Small Metal Particles Research Articles

Sub-nanometric ruthenium clusters prepared by solid-state dispersion for catalytic selective aerobic oxidation of aromatic alcohols

The selective aerobic oxidation of alcohols to corresponding aldehydes is one of the most important challenges in the green chemical industry. In this work, Ru/Al2O3-SSD catalyst with highly dispersed metallic ruthenium clusters (average particle size of 0.97 nm) was prepared by solid-state dispersion (SSD) for efficient selective aerobic oxidation of aromatic alcohols to aldehydes. Compared with the counterpart catalyst Ru/Al2O3-IM prepared by wet impregnation (IM), this catalyst has smaller metal particles (0.97 nm vs. 3.4 nm), resulting in a special electronic structure, and exhibits much higher TOF (234 h−1 vs. 98 h−1) in the aerobic oxidation reaction of benzyl alcohol at 80 °C. The catalyst also shows excellent catalytic activity in the preparation of vanillin by selective aerobic oxidation of vanillyl alcohol at 100 °C, delivering a vanillin yield of 99%. The solid-state dispersion strategy provides an efficient and facile way for the fabrication of high-performance sub-nanometric metal catalysts.

The Effect of Loading W&V:TiO2 Nanoparticles with Noble Metals for CH4 Detection

TiO2 nanoparticles (NPs) doped with W (W:TiO2), double-doped with W and V (W&V:TiO2), and loaded with noble metals (W:TiO2 @Pt/Pd/Ag and W&V:TiO2@Pt/Pd/Ag) were synthesized by laser pyrolysis followed by chemical impregnation and reduction. Due to its exceptional properties, TiO2 is considered a key material being used in a wide range of applications. To improve its detection activity, the increase in the specific surface of the material, and the presence of defects in its structure play a decisive role. Doped and double-doped TiO2 nanoparticles with dimensions in the range of 25–30 nm presented a mixture of phases corresponding to titania, with the anatase phase accounting for the majority (95%). By loading these nanoparticles with small particles of noble metals, a significant increase in the specific surface area by three or even five times the original values was achieved. Sensitive thin films for surface acoustic wave (SAW) sensors were made with the NPs, embedded in polyethyleneimine (PEI) polymer and deposited by spin-coating. Each sensor was tested at CH4 concentrations between 0.4 and 2%, at room temperature, and the best results were obtained by the sensor with NPs doped with V and decorated with Pd, with a limit of detection (LOD) of 17 ppm, due to the strong catalytic effect of Pd.

Transition Metal Carbides as Supports for Catalytic Metal Particles: Recent Progress and Opportunities.

Transition metal carbides (TMCs) constitute excellent alternatives to traditional oxide-based supports for small metal particles, leading to strong metal-support interactions, which drastically modify the catalytic properties of the supported metal atoms. Moreover, they possess extremely high melting points and good resistance to carbon deposition and sulfur poisoning, and the catalytic activities of some TMCs per se have been shown to be similar to those of Pt-group metals for a considerable number of reactions. Therefore, the use of TMCs as supports can give rise to bifunctional catalysts with multiple active sites. However, at present, only TiC and MoxC have been tested experimentally as supports for metal particles, and it is largely unclear which combinations may best catalyze which chemical reactions. In this Perspective, we review the most significant works on the use of TMCs as supports for catalytic applications, assess the current status of the field, and identify key advances being made and challenges, with an eye to the future.

