How does the Carbon-Nitrogen-Oxygen (CNO) cycle function differently than the $p$-$p$ chain in massive stars?

It utilizes heavier elements ($ ext{C}$, $ ext{N}$, $ ext{O}$) as catalysts during hydrogen conversion to helium.

While both the proton-proton (p-p) cycle and the CNO cycle achieve the fundamental goal of fusing hydrogen into helium to release energy, their mechanisms and temperature dependencies differ significantly. The CNO cycle operates primarily in stars significantly hotter than the Sun because it requires higher kinetic energy to overcome the greater electrical repulsion of the heavier catalyst nuclei involved. In this cycle, carbon, nitrogen, and oxygen nuclei act as intermediaries; they capture protons, undergo a series of transformations, and eventually eject a helium nucleus, returning the original carbon nucleus unchanged to restart the cycle. This catalytic nature makes the CNO cycle highly sensitive to temperature and the dominant energy source in hot, massive main-sequence stars.