Modification of Cobalt Oxide Electrochemically Deposited on Stainless Steel Meshes with Co-Mn Thin Films Prepared by Magnetron Sputtering: Effect of Preparation Method and Application to Ethanol Oxidation

Květa Jirátová,Jana Balabánová,Zdeněk Hubička,Martin Koštejn,František Kovanda,Michaela Dvořáková,Roman Perekrestov,Pavel Topka,Dana Pokorná,Martin Čada,Martin Veselý

doi:10.3390/catal11121453

Abstract

Magnetron sputtering is an advantageous method for preparing catalysts supported on stainless steel meshes. Such catalysts are particularly suitable for processes carried out at high space velocities. One of these is the catalytic total oxidation of volatile organic compounds (VOC), economically feasible and environmentally friendly method of VOC abatement. The reactive radio frequency (RF) magnetron sputtering of Mn and Co + Mn mixtures in an oxidation Ar + O2 atmosphere was applied to form additional thin oxide coatings on cobalt oxide layers prepared by electrochemical deposition and heating on stainless steel meshes. Time of the RF magnetron sputtering was changed to obtain MnOx and CoMnOx coatings of various thickness (0.1–0.3 µm). The properties of the supported CoOx-MnOx and CoOx-CoMnOx catalysts were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), temperature programmed reduction (H2-TPR), Fourier-transform infrared (FTIR) and Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The catalytic activity was investigated in the deep oxidation of ethanol, which was employed as a model VOC. According to the specific activities (amount of ethanol converted per unit mass of metal oxides per hour), the performance of CoOx-MnOx catalysts was higher than that of CoOx-CoMnOx ones. The catalysts with the smallest layer thickness (0.1 µm) showed the highest catalytic activity. Compared to the commercial pelletized Co-Mn-Al mixed oxide catalyst, the sputtered catalysts exhibited considerably higher (23–87 times) catalytic activity despite the more than 360–570 times lower content of the Co and Mn active components in the catalytic bed.

Highlights

Due to the toxic, narcotic or carcinogenic properties of volatile organic compounds (VOCs), their emissions in industrial gases are a serious environmental problem
The stainless steel meshes coated with the cobalt oxide thin film were used as substrate for the electrochemical deposition, when a cobalt hydroxide layer was formed on the surface
The thin layer of cobalt oxide, obtained from the precursor electrochemically deposited on stainless steel meshes, was modified by additional thin coatings of MnOx and CoMnOx prepared by radio frequency (RF) magnetron sputtering of Mn and Co + Mn mixture in the Ar + O2 atmosphere

Summary

Introduction

Narcotic or carcinogenic properties of volatile organic compounds (VOCs), their emissions in industrial gases are a serious environmental problem. VOCs can react with nitrogen oxides and oxygen to form harmful ozone. Transition metal oxides catalysts are usually produced in the form of pellets or extrudates, which, exhibit a high pressure-drop of the catalyst bed. For this reason, monoliths or meshes are often used, in which a thin film of the active phase on the support allows its high utilization in catalytic reaction due to the low influence of internal diffusion of reactants and products. Structured catalysts in the form of meshes show a lower pressure drop of a catalytic bed than the packed bed of pelletized catalysts, which is especially advantageous for applications with high space velocities as, e.g., VOC oxidation [3]

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