Search

A molecular pre-catalyst complex, [CuII(indH)(OClO3)(NCCH3)](ClO4)·CH3CN (1·CH3CN) with the 3N pincer ligand 1,3-bis(2′-pyridyl)iminoisoindoline (indH) was immobilized on indium tin oxide (ITO) transparent conducting substrate to generate O2 electrocatalytically for over 20 hours at pH 10 in a carbonated buffer, reaching a turnover of 139 with no signs of CuOx/Cu(OH)2 formation at the surface. Further electrolysis experiments revealed that the catalyst was present in the aqueous phase, despite the poor initial solubility of the pre-catalyst (1). In order to identify the actual form responsible for this important catalytic reaction, the aquo complex [CuII(ind)(OClO3)(OH2)]·CH3OH (2·CH3OH) was structurally characterized. Spectroscopic investigations of a solid isolated from the buffer used in the electrolysis reaction and solution equilibrium studies using 2 indicated that the [CuII(ind)(OH)] form occurs at pH 10. Electron paramagnetic resonance (EPR) spectroscopy and DFT calculations confirmed a distorted {3N,O}eq coordination plane in solution, as found in 2. The buffer (i.e. bicarbonate/carbonate) may affect reactivity in two ways: as an external base facilitating the proton-coupled electron transfer steps; and/or displacing the inner-sphere solvent molecules from the favourable quasi-equatorial position, thus inhibiting the catalysis. Structural features of a tri-nuclear cluster [CuII3(ind)3(μ3-CO3)(CH3OH)(OClO3)] (3) isolated under basic conditions confirmed that beside acting as an external base, the inhibiting effect of carbonate anions may also play a role. In acetonitrile-water solutions, where both 1 and 2 exhibit reasonable solubility, experimental findings supported by DFT calculations suggest that it is the ind− ligand which is being oxidized while the cupric ion remains redox-inactive which is very unusual yet of great significance for the creation of a new generation of low-cost Cu-based water oxidation catalysts as well as potentially other 1st row transition metals.

Pincer ligands occupy three coplanar sites at metal centers and often support both stability and reactivity. The five-coordinate [FeIIICl2(tia-BAI)] complex (tia-BAI&minus, = 1,3-bis(2&rsquo, thiazolylimino)isoindolinate(&minus, )) was considered as a potential pre-catalyst for water oxidation providing the active form via the exchange of chloride ligands to water molecules. The tia-BAI&minus, pincer ligand renders water-insolubility to the Fe&ndash, (tia-BAI) assembly, but it tolerates the presence of water in acetone and produces electrocatalytic current in cyclic voltammetry associated with molecular water oxidation catalysis. Upon addition of water to [FeIIICl2(tia-BAI)] in acetone the changes in the Fe3+/2+ redox transition and the UV-visible spectra could be associated with solvent-dependent equilibria between the aqua and chloride complex forms. Immobilization of the complex from methanol on indium-tin-oxide (ITO) electrode by means of drop-casting resulted in water oxidation catalysis in borate buffer. The O2 detected by gas chromatography upon electrolysis at pH 8.3 indicates &gt, 80% Faraday efficiency by a TON &gt, 193. The investigation of the complex/ITO assembly by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) before and after electrolysis, and re-dissolution tests suggest that an immobilized molecular catalyst is responsible for catalysis and de-activation occurs by depletion of the metal.

Herein, we compare the electrochemical and electrocatalytic properties of two selected, water-insoluble Fe(II) coordination complexes made with the non-symmetric, bidentate ligands, 2-(2′-pyridyl)benzimidazole (PBI) in [Fe(PBI)3](OTf)2 (1, OTf− = trifluoromethyl sulfonate anion) and 2-(2′-pyridyl)benzoxazole (PBO) in [Fe(PBO)2(OTf)2] (2) . Cyclic voltammetry in water/acetonitrile mixture indicates considerable activity for both compounds. However, only 1 acts as homogeneous catalyst. The complexes have been successfully immobilized on indium-tin-oxide (ITO) electrode surface. The hydrophobic ligands allowed for a simple dip-coating and drop-casting of 1 and 2 onto ITO. Both 1/ITO and 2/ITO showed increased activity in electrocatalytic O2 evolution in borate buffer at pH 8.3. According to scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), moreover, re-dissolution tests, the Fe remains in complex with PBI during electrolysis in the drop-casted, nano-porous films of 1/ITO. In contrast, the PBO complex in 2/ITO undergoes a rapid in situ decomposition yielding a mineralized form that is responsible for catalysis.

