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Propylene is a very essential building block in the petrochemical industry. There is a fast growing in its demand that is steadily expanding its market. Fluid catalytic cracking units is the second largest propylene source for petrochemical application. FCC units are primarily used in the production of gasoline. However, refiners have taken advantage with the aim of producing and recovering large amounts of propylene from their Fluid catalytic cracking unit by raising the severity of reaction through riser temperature, installation of a propylene recovery unit and addition of a catalyst that is shape selectivity. ZSM-5 is nowadays used as a very efficient fluid catalytic cracking additive for increasing light olefins production i.e. propylene. This short review will be exclusively focused on ZSM-5-containing additives and look at the main strategies used in the design and modifications of ZSM-5 catalysts to increase the propylene production in the FCC units. The review will highlight the most important and the recent modification methods used in enhancing ZSM-5 performance in the FCC process to maximize the yield of light olefins in general, and in particular that of propylene. These methods include particle size and acidity modification, phosphorus treatment, mesoporous/hierarchical structure creation, incorporation alkali metals and some selected transition metals and introduction of rare-earth metal.

Archaeological high-tin copper-based artefacts, dated back to VIII and IV centuries BC and recently discovered in the Italic necropolises of ancient Abruzzo (Central Italy), were investigated in order to determine the micro-chemical and micro-structural nature of the corrosion products and the chemical composition and metallurgical features of the alloys. The Cu-based artefacts were defensive weapons mainly as bronze belts and pectoral disc armours with engraved decorations. A rather detailed picture of the chemical composition, structural and morphological characteristics of such Cu-based artefacts was provided by combining different techniques as scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), optical microscopy (OM) and X-ray diffraction (XRD) analysis. The results, as a whole, evidence that some artefacts were manufactured by casting and shaping uncommon high-tin bronze alloys thus conferring an attractive silver-like appearance. The manufacturing process was based on tailored multiple hot hammering, carefully carried out at about 700 °C to shape the high-tin alloys in the form of sheets avoiding breaking. The mechanical work was followed by an annealing treatment, polishing and final decorative finishing. Furthermore, our investigation on the corrosion process, suggest that it is a mixture of rather complex phenomena leading to the degradation of the main alloying elements which give rise to mineral alteration products in the form of complex structures. These latter contain SnO2 (cassiterite), cuprous oxide, copper carbonates (azurite and malachite) and, in particular, chlorine-based compounds like nantokite and atacamite and its polymorphs, which have heavy detrimental effects, their presence being considered a symptom of the destructive “bronze disease” degradation phenomenon. Moreover, it was found an unusual presence of re-deposited Cu inclusions to be likely related to long-term corrosion processes and to a low oxygen availability in the burial environment. All these findings show, as a whole, that there is a strict relationship between alloy elements, metallurgical features, burial soil conditions and chemical and structural features of the corrosion products. This paper highlights also as the combined use of different techniques as SEM-EDS, ATR-FTIR, XPS, XRD and OM can be one of the possible successfully way to study the corrosion products of archaeological copper-based artefacts, thus helping to choose the more appropriate strategies for the long-lasting conservation of archaeological bronze artworks, in most cases so valuable for the cultural heritage.

The removal of the commonly used herbicides is essential for environmental remediation. In this study, mesoporous TiO2 photocatalysts modified with PtO were synthetized by the template-assisted scheme to develop highly effective materials for the elimination of Imazapyr herbicide under visible-light preservation. The effect of the PtO loading was investigated, and the xPtO-TiO2 materials were deeply considered by N2 physisorption, XRD, HRTEM, FTIR, DRS UV-Vis, Raman, XPS, PL and photocurrent measurements. Total Imazapyr photodegradation was archived on mesoporous TiO2 photocatalysts loaded with 0.6 and 0.8 wt% of PtO. The optimized xPtO-TiO2 photocatalyst degrades the Imazapyr under solar light more efficiently than the pure TiO2 and the commercial Degussa P25 (photoefficiency of 35%, 1%, and 0.5%, respectively). The improvement in the photoefficiency of the xPtO-TiO2 photocatalysts respect to the pure TiO2 was associated to the cooperative effect between PtO and TiO2 nanoparticles leading to a lessening in the energy gap and lower recombination of excited electron-hole pairs. The optimized 0.6PtO-TiO2 photocatalyst demonstrated to be stable and recyclable after up to five consecutive photocatalytic runs. Therefore, it can be a potential candidate for the significant mineralization of Imazapyr herbicide under solar light irradiation.

