Kenneth E. Voss

Monolithic diesel oxidation catalysts

Abstract A flow-through ceramic monolithic catalyst, containing bulk CeO 2 as the catalytically active component, is reported for the catalytic oxidation of the liquid portion of the particulates present in diesel engine exhausts. This new technology has been successfully implemented into medium duty trucks in the U.S. beginning in 1994 meeting all required emission standards. Catalyst screening and engine durability/aging results and a proposed mechanism of operation are presented. The addition of a proprietary zeolite as a hydrocarbon trap and a small amount of Pt to the platform CeO 2 catalyst enables european emission standards for CO, HC and particulates to be met. Commercialization of this technology in Europe began in the first part of 1996.

Plasma-assisted catalytic reduction of NOx

Many studies suggest that lean-NOx SCR proceeds via oxidation of NO to NO¬ by oxygen, followed by the reaction of the NO¬ with hydrocarbons. On catalysts that are not very effective in catalyzing the equilibration of NO+O¬ and NO¬, the rate of N¬ formation is substantially higher when the input NOx is NO¬ instead of NO. The apparent bifunctional mechanism in the SCR of NOx has prompted the use of mechanically mixed catalyst components, in which one component is used to accelerate the oxidation of NO to NO¬, and another component catalyzes the reaction between NO¬ and the hydrocarbon. Catalysts that previously were regarded as inactive for NOx reduction could therefore become efficient when mixed with an oxidation catalyst. Preconverting NO to NO¬ opens the opportunity for a wider range of SCR catalysts and perhaps improves the durability of these catalysts. This paper describes the use of a non-thermal plasma as an efficient means for selective partial oxidation of NO to NO¬. When combined with some types of SCR catalyst, the plasma can greatly enhance the NOx reduction and eliminate some of the deficiencies encountered in an entirely catalyst-based approach. efficiency for reduction of NOx

Catalytic oxidation of diesel particulates with base metal oxides

Abstract Reduction of emissions from diesel engines using novel flow-through oxidation catalysts containing base metal oxides has been demonstrated. The soluble organic fraction (SOF) of the particulates can be converted and gas phase hydrocarbons can be removed via the proper choice of oxides. Low levels of platinum on the catalysts also compliment HC and CO conversion without leading to “sulfate-make”. Catalyst performance is shown for transient and steady state engine testing relative to emissions standards for U.S. truck and European auto applications. Laboratory studies using PYRAN TM thermal chromatography and engine storage & release test results provide insight of the mechanisms of removal and conversion of SOF and HCs by the catalysts.

New Catalyzed Cordierite Diesel Particulate Filters for Heavy Duty Engine Applications

A family of cordierite DPF filters were developed and studied for their efficacy for catalyzed soot filter applications. In addition to porosity and median pore size of DPF filters, breadth of pore size distribution, microstructure, and pore connectivity have a profound influence not only in filter performance (pressure drop, catalyst coatability, and filtration efficiency) but also on mechanical and physical properties. Through filter material composition development, optimum values for the %porosity, median pore diameter, and breadth of the pore size distribution for minimizing pressure drop have been identified, leading to the development of a new family of high-porosity cordierite diesel particulate filters that possess a unique combination of high filtration efficiency, high strength, and very low clean and soot-loaded pressure drop in both the catalyzed and non-catalyzed states. By controlling the microstructure, the impact of the catalyst on pressure drop has been minimized. Soot-loaded pressure drops of these new filters in their catalyzed state are less than 50% of other catalyzed commercial filters with the same cell geometry. In contrast, large pore size and high porosity filters raise concerns of low filtration efficiency and low mechanical strength at both catalyzed and uncatalyzed states. Addition of catalyst into the filters seems to have little or no impact on filter filtration efficiency, static mechanical and thermal properties.