(12) Ulllted States Patent
`(10) Patent N0.:
`US 6,248,684 B1
`
`Yavuz et al.
`(45) Date of Patent:
`"‘Jun. 19, 2001
`
`U3006248684B1
`
`(54) ZEOLITE-CONTAINING OXIDATION
`CATALYST AND METHOD 014‘ USE
`
`(75)
`
`Inventors: Bulent O. Yavuz, Plainficld; Kenneth
`E. Voss, Somerville; Michel Deeba,
`North Brunswick; John R. Adomaitis,
`,
`Old Bridge; Robert J. Farrauto,
`Wcslficlda all of NJ (US)
`
`_
`.
`(73) Assrgnee: Englehard Corporation, lselln, NJ
`(US)
`
`4,727,052
`4,749,671
`4,757,045
`
`49759918
`13222::
`4,849,399
`,
`,
`4,857,088
`4,872,038
`4,923,835
`4,929,581
`4,934,142
`
`........................... 502/327
`2/1988 Wan el al.
`.
`6/1988 Saito et al.
`7/1988 Turner et a1.
`
`.
`
`q
`717988 Hmmler 9‘ al- -
`13/13:: will]. 6: ai'
`------------------------- 02/303
`7', H
`Ta?
`1 C a' '
`/1989 Joy, III et al.
`.
`8/1989 Mizrah a at.
`.
`10/1989 Gandhi et al.
`.
`5/1990 Travers et al.
`5/1990 Steinwandel et a1,
`6/1990 IILtyashi et all r
`
`502/66
`
`,
`
`( *) Notice:
`
`This patent issued on a continued pros-
`ecution application filed under 37 CPR
`1.53(d), and is subject to the twenty year
`patent
`term provisions of 35 U.S.C.
`154009).
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.SlC. 154(b) by 0 days.
`
`9
`.
`7
`(-1) Apple N0~- 03/255,287
`92
`4
`.
`(2“) F11“
`
`J‘m' 7’ 1994
`
`Related US. Application Data
`.
`.
`.
`.
`(63) Contlnuatlon of application No. 08/038,378, filed on Mar.
`29, 1993, now abandoned, which is a continuatio11-i11-pa1‘t of
`application No. 07/973,461, filed on Nov. 19, 1992, now
`abandoned.
`
`
`
`
`.......
`(51)
`Int. Cl.7 _
`B01] 29/06
`9
`7
`‘
`9
`'2
`9
`7
`(52) US. Cl.
`................................. 502/66, 502/64, 5362/6752;
`(58) Field Of Search .................................. 502/65, 64, 66,
`503/74; 423/2132. 244-11
`
`(56)
`
`References Cited
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`
`(USt continued 011 HCXI page.)
`
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`12/1990 (AU).
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`2/1994 (DE).
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`211233
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`,,
`I
`.
`83133?)
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`
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`OTHER PUBLICATIONS
`HOFIUChI 61 al, “The ElTects of Flow—Through Type Oxida-
`tion Catalysts .
`.
`.
`SAE. paper 900600, Feb, 1990.
`The Effects of Flow—Through Type Oxidation Catalysts on
`the Particulate Reduction of 1990’s Diesel Engines, M.
`HOI'lllChl 61 a], SAE Paper 900600., Feb. 1990.
`
`(Ilist continued on next page.)
`
`Primary Examiner—Tom Dunn
`
`ABSTRACT
`(57)
`.
`.
`.
`i
`.
`.
`,Omdatlon 931313“ COFDPOSIUOHS f?” ”smug @561 Wham
`“Elude Gem and; Opuonaflya 411141134 W311 hwmg a surface
`area of at least about 10 m“/g, and a zeolite, e.g., Beta
`zeolite. Optionally, platinum may be included in the cata-
`lytic material, preferably in amounts which are sufficient to
`promote some gas-phase oxidation of carbon monoxide
`(“CO”) and hydrocarbons (“HC”) but which are limited to
`preclude excessive oxidation of SO2 to 803. Alternatively,
`palladium in any desired amount may be included in the
`catalytic material. The zeolite is optionally doped, e.g.,
`ion-exchanged, with one or more of hydrogen, a platinum
`group metal or other catalytic metals. The catalyst compo-
`sitions may be used in a method to treat diesel engine
`exhaust by contacting the hot exhaust with the catalyst
`composition to promote the oxidation of gas-phase CO and
`HC and of the volatile organic fraction component of
`.
`.
`particulates 1n the exhaust.
`
`23 Claims, HI Drawing Sheets
`
`1
`
`JM 1015
`
`3,151,505
`3,331,190
`3,864,452
`3 93,572
`
`4,053,556
`4,123,391
`4,134,860
`4,171,288
`4,171,289
`4,189,404
`4,200,552
`4,297,328
`4,407,785
`4,418,046
`4,477,417
`4,492,769
`475297828
`4,568,655
`4,581,343
`4,613,583
`4,621,071
`4,624,940
`4,683,214
`4,707,341
`4,711,864
`4,714,694
`
`.