Progress in non-covalent/self-assembled immobilization methods on (photo)electrode materials for molecular catalysts could broaden the scope of attainable systems. While covalent linkage (though considered more stable) necessitates functional groups introduced by means of often cumbersome synthetic procedures, non-covalent assemblies require sufficient propensity of the molecular unit for surface adsorption, thus set less rigorous pre-requisites. Herein, we report efficient electrodeposition (ED) of two Fe(III) complexes prepared with closely related NN’N pincer ligands yielding stable and active ad-layers for the electrocatalysis of the oxygen-evolving reaction (OER). The ED method is based on the utilization of a chloride precursor complex [FeIIICl2(NN’N)], which is dissolved in an organic electrolyte undergoes chloride/aqua ligand exchange upon addition of water. ED provides patchy distribution of a chloride-depleted catalyst layer on indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) surfaces, which can be applied for long periods as OER electrocatalysts. Compared to drop-casting or layering of [FeIIICl2(NN’N)] with Nafion (a commonly used support for molecular electrocatalysts), the surface modification by ED is a material saving and efficient method to immobilize catalysts.

The crystal structure, the magnetic properties, and the valence band density of states of an oxide dispersion strengthened (ODS) steel with nominal composition of Fe–18%Cr–13%Ni-2.5%Mo-3.2%Si-0.1%C +1 wt% Y2O3 was investigated applying volumetric and surface sensitive methods. The sample volume contained majority fcc and minority bcc phases according to XRD and volumetric magnetic measurements, while the top layer of the grains contained only the paramagnetic fcc phase, revealed by conversion electron Mossbauer spectrometry (CEMS) and by photoelectron measurements. The valence band photoelectron emission spectra reflected well the average distribution of the theoretically expected DOS, however, there were no signs of abrupt peaks in the region of 0–4 eV below the Fermi level that could have been attributed to 3d Fe states (bcc phase). It was demonstrated that the photoelectron emission can be utilized to distinguish the Fe atoms located in different crystallographic structures. The valence band data of the ODS steel was compared to that of originating from a bcc iron based magnetic alloy.

SiO2 supported Au–Ag nanoparticles prepared by the adsorption of bimetallic colloids of various Ag/Au molar ratio (0/100, 13/87, 23/77, 33/67, 51/49, 100/0) were characterized and studied in selective glucose oxidation reaction earlier (Benko et al., Applied Catalysis A 479:103–111, 2014 [32]). The same catalysts of mean metal particle size between 3 and 5 nm were applied and compared in benzyl alcohol and CO oxidation after both calcination and successive reduction treatments. In temperature programmed CO oxidation tests of the Au-containing samples, different activity zones appeared with several conversion maxima, which were affected differently by the Au/Ag ratio and pretreatment conditions. CO oxidation results suggested the coexistence of several types of active sites in various population in the different samples. In all the three reactions, the sample with Ag/Au = 23/77 composition was the most active in calcined and also in reduced state, showing synergetic effect compared to the monometallic analogous. Upon H2-treatment in benzyl alcohol oxidation, a significant, in glucose oxidation, a slight activity increase was observed for all the samples. In CO oxidation, the reduction treatment induced deactivation of sample with Ag/Au = 23/77 and 13/87 below 125 °C, while in the higher temperature region, all the samples were highly activated.

SiO2 supported Ag–Au bimetallic catalysts were prepared by sol adsorption method with 10/90, 20/80, 33/67, and 50/50 Ag/Au molar ratios. Reduction of HAuCl4 in Ag sol resulted in alloyed Ag–Au colloid particles and that structure remained after calcination and reduction treatment. The alloy structure of the catalysts was confirmed by UV–visible spectroscopy and high resolution transmission electron microscopy. The Au–Ag bimetallic effect and its dependence on the Ag/Au molar ratio was studied in glucose oxidation where synergistic activity increase was observed compared to the Au/SiO2 reference sample in the case of the bimetallic samples with less than Ag/Au = 50/50 molar ratio. The Ag/SiO2 was inactive at the same conditions. The Ag/Au surface atomic ratios – calculated by X-ray photoelectron spectroscopy (XPS) – were slightly higher than in the bulk—determined by prompt gamma activation analysis (PGAA). The higher activity of the bimetallic samples is suggested to be caused by the improved O2 activating ability provided by Ag sites. The further increase of Ag loading above the optimal concentration may dilute or cover the Au to such an extent that the number of gold ensembles necessary for glucose activation decreases deteriorating the activity.

