KR102712982B1 - Catalyst for non-oxidative methane conversion and selective hydrogenation of acethylene and method for preparing the same - Google Patents

Abstract

The present invention relates to a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, and more particularly, to a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, which uses methane as a raw material and performs a non-oxidative methane conversion reaction and a selective hydrogenation reaction for acetylene produced in the reaction through a series of reactions, thereby minimizing coke production and increasing ethylene production efficiency.

Description

Catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene and method for preparing the same

The present invention relates to a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, and more particularly, to a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, which uses methane as a raw material and performs a non-oxidative methane conversion reaction and a selective hydrogenation reaction for acetylene produced in the reaction through a series of reactions, thereby minimizing coke production and increasing ethylene production efficiency.

Ethylene is a substance used as a monomer in the production of various types of polymers, and is produced by thermal cracking of naphtha or catalytic catalytic cracking of petroleum gases such as ethane, propane, and butane. In general, ethylene produced by the above method contains about 0.5 to 2.0 wt% of acetylene. However, in order to be used as a polymer monomer, it is necessary to reduce acetylene, which can lower the activity of the polymerization catalyst and the properties of the produced polymer material, to an appropriate concentration or less. Reducing the concentration of acetylene contained in ethylene is generally achieved by selective hydrogenation of acetylene using a hydrogenation catalyst, and such acetylene hydrogenation catalysts are disclosed in U.S. Patent Nos. 4,387,258 and 4,839,329.

However, in the case of prior art literature, since the catalyst carrier exhibits a high specific surface area and weakly acidic properties, when the reaction proceeds at a relatively high temperature of 500°C or higher, acetylene or ethylene is polymerized within the pores to form green oil and coke having 4 or more carbon atoms, and the green oil and coke formed in this way block some of the catalyst pores, blocking the access of reactants or promoting the deactivation of the catalyst, resulting in shortening the regeneration cycle and lifespan of the catalyst.

Accordingly, in the hydrogenation reaction of acetylene contained in ethylene, a catalyst that can extend the activity cycle of the catalyst by suppressing coke formation even when the reaction is carried out at a relatively high temperature is developed, and as the demand for ethylene increases, the cost of raw materials for ethylene production is also steadily increasing, so alternative raw materials are required to reduce the cost of ethylene production.

Methane (CH ₄ ) is a material that can be used to produce light olefins, including ethylene, and can be obtained from natural gas, shale gas, etc., so it can ensure a smooth supply of raw materials and achieve cost efficiency in ethylene production. Methane is generally known to be the most feasible technology for producing light olefins via methanol from synthesis gas (H ₂ + CO) obtained through methane reforming, and the FTO (Fischer-Tropsch to Olefins) technology for directly producing light olefins from synthesis gas. However, in the case of technologies that produce high value-added products via synthesis gas, the energy efficiency of the methane reforming reactor for generating synthesis gas is low, and H ₂ or CO is additionally required to remove O atoms from CO, which are converted into greenhouse gases such as carbon dioxide (CO ₂ ) and water (H ₂ O) as products, which results in a decrease in the utilization efficiency of H or C atoms in the overall process.

Accordingly, research has been actively conducted on the oxidative coupling of methane (OCM) technology, which activates methane using oxygen as a new technology that can directly convert methane into high value-added products without going through synthesis gas. However, in the OCM reaction, due to the violent reactivity of O ₂ , a large amount of thermodynamically stable H ₂ O and CO ₂ are formed, which is still a problem in that the utilization efficiency of H or C atoms is reduced.

To solve these problems, technology for producing ethylene, aromatic compounds, etc. by direct conversion of methane under anaerobic or oxygen-free conditions has been developed recently. However, due to the low reactivity of methane, this process is being carried out at high temperatures, and catalyst development is essential. However, according to research results to date, the rapid decrease in catalytic activity due to carbon (coke) deposition on the catalyst under high-temperature conditions has emerged as a key issue (see Non-Patent Documents 0001 and 0002).

In addition, in the case of non-oxidative direct conversion of methane, the effective substance (acetylene) capable of producing ethylene other than ethylene is produced as a by-product and separated, so there is a limit to the ethylene yield by the above method.

To solve these problems, a catalyst and process have been developed recently for producing ethylene by selectively hydrogenating only acetylene, an effective substance among the by-products produced by the non-oxidative direct conversion reaction of methane. U.S. Patent Publication No. 2014-0058145 relates to the production of ethylene by direct conversion of methane and selective hydrogenation of acetylene, and uses a SAPO catalyst modified with palladium.

However, in the case of prior art literature, when a SAPO carrier including pores and a large surface area is used as a catalyst, coke deposition increases on the active catalyst surface and some of the pores, thereby shortening the catalyst efficiency and the catalyst activity cycle and reducing the ethylene yield.

Therefore, a catalyst for direct conversion of methane and selective hydrogenation of acetylene is required that can solve this coke formation problem and improve ethylene yield.