An active and stable catalyst of Zn modified Pt nanoparticles encapsulated within silicalite-1 zeolite for dehydrogenation of ethane

The rapid deactivation of catalysts for ethane dehydrogenation (EDH) at considerably higher temperature and the relatively inert feature of ethane makes it urgent to develop highly active and stable catalysts. Herein, a Zn modified Pt nanoparticles confined within silicalite-1 (S-1) zeolite catalyst for EDH reaction was synthesized by hydrothermal synthesis using the PtZn/SiO2 precursor without any protective ligands, which achieved extremely high catalytic performance (e.g., 15.9 % conversion which was close to the thermodynamic equilibrium limitation, 99.5 % ethylene selectivity, and 0.001 h−1 the deactivation rate). Multiple characterizations with XPS, in situ CO-DRIFTS, in situ C2H6-DRIFTS, TG-DTA, and Raman techniques on these catalysts revealed that the electron-rich Pt sites with stable electronic environment formed by Zn promoter introduced, resulting in enhanced anti-reduction and coke-resistance abilities. Furthermore, characterizations with XRD, HRTEM, Py-IR, hydroxyl vibration region of DRIFT spectra and 1H MAS NMR spectroscopic analysis showed that the dilution effect of Zn and the trapping of zinc and platinum species by Si-OH groups in the form of (≡Si-O-Zn)xPt complex could inhibit migration and aggregation, resulting in smaller metal particles and increase anti-sintering ability. The superior catalytic performance as well as the environmental benign preparation route with no-ligand will further contribute to the advantages for future applications.

Theoretical and Experimental Studies of the Shock-Compressed Gas Parameters in the Welding Gap.

This work is devoted to the study of the processes that take place in the welding gap during explosive welding (EW). In the welding gap, when plates collide, a shock-compressed gas (SCG) region is formed, which moves at supersonic speed and has a high temperature that can affect the quality of the weld joint. Therefore, this work focuses on a detailed study of the parameters of the SCG. A complex method of determining the SCG parameters included: determination of the detonation velocity using electrical contact probes, ceramic probes, and an oscilloscope; calculation of the SCG parameters; high-speed photography of the SCG region; measurement of the SCG temperature using optical pyrometry. As a result, it was found that the head front of the SCG region moved ahead of the collision point at a velocity of 3000 ± 100 m/s, while the collision point moved with a velocity of 2500 m/s. The calculation of the SCG temperature showed that the gas was heated up to 2832 K by the shock compression, while the measured temperature was in the range of 4100-4400 K. This is presumably due to the fact that small metal particles that broke off from the welded surfaces transferred their heat to the SCG region. Thus, the results of this study can be used to optimize the EW parameters and improve the weld joint quality.

Cu-(Ga0.2Cr0.2Mn0.2Ni0.2Zn0.2)3O4 heterojunction derived from high entropy oxide precursor and its photocatalytic activity for CO2 reduction with water vapor

The construction of metal–semiconductor heterojunction has been proven to be an effective way to improve the separation efficiency of photogenerated electrons and holes, thus enhancing photocatalytic activity of semiconductor with narrow band gap. Here, we construct a Cu-(Ga0.2Cr0.2Mn0.2Ni0.2Zn0.2)3O4 high entropy oxide (HEO) heterojunction by using Cu-containing HEO precursor, and the effect of Cu addition method on the photocatalytic performance was investigated. The results show that the addition method of Cu has a great influence on the size of Cu nanoparticles (NPs), heterojunction amount and photocatalytic activity of Cu-HEO catalysts. Cu-HEO samples prepared by direct introduction method possess much smaller Cu particles due to the uniform distribution and stronger diffusion hysteresis effect of Cu in HEO, and exhibit superior photocatalytic activity and CH4 selectivity for CO2 reduction. With the increase of Cu loading, the photocatalytic activity of Cu-HEO samples firstly increases and then decreases. Among these photocatalysts, Cu0.5-HEO obtained by the direct introduction method displays the highest CO2 reduction activity, and the yields of CO and CH4 reach to 5.66 and 33.84 µmol/h/gcat, respectively. This work innovatively uses HEO precursors with unique properties to construct metal-HEO heterojunctions with smaller metal particles and more active sites.

