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Okay so I've never seen anything about this before, and that's probably for a very obvious, very simple reason I am far too dim to think of, but here goes:
Most combustion reactions in rocket chambers are of two or three reactants forming products in one "stage" of reaction. (i.e. 2(H2(l)) + (O2(l)) => 2(H2O(l)) + energy)

Generally a monopropellant rocket engine achieves lower efficiencies due to having heavier atomic-mass exhaust products and lower exhaust velocity.

My question relates to decomposing a complex molecule monopropellant into products that then react further:
W(l) + Catalyst => Z(?) + Y(?), Z + Y => A + B + ... Basically a low energy monoprop => biprop + energy => combustion products and even more energy.

I assume the reason for not using such a cycle is due to complex molecules being difficult to work with as propellants, and perhaps the most important: Maybe this is impossible, as a fuel? (such a reaction would have to be relatively fast to occur within the rocket engine and provide energy for heating and accelerating the fuel.)

Anyway cheers.

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Chemical reactions in rocket exhaust often occur in multiple stages and usually involve a number of by-products at some concentration.

https://www.nature.com/articles/s41467-020-19497-z/figures/1

In the above example of methane and oxygen combustion both carbon dioxide and carbon monoxide present. Not all of the carbon monoxide has reacted to form carbon dioxide when the exhaust leaves the nozzle. In this case it is beneficial as it lowers the overall atomic mass of the exhaust products.

But the problem in general with multistage reactions is that unless both reactions are extremely rapid there is the danger that some part of the second reaction would occur in the exhaust plume. So depending on the reaction, propellant energy might be wasted after exiting the nozzle.

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