2654
Ind. Eng. Chem. Res. 1998, 37, 2654-2661
Comparative Study of Catalytic Reduction of Nitric Oxide with Carbon Monoxide over the La1-xSrxBO3 (B ) Mn, Fe, Co, Ni) Catalysts Shiaw-Tzong Shen and Hung-Shan Weng* Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan 70101, Republic of China
In this study, we select a catalyst with the highest activity to reduce NO with CO as a reducing reactant from four series of perovskites La1-xSrxBO3 where B ) Mn, Fe, Co, or Ni. The cause for different activities is also closely examined by characterizing the perovskites by XRD, XPS, NO-TPD, and CO-TPR. Activity test results indicate that the LaFeO3 catalyst has the highest activity. Also, substituting La with Sr increases the activity in the Mn, Co, and Ni series. In addition, an optimal substitution fraction exists for each series, whereas adding Sr does not promote the activity of the LaFeO3 catalyst. The atomic ratio of B/(La + Sr) obtained from the XPS analysis can be correlated to the substitution fraction of Sr (x) and, subsequently, with the catalytic activity. By increasing x, this ratio initially increases but later decreases when the SrBO3 phase appears. Among the catalysts in the same series, the one with a higher B/(La + Sr) ratio on the surface yields a higher activity. The NO-TPD experimental results indicate that the NO adsorption plays an influential role in this catalytic reduction reaction. Moreover, the temperature range of NO desorption is the same as that of the reaction and the amount of NO desorbed is roughly proportional to the catalyst activity. The CO-TPR reveals that the reducibility of the catalyst is another factor influencing the activity. A catalyst having a larger fraction of Sr is more easily reduced. However, such reduction becomes difficult when the SrBO3 phase appears. Introduction
Table 1. Maximum Calcination Temperature (°C) for the Catalyst
NOx is a major pollutant which forms during combustion as in automotive engines, thereby necessitating the need to reduce the levels of NOx as a viable means of air pollution control. According to previous investigations, Rh is the most effective catalyst for reducing the emission levels of NOx (Iizuka and Lansford, 1980; Pande and Bell, 1986; Havdee and Hightower, 1984). However, it is very expensive and sensitive to deactivation by Pb and P. Therefore, many investigators have attempted to develop a catalyst with a relatively low cost and better poison resistance to replace the Rh catalyst. In 1970-1971, cobalt perovskites were suggested as low-cost substitutes for noble metals in electrocatalysis (Meadowcraft, 1970) and automotive exhaust treatment systems (Libby, 1971). Encouraging results were obtained while oxidizing CO and reducing NO using manganite and cobaltate perovskites (Voorhoeve, 1972, 1973). Perovskite-type catalysts hence have attracted much attention and the successive investigations are more extensive and detailed in diversified areas such as how to improve the preparation method (Tascon et al., 1981; Chang and Weng, 1992), the promotion effects by partially substituting A or B cations (Yao, 1975; Nakamura et al., 1983; Zhang et al., 1988; Seiyama et al., 1985), the adsorption phenomena of oxygen (Kremenic et al., 1985; Seiyama et al., 1981; Nakamura et al., 1983), and the characterization of surface properties (Ichimura et al., 1980; Nakamura et al., 1982, 1983). However, most of these investigations have emphasized * To whom all correspondence should be addressed. Fax: 886-6-2344496.
max. calcination temp catalyst
x)0
x ) 0.3
x ) 0.5
x ) 0.7
x)1
La1-xSrxMnO3 La1-xSrxFeO3 La1-xSrxCoO3 La1-xSrxNiO3
850 850 850 850
1000 1020 1000 1020
1000 1000 1000 1050
1000 1020 1050 1020
1050 1050 1000 1050
applications for oxidation reactions, rarely addressing the reduction reactions. In addition, most investigators used H2 or NH3 as the reducing agent for the reduction reaction of NO (Voorhoeve et al., 1976, 1977; Sorenson et al., 1974; Ladavos and Pomonis, 1992). CO is a major air pollutant, thereby making it worthwhile to investigate the NO + CO reaction over the perovskite catalysts. Therefore, in this study, we perform such a task. According to Liang and Weng (1993), the B cation and the substitution fraction of La by Sr in La1-xSrxBO3 (B ) Mn, Fe, Co, Ni) catalysts influence the catalyst activity in the oxidation reaction, and therefore we investigate these effects as well. XRD and XPS are used to analyze the structure and surface composition. TPD of NO and TPR of CO are employed to characterize the catalyst’s ability to adsorb NO and to be reduced by CO. Experimental Section Catalyst Preparation. All La1-xSrxBO3 catalysts (where x ) 0, 0.3, 0.5, 0.7, 1 and B ) Mn, Fe, Co, Ni) were prepared by the alkaline coprecipitation method using K2CO3 solution as a precipitant. The precipitates were filtered, dried, and calcined in air for 6 h at the maximum calcination temperatures (see Table 1), as determined from TGA thermograms.
