Table IV.
Viscosities of Maltenes from Various Coating Asphalts
.4sphalt
Weather-Ometer Life, Cycles to Failure
A B C D E
1 4 7 43 88
Viscosity of Maltenes, Poises 722” F. 780” F
77’ F. ... , . .
1.550 20;500 >100,000
7.73 17.4 37.0 114 2110
1.17 2.33 3.60 10.6 56.2
greater than that of the maltenes from asphalt A (one cycle) by a factor of about 50. The correlation between WeatherOmeter cycles to failure and maltene viscosity a t 180’ F. (panel temperature during radiation) is shown in Figure 5.
in the usual weathering process is determined by diffusion, not of oxygen. but of larger particles which may be considered as dispersed in the maltenes. Such particles might include asphaltene and resin molecules, free radicals, and complexes of the foregoing with oxygen. However, we are not yet able to specify the nature of the reactants more definitely. The correlation of maltene viscosity with weather resistance emphasizes the importance of physical factors in the deterioration of bituminous coatings. The rate of the reactions appears to be controlled largely by diffusion rather than by differences in inherent reactivity of the material. The measurement of maltene viscosity may also be useful in screening asphalts in respect to weather resistance, if the asphalts do not differ greatly in penetration. literature Cited (1) Abraham, H., “Asphalts and Allied Substances,” pp. 1463 ff,
Van Nostrand. New York. 1945. (2) Beitchman, B. D., J . Res. Natl. Bur. Std. 63A, 189 (1959);
64C, 13 (1960). (3) Ford. T. F., Arabian, K. G., Am. Soc. Testzng Mater. Proc. 40,
Conclusion
A reasonable hypothesis can be advanced to explain the correlation of Weather-Ometer life with maltene viscosity: that the rate of the condensation reactions leading to hardening is controlled by the rate of diffusion of the asphaltenes or other reacting species. The diffusion rate will be determined largely by the viscosity of the medium through which the reactants must diffuse. This medium is approximated by the maltenes. Thus. a more viscous maltene phase will retard diffusion and resultant hardening. with a consequent increase in weather resistance. Oxygen is known to be involved in the reactions leading to hardening. However, the rate of diffusion of oxygen would be supposed to be governed by the viscosity of the asphalt as a whole, rather than by that of on1)- a fraction of the asphalt. The observed correlation of weather resistance with the viscosity of the maltenes suggests that the rate of the reactions occurring
I 174’ (104m \ - ’ ‘-1.
(4)”Greenfeld, S. H., J . Res. -Vatl. Bur. Std. 64C, 299 (1960). (5) Heithaus. J. J., ASTM Spec. Tech. Publ. No. 309, 63 (1961). (6) Heithaus, J. J., J . Inst. Petrol. 48,45 (1962). (7) Hubbard, P., Gollomb. H., Proc. Assoc. Asphalt Paving Technologists 1937, 165. (8) Knotnerus, J., J . Inst. Petrol. 42, 355 (1956) (9) Martin, K. G., Ibzd., 47, 321 (1961). (10) Mertens. E. \$’., ASTM Bull. No. 260,40 (1960) (TP 218). (11i hlertens, E. FY., Greenfeld. S. H., ASTM Spec. Tech. Publ. ho. 280, 20 (1960). (12) Pfeiffer. J . Ph., “Properties of Asphaltic Bitumen,” p. 172, Elsevier, New York, 1950. (13) Snoke. H. R.. Gallup. B. E.. J . Res. Natl. Bur. Std. 18, 669 / I 017) \-’-
(14) Stlwart, J. E., Ibid., 58, 265 (1957). (15) Strieter. 0. G., Snoke, H R., Ibid., 16, 481 (1936). (16) N’oodruff. R. L.. Martinez Research Laboratorv. Shell Oil ‘ e o . . unpublished results. RECEIVED for review April 9, 1962 ACCEPTEDJuly 12, 1962
CATALYTIC OX I DATION OF AUTOMOTIVE n
EXHAUSTS. W
. A.
Laborat09 Evaluation of Catalysts
CA NN0N
1
A ND C
. E.
W EL
L
I NG
,2
Scientific Laboratory, Ford Motor Co., Dearborn, Mich.