The possibility of fabricating nanoparticles by ion bombardment was investigated by the ion bombardment of indium films on oxide covered Si and Cr surfaces. The different masses of implanting specimen ensured the different energy transfer while the same Si substrate ensured the same thermal conductivity for the In and Cr layers. Chromium served as a reference for the effect of ion bombardment and as a substrate as well. The SRIM program was used to simulate the ion surface interaction process. The nanoparticles were detected by scanning electron microscopy (SEM). We found that the melting of the In layer results in the formation of nanoparticles of 50-300 nm diameter and 5-10 nm height. This method can be promising for nanoparticle formation of materials with low melting point.

Non-stoichiometric Mn-oxides (MnO x and MnO y ) were prepared by temperature-programmed oxidation (TPO) of Mn-oxalates, MnC 2 O 4 ·3H 2 O and MnC 2 O 4 ·2H 2 O. Both oxides provide high specific surface areas (525 m 2 g −1 and 385 m 2 g −1 , respectively) and identical CO oxidation reaction rates of 10 −2 molecules nm −2 s −1 (0.017 μmol CO m −2 s −1 ) at 298 K. A “spinodal” transformation of oxalates into oxides was observed by transmission electron microscopy (TEM). The quantitative evaluation of TPO and temperature-programmed reduction with CO allowed x -values of 1.61, … , 1.67 to be determined for MnO x . The Mn oxidation state in MnO x was found to be 3.4 ± 0.1 by X-ray absorption near-edge structure analysis and X-ray photoelectron spectroscopy. In accordance with the high specific surface area and mixed-type I/IV adsorption isotherms of MnO x , high resolution TEM demonstrated the occurrence of nested micro-rod features along with nanocrystalline particles in the endings of the rods. After CO oxidation MnO and Mn 3 O 4 phases were able to be identified in the regions between rods.

FeO x , TiO 2 and CeO x layers were deposited by pulsed laser deposition (PLD) technique onto Au films or Au nanoparticles supported on SiO 2 /Si(100). The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and their reactivity was studied in catalytic CO oxidation. Comparison was made with reference samples of FeO x /SiO 2 /Si(100), TiO 2 /SiO 2 /Si(100), CeO x /SiO 2 /Si(100) and Au/SiO 2 /Si(100) layers. The catalytic activity of the metal-oxide/Au/SiO 2 /Si(100) samples must be attributed to active sites located on the metal-oxides overlayer modified by gold underneath, since no Au was exposed to the surface according to the XPS and SIMS. We found a promoting effect of gold on the catalytic activity of the FeO x overlayer and an inhibiting effect of gold on the TiO 2 and CeO x overlayers. These findings are discussed in terms of electronic interactions at the Au/metal oxide interface.

The selectivity obtained in the aromatization of propane over Zn-ZSM-5-based catalysts (Si/Al nominal ratio = 35) increased from about 69% (carbon basis) to 74–91% when a second transition metal ion is introduced into the catalyst. The effect, previously reported for the case of Fe3+ ions, has now been shown to be more general and is seen also for the ions of chromium, cobalt or manganese. It is likely that these ions are present under aromatization conditions in a partially reduced state. H2/D2 isotope exchange rates show large enhancements on the reduced Fe-Zn/ZSM-5 and Co-Zn/ZSM-5 samples. This aspect of aromatization catalysis has not been reported before.

Identification of the active sites is a key factor in understanding the mechanism of gold-catalyzed reactions. In this work we investigated the CO adsorption properties of gold-based model catalysts ranging from native and surface-modified single crystal surfaces to polycrystalline thin films promoted by iron oxide layers. The results, completed with those obtained on a gold nanoparticle-containing system, clearly demonstrate the role of the defect sites in the CO adsorption. In addition, a promoter such as iron oxide can further enhance CO adsorption, probably through a mechanism connected to the interface formation between gold and iron oxide.

