For decades, carbons have been the support of choice in acetylene hydrochlorination, a key industrial process for polyvinyl chloride manufacture. However, no unequivocal design criteria could be established to date, due to the complex interplay between the carbon host and the metal nanostructure. Herein, we disentangle the roles of carbon in determining activity and stability of platinum-, ruthenium-, and gold-based hydrochlorination catalysts and derive descriptors for optimal host design, by systematically varying the porous properties and surface functionalization of carbon, while preserving the active metal sites. The acetylene adsorption capacity is identified as central activity descriptor, while the density of acidic oxygen sites determines the coking tendency and thus catalyst stability. With this understanding, a platinum single-atom catalyst is developed with stable catalytic performance under two-fold accelerated deactivation conditions compared to the state-of-the-art system, marking a step ahead towards sustainable PVC production.
We describe a functional wood triboelectric nanogenerator (FW-TENG) made by modifying a wood scaffold respectively with ZIF-8 and PDMS. Our approach enables wood with a wide spectrum of triboelectric polarities while preserving its sustainability and aesthetic appearance. We demonstrate the application of our FW-TENG as an energy-harvesting wooden floor or panel, allowing it to power household lamps and other electronic devices when activated by walking or tapping.
The application of nitrogen‐doped carbons (NDCs) as host materials for single‐atom catalysts (SACs) is increasing because of the strong binding affinity of the heteroatom with transition metals. Establishment of the relation between the properties of NDCs, their interaction with metals, and the performance of the resulting catalysts is crucial to guide the design of more effective SACs but has not been critically addressed. Here, a series of NDCs is prepared and studied as hosts for palladium atoms. The amount of nitrogen incorporated primarily depends on the choice of carbon followed by the doping temperature and nitrogen source. Pyridinic and pyrrolic species predominate in all cases, especially at lower doping temperatures. The stabilization of palladium atoms is successful above a critical nitrogen content that depends on the carbon type. Evaluation in the catalytic semi‐hydrogenation of 2‐methyl‐3‐butyn‐2‐ol readily distinguishes the reactivity of single atoms and nanoparticles, which correlates with the electronic properties of palladium described by the average oxidation state. Comparison with SACs based on compositionally‐related carbon nitride hosts shows that similarly high stability and tunability of the metal is achievable over NDCs, despite their lower nitrogen contents and greater heterogeneity of coordination sites.
The emergence of nickel single-atoms on nitrogen-doped carbons as high-performance catalysts amenable to rationalization due to their well-defined structure could lead to applicable technologies for the electrocatalytic CO2 reduction reaction (eCO2RR). However, real materials are unlikely to display a uniform site structure, which limits the scope of current efforts focused on idealized models for future implementation. Here, we prepare distinct nickel entities (single atoms or nanoparticles) on nitrogen-doped carbons and evaluate them in eCO2RR. Single atoms demonstrate a characteristic high selectivity to CO. However, this is not altered by the presence of metal nanoparticles formed upon reducing the nitrogen content of the carrier. In contrast, nanoparticles incorporated via a colloidal route promote the parasitic hydrogen evolution reaction. In these systems, the CO selectivity evolves upon repeated exposure to potential, reaching values comparable to single atoms. By introducing CO stripping voltammetry as a characterization tool for this class of materials, we identify a decreased metallic surface, suggesting that the nanoparticle surface is altered by CO. The findings highlight the critical role of dynamic effects in catalyst design for eCO2RR.
Chemical modifiers enhance the efficiency of metal catalysts in numerous applications, but their introduction often involves toxic or expensive precursors and complicates the synthesis. Here, we show that a porous boron nitride carrier can directly modify supported palladium nanoparticles, originating unparalleled performance in the continuous semi‐hydrogenation of alkynes. Analysis of the impact of various structural parameters reveals that using a defective high surface area boron nitride and ensuring a palladium particle size of 4–5 nm is critical for maximizing the specific rate. The combined experimental and theoretical analyses point towards boron incorporation from defects in the support to the palladium subsurface, creating the desired isolated ensembles determining the selectivity. This practical approach highlights the unexplored potential of using tailored carriers for catalyst design.
