KR102654667B1 - Metal Phosphide Catalysts and Method for Preparing High Value Compounds Using the Same - Google Patents

Abstract

In the present disclosure, a metal phosphide-based catalyst having a yolk-shell structure and a hydrogenation reaction using the same are used to produce organic acids, especially organic acids derived from biomass such as levulinic acid or derivatives thereof, as fuel additives and bioplastics. , a method of converting it into a high value-added compound that can be used as a raw material such as a solvent is described.

Description

Metal Phosphide Catalysts and Method for Preparing High Value Compounds Using the Same}

The present disclosure relates to a metal phosphide catalyst and a method for producing high value-added compounds using the same. More specifically, the present disclosure relates to a metal phosphide-based catalyst having a yolk-shell structure and using the same to convert organic acids, especially organic acids derived from biomass such as levulinic acid or derivatives thereof, into fuel through a hydrogenation reaction. It concerns a method of converting it into a high value-added compound that can be used as a raw material for additives, bioplastics, solvents, etc.

Petroleum energy, which led to the development of mankind, has recently been actively researched to replace petroleum resources in whole or in part with biomass due to problems such as finiteness of resources, unbiasedness, and environmental pollution.

Biomass is used broadly to include all materials derived from biological origin, while narrowly used to refer primarily to materials derived from plant sources such as corn, soybeans, linseed, sugarcane and palm oil. do. However, it can generally be extended to all living organisms, or to metabolic by-products that play a part in the carbon cycle.

The most widely used biomass is lignocellulosic biomass, which can be widely used in the production of biofuels and biochemicals. Lignocellulosic biomass consists of cellulose, hemicellulose, and lignin combined into a complex and rigid structure. Recently, research has been actively conducted to manufacture various chemical substances using materials formed through the saccharification step of lignocellulosic biomass.

In this regard, organic acids derived from biomass, such as levulinic acid (LA), are used as starting materials for the synthesis of commercially useful compounds, for example by acid hydrolysis of biomass (e.g. hexose). , can be produced through the dehydration reaction of fructose, etc. Compounds that can be prepared from levulinic acid include diphenolic acid, acetoacrylic acid, 1,4-pentanediol, acrylic acid, aminolevule, gamma-valerolactone (GVL), and 2-methyltetrahydrofuran (2-MTHF). ) can be exemplified.

Typically, gamma-valerolactone (GVL) and 2-methyltetrahydrofuran (2-MTHF) can be produced through a hydrogenation reaction using a catalyst. In this case, levulinic acid is dehydrated through primary hydrogenation. Dehydration and cyclization are performed to form gamma-valerolactone, and through additional hydrogenation (secondary hydrogenation), dehydration and cyclization are performed again to form 2-methyltetrahydrofuran. is formed.

In this way, attempts to use noble metal catalysts as hydrogenation catalysts for organic acids such as levulinic acid (or its derivatives) have been reported (e.g., U.S. Patent Publication No. 2003/0055270, CN105566258 A, etc.), and nickel phosphatase The use of a transition metal phosphide catalyst as a phide catalyst is also known (for example, CN112824395 A, etc.).

However, in the case of the noble metal-based catalyst among the above-mentioned prior arts, it is undesirable from an economic perspective because it uses expensive noble metal components, and it is necessary to carry out the reaction at a relatively high hydrogen pressure. Additionally, in the case of nickel phosphide catalysts, the conversion rate of organic acids and target products (e.g., in the case of producing gamma-valerolactone (GVL) and 2-methyltetrahydrofuran (2-MTHF) from levulinic acid) Because the selectivity is low, there is a need for improvement in overall yield.

Moreover, the conversion reaction using a catalyst according to the prior art is generally carried out in a liquid medium, that is, a solvent, and after completion of the reaction, the product must be separated from the solvent, so an additional separation and purification process is required.

Accordingly, there is a need for a hydrogenation catalyst that can overcome the limitations of the above-described prior art and convert organic acids into high-value compounds with high conversion rate and selectivity even under milder conditions (additionally solvent-free conditions).

One embodiment of the present disclosure seeks to provide a transition metal phosphide-based catalyst that exhibits improved hydrogenation activity compared to the prior art and can produce high-value compounds from organic acids in high yield and a method for producing the same.

Another embodiment of the present disclosure seeks to provide a conversion process that can effectively produce high-value compounds from organic acids or derivatives thereof even under solvent-free conditions using the above-described transition metal phosphide-based hydrogenation catalyst.

According to the first aspect of the present disclosure,

It is represented _by the general formula _Ni A method for converting an organic acid comprising performing a hydrogenation reaction is provided.

According to an exemplary embodiment, the hydrogenation reaction may involve a cyclization reaction.

According to an exemplary embodiment, the organic acid is levulinic acid, and the hydrogenation reaction is performed in one step or at least two steps,

Here, gamma-valerolactone (GVL) may be formed through the one-step hydrogenation reaction, while 2-methyltetrahydrofuran (2-MTHF) may be formed through the at least two-step hydrogenation reaction.

According to an exemplary embodiment, the hydrogenation reaction can be performed without the use of a solvent.

According to an exemplary embodiment, the first hydrogenation reaction is carried out under conditions of a temperature of 120 to 300 ° C. and a hydrogen pressure of 10 to 50 bar, and

The secondary hydrogenation reaction may be performed under conditions of a temperature of 180 to 320° C. and a hydrogen pressure of 30 to 80 bar.

According to the second aspect of the present disclosure,

A metal phosphide catalyst with a York-shell structure represented by the general formula Ni _x Co _y P (x and y are the molar ratio of Ni and Co, ranging from 1: 0.2 to 5),

(i) A catalyst is provided in which the overall size (diameter) of the catalyst is in the range of 10 to 100 nm, the thickness of the cell layer is in the range of 1 to 10 nm, and the size (diameter) of the yoke is in the range of 5 to 50 nm.

According to the third aspect of the present disclosure,

a) preparing a nickel and cobalt precursor solution by dissolving the nickel precursor and the cobalt precursor in a solvent;

b) subjecting the precursor solution to a first hydrothermal synthesis reaction to form a precipitate containing nickel-cobalt;

c) subjecting the precipitate to a second hydrothermal synthesis reaction to form nickel-cobalt hydroxide; and

d) The nickel _- cobalt hydroxide is subjected to a substitution reaction with a phosphide _agent under an inert gas atmosphere and elevated temperature conditions to obtain the general formula Ni Converting to a nickel-cobalt phosphide catalyst with a yoke-shell structure represented by (im);

Includes,

(i) The overall size (diameter) of the nickel-cobalt phosphide catalyst ranges from 10 to 100 nm, the thickness of the shell layer ranges from 1 to 10 nm, and the size (diameter) of the yoke ranges from 5 to 50 nm. A method for producing a catalyst is provided.

According to an exemplary embodiment, the weight ratio of the yoke in the yoke-shell structured metal phosphide catalyst may range from 1:1.5 to 5.

According to an exemplary embodiment, the acid amount (NH ₃ -TPD) of the metal phosphide catalyst may be in the range of 200 to 600 mmol/g.

According to an exemplary embodiment, the molar ratio of the reduced form of the metal to the unreduced form of the metal in the metal phosphide catalyst may range from 1:2 to 5.

Compared to conventional hydrogenation technology of organic acids (specifically, biomass-derived organic acids), the metal phosphide catalyst of the yoke-shell structure according to an embodiment of the present disclosure uses an inexpensive transition metal (i.e., base metal). Economic feasibility can be improved by achieving a good conversion rate of organic acids and selectivity for target compounds (specifically, compounds that can be used as raw materials for biofuels and/or fuel additives, solvents, bioplastics, etc.) while using it as an active metal. there is. In addition, when carried out as a liquid phase reaction, the target compound can be obtained by hydrogenating the reactant as is without the use of a separate solvent, so post-treatment processes such as separation of the solvent from the reaction product can be omitted, etc. It is also advantageous in terms of commercialization. Therefore, widespread application is expected in the future.