`
`.............................. 55/63
`
`.
`
`_
`
`12/1964 Beck e1 (11.
`7/1967 Glew et all
`2/1975 Chi et a1.
`.
`11/1976 Hindin et a1.
`10/1977 Acres .
`.
`10/1978 Noguchi ct al.
`1/1979 Hindin ct a].
`........................ 252/466
`10/1979 Keith et al.
`.......................... 252/462
`10,4979 Wheelock.
`.
`2/1980 Keith et a1,
`4/1980 Nogllchi er a1,
`10/1981 Ritschel‘ et al. .
`10/1983 Pfeflerle .
`.
`11,11,983
`Izumo et al.
`-
`10/1984 Domesle et al.
`1/1985 Blanchard 94 film
`7/1985 Autos Ct 31-
`------------------------- 585/823
`2/1986 Olcck ct al.
`........................... 502/66
`4/1986 Blanchard et a1.
`.
`9/1986 Koch et al. .
`“/1986 Blanchard et al. .
`11/1986 W'an et al. .
`7/1987 Angevine et a].
`11/1987 Koch et al. .
`12/1987 Pellet et al.
`12/1987 Wan et al. .
`
`..................... 502/66
`
`............................ 502/65
`
`1
`
`JM 1015
`
`

`

`US 6,248,684 B1
`
`Page 2
`
`.
`
`.
`
`.
`
`US. PATENT DOCUMENTS
`
`
`7/1990 Barcscl C1. 31. ................ 123/440
`4,944,273
`10/1990 Byl‘ne ............................ 423/239
`4,961,917
`10/1990 Green et a1.
`.
`4,962,075
`11/1990 Green et al- ~
`459737399
`..................... 423/2132
`2/1991 Diwell et al.
`4.996,180 *
`3/1991 Horiuchi et al.
`.
`5,000,929
`3/1991 Lussier et all.
`.
`5,002,742
`4/1991 10791114 91 -
`5,008,090
`
`5/1991 'lhkeshima ~~~~~~~~~~~~~~
`5,017,538
`
`6/1991 Speronello et a1.
`5,024,981
`9/1991 Dunn et a].
`.
`5,051,244
`10/1991 Jorgcnscn Ct a1.
`5,059,575
`12/1991 H01‘111Cl11 Ct al.
`5,071,816
`1/1992 Dunne .
`5,078,979
`1/1992 Bediord et a1.
`5,081,095
`4/1992 Beck et al.
`.
`5,102,838
`4/1992 Horiuchi et al.
`5,106,802
`6/1992 Putil e1 11].
`.
`5,125,231
`.
`9/1992 Deeba el al.
`5,145,825
`10/1992 Montrevil et a1.
`5,155,077
`.
`10/1992 Domesle et a1.
`5,157,007
`5,164,350 * 11/1992 Abe et €11.
`.............................. 502/66
`5,206,196 *
`4/1993 Nakano at al.
`. 502/65
`
`
`.
`. 502/79
`5,234,876
`8/1993 Swaroop ct al.
`~ 502/73
`33236879
`874993 1110116 4 3L
`
`. 502/66
`5,244,852
`9/1993 Lachman et a].
`............................. 502/67
`5,248,643
`9/1993 Patil et a].
`5,284,638
`2/1994 Hertl et al.
`........................ 423/2451
`. 585/850
`5,292,991
`3/1994 Lachman et a].
`
`422/180
`5,296,198
`3/1994 Abe et al,
`........
`7/1994 Beckmeyer et a].
`. 502/66
`5,330,945
`
`
`11/1994 Ramachandran et al.
`585/829
`5,365,011
`. 502/304
`...........
`5,491,120 *
`2/1996 Voss 61 0.1.
`
`..................... 502/347
`5,504,052
`4/1996 Rim/110 el al.
`5,538,697
`7/1996 Abe ct a1.
`............................ 422/171
`5,538,698
`7/1996 Abe et a1.
`.
`422/174
`
`2/1997 Rizkalla ........................ 502/347
`5,602,070
`5,772,972
`6/1998 Hepburn et a].
`.................. 428/2135
`
`.
`
`..................... 502/66
`
`FOREIGN PATENT DOCUMENTS
`
`31,1323 $3
`3:53:
`11,1990 (1.312) .
`397411
`11/1990 (EP) .
`399891
`12/1990 (EP).
`404385
`0404385 * 12/1990 (EP) .
`449423
`10/1991
`(PP) _
`462593
`124991 (Pp) _
`............................... 423/2132
`0459396 * 12/1991 (EP)
`
`0 48507795142
`333% Egg;
`BOND/5336
`0 488 250
`6/1992 (EP)
`.............................. B01D/53/36
`0 491 360 A1
`6/1992 (EP) .
`499931
`8/1992 (EP) .
`921021614
`8/1992 (EP) .
`0 503 500 A1
`9/1992 (EP) .
