Single Ir Atoms Anchored on Ordered Mesoporous WO₃ Are Highly Efficient for the Selective Catalytic Reduction of NO with CO under Oxygen‐rich Conditions

Abstract

Under oxygen‐rich conditions, achieving a selective and efficient reduction of NO by CO is always challenging. Here, we report the synthesis of the catalyst consisting of single Ir atoms anchored on mesoporous WO3 (denoted as Ir1/m‐WO3) using a facile template method followed by wet impregnation. X‐ray diffraction and transmission electron microscope studies indicated that the Ir atoms were distributed uniformly on the internal surface of m‐WO3. When tested for the reduction of NO by CO, the Ir1/m‐WO3 catalyst with a low Ir loading of 0.28 wt % exhibited excellent catalytic performance in the presence of 2 vol % O2 (volume ratio of CO to O2 being 1 : 10), achieving a NO conversion of 73 % and N2 selectivity of 100 % at 350 °C. In particular, its turnover frequency (TOF) value reached 0.30 s−1 at 200 °C, which is six times higher than that of the catalyst with Ir nanoparticles supported on mesoporous WO3 (0.05 s−1). The superior catalytic performance of Ir1/m‐WO3 is attributed to the formation of the isolated Ir atoms and the more newly generated Ir‐WO3 interfaces that can promote the adsorption and activation of NO, and the presence of accessible mesopores in m‐WO3 that facilitates the mass transfer of NO and CO. This study brings a new fundamental understanding of active sites in Ir‐based catalysts for the CO+NO reaction and provides a new way to the design and synthesis of single‐atom catalysts, especially precious metal catalysts for emissions control.

Relevance of IR Spectroscopy of Adsorbed CO for the Characterization of Heterogeneous Catalysts Containing Isolated Atoms

“…The same mistake assigning CO­(g) branches to adsorbed CO species can be found in another contribution dealing with Ir iso /WO 3 . The P-branch band (located at ca.…”

First-Principles Study of NO Reduction by CO on Cu2O(110) and Pd1/Cu2O(110) Surfaces

“…In recent decades, with the dramatic increase of the number of automobiles, the problem of automobile exhaust pollution has become more and more serious. Nitrogen oxides (NO x ), as one of the main pollutants of automotive exhaust, not only cause environmental problems such as photochemical smog and ozone layer destruction but also have adverse effects on human health. − Therefore, catalytic removal of NO x (NO usually accounts for about 90%) is a method of great significance to control air pollution. Currently, selective catalytic reduction (SCR) is considered as one of the most effective methods for NO elimination.…”

Catalysts Optimization of WO3‐SiO2 Supported Iridium for NOx Reduction by CO under Excess Oxygen Conditions

“…The Ir 4 f spectrum of the catalyst was shown in Figure 5(b), which was composed of two main peaks, Ir 4f 7/2 and Ir4f 5/2 , and the peaks were fitted separately. The peaks at 60.6∼61.3 eV and 61.7∼62.3 eV was belonged to Ir 0 and Ir 4+ , respectively; in Ir 4f 5/2 , the peaks at 63.5∼64.2 eV and 64.4∼65.1 eV was attributed to Ir 0 and Ir 4+ , [25] respectively. According to the result of area integration, the contents of Ir 0 and Ir 4+ can be calculated (Table 1).…”

“…If the load was low, the Ir species will disperse unevenly and the active sites will be too few. If the load is high, the active components would agglomerate on the catalyst surface, which would then block the pores of the catalyst and reduce the specific surface area, thus adversely affecting the catalytic activity [24–27] . As shown in Figure 4(a), when the Ir species load was 2 wt%, the catalyst could achieve 49 % NOx conversion at the reaction temperature of 225 °C.…”