Nowadays, catalysis plays a leading role in tackling several environmental issues and working towards a more sustainable development. The design of novel eco-friendly and effective catalytic materials for decomposition of pollutants for air remediation can help in this regard, contributing to meet the ever more stringent criteria of sustainability and efficiency. In this context, hydroxyapatite (HAP, chemical formula Ca10-x(PO4)6-x(HPO4)x(OH)2-x, with 0<1) has emerged as an interesting material in industrial and environmental catalysis. Recently our research group has demonstrated that the deposition of transition metal phase (e.g. Cu, Fe) onto hydroxyapatite results in effective and selective catalysts for the NH3-SCR reaction [1-4]. However, the control of metal sitting, speciation and nuclearity of metal centres at the surface of HAP still remains an open challenge for the attainment of catalysts with enhanced catalytic performances. Therefore, improved understanding and targeted investigation of the factors influencing the arrangement and local environment of Cu and Fe on HAP surface are required. In this work, we examined in depth the catalytic behaviour of copper or iron ions deposited onto the HAP framework in different amount (ca. 1-10 wt.%). Catalysts have been prepared from copper(II)- or iron(III)nitrate as precursors, according to the conventional ion exchange procedure (IE). Depending on the metal loading on HAP, the added metal centres could be allocated as isolated species in two Ca2+ sites with different coordination environment (Ca(I) and Ca(II)), or undergo surface adsorption with formation of nano-oxides of different nuclearity. A combination of characterisation techniques (XPS, TEM-EDX, XRPD, N2-physisorption) has been then used to investigate on metal speciation and sitting on the HAP surface. The catalytic performances of copper or iron functionalized hydroxyapatite catalysts in the NH3-SCR reaction have been explored in the 200-500°C interval at fixed contact time (0.03 s) and evaluated also under real conditions (presence of 5% of water in the feed of gases). Time-on-stream stability tests have been performed on the most promising samples in absence/presence of water at fixed temperature for 72 h. All the Cu/HAP and Fe/HAP samples were able to selectively convert NOx to N2 in the NH3-SCR reaction. By way of example, Figure 1 reports the profiles of NO conversion (a) and N2 selectivity (b) as a function of temperature for Cu/HAPIE and Fe/HAPIE loaded with 6 wt.% of metal species. As a general trend, all the Cu/HAP samples resulted more active than Fe-based ones. All the catalysts worked in the temperature interval of ca. 300-400°C with high selectivity to N2 (ca. 90%) and a maximum NO conversion in the range of ca. 50-80% in absence of water. Conversely, a decrease of activity of ca. 30-40% was observed when water vapour was present in the feed of gases. In conclusion, copper and iron exchanged hydroxyapatites result to be promising catalysts in the NH3-SCR reaction. Further studies for the optimization of these systems in this field are in progress.

Activity and stability of copper and iron exchanged hydroxyapatite catalysts in NH3-SCR / M.G. Galloni, S. Campisi, A. Gervasini, A. Giroir Fendler. ((Intervento presentato al 11. convegno ICEC- International Conference on Environmental Catalysis tenutosi a Manchester-online nel 2020.

Activity and stability of copper and iron exchanged hydroxyapatite catalysts in NH3-SCR

M.G. Galloni
;
S. Campisi;A. Gervasini;
2020

Abstract

Nowadays, catalysis plays a leading role in tackling several environmental issues and working towards a more sustainable development. The design of novel eco-friendly and effective catalytic materials for decomposition of pollutants for air remediation can help in this regard, contributing to meet the ever more stringent criteria of sustainability and efficiency. In this context, hydroxyapatite (HAP, chemical formula Ca10-x(PO4)6-x(HPO4)x(OH)2-x, with 0<1) has emerged as an interesting material in industrial and environmental catalysis. Recently our research group has demonstrated that the deposition of transition metal phase (e.g. Cu, Fe) onto hydroxyapatite results in effective and selective catalysts for the NH3-SCR reaction [1-4]. However, the control of metal sitting, speciation and nuclearity of metal centres at the surface of HAP still remains an open challenge for the attainment of catalysts with enhanced catalytic performances. Therefore, improved understanding and targeted investigation of the factors influencing the arrangement and local environment of Cu and Fe on HAP surface are required. In this work, we examined in depth the catalytic behaviour of copper or iron ions deposited onto the HAP framework in different amount (ca. 1-10 wt.%). Catalysts have been prepared from copper(II)- or iron(III)nitrate as precursors, according to the conventional ion exchange procedure (IE). Depending on the metal loading on HAP, the added metal centres could be allocated as isolated species in two Ca2+ sites with different coordination environment (Ca(I) and Ca(II)), or undergo surface adsorption with formation of nano-oxides of different nuclearity. A combination of characterisation techniques (XPS, TEM-EDX, XRPD, N2-physisorption) has been then used to investigate on metal speciation and sitting on the HAP surface. The catalytic performances of copper or iron functionalized hydroxyapatite catalysts in the NH3-SCR reaction have been explored in the 200-500°C interval at fixed contact time (0.03 s) and evaluated also under real conditions (presence of 5% of water in the feed of gases). Time-on-stream stability tests have been performed on the most promising samples in absence/presence of water at fixed temperature for 72 h. All the Cu/HAP and Fe/HAP samples were able to selectively convert NOx to N2 in the NH3-SCR reaction. By way of example, Figure 1 reports the profiles of NO conversion (a) and N2 selectivity (b) as a function of temperature for Cu/HAPIE and Fe/HAPIE loaded with 6 wt.% of metal species. As a general trend, all the Cu/HAP samples resulted more active than Fe-based ones. All the catalysts worked in the temperature interval of ca. 300-400°C with high selectivity to N2 (ca. 90%) and a maximum NO conversion in the range of ca. 50-80% in absence of water. Conversely, a decrease of activity of ca. 30-40% was observed when water vapour was present in the feed of gases. In conclusion, copper and iron exchanged hydroxyapatites result to be promising catalysts in the NH3-SCR reaction. Further studies for the optimization of these systems in this field are in progress.
set-2020
Settore CHIM/02 - Chimica Fisica
Settore CHIM/04 - Chimica Industriale
University of Manchester
Activity and stability of copper and iron exchanged hydroxyapatite catalysts in NH3-SCR / M.G. Galloni, S. Campisi, A. Gervasini, A. Giroir Fendler. ((Intervento presentato al 11. convegno ICEC- International Conference on Environmental Catalysis tenutosi a Manchester-online nel 2020.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/777896
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