RU2065326C1 - Catalyst for synthesis of hydroxylamine - Google Patents

Abstract

FIELD: application to carbon materials of platinum catalysts useful in the processes of organic synthesis, production of electrocatalysts, for instance, for fuel elements and, more precisely, catalysts Pt/C for synthesis of hydroxylamine by reduction of NO with hydrogen. SUBSTANCE: catalyst for synthesis of hydroxylamine is dispersed metallic platinum applied to the surface of graphitic material with real density of 1.8-2.1 g/cu.cm and pore volume of 0.2-1.0 cu.cm/g in which layers of carbon are packed in crystallites oriented in space in form of faces of polyhedron and having interplanar distance d 002= 0.340-0.350 nm, average size of crystallite in direction a L_a= 3.0-18.0 nm; average size of crystallite in direction c L_c=3.0-14 nm. EFFECT: provision of production of catalyst for synthesis of hydroxylamine by hydrogenation of nitrogen oxide featuring high activity and resistance to oxidizing corrosion. 1 cl, 1 tbl

Description

 The present invention relates to the field of platinum catalysts supported on carbon materials of interest for organic synthesis processes, the preparation of electrocatalysts, for example, fuel cells, and more specifically to Pt / C catalysts for the synthesis of hydroxylamine by the reduction of NO by hydrogen.

Hydroxylamine is widely used in the production of caprolactam and a number of other valuable chemical products. The process of producing hydroxylamine is based on hydrogenation of nitric oxide in an acidic environment in the presence of a Pt / C catalyst [1]
The main methods for the preparation of platinum catalysts on carbon supports are described in [2] When using activated carbon with a developed specific surface as a carrier, the catalysts are prepared by adsorption of platinum from an aqueous solution of platinum hydrochloric acid, followed by reduction of platinum to a metal [3] Another method for preparing the catalyst is platinum deposition on graphite or soot from a colloidal solution obtained from platinum hydrochloric acid in the presence of sodium dithionite, followed by by reduction with formic acid [4]
The process of producing hydroxylamine proceeds in a highly aggressive medium containing nitric oxide in sulfuric acid [3], which causes oxidative corrosion of the carbon support and recrystallization of platinum, leading to deactivation of the catalyst. The regeneration of the catalyst for the synthesis of hydroxylamine is usually carried out by dissolving platinum in aqua regia and re-precipitating it on a carrier. Moreover, under the action of nitric acid and nitrogen oxides, the destruction of the carbon carrier occurs.

A known catalyst [4] used as electrodes for fuel cells, containing 15% Pt on soot VULKAN XC-72, having an average particle size of 30 nm, an interplanar distance d _{002 of} 0.36 nm, the size of microcrystallites in the direction of "a" L _a 2 , 2 nm and in the direction of "c" L _c 1.8 nm. The disadvantage when using this catalyst in the synthesis of hydroxylamine is the difficulty in separating the fine particles of the catalyst from the reaction products.

A known catalyst for the synthesis of hydroxylamine, including 1.2-11.3% (weight) of Pt on activated carbon [3] The disadvantage of this catalyst is its low efficiency due to its deactivation in aggressive conditions of the process of synthesis of hydroxylamine, as well as the complexity of the regeneration of the catalyst due to destruction of the carbon carrier. The low corrosion resistance of platinum catalysts on activated carbons is due to a significant number of structural defects of the carrier, which is manifested in a low true density, small sizes of carbon microcrystals and an increased interplanar distance d ₀₀₂ compared to graphite.

The closest in technical essence to the claimed one is a catalyst containing platinum metal on powdered electrographite [5] having a pore volume <0.01 cm ³ / g, particle size 1-100 μm, true density 2.2 g / cm ³ and structural characteristics d ₀₀₂ 0.338 nm, L _a > 100 nm, L _c > 100 nm. A significant disadvantage of this catalyst is the low activity in the hydrogenation of nitric oxide to hydroxylamine. Graphite has a well crystallized structure, its surface is formed mainly by basal faces that are resistant to oxidizing agents. However, the weak interaction of platinum particles with the chemically inert surface of the basal faces causes the migration of platinum on the surface, the enlargement of the deposited platinum particles and, ultimately, a decrease in the activity of the catalyst.

