stability of the catalyst is lowered by the aggregation of the active metal due to the shrinkage behavior of the support and the like due to the continuous exposure to high temperature during the dehydrogenation reaction. In addition, due to the influence of the alkali metal introduced during the preparation of the catalyst, the volume of the silica support rapidly decreased during the dehydrogenation reaction, resulting in aggregation or sintering of metal ions due to the decrease in the surface area. Moreover, when an alkali metal is used in the process of supporting an active metal in the form of a monoatomic, it is difficult to synthesize a monoatomic catalyst on a commercial scale, such as requiring a complicated and expensive process for synthesis. Accordingly, 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 type of cobalt (Co) supported catalyst capable of maintaining catalyst stability or long-term activity even when exposed to high temperatures as in a reaction for producing olefin through the dehydrogenation reaction of paraffin, and a catalyst thereof To provide a manufacturing method.

Another embodiment of the present disclosure is to provide a dehydrogenation process with high paraffin conversion and excellent selectivity for corresponding olefins even for high concentrations of paraffin-containing feedstock suitable for commercialization.

According to the first aspect of the present disclosure,

A method for preparing a monoatomic type cobalt-based catalyst, the method comprising:

a) Heat treatment of silica as a support under temperature conditions 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 comprising performing a high-temperature aqueous reaction on silica selectively activating hydroxyl groups to form pretreated silica;

b) preparing the pretreated silica-containing aqueous dispersion;

c) preparing an aqueous dispersion of pH-adjusted pre-treated silica by adjusting the pH to at least 10 by adding a base component to the aqueous dispersion of pre-treated silica;

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

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

f) removing cobalt ions that are not adsorbed on the pre-treated silica surface; and

g) heat-treating the silica to which the cobalt ions obtained from step f) are adsorbed;

including,

Here, in the cobalt-based catalyst, cobalt having an oxidation number of 2+ exists in a monoatomic form isolated on the pre-treated silica, and cobalt having an oxidation number of 2+ is a tetrahedron in a three-membered hydroxide ring present on the surface of the pre-treated silica. A method of forming and coordinating 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 method described above; and

recovering the olefin corresponding to the light paraffin from the dehydrogenation reaction product;

There is provided a method for producing olefins from paraffin comprising:

The dehydrogenation catalyst according to an embodiment according to the present disclosure is a form in which cobalt in monoatomic form is supported on a silica support pretreated in such a way that heat treatment and activation of a selective hydroxyl group are performed, and paraffin, particularly hard paraffin, is corresponding to it. Even when exposed to high temperatures (for example, about 500° C. or higher) during the dehydrogenation reaction with Aggregation or sintering can be effectively suppressed. Therefore, even when exposed to high temperatures for a long time in the course of the dehydrogenation reaction or when in contact with hydrogen generated from the dehydrogenation reaction, the deformation or denaturation of the catalyst is effectively suppressed, so that the catalytic activity can be maintained for a long time.

In particular, in the case of a silica-based cobalt metal catalyst intended to secure thermal stability by using the introduction of an existing alkali metal, the volume of the silica support during the dehydrogenation reaction rapidly decreased due to the effect of the alkali metal introduced into the silica. Aggregation or sintering of metal ions occurs due to a decrease in the surface area, so there is a limit in prolonging the catalytic activity for a long period of time. However, in one embodiment, the 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 the hydroxyl group is lost by heat treatment. It provides the advantage of effectively supporting active metal ions by reassembling the surface active group in a manner that performs a selective hydroxyl group activation step later. 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 paraffins in dehydrogenation reactions.

1 is 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) Dehydration using each It is a graph showing the conversion rate and selectivity according to time during the digestion reaction,
2 is an SEM photograph showing the changes before and after the dehydrogenation reaction of a Co monoatomic catalyst prepared by using silica particles that have not undergone pretreatment, silica that have undergone only heat treatment during pretreatment, and silica particles that have undergone heat treatment-hydroxyl activation as supports, respectively; and
3 is a graph showing the results of EXAFS Wavelet Transform analysis of the cobalt monoatomic catalyst before and after the dehydrogenation reaction.

The present invention can all be achieved by the following description. It is to be understood that the following description describes preferred embodiments of the present invention, and the present invention is not necessarily limited thereto. In addition, it should be understood that the accompanying drawings are provided to aid understanding, and the present invention is not limited thereto.

Terms used in this specification may be defined as follows.

"Heterogeneous catalyst" may mean a catalyst that exists in a phase different from that of a reactant during a catalytic reaction, for example, it may mean a catalyst that is not dissolved in the reaction medium. In the case of a heterogeneous catalyst, in order for the reaction to occur, at least one reactant needs to be adsorbed by being diffused onto the surface of the heterogeneous catalyst, and after the reaction, the product needs to be desorbed from the surface of the heterogeneous catalyst.