U.S. Patent No. 4,387,258 U.S. Patent No. 4,839,329 U.S. Patent Publication No. 2014-0058145

X, Guo et al., Direct, Nonoxidative Conversion of Methane to Ethylene, Aromatics, and Hydrogen, Science, 344, 2014, 616 ~ 619 Mann Sakbodin et al., Hydrogen-Permeable Tubular Membrane Reactor: Promoting Conversion and Product Selectivity for Non-Oxidative Activation of Methane over an FeVSiO2 Catalyst, Angew. Chem. 2016, 128, 16383 ~ 16386

Accordingly, the first task of the present inventors is to provide a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, which produces ethylene through non-oxidative methane conversion and selective hydrogenation of acetylene, while minimizing coke deposition on the catalyst and producing ethylene with high catalytic efficiency.

In addition, the present invention, in order to solve the above problems, has as its second object a method for producing a catalyst for non-oxidative methane conversion of methane and selective hydrogenation of acetylene.

In addition, the third object of the present invention is to provide a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, manufactured by the above method, in order to solve the above problems.

In addition, the fourth object of the present invention is to provide a method for non-oxidative methane conversion and selective hydrogenation of acetylene using a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene in order to solve the above problems.

In order to solve the first problem above, a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene is provided, characterized in that the catalyst comprises an α-alumina catalyst support; a coating layer including a -Si-N- bond crosslinked on the catalyst support; and palladium dispersed and supported on the coating layer.

In one embodiment, the specific surface area of the coating layer including the cross-linked -Si-N- bond on the catalyst carrier may be 0.08 to 0.2 m ² /g, and the average particle size of the supported palladium may be 2 to 20 nm.

In one embodiment, the most frequent particle size of the supported palladium may be 7 nm to 9 nm.

In order to solve the second problem, the present invention provides a method for producing a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, comprising: a first step of coating an α-alumina support with a compound having a -Si-N- bond; a second step of preheating the support obtained in the first step to crosslink the compound having a -Si-N- bond on the α-alumina support; a third step of heat-treating the support obtained in the second step to form a coating layer having a -Si-N- bond on the α-alumina support; and a fourth step of impregnating the support obtained in the third step with a Pd precursor.

As an example, the compound having the -Si-N- bond may be formed of perhydropolysilazane (PHPS).

In one embodiment, the preheating in the second step may be performed at 150 to 450°C.

In one embodiment, the heat treatment in the third step can be performed at 700°C to 1000°C.

As an example, the fourth step may include impregnating a Pd precursor into the carrier obtained in the third step, drying the carrier at 80 to 120°C, and then heat-treating the carrier at 300 to 1000°C to support Pd in the coating layer.

In order to solve the third problem, a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, manufactured by the above manufacturing method, is provided.

In order to solve the fourth problem, a method for non-oxidative methane conversion and selective hydrogenation of acetylene is provided using a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene.

The catalyst of the present invention uses α-alumina as a carrier coated with a compound having a -Si-N- bond, and by supporting Pd on the coating layer, coke generated in the catalyst is minimized, thereby improving the efficiency of ethylene production.

In addition, when the catalyst of the present invention is used, the non-oxidation conversion reaction of methane and the selective hydrogenation reaction of acetylene can proceed continuously as a series of reactions, thereby improving process efficiency.

FIG. 1 is a drawing showing the manufacturing process of Example 1 and Comparative Examples 1 and 2 according to one embodiment of the present invention.
FIG. 2 is a SEM photograph of PHPS/α-Al ₂ O ₃ according to the preheating temperature in one embodiment of the present invention.
FIG. 3 is a TEM photograph of a catalyst of an example and a comparative example according to one embodiment of the present invention.
FIG. 4 is a graph showing the Pd particle sizes of Example 1 and Comparative Example 1 according to one embodiment of the present invention.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is well known and commonly used in the art.

Whenever it is said throughout this specification that a part "includes" a component, this does not exclude other components, but rather includes other components, unless otherwise stated.

Hereinafter, the present invention will be described in detail.

The present invention provides, in one aspect, a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, characterized in that the catalyst comprises an α-alumina catalyst support; a coating layer including a -Si-N- bond crosslinked on the catalyst support; and palladium dispersed and supported on the coating layer.

In the present invention, the α-alumina catalyst support comprises a coating layer including a cross-linked -Si-N- bond on the catalyst support.

α-Alumina refers to aluminum oxide of the alpha phase among alumina having various crystal phases, and is a material that generally has a low specific surface area of less than 1 m ² /g, low acidity, low surface crystal concentration, and high density, and can be used as a catalyst support. However, when Pd is directly supported on the α-alumina support, the dispersibility and particle size uniformity of Pd cannot be controlled, coke formation in the non-oxidative methane conversion reaction and the selective hydrogenation reaction of acetylene cannot be suppressed, and the catalytic activity decreases.

