Tuning the Interaction between Platinum Single Atoms and Ceria by Zirconia Doping for Efficient Catalytic Ammonia Oxidation

Asymmetric Pt1O4-Ov Dual Active Sites Induced by NbOx Clusters Promotes CO Synergistical Oxidation

Pt/CeO2 single-atom catalysts are attractive materials for CO oxidation but normally show poor activity below 150 °C mainly due to the unicity of the originally symmetric Pt1O4 structure. In this work, a highly active and stable Pt1/CeO2 single-site catalyst with only 0.1 wt % Pt loading, achieving a satisfied complete conversion of CO at 150 °C, can be obtained through fabricating asymmetric Pt1O4-oxygen vacancies (Ov) dual-active sites induced by well-dispersed NbOx clusters. Specifically, the formation of new Ce-O-Nb interactions weakened the strength of the original Pt-O-Ce bond, thus transferring the originally near-perfect square-planar Pt1O4 into the distorted square-planar one, along with forming abundant Ov around the Pt site. Hence, the promoted CO activation on the asymmetric Pt1O4 structure and the facilitated dissociation of the O2 on the neighboring Ov site synergistically improved the CO catalytic oxidation performance. The fabrication of such asymmetric Pt1O4-Ov double-active sites was also active for the oxidation of other typical hydrocarbons pollutants such as C7H8 and C3H6 from exhaust gases, shedding light on engineering high-efficiency Pt-based oxidation catalysts for low-temperature environmental catalysis.

Polyoxometalates-Mediated Selectivity in Pt Single-Atoms on Ceria for Environmental Catalysis

Optimizing the reactivity and selectivity of single-atom catalysts (SACs) remains a crucial yet challenging issue in heterogeneous catalysis. This study demonstrates selective catalysis facilitated by a polyoxometalates-mediated electronic interaction (PMEI) in a Pt single-atom catalyst supported on CeO2 modified with Keggin-type phosphotungstate acid (HPW), labeled as Pt1/CeO2-HPW. The PMEI effect originates from the unique arrangement of isolated Pt atoms and HPW clusters on the CeO2 support. Electrons are transferred from the ceria support to the electrophilic tungsten in HPW clusters, and subsequently, Pt atoms donate electrons to the now electron-deficient ceria. This phenomenon enhances the positive charge of Pt atoms, moderating O2 activation and limiting lattice oxygen mobility compared to the conventional Pt1/CeO2 catalyst. The resulting electronic structure of Pt combined with the strong and local acidic environment of HPW on Pt1/CeO2-HPW leads to improved efficiency and N2 selectivity in the degradation of NH3 and NO, as well as increased CO2 yield when inputting volatile organic compounds. This study sheds the light on the design of SACs with balanced reactivity and selectivity for environmental catalysis.

Transformation of Arsenic from Poison into Active Site by Construction of Unique AsOx/CeO2 Interface for Stable NOx Removal

Arsenic in the flue gas has been widely reported as a common poison for SCR catalysts; however, an appropriate coping strategy is still lacking to improve the arsenic resistance performance. Herein, a unique AsOx/CeO2 interface is constructed to transform arsenic from poison into active site with balanced acid-redox property, successfully achieving efficient NOx removal. The optimized AsOx/CeO2 exhibits high NOx removal efficiency, four times that of the As-poisoned V2O5/TiO2 catalyst, and even comparable to the state-of-the-art SCR catalysts. It was found that the As-O-Ce interfacial sites in oxygen-bridged As dimers on CeO2 can provide both Lewis acid sites and active lattice oxygen species, enhancing the adsorption and activation of NH3 to form key -NH2 intermediates, thereby facilitating the NH3-SCR reaction. More surprisingly, a thin CeO2 layer on the top of V2O5/TiO2 can capture arsenic to protect catalysts from arsenic attacking, which improves the catalytic activity to 2.8 × 10-7 mol g-1 s-1, even higher than that of fresh V2O5/TiO2 (2.0 × 10-7 mol g-1 s-1). Therefore, this strategy provides new ideas not only for designing antipoisoning SCR catalysts but also a feasible solution for the stable operation of commercial SCR catalysts in arsenic-containing flue gas.