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

The term "crystalline" or "crystalline" can refer to any solid material, typically in which the atoms are arranged to have a lattice structure (eg, three-dimensional order), whereas "amorphous" may 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 and 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 carbon number from which hydrogen molecules have been removed from light paraffin in the feedstock of 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 consist of an aggregate of primary silica particles.

It is contemplated that "heat treatment" may involve intentionally raising the temperature of an entire object or a portion thereof and, if necessary, chemical or additional physical treatment to achieve a desired specific structure and physical property (or change). .

The expression "substantially free" is intended to mean that a specific component is not intentionally incorporated, provided that it can be understood to include a case in which the component is present in the form of an impurity.

It may be understood that the expressions “on” and “on” are used to refer to the concept of relative position. Accordingly, not only the case where other components or layers are directly present in the mentioned layers, but also 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 with respect to location. Also, the expression “sequentially” may be understood as a concept of relative position.

In the present specification, when a specific numerical range is described, it may be considered that any value within the range and sub-combinations in which any two values within the range are 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 sub-combination.

In the present specification, when a component is "included", it means that other components and/or steps may be further included, unless otherwise specified.

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

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

Pretreatment of silica support

According to one embodiment, in order to provide the properties of the silica support described above, a pretreatment step including heat treatment and high temperature water-based treatment (hydroxyl group activation) may be performed on 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, may include fumed silica, wet 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 above-described particle size range may 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, in the range of at least about 100 m 2 /g, specifically about 200 to 1500 m 2 /g, more specifically about 300 to 1000 m 2 /g. can Also, the initial silica pore volume 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, more specifically about 3 to 30 nm. It is to be understood that the above numerical ranges are set forth for illustrative purposes.

Also, according to an exemplary embodiment, the initial silica surface hydroxyl group concentration is, for example, in the range of about 3 to 5 mmol/cc, specifically about 3.2 to 4.8 mmol/cc, and more specifically 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 weakness of silica used as a support in the conventional cobalt monoatomic catalyst, for example, amorphous silica at high temperature.

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 the heat treatment temperature is too high, recovery (or activation) of hydroxyl groups is not easy in a subsequent step (hot water treatment) due to excessive shrinkage. Therefore, it is advantageous to set it in the above-mentioned heat treatment temperature range.

According to an exemplary embodiment, the heat treatment of silica may be performed over, for example, about 3 to 12 hours, specifically, about 4 to 11 hours, and more specifically, about 5 to 10 hours. Further, the heat treatment may be performed under an oxygen-containing atmosphere, for example, an air atmosphere. The rate of temperature increase 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-described heat treatment process, silica, specifically amorphous silica, is crystallized as it is exposed to high temperatures, and in the process, water molecules are removed and the volume thereof is contracted. 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%, particularly specifically about 20 to 50%, compared to the silica before pretreatment (initial) volume (ie, contracted).

However, since the heat treatment step converts not only the inside of the silica (specifically, amorphous silica) but also the hydroxyl groups on the surface to silicon oxide, it removes even the hydroxyl functional group that provides a site for fixing cobalt, an active metal. Specifically, the surface of the heat-treated silica loses surface hydroxyl groups due to high temperature, and as will be described later, the cobalt precursor cannot be effectively adsorbed or fixed to the surface of the silica support by electrostatic interaction. As such, as a result of performing the preemptive heat treatment step on the silica support in the catalyst preparation process, the volume contraction of the catalyst caused by the dehydrogenation reaction can be suppressed to some extent, while the active metal, cobalt, is supported in a monoatomic form. function is reduced. 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.

In consideration of this, in one embodiment, a high-temperature water-based treatment is performed to selectively activate surface hydroxyl groups (ie, hydroxyl function) present on silica that has undergone a volumetric shrinkage process by heat treatment. The high-temperature water-based treatment forms free hydroxyl groups on the surface of silica to effectively adsorb or immobilize 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 normal silica (initial silica), hydroxyl groups due to hydrogen bonding, free hydroxyl groups, and the like exist together. However, when hydroxyl groups on the silica surface are removed by the above-mentioned heat treatment and then hydroxyl groups on the surface are activated by performing a high-temperature water-based treatment, free hydroxyl groups may be generated in a large amount. Since the free hydroxyl group thus generated can fix the cobalt ion, it is suitable for forming a tetrahedral structure with a cobalt atom and a three-membered hydroxide ring.

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

According to an exemplary embodiment, the silica support comprises, 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 aforementioned pretreatment (specifically, high temperature water-based treatment). %, more specifically 1 to 2% by weight, and particularly specifically about 1.2 to 1.5% by weight of cobalt ions.