1 is a diagram showing the various reaction mechanisms involved in the hydrogenation reaction of levulinic acid according to an exemplary embodiment;
Figure 2 shows (a, b) Ni-Co glycerate precursor (produced from the first hydrothermal synthesis reaction), (c, d) Ni-Co phosphide precursor (second hydrothermal synthesis reaction) during the preparation of the transition metal phosphide catalyst. (generated from), (eg) Ni ₂ Co ₁ P, (h) CoP precursor, (i) CoP, and (j) NiP;
Figure 3 shows (ac) TEM images of the York-shell structured nickel-cobalt phosphide catalyst at different magnifications, (d) HRTEM images recorded from the basal plane, (e, f) HAADF-STEM images and EDS. elemental (Ni, Co, and P) mapping by (energy-dispersive X-ray spectroscopy);
Figure 4 is a HRTEM photo of Ni ₂ Co ₁ P catalyst;
Figure 5 shows (a, b) nickel-cobalt phosphide catalyst (Ni ₂ Co ₁ P-150 ℃ and Ni ₂ Co ₁ P-100 ℃) prepared by performing the second hydrothermal synthesis reaction at 150 ℃ and 100 ℃, respectively. , and (c) a TEM image showing the respective structures of Ni-Cu/Al ₂ O ₃ ;
Figure 6 is a graph showing the H ₂ -TPD and NH ₃ -TPD results of various transition metal phosphide catalysts, respectively;
_{Figure 7 shows the ​ ​} , and (c) P 2p spectra for NiP, Ni ₂ Co ₁ P, and CoP, respectively;
Figure 8 shows various phosphides of Ni and/or Co (NiP, CoP, NiCoP, Ni ₅ P ₄ , NiP ₂ , Ni3Co1P, Ni ₂ Co ₁ P, Ni ₁ Co ₁ P, Ni ₁ Co ₂ P, Ni ₁ Co ₃ P and CoP) are the XRD patterns for each;
Figure 9 is a graph showing the conversion rate and selectivity measured by hydrogenating levulinic acid to gamma-valerolactone using various transition metal phosphide catalysts under solvent-free conditions;
Figure 10 is a graph showing the conversion rate and selectivity measured by hydrogenating levulinic acid to gamma-valerolactone using various solvents in the presence of a Ni ₂ Co ₁ P catalyst;
Figure 11 is a graph showing the conversion rate and selectivity measured by hydrogenating reactants (or substrates) of various levulinic acid esters with gamma-valerolactone in the presence of a Ni ₂ Co ₁ P catalyst; and
Figure 12 shows nickel-cobalt phosphide catalysts (Ni ₂ Co ₁ P-100 ℃ and Ni ₂ Co ₁ P-150 ℃) and commercial nickel-copper prepared by performing the second hydrothermal synthesis reaction at 100 ℃ and 150 ℃, respectively. /Selection for levulinic acid conversion and gamma-valerolactone in the reaction for preparing gamma-valerolactone (GVL) from levulinic acid (LA) in the presence of alumina catalyst (Ni-Cu/Al ₂ O ₃ ), respectively. It is a graph representing a degree.

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, the attached drawings are intended to aid understanding, and the present invention is not limited thereto, and details regarding individual configurations can be appropriately understood based on the specific purpose of the related description described later.

Terms used in this specification may be defined as follows.

“Heterogeneous catalyst” may refer to a catalyst that exists in a different phase from the reactants during a catalytic reaction, for example, a catalyst that is not dissolved in the reaction medium. In the case of a heterogeneous catalyst, in order for a reaction to occur, at least one reactant must diffuse to the surface of the heterogeneous catalyst and be adsorbed, and after the reaction, the product needs to be desorbed from the surface of the heterogeneous catalyst.

“Biomass” generally refers to organic matter produced through photosynthesis, but can be understood as a concept that also includes organic waste such as livestock manure and food waste. In a broad sense, plant biomass, specifically a variety of biological resources known in the art including cellulose, hemicellulose and/or lignin (i.e. lignocellulosic biomass) (e.g. corn, soybean, linseed, Vegetable sources such as sugar cane and palm oil, and more specifically, rice straw, wheat straw, starch-containing grains, corn cobs, corn stover, rice husk, paper products, wood, sawdust, agricultural waste, grass, and candy. sorghum, cotton, flax, bamboo, abaca, algae, fruit peel, seaweed, palm waste, plant stems, roots and leaves, etc.). More specifically, carbohydrates obtained by saccharification or decomposition from the above-described biomass, such as starch and sugars, specifically monosaccharides (glucose, fructose, galactose, xylose, arabinose, mannose, etc.), disaccharides (sucrose, lactose, maltose, cellobiose, etc.), other (oligo)saccharides, etc.

The term “crystalline” or “crystalline” can typically refer to any solid-state material in which the atoms are arranged to have a lattice structure (e.g., a three-dimensional order), typically -It can be specified by line diffraction analysis (XRD), nuclear magnetic resonance analysis (NMR), differential scanning calorimetry (DSC), or a combination thereof.

“Catalyst” may mean a component that increases the rate of a reaction and can participate in the reaction without being consumed by the reaction itself, although it itself participates in the electrolysis reaction.

“Hydrothermal synthesis reaction” is a liquid synthesis method and may refer to a reaction in which a material is synthesized using water or an aqueous solution under high temperature and high pressure conditions.

Terms such as “on” or “above” and “below” or “below” can be understood to describe a relative positional relationship between components or members, and can be understood as “located above” or “below”. The term “located” can be understood as expressing a relative positional relationship not only in a state of being in contact with a specific object, but also in a state of not being in contact with a specific object.

When any component or member is described herein as being “connected to” another component or member, unless otherwise stated, it refers not only to being directly connected to said other component or member, but also to the other component or member. Alternatively, it may be understood that cases of being connected through the intervention of a member are also included.

Similarly, the term “contact” may also be understood to include not only direct contact, but also contact through the intervention of other components or members.

When it is said to “include” a certain component, this means that it may further include other components, unless otherwise specified.

metal phosphide catalyst

According to one embodiment of the present disclosure, through hydrogenation reaction, an organic acid (e.g., levulinic acid) or a derivative thereof (e.g., an ester compound of an organic acid) is converted to gamma-valerolactone (GVL) and/or A bifunctional metal phosphide catalyst capable of conversion to high value-added compounds such as 2-methyltetrahydrofuran (2-MTHF) is provided. In this regard, in order to convert levulinic acid into a cyclic compound (heterocyclic compound) such as GVL and/or 2-MTHF, a metal active site for hydrogenation and cyclization (specifically, dehydration/ring) are required. It is necessary to have bifunctional catalyst properties with an acidic site for reaction.

The metal phosphide catalyst according to one embodiment may use a transition metal phosphide catalyst, and more specifically, a combination of two types of base metals among Group VIII metals on the periodic table. According to certain embodiments, the metal phosphide catalyst may be a nickel-cobalt phosphide catalyst represented by the general formula Ni _x Co _y P. At this time, the molar ratio of nickel (Ni):cobalt (Co) in the catalyst is, for example, 1:about 0.2 to 5, specifically 1:about 0.3 to 3, more specifically 1:about 0.4 to 2, especially specifically 1: Can be adjusted in the range of about 0.5 to 1. According to certain embodiments, the transition metal phosphide catalyst may be a catalyst represented by the formula Ni ₂ Co ₁ P. At this time, if the relative amount of cobalt in the combination of the two transition metals is too low or too high, it may have an undesirable effect on the selectivity for the target product (specifically, GVL), so it is advisable to adjust it appropriately within the above-mentioned range. It can be advantageous.

The metal phosphide catalyst according to this embodiment may have a spherical shape, and in particular has a yolk-shell structure. The “yolk-shell structure” means at least one particle (yolk-shell structure) in the central space (compartment). That is, it may mean a hollow structure with a yoke, and specifically, the yoke may be separated from at least part of the cell layer, so that an empty space may exist, and in some cases, all surfaces of the yoke may be separated from the cell layer. It may be possible. At this time, what is noteworthy is that the cell layer and the yoke are made of the same nickel-cobalt phosphide material. In this case, the space between the cell layer and the yoke can function as a nano-sized reaction area. The contact area between the yoke, which is located away from the inner surface of the cell layer, and the reactant increases, and the hydrogenation reaction performed in the cell layer increases. The product may move to the yoke side and additional hydrogenation reaction may occur. This yoke-shell structure is a morphological characteristic that differentiates it from nickel phosphide (NiP) catalysts or cobalt phosphide (CoP) catalysts.

According to an exemplary embodiment, the overall size (diameter) of the metal phosphide catalyst may range, for example, from about 10 to 100 nm, specifically from about 20 to 80 nm, more specifically from about 40 to 60 nm, especially It may have a size of about 50 nm. The smaller the catalyst size, the larger the surface area, and considering that the reaction rate increases as the possibility of collision with reactants increases, it may be advantageous to adjust it within the above-mentioned range.

According to an exemplary embodiment, the thickness of the shell layer in the core-shell structured metal phosphide catalyst ranges, for example, from about 1 to 10 nm, specifically from about 2 to 8 nm, more specifically from about 4 to 6 nm, In particular, it may be approximately 5 nm. In this regard, if the thickness of the cell layer is too thin, deactivation of the yoke portion in the cell layer may occur, whereas if it is too thick, the cell layer becomes rigid, reducing the mass transfer efficiency of reactants, and also As the space in which the reaction can occur is reduced due to an increase in the ratio of cell layers in the catalyst, and the reaction efficiency may be lowered, it is desirable to adjust it appropriately within the above-mentioned range.

In an exemplary embodiment, the size (diameter) of the yoke in the catalyst may range, for example, from about 5 to 50 nm, specifically from about 10 to 40 nm, more specifically from about 20 to 30 nm, and especially about 25 nm. It may be at the nm level. In this regard, the yoke functions as a primary active site where a reaction can occur, while the empty space functions as a passage that can increase mass transfer efficiency and has a significant impact on the effective reaction, as described above. It can be adjusted appropriately within the range. Additionally, the proportion of the yoke present inside the cell layer can act as a factor affecting the deactivation of the catalyst. Considering the above, the weight ratio of the yoke in the catalyst can be adjusted, for example, in the range of 1: about 1.5 to 5, specifically 1: about 1.8 to 4, more specifically 1: 2 to 3. there is.

