A Systems Approach to Improved Exhaust Catalyst Durability: The Role of the MMT Fuel Additive

The long-term durability of a vehicle's exhaust catalyst is essential for emission control. Catalyst durability can be affected by a variety of factors including engine oil consumption. During normal engine operation, some of the lubricating oil is combusted. The deposition of combustion products from phosphorus containing lubricant additives on the catalyst can adversely affect catalyst durability. In an attempt to minimize the impact of oil consumption on additive performance, engines have been designed to reduce oil consumption and oils are being formulated with lower concentrations of phosphorus compounds. However, these phosphorus compounds protect the engine from excessive wear and cannot be easily removed from lubricant oil due to concerns over engine durability. The use of a phosphorus scavenger is an approach that works together with engine design to minimize catalyst deterioration. This in turn allows the use of effective levels of phosphorus compounds in oil formulations to provide robust engine wear protection.

In this paper, the use of the fuel additive methylcyclopentadienyl manganese tricarbonyl (MMT) to minimize the adverse impact of lubricant additives on catalyst durability is addressed. High mileage vehicle tests were conducted to evaluate the ability of gasoline containing the MMT fuel additive to reduce the adverse impact of phosphorus compounds on exhaust catalyst performance. This testing demonstrated that using MMT in gasoline reduces phosphorus deposition on catalysts. Improved catalyst activity was related to the lower phosphorus deposition on the MMT catalyst. The protective function of the fuel additive MMT and its impact on exhaust catalyst durability are discussed in detail.