INVESTIGATION OF THE PROCESS OF ELECTRIC ARC METALIZATION OF COATINGS FROM STEEL 30KhGSA

The article considers the electric arc metallization technological modes of steel 30KhGSA wires, which affect thestructure formation and properties ofcoatings.Electric arc spraying was carried out using an SX-600 electric arc metallizer. The properties and characteristics of the resulting coatings depend on several plating parameters such as wire feed speed, voltage, and amperage. The coating structure was studied by electron microscopy and metallographic analysis. The coating has a layered structure, which consists of frozen convective metal flows, micro-welded small metal particles and oxides. The results of the study show that an increase in the wire feed speed during metallization leads to an increase in the resulting coating thickness per unit time. On the surface of steel 45, depending on the selected mode, coatings were formedfromsteel30KhGSAwithathicknessintherangefrom50μmto370μm.Ithasbeenestablishedthat when electric arc metallization coatings are sprayed with 30KhGSA wire, the microhardness of the surface layer increases by a factor of 2 relative to the microhardness of 45 steel. Based on studies investigating the impact of various factors in the electric arc spraying process on the formation of coating structures and properties, it can be deduced that utilizing electric arc metallization on steel 30KhGSA substrates allows for the production of coatings with enhanced hardness.

Search for a new material for a medical Cherenkov radiation detector

In this work, using Geant4, we simulate a time-of-flight positron emission tomography detector based on Cherenkov radiation. We consider various materials as a basis for the detector, including a pure PMMA and PMMA used as a matrix containing small resonant particles of copper and gold. For that, in CST studio, we determine the dielectric permittivity for a composite material, which we then use for simulations in Geant4. The resonant nature of the small metal particles allows producing Cherenkov photons by secondary electrons with lower energy, increasing the output of the radiated photons. We consider it as the way to increase temporal resolution as well as efficiency of the detector.

Hydrogen source controlled hydrodeoxygenation of phenolic compounds to cycloalkanes/cycloalkanols over NiFeAlOx catalysts

Catalytic hydrodeoxygenation (HDO) of phenolic compounds is a promising strategy for bio-oil upgradation to produce high-value chemicals and fuels. Herein, a series of NiFeAlOx catalysts prepared by a co-precipitation method were applied in HDO of guaiacol as a typical model compound. The characterization results revealed that the catalyst with Ni/Fe/Al ratio of 3/0.5/2.5 possessed developed textural properties, small metal particles, abundant oxygen vacancies and acid sites. HDO of guaiacol occurred in two pathways with different hydrogen sources: the direct hydrogenation of benzene ring to 2-methoxycyclohexanone and the further hydrogenolysis and dehydration of intermediates to cyclohexane at 260 °C in n-hexane under H2 for 6 h, while demethoxylation affording phenol followed by hydrogenation of phenol to cyclohexanol at 220 °C in isopropanol under N2 for 2 h. The different product composition results from the type of reactive H species, where active hydrogen species are hydrogen radicals using H2 as the hydrogen source and hydrogen ions with opposite charges using isopropanol as the H-donor solvent, respectively. The Ni3Fe0.5Al2.5Ox catalyst maintained good performance after five recycle experiments with a slight decrease in the conversion of guaiacol. Moreover, the catalyst showed excellent universality for selective HDO of other phenolic compounds to cycloalkanes or cycloalkanols.

B-160 Quantification of Titanium using Inductively Coupled Plasma Mass Spectrometry ICP-MS to Monitor Toxic Levels in Blood

