KR20150139040A - A plasma-catalyst for c-h bond cleavage with the metal oxide deposed by atomic layer deposition on the surface of porous support ; and a use thereof - Google Patents

Abstract

The present invention relates to a C-H bond-activating catalyst by plasma, deposited with metal oxide on a porous support by an atomic layer deposition method, and to a use thereof. More specifically, the present invention relates to a C-H bond-activating catalyst in a novel structure; a plasma reactor deposited with the catalyst; a method for producing hydrocarbon having at least two carbon atoms in the reactor; and a method for producing hydrogen (H_2). According to the present invention, the composite system of the plasma and the catalyst increases reaction efficiency and improves selectivity of a product due to mutual and complex interaction.

Description

TECHNICAL FIELD [0001] The present invention relates to a C-H bond activation catalyst by plasma and a metal oxide deposited on the surface of a porous support by atomic layer deposition, of porous support;

The present invention relates to a CH bond activation catalyst by plasma and a use thereof, wherein a metal oxide is deposited on the surface of a porous support by atomic layer deposition. Specifically, the present invention relates to a method for producing hydrocarbons from C2 or more CH bond activation catalyst, the plasma reactor, the reactor the catalyst is filled in the new structure, a method for producing hydrogen (H _2).

Oil, which is widely used as an energy source globally, is getting depleted, and oil prices are expected to remain high due to political unrest in the Middle East, which is the world's largest oil reserves. Compared to petroleum, natural gas is mainly methane, which is about 40% richer than petroleum. It is a cheap and rich energy source buried all over the world. However, such a useful resource, natural gas, has a problem in that it is difficult to transport and store the product because the distance between the production site and the consumer site is long.

As a result, much of the natural gas produced in the mountains is sent back to the basement or burned. Therefore, research on the production of hydrocarbons of C ₂ or more, which is a petrochemical fuel, with methane as a main component of natural gas is significant in terms of efficient utilization of resources.

However, since methane is a very stable compound, a high energy is required for the conversion to a hydrocarbon compound of C ₂ or more, and the selective activation reaction to a specific product is controlled by the high dissociation energy of CH bond (435 kJ / mol) There is a difficulty. In addition, since the decomposition of CH bonds acts as a reaction rate determining step, a high temperature reaction condition of 700 or more is required, and a catalyst having commercialization potential has not yet been developed. Accordingly, in recent years, extensive researches related to the activation of the CH bonds of the hydrocarbons have been conducted.

In recent years, researches using plasma have been conducted to solve the above difficulties. The activation of methane by the plasma is advantageous in that it can easily decompose the C-H bond by the high energy of the plasma and the reaction time is very short. At the beginning of the plasma research, a study on the conversion reaction of methane using glow discharge in a vacuum atmosphere was performed. However, since the glow discharge is generated in a vacuum atmosphere, there is a problem that an investment cost and an operation cost of the process are inevitably increased.

Conventional methods for producing hydrocarbons useful in methane include an indirect conversion method through a reforming reaction and a direct conversion method in which each product is directly converted. The indirect conversion method is a method of converting synthesis gas into natural gas reforming gas and converting it into basic petrochemical raw materials through various routes using this synthesis gas. However, the indirect conversion method has a problem that a large amount of energy is consumed in the reforming reaction for producing syngas and the initial investment cost is high. Direct conversion is a method of direct conversion of methane, which is the main component of natural gas, without passing through syngas. Typical processes include oxidative coupling of methane, Partial Oxidation of Methane (POM) Non-oxidative coupling of methane. However, these processes have problems in optimizing activation of hydrocarbons to commercialization level in the field of their use and failing to obtain such selective products. However, in the case of the nonoxidation reaction, it is advantageous in that a hydrocarbon or a C ₂ or more hydrocarbon compound can be obtained simply by a single step.

It has been found that the metal oxide catalyst used in the conventional plasma methane conversion reaction is deposited on the surface of the porous support by atomic layer deposition (ALD) to increase the plasma energy efficiency required for the reaction and increase the selectivity of the olefin Respectively. The present invention is based on this.

A first aspect of the present invention relates to a microporous membrane comprising as a core a porous support; And a shell on which a metal oxide is deposited by atomic layer deposition on the surface of the support.

A second aspect of the present invention provides a plasma reactor filled with a C-H bond activation catalyst according to the first aspect.

