KR100231532B1 - Catalyst composition for diesel automobile - Google Patents

Abstract

The present invention relates to a catalyst composition for a diesel vehicle, but conventionally developed a way catalyst of a gasoline engine, a diesel engine, HC, CO, PM of the oxidation catalyst, De-NO _X purifying NO _X to purify SOF component It was inefficient because the angle was separated by a filter trap that filters the SOOT in the catalyst and PM.

The present invention combines the functions of the conventional oxidation catalyst and the De-NO _X catalyst, γ-Al ₂ O ₃ : 20-50 wt%, TiO ₂ : 20-50wt% and Pt ion exchange ZSM-5: 10-30wt% Mix and wash coat the cordierite monolith and impregnate 1-3 g per liter of catalyst in the range of Pt: Rh = 2: 1 to 10: 1.

Description

Catalyst composition for diesel vehicle

The present invention relates to a catalyst composition for a diesel vehicle, and more particularly, to a catalyst composition for a diesel vehicle capable of simultaneously removing HC, CO, SDF, and NO _X by improving a washcoat component in the catalyst.

Diesel exhaust consists of HC (hydrocarbon), CO (carbon monoxide), NO _X (nitrogen oxide), PM (particulate matter), and the post-treatment converts these harmful emissions into harmless H ₂ O or CO ₂ The material is a diesel catalyst.

As a gasoline catalyst, a three-way catalyst has been developed that simultaneously purifies HC and CO NO _X at a constant air-fuel ratio (air and fuel ratio) .However, in diesel engines, SOF (soluble organic matter) components of HC, CO and PM are purged. are each divided into an oxidation catalyst, De-NO _X catalyst, such as a filter to filter out raepteu SOOT (carbon particles) of the PM purifying NO _X.

Looking at them in detail as follows.

Since there is a limit in purifying exhaust gas by engine modification, a purifying method by post-treatment of an engine has been attempted. The exhaust gas aftertreatment of the diesel engine includes a particulate collecting device, SOF (Soluble Organic Fraction) contained in the particulate material, an oxidation catalyst device for reducing HC and CO in the exhaust gas, and a reduction to reduce NO _X. Catalytic equipment;

Particulate matter from diesel engines consists of carbon insoluble materials and SOF components from unburned HC (including combustion intermediates) in fuel and engine oils entering the fuel compartment. There are three methods for collecting particulate matter: cyclone method, electrostatic dust collection method, and filter method.

The cyclone method separates and collects particulate matter by centrifugal force.However, in the case of diesel engines, active development is not promoted because the particulate matter is extremely small, such as submicron several microns, and has a low density and is very difficult to use. It seems.

In addition, the electrostatic precipitating method has an excellent collecting ability, but requires a high voltage of several kV, so that the leakage prevention technology when the particulate matter is deposited in the device is insufficient, and the volume is increased to secure the collecting area. It is difficult to regenerate, troublesome, and troublesome, but it is still in practical use in some stationary diesel engines.

Since the filter method is the closest to practical use for automobiles, many companies and research institutes are promoting development.

The filter type is a trapping structure in which a ceramic material is first roasted (baked with low heat without glazing), and particulate matter is filtered and collected into a foamed space formed by a whirlpool, a bubble formed of ceramic and metal, and a ceramic fiber is twisted. To form a coil-shaped nonwoven fabric wound into a coil, and to filter and collect a fiber, and a metal mesh to filter and collect a metal wall in a filled space. In terms of material, it is excellent in heat resistance and oxidation resistance like ceramics or stainless steel metals such as corrierite (2MgO · 2AL ₂ O ₃ · 5SiO ₂ ), silicon carbide (SiC), and lite (3AL ₂ O ₃ · 2SiO ₂ ) The material is being used.

Among them, the development of a collection device using honeycomb-shaped wall flomonolith made of cordierite has been reported to be excellent in terms of back pressure, collection efficiency and size.

As combustion improvement progresses due to engine modulation, the decrease in the concentration of black smoke emitted from the engine decreases the proportion of insoluble matter in the particulate matter, but correspondingly, the proportion of soluble organic matter (SOF) increases relatively. . Therefore, when it is necessary to reduce the particulate matter again, measures focused on reducing the SOF content become important. The SOF fraction is composed of unburned fuel, unburned engine oil and combustion products that cannot be identified, and consist of hydrocarbons having a relatively high carbon number.

