High porosity honeycomb and method

#The present invention relates to ceramic bodies for use in automotive catalytic converter systems, and in particular to high porosity honeycomb substrates having reduced thermal mass and offering faster light-off performance.

#The exhaust gases emitted by internal combustion systems utilizing hydrocarbon fuels, such as hydrocarbon gases, gasoline or diesel fuel, can cause serious pollution of the atmosphere. Among the many pollutants in these exhaust gases are hydrocarbons and oxygen-containing compounds, the latter including nitrogen oxides (NOx) and carbon monoxide (CO). The automotive industry has for many years attempted to reduce the quantities of pollutants from automobile engine systems, the first automobiles equipped with catalytic converter systems having been introduced in the mid 1970's.

#Cordierite substrates, typically in the form of honeycomb structures, have long been preferred for use as substrates to support catalytically active components in part due to the high thermal shock resistance of such structures. Increasingly stringent regulations in recent years have been requiring higher conversion efficiencies in catalytic converters for the automotive market. Automobile emissions can be significantly reduced by controlling the light-off process. More than fifty percent of a vehicle's total emission is generated before light-off takes place.

#A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent detailed description, in which:

#FIG. 1 is a graph based on chemical reaction modeling illustrating the predicted improved light-off time in a high porosity cordierite honeycomb substrate according to the present invention;

#FIG. 2 is a scanning electron micrograph taken at 487× magnification of a high porosity cordierite honeycomb substrate according to the present invention; and,

#The ceramic honeycomb substrate of the present invention combines the attractive attributes of a very thin-walled structure having a fast-light off time, as a virtue of high porosity in the range of 45 to 75%, with a more conventional substrate geometry defining cell webs having a thickness of greater than 2.0 mil (0.0020 inch, 0.0508 mm). In a preferred embodiment the porosity is preferably in the range of 50 to 65%, and most preferably 55%. In another preferred embodiment the wall thickness is between 2.5 mil (0.0025 in., 0.0635 mm) to 7 mil (0.0070 in., 0.1778 mm), and more preferably between 2.5 mil (0.0025 in., 0.0635 mm) to 3 mil (0.0030 in., 0.0762 mm).

#The cell density of the inventive honeycomb is not critical, but depends on particular applications. Generally, cell densities of 400 cells/in2 (62 cells/cm2) to 900 cells/in2 (140 cells/cm2) are suitable for purposes of the present invention.

#In an embodiment the inventive structure exhibits a low coefficient of thermal expansion (CTE) (25-800° C.) of less than 15×10−7/° C., preferably less than 10×10−7/° C. The low thermal expansion imparts the honeycomb body with a high thermal shock resistance making it suitable for use in harsh environments. In another embodiment the inventive structure demonstrates high structural strength as provided by a modulus of rupture (MOR), as measured on a cellular bar sample, of 200-400 psi, preferably 350 psi.