Abstract Background When titanium is used as a metallic implant, it can potentially cause toxicity to humans due to wear of the implant. As the implant wears, small particles of titanium and other metals may be released into the surrounding tissue. These particles can cause an immune response, leading to adverse reactions such as allergies and implant-associated infections. Additionally, the wear of the implant can also lead to the release of metallic ions, which can have toxic effects on surrounding tissue and cells. Workers may be exposed in factories that use the metal in the manufacture of paints, varnishes, ceramics, plastics, rubber, soldering rods, floor coatings, food dyes, industrial textiles, cosmetics, glass products, pharmaceuticals, manufacturing of rubber tires and in the production of electronic components. This highlights the importance of regular monitoring and maintenance of titanium prostheses to minimize the wear and toxicity as well as monitoring commonly exposed professionals. The aim of the study was to validate a reliable method for quantification of titanium in blood. Methods Validation was performed using an Inductively Coupled Plasma Mass Spectrometry, 7850 ICP-MS. Analytical specificity is ensured using single particle analysis with fragmented ions that are exclusive to Ti, quantifier ion 47 Da. The procedure involves a small amount of 125 µL of blood, followed by dilution with 100 µL of internal standard at concentration of 1.0 µg/L more 2.275 µL of diluent containing 1-Butanol, Ammonium Hydroxide, EDTA and Triton X-100. After that, samples are submitted to hydrolysis to 37 °C for 40 min. The internal standard was purchased from Agilent at a concentration of 10.0 µg/mL. Finalizing the preparation samples are followed by aspiration into the SPS 4 model injector. Quantitation is achieved by the comparison of the responses from a given sample with the responses of calibrators with known concentrations prepared through Multi Element Cabibration at concentration of 10.0 µg/mL of Ti. Linearity was observed in the expected concentration range from 2.0 to 7.0 µg/L and blood samples were evaluated at six different concentrations and six times each at the same time of the study. Diluent was used as a biological matrix for the study and the standard acquired was Agilent. Results The linearity coefficient of determination (R) was 0.9998. The method showed 100% selectivity and no residual effect interference that was evaluated in blood matrix. To determine the average inter-assay CV%, three different concentrations were analyzed over three days and the results for each low, medium, and high concentration level were 4.27%, 4.22% and 3.33%, respectively. The accuracy of the method was cheeked by analyzing samples of known concentration and expressed as a percentage. A time total analysis was 3.5 min. Conclusion The method was efficient for the determination of titanium in blood. The efficiency and selectivity promoted by the ICP-MS technique, combined with the reliable preparation method, can be used in the diagnosis of wear in metallic titanium prostheses and occupational exposure.

Quantitative 3D Characterization of Functionally Relevant Parameters in Heavy-Oxide-Supported 4d Metal Nanocatalysts.

Accurate 3D nanometrology of catalysts with small nanometer-sized particles of light 3d or 4d metals supported on high-atomic-number oxides is crucial for understanding their functionality. However, performing quantitative 3D electron tomography analysis on systems involving metals like Pd, Ru, or Rh supported on heavy oxides (e.g., CeO2) poses significant challenges. The low atomic number (Z) of the metal complicates discrimination, especially for very small nanoparticles (1-3 nm). Conventional reconstruction methods successful for catalysts with 5d metals (e.g., Au, Pt, or Ir) fail to detect 4d metal particles in electron tomography reconstructions, as their contrasts cannot be effectively separated from those of the underlying support crystallites. To address this complex 3D characterization challenge, we have developed a full deep learning (DL) pipeline that combines multiple neural networks, each one optimized for a specific image-processing task. In particular, single-image super-resolution (SR) techniques are used to intelligently denoise and enhance the quality of the tomographic tilt series. U-net generative adversarial network algorithms are employed for image restoration and correcting alignment-related artifacts in the tilt series. Finally, semantic segmentation, utilizing a U-net-based convolutional neural network, splits the 3D volumes into their components (metal and support). This approach enables the visualization of subnanometer-sized 4d metal particles and allows for the quantitative extraction of catalytically relevant structural information, such as particle size, sphericity, and truncation, from compressed sensing electron tomography volume reconstructions. We demonstrate the potential of this approach by characterizing nanoparticles of a metal widely used in catalysis, Pd (Z = 46), supported on CeO2, a very high density (7.22 g/cm3) oxide involving a quite high-atomic-number element, Ce (Z = 58).

