KR20200044362A - Cold start catalyst with sulfur resistance - Google Patents

Abstract

The present invention relates to a sulfur-resistant cold start catalyst and a use thereof in an internal combustion engine exhaust system, the cold start catalyst adsorbing NO_x in a cold start section and emitting the adsorbed NO_x at an operation temperature, and comprising: (1) a noble metal catalyst composed of a noble metal and sulfated mixed oxides; and (2) a supported platinum group metal catalyst comprising one or more platinum group metals and one or more inorganic oxide supports, wherein the sulfated mixed oxides are a mixture of magnesium oxide and ceria.

Description

Cold start catalyst {COLD START CATALYST WITH SULFUR RESISTANCE}

The present invention relates to a sulfur tolerant cold starting catalyst and use in an internal combustion engine exhaust system.

Internal combustion engines cause exhaust gases containing various pollutants, including nitrogen oxides (NO _x ), carbon monoxide and unburned hydrocarbons. Various catalyst systems that reduce or eliminate contaminants are applied, but this is the case when the catalyst system reaches an operating temperature of 200 ° C or higher, and the removal efficiency is lowered under an operating temperature, commonly referred to as a cold starting section.

Conventional Pd / OSC materials are known as cold starting catalysts and typically OSC materials consist of inorganic oxides such as alumina, silica, ceria, zirconia, titania or mixed oxides thereof, but these materials, particularly ceria, are susceptible to sulfur content. there was.

Therefore, research on a catalyst material having strong resistance to sulfur poisoning while storing pollutants discharged from the cold starting section is required. The present inventors have developed a new cold start catalyst for purifying exhaust gas of an internal combustion engine.

The present invention relates to a sulfur tolerant cold starting catalyst effective for adsorbing NO _x in a cold starting section and releasing adsorbed NO _x at an operating temperature.

According to the present invention, the sulfur tolerant cold starting catalyst includes 1) a precious metal catalyst dispersed in a sulfated mixed oxide of magnesium oxide and ceria and 2) a platinum group catalyst supported on an inorganic oxide.

The noble metal catalyst consists essentially of a noble metal and a sulfated mixed oxide. The platinum group catalyst includes one or more platinum group metals and one or more inorganic oxide supports. The present invention also includes a method for treating sulfur-containing exhaust gases, particularly from internal combustion engines, using the cold starting catalyst.

The cold starting catalyst effectively treats contaminants during the cold starting period through improved NO _x storage performance, sulfur resistance and improved CO oxidation.

1 is a view illustrating sulfur toxicity of a ceria support.
Figure 2 schematically shows Comparative Catalyst 1 and the catalysts deposited on a substrate.
3 is a comparison of the degree of NOx adsorption between Comparative Catalyst 2 and the present catalyst.
4 is a view showing the CO conversion performance of the catalyst.
5 is a view showing the NOx adsorption performance of the catalyst.

Pd / ceria material is used as a cold starting catalyst, but ceria is excellent in NOx storage performance, but is susceptible to sulfur. Referring to FIG. 1, it can be seen that when the supporter ceria is poisoned with sulfur or the like contained in exhaust gas, the NOx absorbency is rapidly reduced and performance is not recovered even after desulfurization due to regeneration. In the figure, HTA means Hydro thermal aging at 800 ° C./25 h, and test conditions are 2.5 g / L SO ₂ exposure poisoning and desulfurization treatment is performed at 700 ° C./30 min.

The present invention applies a sulfated oxide instead of a conventional ceria material as a dispersion support of a precious metal Pd, but applies oxides of magnesium oxide and cerium oxide as oxides, and improves NOx storage properties in the cold starting section by adding a platinum group catalyst. It relates to a catalyst that improves sulfur resistance.

That is, the cold starting catalyst of the present invention includes a noble metal catalyst and a platinum group catalyst, and the cold starting catalyst adsorbs NO _x at a low temperature of about 200 ° C. or less and releases the adsorbed NO _x at an engine operating temperature higher than the low temperature. effective. The noble metal is preferably palladium, platinum, rhodium, gold, silver, iridium, ruthenium, osmium or mixtures thereof; More preferably palladium, platinum, rhodium or mixtures thereof. Palladium is particularly preferred.

