Cold Catalysts

In addition, every effort should be made to avoid flow over a cold catalyst bed for any extended period of time, as a process stream containing volatile organics may condense on a cold catalyst bed (5). 

Preparation of Nanosized Cold Catalysts and Oxidation at Room Temperature... 

Probably the major problem in designing the ACC is the maintenance of activity as the catalyst ages (law requires performance within tight specifications to at least 50,000 miles). Rapid activation of the cold catalyst in startup is related to aging because the inactive catalyst generates less heat. 

Since 1981, three-way catalytic systems have been standard in new cars sold in North America.6,280 These systems consist of platinum, palladium, and rhodium catalysts dispersed on an activated alumina layer ( wash-coat ) on a ceramic honeycomb monolith the Pt and Pd serve primarily to catalyze oxidation of the CO and hydrocarbons, and the Rh to catalyze reduction of the NO. These converters operate with a near-stoichiometric air-fuel mix at 400-600 °C higher temperatures may cause the Rh to react with the washcoat. In some designs, the catalyst bed is electrically heated at start-up to avoid the problem of temporarily excessive CO emissions from a cold catalyst. Zeolite-type catalysts containing bound metal atoms or ions (e.g., Cu/ZSM-5) have been proposed as alternatives to systems based on precious metals. 

For an exothermic reaction the gas now entering at O will be heated as it flows over the hot bed, and the bed is cooled. Reaction then occurs as the E end is approached, and the gas leaves with the appropriate conversion at E. The O end of the reactor now has an axial temperature gradient resulting from the passage of the cool gas. At an appropriate moment the reactive gas is switched back to E. The feed is now heated by the hot catalyst and reacts, but further down the bed it encounters the cold catalyst layers, where its conversion continues to increase for a reversible exothermic reaction such as the oxidation of SO2. Before the temperature at O... 

Related Precedents to the Use of Cold Catalysts for the Aerobic Oxidation of Alcohols... 

Conditions of Activation of Cold Catalysts and State of Cold in Active Catalysts... 

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