Ancient silver-based alloys objects are of a great interest because they were world-wide used to produce high value works of art and precious items as jewels and ornaments with a relevant artistic, religious or historical value. Silver-based alloys were also largely used everyday as monetary currency and form of saving playing a relevant role for the development and growth of the economy. By means of the combined use of complementary surface analytical techniques such as scanning electron microscopy coupled with energy dispersive spectrometry (SEM + EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and optical microscopy (OM) we have investigated the micro- and nano-chemical nature of the products of corrosion naturally formed on archaeological silver-based Roman objects characterised by different burial conditions. The results allow the identification of different corrosion products formed during the long interaction between the elements constituting the alloy, i.e. Ag and Cu, and degradation agents present in the surrounding environment. The results of the integrated analytical methodologies highlight the role of chlorine, that is always present in the patina as chloroargyrite (AgCl, also known as cerargyrite or horn silver) and also in some cases of bromine which forms bromargyrite (AgBr) or bromian-chloroargyrite [Ag(Br,Cl)] as dominant corrosion products. The unusual presence of Br in the silver patina reflects the peculiar environmental chemistry suffered by the buried object likely due to the presence of degrading organic matter under aerobic conditions. Furthermore, the results reveal that chlorine often preferentially corrodes the numerous local copper enrichments randomly dispersed in the silver host matrix inducing the formation of harmful copper-chlorine compounds including Cu2Cl(OH)(3) (atacamite and its polymorphs) and likely CuCl (nantokite) generally related to the copper cyclic corrosion called by conservators "bronze disease". Finally, different corrosion patterns have been observed with the outermost layers often enriched by soil elements as S, Ca, Al, Si and Fe thus confirming the strong interaction of the alloys elements with the burial soil components. (C) 2017 Elsevier B.V. All rights reserved.

A detailed XPS investigation, supported by XRD analysis, was performed on Co-Zn-Mn oxide-based spinels as a function of cobalt concentration and calcination temperature (723 and 973 K). Results revealed for the first time that a recarbonation occurred under ambient conditions but only for the Co-containing materials calcined at 973 K. Indeed, such effect was not observed for the homologous preparations at 723 K. This evidence was quite surprising because the solids calcined at 973 K, for which a sintering occurred as reflected by the low surface areas, were supposed to be almost inert under ambient conditions. Such an intriguing recarbonation chemistry, leading even to a bulky rhodochrosite-like (MnCO3) phase in the cobalt most enriched samples, arises from the combined effect of the calcination treatment at high temperature and the presence of cobalt ions. The spinels calcined at higher temperature are characterized by a high surface defectivity, due to anionic vacancies produced by a partial self-reduction of a fraction of Mn3+ ions that occurs only at 973 K but not at 723 K. Consequently, the presence of anionic vacancies and the incomplete coordination of the outermost layers promoted a higher reactivity of the solids calcined at 973 K with CO2 and moisture from ambient air. However, a carbonate phase was absent in the sample at 973 K with no cobalt. This suggests that the presence of cobalt is another crucial factor for the recarbonation process to take place. Cobalt ions appear to play a catalytic role. An attempt is made to provide a reasonable explanation of this intriguing recarbonation chemistry, trying to shed some more light on the rather complex chemistry behind the attack of moisture and CO2 to oxide solid surfaces. These results, as a whole, may provide new insight on phenomena observed in the case of some Mn-based catalysts, as the severe deactivation by traces of moisture occurring in hopcalite during CO oxidation at RT. They may also give an additional perspective to environmental processes that involves the interaction of moisture and CO2 with the surface of Mn-based solids or other materials as environmental interfaces.