Fabrication of Highly Dispersed Ru Catalysts on CeO2 for Efficient C3H6 Oxidation

Emissions of volatile organic compounds (VOCs) threaten both the environment and human health. To realize the elimination of VOCs, Ru/CeO2 catalysts have been intensively investigated and applied. Although it has been widely acknowledged that the catalytic performance of platinum group metal catalysts was highly determined by their dispersion and coordination environment, the most reactive structures on Ru/CeO2 catalysts for VOCs oxidation are still ambiguous. In this work, starting from Ce-BTC (BTC = 1,3,5-benzenetricarboxylic acid) materials, atomically dispersed Ru catalysts and agglomerated Ru catalysts were successfully created via one-step hydrothermal method (Ru-CeO2-BTC) and conventional incipient wetness impregnation method (Ru/CeO2-BTC), respectively. In a typical model reaction of C3H6 oxidation, atomically dispersed Ruδ+ species with the formation of abundant Ru-O-Ce linkages on Ru-CeO2-BTC were found to perform much better than agglomerated RuOx species on Ru/CeO2-BTC. Further characterizations and mechanism study disclosed that Ru-CeO2-BTC catalyst with atomically dispersed Ru ions and more superior low temperature redox performance compared to Ru/CeO2-BTC could better facilitate the adsorption/activation of C3H6 and the decomposition/desorption of intermediates, thus exhibiting superior C3H6 oxidation activity. This work elucidated the reactive sites on Ru/CeO2 catalysts in the C3H6 oxidation reaction and provided insightful guidance for designing efficient Ru/CeO2 catalysts to eliminate VOCs.

Pt-O-Ce interaction enhanced by Al substitution to promote the acetone degradation through accelerating the breaking of CC bond in acetic acid intermediate

The reaction rate of volatile organic compounds (VOCs) oxidation is controlled by the rate-limiting step in the total reaction process. This study proposes a novel strategy, by which the rate-limiting step of acetone oxidation is accelerated by enhanced chemical bond interaction with more electrons transfer through Al-substituted CeO2 loaded Pt (Pt/Al-CeO2). Results indicate that the rate-limiting step in the process of acetone oxidation is the decomposition of acetic acid. Al substitution enhances the Pt-O-Ce interaction that transfers more electrons from Pt/Al-CeO2 to acetic acid, promoting the breaking of its CC bond with a lower free energy barrier. Attributing to these, the reaction rate of Pt/Al-CeO2 is 13 times as high as that of Pt/CeO2 and its TOFPt value is 11 times as high as that of Pt/CeO2 at 150 °C. Moreover, the CO2 selectivity of Pt/Al-CeO2 also increases by 22 %. This work establishes the relationship between Pt-O-Ce interaction and acetone oxidation that provides novel perspectives on the development of efficient materials for VOCs oxidation.

Unraveling the Mechanistic Origin of High N2 Selectivity in Ammonia Selective Catalytic Oxidation on CuO-Based Catalyst

NH3 emissions from industrial sources and possibly future energy production constitute a threat to human health because of their toxicity and participation in PM2.5 formation. Ammonia selective catalytic oxidation to N2 (NH3-SCO) is a promising route for NH3 emission control, but the mechanistic origin of achieving high N2 selectivity remains elusive. Here we constructed a highly N2-selective CuO/TiO2 catalyst and proposed a CuOx dimer active site based on the observation of a quadratic dependence of NH3-SCO reaction rate on CuOx loading, ac-STEM, and ab initio thermodynamic analysis. Combining this with the identification of a critical N2H4 intermediate by in situ DRIFTS characterization, a comprehensive N2H4-mediated reaction pathway was proposed by DFT calculations. The high N2 selectivity originated from the preference for NH2 coupling to generate N2H4 over NH2 dehydrogenation on the CuOx dimer active site. This work could pave the way for the rational design of efficient NH3-SCO catalysts.

Fine-Tuning of Pt Dispersion on Al2O3 and Understanding the Nature of Active Pt Sites for Efficient CO and NH3 Oxidation Reactions

Fine-tuning the dispersion of active metal species on widely used supports is a research hotspot in the catalysis community, which is vital for achieving a balance between the atomic utilization efficiency and the intrinsic activity of active sites. In this work, using bayerite Al(OH)3 as support directly or after precalcination at 200 or 550 °C, Pt/Al2O3 catalysts with distinct Pt dispersions from single atoms to clusters (ca. 2 nm) were prepared and evaluated for CO and NH3 removal. Richer surface hydroxyl groups on AlOx(OH)y support were proved to better facilitate the dispersion of Pt. However, Pt/Al2O3 with relatively lower Pt dispersion could exhibit better activity in CO/NH3 oxidation reactions. Further reaction mechanism study revealed that the Pt sites on Pt/Al2O3 with lower Pt dispersion could be activated to Pt0 species much easier under the CO oxidation condition, on which a higher CO adsorption capacity and more efficient O2 activation were achieved simultaneously. Compared to Pt single atoms, PtOx clusters could also better activate NH3 into -NH2 and -HNO species. The higher CO adsorption capacity and the more efficient NH3/O2 activation ability on Pt/Al2O3 with relatively lower Pt dispersion well explained its higher CO/NH3 oxidation activity. This study emphasizes the importance of avoiding a singular pursuit of single-atom catalyst synthesis and instead focusing on achieving the most effective Pt species on Al2O3 support for targeted reactions. This approach avoids unnecessary limitations and enables a more practical and efficient strategy for Pt catalyst fabrication in emission control applications.