Performance of Preformed Au/Cu Nanoclusters Deposited on MgO Powders in the Catalytic Reduction of 4‐Nitrophenol in Solution

Abstract

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

Embedding Ultrasmall Au Clusters into the Pores of a Covalent Organic Framework for Enhanced Photostability and Photocatalytic Performance

“…Furthermore,the traditional strategy of loading Au NCs on metal oxide and TiO 2 supports failed to achieve long-term stability under in situ illumination conditions, which limits the further development of catalysts based on Au NCs for practical application. [12] Thus,photostability over an extended period was explored by exposing Au@COF to irradiation with light (l > 420 nm) for 5h.T EM images showed that Au NCs supported on COF-S-SH maintained ultrafine and high dispersion after continuous light irradiation (Figure 3g,h). The result suggests that the ultrasmall pore structure of the COF and the strong S-Au binding energy provide double assurance for stabilizing Au NCs under light illumination conditions for an extended period of time.…”

“…Among various types of NPs,A uNPs as aprototype with adjustable size have drawn extensive attention for their excellent catalytic performance. [12] However,A uN Cs can be aggregated more readily than various other NCs and NPs for higher surface energy. [13] Thet raditional strategy of loading Au NCs on ametal oxide or SiO 2 has the disadvantage that it is difficult to maintain the stability of the composite under in situ photoirradiation conditions for al ong period of time, which is ab ottleneck for the development of catalysts based on Au NCs for practical applications.…”

Synthesis, characterization, and catalytic application of ecofriendly Ca‐bridged aminoclay

“…The 4‐NP isomer showed the k app value of 4.88 × 10 −3 s −1 . Au/Cu nanoclusters deposited on MgO powder was used as a catalyst for the reduction of NP . Similarly, other catalyst systems such as Ag/TiO 2 , copolymer/CuO nanocomposites, Co nanoparticles, Au‐supported carbon nanotube, and Zn nanoparticle functionalized aminoclay were used for the catalytic reduction of NP in the presence of NaBH 4 .…”

“…2 Au/Cu nanoclusters deposited on MgO powder was used as a catalyst for the reduction of NP. 3 Similarly, other catalyst systems such as Ag/TiO 2 , 4 copolymer/CuO nanocomposites, 5 Co nanoparticles, 6 Ausupported carbon nanotube, 7 and Zn nanoparticle functionalized aminoclay 8 were used for the catalytic reduction of NP in the presence of NaBH 4 . Ni nanoparticle encapsulated carbon nanotube was used as catalyst for the reduction chromium (VI).…”

“…10 In 2017, Shao et al 11 reported the catalytic reduction of chromium (VI) using the AuPd@Pd catalyst system. The other catalyst systems like SrTiO 3 and Pd 12 were used for the reduction of chromium (VI). The fluor dye is used in biomedical engineering field and in the textile industry.…”