Phosphates:

 

Zinc
dialkyldithiophosphate (ZDDP) is an antiwear, antioxidant, and corrosion
inhibiting additive that is used in engine lubricating oils, hydraulic oils,
and other lubricants. ZDDP is produced by first letting an alkyl or aryl
alcohol react with phosphorous pentasulphide (P2S5), and then neutralizing the
resultant acid with zinc oxide. 37

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The phosphorus composition  depends on many factors, such as the chemical
composition of oil and oil additives, the age of the oil used, and conditions
in the motor 38.Phosphorus contamination can be observed on the
surface of catalytic converters as several different compounds

 

Secondly, phosphate compounds can also
be formed directly with washcoat components. In that case, the resulting
compounds are, for instance, aluminium and cerium phosphates

 

Poisoning
by other compounds

 

Automotive catalysts can also be
deactivated by compounds commonly used in the structure of an engine. The ,
iron (Fe) is a poison for platinum group metals39 .Iron detected
on the catalytic surface is often assumed to originate from the corrosion of
metal components in the engine. Other similar impurities may be copper (Cu),
nickel (Ni), and chromium (Cr). Chromium and nickel are added to the
construction materials in order to improve the thermal stability of engines.

 

 

 Effects on PGM

 

Precious metals have different types of
resistance against poisoning. Palladium is more sensitive than platinum and
rhodium to chemical deactivation, in particular to poisoning by sulfur and lead
40,41.

 

Pd is easily oxidized at room temperature to
PdO and it reduces to metallic Pd in the temperature range of 500°– 1200°C. At normal operation temperatures of the
catalytic converter, Rh is in the form of Rh2O3, if the
oxidation of Rh is kinetically favoured. The oxygen content in the exhaust gas
strongly affects the formation of Rh oxides; the higher the amount of oxygen,
the higher the transition temperature is.