According to an exemplary embodiment, as described above, for the cyclization (specifically dehydration/cyclization) reaction of an organic acid or its derivative, the metal phosphide catalyst is required to contain a certain level or more of acid sites. At this time, the amount of acid (or amount of acid sites) of the catalyst can be measured by NH ₃ -TPD, for example, about 200 to 600 mmol/g, specifically about 250 to 550 mmol/g, more specifically about 300. It may range from 450 mmol/g. However, if the acid amount is too large, the selectivity may decrease due to additional hydrogenation light dehydration reaction of the target hydrogenation product (specifically, GVL), so it may be advantageous to appropriately adjust it within the above-mentioned range. Although the present disclosure is not bound by any particular theory, the acidic nature of metal phosphide catalysts can be explained as originating from the presence of unreduced metal and/or P-OH species in the catalyst. Exemplarily, the molar ratio of the reduced form of the metal to the non-reduced form of the metal in the catalyst is in the range of 1:about 2 to 5, specifically 1:about 2.5 to 4.5, more specifically 1:about 3 to 4. It can be determined.

Furthermore, the number of acid sites (or acid amount) in the catalyst can have a greater impact on the conversion from GVL to 2-MTHF, which is the second step in the hydrogenation reaction pathway of an organic acid (specifically levulinic acid) or a derivative thereof. This is because a larger amount of acid sites are required for conversion from 1,4-PDO to 2-MTHF.

Meanwhile, according to an exemplary embodiment, a metal phosphide catalyst with a yoke-shell structure may exhibit crystallinity, and as cobalt is introduced into nickel, crystallinity may increase or improve, which can be achieved by XRD This can be confirmed from well-defined peaks in the pattern. In this regard, the metal phosphide catalyst has, for example, a lattice fringe in the range of about 0.1 to 0.4 nm, specifically about 0.15 to 0.35 nm, more specifically about 0.2 to 0.4 nm, especially specifically about 0.23 to 0.27 nm. may have a fringe. The above-described crystal characteristics may correspond to, for example, the (111) and (201) planes.

According to an exemplary embodiment, the metal phosphide, specifically the nickel-cobalt phosphide catalyst, may be a bulk catalyst and may be applied in the form of powder, pellets, etc. According to an exemplary embodiment, the bulk catalyst may be a powder catalyst, the specific surface area (BET) of which is, for example, about 10 to 80 m ² /g, specifically about 15 to 70 m ² /g, more Specifically, it may be in the range of about 30 to 60 m ² /g, but this can be understood as an example.

Meanwhile, the transition metal phosphide catalyst according to an exemplary embodiment, specifically the nickel-cobalt phosphide catalyst, can exhibit good hydrogen adsorption activity, and when measured using H ₂ -TPD (hydrogen temperature-programmed desorption), The chemical adsorption amount (mol) of hydrogen atoms per mole (mol) of the total metal is, over a temperature range of 50 to 250° C., for example, about 100 to 250 mmol/g, specifically about 120 to 220 mmol/g, More specifically, it may be in the range of about 150 to 200 mmol/g, but this can be understood as an example.

Method for producing metal phosphide catalyst with yoke-shell structure

Hereinafter, the description will focus on the manufacturing method of a yoke-shell structured metal phosphide catalyst (bulk type) using nickel and cobalt as metals.

According to one embodiment, the metal phosphide catalyst performs at least two hydrothermal synthesis reactions (hydrothermal treatment) using a nickel (Ni) precursor and a cobalt (Co) precursor, and then performs phosphidation. It can be manufactured in this way.

According to an exemplary embodiment, the nickel precursor may typically be a water-soluble nickel compound, specifically a nickel compound with an oxidation number of 2, and may particularly be in hydrated or hydrated form. For example, the nickel compound may be at least one selected from nickel halide (specifically nickel chloride, nickel bromide, etc.), nickel acetate, nickel nitrate, nickel sulfate, nickel carbonate, nickel hydroxide, etc., and specifically, the types listed above. It may be hydrated. According to certain embodiments, the nickel precursor is nickel(II) chloride hexahydrate (NiCl ₂ ·6H ₂ O), nickel nitrate (Ni(NO ₃ ) ₂ ·6H ₂ O) and nickel(II) sulfate·7 hydrate ( It may be at least one selected from the group consisting of NiSO ₄ ·7H ₂ O). Meanwhile, the cobalt precursor may also typically be a water-soluble cobalt compound, and specifically, it may be a cobalt compound with an oxidation number of 2. Illustratively, the cobalt compound may be at least one selected from cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt carbonate, cobalt halide (e.g., cobalt chloride, cobalt bromide, etc.), and specifically may be in the form of a hydrate thereof. You can. More specifically, cobalt (II) chloride hexahydrate (CoCl ₂ ·6H ₂ O), cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), and cobalt (II) sulfate heptahydrate (CoSO ₄ ·7H ₂ O) may be at least one selected from the group consisting of In this way, when a metal with an oxidation number of 2 is used, it is advantageous in that a greater amount of Lewis acid sites can be formed within the catalyst. Additionally, when a hydrate is used as a metal precursor, the metal precursor can be better dissolved in the solvent.

Considering the ratio between nickel and cobalt in the final catalyst, a nickel-cobalt precursor solution can be prepared by dissolving the nickel precursor and cobalt precursor in a solvent. At this time, as described above, as a solvent for dissolving the nickel precursor and the cobalt precursor, a type that can be converted into a material that provides a self-sacrificing template function in forming the yoke-shell structure can be used. For this purpose, at least It may be advantageous to include a solvent having one hydroxyl group, specifically at least a dihydric alcohol. According to a specific example, the solvent for preparing the precursor solution may be, for example, a mixed solvent of at least a dihydric alcohol (i.e., polyhydric alcohol) and a monohydric alcohol. Specifically, the at least dihydric alcohol may be, for example, at least one selected from glycerol, ethylene glycol, etc. Additionally, the monohydric alcohol may be, for example, at least one selected from ethanol, isopropyl alcohol, etc.

The volume ratio of at least dihydric alcohol:monohydric alcohol in this mixed solvent is adjusted within the range of, for example, 1:about 1 to 10, specifically 1:about 1.5 to 7, and more specifically 1:about 2 to 5. It can be. Additionally, the total concentration of the nickel precursor and cobalt precursor in the aqueous metal precursor solution may be adjusted, for example, to a range of about 30 to 150 mM, specifically about 50 to 100 mM, and more specifically about 60 to 90 mM.

After preparing the metal precursor solution as described above, the first hydrothermal synthesis reaction can be performed. At this time, the hydrothermal synthesis reaction temperature may be adjusted in the range of, for example, about 150 to 220 °C, specifically about 160 to 200 °C, and more specifically about 170 to 190 °C, and the reaction time may be, for example, about It may be set in the range of 4 to 10 hours, specifically about 5 to 9 hours, and more specifically about 6 to 8 hours. Through the first hydrothermal synthesis reaction, a precipitate of metal (nickel-cobalt) may be formed. Optionally, separation and purification steps known in the art may be performed. For example, metal precipitates may be washed and dried through solid-liquid separation (e.g., filtering, centrifugation, etc.). At this time, alcohol (eg, methanol, ethanol, etc.) washing and/or water washing may be performed, or washing may be performed with a mixed solvent of alcohol and water. Additionally, drying may be performed using known drying methods such as methods known in the art, heat drying, vacuum drying, etc. Exemplarily, in the case of a heat drying method, the drying temperature may be adjusted within a range of, for example, about 40 to 90° C., specifically, about 50 to 80° C., and the drying time is typically, for example, about 3. to 10 hours, specifically about 4 to 7 hours.

The metal precipitate obtained in this way is influenced by the medium used during the first hydrothermal synthesis, and as described above, when glycerol is used as the polyhydric alcohol, it may be in the form of a metal glycerate.

Next, a second hydrothermal synthesis reaction is performed on the metal precipitate. For this purpose, metal precipitates are added to an aqueous medium (specifically deionized water). Exemplarily, the content of metal precipitates is, for example, about 2 to 8% (w/w), specifically about 3 to 6% (w/w), more specifically about 3.5 to 5.5% (w/w). , In particular, it can be specifically adjusted in the range of about 3.75 to 5% (w/w). In the case of the second hydrothermal synthesis reaction, the reaction temperature may be set in the range of, for example, about 130 to 170 °C, specifically about 140 to 165 °C, more specifically about 145 to 160 °C, and especially for the first hydrothermal synthesis Compared to the reaction, the temperature may be set to be, for example, about 20 to 40°C lower, specifically about 25 to 35°C lower. In this regard, if the second hydrothermal synthesis reaction temperature is below a certain level or exceeds a certain level, the cell layer may not be formed in the final metal phosphide catalyst, making it difficult to provide a yoke-cell structure. It may be advantageous to perform hydrothermal synthesis in this range. In addition, the second hydrothermal synthesis reaction time may be adjusted, for example, in the range of about 1 to 8 hours, specifically about 2 to 6 hours, and more specifically about 3 to 4 hours, but this will be understood as an example. You can.

As described above, a metal hydroxide, specifically nickel-cobalt hydroxide, can be formed through the second hydrothermal synthesis reaction, which corresponds to a precursor or intermediate for forming metal phosphide. Additionally, as an optional step, a separation and purification step may be performed, which is similar to that described with respect to the first hydrothermal synthesis reaction product (metal precipitate) (however, water can be used as a washing liquid).