S0888-5885(97)00691-X CCC: $15.00 © 1998 American Chemical Society Published on Web 05/20/1998
Ind. Eng. Chem. Res., Vol. 37, No. 7, 1998 2655
Figure 1. Activity test of the prepared catalysts: (a) La1-xSrxMnO3; (b) La1-xSrxFeO3; (c) La1-xSrxCoO3; (d) La1-xSrxNiO3 (9, x ) 0; b, x ) 0.3; 2, x ) 0.5; 1, x ) 0.7; [, x ) 1).
Characterization Measurements. X-ray diffraction measurements were carried out in an X-ray diffractometer (Shimadz XD-D1) using Cu KR radiation. ASTM powder diffraction files were used to identify the phase in the sample. The BET surface properties were acquired by using a surface area analyzer (Micromeritics Flow Sorb II 2300). Finally the surface composition was measured by an X-ray photoelectron spectrometer (VG Micro Lab. MK III). Activity Test. Catalytic activity was measured in a fixed bed reactor made of quartz. Catalyst powder (3248 mesh, 0.3 g) was placed on quartz wool in the middle of the reactor. The reactor was heated by a furnace with a PID controller. Prior to each experimental run, the catalyst was pretreated in a He stream for 1 h at 150 °C to remove the water adsorbed on the surface. Next, the gaseous mixture of NO (1500 ppm), CO (1500 ppm), and He (balance) was fed into the reactor at a flow rate of 120 mL/min. The NO and CO were measured by a NO analyzer (Beckman Model 951A) and an ND-IR (nondispersive infrared) CO analyzer, respectively. The other components of the gas mixture such as N2, CO2, and O2 were analyzed by a gas chromatograph (Shi-
madzu GC. 9A) using a 1.5-m CTR-I column maintained at 35 °C. The conversion of NO at the reactor exit X is defined as follows:
X)
CAi - CAo CAi
where CAi and CAo denote the inlet and outlet NO concentration, respectively. TPD of NO. The NO-TPD experiment was performed with a flow system using He as a carrier gas. Prior to each run, the catalyst (0.5 g) was initially outgassed, by passing a He stream through it for 0.5 h at 850 °C, and, then, cooled to 150 °C. Next, the adsorption of NO was conducted by flowing a NO (1500 ppm)-He gas mixture for 1 h at 150 °C. After removing the physisorbed NO was removed by flowing He for 0.5 h, the desorption of NO was undertaken by heating up the sample at a constant rate of 10 °C/min from 150 °C to 800 °C in the He stream. The flow rates used in the outgassing, adsorption, and TPD runs were all 60 mL/ min.
2656 Ind. Eng. Chem. Res., Vol. 37, No. 7, 1998
Figure 2. X-ray diffraction patterns of the prepared catalysts: (a) La1-xSrxMnO3; (b) La1-xSrxFeO3; (c) La1-xSrxCoO3; (d) La1-xSrxNiO3.