Naturally grown patinas are typically detected onto the surface of modern copper-based artefacts and strictly affect their surface reactivity and appearance. The production of representative patinas is a key issues in order to obtain model systems which can be used for the development and validation of appropriate conservation materials and methods. In this study, we have prepared different artificial representative patinas by using a quaternary Cu-Sn-Zn-Pb alloy with chemical composition and metallurgical features similar to those of valuable modern works of art. In order to produce degradation products usually observed onto their surface, chloride and sulphate species were used to induce corrosion processes. Different patinas were produced by changing the nature of corrosive species and the set-up for the accelerated degradation. The composition and structural properties of the patinas were investigated by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray diffraction, optical microscopy and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. The results allow to identify degradation products and to distinguish copper hydroxychloride polymorphs and copper hydroxysulphates with similar structure. Our findings show that patina composition can be tailored by modifying the degradation procedure and patinas representative of modern artefacts made of quaternary Cu-Sn-Zn-Pb alloy can be obtained.

Gilded brooches dating back to 16th-17th centuries CE were investigated by means of integrated and complementary analytical techniques such as high spatial resolution field emission scanning electron microscopy coupled with energy dispersive X-ray spectrometry (FE-SEM+EDS), time of flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and optical microscopy (OM). The results reveal in detail the surface and subsurface morphology and the chemical features of the micrometric decorative Au layer that has been deposited by means of the so-called fire-gilding technique based on the use of an amalgam. Moreover, the results allow to recognise chlorine, sulphur and phosphorous species as the main degradation agents and to identify the corrosion products naturally formed during the long-term interaction with the burial soil constituents. The findings show also that the galvanic coupling between the two dissimilar metals, i.e. Cu and Au, lead to enhancement of corrosion phenomena causing the spalling of the gold thin film and the disfigurement of the object. From a conservation point of view, the results suggest a targeted use of low-toxic inhibitors to hinder the detrimental role of chlorine as possible responsible of future further severe degradation phenomena. In conclusions, the micro and nano-chemical, structural and morphological investigations in a depth range from a few nanometers to micrometers have revealed the complex nature of corroded surface of ancient gold coated artefacts, highlighting some specific aspects related to their peculiar degradation mechanisms thus extending the scientific relevance of the tailored use of complementary and integrated surface and subsurface analytical techniques for the investigation of ancient coated artefacts. (C) 2018 Elsevier B.V. All rights reserved.

By means of the combined use of X-ray photoelectron spectroscopy (XPS), optical microscopy (OM) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) the surface and subsurface chemical and metallurgical features of silver counterfeited Roman Republican coins are investigated to decipher some aspects of the manufacturing methods and to evaluate the technological ability of the Roman metallurgists to produce thin silver coatings. The results demonstrate that over 2000 ago important advances in the technology of thin layer deposition on metal substrates were attained by Romans. The ancient metallurgists produced counterfeited coins by combining sophisticated micro-plating methods and tailored surface chemical modification based on the mercury-silvering process. The results reveal that Romans were able systematically to chemically and metallurgically manipulate alloys at a micro scale to produce adherent precious metal layers with a uniform thickness up to few micrometers. The results converge to reveal that the production of forgeries was aimed firstly to save expensive metals as much as possible allowing profitable large-scale production at a lower cost. The driving forces could have been a lack of precious metals, an unexpected need to circulate coins for trade and/or a combinations of social, political and economic factors that requested a change in money supply. Finally, some information on corrosion products have been achieved useful to select materials and methods for the conservation of these important witnesses of technology and economy.

A series of γ-Al2O3-supported molybdenum phosphide catalysts containing fixed Mo-loading (9.9 wt %) and variable P amounts (1.5−9.6 wt %) were prepared by temperature-programmed reduction (TPR) from their oxide precursors in hydrogen. The effect of the P/Mo atomic ratio on the structure of the molybdenum phosphide materials was studied by SBET, XRD, HRTEM, TPD−NH3, H2 chemisorption, XPS, and 31P- and 27Al-MAS NMR techniques. The reactions involved in the transformation of oxide precursor to Mo−phosphide were followed by TPR. Specific surface areas of samples subjected to reduction at 1123 K were rather high (210−263 m2 g-1). These catalysts were tested in the gas-phase hydrodesulfurization (HDS) of dibenzothiophene (DBT) at 553 K and 3.4 MPa. All Mo−phosphide catalysts were more active than a molybdenum sulfide sample with the same Mo-loading. The Mo−phosphide catalysts with P/Mo ratios of 1 and 1.1 were found to be the most active among the catalysts studied. The activity drop observed for higher P-loadi...