In a third aspect of the present invention, there is provided a plasma reactor filled with a CH bond activation catalyst according to the first aspect, comprising the step of plasma-treating a mixed gas of methane and an inert gas, Characterized in that it has a pore size capable of containing hydrocarbons

A fourth aspect of the present invention is a method for producing hydrogen (H ₂ ), which comprises the step of plasma-treating a mixed gas of methane and an inert gas in a plasma reactor filled with a CH bond activation catalyst according to the first aspect ≪ / RTI >

Hereinafter, the present invention will be described in detail.

The nonoxidation reaction of methane by plasma is decomposed into active molecules (free radicals) such as CH ₃ ·, CH ₂ ·, CH · and hydrogen atoms by collision of electrons and methane molecules generated under plasma (Formula 1).

[Chemical Formula 1]

CH ₄ + e CH ₃ + H + e

CH ₄ + e? CH ₂ ? + 2H + e

CH ₄ + e CH 3 + H + e

^{_{CH 4 + e → CH 4 +}} + 2e

^{_{CH 4 + e → CH 3 +}} + H · + 2e

The resulting active intermolecular free radicals are recombined to produce products such as ethane, ethylene, and acetylene, which are mainly hydrocarbon or hydrocarbon compounds with C ₂ or more. Representatively, the formation of hydrogen and a C ₂ -based hydrocarbon compound is represented by the following general formula (2).

(2)

CH ₄ + H? CH ₃ + H ₂

CH ₃ + CH _{3 -} > C ₂ H ₆

CH ₂揃 CH ₂揃 C ₂ H ₄

CH ₂ + CH ₂ C ₂ H ₂

However, the understanding of the mechanism of the methane conversion reaction using plasma is limited, and the hybridization technique of the catalyst and the plasma according to the present invention complicates the mechanism of the methane conversion reaction, and the theoretical prediction of the final product is difficult. Thus, the mechanism and products of the methane conversion reaction according to the above formula are illustrative and not limiting.

The C-H bond activation catalyst by plasma according to the present invention comprises a porous support as a core; And a shell on which a metal oxide is deposited by atomic layer deposition (ALD) on the surface of the support.

The porous support, which is the object to which the metal oxide is deposited on the surface by ALD, may be a porous body in which one particle has a plurality of pores on the surface and / or inside (Fig. 1A), but the individual nanoparticles combine to form secondary particles (Fig. 1B). The secondary particles have nano-pores formed by adjacent nanoparticles. The pores in the porous support are preferably open pores connected to each other.

When the metal oxide is deposited by ALD, the metal oxide is hardly penetrated into the inner pores, or in the case of the secondary particles formed by the binding of the nanoparticles, the metal oxide is deposited only on the outer surface of the secondary particle, The formed nano-pores can be controlled so that the metal oxide is hardly deposited.

At this time, if the active molecules formed by the plasma continue to flow into the pores, the pores of the porous support can serve as a micro-reactor capable of producing a desired result of reaction products with high selectivity owing to the molecular sieve function, Separate catalytic reactions can be performed in the pores by appropriately selecting the material of the support. Porous bodies having various pore sizes can be present and manufactured, and the size of nano pores can be easily controlled by controlling the size of the nano particles.

Furthermore, since the growth rate of the ALD thin film is proportional only to the number of times of the supply period of the raw material, the thickness of the thin film can be precisely controlled in units of several angstroms (Angstrom, 1 Å = 0.1 nm) and the composition of the thin film can be precisely adjusted .

Therefore, when the metal oxide is coated on the porous support particles with ALD, only the outer surface of the porous support particles can form the metal oxide shell, so that the molecular sieve or the catalyst function of the porous particles themselves can be maintained. Through this, the charge and electronic structure of the catalyst surface such as dielectric constant can be controlled.

Further, in the present invention, the metal oxide shell may be a laminated structure of a composite metal oxide containing two or more metals, a mixture of two or more metal oxides, or two or more metal oxide atom layers.

The process of generating plasma using the simplest plasma generating apparatus will be described below. First, two planar conductors are dropped by a certain distance d, and a DC voltage V is applied to the conductor. In this case, a constant electric field is generated between the two conductors. The generated electric field E is generated in the condition of E = V / d, which is proportional to the voltage and inversely proportional to the distance. At this time, when the voltage is above a certain level, a small number of electrons are generated on the conductive plate connected to the cathode, and these electrons move to the anode along the electrode, causing collision with the gases existing between the two conductors. As a result, The gases are ionized and discharge occurs. This process is called discharge initiation by an electric field. At this time, the ions move to the cathode along the electric field and hit the conductor plate connected to the cathode so that the electrons protrude from the cathode to accelerate the plasma generation. This process is called the second diffusion.

