FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
CATALYST FOR TREATING EXHAUST GAS;
MITSUBISHI HEAVY INDUSTRIES, LTD., A JAPANESE CORPORATION, WHOSE ADDRESS IS 16-5, KONAN 2-CHOME, MINATO-KU, TOKYO 108-8215, JAPAN.
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE
PERFORMED. 1

DESCRIPTION TECHNICAL FIELD
The present invention relates to a catalyst for treating exhaust gas having a denitration activity and a mercury oxidation activity. BACKGROUND ART
Among methods for treating exhaust gas in which NO is removed from exhaust gas in a reduction denitration unit and then SO2 is removed in a wet desulfurization unit using an alkaline absorbing solution as an absorbent, there has been studied a method for treating metallic mercury and a mercury compound (hereinafter, collectively referred to as mercury, unless otherwise stated) in exhaust gas while performing denitration and desulfurization at the same time.
Mercury in flue gas exists in forms of metallic mercury which is insoluble in water and mercury chloride which is soluble in water. When in the form of metallic mercury, mercury is hardly dissolved in water. When mercury is in the metallic form, the efficiency of removing mercury by a wet desulfurization unit is lowered. Meanwhile, when mercury is in the form of HgCl or HgCl2, HgCl or HgCl2 in exhaust gas is dissolved in water through the gas-liquid contact in the wet desulfurization unit, and thereby mercury can be removed. In other words, if metallic mercury can be converted into mercury chloride in the presence of a catalyst such as a denitration catalyst, mercury can be removed in the desulfurization unit located in the downstream.

An example of such a conventional method for treating exhaust gas utilizing this scheme will be described with reference to Fig. 2. In Fig. 2, a NH3 supply spot 20 and a supply spot 21 are provided in a flow path from a boiler 10 to a reduction denitration unit 60. At the NH3 supply spot 20, NH3 supplied from a NH3 tank 30 is injected into exhaust gas. At the supply spot 21, a mercury-chlorinating agent such as HC1 is injected into the exhaust gas from a tank 40 for supplying the mercury-chlorinating agent. The exhaust gas from the boiler 10 is introduced into the reduction denitration unit 60. In the reduction denitration unit 60, NH3 and NOx in the exhaust gas into which NH3 and HC1 are injected react with each other, and simultaneously metallic Hg is oxidized to HgCl2 in the presence of HC1. After passing through an air heater 70 and a heat exchanger 80, the soot and dust are removed in a dust collector 90. Then, SO2 and HgCl2 in the exhaust gas are simultaneously removed in a wet desulfurization unit 100. At this point, an excessive amount of HC1 is contained in the exhaust gas having passed through the reduction denitration unit 60, but is never discharged from a stack, since HC1 is absorbed by an alkaline aqueous solution such as lime milk in the desulfurization unit 100. Together with the above-described method, a system is proposed in which a chlorinating agent such as HC1 is sprayed at an upstream of a denitration catalyst to oxidize (chlorinate) mercury on the catalyst, and then the mercury is removed in a wet desulfurization unit located at a downstream (see, for example, Patent Literature 1). Patent Literature 1: JP-A Hei 10-230137 DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION
However, in a case of a coal with a low Cl content, a large amount of a mercury-chlorinating agent such as HC1 needs to be supplied into exhaust gas to maintain the rate of conversion to mercury chloride. Moreover, in order to vaporize HC1, a large amount

of a high-temperature heat source, steam, or the like is needed. Furthermore, in addition to NH3, which is considered hazardous in power plants, highly corrosive HC1 is used, which induces material corrosion, thereby presenting problems of increased utility and storage costs.
Accordingly, an object of the present invention is to provide a method and an apparatus for treating exhaust gas which are capable of reducing the amount of a highly corrosive mercury-halogenating agent such as a mercury-chlorinating agent to be added in an exhaust gas treatment with the mercury-removing efficiency kept high.
In order to achieve the above object, according to the present invention, a catalyst for treating exhaust gas in which nitrogen oxide in the exhaust gas is removed upon contact with ammonia serving as a reducing agent, and in which mercury is oxidized using a halogen as an oxidant includes: T1O2 as a support; an oxide of at least one selected from the group consisting of V, W and Mo, which is supported as an active component on the support; and at least one selected from the group consisting of Bi, P, and compounds containing Bi and/or P, which is supported as a co-catalyst component on the support. The halogen as the oxidant for mercury is preferably a compound containing chlorine (Cl) such as NH4Cl besides HC1 or a compound containing bromine (Br). Moreover, the co-catalyst component can be used in forms as follows.
(a) in a form of only a Bi element.
(b) in a form of only a P element.
(c) in a form of containing both a Bi element and a P element.
(d) in a form of a compound of Bi and P.
(e) in a form of a compound containing Bi.
(f) in a form of a compound containing P.

