Platinum palladium mixture, thermally

At the time, automobile manufacturers expected to have to meet the original statutory 1975 Federal Standards of 0.41 g HC/mile and 3.4 g CO/mile, and therefore only PZ-236 was submitted for their consideration. In March 1973, while the automakers were seeking (successfully) a delay of the statutory 1975 Standards, General Motors Corp. (GM) testified (4) that only six vehicles in their corporate fleet had accumulated 50,000 miles. All six used UOP catalysts on the same low density support. Five of the six catalysts contained 2.24 g platinum per vehicle. The sixth, PZ-236, had 25% of that amount, but in a thermally-optimized, platinum—palladium mixture. As the automaker indicated, this... 

The hexakis(methyl isocyanide) dimers, [Pt2(CNMe)6], undergo photolytic cleavage of the Pt—Pt bond to give 15-electron radicals, Pt(CNMe)3.94 Mixtures of platinum and palladium dimers give rise to heteronuclear complexes under photolytic conditions. Mixtures of normal and deuterium-labeled methyl isocyanide complexes reveal that the metal-ligand bonds undergo thermal redistribution.94... 

A palladium complex of tropyne (230) has been prepared by the same method used for 223.86 Interestingly, in contrast to all of the platinum tropyne complexes (223, 226, 235), which are stable at room temperature, the palladium complex is thermally labile, decomposing at -35°C with a half-life of about 3 h. Reactions of 230 with KBEt3H, LiAl(0-f-Bu)3H, HBr, or cyclopentadiene gave only intractable mixtures. 

Fresh and thermally aged catalysts containing mixtures of platinum and palladium were laboratory tested for the oxidation of carbon monoxide, propane, and propylene. For both monolithic and particulate catalysts, resistance to thermal deactivation was optimum when palladium content was 80%. Full-scale vehicle tests confirmed these findings. Catalysts of this composition were developed which, on the basis of durability tests at Universal Oil Products and General Motors, appeared capable of meeting the 1977 Federal Emissions Standards with as little as 0.56 g noble metal per vehicle. The catalyst support was thermally-stabilized, low density particulate. 

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