I sometimes get the same "gunpowdery" smell on hard acceleration in my '09 Touring. My theory is that the cats are temporarily overloaded and I am smelling unburned hydrocarbons and products of incomplete combustion (PIC) (eg, CO, incompletely burned gas, &c) that are making it through the cat. I'm assuming that, with a modern, computer-controlled engine, unburned gasoline will be a very minor component, so PIC will be what is making the smell. YMMV.
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