Next, a phosphide reaction can be performed on the metal hydroxide, and a substitution reaction using a phosphide agent can be used. As an example, the phosphide agent may typically be at least one selected from hypophosphite, phosphine gas, red phosphorus, etc., and may specifically be sodium hypophosphite, and more specifically, sodium hypophosphite hydrate. In this regard, the substitution reaction can be carried out under inert atmosphere and elevated temperature conditions. Illustratively, the inert atmosphere gas may be at least one selected from arcon, neon, nitrogen, etc., and more specifically, may be argon. In addition, the substitution reaction temperature may be set in the range of, for example, about 280 to 400 °C, specifically about 300 to 370 °C, and more specifically about 320 to 360 °C, where the temperature increase rate is, for example, about 0.5 It can be adjusted in the range of from about 5°C/min, specifically about 0.8 to 3°C/min, and more specifically about 1 to 2°C/min. In addition, the substitution reaction may be performed, for example, over about 2 to 10 hours, specifically about 2.5 to 8 hours, and more specifically about 3 to 5 hours, but this can be understood as an example.

Although the present disclosure is not bound by a particular theory, in the case of sodium hypophosphite hydrate in the above-described embodiment, phosphine (PH ₃ ) gas can be generated under elevated temperature conditions, and this phosphine gas reacts with metal hydroxide to It is believed that it can form phosphide. Therefore, instead of using sodium hypophosphite hydrate, the phosphide reaction may be performed using phosphine (PH ₃ ) gas directly.

According to an exemplary embodiment, the phosphidation reaction of a metal hydroxide using sodium hypophosphite hydrate may be performed in a tubular furnace. At this time, two crucibles are placed at both ends in a tubular furnace, and an inert gas can be flowed. Of the two crucibles, the crucible containing the phosphide agent such as sodium hypophosphite is placed upstream, and the crucible containing the metal hydroxide is placed upstream. is disposed downstream, and the phosphine gas converted under elevated temperature conditions in the upstream crucible is transferred to the downstream crucible by argon and reacts with metal hydroxide to form a metal phosphide catalyst.

Meanwhile, the metal phosphide catalyst according to this embodiment can easily recover its activity to the initial activity or a level close to it through regeneration. In this regard, the regeneration process involves simple separation (solid-liquid separation, such as filters or centrifugation), washing (e.g., washing at least once with alcohol and/or water), and drying (e.g., approx. It may be carried out at 40 to 90° C. for about 3 to 10 hours.

Conversion (cyclization) reaction of organic acids or their derivatives

According to one embodiment of the present disclosure, a process for producing various high value-added compounds from organic acids or their derivatives through a hydrogenation reaction using a York-shell structured metal phosphide catalyst is provided, wherein the metal phosphide catalyst has the general formula Ni It may be a nickel-cobalt phosphide catalyst represented by _x Co _y P.

According to an exemplary embodiment, the organic acid may be an organic acid typically derived from biomass, for example, an organic acid in the range of 1 to 8 carbon atoms, specifically 2 to 7 carbon atoms, and more specifically 4 to 6 carbon atoms; , In particular, it may be an organic acid with 5 carbon atoms. Additionally, the derivative of the organic acid may be an ester compound. These organic acids can form cyclic compounds through hydrogenation in the presence of a metal phosphide catalyst. As an example, organic acids include levulinic acid, succinic acid, fumaric acid, itaconic acid, aspartic acid, 2,5-furandicarboxylic acid, glutaric acid, lactic acid, etc. It may be at least one selected from. In addition, with respect to the Koryo-type compounds produced through hydrogenation reactions, when levulinic acid and/or its derivatives (specifically, esters) are used as the organic acid, gamma-valerolactone (GVL) and/or 2-methyltetra Hydrofuran (2-MTHF) may be produced. Additionally, when succinic acid or fumaric acid is used as the organic acid, butyrolactone and tetrahydrofuran may be produced. In addition, when itaconic acid is used as an organic acid, 3-methylbutyrolactone and 3-methyltetrahydrofuran can be produced. As mentioned above, since the production of cyclic compounds through hydrogenation of organic acids is well known in the art, detailed description will be omitted.

- Primary hydrogenation reaction

In a specific embodiment, the organic acid may be levulinic acid, and as described above, through hydrogenation reaction, dehydration/cyclization reaction may occur to form gamma-valerolactone (GVL) (first hydrogenation step). In this regard, two types of reaction routes are known to convert levulinic acid to gamma-valerolactone (via lactone as an intermediate and via 4-hydroxypentanoic acid). In a specific example, it is believed to be via 4-hydroxypentanoic acid. Gamma-valerolactone (GVL) is a raw material used in the synthesis of adipic acid, a precursor of polyamides such as polyamide 6,6 and polyamide 4,6.

According to an exemplary embodiment, the primary hydrogenation reaction may be performed by adding an organic acid and a catalyst into a reactor, supplying or injecting hydrogen into the reactor until it reaches a predetermined pressure, and performing the reaction under elevated temperature conditions. At this time, the hydrogenation temperature may be adjusted, for example, to about 120 to 300°C, specifically about 150 to 250°C, and more specifically about 170 to 200°C, and the reaction pressure (hydrogen pressure or hydrogen partial pressure) is, For example, it can be appropriately adjusted in the range of about 10 to 50 bar, specifically about 15 to 40 bar, and more specifically about 20 to 35 bar. Since hydrogenation temperature and pressure affect the conversion rate of reactants and selectivity of products, it may be desirable to adjust them appropriately within the above-mentioned range, but can be changed depending on the type of organic acid, activity of catalyst, use of solvent, etc. . These reaction conditions indicate that the reaction can be performed at a lower temperature (i.e., milder conditions) due to the intrinsic metallicity and acid characteristics of the active phosphide in the catalyst. This is because (i) an inexpensive base metal is used, (ii) the conversion rate of reactants can be increased and the selectivity to the target product can be increased through a bimetal catalyst system, and (iii) solvent-free. This is an additional advantage that differentiates the process according to this embodiment from the prior art in addition to not requiring a solvent separation process as the reaction is performed (solvent-free). Although the present disclosure is not bound by a particular theory, the hydrogenation reaction starts from the adsorption and activity of hydrogen on the surface of the catalyst, and the nickel-cobalt phosphide catalyst according to this embodiment can adsorb hydrogen at a lower temperature. This can be explained because it exists and can be activated. In addition, the hydrogenation reaction time may be adjusted, for example, in the range of about 1 to 10 hours, specifically about 2 to 8 hours, and more specifically about 3 to 6 hours.

According to an exemplary embodiment, the weight ratio of the reactant organic acid (specifically levulinic acid) or derivative thereof: catalyst is 1: about 0.015 to 0.03, specifically 1: about 0.018 to 0.026, more specifically 1: about 0.02 to 1: It may be in the 0.025 range, especially at the 1:0.023 level. Considering that the ratio of reactants to catalyst can affect the conversion of reactants and selectivity to the target product, and also provides more active sites for the catalyst as the amount of catalyst is relatively increased. , it is advantageous to adjust it within the above-mentioned range.

According to an exemplary embodiment, the hydrogenation reaction may be performed in a continuous mode as well as a batch mode, for example, a fixed bed reactor, a semi-batch reactor, etc. may be used. More typically, a batch mode can be adopted.

When the above-described reaction is completed, the target compound, specifically gamma-valerolactone, can be separated and recovered from the hydrogenation product. This separation and recovery process is known in the art and can be performed using, for example, distillation, extraction, separation membrane, flash drum, etc.

According to an exemplary embodiment, the conversion of the organic acid (particularly levulinic acid) in the primary hydrogenation reaction is, for example, at least about 45% (specifically at least about 70%, more specifically at least about 80%, particularly specifically at least about 95%, substantially up to 100%), and the selectivity to its cyclization product (particularly gamma-valerolactone) may be, for example, at least about 70% (specifically at least about 90%, more specifically at least about 95%, especially up to substantially 100%).

- Secondary hydrogenation reaction

According to an exemplary embodiment, the metal phosphide catalyst according to this embodiment can be used to convert the hydrogenation product (or cyclization reaction) of an organic acid into other types of high-value compounds or cyclic compounds through additional hydrogenation reaction.

As an example, when levulinic acid is converted to gamma-valerolactone using an organic acid during the previous primary hydrogenation reaction, the converted gamma-valerolactone is reacted in the presence of the above-mentioned metal phosphide catalyst (new catalyst or regenerated catalyst). After forming a decyclization intermediate (e.g., 1,4-pentanediol) through an additional hydrogenation reaction, 2-methyltetrahydrofuran (2-MTHF) can be produced by performing a dehydration/cyclization reaction again. (secondary hydrogenation reaction). 2-Methyltetrahydrofuran (2-MTHF) can be applied as biofuel, solvent, etc., and can especially replace the widely used THF. In particular, it exhibits low water miscibility, high stability, and low volatility compared to THF, and can be applied to drug manufacturing processes, etc.

In this regard, the hydrogenation reaction temperature can be adjusted, for example, in the range of about 180 to 320 °C, specifically about 200 to 280 °C, more specifically about 220 to 250 °C, and also the reaction pressure (hydrogen pressure or hydrogen partial pressure) ) can be appropriately adjusted, for example, in the range of about 30 to 80 bar, specifically about 40 to 70 bar, and more specifically about 45 to 60 bar. Hydrogenation temperature and pressure affect the conversion rate of the primary hydrogenation product (e.g., GVL) and the selectivity for the secondary hydrogenation product (e.g., 2-MTHF), so they are appropriately adjusted within the above-mentioned range. This may be preferable, but this may be understood as illustrative. In addition, the reaction time may be adjusted, for example, in the range of about 2 to 15 hours, specifically about 5 to 12 hours, and more specifically about 6 to 10 hours.

