CO + O2 and CO + NO Reactions over Pd/Al2O3 Catalysts

Rainer, D. R.; Koranne, M.; Vesecky, Scott M.; Goodman, D. W.

doi:10.1021/jp971262z

Cited by 125 publications

(90 citation statements)

References 34 publications

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“…14 There is good agreement between these two studies concerning the isotopic shifts. Our current isotopic studies on Pd(111) indicate that the surface feature corresponding to the vibrational band at 2240-2257 cm -1 contains both C and N. However, considering previous experimental [6][7][8][9][10] and theoretical 23 studies concerning CO adsorption on Pd(111), CO dissociation leading to atomic C can be ruled out due to its high activation energy (4.4 eV). 23 Therefore, intact CO molecules adsorbed on Pd(111) can be the only source of the carbon for the observed species, which further supports the assignment mentioned above.…”

Section: Published On Web 06/27/2002mentioning

confidence: 74%

Isocyanate Formation in the Catalytic Reaction of CO + NO on Pd(111): An in Situ Infrared Spectroscopic Study at Elevated Pressures

2002

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The catalytic conversion of environmentally hazardous pollutants in automobile exhausts is one of the most thoroughly studied problems in heterogeneous catalysis. Three-way catalysts (TWC) are used to remove the major pollutants in the exhaust gases by the simultaneous reduction of NO x and the oxidation of CO and unburned hydrocarbons. Recently, Pd-based catalysts have been considered as an alternative to the more commonly used Pt/Rhbased catalysts. 1,2 In this study vibrational spectroscopy is used to examine the in situ adsorption of CO + NO to form CO 2 , N 2 O and N 2 on a Pd(111) model catalyst under high-pressure conditions. We employ polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS), [3][4][5] an adaption of the well-known IRAS technique. The surface sensitivity of PM-IRAS relies on the fact that IR absorption by an adsorbed species on a metal surface shows a strong dependence on the polarization of the incoming IR beam, while gas-phase species are isotropic with respect to the polarization. Figure 1 shows PM-IRA spectra of Pd(111) in the presence of a 240 mbar CO + NO mixture within the temperature range 300-600 K (CO:NO ) 3:2). The spectra were obtained by increasing the CO + NO gas mixture pressure at T surface ) 300 K until an equilibrium pressure of 240 mbar was established. The data were acquired in the presence of 240 mbar of ambient pressure at the given temperatures. The spectrum at 350 K shows a feature at 1922 cm -1 , which corresponds to CO residing on either two-fold or threefold Pd sites. [6][7][8][9][10] The feature at 1876 cm -1 can be assigned to CO located on the three-fold sites 7,[8][9][10] while the peak at 1745 cm -1 is assigned to NO bound to atop sites. 11 At 350 K, atop sites are predominantly occupied by NO whereas three-fold sites are occupied by CO and possibly NO (considering the broad band at approximately 1550 cm -1 ). Interestingly, at 600 K and under reaction conditions, the spectrum is dominated by a new band at 2255 cm -1 besides the CO-related feature at 1908 cm -1 . The feature at 2255 cm -1 is assigned to the asymmetric stretching mode of an isocyanate (-NCO) species. [12][13][14][15][16][17][18][19][20] Once produced at high temperatures (500-625 K), this species is stable within the 300-625 K temperature range as well as after reducing the chamber pressure to 1 × 10 -7 mbar at room temperature. In previous infrared studies on Pd/Al 2 O 3 16,17 a broad band near 2242 cm -1 has been observed and assigned to a substrate-bound isocyanate species. According to these previous studies, the formation of isocyanate takes place on metal sites followed by spillover to the substrate. Although a metal-bound isocyanate species was not reported for the Pd/Al 2 O 3 system, 16 isocyanate formation in the CO + NO reaction on Pd(111) was postulated in a recent theoretical study. 20 To explore the conditions under which the metal-bound isocyanate species is formed on Pd(111), experiments with different total pressures were conducted (see Figure 2). At 10 -4...

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Section: Published On Web 06/27/2002mentioning

confidence: 74%

Isocyanate Formation in the Catalytic Reaction of CO + NO on Pd(111): An in Situ Infrared Spectroscopic Study at Elevated Pressures

2002

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“…For example, Reiner et al [6,7] and Holles et al [8,9] have published data obtained from a conventional flow reactor, while Prevot et al [10,11], Nakao et al [12] and Thirumoorthy et al [13] used molecular beam techniques.…”

Section: Introductionmentioning

confidence: 99%

Time Decay of the Activity of the Reduction Reaction of NO by CO on a Pd/Al2O3 Catalyst

et al. 2008

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An experimental study is made of the time decay of activity of the CO-NO reaction on a Pd/Al2O3 looking at the effect on reaction order and apparent activation energy. The optimum kinetics parameters fitting the steady state data at moderate pressures are determined. The time decay curves are analyzed through various catalyst deactivation models.The authors acknowledge the financial support of this work by FONDECYT under Project 1070351

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“…Therefore, properties of the Pd based model heterogeneous catalyst systems for gas/solid interfaces have been investigated extensively in our laboratories . Particularly, Pd single crystal surfaces [3], [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Pd/X bimetallic systems (X= Mo [22][23][24][25], Ru [26][27][28][29], Cu [28;30], Ta [25;29;31], W [25;29;32;33], Re [25-27;29] ), Pd/X/Y trimetallic systems (X/Y= Cu/Mo [34], Au/Mo [34]), Pd clusters deposited on SiO 2 [10;35-41], Al 2 O 3 [42][43][44][45][46][47], TiO 2 [48][49][50][51] and MgO [49;51] have been examined using various surface spectroscopic tools.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Catalytic Conversion of Automobile Exhaust Emissions Using Model Catalysts: CO + NO Reaction on Pd(111)

Özensoy

Heß

Goodman

2004

Topics in Catalysis

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The CO + NO reaction is one of the profoundly important reactions that take place on Pd-based industrial three-way catalysts (TWC). In this review, we discuss results from polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) and conventional IRAS experiments on CO adsorption, NO adsorption and the CO + NO reaction on a Pd(111) model catalyst surface within a wide range of pressures (10 -6 -450 Torr) and temperatures (80 -650 K). It will be shown that these studies allow for a detailed understanding of the adsorption behavior of these species as well as the nature of the products that are formed during their reaction under realistic catalytic conditions. CO adsorption experiments on Pd(111) at elevated pressures reveal that CO overlayers exhibit similar adsorption structures as found for ultrahigh vacuum (UHV) conditions. On the other hand, in the case of the CO + NO reaction on Pd(111), the pressure dependent formation of isocyanate was observed. The importance of this observation and its effects on the improvement of the catalytic NOx abatement is discussed. The kinetics of the CO + NO reaction on Pd(111) were also investigated and the factors affecting its selectivity are addressed.

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CO + O₂ and CO + NO Reactions over Pd/Al₂O₃ Catalysts

Cited by 125 publications

References 34 publications

Isocyanate Formation in the Catalytic Reaction of CO + NO on Pd(111): An in Situ Infrared Spectroscopic Study at Elevated Pressures

Isocyanate Formation in the Catalytic Reaction of CO + NO on Pd(111): An in Situ Infrared Spectroscopic Study at Elevated Pressures

Time Decay of the Activity of the Reduction Reaction of NO by CO on a Pd/Al2O3 Catalyst

Understanding the Catalytic Conversion of Automobile Exhaust Emissions Using Model Catalysts: CO + NO Reaction on Pd(111)

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