Honeycomb carbon filters

The second method used to reduce exliaust emissions incorporates postcombustion devices in the form of soot and/or ceramic catalytic converters. Some catalysts currently employ zeolite-based hydrocarbon-trapping materials acting as molecular sieves that can adsorb hydrocarbons at low temperatures and release them at high temperatures, when the catalyst operates with higher efficiency. Advances have been made in soot reduction through adoption of soot filters that chemically convert CO and unburned hydrocarbons into harmless CO, and water vapor, while trapping carbon particles in their ceramic honeycomb walls. Both soot filters and diesel catalysts remove more than 80 percent of carbon particulates from the exliatist, and reduce by more than 90 percent emissions of CO and hydrocarbons. 

One of the potentially wide-spread applications under development is catalytic filters for air pollution control. This combines separation and catalytic oxidation into one unit operation. One possibility is the oxidation of volatile organic carbon (VOC) by employing a porous honeycomb monolithic ceramic membrane filter. Inside the pores are deposited an oxidation catalyst such as precious metals. The resulting VOC removal efficiency can exceed 99% [Bishop et al., 1994]. 

They contain Ti02 and activated carbon (C), the latter trapping pollutants for subsequent destruction by the irradiated Ti02. These filters feature a honeycomb-type construction for minimum pressure drop. 

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