`503500
`9,1992 (EP) I
`508513
`10/1992 (PP) _
`0508513 * 10/992 (PP) '
`0499931
`2/1993 (EP)
`0559021
`2/1993 (EP)
`0 369 576
`6/1994 (EP)
`0 485 119 B1
`5/1995 (EP)
`0 69143121
`1",1996 (EP)‘
`0 638 710 B1
`8199? (EP)
`2546770
`12/1984 (PR) _
`1060424
`3/1907 (GB) I
`1071373
`6/1967 (GB) .
`1551348
`12/1976 (GB) .
`
`,
`.............................. B01D/53/36
`BO1D/53/36
`
`B01J/29/06
`.............................. F01N/3/20
`,
`................................. F01N/3/20
`
`Bo1J/29/24
`502/65
`
`4/1991 (GB) .
`2236493
`1/1981 (JP) .
`56—2920
`1/1981 (JP) .
`56-5419
`8/1984 (JP).
`142851
`8/1985 up) _
`60—147240
`8/1987 (JP) ................................... 423/2132
`2187111 *
`5/1939 (JP) _
`1.139144
`6/1989 (JP) I
`1—155611
`5/1990 (JP) I
`2—126936
`10/1990 (JP)
`2251247
`3270732 * 12/1991 (JP)
`5317701
`12/1993 (JP) .
`67126165
`5/1994 (JP) .
`67210163
`8/1994 (JP) I
`6-210164
`8/1994 (11)) .
`6—312132
`11/1994 (J1!) I
`7402957
`4/1995 (JP) _
`7-88364
`4/1995 (JP) _
`7-96178
`4/1995 (J13) .
`7—155613
`6/1995 (JP) I
`7—185326
`7/1995 (JP) .
`8—10566
`1/1996 (J13) I
`8410613
`1/1996 (JP) I
`8799033
`4/1996 (JP) I
`wog000441
`1/1990 (“70) I
`WO 94/01926
`1,1994 (“70) I
`wo 94/11623
`5/1994 (wo) ............................... 1*‘01N/‘3/20
`W0 94/22564
`10/1994 (“70) I
`WO 96/15992
`5/1996 (W0) _
`WO 96/39576
`12/1996 (xx/0) I
`WO 96/40419
`12/1996 (W0) I
`WO 97/00119
`1/1 997 (“70) _
`
`I
`OTHER PUBLICMIONS
`.
`.
`.
`15- Feeley et 41, “Abatement 01 NOX from Diescl EIIngSI
`Status and Technical Challenges", SAE Technical Paper
`Series, No. 950747, Feb. 1995.
`.
`_
`.
`,
`_
`RH. Engler et 81, “Reduction 01 Exhaust Gas Emlssmns by
`Using Hydrocarbon Adsorbcr Systems”, SAE Technical
`Paper Ser1es, No. 930738, Mar. 1993.
`S. Kagawa et al, “Cocation Effect in Catalytic Property of
`Copper
`Ion—Exchanged ZSM—D Zeohtes for the D1rect
`Decomposition of Nitrogen Monoxide”, Chemistry Letters,
`pp.407—410, 1991.
`.
`.
`D W E
`II,
`.
`.
`.
`rcch, ZcoIlitc Molecular Sicvcs, Structure, Chc-nns-
`try and Use”, .1. W1ley & bons, New York, 1974, pp. 305, 309
`and 348.
`RA. Jacobrs and J.A.I MIartens, I“Synthesis of High—Silica
`AIM/1111954046 26011165 '= 5119165 “1 Surface 5016906 and
`Catalysls, v01. 33, Ed. B. Delmon and J.T. Yates, Else-Vler,
`Amsterdam—Oxford—New York—Tokyo, 1987, Table of Con-
`tents pp. V41X.
`.
`.
`.
`.
`“
`M. IwamoIto, Decompnsnion of N1trogen Ox1des by Con-
`tact Reaction”, Petrotech 12(11), pp. 888—892, (1989).
`of
`M.
`lwarnoto,
`“NOX Reduction Characteristics
`l
`PT ZQM 5 C
`tW'th D.
`1 E
`.
`E 11
`,,
`IQAE
`‘ ‘
`_’
`.
`'ata YS
`‘
`‘3“
`"gm X “5‘ = -*
`(Japan) Rcvmw, 16,139 21723, (19951
`Burch ct ,1 An Investigation of the Mechanism of the
`Selective Catalytic Reduction of NO on Various Metal/
`.
`-,
`.
`.
`_
`.
`,
`.
`ZSM—S Latalysts. Reactlon of H2/NU Mlxtures , Cataly51s
`Letters 27 (1994), pp. 177—186.
`
`* cited by examiner
`
`2
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 1 0f 10
`
`US 6,248,684 B1
`
`'00 % GAS PHASE HC CONVERSION
`
`80
`
`E-l
`
`60
`
`4O
`
`20
`
` o . '
`
`
`IOO
`I50
`200 250
`300 350
`400 450
`500 550 600
`
`CATALYST INLET TEMP. (DEG c)
`
`_._ SAMPLE c-2. 0.59lft3Pt
`+ SAMPLE c-s. 2.09/ft3Pt
`
`_,,,_ SAMPLE C—l. No PI
`_._ SAMPLE E—I. 2.59/f13Pt
`
`FIG.
