Reformate assisted hydrocarbon selective catalytic NOx reduction over silver supported on alumina catalysts.

Due to increasingly stringent regulations limiting the emissions of nitrogen oxides worldwide from lean exhaust mobile and other sources, there is great technological need for catalytic reduction of NOx. There is great interest in developing catalysts capable of reducing NOx species in this chemically complex exhaust environment. Currently, no such commercial catalyst is available using hydrocarbon selective catalytic reduction of NO x (HC SCR NOx) technology that will enable manufacturers to comply with future worldwide NOx emissions standards. HC SCR NOx would be the most attractive solution given that hydrocarbon fuel is already on-board. The objectives of this work were to develop a highly active catalyst for reformate assisted HC SCR NOx, determine the effects of the exhaust environment on NOx conversion activity, and develop a mechanism and kinetic model to predict the performance of the active catalyst. A series of Al2O3 supported catalysts with either Pd, Ag, An, or Pd-Ag were made using various catalyst synthesis methods. The catalysts were characterized and their activity evaluated at steady state conditions for NOx conversion under a surrogate diesel exhaust environment with varied reformate and propylene feed conditions. The evaluation procedure was developed using a factorial design method containing four factors: temperature, H2/CO ratio, HC1/NOx ratio, and total reductant composition (H2, CO, and propylene). Temperature had 8 levels in the temperature range of 200-550°C evenly spaced while the other factors each had three. The factor values were chosen using envisioned typical diesel exhaust aftertreatement conditions as the basis including the concept of secondary reductant injection. Silver supported on gamma alumina (Ag/gamma-Al2O3) catalysts showed the highest NOx conversion at all conditions. The factorial design results showed that one main factor, HC1/NO x ratio, and interactions such as H2/CO with HC1/NOx, H2/CO with temperature, and HC 1/NOx with temperature most significantly effected NO x conversion. For all scenarios investigated, the higher inlet propylene concentrations (1000 and 1400 ppm) reformate widened the NOx conversion activity window in the case of higher H2/CO ratios (1 and 2). For the CO dominant H2/CO ratio (0.6) the activity window was narrower than for the H2 dominant conditions at propylene conditions evaluated.Ph.D.Applied SciencesChemical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126455/2/3253303.pd