Abstract
Solar photothermo-catalysis is a fascinating multi-catalytic approach for volatile organic compounds (VOCs) removal. In this work, we have explored the performance and the chemico-physical features of non-critical, noble, metal-free MnOx-ZrO2 mixed oxides. The structural, morphological, and optical characterizations of these materials pointed to as a low amount of ZrO2 favoured a good interaction and the ionic exchange between the Mn and the Zr ions. This favoured the redox properties of MnOx increasing the mobility of its oxygens that can participate in the VOCs oxidation through a Mars-van Krevelen mechanism. The further application of solar irradiation sped up the oxidation reactions promoting the VOCs total oxidation to CO2. The MnOx-5 wt.%ZrO2 sample showed, in the photothermo-catalytic tests, a toluene T90 (temperature of 90% of conversion) of 180 °C and an ethanol T90 conversion to CO2 of 156 °C, 36 °C, and 205 °C lower compared to the thermocatalytic tests, respectively. Finally, the same sample exhibited 84% toluene conversion and the best selectivity to CO2 in the ethanol removal after 5 h of solar irradiation at room temperature, a photoactivity similar to the most employed TiO2-based materials. The as-synthetized mixed oxide is promising for an improved sustainability in both catalyst design and environmental applications.
Highlights
Nowadays, the quality of air, both in indoor and outdoor environments, is an extremely important concern
We have investigated the photothermo-catalytic properties of MnOx ZrO2 mixed oxides, with the aim of finding new and sustainable alternatives to the most common TiO2 -based photocatalysts, and without the addition of noble metal co-catalysts, usually used in the catalytic and photocatalytic removal of volatile organic compounds (VOCs) [11], to obtain even more environmentally friendly catalysts, in the end
The signals fitted with the PDF card No 00-079-1771 of zirconium oxide, with the typical diffraction peaks at 2θ = 30.2◦, 35.2◦ and 50.3◦
Summary
The quality of air, both in indoor and outdoor environments, is an extremely important concern. Different strategies were employed to remove VOCs from the air, and an innovative and sustainable solution is represented by solar photocatalytic or photothermo-catalytic oxidation [1,2]. To photocatalysis, it is necessary to have a semiconductor material that, after solar irradiation, is able to generate photoelectrons and photoholes in its conduction (CB) and valence (VB) bands, respectively It should have redox properties activated with the temperature; in this way, the superficial/mobile oxygens of the catalyst or of the support can participate in the oxidation of VOCs increasing the overall activity [3,6]. The TiO2 -CeO2 composites showed promising performance in the photo-thermal approach for both VOCs removal and CO2 reduction [3,9]; one of the side effects of the current pandemic situation is the crisis of raw materials exportation, and as a consequence, in 2020, titanium featured in the EU critical raw materials list [10]
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