Hydroxyapatite
(Ca10(PO4)6(OH)2 or HAp)the
main mineral component of bones
and teethis
a material of great interest not only in biomedical applications but
also in heterogeneous catalysis. Its framework Ca2+ cations
can be substituted by a wide variety of catalytically active metals
(Cu2+, Ni2+, Ag+, etc.). In the present
work, for the first time, to our knowledge, we demonstrate that highly
valuable HAp-based catalysts can be obtained through a novel advantageous
bottom-up approach. Unlike classical surface cation deposition in
the excess of solution, this approach is one-pot. It consists in preparing
the bulk-metal-substituted HAp by coprecipitation and then submitting
it to a finely adjusted thermal treatment under a H2-containing
gas flow. For a Cu(∼1.5 wt %)-HAp, we show that such a treatment
at 450 °C leads to the exsolution of the whole Cu contained in
the material, leading to highly dispersed Cu species at the HAp surface.
After appropriate activation, these Cu species are active in the selective
catalytic reduction of NO
x
by NH3. The phenomenon of exsolution has been reported so far mainly for
perovskites but to lead to metal nanoparticles and not to highly dispersed
species as achieved here.