JPS60244339A - Catalyst for high temperature catalytic combustion - Google Patents

Abstract

PURPOSE:To enhance heat resistance and to enable clean combustion reduced in the discharge of NOX, by containing oxide of one or more of a rare earth element selected from Pr, Nd, Sm, Eu, Gd, Tb or the like and Pd. CONSTITUTION:The titled catalyst is formed by supporting the catalyst, which consists of oxide of one or more of a rare earth element selected from Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and palladium, by a carrier comprising a refractory material. This catalyst is excellent in heat resistance and, by using this catalyst, combustion exhausting no NOX is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] The present invention relates to a catalyst for high-temperature catalytic combustion used at temperatures of 800 to 1600°C.

Catalytic oxidation catalysts are used as catalysts for treating (deodorizing) organic solvent-based exhaust gases from stationary sources such as printing factories such as Osset rotary printing and metal printing, painting factories, and chemical plants for the purpose of preventing air pollution. ing. Furthermore, a catalyst that combines an oxidation catalyst with a reduction action is used as a three-way catalyst for simultaneously treating hydrocarbons, carbon oxides, and nitrogen oxides (NOx) discharged from automobiles. Oxidation catalysts are also commercially available as deodorizing filters for kerosene stoves for consumer use.

In recent years, technologies related to these oxidation catalysts have been developed to develop catalytic combustion catalysts for the purpose of heating.

Attempts have been made to apply it to combustors or heaters. For example, by replacing part of the burner of a gas stove, gas water heater, or stove with a catalytic combustion catalyst, it is possible to achieve highly efficient and stable flameless combustion. ,
Moreover, compared to flame combustion in traditional burners, it emits less carbon monoxide and unburned hydrocarbons.

In addition, catalytic combustion for the purpose of reducing nitrogen oxides has been attracting attention. In boilers and gas turbines, there is a high temperature part in the combustion chamber that exceeds 2000°C, so nitrogen in the air is oxidized and nitrogen oxides with a high concentration of several hundred pIxl are emitted. Emissions of nitrogen oxides are regulated under the Air Pollution Control Law. Measures to reduce nitrogen oxides include improving the combustion method by using a low-nox burner or performing two-stage combustion, and denitration by ammonia catalytic reduction, each of which is effective. However, Knox regulations are likely to become increasingly strict in the future.
In order to deal with this, more effective methods are needed. Therefore, attempts have been made to apply the catalytic combustion method. This method makes it possible to perform stable and uniform combustion, without causing local high temperatures, and suppressing the occurrence of thermal nox.In this case, the catalyst temperature is 10DD℃. Because of the high temperatures above, a catalyst with excellent heat resistance is required.

An object of the present invention is to provide a catalyst with excellent heat resistance that allows catalytic combustion to occur at high temperatures of 800 to 1,600°C.

Catalysts for purifying automobile exhaust gas are known as catalysts that have relatively good heat resistance. These catalysts are basically spherical carriers made of activated alumina or honeycomb-shaped carriers made of ceramics coated with oil-based alumina, on which noble metals are supported. Methods have been developed to prevent the transformation of alumina to alpha alumina.

Under these circumstances, a method has been proposed to improve heat resistance by adding rare earth oxides to activated alumina. For example, JP-A-48-14600 describes a method of preparing a catalyst by impregnating a catalytic metal component into a thermally stabilized carrier by adding a rare earth oxide to activated alumina.
Ru. Further, JP-A-58-156349 discloses a catalyst in which hepalladium is supported on a stabilized carrier by adding a rare earth oxide and a perovskite type composite oxide to activated alumina. JP-A-57-19036 discloses a support stabilized by adding a perovskite type composite oxide containing a rare earth element to alumina.

However, these methods only improve the heat resistance of the underlying alumina, and when noble metals are supported, rare earth oxides and rare earth perovskite oxides added to alumina act directly on the noble metals in terms of thermal stability. It is thought that there is no sparrow. Therefore, in the above example, it cannot be expected to have much of an effect of suppressing sintering of the noble metal at high temperatures of 800° C. or higher.

There are also systems similar to these in which rare earth oxides are added to mainly aim for a catalytic effect. For example, JP-A-58
Publication No. 36634 states that when platinum and palladium are supported on a porous carrier containing neodymium oxide or neodymium oxide and cerium oxide, NOx can be removed without containing expensive rhodium as in conventional three-way catalysts. It is stated that it is possible. Also, JP-A-58-79
544, when a palladium catalyst in combination with a transitional aluminum oxide lattice-stabilized with alkaline earth metal oxides and/or oxides of lanthanide elements is supported on a heat-resistant steel alloy, an alcohol-operated internal combustion It has been shown to be effective in burning aldehydes in engine exhaust gas. The heat resistance of these catalysts appears to be approximately the same as that of the technologies described above.

In view of this situation, we have completed the present invention as a result of careful consideration.

According to the present invention, there is provided a high-temperature catalytic combustion catalyst characterized by comprising a rare earth oxide excluding lanthanum oxide and cerium oxide, and palladium.

[Structure of the invention]

The catalyst of the present invention is characterized by excellent thermal stability because the rare earth oxide has a specific bond with palladium and palladium is stabilized. This cannot be achieved with a catalyst consisting of lanthanum oxide and palladium or cerium oxide and palladium.