At this time, a plasma can be generated by a dielectric substance on two substrates to which a voltage is applied, and even if a dielectric is present between the two substrates, charges are generated on the surface due to a capacitor action. Therefore, silica having a small dielectric constant is not enough to play such a role. Materials that can control this charge are important, because the metal oxide shell formed by ALD on the surface of the porous support can serve as such a dielectric.

In addition, the metal oxide shell formed by ALD allows electrons to be well dispersed into the metal oxide coating layer and into the pores. In addition, the metal oxide deposited on the surface by ALD may serve to lower the activation energy in the C-H bond cleavage reaction by the plasma.

In general, at atmospheric plasma such as DBD, the life-time of the active molecules formed during the plasma reaction is very short as nano-seconds and can not reach into the pores of the porous particles. Therefore, in order to allow radicals and ionic paper, which are active molecules, to enter into the pores of the porous particles, active molecules are formed by the plasma near the surfaces of the porous particles and the active molecules are immediately introduced into the pores of the porous particles. h ₂ ) is preferably 0.1 to 100 nm, and this thickness can be realized by ALD. Preferably 0.5 to 50 nm, and more preferably 0.5 to 20 nm.

In short, according to the present invention, a CH bond activation catalyst by a plasma having a shell on which a metal oxide is deposited by atomic layer deposition on the surface of a porous support is formed by plasma, in which active molecules and electrons are formed in the ALD surface coating layer, The active molecules are introduced directly into the pores of the porous support so that subsequent reactions can take place in the pores that can act as molecular sieves. Therefore, active molecules having a short half-life formed by plasma can be combined with intermediates trapped in pores to form hydrocarbons of C2 or more.

Plasma can also be formed between dielectric particles and particles, so that if the outer surface of the porous support is coated with a metal oxide (Figs. 1A and 1B), a lot of active molecules are generated by the plasma at the grounded portion and can enter the porous support pores have. Thus, additional multistep-reaction, cascade reaction is possible in the pores.

It is also preferred that a crack is formed in the shell to such an extent that the active molecule formed by the plasma can move, so that the active molecules can be easily introduced into the porous support through the metal oxide shell. For example, the catalyst according to the present invention can be fired to form cracks in the ALD layer.

The catalyst of the present invention is economically advantageous in that the active metal is deposited only in the vicinity of the surface of the catalyst on which the reaction on the plasma-catalyzed phase is performed, thereby reducing the amount of active metal required compared to the conventional plasma-catalyst.

In addition, under the same energy application range as compared with the conventional metal oxide catalysts, higher methane conversion is recorded, and thus, it exhibits better performance in terms of energy efficiency. Furthermore, product selectivity is also higher for olefins than conventional metal oxide catalysts (Experimental Examples 1 and 2).

Further, since the catalyst according to the present invention may not be subjected to a separate firing process, a-OH group exists in the case of a layer present on the surface of the catalyst, and a-OH group may exist in comparison with a conventional catalyst. These -OH groups function as active sites, and the above effects can be generated.

<Catalyst Preparation>

The porous support usable in the present invention is not limited in the size of the pores, but it is preferable to have a pore size capable of accommodating the C 2 or higher hydrocarbons to be formed using the catalyst of the present invention.

Non-limiting examples of the porous support usable herein include alumina, silica, MgO, TiO ₂ , ZnO, cordierite, zeolite, or a mixture thereof.

In addition, in the present invention, the average particle diameter (h ₁ ) of the porous support is not limited, but preferably 0.1 μm or more, and more preferably 1 μm to 30 mm. More preferably 0.1 mm to 10 mm.

Non-limiting examples of the support form used in the present invention include sphere, pellet, monolith, honeycomb, fibers, porous solid foam, powder ) And the like.

The metal oxide deposited by ALD has no limitation as long as it can function as a dielectric or lower the activation energy in a C-H bond cleavage reaction under plasma. In addition, it is preferable that the metal oxide can exhibit the electrical conductivity of the metal oxide itself or the metal thereof. Such a metal oxide ALD coating layer can well allow electrons to be well dispersed into the metal oxide coating layer and into the pores. .

Non-limiting examples of metals among the metal oxides that can be used in the present invention include noble metals, transition metals, and typical metals. For example, Pt, Ru, Ni, Co, V, Fe, Cu, Ti, Nb, Mo, W, Ta, Pd, Cu or Zn.