`
`I
`
`3
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 2 0f 10
`
`US 6,248,684 B1
`
`°/o CO CONVERSION
`
`IOO
`
`6O
`
`40
`
`20
`
`—20
`
`IOO
`
`I50
`
`200 250 300 350 400 450 500 550 600
`
`CATALYST INLET TEMPERATURE (DEG C)
`
`__.__SAMPLE (3-3. 2.Og/ft3P1 __4_ SAMPLE E-l. 2.5g/ft3P1
`
`FIG. 2
`
`4
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 3 0f 10
`
`US 6,248,684 B1
`
`°/o VOF REMOVAL
`
`C-3
`
`I00
`
`80
`
`60
`
`40
`
`20
`
`O
`
`IOO
`
`I50
`
`200 250 300 350 400 450 500 550 600
`
`CATALYST INLET TEMPERATURE (DEG C)
`
`+ SAMPLE c-s. 2.09Ifl3Pf
`
`_,__SAMPLE E-l. 2.59/ft3P1
`
`FIG. 3
`
`5
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 4 0f 10
`
`US 6,248,684 B1
`
`% TPM REMOVAL
`
`IOO
`
`E-|
`
`50 v\\
`0
`
`C—3
`
`\
`
`E4
`
`—50
`
`-IOO
`
`-I50
`
`-200
`
`-250
`
`DO I50
`
`200 250 300 350 400 450 500 550 600
`
`CATALYST INLET TEMPERATURE (DEG C)
`
`_._ SAMPLE c—s. 2.0glf13Pi
`
`_._ SAMPLE E—l. 2.5g/ft5P1
`
`FIG. 4
`
`6
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 5 0f 10
`
`US 6,248,684 B1
`
`803 PLUS H20 (SULFURIC ACID) EMISSIONS (g/bhp-hr)
`
`0.25
`
`0.2
`
`0.I5
`
`0.05
`
`0.l
`
`O
`
`IOO
`
`ISO
`
`200 250 300 350 400 450 500 550 600
`
`CATALYST INLET TEMPERATURE (DEG C)
`
`__._BASE LINE — N0 CATALYST +SAMPLE E-l.2.5 glfI3PI
`
`+SAMPLE c-s, 2.0 glfl3PI
`
`FIG. 5
`
`7
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 6 0f 10
`
`US 6,248,684 B1
`
`onmmak<mNQEMF
`
`00mnwvOwnmPN
`
`
`
`U:.x.zo_mmm>zoo
`
`00.
`
`8
`
`mm.
`
`mm8
`
`\ON
`
`o¢
`
`0
`
`
`
`
`
`E02.Tom._n_2<mlTaminoMm.mdzfiilEmEmtm.35&3ll
`
`0.0.“—
`
`8
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 7 0f 10
`
`US 6,248,684 B1
`
`8vmmDH<mmm2m.—.
`
`8mmmv0%EN
`
`To
`
`mm.mm.
`
`
`
`OI.x.zmem>zOU
`
`oo.
`
`8
`
`8
`
`8
`
`8
`
`0
`
`
`
`r".0:Junomn_n_2<m*EmEmQO.Numunisaw_EmEmwN.Mumm3n=2<m.
`
`
`
`
`
`9
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 8 0f 10
`
`US 6,248,684 B1
`
` 20.2ngNow.3
`
`OO—
`
`00
`
`cm
`
`0v
`
`ON
`
`000mN¢
`
`Can
`
`th
`
`8Vmmnh<mmn§m._.
`
`EE86E02.Tomisqm.N-m¢z<m
`
`ITll
`
`.mum@573
`
`EEgm
`
`III
`
`m.07...
`
`10
`
`10
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 9 0f 10
`
`8,
`
`1B
`
`6.,uE025E30.To312%..N-m:3mIT[T
`
`
`
`
`
`
`
`mmGE
`
`8mmmw8m
`
`QNEEEmEE
`
`.3.“:3
`
`a:qu
`
`
`
`00.x.zo_wmm>zov
`
`oo.
`
`8mm.9
`
`om/mm.8
`
`Toom-
`
`ohm
`
`ow-
`
`o
`
`11
`
`11
`
`
`

`

`US. Patent
`
`Jun. 19, 2001
`
`Sheet 10 0f 10
`
`US 6,248,684 B1
`
`oO Q
`
`o 8
`
`0ot
`
`o
`
`O 9 L
`
`I.