In the present invention, rare earth elements combined with palladium include praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), and gadolinium (
Gd), terbium (Tb), dysprosium (DY)
, holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu
), these can be used alone or in combination. Further, in this case, even if a small amount of lanthanum or cerium, which is equivalent to an impurity, is contained, there is no particular problem in implementing the present invention.

The catalyst carrier may be any material that has heat resistance of 1300° C. or higher in an oxidizing atmosphere, such as cordierite, zirconia, mullite, alpha alumina, titania, silicon carbide, silicon nitride, sialon, etc. I can do it. The shape of the carrier is not particularly limited, and for example, a pellet-shaped, honeycomb-shaped, or foam-shaped carrier having a three-dimensional network structure can be used.

The amount of palladium and rare earth oxide supported on the carrier is 0.1~
3Qwt%, preferably 1 to 20Wt. Even if the supported amount exceeds 30 wt4, no improvement in activity is observed, and if the supported amount is less than 0.1 wt1, sufficient performance cannot be obtained.

The atomic ratio of the rare earth element to palladium is 1 to 1 of the rare earth element to 0.05 to 4 palladium, preferably 0.01 to 2. Even if the atomic ratio of palladium to the rare earth element exceeds 4, no commensurate improvement in performance can be expected, and if it is less than 0.05, optical performance cannot be obtained.

The catalyst can be produced, for example, by preparing a mixed aqueous solution of a soluble salt of palladium and a soluble salt of a rare earth element, and performing an impregnation method. The soluble salt used as a raw material may be any salt as long as it is soluble in water, and for example, nitrates, chlorides, etc. can be used. According to the impregnation method, the carrier is immersed in a solution prepared to a predetermined concentration for 60 minutes to 1 hour, and then dried at 70 to 150° C. for 2 to 10 hours. moreover,
The finished catalyst can be obtained by calcination for 6 to 12 hours at a temperature above the decomposition temperature of the salt used. If a predetermined amount of support cannot be obtained in one impregnation operation, the impregnation can be repeated after net formation.

Examples of the present invention are shown below.

Example 1 A mixed aqueous solution of palladium nitrate and praseodymium nitrate of 0.1 mol/liter and 12 mol/liter of O, respectively, was prepared, and a cordierite-based nickel-based carrier having square through-holes was added to the solution. 25 dragons x 50 feet) 6
Immersed for 0 minutes, dried at 110℃ for 2 hours, and then dried at 1100℃ for 4 hours.
After calcination for an hour, a finished catalyst was obtained. The amount of catalyst component supported is 1
．． It was 2'wt%.

Example 2 Using samarium nitrate instead of praseodymium nitrate
A finished catalyst was obtained in the same manner as in Example 1 in all other respects. The amount of catalyst components supported was 1.2 wtq&.

Example 6 A finished catalyst was obtained in the same manner as in Example 1 except that lanthanum nitrate was used instead of praseodymium nitrate. The amount of catalyst component supported was 1.3 wL%.

Example 4 57 g of activated alumina, 3 g of cerium oxide, 0.9 L of gum arabic, and 120 cc of pure water were mixed in a ball mill to prepare an alumina slurry. Using this slurry, the same carrier used in Example 1 was coated with alumina, and after drying, it was calcined at 500°C for a period of time. As a result, the carrier contains 5w of activated alumina containing 5wt4 of cerium oxide.
t4 coated.

This carrier was immersed in an aqueous radium solution containing 0.1 mol/liter of chloride for 60 minutes, dried at 110°C for 2 hours, and then calcined in a hydrogen stream at 250°C for 1 hour to obtain a completed catalyst.

〔Effect of the invention〕

The same procedure was carried out for other catalysts other than those shown in the examples above. Each of these catalysts was evaluated for catalytic activity using a flow reaction test device. The test was conducted at a catalyst inlet temperature of 600°C and a gas flow rate of 16.3 Nll/min.
, combustion gas concentration propy900p4, catalyst amount 24.5
The test was carried out at c c and space velocity of 4×10 hr.

The test results are shown in Table 1.

Table 1 Note: Activity determination 800℃ firing ◎ Conversion rate 95 Exposure rate 090-94 △80
Seating stand x less than 80% 900'C firing ◎ Conversion rate 90 taku or more 0
80% level △70 level × Less than 70 level 1000℃ firing◎
Conversion rate 80 or higher 070 ratio △60 ratio x 40 (
Firing at 100℃ ◎ Conversion rate 60 or more 050 △
It is clear from Table 1 that the heat resistance of the catalyst for high temperature catalytic combustion of the present invention is superior to other catalysts.

According to the method of the present invention described above, a catalyst for high-temperature catalytic combustion with excellent heat resistance can be obtained, and by using this catalyst, clean combustion with less emissions of nox and the like becomes possible.

Patent applicant Nihon Kagaku Sangyo Co., Ltd. Agent: Patent Attorney Shukichi Donakagawa

Claims (2)

[Claims] (1) Praseodymium (Pr), neodymium (Nd)
, samarium (Sm), europyram (Eu), gadolinium (Gd), terbium (Tb), dysproscilla (Dy), holmium (Ho), erbium (Er)
A catalyst for high-temperature catalytic combustion, comprising palladium and an oxide of at least one rare earth element selected from , thulium (Tm), ytterbium (Yb), and lutetium (Lu). (2) The catalyst according to claim 1, wherein the catalyst is supported on a carrier made of a refractory material.