The sulfated oxide means a mixture of preliminarily sulfated magnesium oxide and cerium oxide, wherein the precious metal is dispersed in an amount of 0.1 to 2% by weight. The dispersion support herein refers to a support applied in a noble metal catalyst, and is distinguished from a support applied to a platinum group catalyst. The mixed oxide may be composed of 30 to 70% magnesium oxide and 70 to 30% ceria by weight. The preliminarily sulfated mixture of magnesium oxide and cerium oxide is first impregnated with a MgO and CeO ₂ dispersion support in an aqueous solution containing ammonium nitrate, and then impregnated with a sulfate solution, and then the obtained pre-sulfurized mixed oxide is obtained. It can be obtained by impregnating a precious metal such as an aqueous Pd solution (such as palladium nitrate) and calcining it. The noble metal catalyst can be produced by any other known method. For example, the noble metal can be added to the sulfated mixed oxide to form a noble metal catalyst dispersed on a support by any known method, wherein the mode of addition need not be specified. For example, the noble metal compound can be dispersedly supported by immersion, adsorption, wet impregnation, precipitation, and the like in the mixed oxide.

Platinum group metal catalysts include one or more platinum group metals (PGM) and one or more inorganic oxide supports. The PGM can be platinum, palladium, rhodium, iridium or combinations thereof, most preferably platinum and / or palladium. The inorganic oxide support is also referred to as a carrier and is preferably alumina, silica, titania, zirconia, ceria, niobia, titanium oxide, molybdenum oxide, tungsten oxide, or any two or more mixed oxide or composite oxides thereof, such as silica-alumina, Ceria-zirconia or alumina-ceria-zirconia. Alumina and ceria are particularly preferred.

The platinum group metal catalyst can be produced by any known method. Preferably, one or more platinum group metals are loaded onto one or more inorganic oxides by any known method to form a supported PGM catalyst, wherein the mode of addition is not considered particularly important. For example, platinum compounds (such as platinum nitrate) can be supported on the inorganic oxide by immersion, adsorption, wet impregnation, precipitation, and the like. Other metals such as iron, manganese, cobalt and barium can also be added to the platinum group catalyst.

The cold starting catalyst of the present invention can be prepared by processes well known in the prior art. The noble metal catalyst and the platinum group metal catalyst can be physically mixed to produce a cold starting catalyst. Preferably, the cold start catalyst is coated on a through substrate or filter substrate, and is preferably deposited on the through or filter substrate using a washcoat process to produce a cold start catalyst system. The base material is usually a cordierite, but is not limited thereto, and a description of a cold starting catalyst manufacturing process using a washcoat process apparent to those skilled in the art is also omitted.

The present invention also provides a method for treating exhaust gas from an internal combustion engine, whereby NO _x is adsorbed onto the cold starting catalyst at a cold starting temperature, and NO _x from the cold starting catalyst is higher than the cold starting temperature. Thermally desorbing at temperature, and catalytically removing the desorbed NO _x on the catalyst component downstream of the cold starting catalyst. At this time, the catalyst component downstream of the cold starting catalyst may be an SCR catalyst, a particulate filter, an SCR filter, a NO _x adsorber catalyst, a ternary catalyst, an oxidation catalyst, or a combination thereof.

The following examples illustrate the invention herein, and those skilled in the art will recognize various implementations.

Example: Preparation of catalyst

Comparative catalyst 1 : Pd / beta zeolite + Pt / Al ₂ O ₃

Beta zeolite and silica binder are added to form an aqueous slurry. The slurry was coated on a penetrating cordierite substrate to dry the substrate, then calcined, and palladium was added to the zeolite-coated substrate by immersion in an aqueous Pd nitrate solution to achieve Pd loading, and Pd / zeolite- After the coated substrate is dried, it is fired.

Platinum nitrate is added to the aqueous slurry of alumina particles (milled to an average particle size of less than 10 microns in diameter) to form a Pt / alumina catalyst slurry. Then, the Pt / alumina catalyst slurry is coated on a Pd / zeolite-coated substrate to achieve Pt loading, and the final coated substrate is dried and calcined by heating to compare the catalyst (Pd component is 72g / L, 2Pt / 3Pd ratio).

Comparative catalyst 2 : Pd / non-sulfurized mixed oxide + Pt / Al ₂ O ₃

It was carried out in the same manner as the catalyst described below, but the pre-sulfurization treatment was not performed on the mixed oxide of MgO + CeO2.