(g) in a form of a compound containing Bi and P.
According to another aspect of the present invention, in the catalyst for treating exhaust gas, the co-catalyst component is formed of any one of P and a compound containing P.
According to yet another aspect of the present invention, in the catalyst for treating exhaust gas, the co-catalyst component is formed of any one of Bi and a compound containing Bi. EFFECTS OF THE INVENTION
The present invention provides a catalist for treating exhaust gas capable of reducing the amount of a highly corrosive mercury-chlorinating agent to be added while keeping the mercury oxidation efficiency high in an exhaust gas treatment. BRIEF DESCRIPTION OF THE DRAWINGS
[Fig. 1] Fig. 1 is a conceptual diagram for describing arrangement of catalysts for treating
exhaust gas in Examples 1 and 2.
[Fig. 2] Fig. 2 is a conceptual diagram for describing a conventional method for treating
exhaust gas.
EXPLANATION OF REFERENCE NUMERALS
1 Catalyst for treating exhaust gas
21 HC1 injection spot
40 Mercury-chlorinating-agent tank
60 Reduction denization unit

70 Air heater
80 Heat exchanger
90 Dust collector
100 Desulfurization unit
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a catalyst for treating exhaust gas according to the present invention will be described in further details with reference to an embodiment thereof.
A support of the catalyst for treating exhaust gas according to the present invention is formed of TiO2. As the catalyst support, generally, at least one selected from the group consisting of TiO2, SiO2, ZrO2, A12O3, complex oxides thereof, and zeolite can be used.
Moreover, the catalyst for treating exhaust gas according to the present invention supports an oxide of at least one selected from the group consisting of V, W and Mo as an active component on such a support.
Furthermore, the catalyst for treating exhaust gas according to the present invention supports at least one selected from the group consisting of Bi, P, and compounds containing Bi and/or P as a co-catalyst component on the support. The co-catalyst component exists preferably in the form of an oxide, complex oxide or heteropoly acid. Since the compound containing Bi or P is in the form of a compound having a different oxidation number, the oxidation of mercury can be promoted owing to the effect of the oxidation-reduction cycle. Bi can form a complex oxide with Mo, and thus functions as a co-catalyst. Meanwhile, P can form a heteropoly acid having a considerably strong oxidizing power by combining with

Mo or W. Both Bi and P do not exist independently and they are an element that can form a compound. Thus, Bi and P function as a co-catalyst.
The compounding ratio of the co-catalyst component with respect to the active component is as follows.
For example, suppose a case where V oxide is used as the active component and a heteropoly acid containing P (molybdophosphoric acid) is used as the co-catalyst component. In this case, the ratio of the number of V atoms contained, the number of Mo atoms contained and the number of P atoms contained is preferably 32:12:1 to 10:12:1.
As another example, suppose a case where V oxide is used as the active component and a compound containing Bi is used as the co-catalyst component. In this case, the ratio of the number of V atoms contained, the number of Mo atoms contained and the number of Bi atoms contained is preferably 1:3:0.1 to 1:10:1.5.
In the above cases, preferably 0.1 to 2 mass% of the active component is supported per 100 g of the support.
Schematically, the catalyst for treating exhaust gas according to the present invention is produced as follows.
(1) For example, a catalyst paste containing a support component and an active component is molded into a honeycomb shape and fired.
(2) The honeycomb is impregnated with a co-catalyst component and fired.
A specific mode of preparing Bi203(l .5)-Mo03(7)-V2Os/Ti02 will be described in Example 1 below.

A specific mode of preparing P-MoO3(7)-V2O5(0.5)/TiO2 will be described in Example 2 below. EXAMPLE 1
[Preparation of Bi203(l .5)-Mo03(7)-V205/Ti02]
A Ti02-V2CVbased denitration catalyst (Ti02:V2Os=95.5:0.5 (mass ratio)) was prepared as follows.
Ammonia water with a NH3 content of 25% was added to 3600 g of a metatitanic acid slurry (Ti02 content: 30 mass%), and the pH was adjusted to 6.5, followed by wet-kneading for 2 hours, drying, and furthermore firing at 550°C for 5 hours. Thereby, a titanium oxide powder was obtained. To the powder, an ammonium metavanadate aqueous solution and an ammonium molybdate aqueous solution were added so as to make the V2C>5 and M0O3 contents be 0.5 mass% and 7 mass%, respectively, and then were sufficiently mixed with the powder. Thereafter, the mixture was dried and fired at 450°C for 4 hours. Thereby, a powder (A) formed of titanium oxide [Ti02]-vanadium oxide [V205]-molybdenum oxide [M0O3] was obtained. To 1000 g of the powder (A), 25 g of carboxymethyl cellulose and 12.5 g of polyethylene oxide were put and kneaded together in a kneader for 30 minutes with an adequate amount of water being added thereto, followed by extrusion into a honeycomb shape with 30 mm2, drying and then firing at 500°C for 5 hours. A bismuth nitrate aqueous solution was further prepared, and the honeycomb was impregnated therewith so as to make the B12O3 content be 1.5 mass%. The resultant was fired at 500°C for 3 hours. Thus, a Bi203(1.5)-Mo03(7)-V205/Ti02 catalyst was prepared.
[Test for mercury oxidation activity]

