Structure and Catalytic Behavior of Alumina Supported Bimetallic Au-Rh Nanoparticles in the Reduction of NO by CO

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.

Potassium Titanate Nanobelts: A Unique Support for Au and AuRh Nanoparticles in the Catalytic Reduction of NO with CO

“…Despite the significant difference in the BET surface area of the TiO 2 ‐ and KNT‐supported catalysts, the metal particle sizes did not differ much. The energy‐dispersive X‐ray (EDS) line scans presented in Figures 1i and j show that the signals of Au and Rh components overlap with each other, hinting to the formation of AuRh alloy nanoparticles, in line with earlier reported results of similarly prepared AuRh catalysts [24] …”

“…The addition of metal oxides, such as FeO x [22] and alloying of Au with Pd [23] or Rh, [24] considerably improves the catalytic performance in terms of both activity and selectivity. The catalytic performances of alumina‐supported Au, bimetallic AuRh, and Rh catalysts follows the order of Rh>AuRh>Au [24] . In situ infrared spectroscopic studies demonstrated that CO and NO adsorb on the Au surfaces in different adsorption configurations; on‐top Au 0 −CO, on‐top Au δ+ −CO, bridged CO, Au 0 −NO, Au δ+ −NO, and bridged NO [20,25–27] .…”

“…[16][17][18][19] Gold nanoparticles are also reported to catalyze the NO reduction efficiently at low temperature, but Au itself is not active enough to promote reaction 3, leading to fairly poor selectivity to N 2 . [20,21] The addition of metal oxides, such as FeO x [22] and alloying of Au with Pd [23] or Rh, [24] considerably improves the catalytic performance in terms of both activity and selectivity. The catalytic performances of alumina-supported Au, bimetallic AuRh, and Rh catalysts follows the order of Rh > AuRh > Au.…”

“…The catalytic performances of alumina-supported Au, bimetallic AuRh, and Rh catalysts follows the order of Rh > AuRh > Au. [24] In situ infrared spectroscopic studies demonstrated that CO and NO adsorb on the Au surfaces in different adsorption configurations; on-top Au 0 À CO, on-top Au δ + À CO, bridged CO, Au 0 À NO, Au δ + À NO, and bridged NO. [20,[25][26][27] Their reactions afford isocyanate (-NCO) species on both Au and metal oxide support.…”

“…Alloying of Au with Rh facilitates reaction 4 and enhances both conversion and selectivity. [24] Titanium oxide has been extensively employed in the selective catalytic conversion of NO x (NO x À SCR). [28][29][30][31][32] To extend the scope of the catalytic properties of TiO 2 , 2-dimensional (2D) nanostructures of TiO 2 , such as nanobelts, nanowires, and nanotubes, have been evaluated for several heterogeneously catalyzed reactions due to their large surface areas, [33] chemical and thermal stability.…”