Abstract
We present an efficient strategy for synthesising the PdAu catalysts with a homogeneous PdAu alloy phase for environmentally important hydrodechlorination of tetrachloromethane in the gas phase. The synthesis of carbon-supported catalysts involved two major steps: (i) incorporation of palladium and gold nanoparticles into carbon support and (ii) activation of the catalysts. The critical part of this work was to find the optimal conditions for both steps. Thus, the incorporation of the nanoparticles was carried out in two ways, by impregnation and direct redox reaction method using acetone solutions of metal precursor salts. The activation was performed either by a conventional thermal reduction in hydrogen or flash irradiation in a microwave oven. The homogeneity and structure of the PdAu alloy were found to depend on the catalyst activation method critically. In all cases, we observed better homogeneity for catalysts that were subject to microwave irradiation. Moreover, the flash microwave irradiation of prepared catalysts provided catalysts of better stability and selectivity towards the desired products (hydrocarbons) in the hydrodechlorination of tetrachloromethane as compared to the catalyst obtained by conventional thermal activation in hydrogen.
Highlights
Tetrachloromethane (CCl4) and many other chlorine-containing organic compounds are classified as hazardous gaseous waste due to their toxicity, carcinogenic nature, high global warming impact, and photochemical smog formation
Ozone Depletion Potential (ODP) and Global Warming Potential (GWP) for the both compounds are: ODPCCl4 = 1.1, GWPCCl4 = 1730, ODPCHCl3 = 0.01, GWPCHCl3 = 16 [6]
We have shown that application of a flash microwave radiation (MW) irradiation (1050 W/5 s.) as an activation step in the preparation of PdAu/CSibunit bimetallic catalysts provides the active phase of high metallic homogeneity, way higher than obtained in a conventional thermal activation in hydrogen flow (653 K/3 h)
Summary
Tetrachloromethane (CCl4) and many other chlorine-containing organic compounds are classified as hazardous gaseous waste due to their toxicity, carcinogenic nature, high global warming impact, and photochemical smog formation. Despite stringent limits on CCl4 production, use, and even transportation, global observations still indicate significant emissions of this pollutant to the atmosphere [1] and several industrial processes have been suggested as contributors to its persisting emission [2,3,4]. Methods for safe and environmentally acceptable destruction of recovered wastes or stocks of CCl4 are still needed. From the economic and environmental point of view, catalytic hydrodechlorination (HdCl), which operates at low temperatures and ambient pressures [5] is regarded as one of the most prospective methods of destruction of harmful chlorine-containing compounds.
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