Thermally stable single atom Pt/m-Al2O3 for selective hydrogenation and CO oxidation

Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsaturated pentahedral Al3+ centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period

Heterometal Incorporation in Metal-Exchanged Zeolites Enables Low-Temperature Catalytic Activity of NO_<i>x</i> Reduction

A series of new heterobimetallic zeolites has been synthesized by incorporating a secondary metal cation M (Sc³⁺, Fe³⁺, In³⁺, and La³⁺) in Cu-exchanged ZSM-5, zeolite-β, and SSZ-13 zeolites under carefully controlled experimental conditions. Characterization by diffuse-reflectance ultraviolet–visible spectroscopy (UV–vis), X-ray powder diffraction (XRD), extended X-ray absorption fine structure spectroscopy (EXAFS), and electron paramagnetic resonance spectroscopy (EPR) does not permit conclusive structural determination but supports the proposal that M³⁺ is hosted in zeolite structures in the vicinity of Cu­(II), resulting in high NO_<i>x</i> conversion activity at 150 °C. Among various zeolites reported here, CuFe-SSZ-13 offers the best NO_<i>x</i> conversion activity in the 150–650 °C range and is hydrothermally stable when tested under accelerated aging conditions. Mechanistic studies employing stopped-flow diffuse reflectance FT-IR spectroscopy (DRIFTS) suggest that the high concentration of NO⁺ generated by heterobimetallic zeolites is probably responsible for their superior low-temperature NO_<i>x</i> activity

Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina

Catalysis by single isolated atoms of precious metals has attracted much recent interest, as it promises the ultimate in atom efficiency. Most previous reports are on reducible oxide supports. Here we show that isolated palladium atoms can be catalytically active on industrially relevant g-alumina supports. The addition of lanthanum oxide to the alumina, long known for its ability to improve alumina stability, is found to also help in the stabilization of isolated palladium atoms. Aberration-corrected scanning transmission electron microscopy and operando X-ray absorption spectroscopy confirm the presence of intermingled palladium and lanthanum on the gamma-alumina surface. Carbon monoxide oxidation reactivity measurements show onset of catalytic activity at 40 degrees C. The catalyst activity can be regenerated by oxidation at 700 degrees C in air. The high-temperature stability and regenerability of these ionic palladium species make this catalyst system of potential interest for low-temperature exhaust treatment catalysts.close201

Evolution and stabilization of subnanometric metal species in confined space by in situ TEM

Understanding the behavior and structural transformation of metal species under reaction conditions is instrumental for developing more efficient and stable catalysts. Here, the authors reveal the evolution and stabilization of subnanometric Pt species confined in MCM-22 zeolite using in situ transmission electron microscopy