Two series of gold catalysts supported on TiO2, SiO2, and CeO2 have been prepared by colloidal gold deposition with 2 wt% of nominal gold loading. The diameter of gold particle stabilized by polyvinylalcohol (PVA) or by tannic acid-citrate was 2–3 nm and 6–7 nm, which increased to 5–7 nm and 7–13 nm, respectively, after calcination in air. Catalytic activities were investigated and compared in CO oxidation and glucose oxidation reactions. Inverse correlation was found between the activities in glucose oxidation and CO oxidation suggesting that the mechanisms are different. Besides the high dispersion the nature of the support seems to play a significant role in the liquid phase reaction.

Hydrogenation of acetylene has been investigated on Au-iron oxide catalysts containing 4.5, 3.0, 5.6 wt% Au prepared by deposition–precipitation (DP) with urea, adsorption of Au sol (SA) and by co-precipitation (CP) of HAuCl 4 and Fe(NO 3 ) 3 , respectively. The latter method produced Au particles supported on 2-line ferrihydrite (Fe 5 HO 8 ·4H 2 O). Au/iron oxide catalyst precursors (Au/α-Fe 2 O 3 and Au/2-line ferrihydrite) were characterized by BET, TGA, TPR and XRD, and the Au particle size by TEM measurements. The TPR measurements confirm the ease of transformation of 2-line ferrihydrite to magnetite (Fe 3 O 4 ) and that the formation of magnetite from α-Fe 2 O 3 depends strongly on the size of the gold and the supporting oxide particles. Particle size effect of gold has been investigated in semi-hydrogenation of acetylene. Temperature of hydrogen treatment has been observed to play a crucial role in the activity and ethylene selectivity. Au/FeO x samples hydrogen treated at 353–473 K prior to introduction of the reactants (H 2 :C 2 H 2 = 140, 0.11% C 2 H 2 ) show very limited over-hydrogenation (ethane formation is less than ≈1%) and 2–4% selectivity of oligomer (C4+) formation at 353–473 K. Hydrogen treatment of the samples at T > 573 K but lower than the wustite (FeO) stability point (≈843 K) resulted in partial reduction of Fe 3 O 4 and formation of Fe 0 . The shift of Au(1 1 1) XRD line to higher 2 Θ provided evidence for the incorporation of Fe 0 into the Au particles. Modification of the Au/Fe 2 O 3 perimeter and appearance of Fe 0 co-catalyst and Fe–Au ensembles on the surface increased the hydrogenation activity but decreased the selectivity of ethylene formation.

Manganese oxides of various stoichiometry were prepared via Mn-oxalate precipitation followed by thermal decomposition in the presence of oxygen. A non-stoichiometric manganese oxide, MnO x (x = 1.61…1.67) was obtained by annealing at 633 K and demonstrated superior CO oxidation activity, i.e. full CO conversion at room temperature and below. The activity gradually decreased with time-on-stream of the reactants but could be easily recovered by heating at 633 K in the presence of oxygen. CO oxidation over MnO x in the absence of oxygen proved to be possible with reduced rates and demonstrated a Mars—van Krevelen—type mechanism to be in operation. A TEM structural analysis showed the MnO x phase to form microrods with large aspect ratio which broke up into nanocrystalline manganese oxide (MnO x ) particles with diameters below 3 nm and a BET specific surface area of 525 m2/g. Annealing at 798 K rather than 633 K produced well crystalline Mn2O3 which showed lower CO oxidation activity, i.e. 100% CO conversion at 335 K. The catalytic performance in CO oxidation of various Mn-oxides either studied in this work or elsewhere was compared on the basis of specific reaction rates.

In this work a complex experimental setup is described which was developed by connecting an ultra-high vacuum multi-technique surface analysis system and a sum frequency generation vibrational spectrometer. This arrangement provides a unique environment to study interfaces under in situ conditions by a combination of complementary techniques. Preliminary results of CO adsorption experiments on gold and iron oxide thin layers grown on gold are presented as application examples of the experimental setup.