`
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`
`8
`¢
`
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`
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`
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`
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`
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`
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`
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`
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`
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`
`“P
`
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`
`2‘9
`I—
`
`<+
`
`— 0
`
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`
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`s:
`
`8
`
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`g
`
`2
`
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`9
`
`8
`
`8
`
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`
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`
`12
`
`12
`
`

`

`US 6,248,684 B]
`
`1
`ZEOLITE-CONTAINING OXIDATION
`CATALYST AND METHOD OF USE
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This is a continuation of application Ser. No. 08/038,378
`filed Mar. 29, 1993, now abandoned which is a continuation
`in part of Ser. No. 07/973,461 filed Nov. 19, 1992, now
`abandoned.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`This invention relates to a catalyst composition and
`method for the oxidation of oxidizeable components of
`diesel engine exhaust, and more specifically to the treatment
`of such diesel exhaust to reduce the content of particulates
`and other pollutants discharged to the atmosphere.
`2. Background and Related Art
`As is well-known, diesel engine exhaust is a heteroge-
`neous material which contains not only gaseous pollutants
`such as carbon monoxide (“CO”) and unburned hydrocar-
`bons (“IIC”), but also soot particles which comprise both a
`dry, solid carbonaceous fraction and a soluble organic frac-
`tion. The soluble organic fraction is sometimes referred to as
`a volatile organic fraction (“VOF”), which terminology will
`be used herein. The V017 may exist in diesel exhaust either
`as a vapor or as an aerosol
`(fine droplets of liquid
`condensate) depending on the temperature of the diesel
`exhaust.
`
`Oxidation catalysts comprising a platinum group metal
`dispersed on a refractory metal oxide support are known for
`use in treating the exhaust of diesel engines in order to
`convert both HC and CO gaseous pollutants and
`particulates, i.e., soot particles, by catalyzing the oxidation
`of these pollutants to carbon dioxide and water. One problem
`faced in the treatment of diesel engine exhaust is presented
`by the presence of sulfur in diesel fuel. Upon combustion,
`sulfur forms sulfur dioxide and the oxidation catalyst cata-
`lyzes the S02 to SO3 (“sulfates”) with subsequent formation
`of condensiblc sulfur compounds, such as sulfuric acid,
`which condense upon, and thereby add to,
`the mass of
`particulates. The sulfates also react with activated alumina
`supports to form aluminum sulfates, which render activated
`alumina-containing catalysts inactive. In this regard, see
`US. Pat. No. 4,171,289 at column 1, line 39 et seq. Previous
`attempts to deal with the sulfation problem include the
`incorporation of large amounts of sulfate-resistant materials
`such as vanadium oxide into the support coating, or the use
`of alternative support materials such as a-alumina (alpha),
`silica and titania, which are sulfate-resistant materials.
`The prior art also shows an awareness of the use of
`zeolites,
`including metal-doped zeolites,
`to treat diesel
`exhaust. For example, U.S. Pat. No. 4,929,581 discloses a
`filter for diesel exhaust, in which the exhaust is constrained
`to flow through the catalyst walls to filter the soot particles.
`Acatalyst comprising a platinum group metal-doped zeolite
`is dispersed on the walls of the filter to catalyze oxidation of
`the soot to unplug the filter.
`As is well-known in the art, catalysts used to treat the
`exhaust of internal combustion engines are less effective
`during periods of relatively low temperature operation, such
`as the initial cold-start period of engine operation, because
`the engine exhaust is not at a temperature sufficiently high
`for efficient catalytic conversion of noxious components in
`the exhaust. To this end, it is known in the art to include an
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`adsorbent material, which may be a zeolite, as part of a
`catalytic treatment system in order
`to adsorb gaseous
`pollutants, usually hydrocarbons, and retain them during the
`initial cold-start period. As the exhaust gas temperature
`increases, the adsorbed hydrocarbons are driven from the
`adsorbent and subjected to catalytic treatment at the higher
`temperature. In this regard, see for example U.S. Pat. No.
`5,125,231 which discloses (columns 5—6) the use of plati-
`num group metal-doped zeolites as low temperature hydro-
`carbon adsorbents as well as oxidation catalysts.
`SUMMARY OF THE INVENTION
`
`Generally, in accordance with the present invention, there
`is provided a catalyst composition and a method for oxidiz-
`ing oxidizeable components of diesel engine exhaust in
`which at least some of a volatile organic fraction of the
`diesel exhaust is converted to innocuous materials, and in
`which gaseous IIC and CO pollutants may also be similarly
`converted. The objectives of the invention are attained by an
`oxidation catalyst comprising a catalytic material compris-
`ing a mixture of high surface area ceria, a zeolite and,
`optionally, a high surface area alumina. The catalytic mate-
`rial optionally may carry a low loading of platinum catalytic
`metal dispersed thereon or palladium catalytic metal dis-
`persed thereon. Alternatively, or in addition, the zeolite of
`the catalyst composition maybe doped, e.g., ion-exchanged,
`with a catalytic moiety such as one or more of hydrogen ion,
`platinum, copper, nickel, cobalt, iron, etc. The method of the
`invention is attained by flowing a diesel engine exhaust, e.g.,
`the exhaust of a diesel-powered automobile or light truck,
`into contact under oxidation reaction conditions with a
`
`catalyst composition as described above.
