Abstract
Au, Pt, and Pt-Au catalysts supported on Al2O3 and CeO2-Al2O3 were studied in the oxidation of dichloromethane (DCM, CH2Cl2). High DCM oxidation activities and HCl selectivities were seen with all the catalysts. With the addition of Au, remarkably lower light-off temperatures were observed as they were reduced by 70 and 85 degrees with the Al2O3-supported and by 35 and 40 degrees with the CeO2-Al2O3-supported catalysts. Excellent HCl selectivities close to 100% were achieved with the Au/Al2O3 and Pt-Au/Al2O3 catalysts. The addition of ceria on alumina decreased the total acidity of these catalysts, resulting in lower performance. The 100-h stability test showed that the Pt-Au/Al2O3 catalyst was active and durable, but the selectivity towards the total oxidation products needs improvement. The results suggest that, with the Au-containing Al2O3-supported catalysts, DCM decomposition mainly occurs via direct DCM hydrolysis into formaldehyde and HCl followed by the oxidation of formaldehyde into CO and CO2.
Highlights
Chlorinated volatile organic compounds (CVOCs) are widely used in the industry as solvents, degreasing and cleaning agents, and paint strippers and as additives for paints, inks, and adhesives, as well as raw materials in the synthesis of chemicals, plastics, and pharmaceuticals [1,2,3].Dichloromethane (CH2 Cl2, DCM) was chosen as the model CVOC in this work
In the International Chemical Safety Cards (ICSC), the effects of DCM are identified as: irritating to the eye, skin, and respiratory tract; causing effects on the central nervous system, blood, liver, heart, and lungs; exposure at high concentrations causing a lowering of consciousness and death; and, probably, being a carcinogenic to humans [7]
The results showed that Au/Al2 O3 is active and highly hydrochloric acid (HCl) selective, even outperforming Pt/Al2 O3, which was found as the most active and HCl selective catalyst in our previous study
Summary
Dichloromethane (CH2 Cl2 , DCM) was chosen as the model CVOC in this work. DCM is one of the three main chlorinated solvents used in Europe, the others being perchloroethylene (PCE) and trichloroethylene (TCE) [4]. DCM is the most stable chlorinated alkane, and it is very difficult to be decomposed naturally in the environment [5]. The 100-year global warming potential (GWP) value for DCM is nine [6]. In the International Chemical Safety Cards (ICSC), the effects of DCM are identified as: irritating to the eye, skin, and respiratory tract; causing effects on the central nervous system, blood, liver, heart, and lungs; exposure at high concentrations causing a lowering of consciousness and death; and, probably, being a carcinogenic to humans [7]
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