Recent Progress of Catalysts for Reforming of Biomass Tar/Tar Models at Low Temperatures – A Short Review

AbstractCatalytic tar reforming is considered as a promising technology to convert tar into useful syngas such as H2 and CO as well as chemicals such as benzene, toluene, and xylene (BTX). Up until now, few review works have reported the recent progress focusing on the catalyst design for low‐temperature reforming of biomass tar. Therefore, in this work, we focused on the design and preparation of tar cracking and reforming catalysts with high performances to achieve an efficient conversion of tar at temperatures lower than 700 °C. Char supported Ni or Co catalysts with high specific surface area, small metallic particle size and high dispersion are conductive to produce more amount of syngas. Moreover, HZSM‐5 and metal‐promoted zeolites are more suitable for high conversion of tar and selectivity of BTX due to the excellent mesopore structure, thermal stability and medium acidity. Based on those literatures, the adjustment of the catalyst‘s structure, the deactivation mechanism, and the reforming mechanism were also summarized and discussed. In addition, some futural insights were proposed in order to promote the catalyst‘s performance in terms of activity and stability, as well as reveal the clear tar reforming mechanism.

Looking for an Optimal Composition of Nickel-Based Catalysts for CO2 Methanation

A detailed critical analysis of the scientific literature data concerning catalysts for CO2 methanation based on nickel supported over oxides was performed. According to the obtained information, it seems that an ionic support is necessary to allow a good nickel dispersion to produce very small nickel metal particles. Such small metal particles result in being very active toward methanation, limiting the production of carbonaceous materials. The use of support and/or surface additives gives rise to medium surface basicity, allowing medium-strong adsorption of CO2, and it is also advisable to increase the reaction rate. A medium nickel loading would allow the free support geometric surface to be covered densely by small nickel metal particles without the production of larger Ni crystals. It is also advisable to work at temperatures where Ni(CO)4 formation is not possible (e.g., >573 K). The promising properties of systems based on doped Ni/Al2O3, doped with basic and re-active oxides such as MnOx or/and CeO2, and those based on Ni/CeO2 were underlined.

Studies into the reduction of domestic fuel burning emissions by means of facile catalytic abatement technology

The negative health and socio-economic impacts of emissions associated with domestic fuel burning are widely recognized. Although there has been much progress in the provision of electricity to households in South Africa, many still rely on solid fuel sources such as wood and coal. While various investigations have been done on reducing household emissions by reducing the use of polluting fuels and improvements in combustion efficiency, comparatively fewer studies have been conducted on the reduction of emissions through emission reduction using abatement technology. Catalytic oxidation could be utilized to oxidize particulate matter precursors such as volatile organic compounds and soot particles to reduce secondary particulate formation. Although catalytic methods have not been effectively utilized in practical domestic applications, studies have shown effective soot reduction during laboratory testing. This study investigated the synthesis and use of a manganese oxide based catalyst to reduce particulate matter from domestic fuel burning stoves. During field testing, the presence of the catalyst increased the mass of particulate matter collected, with Scanning Electron Microscopy (SEM) analysis showing spherical particles in the pores of the catalyst run filters. The baseline runs had very few of these particle clusters. Energy Dispersive X-Ray (EDX) analysis of the catalyst run filters did not detect manganese, revealing that increased particulate concentrations were not as a result of macroscopic particles of the catalyst being dislodged from the support. Dislodgement of very small metal particles from the catalyst could, however serve as nucleation nodes for particle growth which would have a non-metal coating leading to the non-detection of manganese. The increase in particulate matter could also be caused by the impingement of particulate matter precursors on the catalyst followed by particle growth and dislodgement into the flue gas. The testwork showed that an active catalyst can be synthesized onto a mesh catalyst support in a facile and cost effective manner, which can be utilized in domestic fuel burning devices. It is recommended that a range of optimized, potentially active catalysts be tested to improve the oxidation of particulate matter precursors to carbon dioxide.