A laboratory method has been developed to test in a practical and uniform way the ability of catalysts to oxidize unburned gasoline with space velocities and gas mixtures simulating those of automotive exhausts. The following materials catalyze the oxidation of simulated exhausts from unleaded fuels: manganesecopper oxides, copper chromite, silver oxide-barium peroxide, iron oxide, copper oxide, vanadia, platinum, and palladium.
gases from internal combustion engines generally and of partially burned or altered fuel components (3, 5, 7). Recognition of the role of automobile exhausts in air pollution has led to consideration of ways of removing the unburned and partially burned gasoline from the exhausts. One method which received early (73) and continuing attention is the destructive XHAUST
E contain small percentages of unburned
’ Present address, Boeing Aircraft, Seattle, Wash.
Present address, Aeromechanical Division, Goodyear Aircraft Co.. Akron, Ohio. 152
l&EC P R O D U C T RESEARCH A N D DEVELOPMENT
catalytic oxidation of these residues. I n some respects this resembles commercial processes in fixed installations to remove organic vapors from process streams and vent gases (6, 77, 76). However, process conditions and other factors of automotive application are unlike those of other oxidation processes, and consequently a suitable oxidation catalyst must possess somewhat novel properties. Thus far, little information has been published on the performance of oxidation catalysts under the wide range of conditions encountered with automobile exhaust systems. The
results obtained with a few catalytic devices installed on vehicles (9, 74,79) and tests on selected catalysts with exhausts from stationary engines (4, 72) have been described. A few laboratory results have been reported with chromite catalysts that were effective a t space velocities of 8600 hr.-I for hydrocarbon and carbon monoxide destruction (77). A laboratory study has been reported of the activities of a variety of unsupported single oxide catalysts in oxidizing several hydrocarbons a t reactant concentrations markedly higher than the engine exhaust range and with space velocities of about 500 hr.? ( 75). The present paper describes a laboratory method for the evaluation of oxidation catalysts using simulated exhausts and process conditions anticipated in automotive use, summarizes test results, and discusses thermal stability of some more active materials. From this method, the most promising catalysts can be selected and predictions can be made about their initial performance when installed in a n automobile. Appropriate amounts of unleaded gasoline and water are blended with a stream of gases to give a gas mixture simulating automobile exhaust gas plus secondary air. This mixture is then passed at constant flow rates rhrough an externally heated reactor containing a preheat section and catalyst bed whose temperature is gradually being raised. When oxidation begins, selfheating of the bed occurs and the gas composition changes. The relative effectiveness of different catalysts using the same feed streams and space velocities is then determined by comparing (1) the feed temperature at which oxidation begins as indicated by the onset of seif-heating of the bed and (2) the feed temperature at which oxidation is essentially complete as shown by disappearance of the hydrocarbon gases from reactor effluent and by leveling off of oxygen consumption. Operating Conditions for Exhaust Gas Catalysts
Automobile engines operate over a wide range of conditions embracing cold starts, idling, high speed, and accelerations and decelerations. Consequently, catalytic systems effective for automotive exhausts must operate over wide fluctuations of exhaust temperatures, gas flow rates, and gas composition. Furthermore, they must be insensitive to poisoning by combustion products of fuel and lubricating oil additives. Range of Conditions Encountered in Automobile Exhausts. PRESSURE.Exhaust streams pulsate somewhat but they operate essentially at atmospheric pressure. T E M P E R A T U R E . Temperatures from 150' F. (65' C.) to 1500' F. (815' C.) have been reported (2) for different conditions of engine operation and for different sites of measurement on the exhaust system. Evaluation of a catalyst for engine exhausts should therefore include some determination of the minimum temperature required for effective catalytic action and the maximum temperature which the catalyst will withstand without thermal damage. GASFLOWRATES.Exhaust volumes computed a t 1 atm. and 70' F. (21' C.) from measured air intakes range from 6 to 10 cu. feet per minute (c.f.m.) a t idle to about 30 c.f.m. a t 35 miles per hour road load to 50 c.f.m. a t 50 miles per hour (m.p.h.) road load and 100 c.f.m. a t 70 m.p.h. road load for average passenger cars (2, 8, 20). At acceleration the flow rates may reach 250 c.f.m.. while a t deceleration they are essentially the same as a t idle (2, 8). T o assure excess oxygen for direct catalytic oxidation, secondary air amounting to about 20 to 257, of these volumes would have to be added to the exhaust stream. This air, together with allowances for the higher temperatures in the exhaust, would increase the volumetric flow rates to about 1.5 to 3 times the reduced standard volumes given above. In view of the limitations imposed by available space, weight of catalyst, and pressure drop across beds having practical configurations, it was concluded that the volume of the catalyst
To R e c o r d e r
\
Emulsion Reservoir
@
Zi:er
pump
Preheat Section Catolyst Bed Oxygen Analyzer
To F l a w Indicator Analyzer
Figure 1 .
