Catalysts for low-temperature destruction of volatile...

Details Catalysts for low-temperature destruction of volatile... Catalysts for low-temperature destruction of volatile...

1999-12-20

2002-10-01

Langel, Wayne A. (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S304000, C502S308000, C502S324000, C502S326000, C502S330000, C502S331000, C502S344000, C502S345000, C502S349000, C502S350000, C423S245300

Reexamination Certificate

active

06458741

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to catalysts for destruction of volatile organic compounds (VOCs).
Contamination of the environment by volatile organic compounds (VOCs) is of great concern. VOCs originate in many ways, including spray painting and engine maintenance (degreasing and fuel line repair), indoor air decontamination, dry cleaning, food processing (grills and deep fryers), fume hoods, residential use and solvent-intensive industrial processes. VOCs have direct and secondary (e.g. photochemical smog) effects on health and the environment.
Direct methods for removing VOCs from contaminated air require heating the air stream to relatively high temperatures to incinerate the contaminants. The cost required to maintain such elevated temperatures (around 815 to 925° C.) and to cool the surroundings can be unacceptably high.
Various catalysts have been studied for their use in lower-temperature removal of VOCs (see, for example, Spivey, J. J. (1987) Ind. Eng. Chem. Res. 26:2165-2180). The catalytic properties of ceria and CeO
2
containing materials have been reviewed (Trovarelli, A. (1996) Catal. Rev. Sci. Eng. 38(4):439-520; Bernal, S. et al. (1999) Catal. Today 50:175; Trovarelli, A. et al. (1999) Catal. Today 50:353-356). Pure CeO
2
is reported to be active for the oxidation of CO over the temperature range of 200° to 500° C. (Liu, W. and Flytzani-Stephanopoulos, M. (1995) J. Catal. 153:304-316). However, temperatures of at least 300° C. were reported to be necessary for methane oxidation using compositions such as Ce
0.2
Zr
0.8
O
x
, Cu
0.08
[Ce(La)]
0.92
O
x
, Cu
0.5
[Ce(La)]
0.5
O
x
and Cu
0.5
Zr
0.5
O
x
(where Ce(La) indicates cerium containing 1.5 wt % lanthanum) (Liu, W. and Flytzani-Stephanopoulos, M. (1995) J. Catal. 153:304-316).
In a mixture of CO and NO, CeO
2
can simultaneously oxidize CO and reduce NO to produce CO
2
and N
2
. This quality has led to the application of CeO
2
in three-way catalysts for automotive exhaust systems. In this capacity, CeO
2
is used in combination with other metals to remove unburned hydrocarbons, CO, and NO (Trovarelli, A. (1996) Catal. Rev. Sci. Eng. 38(4): 439-520).
Cerium oxide doped with 10% Zr, 50% Zr, 4.5% La or 10% La, and cerium oxide (doped with Zr or La as above)-supported silver (2-5% Ag) or copper (5-15%) catalysts have been studied for the combustion of methane (Kundakovic, Lj. and Flytzani-Stephanopoulos, M. (1998) J. Catal. 179:203-221). Temperatures of at least 400° C. were required for any appreciable oxidation of methane using these materials.
CeO
2
—ZrO
2
mixed oxides in proportions of Ce
0.92
Zr
0.08
O
2
to Ce
0.5
Zr
0.5
O
2
, and Ce
0.76
Zr
0.19
(Mn or Cu)
0.05
O
2−x
, have been reported for use in oxidation of C1-C4 hydrocarbons (Terribile, D. et al. (1999) Catal. Today 47:133-140). Temperatures of about 650 to about 800K were reported to be required for 50% conversion of methane, ethane, propane, butane and isobutane.
U.S. Pat. No. 5,283,041 describes a ternary compound of vanadium oxide (0.01 to 20 weight percent), zirconium oxide (40 to 88 weight percent) and either manganese oxide, cerium oxide and cobalt oxide (3 to 48 weight percent). Platinum, palladium and rhodium may also be present from 0.01 to 5 weight percent. This compound is used to treat gas streams containing halogenated organic compounds using temperatures of 175° C. to 550° C.
U.S. Pat. No. 5,491,120 describes an inert carrer with a BET surface area of at least 10 m
2
/g used to support a coating of bulk ceria with a BET surface area of at least 10 m
2
/g and one or more bulk metal oxides which are either titania, zirconia, ceria-zirconia, silica, alumina-silica or &egr;-alumina metal oxide for oxidizing components of a gas stream, in particular a diesel engine exhaust.