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

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

On the other hand, the volume of the heat-treated silica through high-temperature water-based treatment can be increased (ie, volume expansion), for example, about 5 to 50%, specifically about 10 to 30%, more specifically about 5 to 50% compared to the heat-treated silica. 15 to 25% increased volume. In addition, the particle size (diameter) of silica after high-temperature aqueous treatment may be, for example, in the range of about 0.3 to 4000 μm, specifically about 5 to 900 μm, and more specifically about 300 to 700 μm, but this is the initial silica particle size. As it depends on the size and the like, it may be understood as an example.

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

Although the present disclosure is not bound by a specific theory, the total amount (concentration) of hydroxyl groups present on the silica surface after high-temperature water-based treatment (reaction) can be restored to a level similar to that of the initial state, but the thermal stability of silica is ensured. Accordingly, the shrinkage of the silica support is suppressed, and with it, free hydroxyl groups suitable for supporting (or fixing) monoatomic cobalt ions exist in a high proportion, while supporting monoatomic cobalt ions such as hydroxyl groups by hydrogen bonding. It is judged that the amount of hydroxyl groups that are not suitable for this purpose decreases.

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

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

Monoatomic cobalt support on pre-treated silica support

According to one embodiment, the pretreated silica is dispersed in an aqueous medium to prepare a pretreated silica-containing aqueous dispersion. At this time, the aqueous medium may be water, specifically distilled water, as described above, 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 weight %, more specifically in the range of about 5 to 10 weight %.

Then, a base component may be added to the pretreated silica-containing aqueous dispersion to prepare a pH-adjusted aqueous pretreated silica dispersion. In this case, the pH of the aqueous dispersion may be adjusted, for example, in the range of at least about 10, specifically at least about 11, and more specifically, 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 pre-treated silica surface (that is, hydrogen from hydroxyl groups). ions can be removed) to make it negatively charged. That is, since ions are not adsorbed at the zero charge point of silica and the hydroxyl group is maintained, it is possible to display a negative charge by deprotonating the silica surface through pH adjustment.

As a result, the hydroxyl anions on the surface of the deprotonated silica and the hydroxyl groups, specifically the ternary hydroxyl groups, on the silica surface form three hydroxyl anions in the basic aqueous medium, which in the subsequent process electrostatic interaction (i.e., Electrostatic adsorption) can provide a site where cobalt is immobilized or grafted in a monoatomic form (ie, selective activation of hydroxyl groups). This fixation mechanism is distinguished from the passive method in which an alkali metal is interposed between the cobalt ions to provide a site for the cobalt ions to be fixed in a monoatomic form. In particular, it is noteworthy in that it effectively suppresses the accelerated shrinkage phenomenon 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, and the like, specifically an ammonium-containing base, more specifically ammonium hydroxide (ammonia water) use In this case, 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 added base.

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

In this regard, the cobalt precursor may be a precursor including 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 (NO ₃ ) ₂ , CoCl ₂ , Co(acac) ₃ After treating at least one cobalt compound (precursor) selected from ammonia water, it is possible to obtain a precursor including a cobalt complex ion through filtration. However, it may be advantageous to use _{Co(NH 3} ) ₆ Cl ₃ as a precursor, which can minimize the manufacturing step for the smooth formation of the 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, it is possible to adjust the pH of the cobalt precursor solution by adding a base component, which also causes the silica surface to be deprotonated (that is, negatively charged when combined with an aqueous dispersion of the pH-controlled pre-treated silica during the subsequent step so as to have a stable maintenance of the modified state) can be fixed by the amount of precursor cobalt ion (electrostatic adsorption method on a silica surface Co ³⁺⁾ having the charge of. In this case, the base component may be used by selecting at least one of the types previously used in the preparation of the aqueous dispersion of pretreated silica, and in this case, the same basic component or basic compound may be used for all, but in some cases, a different base component may be used. have. However, as the base to be added, it will be preferable to use a type 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, through the addition of a base, the pH of the aqueous solution of the cobalt precursor may be adjusted to, for example, at least about 10, specifically at least about 11, and more specifically, about 10.5 to 11.5.