Catalyst test apparatus
bed should be about 0.25 cu. foot. With this assumed volume, the volumes of exhaust gases plus secondary air given above result in standard hourly space velocities of about 2000 to 3000 at idle and about 9000 at a road load speed of 35 m.p.h. The space velocities chosen for the laboratory tests lie within or above this range. GASCOMPOSITION. The chief combustible constituents of exhaust gas are hydrocarbons: carbon monoxide, and hydrogen; their concentration varies greatly depending upon operating conditions and air-fuel ratio. For example, on deceleration the composition varies from essentially unburned air-fuel mixture through partially burned mixtures to streams similar to the idling stream. The water vapor content varies between 5 and 15% of the whole stream, depending upon degree of combustion. composition of fuel. ambient humidity, etc. Table I summarizes the typical range of composition of exhausts from automobiles burning commercial gasolines (78, 20). Experimental
The units for feed stream blending and the catalytic reactor are illustrated in Figure 1,
Feed Stream. Air. nitrogen. and carbon dioxide are continuously metered through calibrated capillary orifice flowmeters into the manifold. Carbon monoxide and hydrogen are added as a previously prepared mixture through a fourth orifice meter. Commercial cylinder gases and compressed air from the laboratory lines are used. For the tests recorded here. an unleaded gasoline containing 27Yc aromatics, 2 7 7 , olefins! and 46To saturates (fluorescent indicator analysis) is used. Although gasoline conveniently affords a wide range of hydrocarbons, it is recognized that the simulation of exhaust is incomplete with respect to the C2-Cd olefins that are prominent in exhaust and to oxygenated structures. It'ith feed gas flow in the range of 2.5 to 5 liters per minute, liquid gasoline requirements are between 1 and
Table 1.
Exhaust Gas Composition
(Volume '%, dry basis)
Hydrocarbons C3 and higher Carbon dioxide Carbon monoxide Hydrogen Oxygen Nitrogen
VOL. 1
Idle 0 08-0 15
5-10 3-1 0 0-4 0-2 78-85
NO. 3
Cruise 30 to 50 .M.P.H. Road Load 0.02-0 08
8-1 4 0.2-5 0-2 0-2 78-85
SEPTEMBER
1962
153
Table II.
Initial Activity of Oxidation Catalysts
Inlet Temp. ,t" Catalyst Bed, C. Threshold Complete oxidation oxidation 130 180 25 25 175 270 165 235 160 265 120 180
Abbarent Bed Density, G.jM1. 0.88 0.88 0.88 0.88 0.88 0.80
4.2 4.5 4.2 4.1 4.2 4.1
Vol. 70in CO Nil 3.0 Nil 3.0 3.0 Nil
2.0 1.1
4.0 4.8
Nil 3.0
Nil 1. o
0.24 0.10
5,700 10,800
230 115
290 295
None None None None 16 hr., 760' C. 100 hr., 500' C. None
1.8 1.8 1.8 1.8 1.8 1.8 1. o
4.0 4.0 3.9 4.0 3.8 4.8 4.0
Nil 3.0 3.0 3.0 3.0 3.0 Nil
Nil 1.o 1. o 1. o 1. o 1.o Nil
0.24 0.10 Nil 0.10
5,500 10,800 10,800 16,000 10,800 10,800 5,700
185 130 150 190 145 280
265 225 180 220 270 250 320
Iron oxide, copper-promoted, deoxidation catalystC
None None 16 hr., 760" C. None None None 16 hr., 760" C.
1.6 1.6 1.6 1.2 1.2 1.2 1.2
4.0 3.9 4.1 4.1 4.0 4.2 3.9
Nil 3.0 3.0 Nil 3.0 3.0 3.0
Nil 1. o 1. o Nil 1. o 1. o 1. o
5,700 10,800 10,800 5,700 10,800 16,000 10,800
200 280 Inactive 215 150 150 275
Iron oxide, copper-chromiumpromoted, desulfurization catalyst
None None 16 hr., 760' C.