High-efficiency desulfurization adsorbents loaded with uniformly dispersed nano-metal particles prepared from phytoremediation

Plants can absorb heavy metals from wastewater due to their biological characteristics, and can evenly disperse these metals into plants. Adsorbents prepared by pyrolysis of metal-rich plants have the advantage of uniform metal loading and small metal particles. Therefore, in this study, Pistia stratiotes was cultured in six monometallic solutions of the same concentration to obtain a monometallic desulfurization adsorbent (ACA-I); after screening, culture in three metal solutions of Ni-Co, Ni-Cu and Co-Cu to obtain bimetallic desulfurization adsorbent (ACA-II). The results of TEM and SEM showed that the diameter of metal nanoparticles supported by ACA-II was smaller and more uniform. The adsorption desulfurization performance of PSLAC-Co-Ni, PSLAC-Cu-Ni and PSLAC-Co-Cu was 87 mg g−1, 83 mg g−1 and 80 mg g−1, respectively, which were better than that of ACA-I. However, the physical structures as well as the adsorption desulfurization performance of ACA-II and ACA-I were better than those of adsorbents prepared by conventional methods. This simultaneously solves environmental problems such as heavy metal pollution of water bodies, treatment of metal-rich plants and excessive sulfur content in fuel oil. This study provides a new idea for the preparation and use of loaded adsorbents, and also provides some data support for further industrial applications.

Dynamics-driven tailoring of sub-nanometric Pt-Ni bimetals confined in hierarchical zeolite for catalytic hydrodeoxygenation

Metal-zeolite catalysts are promising for hydrodeoxygenation of bio-oils, but they always encounter sluggish diffusion kinetics due to sole micropores and inferior metal stability. Here, highly stable sub-nanoscale Pt-Ni bimetals confined in a hierarchical ZSM-5 zeolite (Pt-Ni@HZ) are constructed. The formed Pt-Ni@HZ species create framework-bonding metal sites with zeolite in a confined microenvironment, thereby establishing strong interactions and generating uniform distribution of Pt-Ni bimetals. In the Pt-Ni@HZ-catalyzed hydrodeoxygenation of phenolics, sub-nanometric Pt-Ni facilitates the adsorption and transfer of hydrogen, and hierarchical pores promote the diffusion kinetics of reactants. The designed Pt-Ni@HZ with small metal particles and high coordination numbers of Pt-Ni bonds, favors the complete deoxygenation of phenolics, with a higher yield of cyclohexane than conventional catalysts prepared by impregnation. Benefiting from the protection of the zeolite framework, the Pt-Ni@HZ catalyst exhibits high thermal stability and low leaching of metal active sites, with only 4.4 % catalyst deactivation after five reaction cycles.

Effect of metal site influenced by metal particle size on the catalytic hydrogenolysis of cornstalk lignin

The property of metal site affects the catalyst activity significantly. Herein, the effect of metal site influenced by metal particle size on lignin hydrogenolysis was explored. Four different preparation methods were employed to obtain Ru/Al2O3 catalysts with different Ru metal particle size. Ru/Al2O3-IM catalyst with 10.5 nm Ru particle size only had 16.9 wt% yield of aromatic monomer products. While, Ru/Al2O3–BH catalyst that possessed the metal particle size of 3.6 nm obtained the high monomer yield of 31.7 wt%, with the a low selectivity of methoxy-containing products. Small metal particle size enabled to enhance hydrogen absorption and activation ability, which provided more active hydrogen species and improved lignin hydrogenolysis performance. It can also expose more metal sites to contact with substrates and promote the demethoxylation reaction to achieve more phenols products. The ratio of phenols/guaiacols product kept a good linear relation with Ru particle size. Moreover, Ru/Al2O3–BH catalyst with a small Ru particle size had a high TOF of 0.57 molguaiacol molRu−1 min−1, which was much larger than that of the other Ru/Al2O3 catalysts with a large Ru particle size.