As described above, when an aqueous solution of the pH-adjusted Co(III) precursor is prepared, a step of combining it with an aqueous dispersion of the pH-adjusted pretreated silica is performed. In this case, the mixing ratio of the aqueous dispersion of the pH-controlled cobalt precursor aqueous solution and the pH-controlled pre-treated silica is the amount in which the cobalt ions in the cobalt precursor aqueous solution are fixed to the surface of the pre-treated silica in a monoatomic form (specifically, a monoatomic form of a single layer) can be determined taking into account. In this regard, cobalt ions can be supported in a monoatomic form by up to about 2 to 3 wt% on the surface of the pre-treated silica, but in reality, all of the cobalt precursor used cannot be fixed on the surface of the pre-treated silica, so it is excessive compared to the theoretical amount. of cobalt (Co(III)) precursors can be dissolved. In an exemplary embodiment, the cobalt precursor is, based on the weight of the pretreated silica, for example at least about 1% by weight, specifically about 1 to 20% by weight, more specifically about 2 to 10% by weight, particularly about The mixing ratio of the aqueous dispersion of the cobalt precursor aqueous solution and the pre-treated silica may be adjusted to be in the range of 3 to 8 wt%.

According to an exemplary embodiment, the combination of two water-based fluids (aqueous silica-dispersion and aqueous cobalt precursor solution) is stirred under stirring. As can be carried out, the stirring speed may be, for example, in the range of about 200 to 500 rpm, specifically about 250 to 400 rpm, and the stirring time may be, for example, at least about 3 minutes, specifically at least about 5 minutes. , more specifically, it may be in the range of about 5 to 10 minutes, but is not necessarily limited to the above conditions. In addition, the temperature during the combination is not particularly limited, for example, about 10 to 40 ℃, specifically about 20 to 30 ℃, more specifically can be set to room temperature.

Then, from the aqueous dispersion of silica to which the cobalt precursor has been adsorbed, cobalt that is not fixed in a monoatomic form on the silica surface is removed as completely as possible. This is different from the impregnation method, and is intended to remove and leave only ^{cobalt (or Co 3+} ) fixed to the silica surface in a monoatomic form by electrical interaction. If, as in a conventional impregnation method, the cobalt precursor is attached to the silica surface in a bulk state, a phenomenon that reduces activity such as reduction or aggregation during dehydrogenation may be induced.

In consideration of the above, the solid content in the combined dispersion (pre-treated silica to which the cobalt precursor is adsorbed (immobilized)) can be separated by a conventional solid-liquid separation process such as settling and filtering. If necessary, water, specifically distilled water, is added to the separated solid to perform stirring, and the process of separating the solid again may be repeated. In addition, the separated solid content may be washed at least once, specifically, multiple times using water, specifically distilled water, so that the cobalt precursor remaining unadsorbed may be removed as completely as possible. Thereafter, a step of drying the obtained solid content may be performed, and the drying temperature is not particularly limited, but for example, about 10 to 40° C., specifically about 20 to 30° C., more specifically, can be set to room temperature. have. At this time, the oxidation state of the cobalt ion is still maintained at +3.

As a subsequent step, silica to which cobalt ions are adsorbed (immobilized) is converted into a dehydrogenation catalyst by heat treatment (second heat treatment). At this time, the heat treatment may be performed under 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 about 290 to 400 ° C. range. You can set the heat treatment temperature in In this embodiment, as cobalt adsorbed (immobilized) silica is heat treated, cobalt having an oxidation number of 3+ adsorbed on silica is converted into cobalt having an oxidation number of 2+. In addition, the temperature increase rate in the heat treatment process, for example, about 1 to 20 °C / min, specifically about 1.5 to 10 °C / min, more specifically 2 to 7 °C / min, it can be adjusted within the range.

However, optionally, an additional drying step may be performed prior to the heat treatment step under an oxygen-containing atmosphere, in which case The additional drying temperature may be, for example, in the range of about 50 to 150 °C, specifically about 120 to 150 °C. In the process of drying at a relatively high temperature as described above, at least a portion of cobalt present with an oxidation number of 3+ may be partially reduced to cobalt of an oxidation number of 2+ in advance, and the remaining cobalt may have an oxidation number of 2+ through heat treatment. can be switched

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

In the case of 3+, cobalt occupies 6 electrons in the outermost orbital, so only an octahedral in which 6 bonds are formed is possible. On the other hand, in the case of 2+, since 7 electrons exist in the outermost orbital, a tetrahedral is mainly formed, but an octahedron is also possible as in the case of CoO. In the case of this embodiment, it can be seen that it is changed to 2+ in order to form a tetrahedral structure because it must be structurally bound to a ternary hydroxyl group. On the other hand, to exist as 3+ again, it must form an octahedron in harmony with the surroundings. Silicon (Si) is an element that does not have a structure other than a tetrahedron. do. In addition, since the deactivation is because the connection (communication) with Si is cut and agglomerated into Co metal alone, when it comes into contact with oxygen to form an oxide, it is considered that Co ₃ O ₄ containing cobalt of 3+ can be obtained. .