1.3 1.3 1.3
4.0 4.0 4.0
Nil 3.0 3.0
Nil 1. o
0.24 0.10 0.10
5,700 10,800 10,800
190 120 280
Iron oxide, chromium-promoted, CO shift catalystC 2.5 % manganese oxide on alumina/ Copper-nickel-manganese oxides on silica gelc Chrome-alumina catalyst 1170chromium oxide on aluminaC 10% copper oxide on aluminac
None
1.1
4.0
Nil
Nil
0 25
5,700
200
315 310 Inactive 310 210 220 Incomplete at 400 280 200 Incomplete at 420 350
None
0.85
4.9
Nil
Nil
0.24
5,700
220
340
None
0.60
4.0
Nil
Nil
0.24
5,700
290
330
1. o 1.1 1.1
Nil Nil h'il 3.0 3.0 Nil
Nil Nil Nil 1. o 1. o Nil
Nil 0.24
5,700 11,000 10,800 5,700 5,700 1,400
230 310
340 370 350 360 350 325
aluminae 7% vanadium pentoxide on aluminan
1.1 1.o
4.0 4.0 4.0 4.0 4.0 4.1
0.24 0.24 0.18
10% molybdenum oxide on
None None None None None None None None
0.95 0.95
4.0 4.0
Nil 3.0
Nil 1. o
0.24 Nil
5,500 5,500
170 325
1 '
Catalyst 60 manganese oxide-40 copper oxidec
60 manganese oxide-40 copper oxide-5 silver oxided Copper chromite, unpromotedC Copper chromite, 22010, on low area a-aluminab Copper chromite, bariumpromotedc
4.6% silver oxide on 4-8-mesh aluminac Silver oxide-barium peroxide on 6-1 2 mesh aluminac
Thermal Treatmenta None None 16 hr., 760" C. 16 hr., 760' C. 100 hr.. 550' C. None
None None
02
1.1
Feed Gasb H1 Gasoline Nil 0.25 1. o 0.10 Nil 0.24 1. o 0.10 1. o 0.10 0.24 Nil
1.o
0.10
0.10 0.24 0.24 0.10
0.10 0.24 0.10 0.10 0.10
0.10
Standard Hourly Space Velocity 5,700 10,880 5,700 10,800 10,800 6,500
100
190
170 180 185
320 Incomplete at 450
I n addition to combustibles and oxygen, dry feed gas contains 10 to 12% by a Catalyst heated in mufle furnace in contact with air for indicated time. Prepared by separately volume CO?, and balance is nitrogen to which is added water vapor as 10 uol. % of total. Obtained from commercial sources. precipitating oxides of manganese, copper, and siluer. Oxides were intimately mixed and pelleted and subsequently broken into 8-10-mesh granules. e A low area alumina (less than 1 sq. meterjgram) carrier was vacuum-impregnated with a slurry containing 50% by weight of commercial copper chromite hydrogenatton catalyst in water. f Prepared by method of Crar,er ( I ) . 0 Prepared by ammonium diuanadyl oxalate method of C r a w ( 7 ) . A medium area y a l u m i n a support (52 sq. meterslgram) was used.
5 ml. per hour to obtain the desired concentrations in the feed stream. Such a low rate requires a special technique of addition. Bubbling the gas stream through the liquid fuel to vaporize the correct amount of gasoline, as can be done for pure hydrocarbons, is unsatisfactory because of the range of volatility of the fuel. Inasmuch as the test stream should contain around 10% water vapor to simulate engine exhausts, the water and gasoline are added simultaneously as an emulsion of 4 to lOy0 gasoline in water, depending upon the desired concentration. The emuIsion is blended in a Waring Blendor using 0.1% sodium stearate as a stabilizer and then is pumped by means of a microbellows pump (Research Appliance Co.) into the evaporator which is heated in an oil bath to 125' C.; here the gasoline and water are flashed into vapor and are carried along by the gas stream. For the feed streams in the tests here, two gasoline concentrations-0.10 and 0.25%-are used along with carbon monoxide concentrations of 3 and 0% and hydrogen concentrations of 1 and 0%. Other components of the test gas are oxygen (4%) and carbon dioxide (IO to 12%), the remainder being nitrogen. Stream compositions are expressed on a dry basis; 154
l & E C P R O D U C T RESEARCH A N D DEVELOPMENT
presence of 1Oyo water vapor in the stream over the catalyst is considered only in respect to space velocity. Catalytic Reactor. A short heated line from the evaporator conducts the simulated exhaust gas mixture to the 40-inch-long catalyst tube of I-inch I.D. borosilicate glass tubing. The catalyst tube is positioned inside a 30-inch vertical tube furnace and extends 5 inches a t both top and bottom. With a steel furnace liner, temperature gradients are negligible over a IO-inch distance near the middle of the catalyst tube. T h e catalyst bed rests on a glass spiral held by a constriction in the tube and is placed so that the top of the bed is near the center of the furnace. Crushed quartz is placed on top of the bed to a height of 10 inches to serve as a preheating section. Catalyst samples in the form of pellets or granules "16 inch or smaller in diameter are tested without further size reduction, but materials available only in larger pieces are crushed and 10 mesh before charging to the tube. Bed sieved to -8 volumes of 25 to 100 ml. may be used and hourly standard space velocities from 1000 to 20,000 can be obtained by proper selection of bed volume and flow rate of feed stream. For space velocities of 5000 and above, a 25-ml. bed is used.