The honeycomb-shaped catalysts 1 for treating exhaust gas prepared as described above were provided at three stages, each catalyst having 4 conduits x 7 conduits in 500-mm length as shown in Fig. 1, and a test was carried out for the mercury oxidation activity.
Exhaust gas samples having the following 02 to NOx features shown in Table 1 were allowed to flow under the conditions in the same Table 1, and the mercury oxidation activity of the catalyst 1 for treating exhaust gas was tested. Note that symbols in the table represent the following meanings.
Ugs: superficial velocity
AV: the amount of gas to be treated based on gas-contact area
The exhaust gas samples were extracted at positions S1 and S2 in Fig. 1.
[Table 1]

Gas Amount m3N/hr 8.49
Temperature °C 400
Ugs mN/S 2.30
NH3/ NOx - 0.9
AV m3N/ m2hr 11.96
02 % 4.0
H20 % 12.0
Hg ug/m3N 20
HC1 ppm 50
SOx ppm 1000
NOx ppm 350

Table 2 shows the test result. As seen from the result in Table 2, it is understood that, by using the catalyst 1 for treating exhaust gas according to the present invention, 79.8% of mercury was oxidized after passing through the three stages.

[Table 2]

Sampled Position

AV
m3N/ m2hr

NOx
ppm

NH3
ppm

HC1
ppm

Hg(2+)
Hg/mN

Hg(0)
(xg/m3N

Total Hg
(xg/m N

Hg(2+) Proportion
%

Notes

SI
S2

Inlet
16.0

351
48.8

315
13.1

50.1

6.9
17.4

13.1
4.4

20.0
21.8

34.5
79.8

Humidity: 12.1%
Oxygen Concentration: 4.0 vol%

EXAMPLE 2
[Preparation of P-MoO3(7)-V2O5(0.5)/TiO2]
A TiO2-V2O5-based denitration catalyst (Ti02:V2O5=95.5:0.5 (mass ratio)) was prepared as follows.
Ammonia water with a NH3 content of 25% was added to 3600 g of a metatitanic acid slurry (Ti02 content: 30 mass%), and the pH was adjusted to 6.5, followed by wet-kneading for 2 hours, drying, and furthermore firing at 550°C for 5 hours. Thereby, a titanium oxide powder was obtained. To the powder, an ammonium metavanadate aqueous solution was added so as to make the V2O5 content be 0.5 mass%, and then was sufficiently mixed with the powder. Thereafter, the mixture was dried and fired at 450°C for 4 hours. Thereby, a powder (A) formed of titanium oxide [TiO2]-vanadium oxide [V2O5] was obtained. To 1000 g of the powder (A), 25 g of carboxymethyl cellulose and 12.5 g of polyethylene oxide were put and kneaded together in a kneader for 30 minutes with an adequate amount of water being added thereto, followed by extrusion into a honeycomb shape with 30 mm2, drying and then firing at 500°C for 5 hours. A phosphomolybdic acid aqueous solution was further prepared, and the honeycomb was impregnated therewith so as to make the M0O3 content be 7 mass%. The resultant was fired at 500°C for 3 hours. Thus, a P-MoO3(7)-V2O5(0.5)/TiO2 catalyst was prepared.
[Test for mercury oxidation activityj
As in the case of Example 1, the honeycomb-shaped catalysts 2 for treating exhaust gas prepared as described above were provided at three stages, each catalyst having 4 conduits x 7 conduits in 500-mm length as shown in Fig. 1, and a test was carried out for the mercury oxidation activity.

Exhaust gas samples having the same O2 to NOX features as those shown in Table 1 were allowed to flow under the conditions in Table 3, and the mercury oxidation activity of the catalyst 2 for treating exhaust gas was tested.
[Table 3]

Gas Amount m3N/hr 8.49
Temperature °C 400
Ugs mN/S 2.30
NH3/NOx - 0.9
AV m3N/ m2hr 11.96
o2 % 4.0
H20 % 12.0
Hg M.g/m3N 20
HC1 ppm 50
sox ppm 1000
NOx ppm 350
Table 4 shows the test result. As seen from the result in Table 4, it is understood that, by using the catalyst 2 for treating exhaust gas according to the present invention, 89.1% of mercury was oxidized after passing through the three stages.