Accordingly, the present invention includes a coating layer including a cross-linked -Si-N- bond on the α-alumina carrier, and the coating layer including the cross-linked -Si-N- bond may be derived from perhydropolysilazane (PHPS).

PHPS is a type of silicon compound, a polymer having a Si-N bond skeleton, a polysilazane, a polymer that does not contain carbon and is composed only of Si-H, NH and Si-N, and has "-(SiH ₂ -NH)-" as a repeating unit. When formed as a coating layer including a cross-linked -Si-N- bond on the α-alumina support, it induces a chemical bond with the supported metal (M) and MN, thereby increasing the dispersibility and particle size uniformity of the metal regardless of the surface area, thereby suppressing coke formation, thereby increasing the activity and catalytic life of the catalyst, and can selectively hydrogenate acetylene among substances such as ethane, ethylene, acetylene and C3-C4 generated by the non-oxidative methane conversion of methane.

In general, the hydrogenation reaction rate of ethylene is known to be 10 to 100 times faster than that of acetylene (Bond et al., Catalysis by metals, Academic Press, New York, 281-309, 1962.), but the hydrogenation reaction of acetylene on a catalyst is mainly determined by the adsorption and desorption rates rather than the surface reaction rate. Therefore, when the hydrogenation reaction of the methane conversion product is performed with a catalyst having a coating layer including a cross-linked -Si-N- bond on an α-alumina support, the specific surface area of the coating layer is lowered to 0.08 to 0.2 m ² /g, thereby suppressing strong adsorption of acetylene to the support surface and pores, and suppressing unnecessary C-C bonds and additional dehydrogenation of the adsorbed acetylene, thereby enabling selective hydrogenation of acetylene.

The coating layer including a cross-linked -Si-N- bond on the α-alumina carrier is formed by bonding Si to the catalyst carrier, and contains 2 to 3 wt% of Si in the coating layer and has an N/Si molar ratio of 0.9 to 4.

When the above PHPS contains less than 2 wt% of Si, the content of N present on the surface decreases as the content of Si bonded to the α-alumina carrier decreases, which may reduce the fixation ability of palladium. When it exceeds 3 wt%, the coating layer formed on the carrier becomes thicker, which may weaken the bond between the carrier and the coating layer. When the N/Si molar ratio is less than 0.9, the dispersion of palladium deteriorates due to the decrease in the content of N. When it exceeds 4, the bond between the carrier and the coating layer may weaken.

In the present invention, the palladium supported on the coating layer has an average particle size of 2 to 20 nm, and a mode of 7 to 9 nm. When the Pd particles are supported on the coating layer, they are relatively uniformly dispersed and supported by combining with N of the coating layer, and preferably, the average particle size is adjusted to 3 to 8 nm. When the Pd with the particle size adjusted in this way is used as a catalyst for methane non-oxidation methane conversion and selective hydrogenation of acetylene, it lowers the additional C-C coupling reactivity of aromatics to suppress coke formation, and allows selective hydrogenation of acetylene to proceed due to a reduction in adsorption and desorption portions.

In addition, palladium supported on the coating layer is included in an amount of 0.1 to 1 wt% based on the total weight of the catalyst. When palladium is supported in an amount of less than 0.1 wt%, adsorption and desorption of reactants and products are difficult, resulting in a rapid drop in catalytic activity, and when it exceeds 1 wt%, the dispersion of active materials in the catalyst carrier is reduced, resulting in green oil and coke deposition on the surface, which causes a problem of deactivation.

The present invention provides a method for producing a catalyst for non-oxidative methane conversion and selective hydrogenation of methane, comprising: a first step of coating an α-alumina support with a compound having a -Si-N- bond; a second step of preheating the support obtained in the first step to crosslink the compound having a -Si-N- bond on the α-alumina support; a third step of heat-treating the support obtained in the second step to form a coating layer having a -Si-N- bond on the α-alumina support; and a fourth step of impregnating the support obtained in the third step with a Pd precursor.

FIG. 1(a) is a diagram illustrating a catalyst manufacturing method according to one embodiment of the present invention, and is described with reference thereto.

In the present invention, the first step is a step of coating an α-alumina carrier with a compound having a -Si-N- bond. The coating can be performed by a conventional method without limitation, and preferably, as shown in Fig. 1(a), a dip coating method is used to coat the α-alumina carrier with a compound having a -Si-N- bond by immersing the α-alumina carrier in a compound having a -Si-N- bond.

At this time, the α-alumina support is a material having a low specific surface area of 1 m ² /g or less, low acidity, low surface crystal concentration and high density, and the compound having a -Si-N- bond is polysilazane, preferably perhydropolysilazane.

Next, the second step of the present invention is a step of preheating the carrier obtained in the first step to crosslink a compound having a -Si-N- bond on the α-alumina carrier. Specifically, the α-alumina carrier coated with the compound having the -Si-N- bond is preheated to a temperature of 150 to 450°C to crosslink a compound having a -Si-N- bond on the α-alumina carrier.