+
Using Chromel-Alumel thermocouples attached to a multipoint recording potentiometer, continuous records are made of temperatures in the apparatus. One thermocouple is inserted in the annulus between catalyst tube and furnace liner and three others are placed in a 3/16-inchO.D. borosilicate axial well in the catalyst tube at positions 1 inch above the catalyst bed, '/4 inch below the top of the bed, and 1/4 inch above the bottom of the bed. The couple 1 inch above the bed measures the inlet temperature of the feed stream to the bed. Operations and Analysis. During each test the composition and flow rate of the feed stream are maintained constant and the furnace temperature is raised by manual control from below the threshold temperature for oxidation a t a rate of about 50" C . per hour. When oxidation commences, the temperature of the bed rises above that of the inlet gas stream. If adiabatic conditions prevailed, a temperature increase calculated to be about 150" C. between feed and effluent streams would result from complete combustion of a test gas containing 0.1 volume 7, gasoline (no C O or H2) with the feed a t 300" C. With the small catalyst volumes used here, adiabatic conditions are not obtained, however, and the observed temperature differences are only about 50' to 75' C. Consequently the inlet gas temperatures, rather than the bed temperatures, are used as indexes to specify the conditions for incipient oxidation and for complete oxidation. The progress of the oxidations in the catalyst bed is determined from inlet and outlet gas compositions. with oxygen decreasing from about 4% to 1% or less and the hydrocarbon concentration decreasing to. 0%. A Beckman Model C magnetic oxygen analyzer with a range of 0 to 5% oxygen monitors the oxygen content to 1 0 . 0 5 % ; a valving arrangement permits monitoring either the inlet stream ahead of the evaporator or the outlet stream from the catalyst after most of the water is removed by a n ice trap (Figure 1). An infrared filter photometer (70) which measures absorption a t the carbon-hydrogen bond stretching frequency (3.42 microns) is used to detect hydrocarbon concentrations in the range of 0 to 0.257, n-hexane equivalent to about zkO.017,. In some experiments, an Orsat analysis has been used as an additional check on gas compositions. Using the above instrumentation, the degree of oxidation can be established to about i5%. Blank Experiments. Blank runs were made with the catalyst section filled with pelleted alumina (Harshaw AI 010fT. 3 / 1 6 inch) and with the crushed quartz preheater in place. At bed temperatures up to 440' C. no oxidation has been observed with iso-octane vapor in the test gas at a standard hourly space velocity of 1400. With the test gasoline, only a trace of oxidation has been observed a t 350' C. Therefore, the catalytic effect of the preheater or tube walls may be neglected below 350' C. Results and Discussion
The following catalysts yielded incomplete oxidation of the hydrocarbons in a test gas stream below 375" C. containing 0.24y0 gasoline by volume a t standard hourly space velocities in the range of 5500 to 5700.