Among these, hydrocarbons attributable to fuel make up the lighter side of the molecular weight, so the fraction of SOF fraction is small, but hydrocarbons attributable to engine oil have a high molecular weight and thus have an influence on SOF fraction. For this reason, it is important to reduce engine oil consumption to reduce SOF content, but there are some limitations.

In other words, it maintains airtightness and prevents sticking between sliding surfaces of the engine oil piston and piston ring, cylinder liner, hop / exhaust valve and valve guide, and some engine oil must exist on the sliding surface. do. Since the engine oil on the sliding surface moves in the form of an oil film in conjunction with the counterpart, the engine oil penetrated into the cylinder and the exhaust port by this movement cannot be exposed to hot flame and combustion gas, and part of it evaporates. In order to reduce the SOF content in the particulate matter, which is consumed by incomplete or incomplete combustion, it is important to design the amount of engine oil to be consumed in a range in which tribological problems do not occur.

Even if the improvement by the engine main body is made, there is a limit to the reduction of the SOF powder. Therefore, in order to reduce the SOF powder, it is necessary to use an oxidation catalyst.

Most of the oxidation catalysts for decomposing SOF components are used precious metals such as platinum, palladium and rhodium.

Pt and Pd are known to exhibit high activity in the oxidation reaction of SOF fraction, but when these are used as exhaust aftertreatment for diesel engines, sulfur dioxide (SO ₂ : sulfur dioxide), a combustion product of sulfur contained in diesel fuel, is oxidized. As a result, it becomes a sulfate, and the discharge weight of particulate matter is inversely increased.

For this reason, in the catalyst apparatus actually used, these noble metal catalysts include non-metal catalysts such as oxides such as cobalt (CO), nickel (Ni), manganese (Mn), vanadium (V), chromium (Cr), and titanium (Ti). In addition, the method of suppressing the production of sulfate while promoting the oxidation of SOF powder is taken.

However, the question of what kind of catalyst is mixed and how much is treated and applied to the actual catalyst device is a secret for each company, and it is not clear.

Pt and Pd are expensive precious metals and should be studied to obtain high performance with the use of small amount as much as possible. For this purpose, the surface of the carrier is encoded with a material having a large specific surface area such as γ-alumina, and the precious metal is finely dispersed therein to facilitate efficient use of the precious metal.

Automotive catalysts must remain active under very harsh conditions, such as severe mechanical vibrations, sudden fluctuations in exhaust temperature, and exposure to various impurities in the exhaust gases derived from fuels and engine oils. In order to cope with this, catalyst companies are developing technologies for coating and adjusting catalysts, or coatings such as γ-alumina that underlie catalysts.

Ammonia reduction by V ₂ O ₅ -TiO ₂ catalyst is widely used for the post-treatment of NO _X (nitrogen oxide) from fixed sources such as boilers and gas turbines, and ammonia is selective even in systems with high concentrations of oxygen To NO.

This method is considered that fitness value as that because the facility is large installation koseukeu high as the vehicle after-treatment devices that require ammonia as the reducing agent, but a few percent of the fuel by a catalytic converter mounted on the vehicle, some research institutions H ₂ There is an example of attempting to establish a technology of selectively reducing NO in a diesel vehicle by synthesizing ammonia from H ₂ and N _{2 in the} air generated by decomposition with CO and CO. In addition, cyanuric acid and urea are proposed as selective reducing agents, but the denitration efficiency and practicality are not clear.

In gasoline engines with three-way catalysts, CO and HC in the exhaust gas act as reducing agents to reduce NO to N ₂ .

However, even with this three-way catalyst of a diesel engine having a high oxygen concentration in the exhaust gas, since CO and HC preferentially react with the oxygen in the exhaust gas, they hardly contribute to the reduction of NO.

For this reason, compact contact reduction catalysts for automobiles that can decompose NO in an oxygen-rich atmosphere have been required. NO was originally thought to be possible as a NO reduction catalyst for diesel vehicles because it is thermodynamically unstable compared to N ₂ and O ₂ and in an oxygen-excess atmosphere. It wasn't.