`invention
`Specifically,
`in accordance with the present
`there is provided a catalyst composition for treating a diesel
`engine exhaust stream containing a volatile organic fraction,
`which composition comprises a refractory carrier on which
`is disposed a coating of a catalytic material comprising a
`catalytically effective amount of ceria and, optionally, a
`catalytically effective amount of alumina, each having a
`BET surface area of at least about 10 mZ/g, preferably a
`surface area of from about 25 mZ/g to 200 m /g, and a zeolite,
`for example, Beta zeolite or a zeolite selected from the group
`consisting of Y—zeolitc, pentasil (e.g., ZSM-S), Mordenite,
`and mixtures thereof.
`
`In one aspect of the present invention, the zeolite com-
`prises a three-dimensional zeolite characterized by pore
`openings whose smallest cross-sectional dimension is at
`least about 5 Angstroms and having a silicon to aluminum
`atomic ratio (“SizAl atomic ratio”) of greater than 5, e.g., a
`SizAl atomic ratio of from about 5 to 400.
`
`In another aspect of the invention, the zeolite comprises
`from about 10 to 90, preferably from about 20 to 70, percent
`by weight,
`the alumina comprises from about 60 to 5,
`preferably from about 50 to 20, percent by weight, and the
`ceria comprises from about 60 to 5, preferably from about 50
`to 20, percent by weight, of the combined weight of the
`zeolite, the alumina and the ceria.
`Yet another aspect of the invention provides for the zeolite
`to be doped with a catalytic moiety, e.g., ion-exchanged or
`impregnated, with an ion or with a neutral metal-containing
`species selected from the group consisting of one or more of
`hydrogen, platinum, rhodium, palladium,
`ruthenium,
`osmium,
`iridium, copper,
`iron, nickel, chromium and
`vanadium, preferably, one or both of platinum and iron.
`Still another aspect of the invention provides that the
`refractory carrier has a plurality of parallel exhaust [low
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`US 6,248,684 B]
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`3
`passages extending therethrough and defined by passage
`walls on which the catalytic material is coated, and further
`comprising either dispersed platinum carried on the catalytic
`material in an amount of from about 0.1 to about 60, e.g., 0.1
`to 15, preferably 0.1 to 5, g/ft3 or dispersed palladium
`carried on the catalytic material in a quantity of from about
`0.1 to 200, preferably 20 to 120, g/ft3.
`In accordance with the method aspect of the present
`invention, there is provided a method for treating a diesel
`engine exhaust stream containing a volatile organic fraction,
`the method comprising contacting the stream with any of the
`catalyst compositions described above under oxidizing con-
`ditions including a temperature high enough to catalyze
`oxidation of at least some of the volatile organic fraction.
`For example, the temperature of the exhaust stream initially
`contacted with the catalyst composition may be from about
`100° C. to 800° C.
`
`DEFINITIONS
`
`As used herein and in the claims, the following terms shall
`have the indicated meanings.
`The term “BET surface area” has its usual meaning of
`referring to the Brunauer, Emmett, Teller method for deter-
`mining surface area by N2 adsorption. Unless otherwise
`specifically stated, all references herein to the surface area of
`a ceria, alumina or other component refer to the BET surface
`area.
`
`The term “activated alumina" has its usual meaning of a
`high BET surface area alumina, comprising primarily one or
`more of y-, 0- and o-aluminas (gamma, theta and delta).
`The term “catalytically effective amount” means that the
`amount of material present is sufficient to affect the rate of
`reaction of the oxidation of pollutants in the exhaust being
`treated.
`
`The term “inlet temperature” shall mean the temperature
`of the exhaust, test gas or other stream being treated imme-
`diately prior to initial contact of the exhaust, test gas or other
`stream with the catalyst composition.
`The term “doped” used to refer to a zeolite being doped
`with a metal or hydrogen, and the terms “dope” or “doping"=
`used in the same context, means that the metal or hydrogen
`moiety is incorporated within the pores of the zeolite, as
`distinguished from being dispersed on the surface of the
`zeolite but not to any significant degree within the pores of
`the zeolite. Doping of a zeolite is preferably carried out by
`known ion-exchange techniques in which a zeolite is repeat-
`edly flushed with a solution containing metal cations (or an
`acid to provide hydrogen ions), or the zeolite pores are
`flooded with such solution. However,
`the defined terms
`include any suitable technique for incorporating a catalytic
`moiety, e.g., one or more metals as ions or neutral metal-
`containing species or hydrogen ions, within the pores of the
`zeolite, especially by exchange or replacement of cations of
`the zeolite.
`
`The term “washcoat” refers to a thin, adherent coating of
`a material, such as the catalytic material of the present
`invention, disposed on the walls forming the parallel gas
`flow passages of a carrier, which is typically made of a
`refractory material such as eordierite or other oxide or oxide
`mixture, or a stainless steel.
