The April 22, 2022 Veritasium video The Man Who Accidentally Killed The Most People In History mentions several aspects of the historical use of tetra-ethyl lead in gasoline, the resulting widespread distribution of lead in the environment and within people, and the consequences of that.
As part of the story, it mentions that during Thomas Midgley Jr.'s search1 for a gasoline additive that would reduce premature detonation in a high-compression gasoline engine, a tellurium-based additive was tried. The graphic in the video indicates "tellurium + sodium hydroxide".
Kettering wanted to find an additive which would increase the octane rating of ordinary fuel and eliminate knocking in high-compression engines. So he hired 27-year-old engineer Thomas Midgley Jr. Midgley experimented with all sorts of compounds, from melted butter and camphor, to ethyl acetate and aluminum chloride. He later wrote "Most of them had no more effect than spitting in The Great Lakes."
Ethanol was an interesting exception, it did stop the knocking, but you needed a lot of it, about 10% of the fuel mixture to be effective. That much ethanol would be expensive and hard to turn a profit on. And Midgley was really after an additive that was cheap, easy to produce and effective even at low concentrations. So he kept trying.
Then he hit on tellurium. It worked wonderfully as an anti-knocking agent, but it had a terrible smell. You couldn't get rid of it by changing clothes or bathing. His wide was so offended by the stench that he had to sleep in the basement for seven months. Midgley wrote: "I don't think that, although this doubled fuel economy, humanity would suffer this smell."
Question: Why would tellurium + sodium hydroxide have worked as a good anti-knock gasoline additive (if it wasn't so smelly)?
According to the second quote from Midgley, in addition to reducing/stopping engine knocking it also improved mileage substantially. By what mechanism is a tellurium-based additive able to do this?
1at the behest of Charles Kettering after the higher compression engine of the Model 30 Cadillac exhibited problems with knocking (premature detonation of fuel-air mixture before the electrical spark was triggered)