9 Search Results

Activation of surface lattice oxygen and chemisorbed oxygen on catalyst surfaces constitutes a pivotal step in heterogeneous oxidative catalysis. Herein, we report a strategy for enhancing oxygen activation by rational design of catalysts with single-atom promoters. Single-site Zr species in CeO₂ (Zr₁-CeO₂) are synthesized using the atom-trapping method. The Zr₁-CeO₂-supported Pt catalyst exhibits enhanced catalytic performance over the CeO₂-supported Pt catalyst in the oxidation of CO, C₃H₈, and C₃H₆, achieving significantly lower T₅₀ values (temperature required to reach 50% conversion). This enhanced catalytic activity is attributed to the formation of an asymmetric Zr₁-O-Pt₁ structure, which favors the activation of themore » adjacent surface lattice oxygen and chemisorbed molecular oxygen. This work exemplifies that incorporating single-site atoms into oxide support facilitates oxygen activation, providing new insights into the role of atomically dispersed promoters in heterogeneous catalysis.« less

Abstract Single atoms of platinum group metals on CeO ₂ represent a potential approach to lower precious metal requirements for automobile exhaust treatment catalysts. Here we show the dynamic evolution of two types of single-atom Pt (Pt ₁ ) on CeO ₂ , i.e., adsorbed Pt ₁ in Pt/CeO ₂ and square planar Pt ₁ in Pt _AT CeO ₂ , fabricated at 500 °C and by atom-trapping method at 800 °C, respectively. Adsorbed Pt ₁ in Pt/CeO ₂ is mobile with the in situ formation of few-atom Pt clusters during CO oxidation, contributing to high reactivity with near-zero reaction order inmore » CO. In contrast, square planar Pt ₁ in Pt _AT CeO ₂ is strongly anchored to the support during CO oxidation leading to relatively low reactivity with a positive reaction order in CO. Reduction of both Pt/CeO ₂ and Pt _AT CeO ₂ in CO transforms Pt ₁ to Pt nanoparticles. However, both catalysts retain the memory of their initial Pt ₁ state after reoxidative treatments, which illustrates the importance of the initial single-atom structure in practical applications.« less

Reversibly adjusting the active structures of supported metal catalysts in response to dynamic working conditions has long been pursued. Here we report the reaction-environment-modulated transformations of subnanometre-sized Pd on CeO₂ for efficient methane removal, leveraging the reaction environments at different stages of automotive exhaust aftertreatment. During the cold start of vehicles, inactive Pd₁ single atoms are readily transformed into PdO_$$x$$ subnanometre clusters by CO even at room temperature with excess O₂, resulting in boosted low-temperature CH₄ oxidation. At elevated temperatures, dispersion of PdO_$$x$$ cluster into Pd₁ against metal sintering renders outstanding hydrothermal stability to the catalyst, to be activated duringmore » the next vehicle start. Combined experimental and computational studies elucidate the dynamically evolved Pd speciation on CeO₂ at an atomic level. In conclusion, modulating the reversible nature of supported metals helps overcome the long-existing trade-off between low-temperature activity and high-temperature stability, also providing a new paradigm for designing intelligent catalysts that brings single-atom/cluster catalysts closer to real applications.« less

Requiring catalysts to be both active yet stable over long periods of time under variable reaction conditions including high and low temperatures is a daunting challenge due to the almost mutual exclusivity of these constraints. Using CO oxidation as a probe reaction, in this work we demonstrate that thermally stable single atom copper catalysts prepared by high temperature synthesis (atom trapping) on ceria can achieve this feat by allowing modulation of the Cu charge state through facile charge transfer between active site and support. This provides the catalysts with an ability to activate either lattice or adatom oxygen atoms, accessingmore » additional reaction channels depending on the reaction conditions. Such adaptability allows dynamic response of catalysts enabling them to remain active under variable reaction conditions. The inherent stability of the catalyst arises from the enhanced strength of the Cu-O interactions from high temperature synthesis that exist even when Cu oxidation state varies, which retards sintering and deactivation. As we show here, one can circumvent the dilemma of designing catalysts that are simultaneously active and stable by matching the redox properties of the active site and support and establishing an environmental adaptability around the active sites.« less