The introduction of a foreign metal atom in the coordination environment of single‐atom catalysts constitutes an exciting frontier of active‐site engineering, generating bimetallic low‐nuclearity catalysts often exhibiting unique catalytic synergies. To date, the exploration of their full scope is thwarted by (i) the lack of synthetic techniques with control over intermetallic coordination, and (ii) the challenging characterization of these materials. Herein, carbon‐host functionalization is presented as a strategy to selectively generate Au‐Ru dimers and isolated sites by simple incipient wetness impregnation, as corroborated by careful X‐ray absorption spectroscopy analysis. The distinct catalytic fingerprints are unveiled via the hydrogen evolution reaction, employed as a probe for proton adsorption properties. Intriguingly, the virtually inactive Au atoms enhance the reaction kinetics of their Ru counterparts already when spatially isolated, by shifting the proton adsorption free energy closer to neutrality. Remarkably, the effect is magnified by a factor of 2 in dimers. These results exemplify the relevance of controlling intermetallic coordination for the rational design of bimetallic low‐nuclearity catalysts.
The ability to tailor the properties of metal centers in single‐atom heterogeneous catalysts depends on the availability of advanced approaches for characterization of their structure. Except for specific host materials with well‐defined metal adsorption sites, determining the local atomic environment remains a crucial challenge, often relying heavily on simulations. This article reports an advanced analysis of platinum atoms stabilized on poly(triazine imide), a nanocrystalline form of carbon nitride. The approach discriminates the distribution of surface coordination sites in the host, the evolution of metal coordination at different stages during the synthesis of the material, and the potential locations of metal atoms within the lattice. Consistent with density functional theory predictions, simultaneous high‐resolution imaging in high‐angle annular dark field and bright field modes experimentally confirms the preferred localization of platinum in‐plane in the corners of the triangular cavities. X‐ray absorption spectroscopy (XAS), X‐ray photoelectron spectroscopy (XPS), and dynamic nuclear polarization enhanced 15N nuclear magnetic resonance (DNP‐NMR) spectroscopies coupled with density functional theory (DFT) simulations reveal that the predominant metal species comprise Pt(II) bound to three nitrogen atoms and one chlorine atom inside the coordination sites. The findings, which narrow the gap between experimental and theoretical elucidation, contribute to the improved structural understanding and provide a benchmark for exploring the speciation of single‐atom catalysts based on carbon nitrides.
could be approached by engineering both the geometry and the electronic properties of the active phase at the nanoscale. [2,3] However, in contrast to well-defined homogeneous catalysts, establishing structureperformance relations and identifying the active sites in heterogeneous systems is challenging due to the inherent material complexity. [3,4] In this regard, employing single-atom heterogeneous catalysts (SACs), containing isolated atoms in discrete chemical environments is an effective approach to enable fundamental and mechanistic studies. [3][4][5][6][7] Beyond this, SACs often exhibit unique performance in diverse reactions due to their high degree of metal dispersion, tunable electronic properties, and unsaturated coordination environments of the active centers in tailored host materials. [7][8][9][10][11][12][13][14] In this regard, the first step in the development of a catalyst design strategy entails a detailed assessment on the impact of metal nuclearity and host effects, from single atoms with defined environments to size-controlled nanoparticles, on reactivity patterns for a given application. [15][16][17] A prominent class of reactions, widely used in numerous industrial processes, are hydrogenations, [18][19][20] which are commonly carried out over supported nanoparticles of precious metals with high sensitivity to their specific ensemble design. [21][22][23][24][25][26][27] An example of high practical relevance is the hydrodebromination of dibromomethane (CH 2 Br 2 ) into bromomethane (CH 3 Br), an important transformation for the industrial realization of bromine-mediated natural gas upgrading technologies into chemicals and fuels. [28][29][30] Therein, limited progress has been made toward selective hydrodebromination, where carbon losses in the form of CH 4 and coke represent a major challenge. [30,31] A recent study evaluated the performance of SiO 2 -supported nanoparticle-based (NP-based) metal catalysts (1 wt% of Fe, Co, Ni, Cu, Ru, Rh, Ag, Ir, Pt). Therein, at comparable reaction conditions, iron-, cobalt-, copper-, and silver-based catalysts displayed CH 2 Br 2 conversion levels of 4-7%, showing consistency with the reported poor hydrodebromination ability of these elements. [30] Among the platinum group metals, selective CH 2 Br 2 hydrodebromination to CH 3 Br was reported over Ru/SiO 2 (up to 96%, Table 1), whereas the CH 3 Br selectivity over Rh/SiO 2 (<48%), Ir/SiO 2 (<40%), and Pt/SiO 2 (23%) wasThe identification of the active sites and the derivation of structure-performance relationships are central for the development of high-performance heterogeneous catalysts. Here, a platform of platinum nanostructures, ranging from single atoms to nanoparticles of ≈4 nm supported on activated-and N-doped carbon (AC and NC), is employed to systematically assess nuclearity and host effects on the activity, selectivity, and stability in dibromomethane hydrodebromination, a key step in bromine-mediated methane functionalization processes. For this purpose, catalytic evaluation is coupled to ...
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