Formaldehyde Total Oxidation on Manganese-Doped Hydroxyapatite: The Effect of Mn Content

Dayan Chlala,Madona Labaki,Jean-François Lamonier,Jean-Marc Giraudon

doi:10.3390/catal10121422

Abstract

An aqueous impregnation method using manganese (II) nitrate precursor, followed by calcination at 400 °C, was carried out for the preparation of manganese doped hydroxyapatite catalysts (MnxHap; x = Mn wt.%: 2.5, 5.0, 10, 20, and 30 based on MnO2). Methods of characterization including inductively coupled plasma spectroscopy (ICP), N2 physisorption, X-ray Diffraction (XRD), Fourier-Transform Transmission Infrared (FT-IR), Raman, and Thermal gravimetric analysis (TGA/MS) analysis were used for the identification of Mn species and its surrounding environment. Raman spectroscopy indicated the presence of the ε-MnO2 phase for Mn20Hap and Mn30Hap in agreement with the XRD results and the presence of β-MnOOH species for Mn5Hap and Mn10Hap. The formaldehyde total oxidation was investigated on these catalysts and it was shown that Mn5Hap was the most active catalyst, achieving a normalized rate of formaldehyde (HCHO) conversion into CO2 per mole of Mn of 0.042 h−1 at a temperature of 145 °C. The well dispersed oxidized manganese species on Hap with a medium Mn AOS (average oxidation state) were mainly responsible for this performance. Since HCHO was retained on the surface of all catalysts during the catalytic test, the combined Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT) experiment at room temperature and thermodesorption (TD)-FTIR identified formate species as their oxidation consumed surface OH groups. A stability test and moisture effect study showed that the presence of water vapor has a beneficial effect on the performances of the catalyst.

Highlights

Formaldehyde that is mainly released from coating and adhesive agents for building materials is of great concern due to the fact that formaldehyde (HCHO) is an irritant and carcinogenic volatile organic compound (VOC)
Structural characterizations showed that the nature of Mn species changed significantly with Mn content: β-MnOOH species were predominantly detected in Mn5Hap and Mn10Hap samples while ε-MnO2 phase was present in Mn20Hap and Mn30Hap samples
The catalytic behavior of Hap supported MnOx strongly depended on the Mn content, which is closely related to the nature and local environment of the manganese species

Summary

Introduction

Formaldehyde that is mainly released from coating and adhesive agents for building materials is of great concern due to the fact that formaldehyde (HCHO) is an irritant and carcinogenic volatile organic compound (VOC). This VOC has very harmful effects on the human body, leading to the well-known sick house syndrome. Research investigating less costly active options that do not involve noble metals is of considerable interest from an economic point of view In this context, both supported and unsupported transition metal oxides have been used for the selective eliminate of HCHO due to their acid-base and redox properties [6]. Mnx Oy have been studied by several groups due to Catalysts 2020, 10, 1422; doi:10.3390/catal10121422 www.mdpi.com/journal/catalysts

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Results

Conclusion