Jennifer S. Feeley

In situ high temperature FTIR studies of NOx reduction with propylene over Cu/ZSM-5 catalysts

High temperature in situ FTIR has been used to investigate the surface species present on Cu/ZSM-5 during the reduction of NOx with propylene in a lean environment. Parallels have been observed between adsorbed surface species and catalytic activity for this reaction. Species detected at low temperatures are not representative of those detected at high temperatures where the catalyst is active. An oxidized nitrogen-containing species has been observed at 2580 cm−1 on Cu during reaction conditions (400°C). In contrast, at low temperatures, where the catalyst is less active, coke and Cu+-CO predominated. The effects of Cu weight loading, C/NO ratio, reaction temperature, and catalyst deactivation by steaming have been investigated with IR.

Lean NOx reduction with hydrocarbons over Ga/S-ZrOx and S-GaZr/Zeolite catalysts

Abstract Ga/S-ZrO x and sulfated GaZr/Zeolite catalysts were found to be very effective for the reduction of NO x in a lean environment with hydrocarbons.Ga/S-ZrO x was much more active than S-ZrO x orGa/ZrO x as well as a wide variety of Ga supported amorphous super acids. Incorporating ZSM-5 into the catalyst formulation, i.e.S-GaZr/ZSM-5, increased NO x reduction activity particularly at low temperatures. The effects of zeolite support, sulfation, and mono vs. bimetallic supported samples were investigated. For ZSM-5, sulfation and the combination of Ga with Zr proved to be most active.Ga/S-ZrO x andS-GaZr/ZSM-5 were investigated with C 3 H 8 , C 3 H 6 , CH 4 , and CO as reductants and compared toCu/ZSM-5. UnlikeCu/ZSM-5 which was most active with C 3 H 6 , Ga/S-ZrO x andS-GaZr/ZSM-5 were more active with C 3 H 8 than with C 3 H 6 .S-GaZr/ZSM-5 was also active with CH 4 . All three catalysts were inactive with CO and did not catalyze the NO x decomposition reaction. BothGa/S-ZrO x andS-GaZr/ZSM-5 were more hydrothermally stable thanCu/ZSM-5. However, their activities decreased significantly with increasing space velocity or in the presence of water in the feed making them impractical catalysts for mobile or stationary sources.

Lean NOx: dual sites for NOx reduction on Pt/H-ZSM-5

Abstract Pt/H-ZSM-5 contains independent sites for the reduction of NO x , (1) acidic sites associated with H-ZSM-5 which selectively reduce NO x to N 2 via stored hydrocarbons at low temperatures and (2) conventional Pt sites which reduce NO x to N 2 and N 2 O at higher temperatures. Propylene is trapped on acid sites, undergoes polymerization but retains activity for NO x reduction provided both NO and O 2 are present. Neither O 2 or NO will individually react with the adsorbed polymer but together NO x reduction occurs readily supporting the mechanism of enhanced conversion of NO x via NO 2 . This phenomenon has also been demonstrated with diesel fuel as the added reductant. This understanding suggests a novel strategy for diesel engines in which fuel is pulsed into the exhaust at the conditions where the acidic sites are active (i.e. 185°C) giving enhanced NO x conversion. After aging in the automobile exhaust, deactivation by de-alumination of the acidic sites occurs with a loss of hydrocarbon trapping and low temperature NO x reduction. Thus, improved hydrothermally stable materials are still needed to satisfy the mobile source applications.

Transition Metal/Zeolite Catalysts by Design: Nucleation and Growth of Mono- and Bimetallic Particles in Zeolite Y

Abstract A highly dynamic model emerges for mono- and bimetallic particles inside a Y zeolite under conditions of catalytic CO hydrogenation. Nickel tetracarbonyl and Pd carbonyl clusters are the most probable vehicles in a rather dramatic relocation of Ni and Pd atoms between cages, but also between the outer mantle and the inner core of the zeolite. Zeolite protons interfere by acting as anchors and as nucleation sites. Growing metal particles appear able to destroy their zeolite cages.