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

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

According to this embodiment, negatively charged SiO ⁻ and cobalt ions having an oxidation number of 2+ present on the surface of the pretreated silica may be combined in an isolated monoatomic form by electrostatic interaction or adsorption. This monoatomic type of cobalt is coordinated to form a tetrahedral structure in a three-membered hydroxyl ring by three hydroxyl groups present on the surface of silica.

When the silica support is subjected to heat treatment and high-temperature water-based treatment prior to supporting cobalt as in one embodiment, the advantages that are differentiated from the conventional technique using alkali metals are as follows:

That is, when an alkali metal is introduced to supplement or secure thermal durability, a phenomenon occurs in which the volume of the silica support itself decreases by about 30% or more during the reaction by promoting volumetric shrinkage. On the other hand, in this embodiment, in order to suppress the volumetric shrinkage of silica during the dehydrogenation reaction, the active metal, that is, cobalt (Co), is heat-treated before being supported in a monoatomic form to preemptively perform possible volumetric shrinkage in the reaction process. It is possible to suppress the shrinkage of the supporting body.

In addition, if a trace amount of alkali metal is unavoidably contained in the catalyst as an impurity (for example, based on the catalyst, for example, less than about 0.001 wt %), it may be acceptable, but in the conventional method for preparing a cobalt monoatomic catalyst The case of intentionally introducing an alkali metal to provide a cobalt-supporting site can be excluded. In this respect, the dehydrogenation catalyst according to certain embodiments is substantially free of alkali metals.

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

According to an exemplary embodiment, the content (support) of cobalt in the dehydrogenation catalyst may be, for example, in the range of at least about 1% by weight, specifically at least about 1.1 to 3% by weight, particularly about 1.2 to 2% by weight. have. The above-mentioned loading amount may vary somewhat depending on the type of silica, but as described above, the amount of cobalt that may be present in a monoatomic form is typically at most about 2 to 3 wt%, and 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 type cobalt-based catalyst to the corresponding olefin. A process for converting to In particular, it may contain propane as hard paraffin. In this regard, the feedstock may be provided in the gaseous phase.

At this time, it should be noted that, when the above-described catalyst is applied, good conversion 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, at least about 50% by volume, specifically at least about 70% by volume, more specifically at least about 80% by volume, and furthermore, greater than about 99% by volume. It could be level. This is distinct from the dehydrogenation reaction carried out on feedstocks containing up to about 20% by volume of paraffins in experiments with conventional monoatomic catalysts (eg, Zn catalysts).

In the dehydrogenation reaction according to an exemplary embodiment, the reaction temperature may be, for example, in the range of 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, from about 0.3 to 2 bar, specifically from about 0.4 to 1.5 bar, more specifically from about 0.5 to 1 bar. In addition, the gaseous space velocity (GHSV) in the standard state, for example, about 100 to 2000 hr ^-1 , specifically about 200 to 1500 hr ^-1 , more specifically about 300 to 1000 hr ^{-1 It} can be determined 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 amounts of active metals and alkali metals in the catalyst, and the ratio thereof.

According to an exemplary embodiment, each of the conversion and selectivity in the dehydrogenation reaction process 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 may 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 cobalt monoatomic catalysts and analyze changes in the environment around cobalt monoatomic catalysts, Co at 8C beamline (nano-XAFS, 4keV ∼ 20keV, 10 ¹² photons/sec) of Pohang Radiation Light Accelerator (PAL PLS-II) 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 using a Morlet mother wavelet in the range ^{of k = 2-11 Å -1} and R = 1-4 Å with the HAMA-Fortran program with η=8 and σ=1.

- 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), particles 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 were selected and used, and 6 under 850 ° C and air atmosphere After heat treatment for a period of time, it was cooled to obtain heat-treated silica. Then, 10 g of 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 heat-treated and high-temperature water-based silica is referred to as "silica after pretreatment".

After pretreatment, 10 g of silica was prepared by dispersing it in 100 mL of distilled water, and 28 wt% of aqueous ammonia (Sigma-Aldrich) was added so that the pH of the dispersion was adjusted to 11. After pretreatment, an aqueous dispersion of silica was prepared.

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 wt% of aqueous ammonia (Sigma-Aldrich) was added to adjust the pH to 11. A controlled aqueous cobalt precursor solution was prepared.

Then, the pH-adjusted aqueous solution of cobalt precursor was added to the aqueous dispersion of silica after pH-adjusted pretreatment, and stirred at room temperature for 1 hour. The stirred 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, and then heated to 300° C. at a temperature increase rate of 2° C. per minute, followed by heat treatment 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), particles having an average particle size of 500 µm or more were selected and used, prepared by dispersing 10 g of silica in 100 mL of distilled water, and 28 wt% of aqueous ammonia (Sigma-Aldrich) was added. Thus, the pH of the dispersion was adjusted to 11 to prepare an aqueous dispersion of silica whose pH was 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 wt% of aqueous ammonia (Sigma-Aldrich) was added to adjust the pH to 11 to adjust the pH. A cobalt precursor aqueous solution was prepared.

