  Nanoporous 12CaO$\cdot$Al$_2$O$_3$ (C12A7:e$^-$), known as a famous electride
and electron source material, was recently proposed to boost catalytic activity
in C12A7:e$^-$ based catalysts. However, the fundamental mechanism on such
catalytic enhancement keeps in debate currently. Here, by means of symmetry
analysis and first-principles calculations, we discover that this famous
electride material, surprisingly, hosts interstitial-electrons composed
multiple-fold fermions that helps to understand the catalytic nature of
C12A7:e$^-$ based catalysts. The multiple-fold fermions contain a sixfold- and
a fourfold- degenerate point, locating at high symmetric points near the Fermi
energy. Remarkably, comparing with traditional Weyl/Dirac fermions, the
multiple-fold fermions are found to show extremely longer Fermi arcs on the
C12A7:e$^-$ (001) surface. As the result, this surface is highly active and
carries a relatively low Gibbs free energy ($\Delta \rm G_{H^*} = 0.24$ eV)
during the catalytic process. This G is also much lower than typical Weyl/Dirac
catalysts proposed previously. This work offers a guiding principle for
understanding catalytic nature of electrides and topological quantum catalysts
as well.