In the second step, if the preheating temperature is less than 150°C, the solvent or dispersion cannot be completely removed from the coating solution having the -Si-N- crystal, so that cross-linking between compounds having the -Si-N- crystal does not occur properly, and if it exceeds 450°C, the coating solution may be thermally decomposed, causing the N component to vaporize and be lost.

Therefore, the preheating temperature is 150 to 450°C, preferably 150 to 200°C.

In the present invention, the third step is a step of heat-treating the support obtained in the second step to form a coating layer having a -Si-N- bond on the α-alumina support. Specifically, the compound having a -Si-N- bond cross-linked on the α-alumina support, manufactured in the second step, is thermally decomposed at 700 to 1000°C to convert some components of the compound into SiO ₂ , Si ₃ N ₄ and Si ₂ N ₂ O, and the converted SiO ₂ and the structure having a -Si-N- bond are reacted with the α-alumina support, thereby forming a coating layer having a -Si-N- bond on the α-alumina support.

In the third step, if the heating temperature is less than 700°C, the compound having the crosslinked -Si-N- bond may not be sufficiently thermally decomposed, thereby reducing the stability of the Pd to be supported on the coating layer, and if it exceeds 1000°C, the compound having the -Si-N- bond may be converted into a large amount of silicon dioxide due to thermal curing at high temperature, and as the N component is vaporized and lost due to thermal decomposition, the N content on the coating layer decreases, so that the Pd to be supported on the coating layer cannot be uniformly supported, and the particle size cannot be controlled.

Therefore, the heating temperature is 700 to 1000°C, preferably 900 to 1000°C.

In the coating layer formed by this heat treatment step, the Si content is 2 to 3 wt%. This is because, if the Si content is less than 2 wt%, the surface and bonding stability of the coating layer may deteriorate due to the decrease in the Si content, thereby reducing the fixation ability of Pd, and if it exceeds 3 wt%, the coating layer may become thicker, thereby weakening the bonding between the carrier and the coating layer.

In addition, N of the coating layer is included as a Si/N molar ratio of 0.9 to 4. When N of the coating layer is less than 0.9 as a Si/N molar ratio, the surface concentration of N capable of stabilizing Pd is low, so that the fixation ability of Pd may decrease, and when it exceeds 4, the surface concentration of N is abundant, so that although it may be excellent in controlling the initial Pd dispersion, it may cause low structural stability of the coating layer under reducing conditions, which may induce a sintering phenomenon, and thus may become a factor that reduces catalyst durability. Preferably, N is included as a Si/N molar ratio of 1.3 to 3.3.

In addition, the specific surface area of the coating layer is 0.08 to 0.2 m ² /g, which is smaller than the specific surface area of an α-alumina support (1 m ² /g), so when used as a support for a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, it can suppress coke formation in the non-oxidative methane conversion reaction, thereby increasing CH activation of the catalyst and selectivity to the product. In addition, in the selective hydrogenation reaction, acetylene can be selectively hydrogenated among substances such as ethane, ethylene, acetylene, and C3-C4 produced by the non-oxidative methane conversion of methane by controlling adsorption/desorption.

In the present invention, the fourth step is a step of impregnating a Pd precursor into the carrier obtained in the third step, followed by drying and heat treatment to support Pd on the coating layer. The impregnation may be applied without limitation by any conventional method, and may preferably be an incipient impregnation method, and may be performed at a temperature of room temperature to 80° C. for 0.1 to 10 hours.

In the fourth step, the Pd precursor may be, but _is not limited to, a palladium nitride such as Pd( _NO3 ) ₂ ; a palladium sulfide such as _PdSO4 ; a palladium chloride such as _PdCl2 ; a palladium oxide such as Pd(OAc _{) 2} , _Pd ( _C5H7O2 ) ₂ , _Pd ( _C2H5CO2 ) ₂ ; etc.

The above drying is performed to remove impurities such as solvent contained in the impregnated substance and to smoothly proceed with the heat treatment described later. It can be performed without limitation at any temperature and time at which the solvent can be removed, and preferably, it can be performed at 80°C to 120°C for 0.5 to 36 hours.

Meanwhile, the dried product thus obtained can be heat-treated by heating at a heating rate of 1°C/min or higher, preferably 2°C/min to 1,000°C/min, in air, oxygen or an inert atmosphere from 300°C to 1,000°C. When the heat treatment temperature is less than 300°C, it is not easy to remove impurities remaining in the dried product, and problems may arise in producing a uniform catalyst. When it exceeds 1,000°C, problems may arise in that a clumping phenomenon occurs or the catalytic active component vaporizes and is lost.

At this time, the heat treatment time can be set to a sufficient time for sufficient calcination, and preferably can be about 0.1 to 10 hours.

