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INVENTION
Russian Federation Patent RU2169614

How to prepare catalysts and catalyst for purification of exhaust gas engines

How to prepare catalysts and catalyst for purification of exhaust gas engines

Name of the inventor: Glazunov LD .; Dzisyak AP .; Saprykin OF
The name of the patentee: Research Physical-Chemical Institute. LY Karpov
Address for correspondence: 103064, Moscow, ul. Vorontsovo field of 10, Karpov them. LY Karpov, the patent department
Starting date of the patent: 2000.03.31

It describes a method of preparing a metal honeycomb catalyst block for neutralizing noxious gas emissions comprising pretreating the inert support, coating the surface of a modified intermediate coating of alumina and one or more catalytically active platinum group metals. In this first carrier, which is a unit of Al-containing foil, calcined at a temperature of 850-920 ° C in a stream of air or oxygen for 12-15 hours and then it is applied to the intermediate coating - modified alumina from a slurry at room temperature . And describes a catalyst for purifying exhaust gases of internal combustion engines. The technical result - the reduction process applying time intermediate coating by reducing the number of process steps, reduction of electricity consumption and additional labor costs, thereby reducing the cost of the catalyst, and obtaining a catalyst having high emission efficiency in the gas purification process.

DESCRIPTION OF THE INVENTION

The invention relates to the field of catalyst neutralization exhaust of internal combustion engines (ICE) and the flue gas of industrial productions.

Known methods for preparing catalysts for block of metal and ceramic honeycomb carriers. Due to the fact that the original surface of the carrier is very small (S ud = 0.01 - 0.6 m 2 / g) based on these catalysts have a low catalytic activity. The primary goal in the preparation of such catalysts is to provide a coating on the intermediate carrier with a developed surface. The presence of a high surface area provides the necessary dispersion of the active components (Pt, Pd, Rh), whereby the obtained catalysts have high catalytic activity and durability at decontamination processes gaseous emissions from toxic components.

Known gas emission control catalysts by CO, CH x, NO x at block honeycomb carriers, which increases the surface in various ways.

Thus, the known method of preparing a catalyst of an aluminum-iron alloy [Pat. US 4096095, 1979]. This alloy is precured to form on the surface of aluminum oxide and a transition metal oxide (e.g., iron oxide). The catalytically active substance is deposited on the oxide coating. However, the intermediate coating obtained in this manner does not have the required surface area. The catalyst prepared by using this method is not sufficiently effective and durable.

Described [US Pat. 2411378 FRG 1979] method of preparing an exhaust gas purifying catalyst DVS is that the metallic frame made of carbon steel ligature without additives primer coated aluminum silicate fibers which are dried at 100-250 o C. Then, it is applied a layer of aluminum hydroxide, which dried at 100-250 o C and calcined at 800-1200 o C. Further, the resulting layer is impregnated with one or more platinum group metal salts and calcined. However, the implementation of the method includes multiple steps. Furthermore, calcination of the intermediate oxide layer at 1200 o C leads to the formation of corundum on the surface of a carrier with a small specific surface area, and the use of the metal carrier of carbon steel reduces the catalyst life.

Known method of preparing a block of a metal catalyst [US Pat. RF 2080179, 1997], wherein the intermediate coating of metal oxides (Al, Ce, etc.) And the catalytically active components (Pt, Pd) is applied to the parent metal as a carrier tape by a plasma spraying. Thereafter, the honeycomb block is formed by longitudinal channels in belt corrugating medium and folding it into a block. The described method is rather complicated for general use, but also energy intensive. Furthermore, the formation of the honeycomb structure after the deposition of the intermediate layer and active components results in mechanical deformation of the coating on the fold lines, resulting in the coating flaking, which results in lower catalyst activity.

In [Pat. US 4132673, 1979] discloses a method of applying an intermediate coating of aluminum oxide suspension in which the particles are dispersed, and the noble metals (Pt, Pd). This slurry was applied onto an inert carrier, then the water is removed during drying and calcination. However, this method does not provide strong adhesion with the coating surface of inert carrier, and thus applied platinum and palladium particles have low catalytic activity.

In [Pat. RF 2005538, 1992] discloses a process for coating metallic carrier block layer Al 2 O 3 from sodium aluminate by dissolving aluminum chips in an aqueous solution of sodium hydroxide, followed by drying and calcining. Thereafter, the carrier with an intermediate layer impregnated with an aqueous solution of Ce (NO 3)2 system and calcined to form cerium oxide. Then applied by impregnating the active components (Pt, Pd, Rh) from aqueous solutions of their salts. The catalyst was reduced in a stream of hydrogen.