Ag/TiO2 catalysts with different Ag loadings (2, 4, 7 and 10% (w/w)) have been prepared by means of co-precipitation of Ag- and TiO-oxalates followed by temperature programmed oxidation (TPO). The catalysts were subjected to CO oxidation in a flow reactor at atmospheric pressure and temperatures up to 573 K. Best conversion performance was obtained in a CO/O2 = 1:1 mixture over 10% Ag/TiO2 for which the temperature of 50% CO conversion was T50 = 333 K. The initial reaction rates were determined in a circulation reactor at low conversions and apparent activation energies between 13 and 25 kJ/mol were found for all catalysts. Transmission electron microscopy shows a broad range of nano-sized Ag particles on TiO2 (nearly pure anatase).

TiO 2 layer was deposited by pulsed laser deposition (PLD) technique onto either 8- or 60-nm thick Au films supported by SiO 2 /Si(1 0 0). The samples were characterized in catalytic CO oxidation. Comparison was made with reference samples both of TiO 2 /SiO 2 /Si(1 0 0) and Au/SiO 2 /Si(1 0 0) layers. The initial activity of TiO 2 /Au/SiO 2 /Si(1 0 0) turned out to be significantly lower than that of TiO 2 /SiO 2 /Si(1 0 0), while the Au/SiO 2 /Si(1 0 0) was the least active. The catalytic activity of the TiO 2 /Au/SiO 2 /Si(1 0 0) samples must be attributed to active sites located on the TiO 2 overlayer modified by gold underneath, since no Au was exposed to the surface according to the X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The inhibiting effect of gold on the catalytic activity of TiO 2 overlayer was discussed in terms of electronic interactions at the Au/TiO 2 interface.

Iron oxide layers of 5–10 nm thickness were deposited by pulsed laser techniques (PLD) onto either Au films or nano-sized Au particles supported by SiO 2 /Si(1 0 0). Samples were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS) before and after measurements of the CO oxidation activity. Comparison was made with reference samples either free of iron oxide and/or free of Au particles/films. The initial activity of iron oxide/Au nano-particles/SiO 2 /Si(1 0 0) turned out to be the highest followed by the sample containing a sandwiched Au film. While some reaction-induced changes in the chemical composition of the iron oxide overlayer (“FeO x ”, which can be regarded as a mixture of Fe 2 O 3 , FeO and FeOOH according to the XPS analysis of the Fe 2p and O 1s core levels) were seen, no Au segregation at the surface was detected by TOF SIMS. The XPS Au 4f spectra indicated, however, that Au atoms might be injected and trapped in this layer. The catalytic activity of the FeO x /Au/SiO 2 /Si(1 0 0) samples must be attributed to active sites located on the iron oxide overlayer promoted by gold underneath. Since Au nano-particles and Au films caused promotion we infer that an electronic effect is in operation due to the occurrence of an FeO x /Au interface in both cases. Since the promotion is stronger for Au nano-particles the hypothesis of a particle size dependent electronic effect may be advanced. For thicker FeO x of about 40–80 nm no promotion by Au was found.

A 10-nm-thick gold film was evaporated onto a SiO2/Si(100) substrate and was implanted by Ar+ ions at 40 keV and 1015 at/cm2 dose creating island like Au nanoparticles. An 80-nm-thick gold film was also deposited the onto same substrate and considered as reference. Fe2O3 film was deposited onto the gold nanoparticles and the gold/oxide interface was modeled. The valence band and the structure were measured by means of photoelectron spectroscopy (XPS) and by transmission electron microscopy (TEM), respectively. The catalytic activity was detected by CO oxidation, which was higher after the deposition of Fe2O3 layer onto Au nanoparticles than that on a continuous Au film. This observation was correlated to the nanosize and the redistributed valence band density of states of gold in the Au/Fe2O3 interface.

Bimetallic Au-Pd catalysts supported on silica with different Au/Pd atomic ratios were prepared by simultaneous reduction of palladium and gold precursors by ethanol in the presence of the polymer, polyvinylpyrrolidone (PVP). Formation of alloyed particles was detected by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and CO chemisorption measurements. The catalysts were tested in the catalytic oxidation of CO using a plug–flow reactor. The CO conversion was determined as a function of temperature. The monometallic palladium and the palladium-rich catalysts behaved quite similarly and were the most active catalysts. A drastic reduction of the CO oxidation activity was observed for the 50/50 Au/Pd catalyst and for samples with increasing amount of gold.

