A Comparative Study of Mn/Co Binary Metal Catalysts Supported on Two Commercial Diatomaceous Earths for Oxidation of Benzene

Marco Tomatis,Sailesh Behera,Ming Zhao,Honghui Xu,Hang Xiao,Bencan Tang,Chengjun Wang,Jun He,Matthew Bishop,Chaohui Wei,Huan Yu

doi:10.3390/catal8030111

Abstract

Two commercial diatomaceous earths were used as supports for the preparation of Mn/Co binary metal catalysts at different metal loads (5 to 10 wt % Mn and 5 to 15 wt % Co) by incipient wetness deposition. The activity of the prepared catalysts towards the complete oxidation of benzene to CO2 and water was investigated between 100 and 400 °C. Raw supports and synthesized catalysts were characterized by XRD, N2 physisorption, SEM-EDS, H2-TPR, and TPD. The purification treatment of food-grade diatomite significantly affected the crystallinity of this support while reducing its specific surface area (SSA). A loss of SSA, associated with the increase in the metal load, was observed on samples prepared on natural diatomite, while the opposite trend occurred with food-grade diatomite-supported catalysts. Metal nanoparticles of around 50 nm diameter were observed on the catalysts’ surface by SEM analysis. EDS analysis confirmed the uniform deposition of the active phases on the support’s surface. A larger H2 consumption was found by TPR analysis of natural diatomite-based samples in comparison to those prepared at the same metal load on food-grade diatomite. During the catalytic oxidation experiment, over 90% conversion of benzene were achieved at a reaction temperature of 225 °C by all of the prepared samples. In addition, the formation of coke during the oxidation tests was demonstrated by TGA analysis and the soluble fraction of the produced coke was characterized by GC-MS.

Highlights

Volatile organic compounds (VOCs) are a class of chemicals emitted by natural and anthropogenic sources, such as vegetation, industrial processes, and transportation [1,2]
These results indicated that the crystallinity of the deposited metals might have increased due to the exposure to reaction temperatures adopted during the oxidation tests higher than the calcination temperature (250 ◦ C), which caused sintering of the active phase [42]
X-ray diffraction (XRD) characterization showed clear differences between the two raw supports as the purification process influenced the crystallinity of food-grade diatomite

Summary

Introduction

Volatile organic compounds (VOCs) are a class of chemicals emitted by natural and anthropogenic sources, such as vegetation, industrial processes, and transportation [1,2] These pollutants are known as some of the main precursors for the formation of photochemical smog, resulting in the generation of harmful products [3]. VOCs contribute to climate change as greenhouse gases and affect the ozone layer [3] Due to their hazardous nature towards human health and the environment, the emission limits of VOCs from industrial sources and remediation activities are being lowered by regulatory agencies and organizations worldwide, including the Environmental Protection Agency (EPA, Washington, DC, USA) and the World Health Organization WHO [4,5]. An increase of around 465% in the incidence of lung cancer was observed in China over the last 30 years, which was found to be associated with long-term exposure to severe air pollution, including exposure to VOCs [6]

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