LOW-COST ROUTE TO MIXED-PHASE, HIGH SURFACE AREA NANOPOWDERS FOR ENVIRONMENTAL CATALYST MATERIALS VTA LIQUID-FEED FLAME SPRAY PYROLYSIS (LF-FSP)

摘要

Public concerns for air quality, especially in urban environs, continue to drive the search for increasingly efficient emission control systems for internal combustion engines. Three recent reviews describe the progress, current problems and future needs (legal mandates) that drive efforts to develop better systems. These reviews note that for autos, three way catalyst (TWC) systems composed of an active metal (e.g. Pd) impregnated on a reversible oxygen storage promoter (Ce_xZr_(1-x)O_2)/high surface area alumina washcoat are the industry standard. These systems effectively convert CO, NO_x, and hydrocarbons, the main pollutants in auto exhaust, to CO_2, N_2, O_2, and H_2O. They are now so effective that contributions from the once lower emitting and unregulated diesel engines now constitute a significant component of urban air pollution. TWCs that are effective for autos offer little or no help in eliminating the particulate, unburned hydrocarbon and particularly NO_x emissions produced by diesel engines because of the 5 to 15 mol% excess O_2 in their exhausts. Similar problems occur with the more fuel efficient lean-burn gasoline engines currently being introduced. Reduction of particulate and hydrocarbon emissions from diesels is difficult but not impossible using existing technology. However, coincident NO_x reduction requires new scientific and technical advances. New U.S. regulations require that diesel engine NO_x emissions be cut to 4g/BHP-hr in 1998 and to 2.0 gr./BHP-hr by 2003. Similar requirements apply to Europe and somewhat less stringent requirements are in place in Japan and Korea. This represents an average decrease of 50% or greater in NO_x tailpipe emissions from pre-1998 standards. At present, the only improvements thought to be necessary for TWCs at the moment are reductions in cost.