U.S. Pat. No. 5,851,948 describes an inert porous support such as alumina or silica having a surface area of 10-400 m
2
/g used to support a catalyst composition of 0.5 to 15 wt % of chromium, cobalt, copper, cerium or iron oxide covered with a thin (at most 0.1 mm thick) layer of Pd, Pt, Ru or Rh (concentration of 0.01 to 2 wt %).
U.S. Pat. No. 5,627,124 describes a composition of ceria and alumina (each having a surface area of at least 10 m
2
/g and being 5 to 95 percent of the composition) coated on a refractory carrier for pollution abatement of exhausts containing unburned fuel or oil.
U.S. Pat. No. 5,882,616 describes perovskites of the formula XYO
3
, where X is lanthanum, cerium or yttrium, and Y is a transition metal such as copper, chromium, manganese, iron, cobalt and nickel supported on a support such as alumina, silica, magnesium aluminate, titanium oxide, zirconium oxide and mixtures thereof.
Even with somewhat advanced materials, the technologies currently used for reduction of VOCs from contaminated air still require heating the air stream to relatively high temperatures to reduce the concentration of VOCs.
There remains a need for materials and processes that destroy VOCs at low concentrations at ambient- or near-ambient temperatures under oxygen-rich conditions. These materials should have high oxygen storage capacity, optimal surface oxygen mobility, stability against feedstream poisons, active sites with a propensity for &pgr;-bond systems as well as VOCs in general, and should not require high temperatures to reduce the concentration of VOCs in air.
BRIEF SUMMARY OF THE INVENTION
Catalyst compositions for destruction of VOCs comprising: at least one of cerium and zirconium with at least one member of the group consisting of: Gd, La, Sc, Cr, Ti, V, Mn, Fe, Co, Ni, Au, Ag, Cu Pt, Pd, Rh, Ru, Re, Os and Ir are provided.
Catalyst compositions of the invention may comprise mixed oxides, single-phase materials, or multi-phase materials. Catalyst compositions further comprising a supporting material are also provided.
One class of compounds of the invention include catalyst compositions for destruction of VOCs in a gas comprising one or more first metals selected from the group consisting of: Ce and Zr; and at least one of ((a) (b) or (c)) where (a) is one or more second metals selected from the group consisting of: Gd, La, Sr and Sc; (b) is one or more third metals selected from the group consisting of: Ti, V, Mn, Fe, Co, Cr, Ni, Au, Ag and Cu; and (c) is one or more fourth metals selected from the group consisting of Pt, Pd, Rh, Ru, Re, Os and Ir.
In this class of compounds, preferably the second metals are one or more of Gd, Sr and La. Preferably the third metals are one or more of Cu, Au, Fe, Co and Mn. The second and third metals together preferably comprise less than about 80% of said catalyst composition, more preferably together comprise less than about 50% of the catalyst composition, and most preferably together comprise between about 5 and 50% of the catalyst composition. Preferably the fourth metals are Pt, Pd and mixtures thereof, with Pt being more preferred than Pd. The fourth metals preferably comprise less than about 25% of said catalyst composition, and more preferably comprise less than about 5% of said catalyst composition, and most preferably comprise less than about 2% of said catalyst composition.
One class of compounds of the invention has one member from the group of second and third metals combined. Another class of compounds of the invention has one member from the group of second metals and one member from the group of third metals. Another class of compounds of the invention has more than one member from the group of second metals. Another class of compounds of the invention has more than one member from the group of third metals. Another class of compounds of the invention has more than one member from the group of second and third metals combined. Each of the above classes may optionally contain one or more members of the group of fourth metals.
Another class of compositions provided are the catalyst compositions with the formula:
nN
/Ce
1−x
Zr
c
A
a
A′
a′
A″
a″
B
b
B′
b′
B″
b″
O
2−&dgr;
wherein n is a per

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