Catalytically-boosted hydroxyapatite/ZrO 2 nanocomposites for the heterogenous fixation of dinitrogen and water into ammonium Marc Arnau Roca 1,2 Jordi Sans, 1,2 Pau Turon 3 and Carlos Alemán 1,2,4 1 Universitat Politècnica de Catalunya, Spain, 2 Barcelona Research Center in Multiscale Science and Engineering, Spain, 3 B. Braun Surgical, Spain, 4 Institute for Bioengineering of Catalonia (IBEC), Spain Polarized porous hydroxyapatite (HAp) based catalysts decorated with zirconia (ZrO 2 ) nanoparticles were used for the nitrogen fixation and conversion into ammonium at mild conditions, resulting in a 900 % yield increase with respect to the conventional polarized hydroxyapatite values reported in the literature 1 . Hydroxyapatite is a biocompatible ceramic material capable of demonstrating catalytic active behaviour when applyed a thermal stimulated polarization (application of a DC voltage at high temperature) thus enabling it to act as a catalyst for carbon and nitrogen fixation reactions. Porous hydroxyapatite prepared through a Pluronic® hydrogel assisted route was partially-covered with zirconia nanoparticles using electrophoretic deposition (EPD). Morphological characterization of system by means of SEM microscopy allowed zirconia nanoparticles observation (size distribution center at 300 nm). Structural studies concerning the interactions hydroxyapatite-zirconia were performed using Raman Spectroscopy, XRD and XPS confirming the correct incorporation of the nanoparticles without damaging the hydroxyapatite lattice and compromising its catalytic activation during the polarization. The polarized HAp-ZrO 2 catalysts were tested for the nitrogen fixation reactions using a batch reactor under mild conditions, specifically, 6 bar of N 2 , 120 ºC temperature, UV light (254 nm) and 20mL of water. The products obtained from this heterogenous catalysis were analysed and quantified by 1 H-NMR, displaying complete selectivity towards ammonium. Moreover, the mechanism behind the reaction process was proposed by analysing the catalyst acid/basic active sites, molecules adsorption (BET) and light absorption capabilities (UV-Vis). Overall the HAp-ZrO 2 catalytic system produced approximately 1.5 mmol/g catalyst in the span of 72 h denoting a significant increase with respect to the results published in the literature, providing an example of good synergy between polarized hydroxyapatite and zirconia nanoparticles and thus a step forward towards the use of the catalytic active HAp as a green catalyst for industrial processes involving the synthesis of ammonia. References 1. Jordi Sans, Marc Arnau, Vanesa Sanz, Pau Turon, Carlos Alemán, Fine-tuning of polarized hydroxyapatite for the catalytic conversion of dinitrogen to ammonium under mild conditions, Chemical Engineering Journal , Volume 446, Part 5, 2022, 137440, ISSN 1385-8947.
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