Commercial Catalysts Alumina-silica cracking catalyst Chrome-alumina desulfurization catalyst Chrome-based reforming catalyst 10.6y0 chromium oxide catalvst Cobalt molybdate on alumina Copper deoxidation catalyst 8.3y0molybdic oxide on alumina 10YGmolybdic oxide on y-alumina 107Gnickel on alumina 35Yc nickel hydrogenation catalyst 3.85Y0 si1vt.r oxide on silica gel 1OYGtungstic oxide on alumina L'anadium oxide-sulfuric acid oxidation catalyst Noncommercial Catalysts 9.5% antimony oxide on y-alumina 3.87, cadmium oxide on y-alumina
3.8% cerium oxide on y-alumina lOy0cerium oxide on y-alumina 10% cobalt oxide on y-alumina Copper-bismuth oxides on Celite 170copper vanadate on y-alumina 3.6YGlead oxide on y-alumina 4.8% nickel oxide on y-alumina 6.37, thorium oxide on y-alumina 1.2% zirconium oxide on y-alumina Table I1 lists more active oxidation catalysts and shows the conditions of the test runs. Manganese-Copper Oxides. Physical mixtures of MnOz and C u O with a weight ratio of 3 to 2 are active oxidation catalysts for both gasoline vapor and carbon monoxide. Initially the oxidation of carbon monoxide takes place with the feed gas a t room temperature, even in the presence of water vapor. When heat-treated between 550" and 760" C. the material suffers a decided loss in activity and x-ray inspection detects crystallite growth. That loss in activity attends crystallite growth and a decrease in surface area has been verified by engine test work (4). Thus, manganese oxidecopper oxide mixtures are potentially useful catalysts, but structural promotrrs capable of stabilizing the structure are needed. Copper Chromite. Commercial copper chromite catalysts used for hydrogenation reactions have good initial activity as oxidation catalyst for both the gasoline vapor and carbon monoxide in the simulated exhaust gas. The sample of barium-promoted material used in this study had greater thermal stability than manganese oxide-copper oxide mixtures. Copper chromite deserves further consideration as a catalyst for exhaust gas oxidation. Silver Oxide-Barium Peroxide. T h e Ag20-BaOz on alumina catalyst has fairly good initial activity but is ruined by heat treatment a t 760 O C. Iron Oxide-Based Catalysts. Two commercial iron oxidebased catalysts are active for oxidation of both gasoline and carbon monoxide. Samples heated to 760' C. for 16 hours were almost completely inactive. T h e copper-promoted deoxidation catalyt lost structural water on heating, as shown by x-ray analysis. The desulfurization catalyst contained iron in the form of Fez03 and x-ray inspection gave no evidence of alteration by heating other than a slight decrease in line broadening. Copper Oxide. Copper oxide supported on alumina shows measurable activity a t a rather low temperature, but for complete oxidation requires considerably higher temperature. I t undergoes some reduction and in itself it can therefore serve as an oxidizing agent. This feature could be useful in compensating for temporary deficiencies in secondary air in automotive applications. Vanadia. Selective oxidation of the gasoline occurs with vanadia; it is complete a t an inlet temperature of 320" C. In contrast, the oxidation of carbon monoxide is still incomplete at a n inlet temperature of 450 " C. Platinum and Palladium. The initial activities of these catalysts are summarized in Table 111; all are good except for the laboratory preparation of palladium on alumina. A correlation between these tests is desirable but difficult. since different space velocities and different weights of precious metal were employed. i2ssuming, however, that the variations in inlet gas temperatures for complete oxidation over catalysts -4, B, C. and 11 can be neglected, the catalysts can be compared on the basis of the relative quantities of exhaust oxidized completely per unit weight of metal in the catalyst (last column of Table 111). The higher Lveight effectiveness of catalyst C may be due to a finer dispersion of the platinum on the support, VOL.
1
NO. 3
SEPTEMBER 1962
155
Table 111.
Initial Oxidation Activity of Platinum and Palladium Catalysts [Atmosphericpressure (stream composition, vol. yo)O, ,4.oY0; GOa, 12.7%; gasoline vapor, 0.24%; N2, balance]
Relat ioe Gas Standard Inlet Gas Temp., Flow/Unil Hourly O c. Wt. Pd Sbace Threshold Comblete or Pt VJocity, oxidation oxidition (Cat. A Catalyst V./ V./Hr. = 7.0) .A. 0 . 6 % Pt on silica 5,700 200 280 1 .o gel" B. 0 . 5 % P t o n 5,700 230 295 1.2 aluminab C. 0.31q7,Pton 10,800 190 300 2.5 alumina. D. 0 . 2 % Pd on silica 5,700 220 260 3.6 gela E. Pd on metal sup4,100 205 230 porta F. 0 . 3 % P d o n 1,400 270 400 alumina6 a Oblained from commercial source. Prepared by impregnating tablcted alumina of 82 to 85 sq. meterslgram area.
while that of catalyst D may be attributed in part to the prmence of nearly twice as many atoms of palladium as of platinum per unit weight of metal. Electron-Bombarded Catalysts. Certain catalysts in the form of ',/s X l / 8 inch tablets were exposed to 1000-kv. electron bombardment from a GE 1-m.e.v. resonant transformer. Each specimen received a dose of 8 X 106 rep (roentgens equivalent physical). No change in oxidation activity was produced in any of the following catalysts by irradiation:
1. 10% chromium oxide on y-alumina 2. 10% vanadia on y-alumina 3. 4.