In the above step, the Pd supported is included in an amount of 0.1 to 1 wt% based on the total weight of the catalyst. When palladium is supported in an amount of less than 0.1 wt%, adsorption and desorption of reactants and products are difficult, resulting in a rapid drop in catalytic activity. When it exceeds 1 wt%, the dispersion of active materials in the catalyst support is reduced, resulting in green oil and coke deposition on the surface, which induces deactivation, resulting in a problem in which the reactivity is lowered relative to the palladium content.

In addition, the Pd loaded in the above step is relatively uniformly dispersed and loaded as the Pd particles are combined with the N of the coating layer during the impregnation reaction, so that the average particle size is 2 to 20 nm and the mode is 7 to 9 nm.

The catalyst manufactured by the above method can suppress coke formation by lowering the additional C-C coupling reactivity of aromatics in the methane non-oxidative methane conversion and selective hydrogenation of acetylene, and can enable selective hydrogenation of acetylene to proceed due to a reduction in adsorption and desorption portions.

The present invention provides a method for non-oxidative methane conversion and selective hydrogenation of acetylene using such a catalyst.

Specifically, the non-oxidative conversion reaction of methane is carried out at a reaction temperature of 900 to 1020°C, a weight hourly space velocity (WHSV) for a catalyst surface of 500 to 1500 mlg _cat ^-1 h ^-1 , a gas space velocity for free space of 240 to 2000 h ^-1 , and after the non-oxidative conversion reaction of methane, a selective hydrogenation reaction of acetylene can be carried out in a temperature range of 200 to 850°C.

In the non-oxidative conversion reaction of methane, the ratio of the gas space velocity for the free space / WHSV for the catalyst surface is 0.4 to 2.0 g _cat mL ^-1 . If it exceeds the above range, the reactivity of the free space increases, making it difficult to observe the CH activation effect of methane on the catalyst surface. If it is less than 0.4, the reactivity of the catalyst surface increases, causing problems in increasing the yield of the product.

In the hydrogenation reaction of acetylene, the reaction temperature is 200 to 850°C. If it is lower than 200°C, the selectivity for ethylene decreases and the selectivity for ethane increases relatively. If it exceeds 850°C, the hydrogenation reaction of ethylene or the C-C bond and dehydrogenation reaction of acetylene are promoted, resulting in a decrease in the selectivity for ethylene and the generation of coke due to carbon, which affects the life of the catalyst. It is preferably 200 to 300°C.

Hereinafter, examples will be described in more detail to explain the present invention. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

<Example>

Example 1. Pd/PHPS/α-alumina catalyst

Perhydropolysilazane (PHPS) was dissolved in dibutylether to prepare a polysilazane solution having a mass ratio of 10 wt%. The polysilazane solution thus prepared had no pore structure and a BET surface area of 1 m ² g ^-1 or less. The α-alumina carrier was soaked at room temperature for 30 minutes.

After that, the alumina carrier was separated (taken out) from the polysilazane solution, and then preheated at 200°C for 1 hour in a nitrogen atmosphere while heating at a rate of 10°C min ^-1 . The polysilazane remaining on the surface of the carrier was cross-linked with each other through the preheating treatment. The particles that were primarily cross-linked on the surface of the carrier were heat-treated at 900°C while heating at a rate of 1°C min ^-1 in a nitrogen atmosphere without a separate holding time (without a rest time). By cooling, PHPS/α-Al ₂ O ₃ particles were obtained, in which PHPS was coated on the α-Al ₂ O ₃ surface.

Next, 10 g of the obtained PHPS/α-Al ₂ O ₃ particles were added to a solution of 0.01 g of Pd(NO ₃ ) _2· 2H ₂ O well mixed in 100 g of H ₂ O, stirred at 120 rpm for 6 hours, and then Pd metal was supported by impregnation under vacuum conditions at 60 ^o C. The obtained particles were dried overnight in an oven at 110 ° C., heated to 550 ° C. at a rate of 4 ° C./min in an air atmosphere, and calcined at 550 ° C. for 4 hours to prepare a 0.1 Pd/PHPS/alpha-alumina catalyst.

Comparative Example 1. PHPS/Pd/α-Alumina

Fig. 1 (b) illustrates the manufacturing process of Comparative Example 1, PHPS/Pd/α-Al ₂ O ₃ catalyst. In Comparative Example 1, first, 10 g of an α-alumina support having a thickness of less than 1 m ² g ^-1 and having no pore structure was added to a solution containing 100 g of H ₂ O and 0.01 g of Pd(NO ₃ ) ₂ ·2H ₂ O, stirred at 120 rpm for 6 hours, and then Pd metal was supported by an impregnation method under vacuum conditions at 60° C. The obtained particles were dried overnight in an oven at 110° C., heated to 550° C. at a rate of 4° C./min in an air atmosphere, and calcined at 550° C. for 4 hours.