The catalyst prepared by this method, taken as a prototype. Its oxide coating has the following characteristics: content of Al 2 O 3 - 10-20 wt.%; surface area - 100-120 m 2 / g, a total pore volume of - 0.3 - 0.6 m 3 / g. However, the intermediate coating catalyst has low adhesion strength to the support and unevenness, which reduces the quality of the catalyst and its operation time. Furthermore, the method of preparing the catalyst has the following disadvantages. Firstly, the process of applying the original alumina support sufficiently long (20-25 hours). Secondly, deposition of cerium oxide on the surface - this separate step, which further increases the catalyst preparation. Increasing the duration of the process contributes to energy and labor costs and, accordingly, increase the cost of the catalyst. Third, the application of aluminum oxide process by this method is accompanied by the release of hydrogen gazooobraznogo, t. E. Is an explosion and fire.

The closest method to the claimed catalyst preparation method is described in [Pat. 4587231 US 1986] (prototype method), by which to obtain a block of catalyst purifying exhaust ICE gas source monolithic carrier was repeatedly treated with alumina slurry in which the dispersed alumina powder containing cerium oxide, and cerium oxide is formed by pre-impregnating the alumina powder cerium salt solution and subsequent calcination. media treated slurry and calcined aluminum oxide coating is applied to the active substance - the platinum group metals. For this purpose, an intermediate coating is applied to an aqueous solution of each compound of the deposited noble metal (platinum, rhodium) and separately subjecting it to thermal decomposition.

The disadvantages of the above-described suspension method include low coupling strength of the alumina coating to the original metal surface, thereby reducing the service life of the catalyst due to delamination of the intermediate coating with the active substances. Furthermore, a separate deposition of noble metals on a carrier with an intermediate coating technique significantly complicates and increases the catalyst preparation.

The task to be solved by the invention is to speed up and simplify the technology of preparation of the exhaust gas purifying catalyst block ICE and industrial plants with high catalytic activity.

The technical result is achieved by: 1) the application of the intermediate coating suspension method to block the media, previously heat treated in a stream of air (or O 2) to create on the surface of an aluminum-steel foil germinal centers of adsorption, greatly enhance the adhesion of the subsequent intermediate coating oxides; 2) the use of the suspension of certain chemical composition, allowing a single technological cycle to get high-quality coating, providing high value of the specific surface of the support and dispersion of the applied noble metals; 3) introducing the stabilizing additive (CeO 2) directly into the slurry in the form of Ce (NO 3)2, which reduces the process time.

The inert carrier used steel foil tape (corrugated and rolled into a block) or brand H23YU5 H15YU5 containing about 5% aluminum. This foil is heat treated at a temperature of 850-920 o C in a stream of air or oxygen for 12-15 hours. In this mode, firstly, the migration of Al atoms to the surface of the strip and, secondly, the oxidation of Al to Al 2 O 3. Formed on the surface of aluminum oxide is required to improve adhesion of the coating to the intermediate steel foil surface. Yield after this regime leads to deterioration of the intermediate coating parameters, namely to reduce the strength of its coupling with the original carrier.

On the thus treated carrier is applied an intermediate coating suspension method. Excess slurry purged with compressed air (or nitrogen) into the vessel with the slurry. The temperature of the suspension - room. Thereafter, block provyalivayut in air for several hours. Then it is dried at a temperature of 100-120 o C and calcined at 400-500 o C in a stream of air (or nitrogen).

The slurry is a water-alcohol (e.g., ethanol) solution (ratio of water-alcohol - 1: 1) in which is dispersed from 22 to 32 wt. % Al (OH) 3 dissolved and from 2 to 4 wt.% Al (NO 3)3, and 2 to 5 wt.% Ce (NO 3)2.

Using the proposed suspension allows for a one time (single immersion) applied to the support block 7 to 14 wt.% Of alumina as an intermediate coating which greatly reduces the time of catalyst preparation. The addition of aluminum nitrate in the system is carried out to plasticize the suspension to the required level to provide faster adhesion of the intermediate coating to the metal surface of the carrier. Introduction of Ce (NO 3)2 directly into the suspension has the advantage that it reduces the total number of stages of the catalyst preparation process for the support impregnation step with an intermediate coating nitrate cerium followed by drying and calcining to form CeO 2 or the step of preparing a mixture of aluminum and cerium oxides, as described in the prior art. Cerium oxide is a thermostabilizing additive intermediate coating of aluminum oxide using a catalyst under conditions of possible thermal shocks.

A single application of the intermediate coating on the metal support block of the proposed suspension is sufficient for the preparation of an effective catalyst with a well adherent layer of Al 2 O 3, having developed specific surface area.

If necessary to further increase the weight of the intermediate coating, after the step of drying the block was immersed in the slurry and then re-performed wilting stage, drying and calcination.

After application of the intermediate coating is impregnated with aqueous solutions of H 2 PtCl 6, PdCl 2 and RhCl 3, and if necessary introducing into the catalyst of a few noble metals, e.g., Pt-Rh, Pt-Pd and Pt-Pd-Rh, in the impregnating solution all starting compounds are administered simultaneously, which differs from the prototype, wherein the impregnation is carried out by these compounds in series with intermediate recovery. This procedure and reduces the number of stages of the catalyst preparation and thus reduces process time and labor and energy costs.