Then, the pH-adjusted aqueous solution of cobalt precursor was added to the pH-adjusted silica dispersion and stirred at room temperature for 1 hour. The stirred 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, and then heated to 300° C. at a temperature increase rate of 2° C. per minute, followed by heat treatment in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Preparation 2

Among commercially available silica (Fuji's product name Q6), particles 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 were selected and used, and heated at 600 ° C. for 6 hours. After treatment and cooling, heat-treated silica was obtained. Then, 10 g of 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, the silica that has been subjected to heat treatment and high-temperature water-based treatment is referred to as “silica after pretreatment”.

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

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 wt% of aqueous ammonia (Sigma-Aldrich) was added to adjust the pH to 11. A controlled aqueous solution of cobalt precursor was prepared.

Then, the pH-adjusted aqueous solution of the cobalt precursor was added to the aqueous dispersion of silica after the pH-controlled heat treatment and stirred at room temperature for 1 hour. The stirred 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, and then heated to 300° C. at a temperature increase rate of 2° C. per minute, followed by heat treatment in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Preparation 3

Among commercially available silica (Fuji's product name Q6), particles 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 were selected and used. After heat treatment for a while, it was cooled to obtain heat-treated silica. Then, 10 g of 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 heat-treated and high-temperature water-based silica is referred to as "silica after pre-treatment".

After pretreatment, 10 g of silica was prepared by dispersing it in 100 mL of distilled water, and 28 wt% of aqueous ammonia (Sigma-Aldrich) was added so that the pH of the dispersion was adjusted to 11. After pretreatment, an aqueous dispersion of silica was prepared.

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 wt% of aqueous ammonia (Sigma-Aldrich) was added to adjust the pH to 11. A controlled aqueous cobalt precursor solution was prepared.

Then, the pH-adjusted aqueous solution of cobalt precursor was added to the aqueous dispersion of silica after pH-adjusted pretreatment, and stirred at room temperature for 1 hour. The stirred 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, and then heated to 300° C. at a temperature increase rate of 2° C. per minute, followed by heat treatment in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

Preparation 4

Among commercially available silica (Fuji's product name Q6), particles 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 were selected and used, and 6 under 800 ° C and an air atmosphere After treatment for an hour, it was cooled to obtain heat-treated silica. Then, 10 g of 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 heat-treated and high-temperature water-based silica is referred to as "silica after pre-treatment".

After pretreatment, 10 g of silica was prepared by dispersing it in 100 mL of distilled water, and 28 wt% of aqueous ammonia (Sigma-Aldrich) was added so that the pH of the dispersion was adjusted to 11. After pretreatment, an aqueous dispersion of silica was prepared.

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 wt% of aqueous ammonia (Sigma-Aldrich) was added to adjust the pH to 11. A controlled aqueous cobalt precursor solution was prepared.

Then, the pH-adjusted aqueous solution of cobalt precursor was added to the aqueous dispersion of silica after pH-adjusted pretreatment, and stirred at room temperature for 1 hour. The stirred 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, and then heated to 300° C. at a temperature increase rate of 2° C. per minute, followed by heat treatment 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), particles 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 were selected and used. After heat treatment for a period of time, it was cooled to obtain heat-treated silica. Then, 10 g of 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 heat-treated and high-temperature water-based silica is referred to as “silica after pre-treatment”.

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

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 wt% of aqueous ammonia (Sigma-Aldrich) was added to adjust the pH to 11 to adjust the pH. A cobalt precursor aqueous solution was prepared.

Then, the pH-adjusted aqueous solution of cobalt precursor was added to the aqueous dispersion of silica after pH-adjusted pretreatment, and stirred at room temperature for 1 hour. The stirred 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, and then heated to 300° C. at a temperature increase rate of 2° C. per minute, followed by heat treatment in an air atmosphere for 2 hours to prepare a dehydrogenation catalyst.

The content of cobalt in the catalysts prepared according to Preparation Examples 1 to 3 and Comparative Preparation Examples 1 to 3, respectively, is shown in Table 1 below.

compare
Preparation Example 1 Preparation 2 Preparation 3 Preparation 4 Preparation Example 1 Comparative Preparation Example 2 Co content (wt%) 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 above table, it can be seen that the amount of cobalt supported is affected by the heat treatment temperature during the silica pretreatment step. Specifically, in Comparative Preparation Example 2, the heat treatment temperature is too high, and even if a high-temperature water-based treatment is performed after heat treatment, there is a limit in supporting monoatomic cobalt in an appropriate amount due to insufficient activation of hydroxyl groups.