According to an exemplary embodiment, the weight ratio of reactant primary hydrogenation product (e.g., GVL):catalyst is 1:about 0.015 to 0.04, specifically 1:about 0.016 to 0.033, more specifically 1:about 0.02 to 1: It may be in the range of 0.03, especially at the level of 1:0.026. In this way, the ratio of reactants (i.e., primary hydrogenation products) to catalyst is adjusted within the range described above, as it can affect the conversion rate of the reactants and the selectivity for the target compound of the secondary hydrogenation reaction, as described above. It is advantageous.

According to an exemplary embodiment, the secondary hydrogenation reaction can be performed in a continuous mode as well as a batch mode similar to the primary hydrogenation reaction, and in the continuous mode, for example, a fixed bed reactor, a semi-batch reactor, etc. can be used.

When the above-mentioned reaction is completed, the target compound, specifically 2-methyltetrahydrofuran (2-MTHF), can be separated and recovered from the hydrogenation reaction product. This separation and recovery process is known in the art and can be performed using, for example, distillation, extraction, separation membrane, flash drum, etc.

According to an exemplary embodiment, the conversion rate of the reactant cyclic compound (particularly gamma-valerolactone) in the secondary hydrogenation reaction is, for example, at least about 45% (specifically at least about 65%, more specifically at least about 70%, and also up to about 80%), and the selectivity to other cyclic compounds (particularly 2-MTHF) obtained by the additional hydrogenation reaction may be, for example, at least about 40% (specifically at least about 40%). 44%, more specifically at least about 48%, and also up to about 55%).

What is noteworthy in this specific example is that the conversion reaction can be performed in the absence of a liquid medium (solvent) not only in the primary hydrogenation reaction but also in the secondary hydrogenation reaction. As described above, when a solvent is not used, the need to separate the reaction product from the solvent in a subsequent step can be eliminated.

Meanwhile, according to an alternative embodiment, when the conversion of levulinic acid is low, the reactant organic acid (e.g., levulinic acid) or cyclic compound (gamma-valerolactone) and a solvent are used together to produce primary and /Or a secondary hydrogenation reaction may be performed. At this time, the solvent that can be used may be at least one selected from a protic polar solvent and/or an aprotic polar solvent, and may act as a hydrogen donor without affecting the dehydration/cyclization reaction accompanying the hydrogenation reaction. Can be selected from available types. As an example, usable solvents include, for example, aliphatic alcohols having 1 to 5 carbon atoms (specifically, methanol, ethanol, isopropanol, sec-butanol, etc. as primary and/or secondary alcohols), dioxane (specifically, 1, It may be at least one selected from 4-dioxane), water, etc. In addition, the volume ratio of reactants (organic acid in the primary hydrogenation reaction and cyclic compound such as GVL in the secondary hydrogenation reaction):solvent is, for example, 1:about 4 to 15, specifically 1:about 6 to 12, More specifically, it can be adjusted in the range of about 8 to 10.

Hereinafter, preferred examples are presented to aid understanding of the present invention, but the following examples are provided to facilitate understanding of the present invention and do not limit the present invention thereto.

Example

Hereinafter, a phosphide-based catalyst is synthesized and used to synthesize gamma-valerolactone (GVL) and 2-methyltetrahydrofuran (2-MTHF) from levulinic acid according to the reaction mechanism shown in Figure 1. An experimental example is described.

The materials used in the examples and comparative examples are as follows.

Substances and Reagents

- Nickel nitrate hexahydrate (Ni(NO ₃ ) ₂ ·6H ₂ O) and cobalt nitrate hexahydrate (Co(NO ₃ ) ₂ ·6H ₂ O) were each purchased from Alfa Aesar.

- Glycerol, isopropyl alcohol, and ethanol were each purchased from Alfa Aesar, Daejung Chemical Company, and Daejeong Chemical Company.

- Deionized water was produced in-house in the laboratory.

- Sodium hypophosphite hydrate was purchased from Alfa Aesar.

- Levulinic acid was purchased from Acros Organics.

- All chemicals were used as received without undergoing additional purification.

analysis device

Sample analysis was performed using the following equipment.

- SEM analysis was performed using a Helios 50 scanning electron microscope.

- TEM analysis was performed using a JEM-F200 microscope.

- EDS (energy-dispersive X-ray spectroscopy) analysis was performed using a JEOL-JEM 2100F Transmission Electron Microscope.

- H ₂ -TPD was performed using Microtrac MRB BELCAT II. Specifically, in the pretreatment step, hydrogen was adsorbed under a flow of 50 mL/min of helium at 200°C for 2 hours, followed by adsorption of hydrogen under a flow of 50 mL/min of 10% H ₂ /Ar. In the hydrogen desorption step, physically adsorbed hydrogen was removed at 100 °C over 1 hour under a flow of 50 mL/min helium. The remaining hydrogen was removed by heating the furnace to 300°C at a heating rate of 5°C/min under a helium flow of 30 mL/min.

- NH ₃ -TPD was performed using Microtrac MRB BELCAT II. Specifically, in the pretreatment step, ammonia was adsorbed under a flow of 50 mL of helium at 200°C for 2 hours, and then under a flow of 50 mL/min of 5% NH ₃ /He. In the ammonia desorption step, physically adsorbed ammonia was removed over 1 hour at 100°C under a flow of 50 mL/min of helium. The remaining ammonia was removed by raising the furnace temperature to 800°C at a heating rate of 5°C/min under a flow of 30 mL/min of helium.

Example 1

Synthesis of nickel-cobalt phosphide catalyst

In this example, a nickel-cobalt phosphide catalyst containing nickel and cobalt in various ratios was synthesized through two hydrothermal synthesis steps and a phosphide step.

A predetermined ratio of nickel precursor (Ni(NO ₃ ) ₂ ·6H ₂ O) and cobalt precursor (Co(NO ₃ ) ₂ ·6H ₂ O) is mixed with glycerol and isopropyl alcohol at a volume ratio of 1:3.5. It was added to a mixed solvent and dissolved until a transparent and pink solution was obtained. At this time, the concentration of total metals (nickel and cobalt) in the precursor solution was 62.5mM.

The obtained nickel-cobalt precursor solution was put into a Teflon-lined reactor (200 mL), and the first hydrothermal synthesis reaction (hydrothermal treatment) was performed at 180 ° C. for 6 hours and cooled. Then, the precipitate, i.e., Ni-Co glycerate, was collected through centrifugation, subsequently washed several times with ethanol and deionized water, and dried in an oven maintained at 60 ° C. for 6 hours. .

Afterwards, 4 g of the precipitate of the nickel-cobalt precursor was added to 80 mL of deionized water to prepare a suspension, and a secondary hydrothermal synthesis reaction (hydrothermal treatment) was performed at 150 ° C for 3 hours to form a precipitate of Ni-Co hydroxide. . Subsequently, similar to the separation and purification of the first hydrothermal synthesis reaction product, the precipitate was washed with deionized water and dried to obtain a powder.

1 g of Ni-Co hydroxide powder obtained in the previous step and 20 g of sodium hypophosphite hydrate (NaH ₂ PO ₂ ㅇH ₂ O) were ground into fine powder and placed in crucibles at different positions within the tubular electric furnace. did. At this time, the crucible containing sodium hypophosphite hydrate was placed upstream, and the phosphide reaction was performed at 350°C for 3 hours with argon gas flowing in the electric furnace at a temperature increase rate of 1°C/min. As a result, nickel- Cobalt phosphide powder was obtained. The powder thus obtained was designated Ni _x Co _y P (x and y represent the mole fraction of Ni:Co).

Comparative Example 1

Synthesis of cobalt phosphide (CoP) catalyst

The cobalt precursor (Co(NO ₃ ) ₂ ·6H ₂ O) was added to a mixed solvent of glycerol and isopropyl alcohol at a volume ratio of 1:4 and dissolved until a transparent and pink solution was obtained. . At this time, the concentration of cobalt in the precursor solution was 62.5mM.

The obtained cobalt precursor solution was put into a Teflon-lined reactor (200 mL), and a hydrothermal synthesis reaction (hydrothermal treatment) was performed at 180° C. for 6 hours and cooled. Next, the precipitate, i.e. Co glycerate, was collected through centrifugation, subsequently washed several times with ethanol and deionized water, and then dried in an oven maintained at 60° C. for 6 hours.

Afterwards, 4 g of precipitate of the cobalt precursor was added to 80 mL of deionized water to prepare a suspension, and a secondary hydrothermal synthesis reaction (hydrothermal treatment) was performed at 150°C for 3 hours to form a precipitate of Co hydroxide. Subsequently, similar to the separation and purification of the first hydrothermal synthesis reaction product, the precipitate was washed with deionized water and dried to obtain a powder.

1 g of Co hydroxide powder and 20 g of sodium hypophosphite hydrate (NaH ₂ PO ₂ ㅇH ₂ O) obtained in the previous step were ground into fine powder and placed in crucibles at different positions within the tubular electric furnace. At this time, the crucible containing sodium hypophosphite hydrate was placed upstream, and the phosphide reaction was performed at 350°C for 3 hours at a temperature increase rate of 1°C/min while flowing argon gas into the electric furnace. As a result, cobalt phosphide was produced. Coated powder (CoP) was obtained.