Monometallic Au, Pd and bimetallic AuPd nanoparticles were prepared from Au(III), Pd(II) precursor ions in aqueous media with reduction by a mixture of Na-citrate and tannin producing stable metal sols of narrow size distribution. The nanoparticles of 4–7 nm in diameter as indicated by transmission electron microscopy were adsorbed on TiO2. In situ X-ray absorption spectroscopy (XAS) at Au LIII and Pd K-edges and X-ray diffraction (XRD) techniques evidenced the presence of bimetallic particles in the supported AuPd/TiO2 sample. The high amount of organic residues of the samples was removed by calcination at 400 °C proved by temperature programmed oxidation (TPO). After reduction in H2 the TEM, XRD and the CO chemisorption showed some enlargement in the metal particle sizes. The catalytic activity of the bimetallic AuPd/TiO2 in the CO oxidation revealed a slight synergistic effect compared to the activity of monometallic analogous referred to the estimated surface area of Au and Pd in the bimetallic sample.

The evaluation of experimental data of ion microbeam analysis is often hindered by low counts/pixel statistics of elemental or tomographic images available within limited acquisition time, mainly at low elemental concentrations. In this contribution we present a method based on a non-linear iterative deconvolution scheme, designed to recover step-like profiles with forcibly low counts. To demonstrate its performance and effectiveness, the algorithm was applied for measured one-dimensional profiles with a micrometre resolution, generated by Rutherford backscattering spectrometry (μRBS) at the ATOMKI scanning nuclear microprobe facility. The method can be extended to solve the analogous two-dimensional problem, giving an improvement of nuclear microscopic methods, like channelling contrast microscopy (CCM).

The gas-phase partial oxidation of benzene and toluene to phenol and to cresols over Fe-containing ZSM-5 zeolites prepared by various methods was studied using N2O as oxidant. Over FeZSM-5 synthesized by either isomorphous substitution or ion exchange the phenol selectivity reached nearly 100% at 573 K, however, only 25-30% cresol (mainly p-cresol) selectivity was observed in the oxidation of toluene because of the formation of benzaldehyde and benzoic acid in the fast oxidation of the methyl group.

Nanosize gold particles were prepared by Ar(+) ion implantation of 10-nm thick gold film deposited onto a SiO(2)/Si(100) wafer possessing no catalytic activity in the CO oxidation. Along with size reduction the valence band of the gold particles and the actual size were determined by ultraviolet- and X-ray photoelectron spectroscopy (UPS, XPS) and by transmission electron microscopy (TEM) as well as atomic force microscopy (AFM), respectively. The catalytic activity was determined in the CO oxidation. Energy distribution of the photoelectrons excited from 5d valence band of gold was strongly affected by Ar(+) implantation. This variation was interpreted by the redistribution of the valence band density of states (DOS). The intrinsic catalytic activity of the gold particles increased with decreasing size. When an Au/FeO(x) interface was created by FeO(x) deposition on large gold nanoparticles, a significant increase in the rate of the CO oxidation was observed. These data can be regarded as an experimental verification of the correlation between the catalytic activity and valence band density of states of gold.

The interfacial interaction of gold nanoparticles deposited on either model SiO2/Si(100) or high surface area amorphous or mesoporous silica with minute amounts of promoter oxide like “active” FeOx, TiO2 and CeO2 has been discussed. The role of the active oxide, its contribution to the perimeter along the gold nanoparticles has been interpreted. The oxide may invoke electronic interaction and simultaneously the defect structure of oxides likely has a key issue in the formation and stabilization of very small Au particles. The activity of the Au/oxide perimeter depends not only on the size of the Au particles, but also on the size and morphology of the oxide component (likely amorphous structure) regardless of whether it is supporting Au nanoparticles or decorating them. The activity in CO oxidation over Au catalysts is strongly affected by the length of the Au/“active” oxide perimeter which is regarded as the “active interface”. The longer length of the perimeter is evidenced by the enhanced CO oxidation activity.