Development of a Ru catalyst supported on HY zeolite for the oxidative decomposition of NH3 triggered at room temperature

On-site hydrogen production from the oxidative decomposition of NH3 with a catalyst is highly required in the countryside where external heat is hardly supplied. In this study, Ru-based zeolite catalysts were prepared by impregnation and subsequent washing using RuCl3·3H2O and HY zeolite or H-MOR zeolite for the oxidative decomposition of NH3. The H-MOR-supported Ru catalyst could not be self-heated by feeding 80% NH3/20% O2 to the catalyst bed at room temperature. By contrast, the HY-supported Ru catalyst underwent self-heating to approximately 773 K upon feeding the reactants owing to the heat released by NH3 adsorption and oxidation, leading to excellent performance for the oxidative decomposition of NH3 during five cycles of start-up tests. Characterization results indicated that the Cl-free Ru/HY catalyst exhibited self-heating due to the presence of small well-dispersed Ru metal particles and a large amount of surface acidic sites.

Subnanometer-Resolution Nanoparticle Sensing through the Strong Coupling between Surface Plasmon Polariton Whispering Gallery Resonances and Localized Surface Plasmon

High-resolution nanoparticle sensing is very important, and many schemes have been proposed to achieve this goal. Circular nanocavities in which surface plasmon polariton (SPP) whispering gallery mode (WGM) resonances were excited were designed to sense particles of ultra-small size and with high resolution. Localized surface plasmon resonances (LSPRs) were excited when a metal particle was set in the circular cavity. The SPP WGM split into symmetric mode (SM) and antisymmetric mode (ASM) due to the LSPRs scattering into the SPPs. The strong coupling between SM resonance and LSPRs generated positive and opposite modes, which were sensitive to the variation in nanoparticle size and position. Even a small nanometer-sized metal particle introduced LSPRs and produced mode splitting. The WGM mode splitting induced by LSPRs reduced the sensing limit. The simulation results show that 1 nm changes in nanoparticle radius and position led to SM 11.8 nm and 10.2 nm wavelength shifts, respectively. This means that variations of 0.09 nm in size and 0.1 nm in position can be sensed with a 1 nm spectral resolution. The strong coupling between SPP WGM and LSPRs can be applied to sense at a subnanometer resolution.

Ni/Al2O3 catalysts for CO2 methanation: Effect of silica and nickel loading

Samples containing from 1 to 33 wt.% of NiO on silica and alumina doped with silica (1 and 20 wt.% silica in the support) have been prepared and characterized by BET, XRD, FT-IR, UV–vis–NIR, FE-SEM, EDXS, and TPR techniques. Catalysts have been pre-reduced in situ before catalytic experiments and data have been compared with Ni/Al2O3 reference sample. Characterization results showed that SiO2 support has a low Ni dispersion ability mainly producing segregated NiO particles and a small amount of dispersed Ni2+ in exchange sites. Instead, for the Si-doped alumina a “surface spinel monolayer phase” is formed by increasing Ni loading and, only when the support surface is completely covered by this layer, NiO is formed. Moreover, H2-TPR results indicated that NiO particles are more easily reduced compared to Ni species. Low loading Ni/SiO2 catalysts show high selectivity and moderate activity for RWGS (reverse Water Gas Shift) reaction, likely mainly due to nickel species dispersed in silica exchange sites, as evidenced by visible spectroscopy. High loading Ni/SiO2 catalysts show both methanation and RWGS but evident short-term deactivation for methanation, attributed to large, segregated Ni metal particles, covered by a carbon veil. Ni on alumina -rich carriers, where nickel disperses forming a surface spinel phase, show high activity and selectivity for methanation, and short-term catalyst stability as well. This activity is attributed to small nickel clusters or metal particles interacting with alumina, formed upon reaction. The addition of SiO2 in Al2O3 support decreases the activity of Ni catalysts in CO2 methanation, because it reduces the ability of the support to disperse nickel in form of the surface spinel phase, thus reducing the amount of Ni clusters in the reduced catalysts.