The calcined particles were immersed in a 10 wt% polysilazane solution at room temperature for 30 minutes. Afterwards, only the particles were obtained from the polysilazane solution and preheated at 200 ℃ for 1 hour by increasing the temperature at a rate of 10 ℃ min ^-1 in a nitrogen atmosphere. The particles that were initially cross-linked on the surface were heated at a rate of 1 ℃ min ^-1 without a separate holding time. After heating and heat treatment at 900℃ By cooling, the PHPS/Pd/α-Al ₂ O ₃ catalyst was prepared.

Comparative Example 2. Pd/α-alumina catalyst

Figure 1 (c) illustrates the manufacturing process of Comparative Example 2, Pd/α-Al ₂ O ₃ catalyst.

With reference to this, 10 g of an α-alumina support having a particle size of 1 m ² g ^-1 or less and having no porous structure was added to a solution containing 0.01 g of Pd(NO ₃ ) ₂ ·2H ₂ O and 100 g of H ₂ 0, stirred at 120 rpm for 6 hours, and then Pd metal was loaded by impregnation under vacuum conditions at 60° C.

The obtained particles were dried overnight in an oven at 110°C and then calcined at 550°C (4°C/min) for 4 hours in an air atmosphere. Thus, a Pd/α-Al ₂ O ₃ catalyst was prepared.

Experimental Example 1. Catalyst Analysis

(1) PHPS/α-Al ₂ O ₃ SEM-EDS and ICP analysis according to preheating temperature

In order to determine the appropriate crosslinking temperature of polysilazane remaining on the surface of the α-Al ₂ O ₃ carrier in the catalyst production of Example 1, i.e., the preheating temperature range, PHPS/α-Al ₂ O ₃ balls (1 mm) were produced by varying the preheating temperature from 200 to 500°C, and the surface shape and components were analyzed by SEM-EDS and ICP, which are shown in Fig. 2 and Table 1.

Preheating temperature (℃) Century properties (bulk property) Si content (Wt%) N:Si ratio 200 2.3 3.34 250 2.7 1.30 300 2.5 1.06 500 2.4 0.76

In Table 1, the Si content is shown by analyzing PHPS/α-Al ₂ O ₃ using an ICP (Inductively Coupled Plasma Spectrometer). It can be seen that even when the preheating temperature increases to 500 ℃, the Si loading of PHPS coated on the α-Al ₂ O ₃ carrier is maintained at 2.3 to 2.7 wt%.

In addition, the SEM image of Fig. 2 shows the surface morphology according to the preheating temperature. When the preheating temperature increases to 500℃, the roughness of some surfaces changes, but cracks do not significantly occur, and it can be confirmed that PHPS is stably coated on α-Al ₂ O ₃ with almost no specific surface area. This means that even if the polymer structure of PHPS is preheated at a high temperature and deformation occurs due to crosslinking, peeling does not occur due to the interaction with α-Al ₂ O ₃ .

In addition, in Table 1, it can be confirmed that the ratio of N:Si analyzed by SEM-EDS decreases from 3.34 to 0.76 as the preheating temperature increases. This is because N is vaporized and lost as the PHPS coated on the surface is partially thermally decomposed, and since the surface dispersion of Pd can be affected by N, it is preferable that the PHPS be preheated and crosslinked at 200°C in terms of metal dispersion.

(2) TEM analysis

TEM analysis was performed on each of the manufactured Example 1, Comparative Example 1, and Comparative Example 2, and the results are shown in Figure 3.

FIG. 3(a) shows a case where PHPS is coated on an α-Al ₂ O ₃ carrier (Example 1). Even though it was manufactured by a high-temperature heat treatment at 900°C, it can be confirmed that ^Pd particles are stably maintained and relatively uniformly dispersed on the surface of the PHPS/α-Al ₂ O ₃ carrier having a specific surface area of 1 m 2 /g or less. This is because the N group of PHPS improves the dispersion and thermal stability of Pd.

On the other hand, Fig. 3(b) shows a case where Pd was supported on an α-Al ₂ O ₃ carrier and then PHPS was coated (Comparative Example 1). Although the Pd particles were relatively uniformly supported on the carrier despite being manufactured by a high-temperature heat treatment at 900°C, it can be confirmed that the dispersion of the Pd particles was reduced compared to Example 1, and thus the uniformity of the Pd particles on the carrier was reduced.

In addition, Fig. 3(c) shows that even though Pd was supported on an α-Al ₂ O ₃ carrier and calcination was only performed at 550°C in an air atmosphere (Comparative Example 2), the Pd particle size was confirmed to be 10 nm or larger, and some Pd particles were confirmed to be 100 nm or larger.

(3) Pd particle size analysis

In the above TEM analysis, the Pd particle sizes for Example 1 and Comparative Example 1 were analyzed and presented in the graph in Fig. 4.

