Jimmie Lewis Williams

Monolith structures, materials, properties and uses

Abstract Extruded monolith substrates are widely used in automotive and stationary emission control reactors such as selective catalytic reduction (SCR) units. Monoliths are increasingly being used, developed, and evaluated as catalyst supports in many new reactor applications such as chemical and refining processes, catalytic combustion, ozone abatement, and others. This paper gives a general overview of monolith fabrication, characteristics and typical use. Several commercial product applications and new developments for use of monolith reactors in automotive, stationary and chemical industry are discussed.

Extruded monolithic catalyst supports

Abstract Extruded monolithic catalyst substrates are widely used in automotive and stationary emissions control reactors. They are increasingly being used, developed, and evaluated in many other reactor applications such as for the chemical processing industries, for catalytic combustion, for ozone abatement, and others. This paper will compare the variety of extruded monoliths used for these applications and will review the forming and characterization of them. Emphasis is on the materials used for automotive substrates, catalysts for selective catalytic reduction of NOx and for new high surface area substrates.

In-Line Hydrocarbon Adsorber System for ULEV

An in-line hydrocarbon (HC) adsorber system was developed to reduce cold start HC emissions. The system comprises a first catalyst, adsorber unit, and a second catalyst for oxidation of desorbed HC. During cold start, exhaust gas is directed to the hydrocarbon adsorber using a fluidic flow diverter unit without any mechanical moving parts in the exhaust system. After the first catalyst lights off, the diverter is shut off and the major portion of the exhaust gas then flows directly to the second catalyst without heating the adsorber unit. After the second catalyst reaches light-off temperature additional air was added to oxidize the desorbed HC. The system attributes are: NMHC emissions in ULEV range; straight line axial flow; reliable design; and limited back pressure penalty. The system was tested on a 3.8L US vehicle.

Hydrocarbon adsorber system for cold start emissions

A new adsorber concept has been tested. A zeolite adsorber with a central hole is mounted below the first catalyst, with a second catalyst downstream. During the cold start, when the adsorber is cool and the HC concentration high, HCs are adsorbed from the gas fraction passing-through the channels. The small fraction of exhaust gas passing through the hole impinges directly on and heats the second catalyst. The rationale is to design the hole to maximize the second catalyst heating rate, minimize desorption during heat-up and simultaneously keep the HCs which pass through the hole at an acceptably low level. FTP test results on the 3.8 L engine give 0.081 g/mi NMHC with no hole (same as base line) and decrease to 0.056 g/mi NMHC with the hole. This concept exhibits NMHC performance in the LEV range.

By-pass hydrocarbon absorber system for ULEV

A by-pass zeolite adsorber system consisting of a first catalyst, a by-pass loop containing the zeolite adsorbers followed by a downstream second catalyst was FTP tested using a US vehicle equipped with a 3.8 L, V6 engine. The system exhibited ULEV emissions performance with hydrocarbon adsorption and regeneration (desorption and oxidation) within the FTP cycle and required only a single diversion valve within the exhaust line. Adsorption takes place during the initial 70 seconds of the FTP cycle. The adsorbers were regenerated with the exhaust gas plus injected air.