`Reference herein or in the claims to ceria or alumina being
`in “bulk” form means that the ceria or alumina is present as
`discrete particles (which may be, and usually are, of very
`small size, e.g., 10 to 20 microns in diameter or even
`smaller) as opposed to having been dispersed in solution
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`the thermal
`form into another component. For example,
`stabilization of ceria particles (bulk ceria) with alumina as
`described in US. Pat. No. 4,714,694, results in the alumina
`being dispersed into the ceria particles and does not provide
`the dispersed alumina in “bulk” form,
`i.e., as discrete
`particles of alumina.
`'I'he abbreviation “'I'GA” stands for thermogravimetric
`analysis, which is a measure of the weight change (e.g.,
`weight loss) of a sample as a function of temperature and/or
`time. The abbreviation “D'I‘A” stands for dilferential thermal
`
`analysis, which is a measure of the amount of heat emitted
`(exotherm) or absorbed (endotherm) by a sample as a
`function of temperature and/or time.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS. 1—5 show graphically the results of the engine test
`of the catalysts of Example 1, set forth numerically in
`TABLE I-B: specifically;
`FIG. 1 is a plot of gas-phase HC conversion for sample
`E-l and comparative samples C-1, C-2 and C-3 as a function
`of catalyst inlet temperature;
`FIG. 2 is a plot of carbon monoxide conversion for
`samples E-l and C-3 as a function of catalyst inlet tempera-
`ture;
`
`FIG. 3 is a plot of VOF removal for samples E—l and (3-3
`as a function of catalyst inlet temperature,
`FIG. 4 is a plot of the reduction of the total mass of
`particulates (TMP) for samples E-l and C-3 as a function of
`catalyst inlet temperature;
`FIG. Sis a plot of 503 and H20 emissions for samples E-1
`and C-3 and for untreated exhaust as a function of catalyst
`inlet temperature;
`FIGS. 679 are plots of hydrocarbon, SO2 and CO con-
`version for samples E-2, E-3 and C-4 of Example 2: spe-
`cifically;
`FIG. 6 is a plot of gas-phase hydrocarbon conversion as
`a function of catalyst inlet
`temperature at 50,000 space
`velocity for samples E-2, E-3 and C-4;
`FIG. 7 is a plot of gas-phase hydrocarbon conversion as
`a function of catalyst inlet
`temperature at 90,000 space
`velocity for samples E-2, E-3 and C-4;
`FIG. 8 is a plot ofSOE conversion as a function of catalyst
`inlet temperature at 90,000 space velocity for samples E-Z,
`E-3 and C-4;
`FIG. 9 is a plot of CO conversion as a function of catalyst
`inlet temperature at 90,000 space velocity for samples E-2,
`E-3 and C-4; and
`FIG. 10 is an exemplary TGArDTA plot of sample E-8 of
`Example 5.
`DETAILED DESCRIPTION 01" THE
`INVENTION AND PREFERRED
`EMBODIMENTS THEREOF
`
`invention provides an oxidation catalyst
`The present
`composition which is efiective for treating diesel engine
`exhaust, particularly with regard to reducing the total par-
`ticulates and HC and CO content of the exhaust. The
`carbonaceous particulates (“soot”) component of diesel
`engine exhaust is, as discussed above, known to be com-
`prised of relatively dry carbonaceous particulates and a
`volatile organic fraction (“VOF”) comprising high molecu-
`lar weight hydrocarbons resulting from unburned and par-
`tially bumcd diesel fuel and lubricating oil. The VOF is
`present in the diesel exhaust as either a vapor phase or a
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`US 6,248,684 B]
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`5
`liquid phase, or both, depending on the temperature of the
`exhaust. Generally, it is not feasible to attempt to remove or
`treat the dry, solid carbonaceous particulates component of
`the total particulates by catalytic treatment, and it is the VOF
`component which can be most effectively removed by
`conversion Via utilization of an oxidation catalyst.
`Therefore,
`in order to reduce the total particulates dis-
`charged so as to meet present and impending Government
`regulations concerning maximum allowable total
`particulates, the volatile organic fraction, or at least a portion
`thereof, must be oxidized to innocuous CO2 and H20 by
`being contacted with an oxidation catalyst under suitable
`reaction conditions. The required US. Govemment limits
`for 1991 on HC, CO, nitrogen oxides (“NOx”) and total
`particulate emissions (“TPM”) in diesel engine exhaust have
`been largely met by suitable engine design modifications.
`For 1994 the HC, CO and N01. limits remain unchanged
`from 1991 standards but the upper limit on TPM will be
`reduced from the 1991 level of 0.25 grams per horsepower-
`hour (“g/’l-lP-hr”) to 0.10 gfl-lP-hr. Although the oxidation ,
`catalysts of the present invention, when employed as a diesel
`exhaust treatment catalyst, are efieetive for etfectuating a
`reduction in total particulates, they are also capable, espe-
`cially with the optional addition of platinum or other cata-
`lytic metals as described below, of providing the added
`advantage of also oxidizing a portion of the HC and CO
`contained in the gaseous component of the diesel engine
`exhaust. When sulfur or sulfur compounds are present in the
`exhaust in significant quantities, platinum is eliminated or
`used in limited amounts so as not to promote the unwanted
`died of excessive oxidation of 802 to 803.