In addition, examples of the metal oxide or support that can be used in the present invention include, but are not limited to, ZrO ₂ , CoO, Co ₃ O ₄ , MnO, NiO, CuO, ZnO, TiO ₂ , V ₂ O ₅ , Ta ₂ O ₅ , _{2 O 3, FeO, Fe 2} O 3, Fe 3 O 4, transition metal oxides, MgO, CaO, BaO, Al, such as _{2 O 3, Ga 2 O 3} , SnO, SnO 2, a typical element oxides of SiO _2, etc. , SrTiO ₃ , BaTiO ₃ , (LaSr) ₂ TiO _4, and the like. And lanthanide oxides such as CeO ₂ and La ₂ O ₃ . Examples of usable porous support include zeolite, mesoporous material, activated carbon, layered double hydroxides (LDH), and the like. In particular, zeolites, acid catalysts including ionic liquids, MgO, LDH, base catalysts including ionic liquids, redox catalysts such as Fe ₃ O ₄ and V ₂ O ₅ , and the like are examples of support and catalyst materials. The metal oxide or support that can be used in the present invention can be appropriately selected depending on the kind and size of the product to be produced using the plasma-catalyst according to the present invention.

Atomic layer deposition (ALD), on the other hand, And the elements required for thin film formation are alternately supplied so that one atomic layer is adsorbed on the substrate. The atomic layer deposition method is excellent in step coverage (uniformly depositing portions with high height difference), and enables nano-thick film deposition with excellent uniformity even in a complicated three-dimensional structure.

The basic principle of ALD is explained by taking as an example the case of depositing a thin film made of a solid material AB by using a substance of gaseous form called AX and BY as a raw material and generating gaseous XY as a byproduct. The chemical reaction formula can be summarized as follows.

[Reaction Scheme 1]

AX (gas) + BY (gas) AB (solid) + XY (gas)

As shown in FIG. 2, the ALD process according to the ALD basic deposition principle is as follows.

A) Supplies AX material. There is extra AX that remains adsorbed on the substrate surface.

B) Remove excess AX.

C) Supply BY material. There are extra BY and by-products XY remaining to react.

D) Remove extra BY and byproduct XY.

E) Supply AX material. There are things that react and remain around.

As described above, the AX supply, the excess removal, the BY injection, and the extra removal process are repeated at regular intervals to form a thin film of a desired thickness and composition by stacking the atomic layers one by one. In order to remove the excess gas, a method of flowing an inert gas such as argon (Ar) is mainly used.

In the case of ALD, if the supply of raw materials is sufficient during the supply of the raw material during the deposition process, the growth rate of the thin film is proportional only to the number of times of the raw material supply cycle. Therefore, the thickness of the thin film is precisely controlled in several angstroms (Angstrom, 1 Å = can do.

In one embodiment of the present invention, the cycle is repeated (20 cycles: 1 cycle), in which the alumina (Al ₂ O ₃ ) powder is placed in a monodisperse deposition (ALD) reactor and the "zinc precursor- purge- oxygen precursor- Or 40 cycles). As a result, ZnO was deposited on the alumina support to form a ZnO / Al ₂ O ₃ catalyst. At this time, the metal to be deposited can be varied by different precursors (for example, Ti, Mg). In the case of TiO ₂ and MgO precursors, TiO ₂ and MgO could be deposited on alumina by the same method.

Zinc precursors are organic materials containing zinc. Non-limiting examples of zinc precursors include diethylzinc, bis (2,2,6,6-tetramethyl-3,5-heptanedionato) zinc (II) bis (2,2,6,6-tetramethyl-3,5-heptanedionato) zinc (II), dimethylzinc, diphenylzinc, bis (bis (trimethylsilyl) amido Bis (trimethylsilyl) amido) zinc, bis (pentafluorophenyl) zinc, and the like.

Non-limiting examples of oxygen precursors include H ₂ O, O ₂ , H ₂ O ₂ , O _3, and the like. The use of H ₂ O is most widely used because it is easier to handle in the atmosphere, cheaper, and safer.

In order to form a core-shell structure of alumina-zinc oxide effective for plasma reaction in the present invention, the exposure time of the metal precursor and the oxygen precursor is preferably about 60 seconds. If the time is shorter than 60 seconds, the precursors are not adsorbed to the shell. If the time is longer than 60 seconds, the alumina powder is diffused inward through the internal pores of the alumina powder and the structure is uniformly deposited on the core and the shell.

The pressure inside the reactor before the precursors are injected should be kept below 0.5 mtorr. When the pressure of the precursor is higher than 0.5 mtorr, the precursors are excessively retained in the reactor, and excessive zinc oxide may be deposited in the form of chemical vapor deposition, which has the problem of blocking the pores of the mesoporous alumina granules.

