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

Tuning selectivity of electrochemical reactions by atomically dispersed platinum catalyst

Maximum atom efficiency as well as distinct chemoselectivity is expected for electrocatalysis on atomically dispersed (or single site) metal centres, but its realization remains challenging so far, because carbon, as the most widely used electrocatalyst support, cannot effectively stabilize them. Here we report that a sulfur-doped zeolite-templated carbon, simultaneously exhibiting large sulfur content (17 wt% S), as well as a unique carbon structure (that is, highly curved three-dimensional networks of graphene nanoribbons), can stabilize a relatively high loading of platinum (5 wt%) in the form of highly dispersed species including site isolated atoms. In the oxygen reduction reaction, this catalyst does not follow a conventional four-electron pathway producing H₂O, but selectively produces H₂O₂ even over extended times without significant degradation of the activity. Thus, this approach constitutes a potentially promising route for producing important fine chemical H₂O₂, and also offers opportunities for tuning the selectivity of other electrochemical reactions on various metal catalysts.

Atomically dispersed metal catalysts display high atom efficiency for electrocatalytic processes. Here, the authors report that sulfur-doped zeolite-templated carbon stabilizes highly dispersed platinum species, predominantly as single-atom centres, and probe its oxygen reduction selectivity.

Carbon monoxide oxidation catalysed by defective palladium chloride: DFT calculations, EXAFS, and in situ DRIRS measurements

We examined the potential catalytic role of the palladium chloride catalyst in CO oxidation using density functional theory and experimental investigations. The active plane of the palladium chloride catalyst is identified as (140). We found that the defective PdCl2(140) surface is able to facilitate the activation of O2 and subsequently promote the oxidation of CO. The most significant reaction channel, the Eley-Rideal mechanism (MER1), proceeds first by a peroxo-type (OOCO) intermediate formation, second by O adsorption with the first CO2 release, then by the second CO attraction and the second CO2 formation, and finally by the second CO2 desorption and restoration of the defective PdCl2(140) surface. The rate-determining step is the formation of the second CO2 in the whole catalytic cycle. Compared to the previously reported catalytic systems, the reaction activation barrier (0.54 eV) of CO oxidation in the PdCl2 catalyst is low, indicating PdCl2 as a potential high-performance catalyst for CO oxidation. The present results enrich our understanding of CO oxidation of Pd-based catalysts and provide a basis for fabricating Pd-based catalysts with high activity.

Catalytically Active Rh Sub-Nanoclusters on TiO2 for CO Oxidation at Cryogenic Temperatures

The discovery that gold catalysts could be active for CO oxidation at cryogenic temperatures has ignited much excitement in nanocatalysis. Whether the alternative Pt group metal (PGM) catalysts can exhibit such high performance is an interesting research issue. So far, no PGM catalyst shows activity for CO oxidation at cryogenic temperatures. In this work, we report a sub-nano Rh/TiO2 catalyst that can completely convert CO at 223 K. This catalyst exhibits at least three orders of magnitude higher turnover frequency (TOF) than the best Rh-based catalysts and comparable to the well-known Au/TiO2 for CO oxidation. The specific size range of 0.4-0.8 nm Rh clusters is critical to the facile activation of O2 over the Rh-TiO2 interface in a form of Rh-O-O-Ti (superoxide). This superoxide is ready to react with the CO adsorbed on TiO2 sites at cryogenic temperatures.

Highly water-dispersible magnetite-supported Pd nanoparticles and single atoms as excellent catalysts for Suzuki and hydrogenation reactions

The linker dpa enables the deposition of palladium on magnetite nanoparticles that show excellent catalytic behavior in water or water/ethanol solvents.

Mesoporous Y2Sn2O7 pyrochlore with exposed (111) facets: an active and stable catalyst for CO oxidation

Mesoporous Y₂Sn₂O₇ pyrochlore with exposed (111) facets was successfully synthesized via a simple hydrothermal method and showed superior catalytic performance for CO oxidation.

Towards stable single-atom catalysts: strong binding of atomically dispersed transition metals on the surface of nanostructured ceria

Surface oxygen sites on CeO₂ nanostructures are able to bind atoms of various transition metals strong enough to prevent their sintering. This finding opens a knowledge-driven way to prepare stable single-atom catalysts with maximum metal efficiency.

Magnetite-supported palladium single-atoms do not catalyse the hydrogenation of alkenes but small clusters do

Pd clusters of low atomicity supported on magnetite nanoparticles are extremely active for the hydrogenation of styrene, overcoming the best reported TOFs.

The healing of B- or N-vacancy defective BNNTs by using CO molecule: a DFT study

Boron or nitrogen vacancies of BNNTs can be effectively healed by CO at ambient temperature.

The complex behavior of the Pd7 cluster supported on TiO2(110) during CO oxidation: adsorbate-driven promoting effect

The CO saturation-driven 3D to 2D structural transformation of the Pd₇ cluster supported on TiO₂(110) promotes CO oxidation activity via bifunctional synergy of interfacial sites.