Cerium oxide (ceria) has been shown to be very effective at trapping platinum atoms, due to formation of stable surface complexes at step edges, where coordinatively unsaturated cerium cations are present. But ceria loses its effectiveness when heated to high temperatures, due to loss of surface area and growth in particle size associated with sintering of the oxide. Being a rare-earth, and with limited supplies worldwide, it is important to develop methods to improve the effectiveness of ceria as a catalyst support. Here we explore the performance for trapping Pt atoms when the ceria is supported on a high surfacemore » area alumina carrier. This helps create a more sustainable catalyst formulation, especially if we can retain the high dispersion of Pt seen on ceria supports. For this work, we studied the atom trapping efficacy of ceria/alumina samples with increasing ceria content (8 wt% - 50%) and contrasted the behavior with pure ceria. Electron microscopy reveals that when dispersed on alumina, ceria is present in the form of crystalline nanoparticles as well as isolated cerium ions. These two forms of ceria differ markedly in their ability to trap Pt atoms. Atomically dispersed cerium is present in the form of Ce³⁺ cations on alumina, however this form of ceria is not effective for trapping Pt atoms. Our results show that the atom trapped Pt resides primarily on crystalline ceria nanoparticles. CO oxidation was used as a probe reaction to evaluate the performance of these Pt_AT/ceria-alumina catalysts. As a result, we conclude that over the range of ceria loadings we investigated, 50% ceria/alumina represents the optimal catalyst support for achieving high surface area and atom trapping efficiency while helping reduce the total ceria content in this catalyst system.« less

Abstract A single‐atom Pt ₁ /CeO ₂ catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over‐stabilization of Pt ²⁺ in a highly symmetric square‐planar Pt ₁ O ₄ coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt ²⁺ by thermal‐shock (TS) synthesis leads to a highly active and thermally stable Pt ₁ /CeO ₂ catalyst. Ultrafast shockwaves (>1200 °C)more » in an inert atmosphere induced surface reconstruction of CeO ₂ to generate Pt single atoms in an asymmetric Pt ₁ O ₄ configuration. Owing to this unique coordination, Pt ₁ ^δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low‐temperature performance. CO oxidation reactivity on the Pt ₁ /CeO ₂ _TS catalyst was retained under oxidizing conditions.« less

The treatment of emissions from natural gas engines is an important area of research since methane is a potent greenhouse gas. The benchmark catalysts, based on Pd, still face challenges such as water poisoning and long-term stability. In this work, we report an approach for catalyst synthesis that relies on the trapping of metal single atoms on the support surface, in thermally stable form, to modify the nature of further deposited metal/metal oxide. By anchoring Pt ions on a catalyst support we can tailor the morphology of the deposited phase. In particular, two-dimensional (2D) rafts of PdO_x are formed, resultingmore » in higher reaction rates and improved water tolerance during methane oxidation. The results show that modifying the support by trapping single atoms could provide an important addition to the toolkit of catalyst designers for controlling the nucleation and growth of metal and metal oxide clusters in heterogeneous catalysts.« less

A single-atom Pt₁/CeO₂ catalyst formed by atom trapping (AT, 800 degrees C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over-stabilization of Pt²⁺ in a highly symmetric square-planar Pt₁O₄ coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. In this work, we show that tailoring the local environment of isolated Pt²⁺ by thermal-shock (TS) synthesis leads to a highly active and thermally stable Pt₁/CeO₂ catalyst. Ultrafast shockwaves (>1200 degrees C) in an inert atmosphere induced surfacemore » reconstruction of CeO₂ to generate Pt single atoms in an asymmetric Pt₁O₄ configuration. Owing to this unique coordination, Pt₁^δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low-temperature performance. CO oxidation reactivity on the Pt₁/CeO₂_TS catalyst was retained under oxidizing conditions.« less

Supported precious metals with atomic dispersion are of great interest in catalysis due to their potentials in achieving maximum atom efficiency and unique reactivities. Herein, the active sites for low-temperature CO oxidation are elucidated over single-atom Pd₁/CeO₂ catalysts prepared via high-temperature atom trapping (AT). The increased oxygen vacancies on CeO₂ surface induced by 800 °C air calcination result in decreased Pd–CeO₂ coordinations, i.e., the coordination-unsaturated Pd²⁺ on CeO₂. Light-off and light-out measurements coupled with CO-DRIFTS and X-ray absorption characterization confirm that these coordination-unsaturated Pd²⁺ on CeO₂ are much more reactive than the fully coordinated counterpart, evidenced by a decrease ofmore » T₉₀ (temperature to achieve 90% conversion) by ~100 °C in CO oxidation at a gas hourly space velocity of 300 L g^–1 h^–1.« less