Synthesis of Au nanoparticles supported on 'MnO IND. 2' nanowires for high performances in the silane oxidation (original) (raw)
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Catalysis Today, 2021
Gold nanocatalysts, active in several oxidation reactions, suffer of insufficient time-on-stream stability. The easiest way to solve this problem is modifying the support, due to metal-support interaction. This study compares modifying effects of MgO and La 2 O 3 on textural, electronic, and catalytic properties of Au nanoparticles (NPs) supported on inert nanostructured SiO 2 in CO oxidation and liquid phase 1-octanol oxidation. Modification of the silica support surface with La and Mg increased metal support interaction, leading to gold particles with primary size of 1 nm but with different stability: stable under different pretreatment conditions on Mg-modified samples but highly sensible to the pretreatments on La-modified samples. Both modifiers changed electronic properties of supported gold favoring formation and stabilization of Auδ + states, which are probable gold active sites in catalytic redox processes. Modification with La and Mg oxides changed catalytic properties in CO oxidation before and after pretreatment in H 2 at 300 • C for 1 h. Gold catalysts supported on La-and Mg-modified silica showed similar performance in 1-octanol oxidation with higher conversion than unmodified Au/SiO 2. La and Mg showed better promoting effects of catalytic properties in this reaction than redox modifiers (Fe and Ce) supported on small SiO 2 particles.
2014
Periodic mesoporous organosilicas (PMOs), namely MCM-41, MSU, and SBA-15 ordered mesoporous silicas (OMSs) incorporated with bridging disulfide-ionic liquid moieties prepared either by the one-pot or the post-synthesis procedure, were used as supports for the gold nanoparticle (GNP) catalysts. The catalytic properties of various supported GNP/PMO catalysts were evaluated by epoxidation reaction of various olefins. It was found that the pore architectures of the PMO materials as well as the method by which organic moieties were incorporated onto the mesoporous silica materials play crucial roles in the particle size and dispersion of the GNPs which, in turn, dictate the catalytic performances of the supported GNP/ PMO catalysts. In comparison with those synthesized by the one-pot procedure, PMO materials prepared by the post-synthesis method are more favorable in terms of dispersion of GNPs. Moreover, PMOs originated from OMSs with one-dimensional (1-D) pore structures also exhibit better GNP dispersions and catalytic activities than those with three-dimensional (3-D) pore architectures. This has been ascribed due to the restricted Ostwald ripening and/or migration-coalescence of the GNPs between adjacent pores of the PMOs with 1-D pore structures.
Low-temperature CO oxidation on Au/fumed SiO2-based catalysts prepared from Au(en)2Cl3 precursor
Applied Catalysis A: General, 2007
Many gold catalysts have been actively surveyed, but Au/SiO 2 catalysts that are highly active for CO oxidation still remain evasive. In this work, gold nanoparticles well dispersed on Cab-O-Sil fumed SiO 2 were prepared using Au(en) 2 Cl 3 (en = ethylenediamine) as the precursor, and found to be very active for CO oxidation below 0 8C. The catalyst pretreatment via reduction and calcination, effect of gold loading, post-treatment in acidic and basic media, catalyst deactivation, storage, regeneration, and effect of surface modification by other metal oxides were explored. The results provide new perspective on the activation and promotion of active Au/SiO 2-based catalysts.
Physical Chemistry Chemical Physics, 2011
Supported gold nanoparticles have generated an immense interest in the field of catalysis due to their extremely high reactivity and selectivity. Recently, alloy nanoparticles of gold have received a lot of attention due to their enhanced catalytic properties. Here we report the synthesis of silica supported AuCu nanoparticles through the conversion of supported Au nanoparticles in a solution of Cu(C 2 H 3 O 2 ) 2 at 300 1C. The AuCu alloy structure was confirmed through powder XRD (which indicated a weakly ordered alloy phase), XANES, and EXAFS. It was also shown that heating the AuCu/SiO 2 in an O 2 atmosphere segregated the catalyst into a Au-CuO x heterostructure between 150 1C to 240 1C. Heating the catalyst in H 2 at 300 1C reduced the CuO x back to Cu 0 to reform the AuCu alloy phase. It was found that the AuCu/SiO 2 catalysts were inactive for CO oxidation. However, various pretreatment conditions were required to form a highly active and stable Au-CuO x /SiO 2 catalyst to achieve 100% CO conversion below room-temperature. This is explained by the in situ FTIR result, which shows that CO molecules can be chemisorbed and activated only on the Au-CuO x /SiO 2 catalyst but not on the AuCu/SiO 2 catalyst.
Macromolecular Chemistry and Physics, 2015
A layer-by-layer approach is used to anchor small gold nanoparticles onto organic nanotubes resulting from the selfassembly and polymerization of diacetylene-containing nitrilotriacetic amphiphiles. The obtained nanotube-gold hybrid is used as a catalyst for the aerobic oxidation of various silanes. With minimal gold loading (0.05 mol%), all substrates are converted into the corresponding silanols with hydrogen gas as the only by-product. The catalyst operates under mild conditions and can be easily recycled, losing neither activity nor selectivity.