A novel Pd3O9@α-Al2O3 catalyst under a hydroxylated effect: high activity in the CO oxidation reaction

Considering the importance of palladium-based and doped metal-oxide catalysts in CO oxidation, we design a new Pd3O9@α-Al2O3 catalyst and simulate its efficiency under a hydroxylated effect. The structure, electronic structure and oxidation activity of the hydroxylated Pd3O9@α-Al2O3(0001) surface are investigated by density functional theory. Under the O-rich growth conditions, Pd preferentially replaces Al. The lowest formation energy of the Pd-doped α-Al2O3(0001) surface is 0.21 eV under conditions wherein the coverage of the Pd-doped α-Al2O3 is 0.75 on a pre-hydroxylated surface and the water coverage is 0.25, which leads to formation of a Pd3O9 cluster embedded in the Al2O3(0001) surface. The reaction mechanisms of CO oxidization have been elucidated first by CO adsorption and migration, second by O(v) formation with the first CO2 release, then by the first foreign O2 filling and CO co-adsorption, and finally by the second CO2 desorption and restoration of the hydroxylated Pd3O9@α-Al2O3(0001) surface. The rate-determining step is the formation of the first CO2 in the whole catalytic cycle. The results also indicate that the energy barrier for CO oxidization is obviously reduced compared to that of the undoped surface, which implies that the introduction of Pd can efficiently improve the oxidation reactivity of the α-Al2O3(0001) surface. Compared to the synthesized Ir1/FeO(x) (1.41 eV) and Pt1/FeO(x) (0.79 eV) catalysts, the reaction activation barrier of CO oxidation is lowered by 0.65 eV and 0.03 eV, respectively. Therefore, the Pd3O9@α-Al2O3 catalyst shows superior catalytic activity in CO oxidation. The present results enrich the understanding of the catalytic oxidation of CO by palladium-based catalysts and provide a clue for fabricating palladium-based catalysts with low cost and high activity.

Palladium-Based Nanomaterials: A Platform to Produce Reactive Oxygen Species for Catalyzing Oxidation Reactions

Oxidation reactions by molecular oxygen (O2 ) over palladium (Pd)-based nanomaterials are a series of processes crucial to the synthesis of fine chemicals. In the past decades, investigations of related catalytic materials have mainly been focused on the synthesis of Pd-based nanomaterials from the angle of tailoring their surface structures, compositions and supporting materials, in efforts to improve their activities in organic reactions. From the perspective of rational materials design, it is imperative to address the fundamental issues associated with catalyst performance, one of which should be oxygen activation by Pd-based nanomaterials. Here, the fundamentals that account for the transformation from O2 to reactive oxygen species over Pd, with a focus on singlet O2 and its analogue, are introduced. Methods for detecting and differentiating species are also presented to facilitate future fundamental research. Key factors for tuning the oxygen activation efficiencies of catalytic materials are then outlined, and recent developments in Pd-catalyzed oxygen-related organic reactions are summarized in alignment with each key factor. To close, we discuss the challenges and opportunities for photocatalysis research at this unique intersection as well as the potential impact on other research fields.

Surfactant encapsulated palladium-polyoxometalates: controlled assembly and their application as single-atom catalysts

Two kinds of assembly structures (nanorolls and hollow spindles) based on the palladium substituted Wells–Dawson polyoxometalate (Pd-POM) were synthesised and showed high catalytic activity for both the Suzuki–Miyaura coupling reaction and semihydrogenation reaction.

The challenge with single-atom catalysts (SACs) is in designing a highly definite structure with accurate location of the single atom and high catalytic efficiency. The noble metal substituted polyoxometalates seem to be a kind of SAC because of their well resolved crystal structure. Here, we got two kinds of assembly structures (nanorolls and hollow spindles) based on the palladium substituted Wells–Dawson polyoxometalate (Pd-POM), which consists of isolated Pd atoms. Both the nanorolls and hollow spindles showed high catalytic activity for both the Suzuki–Miyaura coupling reaction and semihydrogenation reaction. The difference of the chemical surroundings between the nanorolls and hollow spindles leads to their discrepancy in the catalytic activity of semihydrogenation.

Room-temperature carbon monoxide oxidation by oxygen over Pt/Al2O3 mediated by reactive platinum carbonates

Room-temperature carbon monoxide oxidation, important for maintaining clean air among other applications, is challenging even after a century of research into carbon monoxide oxidation. Here we report using time-resolved diffuse reflectance infrared spectroscopy, X-ray absorption fine structure spectroscopy and mass spectrometry a platinum carbonate-mediated mechanism for the room-temperature oxidation of carbon monoxide. By applying a periodic reduction-oxidation mode of operation we further show that this behaviour is reversible and can be formed into a catalytic cycle that requires molecular communication between metallic platinum nanoparticles and highly dispersed oxidic platinum centres. A new possibility for the attainment of low-temperature oxidation of carbon monoxide is therefore demonstrated.

Selective hydrogenation of 1,3-butadiene on platinum-copper alloys at the single-atom limit

Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum–copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C–C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions.

Reducing the platinum content of industrial catalysts is an important research target. Here, the authors present a nanocatalyst containing less than 1% platinum, where the isolated platinum atoms contribute to both the catalyst activity and selectivity for butadiene hydrogenation.

A Cu(111) supported h-BN nanosheet: a potential low-cost and high-performance catalyst for CO oxidation

CO oxidation on h-BNNS/Cu(111).

Can metal-free silicon-doped hexagonal boron nitride nanosheets and nanotubes exhibit activity toward CO oxidation?

Si-doped hexagonal boron nitride nanosheets and nanotubes have been investigated by first-principle methods.

Remarkable NO oxidation on single supported platinum atoms

Our first-principles density functional theoretical modeling suggests that NO oxidation is feasible on fully oxidized single θ-Al₂O₃ supported platinum atoms via a modified Langmuir-Hinshelwood pathway. This is in contrast to the known decrease in NO oxidation activity of supported platinum with decreasing Pt particle size believed to be due to increased platinum oxidation. In order to validate our theoretical study, we evaluated single θ-Al₂O₃ supported platinum atoms and found them to exhibit remarkable NO oxidation activity. A comparison of turnover frequencies (TOF) of single supported Pt atoms with those of platinum particles for NO oxidation shows that single supported Pt atoms are as active as fully formed platinum particles. Thus, the overall picture of NO oxidation on supported Pt is that NO oxidation activity decreases with decreasing Pt particle size but accelerates when Pt is present only as single atoms.