Hydroxyapatite
(HAP) is widely used as a loaded catalyst support
due to its excellent ion exchange properties. In this study, a series
of Ni-based hydroxyapatite catalysts were prepared by a novel method,
one-pot co-precipitation (denoted as Ni/HAP-OP), for dry reforming
of methane (DRM) testing. The textural, structure, and physicochemical
properties of the catalysts were studied by inductively coupled plasma
spectroscopy (ICP), X-ray diffraction (XRD), X-ray photoelectron spectroscopy
(XPS), the Brunauer–Emmett–Teller (BET) method, scanning
transmission electron microscopy (STEM), and hydrogen temperature-programmed
reduction (H2-TPR), and the spent catalysts were analyzed
by thermogravimetric analysis (TGA), Raman, and transmission electron
microscopy (TEM). The Ni/HAP-OP catalysts exhibit a typical hydroxyapatite
structure. The Ni0.5/HAP-OP catalyst has the highest dispersion
of Ni among the prepared catalysts, and most of the added Ni is in
the form of Ni2+[I] and Ni2+[II] in the lattice
of hydroxyapatite. When Ni is post-impregnated (Ni0.5/HAP),
almost half of the Ni is present in the form of NiO. The different
coordination configurations of Ni are confirmed to play an important
role in the DRM reaction. Naturally, the Ni0.5/HAP-OP catalyst
shows excellent catalytic activity and catalytic stability in the
200 h stability test compared with Ni0.5/HAP, with stable
CH4 (about 94%) and CO2 (95%) conversion. The
deactivation is only 0.014 and 0.017% h–1, respectively,
and the H2/CO ratio in the syngas is always maintained
close to 1.0. Analyses of the spent catalysts reveal that amorphous
carbon deposits are observed around the metallic Ni on the Ni0.5/HAP catalyst, and Raman analysis indicates the presence
of both amorphous and graphitic carbon deposits. In contrast, only
trace amounts of graphitic carbon are present in the Ni0.5/HAP-OP catalyst after 200 h of the DRM reaction. The Ni-based hydroxyapatite
catalysts prepared by the one-pot co-precipitation method exhibit
high activity and stability for the DRM reaction thanks to the confinement
of Ni particles and the inhibition of carbon deposition.