Particulate emission studies, catalytic

Emission studies show that lead is only a small part of the automotive pollution problem. Prior to control, hydrocarbon emissions were more than 40 times and the oxides of nitrogen emissions more than 15 times the emission of the lead compounds. Obviously, however, legislation will result in the eventual elimination of lead from gasoline. The removal of lead, besides eliminating a possible toxic pollutant, simplifies the problem of handling other automotive exhaust pollutants in that catalytic exhaust chambers perform much better in the absence of lead contaminant. All emission standards become particularly severe in 1975 and 1980. The particulate standards are equivalent to 1 gram Pb/gal in 1975 and 0.3 gram Pb/gal in 1980. Since the particulates include all solid materials, tolerable lead levels will be less than indicated above. 

A key research area is the study of the effect of selective catalytic reduction (SCR), selective noncatalytic reduction (SNCR), dry particulate adsorbent injection, and SOx removal systems on the removal efficiency, pressure drop, and lifetime of the baghouses. The use of fabric filters in PC boilers is increasing every year due to the stringent particulate emission standards. Pennsylvania Power and Light was the first utility to install a bag-house in 1973, and up until 2005, more than 129 RGFFs were installed on 28 GW of power plant capacities [64] (Figure 18.10). 

For this purpose, in addition to the continuous evolution of CR and exhaust gas recirculation (EGR), novel primary measures are under study, including the long route EGR to cool the recirculated exhaust gas, the use of premixed combustion [which implies, however, higher GO and unburned hydrocarbon (U HG) emissions], the reduction of the compression ratio, the shaping of the injection rate and so on. Still, the after-treatment catalytic technologies for O, removal and for CO/hydro-carbon (HG) and particulate matter (PM) reduction in passenger cars must be improved significantly. 

Information presented also indicated that several catalytic reactions are possible on particulate matter, and that future studies should include better data on size and chemical characteristics of particulate matter. In fact, mobile discharges have a high moisture content, reactive acid anhydrides (e.g., NO2) catalytic-adsorptive particulate matter, and contain reactive PAH species. Future research must deal with this reactive matrix and better identify the products of combustion and the reactions induced by sampling the emission stream. 

A promising alternative to reduce soot emission is the development of a multifunctional catalytic filter that combines filtration and oxidation of the emitted particulate matter. Consequently, several authors have carried out studies of catalysts such as perovskite (La-Li-Cr or lanthanum cobaltite)-t)q)e oxides in a temperature-programmed combustion microreactor (>600 °C) offering the best compromise between satisfactory catalytic activity and stability [17,18]. 

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