Catalyst : Pd / sulfur oxide mixed oxide + Pt / Al ₂ O ₃

First, a sulfated mixed oxide is prepared. The supports of MgO (50 wt%) and CeO ₂ (50 wt%) are impregnated in an aqueous solution containing ammonium nitrate (90 umol), stirred, dried and fired (300 ° C./2hr). Then, immersed in ammonia sulfate (90 umol) solution, stirred, dried, and calcined (600 ° C./2 hr). The obtained pre-sulfurized mixed oxide was impregnated with palladium nitrate, dried and calcined to obtain a pre-sulfurized mixed oxide. The mixing ratio of the magnesium oxide and ceria, one component can be mixed at 30 to 70% by weight, showed similar experimental results. This is prepared as a slurry by a conventional method, coated on a cordierite substrate, and then dried and calcined to obtain a Pd / sulfate mixed oxide-coated substrate. Subsequently, the Pt / alumina catalyst slurry was coated on the Pd / sulfurized mixed oxide-coated substrate as in the comparative catalyst to achieve Pt loading, and the final coated substrate was dried and calcined, whereby the catalyst (Pd component was 72 g / L , 2Pt / 3Pd ratio).

Figure 2 schematically shows Comparative Catalyst 1 and the catalysts deposited on a substrate. The values in parentheses are the dry gain in g / L, and alumina was further quantitatively added for simple comparison in addition to the sulfated mixed oxide in the catalyst herein. On the other hand, the comparative catalyst 1 and the main catalyst are the same, the upper layer contains a part of the lower palladium (8%). The Pd component was 72 g / L, and the catalyst was constituted at a ratio of 2 Pt / 3 Pd.

3 is a comparison of the degree of NOx adsorption between Comparative Catalyst 2 and the present catalyst. According to FIG. 3, in the case of the pre-sulfurized mixed oxide, the degree of NOx storage is maintained at about 85% even after sulfur poisoning, and after regeneration, the performance is restored to 100%, but in the case of the pre-sulfurized mixed oxide After the sulfur poisoning, NOx occlusion was reduced to about 57%, and after regeneration, the performance recovered to only 59%. Therefore, it was confirmed that the sulfur resistance was greatly improved.

Experimental Example: Test process

The comparative catalyst 1 and the catalyst of the present application were aged under the above hydrothermal conditions, and the feed gas stream in the reactor was THC: 1,200ppm, CO: 1,800ppm, NOx: 150ppm, 13% O2, 5% H2O, N2 balance, SV: 50,000h-1 CO conversion performance under conditions is tested. The results are presented in Figure 4, and surprisingly, the catalyst of the present application has improved CO LOT50 performance compared to the comparative catalyst.

NO adsorption conditions NO 400 ppm w / 20min @ 100 ° C The results of the test under normal conditions are shown in FIG. 5. This shows that the NOx storage capacity is similar to that of the zeolite comparative catalyst.

The cold starting catalyst system of the present invention (1) has high durability against the sulfur component while improving low temperature NO _x storage performance; (2) It performs a number of functions, including enhanced CO oxidation activity.

Claims (7)

A cold starting catalyst that adsorbs NO _x in a cold starting section and releases adsorbed NO _x at an operating temperature, the cold starting catalyst comprising: (1) a precious metal catalyst composed of a noble metal and a sulfated mixed oxide; And (2) a supported platinum group metal catalyst comprising one or more platinum group metals and one or more inorganic oxide supports, wherein the sulfated mixed oxide is a mixture of magnesium oxide and ceria. The cold starting catalyst according to claim 1, wherein the noble metal is palladium. The cold starting catalyst according to any one of claims 1 to 2, wherein the one or more platinum group metals are selected from the group consisting of platinum, palladium, rhodium, iridium and mixtures thereof. The alumina, silica, titania, zirconia, ceria, niobia, tantalum oxide, molybdenum oxide, tungsten oxide and mixed oxides or composites thereof according to any one of claims 1 to 2, wherein the one or more inorganic oxide carriers are Cold starting catalyst, characterized in that selected from the group consisting of oxides. An exhaust system for an internal combustion engine comprising the cold starting catalyst of any one of claims 1 to 2. A method for treating exhaust gas from an internal combustion engine, comprising adsorbing NO _x on a cold starting catalyst of any one of claims 1 to 2 at a cold starting temperature, and NO _x from a cold starting catalyst at an operating temperature. Converting and thermally desorbing, and catalytically removing the desorbed NO _x on the cold starting catalyst itself or on the catalyst component downstream. 7. The catalyst component according to claim 6, characterized in that the catalyst component downstream of the cold starting catalyst is selected from the group consisting of SCR catalysts, particulate filters, SCR filters, NO _x adsorber catalysts, ternary catalysts, oxidation catalysts and combinations thereof. Way.

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