Mechanistic aspects of the selective reduction of NO by propene over alumina and silver-alumina catalysts

Journal Article · Mon Oct 25 04:00:00 EDT 1999 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1999.2622· OSTI ID:20003845

Meunier, F C; Breen, J P; Zuzaniuk, V; Olsson, M; Ross, J R.H.

The selective catalytic reduction of NO with C{sub 3}H{sub 6} in the presence of a large excess of O{sub 2} (i.e., C{sub 3}H{sub 6}-SCR (selective catalytic reduction)) was studied over {gamma}-Al{sub 2}O{sub 3}, 1.2% Ag/{gamma}-Al{sub 2}O{sub 3}, and 10% Ag/{gamma}-Al{sub 2}O{sub 3} catalysts. The {gamma}-Al{sub 2}O{sub 3} and the low-loading silver material exhibited high conversions to N{sub 2} whereas the high-loading sample predominantly yielded N{sub 2}O. Surprisingly, a comparison of actual No{sub 2} yields to thermodynamically predicted yields of NO{sub 2} showed that the formation of NO{sub 2} during the C{sub 3}H{sub 6}-SCR of NO over {gamma}-Al{sub 2}O{sub 3} was not achieved through the direct oxidation of NO with O{sub 2}. An alternative mechanism involving the formation of organonitrite species followed by their decomposition/oxidation was suggested to be the main route for the formation of NO{sub 2}. The promoting role of low loadings of silver on alumina on the activity for N{sub 2} production was attributed to the higher rate of formation of inorganic ad-NO{sub x} species (e.g., nitrates) as evidenced by in situ DRIFTS and thermogravimetric analyses. It was proposed that these inorganic ad-NO{sub x} species further react with the reductant or a derived species to form various organo-NO{sub x} compounds. In particular, organo-nitro and organo-nitroso compounds and/or their derivatives (e.g., isocyanate, cyanide, amines, and NH{sub 3}) were suggested to react with NO or the organo-nitrite and/or its derivative NO{sub 2} to yield N{sub 2}. When no reductant was present, the low-loading Ag/{gamma}-Al{sub 2}O{sub 3} material was poisoned by strongly bound nitrates and its activity for NO{sub 2} formation was similar to that observed over the alumina.

• Research Organization: Univ. of Limerick (IE)
• OSTI ID: 20003845
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 187; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ALUMINIUM OXIDES
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
NITRIC OXIDE
PROPYLENE
SELECTIVE CATALYTIC REDUCTION
SILVER