Acknowledgment
The authors thank G. E. Fisher for collecting and organizing many of the data and C. H. Ruof for his encouragement and assistance in preparation of the paper.
literature Cited
(1) Graver, A. E. (to Barrett Co.), U. S. Patent 1,914,557 (June 20, 1933). (2) Exhaust System Task Group, Automobile Manufacturers Assoc., Preprint 173, SOC. Automotive Engineers National West Coast Meeting, Seattle, Wash., August 1957. (3) Heaton, I V . B.: Wentworth, J. T., Anal. Chem. 31, 349 (1959). (4) Hill: E. F., Cannon, W. A., Welling, C. E., SAE Journal 66, 36 (January 1958). (5) Hurn, R. \V.,Davis, T. C., P70C. A m . Petrol. Inst. 38, 111, 353 (1 958). (6) Kerry, F. G., Hugill, J. T., Chem. Eng. Progr. 57, 37-41 (April 1961). (7) Magill? P. L., Hutchinson, D. H., Stormes, J. M., Proceedings Second Annual Air Pollution Symposium, pp. 70-83, Stanford Research Institute, Stanford, Calif., 1952. (8) Millar. G. H.? Stahman, R. C., J . Air Pollution Control Assoc. 6, 35 (1956). (9) Nebel, G. J., Bishop, R. W., Preprint 29R, SOC.Automotive Engineers Annual Meeting, Detroit, Mich., January 1959. (10) Parsons, J. L., Irland, M. J., Bryan, F. R., J . Opt. Sod. A m . 46, 164 (1956). (11) Rushton, J. H., Krieger, K. A,, Aduan. Catalysis 3, 107-28 (1951). (12) Schachner, H.. Cobalt, No. 9, 12 (December 1960). (1 31 Southwest Research Institute, San Marino, Calif.. Air
Copper chromite hydrogenation catalyst 8.3% molybdic oxide on y-alumina
Conclusions
Oxidation of 0.1 volume yo or more of gasoline vapor in simulated exhaust plus secondary air is complete with several types of catalysts a t feed temperatures of 350" C. or less and a t space velocities comparable to those anticipated in automotive applications. Volume requirement of secondary air is generally little more than the stoichiometric requirement. The following materials catalyze the oxidation of simulated exhausts from unleaded gasoline : manganese-copper oxides, copper chromite, silver oxide-barium peroxide, iron oxide, copper oxide, vanadia, platinum, and palladium.
156
Manganese-copper oxides, silver oxide-barium peroxide, and copper-promoted iron oxide undergo phase changes and also lose catalytic activity when heated to 760' C. for 16 hours. This suggests that these catalysts might become ineffective on exposure to the conditions which could occur in the treatment of exhausts. Certain catalysts-e.g., copper chromite-oxidize carbon monoxide at a lower temperature than gasoline vapor.
l&EC
P R O D U C T RESEARCH AND DEVELOPMENT
10, 275 (1960). (16) Suter, H. R., Ibid., 5 , 173 (1955). (17) Taylor, F. R., Air Pollution Foundation Rept. 28 (September 10FO\
,/a,,.
118) T w i q q . S B.. ,--,-....
TFavue. D. M.. Bozek. J. W.. Sink, M. F., ~~, J . Air Pollution Control Assoc. 5 , 75 (1955). ' (19) Van Derveer. R. T., Chandlei, J. M., Preprint 29S, SOC. Automotive Engineers Annual Meeting, Detroit, Mich., January 1959. (20) \Vay, G.. Fagley, W. S., Ibid., 11A (January 1958). ~~
I
RECEIVED for review January 18, 1962 ACCEPTED May 29, 1962 Presented in part before Division of Industrial and Engineering Chemistry, 132nd Meeting, ACS, New York, N. Y . , September 1957.