Carbon nanotubes (CNT) are amongst the most studied nano-materials for their application in numerous fields as a result of their exceptional mechanical, thermal, and electronic and optical properties. However, the lack of solubility of CNT in many common solvents limits the exploration of their potential applications. For this reason, it is important to investigate new procedures to functionalize these materials in order to improve their solubility and their processability. Furthermore, functionalization can modify the physical properties of CNT and thus expand their potential applications.We report herein the functionalization of single-wall carbon nanotubes (SWCNT) by cycloaddition reactions with arynes under microwave irradiation. The efficiency of the functionalization was monitored by XPS, FTIR and Raman spectroscopies, TGA and HR-TEM. All experimental results point to the formation of SWCNT with a high degree of functionalization, with mass increases ranging from 6.4% to 15.1% depending on the aryne substitution.

The photodegradation of 4-nitrophenol in aqueous solution was studied by using titania-based photocatalysts, in particular standard commercial titania samples (anatase and rutile, Hunstmann; P25 and Aeroxide VP P90, Evonik) and a mesoporous and nanocrystalline titania synthesized under hydrothermal conditions. A comparison between the commercial products and our preparations made evident a different particle size and phase composition. Moreover, in order to investigate a possible synergism between TiO2 and carbon nanotubes (CNTs), further two samples were purposely synthesized by adding to the reaction mixture used for the catalyst preparation a small amount of single-walled or multi-walled carbon nanotubes (SWCNTs and MWCNTs). Among the investigated solids, the nanocrystalline titania resulted to be the most active photocatalysts. The less active solids were rutile and mesoporous titania. The addition of a small amount of MWCNTs further increased the photoactivity of the nanocrystalline titania.

CuO-ZnO-Al 2 O 3 catalysts with different Cu/Zn/Al atomic ratios were obtained by thermal decomposition of hydroxycarbonate precursors. The hydroxycarbonate precursors, prepared by coprecipitation at pH = 8, depending on the Cu/Zn/Al atomic ratios contain malachite Cu 2 CO 3 (OH) 2 , zincian-malachite Cu 2-x Zn x CO 3 (OH) 2 , aurichalcite Zn 5-x Cu x (CO 3 ) 2 (OH) 6 , hydrozincite Zn 5 (CO 3 ) 2 (OH) 6 , and an hydrotalcite-like: Cu 6-x Zn x Al 2 (CO 3 ): 2 (OH) 16 . Upon calcination, well interdispersed oxidic phases are obtained. In the ternary Cu/Zn/Al catalysts, the aluminium-containing phase was found to be amorphous and, regardless of the composition, only CuO and ZnO oxides are identified by X-ray diffraction analysis. The reduction process in H 2 was studied by XPS and XAES. The reduction of the Cu(II) species leads to the formation of both Cu(I) (Cu 2 O) and Cu(0) species. The reduction process is much slower for the alumina-containing samples compared to the binary CuO/ZnO specimen. Alumina and ZnO play an important role in the stabilization of Cu(II) and Cu(I) chemical states at low temperature. Upon reduction at high temperature, alumina plays a key role by preventing the sintering process of the Cu(0) particles.

Different tungsten oxide catalysts supported on chlorinated activated carbons were prepared by using ammonium tungstate and tungsten pentaethoxide as precursor compounds. The supported catalysts were pretreated in wet air at 623 K for 6 h and characterized by N2 adsorption at 77 K, temperature-programmed desorption, X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results indicate that tungsten oxide is anchored to chlorine surface complexes through the formation of W−Cl bonds during either the preparation or wet air pretreatment of the catalysts. This has a major influence on the particle size and distribution of the metal oxide phase supported on the carbon particles.

Desorption rates of erucamide from erucamide/isotactic polypropylene (i-PP) blends were measured microgravimetrically under vacuum. Experimental data were used for testing our theoretical descripti...