Experimental Example 1

In this experimental example, in the presence of the cobalt-based catalyst prepared according to Preparation Examples 1 to 4 and Comparative Preparation Examples 1 and 2, respectively, a dehydrogenation reaction for synthesizing olefins from a reactant gas containing a high content of paraffin was performed.

The dehydrogenation reaction for catalyst evaluation was performed using a 3/4 inch quartz tube reactor (the diameter of the catalyst loading area was 3/4 inch, and the diameter of the tube except this was 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 on-line gas chromatography apparatus (50 m, HP-Plot column).

The catalyst of 6 cc was weighed and supported on the reaction tube with quartz wool, and then 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 blue fin, the reactant gas was injected into the reactor with 99.5% propane (regas) at a flow rate of 20 cc/min. The composition of the product gas passing through the reactor was analyzed using a flame ionization detector (FID).

- Evaluate conversion rate and selectivity

Dehydrogenation reaction using each of the cobalt-based monoatomic catalyst prepared using the pretreated silica support (Preparation Example 1) and the cobalt-based monoatomic catalyst prepared using the silica support that was not pretreated (Comparative Preparation Example 1) The conversion rate and selectivity with time are shown in FIG. 1 .

According to the drawings, as a result of performing the dehydrogenation reaction, in the case of the catalyst according to Preparation Example 1, the selectivity compared to the catalyst was similar to that of the catalyst according to Comparative Preparation Example 1, but the conversion rate was high. means more than equal.

- SEM analysis

Analysis of changes before and after dehydrogenation reaction by SEM for Co monoatomic catalyst (A) using silica particles that have not been pretreated as a support and Co monoatomic catalyst (C) using silica particles that have undergone heat treatment-hydroxyl activation as a support and the results are shown in FIG. 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 that have undergone 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 silica without pretreatment as a support was reduced by 10% or more due to the shrinkage of the silica support after the dehydrogenation reaction. In addition, the Co monoatomic catalyst (B) using silica as a support subjected to only heat treatment exhibited volume shrinkage of about 40% compared to the Co monoatomic catalyst using silica without pretreatment as a support, but preemptively contracted by heat treatment The volume obtained did not increase or decrease significantly after the dehydrogenation reaction. However, a phenomenon in which the catalyst was damaged due to the generation of cracks on the surface of the catalyst during the dehydrogenation reaction was partially observed.

On the other hand, the Co monoatomic catalyst (C) using silica as a support that has undergone high-temperature water-based treatment (hydroxyl group activation) after heat treatment increased the particle size 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 change in the size of the particles was not large, and the crushing of the particles by the temperature of the dehydrogenation reaction was not observed.

According to the above results, in order to alleviate the volume shrinkage caused by heat during the dehydrogenation reaction of the Co catalyst using untreated silica as a support, when heat treatment on silica is preemptively performed in the pretreatment process, the dehydrogenation reaction It is considered that the volumetric shrinkage of the heavy catalyst support can be suppressed. In addition, resistance to volumetric shrinkage is increased by supplementing the decrease in the loading rate of active metals in the catalyst due to the loss of surface hydroxyl groups of silica by heat treatment through a high-temperature water-based treatment (hydroxyl group activation) process. Since the metal can be supported, it is considered that a catalyst having good thermal durability can be prepared.

- EXAFS Wavelet Transform Analysis

The results of EXAFS Wavelet Transform analysis for the cobalt-based catalyst prepared according to Example 1 and Comparative Preparation Example 2, respectively, 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.

_{In the pattern of Co 3} O ₄ corresponding to a 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 the second adjacent atoms (8, 12) is large compared to 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 oxide, the second pattern is well developed because the structure of the unit cell is repeated because it exists as crystalline 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 cobalt monoatomic catalyst exhibited very strong expression of only a pattern at a low R value (R = 1.5 Å).

Referring to FIG. 3 , in both of the two types of cobalt catalysts (before the 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, which is from Co As the distance increases, it indicates that the structure is not developed. Considering these results, the state before the reaction of both samples suggests that Co exists in the form of a single atom.

Experimental Example 2

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

Specifically, the dehydrogenation reaction was performed in the same apparatus and initial reaction conditions as in Experimental Example 1. At this time, in the initial dehydrogenation reaction, 99.5% propane (regas) 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 the coke generated in the reaction step, and then N ₂ gas was flowed at a flow rate of 10 cc/min for 30 minutes to the reaction tube. The inside was purged.