After the metal precursor is injected, it is sufficiently exposed until it is adsorbed as a monolayer in the pores of the porous support, and then nitrogen or argon gas is injected into the reaction vessel and purged to purify the inside of the reactor. By injecting nitrogen or argon gas and repeating the pumping process using a pump, the pressure inside the reactor can be returned to 10 mTorr or less.

< plasma  Reactor>

The plasma reactor according to the present invention is characterized in that the CH bond activation catalyst of the present invention is filled. The catalyst according to the invention may be filled with properly mixed with the inert carrier (ex. SiO _2).

The catalyst according to the present invention may be packed in a plasma reactor to form a packed-bed reactor (FIG. 5 (d)) and may be coated on the inner wall of the plasma reactor to form a catalyst layer.

A non-limiting example of a plasma reactor to which a catalyst is applied is shown in FIG. 6 shows a catalyst-electrode system configuration diagram capable of inducing a spark discharge. 6 (a) and 6 (b) show a case where there is a catalyst between the electrodes, and Figs. 6 (c) and (d) show the case where there is no catalyst between the electrodes Occation). 6 (a) and 6 (c)), the high voltage can be arranged in a needle shape, and the ground can be arranged in a plate shape (Figs. 6 (b) and 6 (d)). In the case of the catalyst arrangement between the electrodes, it is also possible to fill the gap between the electrodes with an inert bead and fill the space with the catalyst according to the present invention.

As shown in FIG. 6 (c), the dielectric barrier discharge reactor (DBD reactor) apparatus is composed of two parallel metal electrodes. At least one of the electrodes is covered by a dielectric layer. If an insulator is used, the current can not flow through the electrode in the case of DC power, so that the plasma is generated by using alternating current (AC) power having a frequency ranging from several Hz to several hundred Hz. To ensure stable plasma operation, the separation of the electrodes is limited to a few millimeters and the plasma gas flows between these gaps. The dielectric barrier discharge is sometimes referred to as a quiet discharge because there is no locally oscillating or noisy flame. The discharge is ignited by a sine function or a pulsed power supply. Depending on the composition, voltage and excitation frequency of the working gas, the discharge is in the form of filament or glow. At this time, the voltage condition for starting discharge is determined by the kind of gas, the interval of the electrodes, the frequency of the applied power source, and the like.

In the plasma reactor according to the present invention, hydrogen (H ₂ ) and hydrocarbons of C ₂ or more can be formed through the above-mentioned Formulas 1 and 2.

The plasma reactor according to an embodiment of the present invention may include a body having a plasma formed therein, an electrode connected to the body, and a power supply unit connected to the electrode to supply power. In the plasma reactor, an injection tube for supplying the feed gas into the reactor and a discharge tube for sending the gas after the reaction are formed. As described above, the catalyst may be packed or coated in various forms to form a catalyst layer on the body.

The electrode may be composed of two opposing electrodes, a positive electrode and a negative electrode, and may be made of a metal. The shape of the electrode may be, for example, a wire, a rod, a tube, or a spring; Or may be a thin metal plate or metal paste, in particular a thin copper sheet or silver coating. The material and shape of the electrode may be appropriately selected according to the specific reaction conditions.

In the present invention, the plasma reactor may include, but is not limited to, a dielectric barrier discharge reactor in which the body is a dielectric, a pulsed corona discharge reactor in which the power supply unit is a pulse power supply unit, or a spark electrode. However, in the case of the dielectric barrier discharge, it is preferable that the plasma reactor is a dielectric barrier discharge reactor in that a plasma having a high energy level can be formed without direct discharge between the electrodes because the electrode is surrounded by the dielectric.

As for the conversion reaction of methane occurring in the plasma reactor, a mixture of methane and an inert gas is supplied through the injection tube. Depending on the specific reaction, additional substances such as O ₂ , CO ₂ , H ₂ O or H ₂ May be additionally supplied. When a high voltage power supplied from the power supply unit is applied through the electrode, a plasma having a high energy level can be formed inside the body. In the state where the plasma is formed, the supplied methane is decomposed and converted to form hydrogen or hydrocarbons of C ₂ or more. In this process, the catalyst serves to promote the conversion of methane.

< plasma  Methane conversion reaction>

The method for producing hydrocarbons of C2 or higher according to the present invention includes a step of plasma-treating a mixed gas of methane and an inert gas in a plasma reactor filled with a CH bond activation catalyst according to the present invention, And has a pore size capable of accommodating C 2 or higher hydrocarbons to be formed.

The method for producing hydrogen (H ₂ ) according to the present invention is characterized by including a step of plasma-treating a mixed gas of methane and an inert gas in a plasma reactor filled with a CH bond activation catalyst according to the present invention.

