  Carbon is one of the most abundant components in the Universe. While
silicates have been the main focus of solid phase studies in protoplanetary
discs (PPDs), little is known about the solid carbon content especially in the
planet-forming regions ($\sim $0.1 to 10 au). Fortunately, several refractory
carbonaceous species present C-H bonds (such as hydrogenated nano-diamond and
amorphous carbon as well as polycyclic aromatic hydrocarbons (PAHs)), which
generate infrared (IR) features that can be used to trace the solid carbon
reservoirs. The new mid-IR instrument MATISSE, installed at the Very Large
Telescope Interferometer (VLTI), can spatially resolve the inner regions
($\sim$ 1 to 10 au) of PPDs and locate, down to the au-scale, the emission
coming from carbon grains. Our aim is to provide a consistent view on the
radial structure, down to the au-scale, as well as basic physical properties
and the nature of the material responsible for the IR continuum emission in the
inner disk region around HD 179218. We implemented a temperature-gradient model
to interpret the disk IR continuum emission, based on a multiwavelength dataset
comprising a broadband spectral energy distribution (SED) and VLTI H-, L-, and
N-bands interferometric data obtained in low spectral resolution. Then, we
added a ring-like component, representing the carbonaceous L-band
features-emitting region, to assess its detectability in future higher spectral
resolution observations employing mid-IR interferometry.