`Further, the zeolite component of the present invention is
`able to trap hydrocarbon molecules which might otherwise,
`during periods when the exhaust gas is relatively cool,
`escape untreated from the catalyst. It is believed that the
`trapped hydrocarbons are either oxidized within the zeolite
`or released from the zeolite only when the temperature of the
`catalyst composition is high enough to effectively catalyze
`oxidation of the trapped hydrocarbons, or both.
`Abasic and novel characteristic of the present invention
`is believed to reside in a catalyst composition comprising the
`defined combination of ceria, zeolite and, optionally,
`alumina, and one or both of the optional doping of the zeolite
`and dispersal of the catalytic metals, platinum or palladium
`as part of the composition and in the use thereof to treat
`diesel exhaust streams.
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`As noted above, the bulk ceria and the bulk alumina may
`each have a surface area of at least about 10 mz/g, for
`example, at least about 20 mzx'g. Typically, the bulk alumina
`may have a surface area of from about 120 to 180 mZ/g and .,
`the bulk ceria may have a surface area of from about 70 to
`150 mg/g.
`that a diesel oxidation catalyst composition
`The fact
`which may contain activated alumina as a major component
`thereof has prove-n to be successful is in itself surprising, in
`View of the consensus of the prior art that alumina, if used
`at all in diesel oxidation catalysts, must be a low surface area
`alumina (CL-alumina) and/or be used in conjunction with
`sulfate-resistant refractory metal oxides such as zirconia,
`titania or silica.
`It has nonetheless been found that
`in
`accordance with one aspect of the present
`invention,
`surprisingly, a catalyst composition comprising a combina-
`tion of high surface area ceria, a suitable zeolite, and,
`optionally, high surface area alumina, provides a catalytic
`material which effectively catalyzes the oxidation of the
`volatile organic fraction so as to provide a significant
`reduction in total particulates in diesel engine exhaust and is
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`capable of adsorbing and catalyzing the combustion of
`gaseous hydrocarbons. It should be noted that the prior art
`generally considers refractory base metal oxides used in
`diesel oxidation catalysts to be merely supports for the
`dispersal
`thereon of catalytically active metals such as
`platinum group metals. In contrast, the present invention
`teaches that a catalytic material comprising ceria and,
`optionally, alumina of sufficiently high surface area (10 n12/g
`or higher) and zeolite, dispersed on a suitable carrier,
`provides a durable and effective diesel oxidation catalyst.
`It has further been found that beneficial effects are
`attained by the optional incorporation of platinum or palla-
`dium in the catalyst composition, provided that in the ease
`of platinum, the platinum is present at loadings much lower
`than those conventionally used in oxidation catalysts. If the
`catalytic metal platinum or palladium is added to the cata-
`lytic composition, it serves to catalyze the oxidation of
`gas-phase HC and CO pollutants as an added benefit.
`However, such catalytic metal is not needed to supplement
`the action of the ceria-zeolite or ceria-alumina-zeolite cata-
`lytic material in reducing total particulate emissions. Neither
`the platinum or palladium catalytic metal nor the metals or
`hydrogen used to dope the zeolite appear to significantly
`affect the rate of particulates conversion.
`The Zeolite
`
`The zeolite employed serves both to catalyze the oxida-
`tion of VOF and to crack the larger VOF molecules and,
`during periods of relatively low temperature operation, to
`trap gas-phase hydrocarbons within the zeolite pores. If the
`zeolite has been doped with one or more catalytic metals or
`hydrogen, the trapped gas-phase hydrocarbons are brought
`into intimate contact with the catalytically active cations
`which facilitates oxidation of the hydrocarbons, In any case,
`the zeolite pores also serve to retain some of the gas-phase
`hydrocarbons during start-11p or other periods when the
`catalyst
`is relatively cool and therefore less effective in
`catalyzing oxidation reactions, and to release the hydrocar-
`bons only when the catalyst has been heated to higher
`temperatures. The higher
`temperatures impart sufficient
`energy to the trapped hydrocarbon molecules to enable them
`to escape the zeolite pores, but also enhance oxidation of the
`hydrocarbons in contact with the catalyst. The zeolite there-
`fore serves not only as a catalyst for VOF oxidation, but as
`a hydrocarbon filter which traps hydrocarbons during peri-
`ods of relatively low temperature and concomitant 10w
`catalytic activity and retains them until they can be effi-
`ciently oxidized by the catalyst during periods of relatively
`high temperature.
`The Carrier (Substrate)
`The carrier used in this invention should be relatively
`inert with respect to the catalytic composition dispersed
`thereon. The preferred carriers are comprised of ceramic-
`like materials such as cordierite, ct-alumina, silicon nitride,
`zirconia, mullite, spodumene, alumina-silica-magnesia or
`zirconium silicate, or of refractory metals such as stainless
`steel. The carriers are preferably of the type sometimes
`referred to as honeycomb or monolithic c