Patent Application
20210205794
The present disclosure relates to a reformed zeolite and a catalyst composite using the same which have improved heat-resistance and are used in a selective catalytic reduction (SCR) catalyst using ammonia or urea as a reducing agent, or in a filter-type SCR catalyst in which a filter is coated with the SCR catalyst, or in a lean nitrogen oxide diesel oxidation catalyst. The reformed zeolite according to the present disclosure is manufactured by coating or mixing zeolite with alumina sol, and a catalyst including the reformed zeolite according to the present disclosure may be improved at nitrogen oxide (NOx) lowering performance at a high-temperature region and may be improved at thermal durability even when being exposed to high-temperature exhaust gas discharged from an internal combustion engine, etc.
The removal of nitrogen oxide (NOx) from exhaust gas is particularly difficult in a combustion condition which uses more air than required for stoichiometric combustion, i.e., a combustion condition of an internal combustion engine operated in a lean condition.
As a proven technology for lowering NOx applied to a stationary source which is the lean condition, there is a selective catalytic reduction (SCR) using ammonia. In this technology, the NOx reacts with ammonia acting as a reducing agent, on the surface of the SCR catalyst and is lowered as it is reduced to nitrogen (N2). Generally, vanadium-titanium oxide is applied as a selective catalytic reduction (SCR) catalyst that represents 90% or more decrease of nitrogen oxides in a range of 300 to 450° C., and ZSM5 and beta form zeolite and/or ion-exchanged transition metals such as Fe or Cu, zeolite catalysts such as Fe-beta, Cu-beta, Fe-ZSM5, and Cu-ZSM5 are developed and used for applications that require high thermal durability (600° C. or more) and high active temperature range (350 to 550° C.) However, the problem of heat-resistance still exists. Such a SCR may also be applied to a filter structure, and is referred to as a SCRoF (SCR on Filter) or an SDPF. The SCR is called filter-type SCR catalyst in the present disclosure. Meanwhile, recently, a catalyst article including a NOx adsorbing material in a diesel oxidation catalyst (DOC) has been developed and applied to improve a low-temperature activity, which is referred to as a NA-DOC, and is called a NOx adsorbing type diesel oxidation catalyst in the present disclosure. In the NOx adsorbing diesel oxidation catalyst or the filter-type selective catalytic reduction catalyst, it is required to provide a catalyst that has improved high-temperature activity, thermal durability against exposure to high-temperature exhaust gas generated from an internal combustion engine, and poisoning resistance against poisonous material such as sulfur, phosphorus, calcium, zinc, and an alkali metal.
The present disclosure is completed by achieving a catalyst that has excellent heat-resistance and high-temperature activity by applying alumina sol to zeolite to manufacture a reformed zeolite and applying the reformed zeolite to NA-DOC, SCR or SDPF.
The present disclosure relates to a catalyst article. More particularly, the catalyst article may a nitrogen oxide adsorbing type diesel oxidation catalyst, a selective catalytic reduction catalyst, or a filter-type selective catalytic reduction catalyst, and may include zeolite placed in a carrier, and the zeolite may be coated with alumina sol.
According to an embodiment of the present disclosure, zeolite before reformation may be H-beta zeolite or CHA zeolite. The catalyst article according to the present disclosure may further include a platinum group component, and a NOx storing material, for example, barium, strontium, and magnesium, which are typically added in the NOx adsorbing type diesel oxidation catalyst. In addition, typical components, such as a conjugate, which are understood by those skilled in the art may be further included in the selective catalytic reduction catalyst or the filter-type selective catalytic reduction catalyst. The reformed zeolite according to the present disclosure may be placed on the inner wall of the carrier or the pores of the inner wall of the carrier.
According to another embodiment, the present disclosure may provide an exhaust gas treatment system including the catalyst article.
The stability of the reformed zeolite according to the present disclosure may be confirmed by an X-ray diffraction (XRD) and change in Brunauer Emmett Teller (BET) surface area. When the NA-DOC, SCR, or SDPF catalyst coated with reformed zeolite is applied to an exhaust system, adsorption rate or conversion rate of the nitrogen oxide (NOx) of high-temperature exhaust gas is increased due to improvement in the heat-resistance of zeolite. In addition, thermal durability against exposure to high-temperature exhaust gas and poisoning resistance, which remains active even when exposed to high concentration of sulfur and alkali metals, are improved.
There may be factors influencing the stability of the reformed zeolite, such as a physical barrier role of alumina which acts as a shell for the zeolite which is a core, and weakening of dealumination, but is not limited thereto.
The present disclosure relates to a reformed zeolite coated with alumina sol, a catalyst article in which the reformed zeolite is placed on a carrier, and an exhaust gas treatment system including the catalyst article.
Zeolite is a crystalline aluminosilicate material that typically has a uniform pore size of a diameter of about 3 to 10-angstrom, which is depending on the type thereof, and type and quantity of a cation included in the lattice thereof. The purpose of the zeolite, synthetic zeolite, and natural zeolite used to promote a specific reaction including a selective reduction of nitrogen oxide by ammonia acting as a reducing agent is well known to those skilled in the art. The objective of the present disclosure is to improve heat-resistance of zeolite by reforming the zeolite, especially by using alumina sol to manufacture the reformed zeolite. The term ‘alumina sol’ used herein may be interchangeably used with the term ‘aluminum hydroxide’, ‘bayerite’, or ‘boehmite’. In fact, alumina sol is understood to be a substance containing several forms of aluminum hydroxide. In general, alumina sol may be manufactured to a powder form or a cake form as purposed. In the manufacturing process of alumina sol, alumina hydrate obtained by liquid-phase neutralization reaction of an acidic water-soluble aluminum salt such as aluminum chloride and aluminum nitrate with an alkaline substance such as ammonia hydroxide and carbonate is aged and washed to remove impurities, and is filtered, and then the desired alumina hydrate is obtained as a cake form or obtained as an alumina sol powder by heat treatment after drying.