TPR of CO. The CO-TPR experiment was conducted on the same system for TPD of NO. Prior to each run, the sample (0.02 g) was oxidized in an O2 stream for 1 h at 800 °C and then cooled to room temperature in a He stream. Next, the catalyst was heated at a constant rate of 20 °C/min in a CO (4500 ppm)-He stream with a flow rate of 60 mL/min. Finally, the CO and CO2 concentrations of the outlet stream from the reactor were analyzed with a CO and CO2 ND-IR analyzer. Results and Discussion Activity Test. The catalyst activities for the reduction of NO with CO as a reducing agent were evaluated by comparing the conversions at various temperatures. Figure 1 displays the conversion-temperature curves of four series of catalysts. From Figure 1a, all catalysts in the Mn series, except SrMnO3, can catalyze the reaction at around 250 °C. In addition, substituting La by Sr can promote the catalyst activity; however, the effect is weak, and the highest activity is around x ) 0.5. In the Fe series, the LaFeO3 catalyst has the highest activity. It is also the best among all the catalysts we
prepared. Obviously, substituting La with Sr results in a decline in the conversion. The activities of Co series catalysts closely resemble those of Mn series catalysts. Also, adding Sr to the catalyst of this series obviously promotes the activity. A substitution fraction of 0.5 yields the best activity. As is the case for the Mn series, substituting La with Sr does not influence the activity in the Ni series appreciably. Structure and Surface Area. Figure 2 presents the XRD patterns of four series catalysts prepared in this study. Table 2 summarizes their crystalline structures (examined with reference to ASTM cards). This table reveals that the LaMnO3 and LaCoO3 catalysts have only the perovskite structure. However, the LaFeO3 catalyst consists of a perovskite structure and a small amount of La2O3 and Fe2O3, the LaNiO3; catalyst only contains the structure of La2NiO4. On the basis of the above results, we can conclude that a pure perovskite phase cannot be formed if the method used herein is employed to prepare the LaFeO3 and LaNiO3 catalysts. In the range 0 e x e 0.5, the La1-xSrxMnO3 and La1-xSrxCoO3 catalysts have the perovskite structure,
Ind. Eng. Chem. Res., Vol. 37, No. 7, 1998 2657 Table 2. Crystalline Structure of Catalysts
Table 3. BET Surface Area and Surface Composition of the Prepared Catalysts
crystalline structure catalyst La1-xSrxMnO3 La1-xSrxFeO3
x)0 Pa
x ) 0.3 P
x ) 0.5 P
La1-xSrxCoO3
P, Fe2O3 La2O3 P
P SrFeO3 P
P SrFeO3 P
La1-xSrxNiO3
La2NiO4
P, NiO
P, NiO SrNiO3
x ) 0.7
x)1
P SrMnO3 P SrFeO3 P SrCoO3 P, NiO SrNiO3
Hb DPc H NiO H
P )perovskite structure. b H )hexagonal structure. c DP )distorted perovskite structure. a
while the XRD patterns of the SrMnO3 and SrCoO3 catalysts are consistent with those of the four-layer hexagonal SrMnO3 and SrCoO3 structure reported by Negas and Roth (1970) and Nitadori et al. (1986). In the range x > 0.5, the hexagonal SrMnO3 and SrCoO3, whose proportions increase with increasing x, are present in addition to the major perovskite structure. These results are consistent with those of Misono and Nitadori (1985). More closely examining the activity test results in Figure 1a and c reveals that an optimal x exists at which the activity is the highest in the Mn and Co series. Furthermore, the SrMnO3 and SrCoO3 catalysts have the lowest catalytic activities because of the formation of the less active SrMnO3 and SrCoO3 in the major perovskite structure. The LaFeO3 catalyst has the highest activity among all catalysts, because it consists of a small amount of active Fe2O3 (Naruse et al., 1980). Note that Fe2O3 is less stable than LaFeO3 at high temperature though it is more active. By doping Sr into LaFeO3, the Fe2O3 and La2O3 phases disappear, and SrFeO3, which has a lower activity, subsequently forms. Therefore substituting La with Sr does not positively impact the activity. In Ni series catalysts, the La2NiO4 phase decreases and the perovskite and NiO phases increase when the substitution fraction of Sr is increased. When x g 0.5, SrNiO3 is detected in the La1-xSrxNiO3 catalysts; in addition, the catalyst activity decreases with increasing x. Table 3 lists the BET surface areas of four series of catalysts. This table indicates that although the surface area does not correlate with the substitution fraction, the surface area has the lowest value at x ) 1 in all four series. Comparison between Table 3 and Figure 1 reveals that the surface area does not correlate with the catalyst activity. Surface Composition. The surface compositions obtained from XPS analysis (Table 3) correspond to those reported elsewhere (Nakamura et al., 1982, 1983). Because the fact that the reactivity of perovskite is attributed to the active transition B ion (Voorhoeve, 1976, 1977), the atomic ratio of B/A (A ) La + Sr) can be considered as an index representing the catalyst activity. Figure 3 indicates that the ratio of B/(La + Sr) possesses a maximum value at each series (x ) 0.5 for the Mn and Co series, and x ) 0.3 for the Ni series) except for the Fe series. These results correspond to those obtained from activity test (Figure 1) and XRD analysis. In other words, the catalyst with x ) 0.5 (or 0.3) has the highest value of B/(La + Sr) and the optimal activity. The decrease in this ratio and in the catalyst activity beyond the optimal substitution fraction is attributed to the formation of the SrBO3 phase.