Copper–cobalt oxysalts of various Cu : Co atomic ratios (100 : 0. 92 : 8, 85 : 15, 77 : 23, 67 : 33, 15 : 85, 0 : 100) have been prepared by coprecipitation, at constant pH, from solutions of copper and cobalt nitrates added to a solution of NaHCO3; the structure and chemical nature of the Cu—Co oxysalts have been investigated by several complementary techniques such as X-ray diffraction (XRD), magnetic susceptibility, reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS) to obtain information both on their bulk and on their surface properties.In the range of Cu : Co atomic ratios from 100 : 0 to 67 : 33 the materials consist of Co-containing malachite, Cu2 –xCoxCO3(OH)2, while for Cu : Co equal to 0 : 100 and 15 : 85 the products are CoCO3, spherocobaltite, and Cu-containing spherocobaltite Co0.85Cu0.15CO3, respectively. From both reflectance spectroscopy and magnetic susceptibility measurements the presence of only Cu2+ and Co2+ species has been ascertained in all materials. Antiferromagnetic interactions are strong at high copper content and become weaker at increasing cobalt loading. The observed decrease in volume of the malachite monoclinic unit cell with incorporation of Co2+ ions, in spite of the larger Co2+ ion radius with respect to that of Cu2+, indicates that distortion of the MO6 polyhedra at the cation site of the malachite lattice is less when Cu2+ is replaced by Co2+. The presence of Cu2+ in the spherocobaltite trigonal lattice shows a small cell volume decrease as expected from ionic radii difference. XPS has confirmed the presence of only Cu2+ and Co2+ species at the surface of the materials. It is also shown that the local nature of the chemical bond is essentially determined by the nature of the first-neighbour ligands. At higher copper content, where the materials are cobalt-containing malachite, the surface is enriched in cobalt.

The corrosion behaviour of 13Cr-martensitic stainless steel (AISI 420) was investigated in CO2-H2S-Cl− environments typical of oil and gas wells under different CO2 and H2S partial pressures. The corrosion tests indicated that the AISI 420 steel was highly corrosion resistant to CO2-induced phenomena (general corrosion and carbonate S.C.C.), while in the H2S environment a high S.S.C.C. (Sulphide Stress Corrosion Cracking) susceptibility and high corrosion rates were found. Moreover, CO2 in CO2-H2S-Cl− systems inhibited general corrosion and S.S.C.C. phenomena by favouring the formation of a protective film. By means of X-ray photoelectron spectroscopy (XPS) the chemical nature of the films grown on AISI 420 in different environmental conditions was investigated and the following statements were drawn out: Furthermore from XPS results an index of protectivenessI p = Cr+3/ (Cr+3 + Fe OX was defined and related to the environmental parameter $$E_{H_2 S,CO_2 } = p{\text{CO}}_{\text{2}} /p{\text{H}}_{\text{2}} {\text{S + }}p{\text{CO}}_{\text{2}}$$ and to the corrosion rates.

Preparation and characterization of both iron-zinc manganites at different iron content (x = Fe/(Fe + Zn) = 0, 0.01, 0.05, 0.10) and their carbonate precursors are reported. In particular, structural properties and the iron chemical state were investigated. Precursors, obtained by coprecipitation at constant pH, were in all cases monophasic and made by a rhodochrosite-like, FexZnyMn(1-x-y)CO3, phase. Mössbauer spectroscopy proved that, surprisingly, Fe3+ was 95% of total iron. A hypothesis about the charge compensation mechanism in the rhodochrosite-like structure is given. The carbonate precursors were decomposed in air at 723 and 973 K, leading at both temperatures to monophasic iron-zinc manganites characterized by a distorted spinel-like structure with tetragonal symmetry. In such a structure, trivalent Mn3+ ions and bivalent Zn2+ ions are perfectly ordered in the octahedral and tetrahedral sites of the crystal lattice, respectively, as expected for a ‘normal’ spinel. Mössbauer investigation revealed that iron is present as trivalent ions in the octahedral sites and that no iron extra-phases were formed. Moreover, three doublets corresponding to octahedral Fe3+ ions were detected, likely related to different distributions of Fe3+/Mn3+ cations in the next-nearest coordination sphere.

The corrosion behavior of 13Cr-martensitic stainless steel was investigated in CO2-H2S-Cl− environments typical of oil and gas wells under different CO2 and H2S partial pressures, with an ...