Comparative Example 2

Synthesis of nickel phosphide (NiP) catalyst

_{Nickel phosphide powder ( ​ ​} NiP) was obtained.

Comparative Example 3

Preparation of mixed catalyst of cobalt phosphide (CoP) and nickel phosphide (NiP)

CoP and NiP synthesized in Comparative Examples 1 and 2, respectively, were mixed together at a weight ratio of 1:1 and then ground to prepare a uniform physical mixture.

Example 2

Synthesis of gamma-valerolactone (GVL)

A 100 mL stainless steel (SUS 316L) high-pressure reactor was used to synthesize gamma-valerolactone (GVL) by hydrogenating levulinic acid (LA) under solvent-free conditions.

30 mL of LA and 0.8 g of catalyst were charged into the reactor, and a stirrer was installed at the top of the reactor. Afterwards, the reactor was sealed, purged three times with argon gas to remove traces of gaseous impurities, and then pressurized with hydrogen gas at 30 bar. As soon as the target pressure was reached, the reactor was heated to 180° C. over 4 hours and stirring was started (stirring speed: 800 rpm). At this time, the starting point of the reaction was recorded as the time to reach the target temperature. When the hydrogenation reaction was completed, stirring was stopped, the reactor was cooled to room temperature, and the reaction product in the form of a mixture and the catalyst were separated through filtering.

Example 3

Synthesis of 2-methyltetrahydrofuran (2-MTHF)

A 100mL stainless steel (SUS 316L) high-pressure reactor was used to synthesize 2-methyltetrahydrofuran (2-MTHF) by hydrogenating levulinic acid (LA) under solvent-free conditions. A one-pot two-step hydrogenation reaction was performed.

30 mL of LA and 0.8 g of catalyst were charged into the reactor, and a stirrer was installed at the top of the reactor to synthesize gamma-valerolactone (GVL) as in Example 2. Specifically, the reactor was sealed, purged three times with argon gas to remove traces of gaseous impurities, and then pressurized with hydrogen gas at 30 bar. As soon as the target pressure was reached, the reactor was heated to 180° C. over 4 hours and stirring was started (stirring speed: 800 rpm). At this time, the starting point of the reaction was recorded as the time to reach the target temperature. When the hydroxylation reaction was completed, stirring was stopped, the reactor was cooled to room temperature, and the reaction product in the form of a mixture and the catalyst were separated through filtering. The separated catalyst was washed with a mixture of ethanol and water, dried at 60°C for 6 hours, and then reused in the secondary hydrogenation reaction. In the first hydrogenation step, an LA conversion of 100% and a GVL selectivity of 100% were achieved.

In the second hydrogenation step, 30 mL of GVL and 0.8 g of reused catalyst were filled and sealed in a reactor equipped with a stirrer at the top, purged three times with argon gas to remove traces of gaseous impurities, and then heated at 50 bar. Pressurized with hydrogen gas. As soon as the target pressure was reached, the reactor was heated to 230° C. over 12 hours and stirring was started (stirring speed: 800 rpm). At this time, the starting point of the reaction was recorded as the time to reach the target temperature. When the hydrogenation reaction was completed, stirring was stopped, the reactor was cooled to room temperature, the gas generated during the reaction was discharged, and the reaction product in the form of a mixture and the catalyst were separated through filtering.

Comparative Examples 4 to 6

Using the metal phosphide catalyst prepared in Comparative Examples 1 to 3, GVL and 2-MTHF were prepared according to the procedures in Examples 2 and 3, respectively.

Product analysis

In each of Examples 2 and 3 and Comparative Examples 4 to 6, the purity of the product was evaluated by 1H, 13C nuclear magnetic resonance (NMR) spectroscopy using a Bruker Advanced II spectrometer at a rate of 400 MHz and 13 kHz. It was operated at a rotation speed of .

The amount of product was measured by High-Performance Liquid Chromatography (HPLC), Shimadzu UHPLC Nexera, SCL-40 equipped with Agilent Hi-Plax Ca (7.7 x 300 mm, 8 μm) and 2410 refractive index detector. was used.

Results and Discussion

go. Characterization of catalysts

- SEM analysis

In the preparation of the metal phosphide catalyst, (a, b) Ni-Co glycerate precursor (produced from the first hydrothermal synthesis reaction), (c, d) Ni-Co phosphide precursor (produced from the second hydrothermal synthesis reaction), SEM images of (eg) Ni ₂ Co ₁ P, (h) CoP precursor, (i) CoP, and (j) NiP are shown in Figure 2.

According to FIGS. 2A and 2B, the precipitate formed from the first hydrothermal synthesis reaction (or first hydrothermal treatment) has a spherical shape. In addition, referring to FIGS. 2C and 2D, after the second hydrothermal synthesis reaction (or second hydrothermal treatment), the precipitate generated from the first hydrothermal synthesis reaction has a morphological shape showing a spherical shape composed of interconnected nanosheets. You can see that it is going through change. This change in the shape of the precipitate occurs when the precipitate from the first hydrothermal synthesis reaction is hydrolyzed to form a nanosheet. Specifically, Ni ²⁺ and Co ²⁺ ions react with the hydroxyl group of water in the second hydrothermal synthesis reaction to form nano-sheets on the surface. It can be seen as a composite of sheets. At this time, the addition of cobalt plays an important role in maintaining the shape of the precursor.

- TEM analysis

TEM analysis was performed on the nickel-cobalt phosphide catalyst, and TEM pictures at different magnifications are shown in Figures 3a to 3c. Additionally, a high-resolution TEM (HRTEM) image is shown in Figure 3d, and a HAADF-STEM image is shown in Figure 3e.

Referring to the drawing, it was confirmed that the nickel-cobalt phosphide catalyst is composed of interconnected nanosheets and has a spherical yoke-cell structure. In this regard, the yoke-shell structure in the catalyst described above can function as a kind of nano-reactor, where the yoke is an active site where a reaction can occur, and the empty space between the cell layer and the yoke is It functions as a pathway to increase mass transfer efficiency. Additionally, the hollow shell can prevent deactivation of the catalyst by encapsulating the active site.

Additionally, an HRTEM image of the Ni ₂ Co ₁ P catalyst is shown in Figure 4.

Referring to the figure, in the case of the Ni ₂ Co ₁ P catalyst, lattice fringes of 0.24 nm and 0.26 nm were observed, corresponding to the (111) plane and (201) plane of nickel-cobalt phosphide, respectively. In this regard, several discrete bright spots within the SAED pattern support these results, which can be indexed to the (111) plane, (201) plane, and (210) plane of nickel-cobalt phosphide, respectively.

Meanwhile, a nickel-cobalt phosphide catalyst (Ni ₂ Co ₁ P-150 ℃ and Ni ₂ Co ₁ P-100 ℃) prepared by setting the second hydrothermal synthesis reaction temperature to 150 ℃ and 100 ℃, and a commercial catalyst Ni -Cu/Al ₂ O ₃ TEM images showing each structure are shown in Figure 5.

Referring to the drawing, Ni ₂ Co ₁ P-150°C showed a clear yoke-shell structure as described above, but Ni ₂ Co ₁ P-100°C was a solid spherical particle composed of interconnected nanosheets. has. In addition, it was confirmed that the Ni-Cu/Al ₂ O ₃ catalyst had agglomerated particles located on the top of the alumina support.

- EDS (energy-dispersive X-ray spectroscopy) analysis

EDS analysis was performed on the nickel-cobalt phosphide catalyst, and the results are shown in Figure 3f. From the above figure, it was confirmed that cobalt, nickel, and phosphorus atoms were contained in the nickel-cobalt phosphide catalyst.

- Acid point and hydrogen activity analysis

Considering that the acid properties and hydrogen activity of the catalyst are important factors in synthesizing cyclic compounds through the hydrogenation reaction of levulinic acid, H ₂ -TPD and NH ₃ -TPD for various transition metal phosphides. Analysis was performed. The results are shown in Figures 6a and 6b, respectively.

From Figure 6a, the hydrogen activation and hydrogen adsorption abilities of various metal phosphides can be compared, and the single metal cobalt phosphide (CoP) showed the weakest hydrogen adsorption and activation ability, CoP < Ni ₁ Co ₃ P < NiP The same results were obtained as < Ni ₁ Co ₂ P < Ni ₁ Co ₁ P < Ni ₂ Co ₁ P < Ni ₃ Co ₁ P. In general, nickel-cobalt phosphide shows improved hydrogen activation ability compared to single metal cobalt phosphide and nickel phosphide, and addition of nickel to phosphide improves catalyst activation ability, and nickel improves hydrogen activation ability. It was confirmed that it can act as the main active ingredient.

In addition, the acidity of the catalyst can be compared from Figure 6b, and by varying the molar ratio between nickel and cobalt, the acidity and the distribution of each weakly acidic site, medium acidic site, and strong acidic site can be adjusted. As a result of the analysis, it was confirmed that single metal cobalt phosphide has both a weak acid site and a strong acid site, while nickel phosphide is mainly composed of weak acid sites. In addition, it was confirmed that nickel-cobalt phosphide (Ni ₂ Co ₁ P) contains all weak acid sites, medium acid sites, and strong acid sites. As a result of comparing the acidic amount, it can be summarized as follows: CoP < Ni ₁ Co ₃ P < Ni ₁ Co ₂ P < Ni ₁ Co ₁ P < Ni ₂ Co ₁ P < Ni ₃ Co ₁ P < NiP. In addition, the reduced form of the metal component functions as a metal active site in the hydrogenation reaction, while the unreduced metal component (Ni ²⁺ and Co ²⁺ ) provides an acidic site for the phosphide catalyst.