catalyst La1-xSrxMnO3 x)0 x ) 0.3 x ) 0.5 x ) 0.7 x ) 1.0 La1-xSrxFeO3 x)0 x ) 0.3 x ) 0.5 x ) 0.7 x ) 1.0 La1-xSrxCoO3 x)0 x ) 0.3 x ) 0.5 x ) 0.7 x ) 1.0 La1-xSrxNiO3 x)0 x ) 0.3 x ) 0.5 x ) 0.7 x ) 1.0
BET surface area (m2/g)
surface metal atomic percentage La
Sr
B
7.6 5.7 7.9 5.2 5.1
14.18 10.82 10.34 9.27 0.00
0.00 6.86 9.60 9.71 17.96
10.07 12.89 15.64 14.59 10.48
10.5 7.1 9.5 11.6 9.7
11.49 15.70 5.65 3.64 0.00
0.00 5.83 17.13 15.10 22.63
13.13 20.15 19.69 10.98 5.98
3.5 6.7 11.3 4.1 0.7
17.54 5.97 8.73 5.27 0.00
0.00 9.58 10.18 13.83 24.13
11.77 12.56 17.31 11.41 10.62
8.0 8.4 5.4 3.7 2.1
16.27 7.36 7.81 3.19 0.00
0.00 6.77 5.63 10.29 21.82
16.84 15.63 11.58 11.46 18.42
Figure 3. Surface atomic ratio (B/(La + Sr)) of La1-xSrxBO3 catalysts: (a) B ) Mn; (b) B ) Fe; (c) B ) Co; (d) B ) Ni.
TPD of NO. Figure 4 reveals that NO begins to desorb at 150 and desorb completely at around 600 in all four series of catalysts. The desorption amount of NO can be correlated with the Sr content and has the lowest value at x ) 1. Tason et al. (1985) demonstrated that NO adsorbs in dissociative and molecular forms. In addition, the IR spectrum obtained by Pena et al. (1987) reveals the existence of several nitrogen compounds including bands of dinitrosyl species and bidentate, monodentate, and nitrite structures. The results above reveal that NO does not adsorb with only one form on the surface. This fact can be accounted for because some of the spectra have only one broad desorption peak and some of them consist of dual peaks.
2658 Ind. Eng. Chem. Res., Vol. 37, No. 7, 1998
Figure 4. NO-TPD patterns of the prepared catalysts: (a) La1-xSrxMnO3; (b) La1-xSrxFeO3; (c) La1-xSrxCoO3; (d) La1-xSrxNiO3.
