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Well-defined palladium–gold nanoparticles (PdAuNPs) with randomly alloyed structures and broadly tunable compositions were studied in catalytic nitrite (NO 2 – ) reduction. The catalysts were synthesized using a microwave-assisted polyol coreduction method. Pd x Au 100– x NPs with systematically varied compositions ( x = 18–83) were supported on amorphous silica (SiO 2 ) and studied as model catalysts for aqueous NO 2 – reduction in a batch reactor, using H 2 as the electron donor. The reactions followed pseudo-first-order kinetics for ≥80% NO 2 – conversion. The Pd x Au 100– x NP-SiO 2 catalysts showed a volcano-like correlation between NO 2 – reduction activity and x; the highest activity was observed for Pd 53 Au 47, with an associated first-order rate constant of 5.12 L min –1 g metal –1 . Alloy NPs with greater proportions of Au were found to reduce the loss in catalytic activity due to sulfide fouling. Density functional theory calculations indicate that this is because Au weakens sulfur binding at PdAuNP surfaces due to atomic ensemble, electronic, and strain effects and thus reduces sulfur poisoning. The environmental relevance of the most active supported catalyst was evaluated by subjecting it to five cycles of catalytic NO 2 – reduction. The catalytic activity decreased over multiple cycles, but analysis of the postreaction Pd x Au 100– x NP-SiO 2 materials using complementary techniques indicated that there were no significant structural changes. Most importantly, we show that Pd x Au 100– x NP-SiO 2 alloys are significantly more active NO 2 – reduction catalysts in comparison to pure Pd catalysts.
Seraj et al. (Sat,) studied this question.