Diesel through monolith catalyst

Scheme 35.2 Diesel oxidation flow through monolith catalyst...

A schematic of a monolith catalyst is shown in Fig. 19-18a. In cases where pressure drop is limiting, such as for CO oxidation in cogeneration power plant exhausts, monolith catalyst panels may be stacked to form a thin (3- to 4-in-thick) wall. The other dimensions of the wall can be on the order of 35 x 40 ft. CO conversion is over 90 percent with a pressure drop across the catalyst of 1.5 in of water. Alternatively, the monolith may be used as a catalyst and filter, as is the case for a diesel particulate filter. In this case, monolith channels are blocked and the exhaust gases from a diesel truck are forced through the walls (Fig. 19-18b). The filter is a critical component in a continuous regenerable trap. NO in the exhaust... 

The focus for the reduction of harmful diesel emissions is mainly on particulate matter (PM) and NO,. Both components are harmful to health and environment and are present in relatively large quantities. The other regulated harmful emissions, hydrocarbons and carbon monoxide, can be removed with relatively simple measures, such as flow-through monoliths with an oxidation catalyst. Some of the techniques used for removal of particulate matter and/or NO,... 

Another successful application is the so-called Continuously Regenerating -Diesel Particulate Filter (CR-DPF), where a catalytic flow-through monolith is placed upstream of a wall-flow monolithic filter. In this catalyst the NO present in the exhaust gas is oxidised lo NO2 [14], which successively oxidises the soot that is collected on the filter, forming NO. CO. and COj. This system operates well between 575 Kand 675 K and preferably between 625 and 675 K. but is limited to virtually sulfur free fuel (< 10 ppm) and Euro II engines [14]. 

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