This research discusses
the CO
2
valorization via hydrogenation
over the non-noble metal clusters of Ni and Cu supported on graphitic
carbon nitride (g-C
3
N
4
). The Ni and Cu catalysts
were characterized by conventional techniques including XRD, AFM,
ATR, Raman imaging, and TPR and were tested via the hydrogenation
of CO
2
at 1 bar. The transition-metal-based catalyst designed
with atom-economy principles presents stable activity and good conversions
for the studied processes. At 1 bar, the rise in operating temperature
during CO
2
hydrogenation increases the CO
2
conversion
and the selectivity for CO and decreases the selectivity for methanol
on Cu/CN catalysts. For the Ni/CN catalyst, the selectivity to light
hydrocarbons, such as CH
4
, also increased with rising temperature.
At 623 K, the conversion attained ca. 20%, with CH
4
being
the primary product of the reaction (CH
4
yield >80%).
Above
700 K, the Ni/CN activity increases, reaching almost equilibrium values,
although the Ni loading in Ni/CN is lower by more than 90% compared
to the reference NiREF catalyst. The presented data offer a better
understanding of the effect of the transition metals’ small
metal cluster and their coordination and stabilization within g-C
3
N
4
, contributing to the rational hybrid catalyst
design with a less-toxic impact on the environment and health. Bare
g-C
3
N
4
is shown as a good support candidate
for atom-economy-designed catalysts for hydrogenation application.
In addition, cytotoxicity to the keratinocyte human HaCaT cell line
revealed that low concentrations of catalysts particles (to 6.25 μg
mL
–1
) did not cause degenerative changes.