Depending on the type of energy supplied and the amount of energy transferred to the plasma, the physical properties of the plasma, which is represented by electron density and electron temperature, are different.

In the present invention, the plasma is preferably a low-temperature plasma having a relatively higher electron temperature than the gas temperature, and may be formed through a dielectric barrier discharge (DBD), a pulse corona discharge, a spark discharge, It does not.

Dielectric barrier discharge is widely used in industry because it can discharge at atmospheric pressure and room temperature, operate at very high non-equilibrium conditions at atmospheric pressure, can discharge high power, and does not require a complex pulse power supply.

The ALD catalyst according to the present invention may be filled in the dielectric barrier discharge reactor, then methane may be introduced into the dielectric barrier discharge reactor together with the inert gas, and a plasma may be generated by applying a voltage to the electrodes of the reactor. When a direct methane conversion reaction is carried out under a conventional plasma-catalytic system, C2 to C4 hydrocarbons are mainly produced. The catalyst according to the present invention can accommodate hydrocarbons of C2 or more, which is a reaction intermediate in the pores of the porous support, Active molecules are introduced to selectively form C 2 or more olefins.

In the present invention, dissociative activation energy capable of decomposing strong C-H bonds of methane may be provided by a discharge plasma to convert methane to various radical states. At this time, an inert gas may be used as a carrier gas. At this time, methane may be mixed with an inert gas so as to be 0.1 to 50% by volume. Preferably from 1 to 20% by volume.

Non-limiting examples of inert gases usable in the present invention include argon, helium, neon, nitrogen, krypton, or mixtures thereof.

When the argon gas in the inert gas is used as the carrier gas, the CH bond decomposition reaction is carried out in the presence of the catalyst after the low temperature plasma treatment of the methane-containing mixed gas. As compared with the case where another inert gas is used as the carrier gas, Can be decomposed well.

The carrier gas and the reaction material, methane, may be added alone, or hydrogen, water (steam), hydrocarbons or a mixture thereof may be further added. Preferably, the hydrocarbon introduced may be a hydrocarbon of C ₂ to C ₄ , for example, ethane, ethylene, acetylene, propane, propylene, isoprene, Butane, iso-butane, n-butane. The addition of hydrogen or hydrocarbons can increase the number of CC-bonded compounds and increase the amount of olefins in the product. Since the olefin is a comparatively expensive compound, the olefin is advantageous in terms of economics of the product.

On the other hand, the mixing ratio (volume) of the injected methane and the inert gas-containing mixed gas may be in the range of inert gas / methane = 0 to 99.9, but if the methane is excessively increased, the discharge characteristic may become unstable, The inert gas / methane is preferably 1 to 9, and more preferably, the inert gas: methane = 1: 1 is economically feasible. The injection flow rate is preferably adjusted to 10-5000 ml / min.

The reaction temperature can be suitably adjusted within the range of room temperature to 600 ° C.

The applied voltage has a constant value using a wave generator and an amplifier and can be a regular form such as sine, square, triangle, pulse. At this time, it is preferable that 0-6 kV, 1-5 kHz.

On the other hand, in order to increase the methane conversion reactivity, it is preferable to increase the temperature in the plasma reactor. Therefore, it is desirable to introduce a plasma generation method of a structure in which heat generation is effective, for example, in designing a spark discharge.

The combined system of plasma and catalyst according to the present invention can improve reaction efficiency and product selectivity due to the complex action.

The present invention is advantageous in that the active metal is deposited only in the vicinity of the surface of the catalyst on which the reaction of the catalyst phase is performed, thus reducing the amount of active metal required compared to the conventional catalyst.

In addition, it records higher methane conversion rate under a low energy application range as compared with conventional metal oxide catalysts, and exhibits better performance in energy efficiency. Furthermore, product selectivity is also higher for olefins than conventional metal oxide catalysts.

