Catalysis on Singly Dispersed Rh Atoms Anchored on an Inert Support

Abstract

A metal catalyst supported on an inert substrate could consist of both metal nanoparticles and singly dispersed metal atoms. Whether these singly dispersed metal atoms are active and how different their catalytic mechanism could be in contrast to a supported metal catalyst are fundamentally important for understanding catalysis on a supported metal or oxide. By taking reduction of NO with CO on singly dispersed Rh atoms anchored on an inert support SiO2 as a probe system (Rh1/SiO2), here we demonstrated how singly dispersed metal atoms on an inert support could perform a complex multi-step catalytic cycle through a mechanism distinctly different from that for a supported metal nanoparticle with continuously packed metal sites. These singly dispersed Rh1 atoms anchored on SiO2 are active in reducing nitric oxide with carbon monoxide through two reaction pathways that are different from those of Rh nanoparticles. In situ IR studies show that a CO molecule and a NO molecule coadsorb on a singly dispersed Rh atom, Rh1 anchored on SiO2, and couple to form an N atom to adsorb on the surface and a CO2 molecule to desorb. The adsorbed N atom further couples with another CO molecule in the gas phase to form an intermediate −NCO on Rh1; this intermediate can directly couple with an NO molecule adsorbed on the same Rh1 to form N2 and CO2. In another pathway, the adsorbed N atom can couple with a coadsorbed NO on the same Rh1 to form N2O; N2O further reacts with adsorbed CO on the same Rh1 to form N2 and CO2 through a high activation barrier that can be overcome at a high temperature. Our studies show that the singly dispersed metal atoms on an inert support have great potential to perform selective transformation of chemicals. The confirmed catalysis with a singly dispersed Rh1 on SiO2 through a mechanism different from a metal nanoparticle supported on the same substrate suggests the significance of taking the single-atom catalysis (SAC) into fundamental studies of catalysis of a supported metal catalyst, since metal nanoparticles and singly dispersed metal atoms likely coexist on the inert support of many supported catalysts.

Single‐atom Automobile Exhaust Catalysts

“…They believed that it is the aggregates of Rh atoms rather than the mononuclear single‐site Rh(CO) 2 species that facilitates the NO reduction with CO. Besides, single‐atom Rh on inert SiO 2 is confirmed by Zhang et al [157] . to be active to reduce the NO with CO via the totally different reaction pathways compared to Rh NPs.…”

“…[134] They believed that it is the aggregates of Rh atoms rather than the mononuclear single-site Rh(CO) 2 species that facilitates the NO reduction with CO. Besides, single-atom Rh on inert SiO 2 is confirmed by Zhang et al [157] to be active to reduce the NO with CO via the totally different reaction pathways compared to Rh NPs. Very recently, Christopher and co-workers raised a question if the lowtemperature NH 3 formation from NO reduction in the presence of CO and H 2 O is due to single atom Rh?…”

Single-atom site catalysts for environmental catalysis

“…Thus, N2O might easily attach to RhCoNP/CoO, leading to N2 selectivity as low as only 10%. Over the past few years, some excellent SACs have been developed for NSCR reaction in terms of good lowtemperature catalytic activity and N2 selectivity [50,53,123,124]. However, achieving a high fuel economy would require lean-burn engines widely applied to gasoline and diesel vehicles.…”

A Nanosensor for Naked-Eye Identification and Adsorption of Cadmium Ion Based on Core–Shell Magnetic Nanospheres

“…The particles with nano size possess abundant surface active sites for surface modification, and the greatest strength of Fe 3 O 4 @SiO 2 nanoparticles is their targeting ability. These magnetic particles can be attracted to a target zone under the action of an external magnetic field, which makes recovery feasible [ 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Moreover, the inert SiO 2 -shell can prevent the magnetic Fe 3 O 4 -core from oxidation, and the abundant surface hydroxyl of SiO 2 is highly conducive to surface grafting with organic ligands [ 22 , 23 , 24 , 25 ].…”