 The objective of the invention is the creation of a catalyst for the synthesis of hydroxylamine by hydrogenation of nitric oxide, which has increased activity and resistance to oxidative corrosion.

The problem is achieved in that the catalyst for the synthesis of hydroxylamine is a dispersed metal platinum deposited on the surface of a graphite-like material with a true density of 1.8-2.1 g / cm ³ and a pore volume of 0.2-1 cm ³ / g, in which the layers carbon are packed in crystallites oriented in space in the form of faces of a polyhedron and have an interplanar distance d _{002 of} 0.340-0.350 nm, the average crystallite size in the direction "a" L _a 3-18 nm, the average crystallite size in the direction "c" L _c 3 -14 nm.

Distinctive features in comparison with the known Pt / C catalysts are the structural characteristics of the proposed catalyst: the true carrier density is 1.8-2.1 g / cm ³ , the pore volume is 0.2-1 cm ³ / g, the packing of carbon layers in crystallites and their orientation in the form of faces of a polyhedron, interplanar spacing d ₀₀₂ 0.340-0.350 nm, average crystallite size in the direction “a” L _a 3-18 nm, average crystallite size in the direction “c” L _with 3-14 nm.

 The catalyst is prepared by depositing platinum metal on a new porous carbon material having the above structural characteristics.

 The choice of the indicated structural parameters ensures high activity and stability of the catalyst during the synthesis of hydroxylamine by hydrogenation of nitric oxide.

 The following are examples illustrating the properties of known and proposed catalysts.

 Characteristics of known catalysts are given in examples 1 and 2.

Example 1 (for comparison). Preparation of the catalyst. 1 g of a carbon carrier and 20 ml of distilled water are charged into a glass reactor. A mixture of the following solutions is added to the resulting suspension: 0.64 ml of H ₂ PtCl ₆ (0.04 mol / liter), 5 ml of distilled water, 0.075 ml of Na ₂ CO ₃ (1 mol / liter), 0.65 ml of NaOAc (1 mol / liter), 0.2 ml of Na ₂ S ₂ O ₄ (0.02 mol / liter) and 0.5 ml of CH ₂ O (10% aqueous solution). The resulting mixture was kept under stirring for 3 hours and a temperature of 65 ^o C. The catalyst was washed on a filter and dried in air at 100-110 ^o C for 5 hours.

Activated charcoal is used as a carrier. Obtained in example 1, the catalyst has the following composition and structural characteristics: the platinum content of 0.5 weight. the rest is a carbon carrier; the carbon carrier is X-ray amorphous and has a true density of 1.78 g / cm ³ and a pore volume of 0.82 cm ³ / g.

Catalyst test. In a 100 ml jacketed jacketed reactor equipped with a magnetic stirrer, 80 ml of a 19% sulfuric acid solution and a Pt / C catalyst sample (0.1 g) are charged. The temperature in the reactor is set at 40 ^{° C.} , the reactor is purged with hydrogen and then with a H ₂ : NO mixture in a molar ratio of 3: 2. The reactor is closed, the magnetic stirrer is turned on and the absorption rate of the gas mixture is determined using a measuring burette. The activity of the catalyst is 14.6 mol NO / g-at Pt x min.

Determination of the resistance of the catalyst to oxidative corrosion. In a glass thermostated reactor equipped with a magnetic stirrer, load 10 ml of 63% HNO ₃ and 1 g of catalyst. The mixture is heated to 90 ^o C and incubated for 1 hour. Using a burette, the volume of carbon dioxide formed during the oxidation of the carbon carrier is determined. The amount of oxidative corrosion of the catalyst according to example 1, calculated by the formula (100% x mass of oxidized carbon / mass of the initial catalyst) is 4.8%
Example 2 (prototype). It is similar to example 1 with the difference that powdered electrographite is used as a carrier. The prepared catalyst has the following structural characteristics: d ₀₀₂ 0.338 nm, L _a > 100 nm, L _c > 100 nm, true density 2.2 g / cm ³ , pore volume <0.01 cm ³ / g. The activity of the catalyst is 18.3 mol NO / g-at Pt x min. The value of oxidative corrosion of the catalyst according to example 2 is 0,062%
The characteristics of the proposed catalysts are given in examples 3-6.