1 (a), (b) and (c) are schematic views schematically showing a CH bond-activated plasma-catalyst structure produced according to the present invention.
2 is a schematic diagram of an ALD process.
Fig. 3 is a schematic view of a holder capable of fixing powdery material in a vacuum state in an embodiment of the present invention. Fig.
4 is a schematic view of a deposition apparatus used for depositing a metal oxide on the surface of a porous support using atomic layer deposition in the present invention.
5 is a schematic diagram showing various examples of a plasma reactor. Specifically, (a) is a pulsed corona reactor, (b) is a surface discharge reactor, (c) is a dielectric barrier discharge reactor (DBD reactor), and (d) packed-bed reactor).
6 is a schematic diagram showing examples of filling the catalyst in various ways in a spark plasma reactor. Specifically, (a) shows the case where the catalyst is filled between the electrode and the ground in the form of a high voltage electrode needle-to-ground contact, (b) shows the case where the catalyst is filled between the electrode and the ground in the form of a high- , (c) is the case where the catalyst is empty between the electrode and ground in the form of a high-voltage electrode needle-and-ground configuration, and (d) is the case where the catalyst is empty between the electrode and ground in the form of a high- voltage electrode needle-
7 is the Zn 2p binding energy XPS spectrum of the ALD coating catalyst (Example 1).
8 is a Zn mapping SEM image of the ZnO-loaded Al ₂ O ₃ catalyst.
(a) Sasol, (b) - (d) 5, 20, 40 circulating period atomic layer deposited catalysts.
9 is a graph showing the direct conversion rate of methane according to plasma input energy conversion.
10 is a graph showing changes in methane conversion and selectivity in a plasma reaction according to the type of catalyst.

Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

Comparative Example  One: ZnO / r- Al ₂ O ₃  Catalyst preparation method

Zinc oxide (ZnO / r-Al ₂ O ₃ ) supported on a porous alumina support was purchased from Sassol.

Example  One : ALD  - ZnO / r- Al ₂ O ₃   Catalyst preparation method

Zinc oxide was deposited on the surface of alumina (Al ₂ O ₃ ) with irregular pores with an average size of 13 nm by atomic layer deposition. The concrete method is as follows.

The gamma-alumina powder having a certain size (mean diameter 1 mm) was fixed to the atomic layer deposition reactor (FIG. 4) using a holder (FIG. 3) capable of fixing in powder form even in the vacuum state.

The process of making a vacuum state by injecting nitrogen gas and a rotary pump into the reactor by exposing the zinc precursor diethylzinc (DEZ) to the alumina powder located in the inside of the reactor and repeating the process to obtain a chemically adsorbed monolayer Lt; / RTI &gt; The oxidized precursor H ₂ O was then injected into the reactor to oxidize the deposited zinc precursor. Then, a nitrogen gas was injected into the reactor and a vacuum state was established using a rotary pump. This process was repeated to remove excess oxygen precursor. At this time, the process of depositing the zinc oxide is referred to as one cycle, and the amount of the deposited zinc oxide is controlled by repeating the cycle. The time and pressure conditions in this process are shown in Table 1.

The catalyst of Example 1 was prepared by repeating 20 to 40 cycles.

Zinc precursor injection Zinc precursor exposure 1 ^st nitrogen injection / pumping 2 ^nd nitrogen injection / pumping Oxygen precursor injection Exposure to oxygen precursors 3 ^rd nitrogen injection / pumping 4 ^th nitrogen injection / pumping Pressure (mtorr) 1100 1400 1700/2 or less 1700 / 0.5 or less 2 1.8 1700/3 or less 1700 / 0.5 or less Time (seconds) 100 60 20/60 20/60 60 60 20/60 20/60

<Review>

7 is the Zn 2p binding energy XPS spectrum of the ALD coating catalyst.

The peak appearing near 1021 eV in the XPS spectrum of FIG. 7 is a peak showing the characteristic of ZnO. It can be seen that this peak increases as the cycle period increases. On the contrary, the catalyst of Sasol (Comparative Example 1) has a very small peak indicating ZnO. This shows that ZnO can be selectively distributed only on the surface of the external pores when atomic layer deposition is used, even though the atomic ratio of the bulk of the catalyst is similar. These results can be explained more clearly in the SEM element mapping results (FIG. 8). The Zn mapping results of SEM analysis show that the catalyst of sasol contains Zn evenly in the whole region, whereas the catalyst formed by atomic layer deposition contains only Zn in the outer pore (Fig. 8). According to the existing studies, this phenomenon can control the extent to which the precursor can diffuse to the inner pores by controlling the exposure time of the precursor, and thus the deposited structure can be controlled [ J. Phys . Chem . C 2010, 114, 17286 ]. In the case of the plasma catalyst, not only the chemical properties of the catalyst but also the electrical properties of the surface are considered to be very important. Thus, in Example 1, a structure in which ZnO is distributed only on the outer surface is selected in order to control the electrical properties of the porous Al ₂ O ₃ . TEM analysis showed that ZnO was distributed only on the outer side of the sintered Al ₂ O ₃ , and its thickness was about 100 nm.