As described above, 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 drawings, as a result of the analysis after the dehydrogenation reaction using the catalyst according to Preparation Example 1 and Comparative Preparation Example 2, respectively, in Preparation Example 1, almost the same phenomenon as before the reaction was exhibited, but in Comparative Preparation Example 2, the second pattern after the reaction ( It can be seen that R = 2.5 Å) developed relatively more than before the reaction. This indicates that during the dehydrogenation reaction, the Co monoatomic form was converted to the oxide form. Therefore, in the case of Preparation Example 1, the Co monoatomic state before and after the reaction is maintained, whereas in Comparative Preparation Example 2, it suggests that 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 of ordinary skill in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (19)

a) Heat treatment of silica as a support under temperature conditions 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 comprising performing a high-temperature aqueous reaction on silica selectively activating hydroxyl groups to form pretreated silica;
b) preparing the pretreated silica-containing aqueous dispersion;
c) preparing an aqueous dispersion of pH-adjusted pre-treated silica by adjusting the pH to at least 10 by adding a base component to the aqueous dispersion of pre-treated silica;
d) separately, preparing an aqueous solution of a cobalt precursor having an oxidation value of 3+ and adding a base component to prepare an aqueous solution of a cobalt precursor having a pH adjusted;
e) combining the pH-adjusted aqueous dispersion of the pre-treated silica and the pH-adjusted aqueous cobalt precursor solution to prepare an aqueous dispersion in which at least a portion of cobalt ions having an oxidation number of 3+ are adsorbed on the surface of the pre-treated silica step;
f) removing cobalt ions that are not adsorbed on the pre-treated silica surface; and
g) heat-treating the silica to which the cobalt ions obtained from step f) are adsorbed;
including,
Here, in the cobalt-based catalyst, cobalt having an oxidation number of 2+ exists in a monoatomic form isolated on the pre-treated silica, and cobalt having an oxidation number of 2+ is a tetrahedron in a three-membered hydroxide ring present on the surface of the pre-treated silica. The way in which structures are formed and coordinated. According to claim 1, wherein by the heat treatment in step a), the silica exhibits a volume reduced by 75% or less compared to the silica before the pretreatment, and also exhibits a volume increase of 5 to 50% compared to the silica heat-treated by a high temperature aqueous reaction. how to do it with The method according to claim 1, wherein the silica before the pretreatment in step a) is amorphous silica. The method according to claim 3, wherein the silica is in the form of particles before the pretreatment in step a) and the particle size is in the range of 0.5 to 5000 μm. The method according to claim 1, wherein the surface hydroxyl group concentration of silica before heat treatment in step a) is in the range of 3 to 5 mmol/cc, and the surface hydroxyl group concentration of silica after heat treatment is less than 0.2 mmol/cc, and
The method, characterized in that the surface hydroxyl group concentration of silica after the high-temperature aqueous reaction in step a) is in the range of 3 to 5 mmol/cc. The method of claim 1 , wherein the pretreated silica has a carrying capacity of cobalt ions of at least 0.8% by weight. The method of claim 1, wherein the high-temperature water-based treatment in step a) comprises: dispersing the heat-treated silica in an aqueous medium to prepare a heat-treated silica-aqueous dispersion; and
boiling the heat-treated silica-aqueous dispersion under a temperature condition of 70 to 150°C;
A method comprising a. The method according to claim 7, characterized in that the content of silica in the heat-treated silica-aqueous dispersion is in the range of 1 to 30% by weight. The method according to claim 1, wherein the particle size of the pretreated silica obtained from step a) is in the range of 0.3 to 4000 μm. The method according to claim 1, wherein 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 according to claim 1, wherein the base component used in each of steps c) and d) is the same as or different from each other, and is 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 comprising 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 is in the range of 0.1 to 20% by weight. The method according to claim 12, wherein Co(NH ₃ ) ₆ Cl ₃ is directly used as the cobalt precursor, or Co(NO ₃ ) ₂ , CoCl ₂ , and Co(acac) ₃ At least one cobalt compound selected from the group consisting of A method characterized in that using a precursor containing a cobalt complex ion obtained through filtration after treatment with ammonia water. The method according to claim 1, wherein the mixing ratio of the pH-adjusted aqueous solution of the cobalt precursor and the aqueous dispersion of the pH-adjusted pre-treated 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 of claim 1, wherein the heat treatment in step g) is performed in an oxygen-containing atmosphere and a temperature of 250 to 1000°C. The process according to claim 1, characterized in that the content of cobalt in the catalyst is at least 1% by weight. The method of claim 1 , wherein the catalyst does not contain alkali metals. providing a feedstock containing paraffin;
18. A method comprising: 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 the olefin corresponding to the light paraffin from the dehydrogenation reaction product;
A method for producing olefins from paraffin comprising a. 19. The method of claim 18, wherein the content of light paraffins in the feedstock is at least 50% by volume.

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