Table 4 summarizes the total desorbed amounts of NO. Comparison of these results with those in Figure 3 and Table 3 reveals that the total desorbed amount of NO can not be correlated with the surface area but is approximately proportional to the B/(La + Sr) ratio (except Fe series) because the catalyst with a larger ratio of B/(La + Sr) has a higher activity as has been concluded in the above. We can say that the catalyst that adsorbs a larger amount of NO will have a higher activity. In Fe series catalysts, the desorption temperature range of NO exceeds the reaction temperature. For instance, in the range 0 e x e 0.5, the reaction conversion remains nearly unchanged beyond 400 °C; however, the desorption of NO still proceeds with an increasing temperature as the temperature exceeds 400 °C. If we integrate the amount of NO desorbed from 150 to 350 °C, its amount is 401, 314, 331, and 286 µmol/g for x ) 0, 0.3, 0.5, and 0.7, respectively. According to above results, we can infer that the magnitude of the total amount of NO desorbed in this temperature range also correlates with that of the catalyst activity. Comparing the desorbed amount with the activity in
each temperature interval of 50 °C reveals that the NO adsorption prominently influences the catalyst activity in the lower temperature range (below 450-500 °C). The catalyst with a higher NO adsorption amount yields a higher activity. However, the desorbed amount of NO obviously decreases as the temperature exceeds 500 °C, thereby implying that its effect on the catalyst activity does not dominate in a higher temperature range. TPR of CO. Figure 5 summarizes the results of TPR of CO. This figure indicates that the lowest temperature for initiating the reduction is lower than that for initiating the reaction in Figure 1. This finding suggests that CO reduces the catalyst before the NO + CO reaction occurs. Voorhoeve (1977) indicated that the catalytic reduction of NO is an intrafacial process. In other words, the catalyst must initially be reduced before the NO + CO reaction can occur. Our results correlate with this observation. Comparison of the COTPD patterns of the catalysts in each series in Figure 5 reveals that the reduction temperature initially decreases with increasing Sr content and, then, shifts to a higher temperature when the SrBO3 phase appears. This phenomenon reveals that adding Sr can influence
Ind. Eng. Chem. Res., Vol. 37, No. 7, 1998 2659 Table 4. Amounts of NO Desorbed from Catalystsa (µmol/g) in Each Temperature Range (°C) amount of NO desorbed in the given temp range catalyst La1-xSrxMnO3 x ) 0.0 x ) 0.3 x ) 0.5 x ) 0.7 x ) 1.0 La1-xSrxFeO3 x ) 0.0 x ) 0.3 x ) 0.5 x ) 0.7 x ) 1.0 La1-xSrxCoO3 x ) 0.0 x ) 0.3 x ) 0.5 x ) 0.7 x ) 1.0 La1-xSrxNiO3 x ) 0.0 x ) 0.3 x ) 0.5 x ) 0.7 x ) 1.0 a
150-200
200-250
250-300
300-350
350-400
400-450
450-500
500-550
550-600
total
16 22 17 13 2
124 118 109 80 57
101 97 113 85 59
44 60 77 71 2
30 55 115 81 0
14 32 127 23 0
4 11 40 3 0
0 1 16 0 0
1 0 1 0 0
334 396 615 357 119
24 38 39 39 0
150 146 112 107 0
162 82 88 66 3
65 50 92 74 1
25 42 88 118 0
45 37 66 132 0
41 20 48 52 0
6 5 28 31 0
0 0 7 7 0
519 418 568 627 4
11 33 30 21 0
91 93 215 87 11
71 83 86 55 0
37 81 62 41 0
59 53 51 21 0
35 45 48 13 0
10 40 51 5 0
1 19 28 0 0
0 2 7 0 0
318 449 578 243 12
7 48 0 0 0
44 183 3 37 0
34 172 10 11 0
17 169 33 10 1
16 323 83 33 11
91 153 72 77 35
78 97 48 100 2
53 85 27 54 4
4 41 1 0 6
346 1276 276 321 58
The data were obtained from the TPD patterns by integration.
Figure 5. CO patterns of the prepared catalysts in the CO-TPR experiment: (a) La1-xSrxMnO3; (b) La1-xSrxFeO3; (c) La1-xSrxCoO3; (d) La1-xSrxNiO3.
2660 Ind. Eng. Chem. Res., Vol. 37, No. 7, 1998
Figure 6. CO2 patterns of the prepared catalysts in the CO-TPR experiment: (a) La1-xSrxMnO3; (b) La1-xSrxFeO3; (c) La1-xSrxCoO3; (d) La1-xSrxNiO3.
