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Abstract: Atomically-dispersed metal catalysts (ADMCs) on surfaces have demonstrated high activity and selectivity in many catalytic reactions. However, dispersing and stabilising individual atoms in support materials in an atom/energy-efficient scalable way still presents a significant challenge. Currently, the synthesis of ADMCs involves many steps and further filtration procedures, creating a substantial hurdle to their production at industrial scale. In this work, we develop a new pathway for producing ADMCs in which Pt atoms are stabilised in the nitrogen-interstices of a graphitic carbon nitride (g-C3N4) framework using scalable, solvent-free, one-pot magnetron sputtering deposition. Our approach has the highest reported rate of ADMC production of 4.8 mg h-1 and generates no chemical waste. Deposition of only 0.5 weight percent of Pt onto g-C3N4 led to improved hydrogen production by factor of ca. 3333 ± 450 when compared to bare g-C3N4. PL analysis showed that the deposition of Pt atoms onto g-C3N4 suppressed the charge carrier recombination from the photogenerated electron-hole pairs of Pt/g-C3N4 thereby enhance hydrogen evolution. Scanning transmission electron microscope imaging before and after the hydrogen evolution reaction revealed that the Pt atoms stabilised in g-C3N4 have a high stability, with no agglomeration observed. Herein, it is shown that this scalable and clean approach can produce effective ADMCs with no further synthetic steps required, and that they can be readily used for catalytic reactions.

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Abstract: Ceria has been widely used as support in electrocatalysis for its high degree of oxygen storage, fast oxygen mobility and reduction and oxidation properties at mild conditions. However, it is unclear what are the underlying principles and the nature of surface involved. By controlling the growth of various morphologies of ceria nanoparticles, it is demonstrated that the cubic-form of ceria, predominantly covered with higher energy polar surface (100), as support for Pd gives much higher activity in the electrocatalytic oxidation of formic acid than ceria of other morphologies (rods and spheres) with low indexed facets ((110) and (111)). High resolution TEM confirms the alternating layer-to-layer of cations and anions in (100) surface, the electrostatic repulsion of oxygen anions within the same layers gives intrinsically higher oxygen vacancies on this redox active surface in order to reduce surface polarity. DFT calculations suggest that the properties of fast oxygen mobility to re-oxidize the CO-poisoned Pd may arise from the overdosed oxygens on these ceria surface layers during electro-oxidation hence sustaining higher activity.

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Abstract: Doped-ZnO nanoparticles, capped with dioctylphosphinate ligands, are synthesised by the controlled hydrolysis of a mixture of organometallic precursors. Substitutional doping of the wurtzite ZnO nanoparticles with 5 mol% Mg(II), Al(III) and Cu(I) is achieved by the addition of sub-stoichiometric amounts of the appropriate dopant [(n-butyl)(sec-butyl)magnesium, triethylaluminium or mesitylcopper] to diethylzinc in the precursor mixture. After hydrolysis, the resulting colloidal nanoparticles (sizes of 2–3 nm) are characterised by powder X-ray crystallography, transmission electron microscopy, inductively-coupled plasma optical emission spectrometry and X-ray photoelectron spectroscopy. A solution of the doped-ZnO nanoparticles and colloidal Cu(0) nanoparticles [M:ZnO : Cu = 1 : 1] are applied as catalysts for the hydrogenation of CO2 to methanol in a liquid-phase continuous flow stirred tank reactor [210 °C, 50 bar, CO2[thin space (1/6-em)]:[thin space (1/6-em)]H2 = 1[thin space (1/6-em)]:[thin space (1/6-em)]3, 150 mL min−1, mesitylene, 20 h]. All the catalyst systems display higher rates of methanol production and better stability than a benchmark heterogeneous catalyst, Cu–ZnO–Al2O3 [480 μmol mmolmetal−1 h−1], with approximately twice the activity for the Al(III)-doped nanocatalyst. Despite outperforming the benchmark catalyst, Mg(II) doping is detrimental towards methanol production in comparison to undoped ZnO. X-Ray photoelectron spectroscopy and transmission electron microscopy analysis of the most active post-catalysis samples implicate the migration of Al(III) to the catalyst surface, and this surface enrichment is proposed to facilitate stabilisation of the catalytic ZnO/Cu interfaces.

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Abstract: It has only recently been established that doping light elements (lithium, boron, and carbon) into supported transition metals can fill interstitial sites, which can be observed by the expanded unit cell. As an example, interstitial lithium (intLi) can block H filling octahedral interstices of palladium metal lattice, which improves partial hydrogenation of alkynes to alkenes under hydrogen. In contrast, herein, we report intLi is not found in the case of Pt/C. Instead, we observe for the first time a direct ‘substitution’ of Pt with substitutional lithium (subLi) in alternating atomic columns using scanning transmission electron microscopy-annular dark field (STEM-ADF). This ordered substitutional doping results in a contraction of the unit cell as shown by high-quality synchrotron X-ray diffraction (SXRD). The electron donation of d-band of Pt without higher orbital hybridizations by subLi offers an alternative way for ultra-selectivity in catalytic hydrogenation of carbonyl compounds by suppressing the facile CO bond breakage that would form alcohols.

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Abstract: Hydrotalcite-derived Ni and Fe-promoted hydrotalcite-derived Ni catalysts were found to outperform industrial catalysts in the CO2 methanation reaction, however the origin of the improved activity and selectivity of these catalysts is not clear. Here, we report a study of these systems by means of in situ X-ray photoelectron spectroscopy and near-edge X-ray absorption spectroscopy elucidating the chemical nature of the catalysts` surface under reaction conditions and revealing the mechanism by which Fe promotes activity and selectivity towards methane. We show that the increase of the conversion leads to hydroxylation of the Ni surface following the formation of water during the reaction. This excessive Ni surface hydroxylation has however a detrimental effect as shown by a controlled study. A dominant metallic Ni surface exists in conditions of higher selectivity towards methane whereas if an increase of the Ni surface hydroxylation occurs, a higher selectivity towards carbon monoxide is observed. The electronic structure analysis of the Fe species under reaction conditions reveals the existence of predominantly Fe(III) species at the surface, whereas a mixture of Fe(II)/Fe(III) species is present underneath the surface. Our results highlight that Fe(II) exerts a beneficial effect on maintaining Ni in a metallic state, whereas the extension of the Fe oxidation front from the surface towards the bulk is accompanied by a more extended Ni surface hydroxylation with a negative impact on the selectivity towards methane.