FIG. 4 is a graph showing the uniformity of Pd particles according to the composition of the catalyst. It can be seen that Pd/PHPS/α-Al ₂ O ₃ (Example 1) has relatively uniform particle sizes, with Pd particles mostly in the range of 5 to 10 nm, whereas PHPS/Pd/α-Al ₂ O ₃ (Comparative Example 1) has a wide range of Pd particle sizes, from 5 to 45 nm.

In addition, it can be confirmed that the Pd particles of Example 1 have a mode at 8 nm, while Comparative Example 1 has a mode at 6 nm.

1. Catalytic activity analysis (non-oxidative conversion reaction and hydrogenation reaction of methane)

(1) Non-oxidative conversion reaction of methane

0.6 g of the catalyst molded bodies having a size of 425 to 850 ㎛ manufactured in the above Example 1 and Comparative Example 2 were charged into a quartz tube reactor (inner diameter: 7 mm, height 150 mm). After pretreatment in a helium atmosphere at 1020°C for 30 minutes, methane and argon were supplied in a volume ratio of 90:10 to perform a non-oxidative conversion reaction of methane. At this time, the WHSV (Weight hourly space velocity) for the surface of the catalyst was 500 to 1500 mlg _cat ^-1 h ^-1 , the gas space velocity for free space (Space velocity for free space(h ^-1 )) was 249 to 2000 h ^-1 , the reaction pressure (P _total ) was 1 bar, and the methane pressure (P _CH4 ) was 0.9 bar.

The gaseous hydrocarbons obtained after the reaction were analyzed using a GC of Series 6500 from YL Instrument. The gaseous products were analyzed using a thermal conductivity detector (TCD) connected to a ShinCarbon ST column and two flame ionization detectors (FID) detectors each connected to an Rt-alumina BOND and Rtx-VMS column.

_H2 , _CH4 , Ar, _O2 , CO, and _CO2 were separated on a ShinCarbon ST column and detected by TCD, and the conversion was calculated by the area of _CH4 compared to the area of Ar, which is an internal standard. Light hydrocarbons in the range of C1 to C6 were separated on a Rt-alumina BOND column and detected by FID, and aromatic compounds were separated on a RTx-VMS column and detected by FID. All gases were quantified using standard samples. The coke selectivity was calculated by [S _coke = 100 - Σ product selectivity]. The results for the methane conversion and product selectivity at steady state for each catalyst are shown in Table 2.

Example 1 Comparative Example 2 Space velocity for free space(h ^-1 ) 2000 746 498 249 2000 746 498 249 WHSV for catalytic surface (mlg _cat ^-1 h ^-1 ) 995 1500 1000 500 995 1500 1000 500 Conversion rate 1.6 4.2 6.5 12.5 2.7 4.1 5.9 11.9 Choice ethane 13.4 6.7 3.5 1.9 12.2 7.3 4.9 1.8 Ethylene 40.8 34.6 28.2 23.2 41.7 35.8 31.8 24.0 acetylene 9.8 15.0 16.0 15.2 9.1 10.5 13.2 13.8 C3-C4 23.7 21.8 16.0 8.0 18.4 17.8 16.3 8.3 benzene 4.1 7.1 11.2 19.2 2.0 3.7 7.3 15.6 naphthalene 0.6 1.5 3.2 6.5 0.2 0.5 1.4 4.4 Alkyl Aromatics 2.7 5.7 9.6 12.6 1.6 2.2 4.0 5.0 Coke 4.9 7.6 12.3 13.4 14.8 22.2 21.1 27.1

From Table 2, it can be confirmed that the coke selectivity of the catalyst of Example 1 is relatively lower than that of the catalyst of Comparative Example 2 under the same reaction conditions. This means that the Pd particles whose size is controlled by PHPS are effective in lowering the additional C-C coupling reactivity of aromatics.

In addition, from Table 2, it can be confirmed that the lowest coke selectivity is obtained when the weight hourly space velocity (WHSV) for the catalyst surface is 995 mlg _cat ^-1 h ^-1 and the gas space velocity for free space (space velocity for free space(h ^-1 )) is 2000 h ^-1 .

In addition, from Table 2, it can be confirmed that the highest yield (conversion rate) to hydrocarbons is shown when the weight hourly space velocity (WHSV) for the catalyst surface is 500 mlg _cat ^-1 h ^-1 and the gas space velocity for free space (space velocity for free space(h ^-1 )) is 249 h ^-1 .

(2) Selective hydrogenation of acetylene

For the material manufactured by the above methane conversion reaction, the catalytic performance was confirmed by performing a hydrogenation reaction of acetylene using the manufactured catalysts of Example 1, Comparative Examples 1 and 2. The reactor used in the experiment was a fixed-bed reactor, and a tubular reactor made of quartz with an inner diameter of 7 mm was installed in a furnace with a heating zone with a total height of 150 mm. The manufactured catalyst was crushed into a size of 425 to 850 ㎛ and filled into a 0.3 g quartz tube reactor. Thereafter, the reactant containing acetylene was supplied at 80 sccm at 100 to 850 ℃ using mass flow controllers under the reaction conditions (reactant composition: H ₂ /C ₂ H ₂ = 1. He / (H ₂ +C ₂ H ₂ ) = 3).