the ability of reduction by CO. When La3+ is partially replaced by Sr2+, the charge compensation is accomplished by increasing the unstable B ion and oxygen vacancies, thereby facilitating diffusion of oxygen from bulk to surface. Consequently, the catalyst can be more easily reduced with an increasing Sr content (Nakamura et al., 1982, 1983). However, the hexagonal SrBO3 phase appearing in the major phase causes a decline in the rate of oxygen diffusion and the reducibility of the catalyst by CO. Furthermore, Figure 6a, c, and d indicates that the amounts of CO2 generated do not correlate with the amounts of CO consumed at a high temperature in Mn, Co, and Ni series catalysts. This finding implies that CO not only reacts with oxygen on a catalyst but is also adsorbed on the surface; therefore, the amount of consumed CO exceeds those of generated CO2. However, the adsorbed CO desorbs or reacts with the other forms of oxygen at higher temperatures, thereby causing the measured amount of CO to be lower than that of CO2 at high temperature. The desorption peak of CO2 appearing at around 900 °C in Figure 6a, c, and d
reveals this characteristic. Yamazoe et al. (1981) and Seiyama et al. (1985) observed two oxygen desorption peaks in each of the O2-TPD patterns obtained on La1-xSrxBO3 (B ) Mn, Fe, Co) catalysts. The hightemperature peak (β) was assigned as the lattice oxygen, and its intensity increased with an increasing Sr content. Comparing these results with ours reveals that when absorbed oxygen is consumed completely, the CO begins to be adsorbed on the surface of the partially reduced catalyst and, then, the β(lattice) oxygen is delivered and reacted with the adsorbed CO. Thus, a significant desorption peak of CO2 appears and its intensity increases with increasing oxygen content caused by increasing Sr content. Conclusions and Remarks According to results presented herein, the Fe series catalysts have a higher activity than the other three series toward the reduction of NO by CO. Substituting La with Sr in the catalysts of the Mn, Co, and Ni series can enhance the catalyst activity; however, an optimal
Ind. Eng. Chem. Res., Vol. 37, No. 7, 1998 2661
substitution fraction exists in each series. The promoting effect becomes more apparent in Co series. The decline in the activity beyond the optimal substitution fraction of Sr is owing to the formation of SrBO3 (which is detected by XRD). In contrast, adding Sr reduces the catalyst activity in the Fe series. Surface composition analysis reveals that the B/(La + Sr) ratio is an index for representing the catalyst activity. The catalyst with a higher B/(La + Sr) ratio yields a higher activity. The patterns of NO-TPD and CO-TPR can be used to account for the activity test results. In addition, both adsorption of NO and reduction by CO prominently influence NO + CO reaction. The desorbed amount of NO in the TPD, like the B/(La + Sr) ratio, shows a maximum value with an increasing Sr content. This maximum desorbed amount corresponds to the highest activity in each series of catalysts. The TPR of CO indicates that the catalyst with a higher reducibility has a higher activity. In other words, the reaction does not easily occur over stable catalysts. A catalyst with the highest activity is selected herein from four series of perovskites. The causes of its high activity are clarified by characterizing the catalysts by XRD, XPS, NO-TPD, and CO-TPR analyses, as well as activity tests. However the feasibility of further enhancing the catalyst activity by adding a promoter must be closely examined in a future work. Moreover, the kinetics of the NO + CO reaction over the optimal catalyst should be investigated. Acknowledgment The authors would like to thank the National Science Council of the Republic of China for financially supporting this research under Contract No. NSC 85-2214E006-016. Literature Cited Chang, C. C.; Weng, H. S. An Improvement on the Preparation of La-Sr-Co Perovskite by the Oxalate Method. Ind. Eng. Chem. Res. 1992, 31, 1615-1621. Hardee, J. R.; Hightower, J. W. Nitric Oxide Reduction by Methane over Rh/Al2O3 Catalysts. J. Catal. 1984, 86, 137-146. Ichimura, K.; Inoue, Y.; Yasumori, I. Catalysis by Mixed Oxide Perovskites. I. Hydrogenolysis and Ethylene and Ethane on LaCoO3. Bull. Chem. Soc. Jpn. 1980, 53, 3044-3049. Iizuka, T.; Lunsford, J. H. The Reduction of Nitric Oxide by Carbon Monoxide over Rhodium-Y-Zeolites. J. Mol. Catal. 1980, 8, 391400. Kremenic, G.; Nieto, J. M. L.; Tascon, J. M. D.; Tejuca, L. G. Chemisorption and Catalysis on LaMO3 Oxides. J. Chem. Soc., Faraday Trans. 1 1985, 81, 939-949. Ladovas, A. K.; Pomonis, P. J. Effects of Substitution in Perovskites La2-xSrxNiO4-λ on their Catalytic Action for Nitric Oxide + Carbon Monoxide Reaction. Appl. Catal. B 1992, 1, 101-116. Liang, J. J.; Weng, H. S. Catalytic Properties of La1-xSrxBO3(B ) Mn, Fe, Co, Ni) for Toluene Oxidation. Ind. Eng. Chem. Res. 1993, 32, 2563-2572. Libby, W. F. Promising Catalyst for Auto Exhaust. Science 1971, 171, 499-500.