- XPS spectrum analysis

XPS spectra of NiP, Ni ₂ Co ₁ P, and CoP are shown in Figure 7. At this time, Figure 7a is a Ni 2p spectrum for each of NiP and Ni ₂ Co ₁ P, Figure 7b is a Co 2p spectrum for each of Ni ₂ Co ₁ P and CoP, and Figure 7c is a Ni 2p spectrum for each of NiP, Ni ₂ Co ₁ P and CoP. This is the P 2p spectrum for .

Referring to FIG. 7A, peaks located at 857.7 eV and 874.4 eV in the 2p spectrum of nickel correspond to Ni 2p ^3/2 and 2p ^1/2 of Ni ²⁺ , respectively. The peaks located at 853.6 eV and 871.0 eV correspond to Ni 2p ^3/2 and Ni 2p ^1/2 of reduced Ni ^δ+ in Ni-P, respectively.

In Figure 7b, the peaks located at 782.5 eV and 798.7 eV correspond to Co ²⁺ or Co 2p ^3/2 and Co 2p ^1/2 of the oxidized Co component, respectively. Additionally, the peaks located at 779.3 eV and 793.7 eV correspond to Co 2p ^3/2 and Co 2p ^1/2 of the Co component in Co-P, respectively, which has a partial positive charge from Co metal (Co ^δ2+ ).

In addition, the 2p spectrum of phosphorus (P) was confirmed from Figure 7c, and two components were present on the surface of single metal phosphide and double metal phosphide. The peak located at approximately 134 eV corresponds to the unreduced phosphate component (PO ₄ ^3- ) resulting from the oxidation of phosphide, while the peak with a lower binding energy of approximately 129 eV corresponds to the partially reduced phosphate component. It corresponds to the phosphorus component (P ^δ- ) or phosphide phase. At this time, the double metal Ni ₂ Co ₁ P had similar characteristics to the Ni and Co components of the single metal NiP and CoP, and the small shift in the peak was attributed to the electronic interaction between nickel and cobalt in the double metal Ni ₂ Co ₁ P. can see.

From the above-mentioned XPS results, the coexistence of M ^δ+ (M=Ni, Co) and P ^δ- components in the catalyst indicated that covalent bonds were formed between nickel, cobalt, and phosphorus in the synthesized metal phosphide, and nickel-cobalt It can be seen that phosphide was successfully synthesized.

- XRD analysis

Various phosphides of Ni and/or Co (NiP, CoP, NiCoP, Ni ₅ P ₄ , NiP ₂ , Ni ₃ Co ₁ P, Ni ₂ Co ₁ P, Ni ₁ Co ₁ P, Ni ₁ Co ₂ P, Ni ₁ The XRD patterns for each of Co ₃ P and CoP) are shown in Figure 8.

Referring to the figure, it can be seen that the crystallinity of each catalyst is greatly affected by the addition of cobalt through the intensity and width of the XRD peak. Cobalt-based double metal phosphides (CoP, Ni ₁ Co ₃ P and Ni ₁ Co ₂ P) are amorphous, while nickel-based double metal phosphides (NiP, Ni ₃ Co ₁ P and Ni ₂ Co ₁ P) are amorphous. ) showed well-defined peaks, indicating that the crystalline structure was strengthened.

In addition, both double metal phosphides showed peaks corresponding to the (111) plane and (300) plane of nickel-cobalt phosphide, confirming that nickel cobalt phosphide was successfully synthesized. In particular, it was confirmed that the peak intensity of nickel-cobalt phosphide further increased as the molar ratio of nickel:cobalt increased. In addition, additional peaks located at 44.9ㅀ and 48.1ㅀ related to the (201) plane and (210) plane of nickel-cobalt phosphide were observed in the XRD patterns of Ni ₂ Co ₁ P and Ni ₃ Co ₁ P, which will be described later. It is noteworthy that phosphide with high crystallinity has a favorable effect on the activity of the catalyst through hydrogenation reaction tests.

- Specific surface area and pore volume analysis

Various phosphides of Ni and/or Co (NiP, CoP, NiCoP, Ni ₅ P ₄ , NiP ₂ , Ni ₃ Co ₁ P, Ni ₂ Co ₁ P, Ni ₁ Co ₁ P, Ni ₁ Co ₂ P, Ni ₁ The BET specific surface area and pore volume for each of Co ₃ P and CoP) were measured and shown in Table 1 below.

According to the table above, it was confirmed that the specific surface area and pore volume increased as cobalt was added to phosphide.

me. Activity evaluation upon conversion of levulinic acid to gamma-valerolactone

- Conversion rate and selectivity analysis according to catalyst

A graph showing the conversion rate and selectivity measured in an experiment for producing gamma-valerolactone from levulinic acid in the presence of the previously prepared metal phosphide catalyst is shown in Figure 9.

Referring to the figure, binary metal phosphides (particularly Ni ₂ Co ₁ P) provide better catalytic activity than the single metal phosphides CoP and NiP, and also the physical mixture of CoP and NiP provides gamma phosphorylation from levulinic acid. -It was confirmed that both cobalt and nickel act in complete conversion to valerolactone. Additionally, among the binary metal phosphide catalysts, Ni ₂ Co ₁ P showed the best activity.

As can be seen from the catalyst characterization results, the active site of the Ni ₂ Co ₁ P catalyst originates from its bifunctional nature, containing cobalt and nickel components that provide hydrogenation active sites, and the remaining phosphate It contains an acidic moiety, providing the activity necessary for dehydration/cyclization reactions. In particular, as the relative content of nickel among the binary metals in the catalyst increased, the activity of the catalyst was significantly improved. The overall catalyst activity was CoP < NiP < Ni ₁ Co ₃ P < Ni ₁ Co ₂ P < Ni ₁ Co ₁ P < The order was Ni ₃ Co ₁ P < Ni ₂ Co ₁ P.

Referring again to the catalyst screening results according to Figure 9, the CoP catalyst showed a somewhat high GVL selectivity of 74.6%, but the conversion rate of levulinic acid was low at 29.1%. This is because, as confirmed in the H ₂ -TPD results, the CoP catalyst does not have sufficient hydrogen activation ability to initiate the conversion of levulinic acid. On the other hand, the CoP catalyst contains a large amount of strong acid points, making conversion from HPA to GVL possible. These results suggest that the hydrogenation reaction from levulinic acid to HPA is related to the hydrogenation ability and metal content of phosphide, and the dehydration reaction from HPA to GVL is related to the acid characteristics of the catalyst.

- Optimization of reaction conditions

The hydrogenation reaction was performed under different reaction conditions in the presence of the Ni ₂ Co ₁ P catalyst, which was evaluated to have the best activity among the binary metal phosphide catalysts. The results are shown in Table 2 below.

According to the table above, when the hydrogenation reaction was carried out under the conditions of a temperature of 180 ° C and a pressure of 30 bar for 4 hours, the conversion rate of levulinic acid and gamma-valerolactone reached approximately 100%, and other by-products was barely formed.

- Evaluation of the influence of solvent during hydrogenation reaction using solvent

When a solvent is used during the hydrogenation reaction, its influence was tested to evaluate the versatility of the catalyst under various reaction conditions. For this purpose, primary alcohols (i.e., methanol and ethanol), secondary alcohols (isopropanol and 2-butanol (sec-butanol)), 1,4-diox, and water were used as solvents, and Ni ₂ Co ₁ The conversion rate and selectivity measured by performing the hydrogenation reaction in the presence of a P catalyst are shown in Figure 10 along with the results obtained under solvent-free conditions.

According to the figure, when alcohol was used as a solvent, quantitative analysis of the conversion rate and GVL yield of levulinic acid was possible, but the hydrogenation reaction occurred immediately after levulinic acid was esterified with methyl levlinate, ethyl levlinate, etc. Because this occurred, the selectivity for GVL decreased. However, when secondary alcohol was used, improved results were obtained compared to primary alcohol. In this case, the selectivity of GVL for isopropanol and 2-butanol was 78% and 83%, respectively. This is believed to be because the reducing ability of secondary alcohol is better. In addition, when 1,4-dioxane was used as a solvent, the selectivity for GVL was relatively high at 86%, but considering the toxicity and potential risk of the solvent, it is believed that there will be limitations in applying it on a commercial scale.

In this regard, it is noteworthy that the highest conversion of levulinic acid (88%) and selectivity to GVL (98%) can be obtained when using environmentally friendly water as a solvent. This is believed to be due to the fact that water has a high hydrogen surface concentration and the reaction activation energy is reduced due to strong interaction between levulinic acid and water.

Meanwhile, the highest conversion and GVL yields of levulinic acid were obtained when the hydrogenation reaction was performed under solvent-free conditions. It is believed that GVL functions as a solvent when LA is hydrogenated into GVL, and the generated GVL can promote the formation of GVL from LA. In this way, the reaction under solvent-free conditions is advantageous in that it promotes the sustainability of GVL production.

- Analysis of effects depending on reactants

The conversion rate and selectivity measured by hydrogenating reactants or substrates of various levulinic acid esters with gamma-valerolactone in the presence of a Ni ₂ Co ₁ P catalyst are shown in Figure 11, respectively.

