Abstract
Alumina-supported bimetallic AuRh catalysts, as well as monometallic reference catalysts, were examined with regard to their structural and catalytic properties in the reduction of NO by CO. Depending on the molar ratio of Au:Rh, the nanoparticles prepared by borohydride co-reduction of corresponding metal salt solutions had a size of 3.5–6.7 nm. The particles consisted of well-dispersed noble metal atoms with some enrichment of Rh in their surface region. NO conversion of AuRh/Al2O3 shifted to lower temperatures with increasing Rh content, reaching highest activity and highest N2 selectivity for the monometallic Rh/Al2O3 catalyst. This behavior is attributed to the enhanced adsorption of CO on the bimetallic catalyst resulting in unfavorable cationic Rh clusters Rh+-(CO)2. Doping with ceria of AuRh/Al2O3 and Rh/Al2O3 catalysts increased the surface population of metallic Rh sites, which are considered most active for the reduction of NO by CO and enhancement of the formation of intermediate isocyanate (-NCO) surface species and their reaction with NO to form N2 and CO2.
Highlights
Anthropogenic emissions of nitrogen oxides from fuel combustion processes pose a serious threat to human health
Due to its low reactivity, gold has long been disregarded as a candidate for heterogeneous catalysis until its nanoparticles supported on oxidic materials were discovered to catalyze the oxidation of CO
We have investigated the structural and chemical properties of pure and ceria-promoted alumina-supported bimetallic AuRh alloy nanoparticles and examined their potential for the catalytic reduction of NO by CO
Summary
Anthropogenic emissions of nitrogen oxides from fuel combustion processes pose a serious threat to human health. Since the reaction of CO and NO can eliminate two harmful pollution gases simultaneously, it has attracted a great deal of attention especially in automobile exhaust applications in a wide range of temperature and pressure [1,2]. Noble metals such as Rh, Pt, and Pd are employed for the NO reduction and CO oxidation [3,4,5,6,7,8,9]. The unique properties of gold, such as chemical stability, non-toxicity, and biocompatibility [11], make gold catalysts attractive for various reactions, including oxidations and Catalysts 2019, 9, 937; doi:10.3390/catal9110937 www.mdpi.com/journal/catalysts
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