Novel route of synthesis of ultra-small Au nanoparticles on SiO2 supports
Fuel, 2019
A novel route to prepare monodispersed 1-2 nm gold nanoparticles (NPs), based on the use of extremely small SiO 2 NPs (2-4 nm) as a support and increasing their metal-support interaction with surface modifier oxides is presented. The influence of modifier (La, Ce and Fe oxides) and modification method (impregnation (i) or direct synthesis (s)) on the formation of ultra-small Au NPs and their structural and electronic properties was studied. The samples were characterized by N 2 adsorption (BET), FTIR of adsorbed CO, XRD and HR-TEM methods, and tested for the catalytic selective oxidation of 1-octanol. Preparation of monodispersed Au NPs with 1 nm diameter was successfully achieved for all the modified samples studied, with exception of Au/Ce/SiO 2-i, where CeO 2 was not homogeneously distributed. The Au NPs have high degree of monodispersity and are stable when treated in H 2 up to 300°C. Formation of these Au NPs depended on the strong interactions between the cationic gold complex precursor and the surface of modified SiO 2 NPs. Modifiers changed electronic properties of supported gold; favoring the formation and stabilization of Au δ+ states, which are probable gold active sites of selective liquid-phase oxidation of alcohols in redox catalytic processes. 1-octanol oxidation was used as a model reaction for oxidation of fatty alcohols obtained during biomass transformation. The best performance for 1octanol oxidation was found for gold nanoparticles supported on the ultra-small SiO 2 modified cerium oxide by impregnation method. The relative order of activity was: AuCeSiO 2-i > AuFeSiO 2-i ≫ AuLaSiO 2-i ≈ AuLaSiO 2s > AuSiO 2 > AuFeSiO 2-s≫ AuCeSiO 2-s. The obtained results open the possibility of further development of high-performance catalysts for conversion of secondary products of biomass processing into valuable chemicals.
Selective oxidation with dioxygen by gold nanoparticle catalysts derived from 55-atom clusters
Nature, 2008
Supported gold nanoparticles have excited much interest owing to their unusual and somewhat unexpected catalytic properties 1-7 , but the origin of the catalytic activity is still not fully understood. Experimental work 4 on gold particles supported on a titanium dioxide (110) single-crystal surface has established a striking size threshold effect associated with a metal-to-insulator transition, with gold particles catalytically active only if their diameters fall below 3.5 nm. However, the remarkable catalytic behaviour might also in part arise from strong electronic interaction between the gold and the titanium dioxide support 2,3,5 . In the case of industrially important selective oxidation reactions, explanation of the effectiveness of gold nanoparticle catalysts is complicated by the need for additives to drive the reaction 5,7,8 , and/or the presence of strong support interactions and incomplete understanding of their possible catalytic role 1-3,5 . Here we show that very small gold entities ( 1.4 nm) derived from 55-atom gold clusters and supported on inert materials are efficient and robust catalysts for the selective oxidation of styrene by dioxygen. We find a sharp size threshold in catalytic activity, in that particles with diameters of 2 nm and above are completely inactive. Our observations suggest that catalytic activity arises from the altered electronic structure intrinsic to small gold nanoparticles, and that the use of 55-atom gold clusters may prove a viable route to the synthesis of robust gold catalysts suited to practical application.
Gold nanoparticles coated silicon nanowires for efficient catalytic and photocatalytic applications
Materials Science in Semiconductor Processing, 2018
This work is focused on the elaboration of gold (Au) nanoparticles supported silicon nanowires (SiNWs) for catalytic and photocatalytic applications. The SiNWs investigated in this study are synthesized by metal-assisted chemical etching technique, while the gold nanoparticles (AuNPs) are loaded on SiNWs through the redox reaction between HAuCl 4 and HF-treated SiNWs. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and photoelectron spectroscopy (XPS) were used to characterize the morphology, composition and chemical states of the fabricated samples. The catalytic activity of the SiNWs loaded with AuNPs was investigated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with sodium borohydride (NaBH 4). The photocatalytic activity of SiNWs-AuNPs under visible light irradiation was assessed using Rhodamine B (RhB) as a representative organic dye. The course of the above reactions was monitored by UV-vis spectrophotometry. Our results showed that the SiNWs-AuNPs samples could catalyze the reduction of 4-NP and degradation of RhB with excellent efficiency and stability.
The Journal of Physical Chemistry B, 2006
Although Au catalysts can be readily prepared on titania via the deposition-precipitation (DP) method, the direct application of the method similar to the preparation of silica-supported Au catalysts only results in diminished success. This paper reports a novel, efficient method to synthesize highly active Au catalysts supported on mesoporous silica (SBA-15) through a gold cationic complex precursor [Au(en) 2 ] 3+ (en) ethylenediamine) via a wet chemical process. The gold cationic precursor was immobilized on negatively charged surfaces of silica by a unique DP method that makes use of the deprotonation reaction of ethylenediamine ligands. The resulting mesoporous catalyst has been demonstrated to be highly active for CO oxidation at room temperature and even below 273 K, the activity of which is much superior to that of silica-supported Au catalysts previously prepared by various solution techniques. The pH value of the gold precursor solution plays a key role in determining the catalytic activity through the regulation of [Au(en) 2 ] 3+ deprotonation reaction and the surface interaction of silica with the gold precursor. This mesoporous gold silica catalyst has also been shown to be highly resistant to sintering because of the stabilization of Au nanoparticles inside mesopores.