Chelation-mediated in-situ formation of ultrathin cobalt(oxy)hydroxides on hematite photoanode towards enhanced photoelectrochemical water oxidation

In this work,a facile chelation-mediated route was developed to fabricate ultrathin cobalt(oxy)hydroxides(CoOOH)nanosheets on hematite photoanode(Fe_(2)O_(3)).The route contains two steps of the adsorption of[Co-EDTA]^(2-)species on Fe_(2)O_(3) nanorod array followed by the hydrolysis in alkaline solution.The resulting CoOOH/Fe_(2)O_(3) exhibits a remarkably improved photocurrent density of 2.10 mA cm^(-2) at 1.23 V vs.RHE,which is ca.2.8 times that of bare Fe_(2)O_(3).In addition,a negative shift of onset potential ca.200 mV is achieved.The structural characterizations reveal the chelate EDTA plays important roles that enhance the adsorption of Co species and the formation of contact between CoOOH and Fe_(2)O_(3).(Photo)electrochemical analysis suggests,besides providing active sites for water oxidation,CoOOH at large extent promotes the charge separation and the charge transfer via passivating surface states and suppressing charge recombination.It also found CoOOH possesses some oxygen vacancies,which could act as trapping centers for photogenerated holes and facilitate the charge separation.Intensity modulated photocurrent spectroscopy(IMPS)shows that,under low applied potential the water oxidation mainly occurs on CoOOH,while under high applied potential the water oxidation could occur on both CoOOH and Fe_(2)O_(3).The findings not only provide an efficient strategy for designing ultrathin(oxy)hydroxides on semiconductors for PEC applications but also put forward a new insight on the role of CoOOH during water oxidation.

A review of the interactions between ceria and H2 and the applications to selective hydrogenation of alkynes

Cerium oxide(ceria) has found a wide variety of applications in catalysis including as a catalyst, a modifier, or a support, largely thanks to its robust redox properties and versatile acid-base function. While it is often utilized for oxidation reactions, ceria has recently attracted intense research interest for its unusual ability to selectively hydrogenate alkynes to alkenes. The intriguing hydrogenation ability of ceria has sparked renewed research efforts to understand how pure ceria works as a hydrogenation catalyst. In this review, recent advances in both experimental and computational studies of ceria are summarized, focusing on the interaction of ceria with H2 and in hydrogenation reactions. Significant insights from various studies including in situ spectroscopy/microscopy and theoretic modeling of ceria in hydrogen-involved reactions are discussed, which shed light on the origin of the hydrogenation ability of ceria and the reaction mechanisms involved in ceria-catalyzed alkyne hydrogenation. Ways to further improve both the mechanistic understanding and catalytic performance of ceria-based materials for hydrogenation reactions are proposed at the end in the summary and outlook section.

Activation and surface reactions of CO and H2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions

Activation and surface reactions of CO and H2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions were(quasi) in situ studied using temperature programmed surface reaction spectra, diffuse reflectance Fourier transform infrared spectroscopy, inelastic neutron scattering spectroscopy and electron paramagnetic resonance. CO undergoes disproportion reaction to produce gaseous CO2 and surface carbon adatoms, and adsorbs to form surface formate species. H2 adsorption forms dominant irreversibly-adsorbed surface hydroxyl groups and interstitial H species and very minor surface Zn-H species. Surface formate species and hydroxyl groups react to produce CO2 and H2, while surface carbon adatoms are hydrogenated by surface Zn-H species sequentially to produce CH(a), CH2(a), CH3(a)and eventually gaseous CH4. The ZnO nanoplates, exposing a higher fraction of Zn-ZnO(0001) and OZnO(000–1) polar facets, are more active than the ZnO powders to catalyze CO hydrogenation to CH4.These results provide fundamental understanding of the reaction mechanisms and structural effects of CO hydrogenation reaction catalyzed by ZnO-based catalysts.

Preface to Special Issue on Advances in Ceria Catalysis

Ceria,which acts as a“star”among the metal-oxides,has established to be one of the most promising materials for chemical transformations and energy applications owing to its redox and acid–base properties.Ceria has become a key component in three-way catalytic converters,water-gas shift reaction,CO oxidation,methane combustion,and complex organic reactions.More importantly,introducing of other metals to ceria,tailoring the shape of the ceria,and reducing structure size of ceria,usually decrease the formation energy of oxygen vacancy(V?)and lead to unique catalytic performances.

Surface chemistry connecting heterogeneous catalysis, photocatalysis and plasmonic catalysis

Chemical reactions catalyzed by solid catalysts have recently expanded rapidly from traditional heterogeneous catalytic reactions to photocatalytic reactions and further to plasmonic-catalytic reactions, however, the fundamental understanding of the commonalities and differences among heterogeneous catalysis, photocatalysis and plasmonic catalysis is not well established. Adsorption/reactions/desorption on solid catalyst surfaces commonly occur during these catalytic processes, thus surface chemistry of solid catalysts can be taken to bridge the fundamental understanding among heterogeneous catalysis, photocatalysis and plasmonic catalysis.

CO oxidation over ceria supported Au_(22) nanoclusters: Shape effect of the support

Gold（Au） nanoclusters have recently emerged as ideal models for understanding Au catalysis, because the nanosized Au particles have precise atomic numbers and uniform size. In this work, we studied for the first time the support shape effect on the catalysis of Au nanoclusters by using CO oxidation as a model reaction. Au22（L8）6（L = 1,8-bis（diphenylphosphino） octane） nanoclusters were supported on CeO2 rods or cubes, then pretreated at different temperatures（up to 673 K）, allowing the gradual removal of the organic phosphine ligands. CO oxidation test over these differently pretreated samples shows that CeO2 rods are much better supports than cubes for Au22 nanoclusters in enhancing the reaction rate. In situ IR spectroscopy coupled with CO adsorption indicates that the shape of CeO2 support can impact the nature and quantity of exposed Au sites, as well as the efficiency of organic ligand removal. Although CeO2 rods are helpful in exposing a greater percentage of total Au sites upon ligands removal, the percentage of active Au sites（denoted by Au d＋, 0 〈 d 〈 1） is lower than that on CeO2 cubes. The in situ extended X-ray absorption spectroscopy（EXAFS） and high-angle annular dark-field scanning transmission electron microscopy（HAADF-STEM） results show that the Au nanoclusters bound more strongly to the CeO2 rods than to the cubes where the Au nanoclusters show more sintering. Considering the typical redox mechanism for CO oxidation over supported Au nanoclusters and nanoparticles, it is concluded that the reactivity of the lattice oxygen of CeO2 is the determining factor for CO oxidation over Au22/CeO2. CeO2 rods offer more reactive lattice oxygen and abundant oxygen vacancies than the cubes and thus make the rods a superior support for Au nanoclusters in catalyzing low temperature CO oxidation.