Fine-tuning of polarized hydroxyapatite for the catalytic conversion of dinitrogen to ammonium under mild conditions

Hydroxyapatite-based catalysts for CO2fixation with controlled selectivity towards C2 products. Phenomenal support or active catalyst?

“…Accordingly, the systems studied do not show any significant decrease in the resulting yields of the reaction, which is in agreement with the p-HAp stability studies reported. 20,23,25…”

“…CO 2 xation reactions were performed in an inert batch reactor previously described in the literature. 20,23 The reaction products were analysed by means of the proton nuclear magnetic resonance technique ( 1 H NMR), which was calibrated through external standards. Further details on the CO 2 xation reaction and the analysis procedure are meticulously explained in the ESI.…”

“…Accordingly, the systems studied do not show any signicant decrease in the resulting yields of the reaction, which is in agreement with the p-HAp stability studies reported. 20,23,25 Control over the selectivity and plasticity of p-HAp has been explained in terms of electrical properties by locally controlling the surface charge accumulation. Indeed, the role of TiO 2 NPs in the catalytic system under study could be explained similarly.…”

“…In order to achieve the enhanced catalytic activity reported, HAp must undergo a complete lattice rearrangement reaching the permanently polarized state (here-aer denoted as p-HAp) consisting of a highly crystalline HAp where all the hydroxyl groups in the lattice are aligned pointing towards a specic direction. 21 The resulting improved electrical properties of p-HAp not only drive the catalytic xation of CO 2 , CH 4 or N 2 into highly valuable chemical products, [22][23][24] but also result in enhanced proton conductivity and customized surface charge accumulation which allows control by design of the selectivity of the catalyst, termed as catalytic plasticity. 25 Such extraordinary behavior emerging from extremely accurate control and optimization of the crystal lattice structure of p-HAp clearly diverges from the traditionally poor attention given to HAp when used only as a catalytic support in favor of metal optimization.…”

Permanently Polarized Materials: An Approach for Designing Materials with Customized Electrical Properties

“…Although the study of the OH – groups under different operando and stimuli conditions has been explored for the last 50 years, it has not been until recent years that the understanding and optimization of the TSP treatment and, more specifically, the role of temperature have been settled down to successfully develop the first p-HAp. ,, The TSP treatment merits special consideration as it has been demonstrated to generate p-HAp systems with 1) electrical conductivities above and below the intrinsic level of HAp; 2) controlled surface charge accumulation; and 3) anisotropic electrical conductivity. ,, Overall, while conventional HAp is considered a biocompatible ceramic widely used in the biomedical field, p-HAp presents enormous catalytic activity . Hence, p-HAp is able to fix CO 2 , CH 4 and/or N 2 under very mild conditions and with enhanced selectivity toward different products, − which can be controlled by design. , Beyond any doubt, the novel electrical properties provided by the TSP treatment are extremely attractive for a wide range of applications.…”