The corrosion behavior of 13Cr-martensitic stainless steel was investigated in CO2-H2S-Cl- environments typical of oil and gas wells under different CO2 and H2S partial pressures, with an NaCl content of 50 g/L, pH = 2.7 and 4.8, T = 80°C. The 13Cr was highly corrosion resistant to CO2-induced phenomena (general corrosion and carbonate stress corrosion cracking [SCC]), while the presence of H2S resulted in high sulfide stress corrosion cracking (SSCC) susceptibility and high corrosion rates. The CO2 in CO2-H2S-Cl- systems inhibited general corrosion and SSCC phenomena by favoring the formation of a protective film. X-ray photoelectron spectroscopy analysis of the films grown in different environmental conditions revealed that CO2 favors the growth of a Cr oxide-rich protective film with a low Fe oxide-sulfide content; the presence of H2S favors the formation of less protective Fe sulfide- and Fe oxide-rich layers. An index of protectiveness Ip = Cr3+/(Cr3+ + Feox) is defined and related to the environmental parameter EH(2)S,CO(2) = pCO2/pH2S + pCO2 and to the actual corrosion rates.

The authors have studied surface decompositions induced by high-temperature treatments (up to 825 K) at the surface of SnO2 oxide and SnO oxide, the latter being chosen for the purposes of comparison. XPS spectroscopy was used to monitor such modifications. They find that Sn0 forms at the surface when SnO2 and SnO are annealed to 825 K, and non-stoichiometric tin oxide species become apparent in the sub-surface region of the former. Insurgence of Sn metal at the surface of thermally treated tin oxides could be related to the results of recent work by J.W. Erickson and S. Semancik, who reported a significant increase of surface electrical conductivity in SnO2 annealed to 800 K, and higher temperatures.

Films of a few layers in thickness of reduced graphite oxide (RGO) sheets functionalized by the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDPS) are obtained by using the Langmuir-Blodgett method. The quality of the RGO sheets is checked by analyzing the degrees of reduction and defect repair by means of X-ray photoelectron spectroscopy, atomic force microscopy (AFM), field-emission scanning electron microscopy (SEM), micro-Raman spectroscopy, and electrical conductivity measurements. A modified Hummers method is used to obtain highly oxidized graphite oxide (GO) together with a centrifugation-based method to improve the quality of GO. The GO samples are reduced by hydrazine or vitamin C. Functionalization of RGO with the zwitterionic surfactant improves the degrees of reduction and defect repair of the two reducing agents and significantly increases the electrical conductivity of paperlike films compared with those prepared from unfunctionalized RGO.

We report a simple, practical scalable procedure to produce few-layer graphene sheets using ball-milling. Commercially available melamine can be efficiently used to exfoliate graphite and generate concentrated water or DMF dispersions.

Single-walled carbon nanotubes (SWNTs) can be successfully cut with relatively homogeneous sizes using a planetary mill. The optimized conditions produce highly dispersible SWNTs that can be efficiently functionalized in a variety of synthetic ways. As clearly shown by Raman spectroscopy, the milling/cutting procedure compares very favorably with the most common way of purifying SWNTs, namely, treatment with strong oxidizing acids. Moreover a similar milling process can be used to functionalize and cut pristine SWNTs by one-step nitrene chemistry., Part of the work described in this Article was financed by DGICYT of Spain through project CTQ2007–60037/BQU and by Consejería de Educación y Ciencia de Castilla-La Mancha through projects PBI-06–0020 and PCI08–0040, the University of Trieste and MUR (PRIN 2008, prot. 20085M27SS and Firb RBIN04HC3S), and ERC (project Carbonanobridge).

International audience; The influence of small amounts of rhodium on the structure and the reducibility of copper-based catalysts deposited on alumina and ceria-alumina supports has been studied by XRD and H2-TPR techniques. For both supports, the addition of rhodium does not affect the reduction mechanism of copper, which has been shown to involve small clusters/isolated ions at lower temperatures and large particles at higher temperatures. However, rhodium addition inhibits the formation of large size copper particles in favor of small ones, thus making easier the reduction of the catalyst at low temperature.