On the promotional effect of Pd on the propene-assisted decomposition of NO on chlorinated Ce0.68Zr0.32O2

Abstract

The Selective Catalytic Reduction (SCR) of NO x assisted by propene is investigated on Pd/Ce 0.68 Zr 0.32 O catalysts (Pd/CZ), and is compared, under identical experimental conditions, with that found on a Pd/SiO 2 reference catalyst. Physico-chemical characterisation of the studied catalysts along with their catalytic properties indicate that Pd is not fully reduced to metallic Pd for the Pd/CZ catalysts. This study shows that the incorporation of Pd to CZ greatly promotes the reduction of NO in the presence of C 3 H 6. These catalysts display very stable deNO x activity even in the presence of 1.7% water, the addition of which induces a reversible deactivation of about 10%. The much higher N 2 selectivity obtained on Pd/CZ suggests that the lean deNO x mechanism occurring on these catalysts is different from that occurring on Pd 0 /SiO 2. A detailed mechanism is proposed for which CZ achieves both NO oxidation to NO 2 and NO decomposition to N 2 , whereas PdO x activates C 3 H 6 via ad-NO 2 species, intermediately producing R-NO x compounds that further decompose to NO and C x H y O z. The role of the latter oxygenates is to reduce CZ to provide the catalytic sites responsible for NO decomposition. The proposed C 3 H 6-assisted NO decomposition mechanism stresses the key role of NO 2 , R-NO x and C x H y O z as intermediates of the SCR of NO x by hydrocarbons.

Alumina supported cobalt–palladium catalysts for the reduction of NO by methane in stationary sources

“…The HC x O y species are simultaneously transformed to CO 2 and H 2 O. The detailed process has already been described on zeolites based catalysts by Berger et al [21] and on ceriazirconia based catalysts by Thomas et al [19]. The interaction between NO 2 and HCl is clearly located in the second catalytic cycle.…”

“…More recently, a general three-function model for deNO x catalysis [17][18][19][20] was also proposed for metals in cationic form (Fig. 1).…”

DRIFTS–XANES study of Pd-Ni/(Ce,Zr)Ox/Al2O3 model automotive catalysts

“…Former work on this reaction evidenced opposite effects of the establishment of contacts between Pd and CZ entities in this type of systems. On the one hand, it appeared that dispersed CZ entities could facilitate the NO reduction activity of metallic Pd by providing new active interfacial sites in the form of surface oxygen vacancies able to reductively activate NO [18][19][20][21]. However, difficulties could also appear in the presence of such contacts, and in contrast to cerium-free supported systems [14,24], for generating metallic palladium surfaces [22]; these latter are known to be most active for such process [23,24].…”

Selective reduction of NO X in diesel exhaust with hydrocarbons over alumina in NEDC conditions

“…Indeed, thermodynamic limitations permit the oxidation of NO to NO 2 at such low temperatures and with excess of oxygen concentration (8% vol.) [10].…”

“…According to this model, an effective automotive catalyst for lean NO X reduction has to ensure these threecatalytic cycles which have to turn over simultaneously. In previous studies, this model was applied to several catalysts [10][11][12]. Among them, alumina used as simple catalyst has yielded promising results since it provides a significant catalytic activity above 250°C [13].…”