Recently, a number of studies have been submitted to investigate the purification performance of a catalyst which exhibits NO decomposition activity in an oxygen-excess atmosphere such as a metal ion exchange zeolite, a metal oxide, a supported metal, and a perovskite complex oxide. According to the previous test results based on the model gas, the Cu-ZSM-5 system, which exchanges a large amount of copper ions to a synthetic zeolite having a higher SiO ₂ / AL ₂ O ₃ ratio than the natural zeolite, purifies NO at a relatively low temperature around 300 ° C. Performance was shown and the performance at the activation temperature was higher than that of other catalysts.

In the future, it was found that adding some kind of HC to the gas of a real engine selectively reduced NO as a reducing agent. Furthermore, the start temperature of the activity was slightly lowered, and the NO purification rate was improved with the increase of the HC concentration. Came out.

However, the actual exhaust gas of diesel engine contains residual oxygen, sulfur oxide and a large amount of water. In the test results by the test gas simulating the gas of a real engine, the remarkable activity of the poison which is considered to be poisoned by these substances is significant. A heat drop is observed.

The selective reduction of NO in an oxygen-rich atmosphere has tended to be limited to only ammonia until now, suggesting that selective reduction of NO is possible in HC using this type of catalyst. Since ammonia is designated as a dangerous substance, sufficient care must be taken to prevent it from leaking into the atmosphere, whereas HC is suitable as a NO reducing agent emitted from diesel vehicles, which is relatively simple to handle and may use some of the fuel.

However, the reports up to now have a lot of experimental results and in fact, under the exhaust gas exposure under the operating conditions of various engines used in vehicles, that is, coexistence with particulate matter, sulfur oxides, moisture, and additives in the engine lubricating oil, etc. How much purification performance, reliability and durability can be obtained under space velocity (SV value) and exhaust gas temperature (100 to 700 ° C) remains a constant problem.

An object of the present invention is to provide a diesel catalyst capable of simultaneously removing HC, CO, SOF, and NO _X by improving the washcoat component in the catalyst.

The present invention will be described in detail based on examples.

Example 1

γ-Al ₂ O ₃ : 20-50wt%, Tio ₂ : 20-50wt%, Pt ion exchange ZSM-5: 10-30wt% and wash in cordierite monolithic (Cordierite: 2MgO · 2Al ₂ O ₃ ) A catalyst composition coated and impregnated with 1 to 3 grams per liter of catalyst in the range of Pt: Rh = 2: 1 to 10: 1.

Example 2

γ-AL ₂ O ₃ : 20-30 wt%, TiO ₂ : 20-30 wt%, SiO ₂ : 20-30 wt%, CeO ₂ : 10-20 wt%, ZrO ₂ : 5-10 wt%, Pt, Rh are ion exchanged ZSM-5: 10-30 wt% of a catalyst composition coated on cordierite monolith.

Example 3

γ-Al ₂ O ₃ : 20-30 wt%, TiO ₂ : 20-30 wt%, SiO ₂ : 20-30 wt%, CeO ₂ : 10-20 wt%, ZrO ₂ : 5-10 wt%, Pt, Rh are ion exchanged ZSM-5: 10-30 wt% of the mixed catalyst washwashed on cordierite monolith and impregnated with 1 to 3 grams per 1 liter of catalyst in the range of Pt: Rh = 2: 1 to 10: 1.

Conventional oxidation catalyst is Al ₂ O ₃ (alumina), TiO ₂ (titania), carrying a noble metal such as Pt, pd on oesi coat consisting of a component such as SiO ₂ (silica), manufactured by and, De-NO _x catalyst, Since the catalysts are manufactured by ion-exchanging precious metals such as Pt, Pd, and Rh in zeolite materials, each catalyst has a limited function, but the present invention simultaneously removes SOF components in HC, CO, NO _X , and PM with one catalyst. You can do it.

The present invention has the effect of combining the functions of the conventional oxidation catalyst and the De-NO _X catalyst as in the above-described embodiment.

Claims (2)

γ-Al ₂ O ₃ : 20-30 wt%, TiO ₂ : 20-30 wt%, SiO ₂ : 20-30 wt%, CeO ₂ : 10-20 wt%, ZrO ₂ : 5-10 wt%, Pt, Rh are ion exchanged ZSM-5: 10-30 wt% of the catalyst composition for diesel vehicles, characterized in that the coating on cordierite monolith. The catalyst composition for a diesel vehicle according to claim 1, wherein the mixture is washed with cordierite monolith and then impregnated with 1 to 3 g per 1 liter of catalyst in the range of Pt: Rh = 2: 1 to 10: 1. .