H-beta zeolite, BEA zeolite, or CHA zeolite is exemplified and SSZ-13 among the CHA zeolite is exemplified in the present disclosure, but not limited thereto. Furthermore, zeolite may be ion-exchanged by one or more metal cations, and the appropriate metals include copper, iron, and cobalt, but are not limited thereto. The zeolite in the present disclosure is mixed with alumina sol and the alumina sol is included in approximately 5 to 50 weight % by weight of the zeolite, preferably, 10 to 30 weight %, and a mixture thereof will be dried and calcined to manufacture the reformed zeolite. The reformed zeolite of the present disclosure has an egg-shell structure in which zeolite acts as a core and alumina acts as a shell.
The reformed zeolite of the present disclosure is placed on the surface of the inner wall of the carrier or in the pores of the inner wall of the carrier, which forms NA-DOC, SCR, or SDPF catalyst articles. The term ‘catalyst article’ in the present disclosure may be interchangeably used with the term ‘catalyst’ or ‘catalyst composite’, and the term ‘carrier’ may be described as a substrate or support. A honeycombed substrate is exemplified as a carrier. The catalyst article of the present disclosure may further include conventional additives. As an example, the NOx adsorbing type diesel oxidation catalyst may further include platinum-group components, NOx storing material, such as barium, strontium, and magnesium, and the selective catalytic reduction catalyst or filter-type selective catalytic reduction catalyst may further include a component conjugate which is placed on a fire-resistant metal oxide carrier for realizing additional catalytic functions.
The catalyst articles of the present disclosure are mounted in an exhaust gas treatment system, and may further include the diesel oxidation catalyst and/or smoke filter at the upstream of the catalyst articles, and the downstream of the catalyst articles may be provided with an ammonia oxidation catalyst.
<Zeolite Reformation>
As a first method, a zeolite reformation method using a resonant acoustic mixing (RAM) mixer and a ball milling process is proposed. First, an alumina sol solution (30 weight %) and BEA-zeolite (100 weight %) are mixed together, and distilled water (DI) is added to the mixture to produce a slurry having a solid content of 30%. The slurry is treated by using the RAM mixer for 2 minutes. Alumina balls are fed to and processed by wet milling for 24 hours, and then dried at 150° C. and calcined at 600° C. to complete the production of the alumina sol coated with reformed zeolite. A fresh zeolite is aged at 700° C. to 1100° C. in an L/R condition for 12 hours. The alumina sol solution refers to a solution of colloidal dispersion that has a diameter of 2 to 10 nanometers and is produced by injecting commonly acquired 5 to 50-micron alumina powder, such as SASOL, into water or acidic solution.
As a second method, a slurry process is proposed. An alumina sol solution (30 weight %) and BEA zeolite (100 weight %) are mixed together, and distilled water (DI) is added to the mixture, and the mixture is dispersed for 10 minutes, and then milled and adjusted acidity to produce a slurry having a solid content of 30%. The product is dried at 150° C. and calcined at 600° C., so alumina sol coated with reformed zeolite is produced. A fresh zeolite is aged at 700° C. to 1100° C. in an L/R condition for 12 hours.
The first method and the second method proposed to produce reformed zeolites that actually have the same features.
BEA zeolite becomes unstable when the temperature is increased. However, the reformed BEA zeolite of the present disclosure is more stable after 12 h L/R cycle aging at 900° C.
In another embodiment of the present disclosure, the reformed zeolite may have a shape of a particle catalyst, and the catalyst article is provided by placing this particle shape on the carrier. The carrier or substrate may be arbitrary materials typically used in the manufacture of catalysts, and conventionally includes a ceramic or metal honeycombed structure. For example, a ceramic substrate may be formed of arbitrary fire-resistant materials. Specifically, the catalyst article or catalyst composite according to another embodiment of the present disclosure is manufactured by applying the reformed zeolite as a washcoat to the substrate. The washcoat of the reformed zeolite may be manufactured by using a binder. According to one or more embodiments of the present disclosure, an adequate precursor such as zirconium precursor, for example, ZrO2 which is induced from zirconyl nitrate, is used as a binder. According to another embodiment, the reformed zeolite catalyst includes a precious metal component, that is, a platinum-group metal component. For example, to prevent an ammonia slip phenomenon, the platinum-group component as an ammonia oxidation catalyst is typically included in the reformed zeolite catalyst. An adequate platinum metal component includes platinum, palladium, rhodium, and a mixture thereof. A number of components of the catalyst materials (for example, the reformed zeolite and precious metal component) may be applied as a fire-resistant carrier, that is, a washcoat mixture of two or more components, or as a separate washcoat component. The catalyst article may be formed by using a known method. The coating method is well known, and carrying may be performed on the inner wall surface of the carrier, or on some of the surface, or on the rest of the inner wall, or in the entire inside of the wall. The reformed zeolite catalyst article according to the present disclosure may be provided in an exhaust gas treatment system such as a system that may be seen in gasoline and diesel vehicles. In these exhaust gas treatment systems, the reformed zeolite catalyst articles are generally provided for accomplishing fluid communication with other gas treatment articles at the upstream or downstream of the catalyst articles, for example, fluid communication with diesel oxidation catalysts, smoke filters and/or ammonia oxidation catalyst article.
The catalyst article according to the present disclosure has improved catalyst efficiency at high-temperature. This improvement may be due to the improved heat resistance of the reformed zeolite. This conclusion is further supported by
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2018-0057570 | May 2018 | KR | national |
| 10-2019-0039595 | Apr 2019 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2019/005919 | 5/17/2019 | WO | 00 |