[Table 4]

Sampled Position AV NOx NH3 HC1 Hg(2+) Hg(0) Total Hg Hg(2+) Proportion Notes

m3N/m2hr ppm ppm ppm |ig/m3N ug/m3N ug/m3N %

SI Inlet 353 319 51.5 6.3 12.9 19.2 32.8 Humidity: 12.1%
Oxygen Concentration: 4.0 vol%
S2 16.0 38.0 4.4 - 18.8 2.3 21.1 89.1

COMPARATIVE EXAMPLE
[Preparation of MoO3(7)-V2O5(0.5)/TiO2]
A TiO2-V2O5-based denitration catalyst (TiO2:V2Os=95.5:0.5 (mass ratio)) was prepared as follows.
Ammonia water with a NH3 content of 25% was added to 3600 g of a metatitanic acid slurry (Ti02 content: 30 mass%), and the pH was adjusted to 6.5, followed by wet-kneading for 2 hours, drying, and furthermore firing at $50°C for 5 hours. Thereby, a titanium oxide powder was obtained. To the powder, an ammonium metavanadate aqueous solution and an ammonium molybdate aqueous solution were added so as to make the V2O5 ancf MoO3 contents be 0.5 massfo and 7 nmss%, respectively, and men where sufficientry mixed with the powder. Thereafter, the mixture was dried and fired at 450°C for 4 hours. Thereby, a powder (A) formed of titanium oxide [TiO2] -vanadium oxide [V205]-molybdenum oxide [M0O3] was obtained. To 1000 g of the powder (A), 25 g of carboxymethyl cellulose and 12.5 g of polyethylene oxide were put and kneaded together in a kneader for 30 minutes with an adequate amount of water being added thereto, followed by extrusion into a honeycomb shape with 30 mm2, drying and then firing at 500°C for 5 hours. Thus, a MoO3(7)-V2O5/TiO2 catalyst of Comparative Example was prepared.
[Test for mercury oxidation activity]
As in the case of Example 1, the comparative honeycomb-shaped catalysts for treating exhaust gas prepared as described above were provided at three stages, each catalyst having 4 conduits x 7 conduits in 500-mm length as shown in Fig. 1, and a test was carried out for the mercury oxidation activity.

Exhaust gas samples having the same O2 to NOx features as those shown in Table 1 were allowed to flow, and the mercury oxidation activity of the comparative catalyst for treating exhaust gas was tested.
Table 5 shows the test result. As seen from the result in Table 5, it is understood that, by using the comparative catalyst for treating exhaust gas according to the present invention, 79.5% of mercury was oxidized after passing through the three stages.

[Table 5]

Sampled Position AV NOx NH3 HC1 Hg(2+) Hg(0) Total Hg Hg(2+) Proportion _
Notes

m3N/ m2hr ppm ppm ppm \igf m3N (i,g/m3N jj,g/m3N %

SI Inlet 349 320 50.2 6.9 13.0 19.9 34.7 Humidity: 12.1%
Oxygen Concentration: 4.0 vol%
S2 16.0 36.9 7.5 - 15.9 4.1 20.0 79.5

INDUSTRIAL APPLICABILITY
As seen from the results of Example 1, Example 2 and Comparative Example, by using a catalyst for treating exhaust gas according to the present invention, the amount of a highly corrosive mercury-chlorinating agent to be added can be reduced with the mercury oxidation efficiency kept high.
When the catalyst for treating exhaust gas according to the present invention is used, only an addition of a considerably small amount of mercury oxidant suffices for an HCl/HBr spray unit or an NH4CI supply unit for oxidizing mercury. For this reason, flue corrosion due to highly corrosive HC1 can be reduced.
Moreover, when exhaust gas contains several tens ppm of HC1 originating from coal, it is not necessary to install an HC1 spray unit. In that case, the facility cost for safety control measure of HC1 requiring care in handling can be greatly reduced.
Therefore, the catalyst for treating exhaust gas according to the present invention can be used in the method for treating exhaust gas described in Fig. 2.

We Claim :
[I ] A catalyst for treating exhaust gas in which nitrogen oxide in the exhaust gas is
removed upon contact with ammonia serving as a reducing agent, and in which mercury is oxidized using a halogen as an oxidant, the catalyst comprising:
Ti02 as a support;
an oxide of at least one selected from the group consisting of V, W and Mo, which is supported as an active component on the support; and
at least one selected from the group consisting of Bi, P, and compounds containing Bi and/or P, which is supported as a co-catalyst component on the support.
[2] The catalyst for treating exhaust gas according to claim 1, wherein the co-catalyst component is formed of any one of P and a compound containing P.
[3] The catalyst for treating exhaust gas according to claim 1, wherein the co-catalyst
component is formed of any one of Bi and a compound containing Bi.