Example 3. The preparation of the catalyst. 1 g of a carbon carrier and 20 ml of distilled water are charged into a glass reactor. A mixture of the following solutions is added to the resulting suspension: 0.64 ml. H ₂ PtCl ₆ (0.04 mol / liter), 5 ml of distilled water, 0.075 ml Na ₂ CO ₃ (1 mol / liter), 0.65 ml NaOAc (1 mol / liter), 0.2 ml Na ₂ S ₂ O ₄ (0.02 mol / liter) and 0.5 ml of CH ₂ O (10% aqueous solution). The resulting mixture was kept under stirring for 3 hours and a temperature of 65 ^o C. The catalyst was washed on a filter and dried in air at 100-110 ^o C for 5 hours.

As the carrier, a new porous carbon material is used in which carbon layers are packed into crystallites oriented in space in the form of faces of a polyhedron. The prepared catalyst has the following composition: the platinum content of 0.5 weight. the rest is carbon carrier. Structural characteristics of the prepared catalyst: d ₀₀₂ 0.350 nm, L _a 3 nm, L _c 3 nm, true density 1.8 g / cm ³ , pore volume 1 cm ³ / g.

Catalyst test. In a 100 ml jacketed jacketed reactor equipped with a magnetic stirrer, 80 ml of a 19% sulfuric acid solution and a Pt / C catalyst sample (0.1 g) are charged. The temperature in the reactor is set at 40 ^° C., the reactor is purged with hydrogen and then with a H ₂ : NO mixture in a molar ratio of 3: 2. The reactor is closed, the magnetic stirrer is turned on and the absorption rate of the gas mixture is determined using a measuring burette. The activity of the catalyst according to example 3 is 26.4 mol NO / g • at Pt x min.

Determination of the resistance of the catalyst to oxidative corrosion. In a glass thermostated reactor equipped with a magnetic stirrer, load 10 ml of 63% HNO ₃ and 1 g of catalyst. The mixture is heated to 90 ^o C and incubated for 1 hour. Using a burette, the volume of carbon dioxide formed during the oxidation of the carbon carrier is determined. The amount of oxidative corrosion of the catalyst according to example 3, calculated by the formula (100% x mass of oxidized carbon / mass of the original catalyst), is 0.3%
Example 4. Similar to example 3 with the difference that the carrier has the following structural characteristics: d ₀₀₂ 0.349 nm, L _a 4 nm, L _c 3.5 nm, true density 2.05 g / cm ³ , pore volume 0.93 cm ³ / g The activity of the catalyst is 28.6 mol of NO / g-at Pt x min. The value of oxidative corrosion of the catalyst according to example 4 is 0.1%
Example 5. Similar to example 3 with the difference that the carrier has the following structural characteristics: d ₀₀₂ 0.344 nm, L _a 11 nm, L _c 12 nm, true density 2.08 g / cm ³ , pore volume 0.65 cm ³ / g. The activity of the catalyst is 31.3 mol NO / g-at Pt x min. The amount of oxidative corrosion of the catalyst of example 5 is 0.1%
Example 6. Similar to example 3 with the difference that the carrier has the following structural characteristics: d ₀₀₂ 0.340 nm, L _a 18 nm, L _c 14 nm, true density 2.1 g / cm ³ , pore volume 0.2 cm ³ / g. The activity of the catalyst is 21.7 mol NO / g-at Pt x min. The value of oxidative corrosion of the catalyst according to example 6 is 0.1%
The characteristics of the catalysts obtained in examples 1-6 are presented in the table.

 Thus, the above results show that the claimed catalyst in structural characteristics is fundamentally different from the known Pt / C catalysts and is highly active and resistant to oxidative corrosion in the process of hydrogenation of nitric oxide to hydroxylamine. TTT1

Claims (1)

A catalyst for the synthesis of hydroxylamine by hydrogenation of nitric oxide, containing dispersed metal platinum on a carbon graphite-like carrier formed by flat carbon layers, characterized in that the catalyst contains a carrier with a true density of 1.8 to 2.1 g / cm ³ and a pore volume of 0.2 1, 0 cm ³ / g, the carbon layers of which are packed in crystallites oriented in space in the form of faces of a polyhedron and having an interplanar distance d ₀₀₂ 0.340 0.350 nm, the average crystallite size in the direction a L _a 4.0 18 nm, in the direction c - L _c 3.5 14, 0 nm.

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