The hydrocarbons in the gas phase of the obtained product were analyzed using a GC of Series 6500 from YL Instrument, and the gaseous product was analyzed using a thermal conductivity detector (TCD) connected to a ShinCarbon ST column and two flame ionization detectors (FID) detectors each connected to an Rt-alumina BOND and RTx-VMS column.

_C2H2 , _CH4 , and Ar were separated on a ShinCarbon ST column and detected by TCD, and the conversion was calculated from the ratio of the width of acetylene _to that of Ar, the internal standard. Light hydrocarbons in the range of C1 to C5 and benzene were separated on a Rt-alumina BOND column and detected by FID, and aromatic compounds including benzene were separated on a RTx-VMS column and detected by FID. All gases were quantified using standard samples. The selectivity for others including green oil and coke was calculated by [S _others = 100 - Σproduct selectivity].

The results of the conversion rate and product selectivity according to the selective hydrogenation of acetylene using each catalyst performed as described above are shown in Table 3.

catalyst reaction
temperature
(℃) Conversion rate
(%) Choice Ethylene/Ethane Ratio methane ethane Ethylene C3-C4 benzene Others Example 1 100 99.9 0 12.6 70.7 16.2 0 0.5 5.6 Comparative Example 1 3.5 0 8.3 59.7 5.8 0 26.2 7.2 Comparative Example 2 57.4 0 9.4 80.4 10.1 0 0.1 8.6 Example 1 200 99.9 0 7.0 90.3 2.7 0 0 12.9 Comparative Example 1 31.4 0 5.4 88.6 6.0 0 0 16.4 Comparative Example 2 98.4 0 12.1 85.6 2.3 0 0 7.1 Example 1 290 81.9 0 5.0 91.9 2.9 0 0.2 18.4 Comparative Example 1 10.4 0 4.1 93.8 2.1 0 0 22.9 Comparative Example 2 19.5 0 4.7 92.3 3.0 0 0 19.6 Example 1 850 10.9 31.1 15.5 48.1 5.0 0.3 0 3.1 Comparative Example 1 6.7 33.5 16.7 44.3 5.5 0 0 2.7 Comparative Example 2 10.5 43.8 0.7 47.9 7.0 0.6 0 68.4

Through Table 3, it can be seen that the catalyst of Example 1 exhibits superior acetylene conversion reactivity in the range of 100 to 850°C than the catalysts of Comparative Examples 1 and 2, and in particular, it can be confirmed that the ratio of ethylene/ethane reaches a maximum at 290°C.

Claims (11)

In a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene,
The above catalyst is an α-alumina catalyst support;
A coating layer comprising a cross-linked -Si-N- bond on the catalyst carrier; and
A catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, characterized in that it comprises palladium dispersed and supported on the coating layer.
In the first paragraph,
A catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, characterized in that the specific surface area of the coating layer including a cross-linked -Si-N- bond on the catalyst support is 0.08 to 0.2 m ² /g, and the average particle size of the supported palladium is 2 to 20 nm.
In the first paragraph,
A catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, characterized in that the most frequent particle size of the supported palladium is 7 to 9 nm.
A first step of coating an α-alumina carrier with a compound having a -Si-N- bond;
A second step of preheating the carrier obtained in the first step to crosslink a compound having a -Si-N- bond on the α-alumina carrier;
A third step of heat-treating the carrier obtained in the second step to form a coating layer having a -Si-N- bond on the α-alumina carrier; and
A method for producing a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, comprising a fourth step of impregnating a Pd precursor into the carrier obtained in the third step.
In paragraph 4,
A method for producing a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, characterized in that the compound having the above -Si-N- bond is composed of perhydropolysilazane (PHPS).
In paragraph 4,
A method for producing a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, characterized in that the preheating in the second step is performed at 150 to 450°C.
In paragraph 4,
A method for producing a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, characterized in that the heat treatment in the third step is performed at 700°C to 1000°C.
In paragraph 4,
A method for producing a catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, characterized in that the fourth step comprises impregnating a Pd precursor into the carrier obtained in the third step, drying it at 80 to 120°C, and then heat-treating it at 300 to 1000°C to support Pd on the coating layer.
A catalyst for non-oxidative methane conversion and selective hydrogenation of acetylene, manufactured by the manufacturing method of any one of claims 4 to 8.
A method for non-oxidative methane conversion and selective hydrogenation of acetylene using a catalyst according to any one of claims 1 to 3.
A method for non-oxidative methane conversion and selective hydrogenation of acetylene using a catalyst of claim 9.