Meadocraft, D. B. Low-cost Oxygen Electrode Material. Nature (London) 1970, 226, 847-848. Misono, M.; Nitadori, T. Redox and Catalytic Properties of Perovskite-Type Oxides. A Comparative Study of Ln1-xSrxBO3 (Ln ) Rare earth, B ) Mn, Fe, Co). Stud. Surf. Sci. Catal. 1985, 21 (Adsorpt. Catal. Oxide Surf.), 409-419. Nakamura, T.; Misono, M.; Yoneda, Y. Reduction-Oxidation and Catalytic Properties of La1-xSrxCoO3. J. Catal. 1983, 83, 151159. Natuse, Y.; Ogasawasa, T.; Hata, T.; Kishitaka, H. Properties and Performance of Various Iron Oxide Catalysts for NO Reduction with NH3. Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 57-61. Negas, T.; Roth, R. S. The System SrMnO3-x. J. Solid State Chem. 1970, 1, 409-418. Nitadori, T.; Kurihara, S.; Misono, M. Catalytic Properties of Lanthanum Manganese Mixed Oxide (La1-xA’xMnO3 (A’ ) Sr, Ce, Hf)). J. Catal. 1986, 98, 221-228. Pande, N. K.; Bell. A. T. Effect of Promoting Rh/SiO2 with TiO2 on the Reduction of Nitric Oxide. Appl. Catal. 1986, 20, 109122. Pena, M. A.; Tascon, J. M. D.; Fierro, J. L. G.; Tejuca, L. G. A Study of Nitric Oxide and Carbon Monoxide Interactions with Lanthanum Manganese Oxide (LaMnO3). J. Colloid Interface Sci. 1987, 119, 100-107. Seiyama, T.; Yamazoe, N.; Eguchi, K. Characterization and Activity of Some Mixed Metal Oxide Catalysts. Ind. Eng. Chem. Prod. Res. Dev. 1985, 24, 19-27. Tascon, J. M. D.; Medioroz, S.; Tejuca, G. L. Preparation, Characterization and Catalytic Properties of LaMeO3 Oxides. Z. Phys. Chem. (Munich) 1981, 124, 109-127. Tascon, J. M. D.; Tejuca, L. G.; Rochester, C. H. Surface Interaction of Nitric Oxide and Carbon Monoxide with Lanthanum Perovskite (LaMnO3). Oxide. J. Catal. 1985, 95, 558-566. Voorhoeve, R. J. H. Advanced Materials in Catalysis; Academic Press: New York, 1977. Voorhoeve, R. J. H.; Remeika, J. P.; Freeland, P. E.; Matthias, B. T. Rare-Earth Oxides of Manganese and Cobalt Rival Platinum for the Treatment of Carbon Monoxide in Auto Exhaust. Science 1972, 177, 353-354. Voorhoeve, R. J. H.; Remeika, J. P.; Johnson, D. W., Jr. RareEarth Manganites: Catalysts with low Ammonia Yield in the Reduction of Nitrogen Oxides. Science 1973, 180, 62-64. Voorhoeve, R. J. H.; Remeika, J. P.; Trimble, L. E. Defect Chemistry and Catalysis in Oxidation and Reduction over Perovskite-Type Oxides. Ann. N. Y. Acad. Sci. 1976, 272, 3-21. Voorhoeve, R. J. H.; Johnson, D. W.; Remeika, J. P.; Gallagher, P. K. Perovskite Oxides: Materials Science in Catalysis. Science 1977, 195, 827-833. Yamazoe, N.; Teraoka, Y.; Seiyama, T. TPD and XPS Study on Thermal Behavior of Absorbed Oxygen in Lanthanum Strontium Cobalt Oxide (La1-xSrxCoO3). Chem. Lett. 1981, 12, 17671770. Yu Yao, Y. F. The Oxidation of Hydrocarbons and CO over Metal Oxides: IV. Perovskite-Type Oxides. J. Catal. 1975, 36, 266275. Zhang, H. M.; Teraoko, Y.; Yamazoe, N. Preparation of Supported Lanthanum Strontium Manganese Oxide (La1-xSrxCoO3). Appl. Catal. 1988, 41, 137-146.
Received for review September 26, 1997 Revised manuscript received March 24, 1998 Accepted March 31, 1998 IE970691G