Referring to the figure, it was confirmed that GVL can be obtained even when levulinic acid ester is used as a reactant when using the Ni ₂ Co ₁ P catalyst. In particular, when methyl levlinate was used as a reactant (substrate), the selectivity for GVL was as high as 82%. On the other hand, butyl levlinate and ethyl levlinate showed lower results compared to methyl levlinate, which is believed to be due to steric hindrance caused by the long alkyl chain in the ester. In the case of esters, the decrease in GVL selectivity is due to the formation of 4-hydroxy alkyl levlinate, a bulk intermediate that prevents lactonization to GVL. Nevertheless, it is noteworthy that the above-mentioned results show that the Ni ₂ Co ₁ P catalyst also exhibits good activity toward levulinic acid ester.

- Evaluation of the effect of hydrothermal synthesis reaction temperature on hydrogenation reaction when manufacturing metal phosphide catalyst

Two types of nickel-cobalt phosphide catalysts (Ni ₂ Co ₁ P-100°C and Ni ₂ Co ₁ P-150°C) prepared by varying the second hydrothermal synthesis reaction temperature and a commercial nickel-copper/alumina catalyst (Ni- The levulinic acid conversion rate and selectivity for gamma-valerolactone of the reaction for producing gamma-valerolactone (GVL) from levulinic acid (LA) in the presence of Cu/Al ₂ O ₃ ) are shown in Figure 12. It was. At this time, the hydrogenation reaction was performed for 4 hours under conditions of a temperature of 80°C and a hydrogen pressure of 30 bar. Additionally, 30 mL of levulinic acid was reacted under solvent-free conditions, and 0.8 g of catalyst was used. As explained in relation to Figure 5, the Ni ₂ Co ₁ P-150°C catalyst has a yoke-shell structure, whereas the Ni ₂ Co ₁ P-100°C catalyst has a solid (i.e. solid) rather than yoke-shell structure. It represents the shape.

Referring to FIG. 12a, the Ni ₂ Co ₁ P-100°C catalyst showed catalytic performance at a level comparable to that of the Ni ₂ Co ₁ P-150°C catalyst in the first reaction. However, when the reaction was continuously repeated, the catalyst performance deteriorated rapidly. In addition, the Ni-Cu/Al ₂ O ₃ catalyst showed relatively low levulinic acid conversion and GVL yields, and especially showed the most rapid decline in catalyst performance when used repeatedly. The rapid deactivation observed in these two types of catalysts, especially the Ni-Cu/Al ₂ O ₃ catalyst, is believed to be due to sintering of metal particles.

On the other hand, in the case of the Ni ₂ Co ₁ P-150°C catalyst, the catalyst performance was maintained constant due to the active site protection effect of the catalyst resulting from the York-shell structure.

all. Activity evaluation when converting levulinic acid to 2-methyltetrahydrofuran

For producing 2-methyltetrahydrofuran from levulinic acid in the presence of the Ni ₂ Co ₁ P catalyst, which was evaluated to have the best activity among the previously prepared metal phosphide catalysts, and the nickel phosphide (NiP) catalyst as a comparative example. The conversion rate and selectivity measured in the experiment are shown in Table 3 below.

From the table above, it can be seen that the Ni ₂ Co ₁ P catalyst contains a sufficient amount of acid sites to facilitate the dehydration reaction from 1,4-PDO to 2-MTHF. However, in the case of the Ni ₂ Co ₁ P catalyst, the selectivity for 2-MTHF during the secondary hydrogenation reaction in the one-pot two-step reaction was relatively low. That is, in the conversion from GVL to 2-MTHF, when a NiP catalyst was used, the selectivity for 2-MTHF was high, but the conversion rate to GVL was low during the first hydrogenation reaction. In this regard, the acid site of NiP can facilitate the dehydration reaction from the formed 1,4-PDO to 2-MTHF, thereby improving the selectivity for 2-MTHF. However, the metal activity of NiP is insufficient, and conversion to GVL during primary hydrogenation is insufficient. In this way, the primary hydrogenation reaction step from levulinic acid to GVL is believed to depend on the composition of the active metal in the catalyst, while the secondary hydrogenation reaction step from GVL to 2-MTHF is mainly affected by the amount of acid sites.

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)

It is represented _by the general formula _Ni It includes performing a hydrogenation reaction on the derivative,
A method for converting an organic acid, wherein the organic acid is at least one selected from the group consisting of levulinic acid, succinic acid, fumaric acid, itaconic acid, aspartic acid, 2,5-furandicarboxylic acid, glutaric acid, and lactic acid. The method of claim 1, wherein the hydrogenation reaction is accompanied by a cyclization reaction. delete The method of claim 1, wherein the organic acid is levulinic acid, and the hydrogenation reaction is performed in one step or at least two steps,
Here, the method is characterized in that gamma-valerolactone (GVL) is formed through the one-step hydrogenation reaction, while 2-methyltetrahydrofuran (2-MTHF) is formed through the at least two-step hydrogenation reaction. The method of claim 1, wherein the hydrogenation reaction is performed without the use of a solvent. The method of claim 4, wherein the primary hydrogenation reaction is carried out under conditions of a temperature of 120 to 300° C. and a hydrogen pressure of 10 to 50 bar, and
The secondary hydrogenation reaction is characterized in that it is carried out under conditions of a temperature of 180 to 320 ° C. and a hydrogen pressure of 30 to 80 bar. The method according to any one of claims 1, 2, and 4 to 6, wherein the weight ratio of organic acid or derivative thereof: catalyst is adjusted in the range of 1:0.015 to 0.03. delete The method according to claim 1, wherein the weight ratio of the yoke in the yoke-shell structured metal phosphide catalyst is set in the range of 1:1.5 to 5. The catalyst according to claim 1, wherein the acid amount (NH ₃ -TPD) of the metal phosphide catalyst is in the range of 200 to 600 mmol/g. The method according to claim 1, wherein the molar ratio of the reduced form of the metal to the unreduced form of the metal in the metal phosphide catalyst is in the range of 1:2 to 5. The method of claim 11, wherein the metal phosphide catalyst has a chemical adsorption amount (mol) of hydrogen atoms per mole (mol) of total metal, as measured by H ₂ -TPD, over a temperature range of 50 to 250° C. to 250 mmol/g. The method of claim 1, wherein the metal phosphide catalyst is:
a) preparing a nickel and cobalt precursor solution by dissolving the nickel precursor and the cobalt precursor in a solvent;
b) subjecting the precursor solution to a first hydrothermal synthesis reaction to form a precipitate containing nickel-cobalt;
c) subjecting the precipitate to a second hydrothermal synthesis reaction to form nickel-cobalt hydroxide; and
d) The nickel-cobalt hydroxide is expressed by the general formula NixCoyP (x and y are the molar ratio of Ni and Co in the range of 1:0.2 to 5) through a substitution reaction with a phosphide agent under an inert gas atmosphere and elevated temperature conditions. Converting to a nickel-cobalt phosphide catalyst having a York-shell structure;
It is manufactured by a method comprising,
(i) A method characterized in that the overall size (diameter) of the nickel-cobalt phosphide catalyst ranges from 10 to 100 nm, the thickness of the cell layer ranges from 1 to 10 nm, and the size (diameter) of the yoke ranges from 5 to 50 nm. . The method of claim 13, wherein each of the nickel precursor and the cobalt precursor is a compound with an oxidation number of 2,
The nickel precursors include nickel(II) chloride hexahydrate (NiCl ₂ ·6H ₂ O), nickel nitrate (Ni(NO ₃ ) ₂ ·6H ₂ O), and nickel(II) sulfate heptahydrate (NiSO ₄ ·7H ₂ O) is at least one selected from the group consisting of, and
The cobalt precursors include cobalt(II) chloride hexahydrate (CoCl ₂ ·6H ₂ O), cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), and cobalt(II) sulfate heptahydrate (CoSO ₄ ·7H ₂ O) A method characterized in that it is at least one selected from the group consisting of The method of claim 13, wherein the solvent used in step a) is a mixed solvent of at least a dihydric alcohol and a monohydric alcohol,
The at least dihydric alcohol is at least one selected from the group consisting of glycerol and ethylene glycol, and
A method wherein the monohydric alcohol is at least one selected from the group consisting of ethanol and isopropyl alcohol. The method of claim 13, wherein the first hydrothermal synthesis reaction is performed at a temperature of 150 to 220 ° C. for 4 to 10 hours, and
The second hydrothermal synthesis reaction is characterized in that it is carried out for 1 to 8 hours at a temperature of 130 to 170 ° C. The method of claim 13, wherein the phosphide agent is at least one selected from the group consisting of hypophosphite, phosphine gas, and red phosphorus. The method of claim 13, wherein the inert gas in step d) is at least one selected from the group consisting of argon, neon, and nitrogen, and the temperature increase conditions range from a temperature of 280 to 400 ° C. and a temperature increase rate of 0.5 to 5 ° C./min. A method characterized in that it is set in. 14. The method of claim 13, wherein step d) is performed in a tubular furnace with two crucibles disposed at both ends,
At this time, the crucible containing the phosphide agent is placed upstream of the two crucibles, the crucible containing the nickel-cobalt hydroxide is placed downstream, and an inert gas is introduced into the tubular furnace.