Abstract
Commercial activated carbon, pretreated in helium at 1600 °C and largely free of micropores, was used as a support for two series of 2 wt.% Pd–Pt catalysts, prepared by impregnating the support with metal acetylacetonates or metal chlorides. The catalysts were characterized by temperature-programmed methods, H2 chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM) with energy dispersive spectroscopy (EDS). Overall, the results confirmed the existence of well-dispersed Pd–Pt nanoparticles in the bimetallic catalysts, ranging in size from 2 to 3 nm. The catalysts were investigated in the gas phase hydrodechlorination of chlorodifluoromethane (HCFC-22). In this environmentally relevant reaction, both the ex-chloride and ex-acetylacetonate Pd–Pt/C catalysts exhibited better hydrodechlorination activity than the monometallic catalysts, which is consistent with the previous results of hydrodechlorination for other chlorine-containing compounds. This synergistic effect can be attributed to the electron charge transfer from platinum to palladium. In general, product selectivity changes regularly with Pd–Pt alloy composition, from high in CH2F2 for Pd/C (70–80%) to the selective formation of CH4 for Pt/C (60–70%).
Highlights
The widespread interest in bimetallic systems in catalytic research is motivated by the superiority of many alloy catalysts in several technological processes
The temperature-programmed reduction (TPR) profiles of the ‘acac’ series did not show any H2 uptake (Figure 1A), indicating a complete reduction of the metal precursor before starting the temperature ramping. This result is not surprising because precalcination in the O2 /Ar of supported Pd acetylacetonate should lead to the formation of palladium oxide, which is reducible, even at sub-ambient temperatures [48,49,50]
Commercial activated carbon pretreated in helium at 1600 ◦ C, largely free of micropores and impurities, was used as a support for Pd–Pt catalysts, prepared by impregnating the support with metal acetylacetonates or metal chlorides
Summary
The widespread interest in bimetallic systems in catalytic research is motivated by the superiority of many alloy catalysts in several technological processes (better activity/product selectivity/stability). Among these catalysts, carbon-supported bimetallic Pd–Pt catalysts play an important role. Pd–Pt catalysts are commonly used for hydrogenation reactions in the fine chemical industry [1]. They demonstrate high performance in the oxygen reduction reactions (ORRs) in fuel cells [2], the catalytic hydrodechlorination of toxic Cl-containing compounds [3], catalytic hydrodesulfurization [4], hydrogen peroxide production [5], the hydrogenation of aromatics [6], and the catalytic oxidation of sulfur dioxide [7].
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