After impregnation the catalyst was dried and reduced in a stream of H 2 at a temperature rise and a stepped aging at 350-400 o C for 6 hours.

Out of these parameters leads to a drop of catalyst activity and catalyst life. This is due to the fact that, firstly, the qualitative and quantitative composition of the suspension is directly related to the quality and quantity of the applied intermediate coating: the coating may be too thin, and then the surface is not sufficiently developed to produce a highly active catalyst, or uneven, with the possible occurrence of cracks during heat setting, which further leads to shattering of the partial coverage. Secondly, these temperature and time parameters provide the optimum value of the structural characteristics, in particular, the specific surface area catalysts.

The invention is illustrated by the following example:

For the preparation of the catalyst block used corrugated foil stamps H23YU5 diameter and 20 mm height. The calcining furnace metal block carrier calcined at 900 o C in flowing air. The processing time of calcination was 12 hours After cooling block was immersed in a suspension of the following composition: aluminum hydroxide - 25% by weight aluminum nitrate - 2 wt% nitrate cerium - 3 wt%, water - alcohol (1: 1).... - else. Then removed, excess air was blown from the channels and provyalivayut in air for about 5 hours. Then the unit was dried at a temperature of 100-120 o C for 2 hours and heat treated in a calcining furnace under nitrogen at a stepwise temperature rise at a rate in the 20-30 o hour to 450 o C, soaking at this temperature for 2 hours. The heating was turned off. Power is slowly cooled in the furnace to room temperature, discharged and was determined by weighting the mass of the applied intermediate coating, which in this case amounted to 10 wt.%. The specific surface of the sample was determined by the low-temperature nitrogen adsorption, it was 125 m 2 / g of Al 2 O 3.

Then the intermediate coating was applied by impregnation an active phase - PGMs calculated 0,1% Pt + 0,02% Rh in the sample. For this purpose, a metal block with an intermediate coating was impregnated with an appropriate amount of aqueous solution of chloroplatinic acid (PHVK) and rhodium chloride. The sample was dried at a temperature of 100-120 o C and reduced with hydrogen in a reducing furnace with stepwise temperature rise up to 400 o C and holding at this temperature for 6 hours.

The resulting catalyst was tested in the oxidation of CO to CO 2 in a laboratory flow unit under the following conditions: gas mixture - CO 1 vol%, O 2 - 2% by volume, balance nitrogen, the volumetric gas flow rate - 30000 h -1...

Experiments have shown that its catalytic activity in the neutralization reaction of carbon monoxide, characterized by the temperature reach 90% degree of conversion of CO, is 205 o C.

Samples were prepared catalyst block on the metal blocks of steel and H23YU5 H15YU5 analogous manner using the inventive slurry composition:.. Al (OH) 3 - 22-32 wt%, Al (NO 3)3 - 4.2 wt%, Ce ( NO 3)2 - 2.5 wt%, the rest - water-ethanol = 1:. 1. As an active phase applied to 0,1% Pt and 0,1% Pt + 0,02% Rh or 0,25% Pd + 0,01% Rh. Measuring the catalytic activity of the prepared samples showed that this parameter is practically not less than the catalyst activity of the sample described in Example (a 90% CO conversion at 205 o C).

Thus. The claimed method allows to significantly reduce the process time of application of the intermediate coating by reducing the number of process steps, avoid additional labor and power costs, thereby reducing the cost of the catalyst and produce a catalyst having high emission efficiency in the gas purification process.

CLAIM

1. A method for preparing a metal honeycomb catalyst block for neutralizing noxious gas emissions comprising pretreating the inert support, coating the surface of a modified intermediate coating of alumina and one or more catalytically active metals of the platinum group, characterized in that the first carrier, which is unit of Al-containing foil, calcined at a temperature of 850-920 ° C in a stream of air or oxygen for 12-15 hours and then it is applied to the intermediate coating - modified alumina from a slurry at room temperature.

2. A method according to claim 1, characterized in that the coating of the slurry is carried out at the following ratio of components, wt.%:

  • Aluminum hydroxide - 22 - 32
  • Aluminum nitrate - 2 - 4
  • Cerium nitrate - 2 - 5
  • Water - alcohol in a ratio of 1: 1 - To 100

3. The catalyst prepared according to claims 1 and 2, consisting of a block of the metal carrier whose surface has an intermediate coating of a modified aluminum oxide applied thereto with the active phase of platinum-group noble metals, characterized in that it has the following characteristics:

  • The content of Al 2 O 3 catalyst - 7 -. 14% by weight
  • The specific surface area of Al 2 O 3 - 120 - 130 m 2 / g
  • The content of CeO 2 Al 2 O 3 - 8 -. 15% by weight

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Publication date 07.04.2007gg