This report focuses on a novel strategy for the preparation of transition metal–MoS2 hybrid nanoclusters based on a one-step, dual-target magnetron sputtering, and gas condensation process demonstrated for Ni-MoS2. Aberration-corrected STEM images coupled with EDX analysis confirms the presence of Ni and MoS2 in the hybrid nanoclusters (average diameter = 5.0 nm, Mo:S ratio = 1:1.8 ± 0.1). The Ni-MoS2 nanoclusters display a 100 mV shift in the hydrogen evolution reaction (HER) onset potential and an almost 3-fold increase in exchange current density compared with the undoped MoS2 nanoclusters, the latter effect in agreement with reported DFT calculations. This activity is only reached after air exposure of the Ni-MoS2 hybrid nanoclusters, suggested by XPS measurements to originate from a Ni dopant atoms oxidation state conversion from metallic to 2+ characteristic of the NiO species active to the HER. Anodic stripping voltammetry (ASV) experiments on the Ni-MoS2 hybrid nanoclusters confirm the presence of Ni-doped edge sites and reveal distinctive electrochemical features associated with both doped Mo-edge and doped S-edge sites which correlate with both their thermodynamic stability and relative abundance.
clusters (nanoparticles) of tunable size typically below 10 nm are pre-assembled into a beam and then deposited in a vacuum chamber onto the catalyst support. [1][2][3][4] Potential advantages of the approach include the absence of solvent and effluent in the catalyst synthesis; control of cluster size, composition, and morphology; and the absence of ligands compared with colloidal routes. [5][6][7][8] However, the technique is at an early stage, [9] most especially where catalytic behavior under realistic reaction conditions is concerned. Thus, there is an urgent need to validate the performance of this new class of nanomaterials in a series of model chemical transformations, and compare their behavior with catalysts prepared by more traditional and well-established routes. In this work, we report a first investigation of a solution phase transformation performed by nanoalloy catalysts prepared by cluster beam deposition.The discovery of the catalytic activity of gold (Au) nanoparticles for low-temperature oxidation of carbon monooxide (CO) provoked an explosion of interest in gold catalysis. [10,11] Au clusters can catalyze a range of reactions, for example, the water-gas shift reaction [12][13][14] and selective oxidation of carbon-carbon double bonds [15,16] and carbon-oxygen bonds. [17,18] The 4-nitrophenol The deposition of preformed nanocluster beams onto suitable supports represents a new paradigm for the precise preparation of heterogeneous catalysts. The performance of the new materials must be validated in model catalytic reactions. It is shown that gold/copper (Au/Cu) nanoalloy clusters (nanoparticles) of variable composition, created by sputtering and gas phase condensation before deposition onto magnesium oxide powders, are highly active for the catalytic reduction of 4-nitrophenol in solution at room temperature. Au/Cu bimetallic clusters offer decreased catalyst cost compared with pure Au and the prospect of beneficial synergistic effects. Energy-dispersive X-ray spectroscopy coupled with aberration-corrected scanning transmission electron microscopy imaging confirms that the Au/Cu bimetallic clusters have an alloy structure with Au and Cu atoms randomly located. Reaction rate analysis shows that catalysts with approximately equal amounts of Au and Cu are much more active than Au-rich or Cu-rich clusters. Thus, the interplay between the Au and Cu atoms at the cluster surface appears to enhance the catalytic activity substantially, consistent with model density functional theory calculations of molecular binding energies. Moreover, the physically deposited clusters with Au/Cu ratio close to 1 show a 25-fold higher activity than an Au/Cu reference sample made by chemical impregnation.Heterogeneous Catalysts
The generation of beams of atomic clusters in the gas phase and their subsequent deposition (in vacuum) onto suitable catalyst supports, possibly after an intermediate mass filtering step, represents a new and attractive approach for the preparation of model catalyst particles. Compared with the colloidal route to the production of pre-formed catalytic nanoparticles, the nanocluster beam approach offers several advantages: the clusters produced in the beam have no ligands, their size can be selected to arbitrarily high precision by the mass filter, and metal particles containing challenging combinations of metals can be readily produced. However, until now the cluster approach has been held back by the extremely low rates of metal particle production, of the order of 1 microgram per hour. This is more than sufficient for surface science studies but several orders of magnitude below what is desirable even for research-level reaction studies under realistic conditions. In this paper we describe solutions to this scaling problem, specifically, the development of two new generations of cluster beam sources, which suggest that cluster beam yields of grams per hour may ultimately be feasible. Moreover, we illustrate the effectiveness of model catalysts prepared by cluster beam deposition onto agitated powders in the selective hydrogenation of 1-pentyne (a gas phase reaction) and 3-hexyn-1-ol (a liquid phase reaction). Our results for elemental Pd and binary PdSn and PdTi cluster catalysts demonstrate favourable combinations of yield and selectivity compared with reference materials synthesised by conventional methods.
Cu-catalyzed CO2 electroreduction can produce various hydrocarbons and oxygenates. However, it suffers from low activity and poor selectivity. Herein, Cu-decorated CeO2 composites (Cu y /CeO2) with distinct interfacial characteristics were fabricated through a highly controllable synthesis, based on chemical prelithiation of CeO2 and then galvanic displacement with Cu. The Cu decoration induced a strong-binding site for CO2 adsorption at the Cu and CeO2 interface, facilitating the CO2 activation and conversion to the *CO intermediate on the nearby Cu surface. Selective CO2 conversion to C1 or C2+ products was customized by adjusting the Cu decoration amount. With the increase in the Cu loading, the C1 and C2+ products exhibited a declining and volcano-shaped trend, showing a maximum faradaic efficiency of 70 and 63%, respectively. In situ infrared and Raman spectroscopy revealed that the reduction pathway depended on the relative ratio of the low-frequency band *COLFB to the high-frequency band *COHFB. Our findings may contribute to the rational design of heterostructured catalysts toward CO2 electroreduction.
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