Experimental Example 1: Methane conversion reaction

For the plasma-catalyzed reaction experiment, the DBD reactor shown in FIG. 6 (a) was used, and two kinds of reactors were used as the DBD reactor. (One is a 56 mm x 24 mm x 3 mm space between two rectangular plates of dielectric, the outer surface of each dielectric is a reactor with a plate attached and the other is a rod with an outer diameter of 4 mm Type electrode and a dielectric tube having an inner diameter of 13 mm and a dielectric plate was attached to the outer surface of the dielectric so that a plasma could be formed inside the reactor when a voltage higher than a specific value was applied. g was mixed with 1.5 g SiO ₂ spheres in the space between the dielectric plates or between the electrode and the dielectric tube and the mixed gas of methane and Ar mixed gas (10% CH ₄ / Ar) The flow rate was adjusted to 200 ml / min, and the temperature was adjusted to a suitable temperature within the range of from room temperature to 250, and the pressure was 1 atm The voltage was adjusted to 0-6 kV and 3 kHz by using a wave generator and an amplifier, and the voltage and current were measured through an oscilloscope, After the reaction, the product was analyzed using GC chromatograph.

FIG. 9 shows the results of direct conversion of methane conversion according to plasma input energy conversion, and FIG. 10 shows changes in methane conversion and selectivity in a plasma reaction depending on the type of catalyst.

Compared with Sasol's ZnO / r-Al ₂ O ₃ , the selectivity of C2 and C3 olefins increased by more than 30% in the case of ALD-ZnO / r-Al ₂ O ₃ .

Example  2 : ALD - MgO / r- Al ₂ O ₃  Catalyst manufacture

MgO was coated on Al ₂ O ₃ in the same manner as in Example 1 except that bis (ethylcylopentadienyl) was used as a Mg precursor to prepare an ALD-MgO / Al ₂ O ₃ catalyst.

Table 2 below compares the conversion of methane (reaction temperature at room temperature) in a DBD-catalyzed hybrid system.

CH ₄ Conversion (%) Energy used (J / L) 수금 25 2130 MgO / r-Al ₂ O ₃ 29 2220 _{ALD-MgO / r-Al 2} O 3 32 2360

The _{ALD-MgO / r-Al 2} O ₃ For the catalyst in the direct conversion of methane (reaction temperature at room temperature) of 4.8 times the value-added compound, the olefin selectivity, rather than the absence of _{catalyst, MgO / r-Al 2 O} 3 catalyst 1.78 times higher than that of the control group.

Claims (15)

A porous support as a core; And a shell on which a metal oxide is deposited by atomic layer deposition on the surface of the support.
The catalyst according to claim 1, wherein the porous support has open pores in the support particles, or the nanoparticles combine to form secondary particles.
The catalyst according to claim 1, characterized in that -OH is present on the surface of the shell.
The CH bond activation catalyst according to claim 1, wherein a crack is formed in the shell to such an extent that the active molecule formed by the plasma can move.
The method of claim 4, wherein the active molecule is CH ₃ ·, · CH _2, CH · or a mixture thereof characterized in, CH bond activation by the plasma catalyst.
5. The catalyst according to claim 4, wherein the active molecule formed by the plasma is introduced into the pores in the support through a crack in the shell so that the catalytic reaction by the support can be carried out.
The catalyst according to claim 1, wherein the metal oxide shell has a thickness of 0.1 to 100 nm.
The catalyst according to claim 1, wherein the support is alumina, silica, CeO ₂ , MgO, TiO ₂ , ZnO, cordierite, zeolite or mixtures thereof.
The method of claim 1, wherein the metal oxide shell is a laminated structure of a composite metal oxide containing two or more metals, a mixture of two or more metal oxides, or two or more metal oxide atom layers. Activated catalyst.
The catalyst according to claim 1, wherein the metal oxide is ZnO.
A plasma reactor packed with a CH bond activation catalyst according to any one of claims 1 to 10.
12. The method of claim 11, hydrogen (H _2), which is characterized by forming C2 or more hydrocarbons, a plasma reactor.
10. A plasma reactor packed with a CH bond activation catalyst according to any one of claims 1 to 10, comprising the step of plasma-treating a mixed gas of methane and an inert gas, wherein the porous support of the catalyst comprises a C2 Of the total mass of the hydrocarbon. &Lt; RTI ID = 0.0 &gt; 21. &lt; / RTI &gt;
A process for producing hydrogen (H ₂ ), comprising the step of plasma-treating a mixed gas of methane and an inert gas in a plasma reactor filled with the CH bond activation catalyst according to any one of claims 1 to 10 How to.
15. The production method according to claim 14, wherein the plasma treatment is a non-thermal plasma treatment in which the electron temperature generated is higher than the gas temperature.

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