  We discuss a representative selection of particle acceleration mechanisms
believed to be operating in Active Galactic Nuclei. Starting from direct
electrostatic field acceleration in the vicinity of the black hole up to
Fermi-type particle acceleration in the jet and beyond, possible efficiency
constraints on the energization of ultra-high energy cosmic rays (UHECR) are
evaluated. When paradigmatically applied to Cen A, the following results are
obtained: (i) Proton acceleration to energies of $E_c = 5\times 10^{19}$ eV and
beyond remains challenging and most likely requires the operation of an
additional mechanism capable of boosting energetic seed protons up by a factor
of $\sim$ten. It is argued that shear acceleration along the large-scale jet in
Cen A could be a promising candidate for this. (ii) Heavier elements, like iron
nuclei, are more easily accelerated (by, e.g., shocks or direct electrostatic
fields) and may not need additional boosting to reach $E \geq E_c$; (iii) If
Cen A indeed proves to be an UHECR source, the cosmic ray composition might
thus be expected to become heavier above energies of a few times $10^{19}$ eV.
