Good Metal Dispersion Research Articles

Harnessing the Potential of Hollow Graphitic Carbon Nanocages for Enhanced Methanol Oxidation Using PtRu Nanoparticles.

Direct Methanol Fuel Cell (DMFC) is a powerful system for generating electrical energy for various applications. However, there are several limitations that hinder the commercialization of DMFCs, such as the expense of platinum (Pt) at market price, sluggish methanol oxidation reaction (MOR) due to carbon monoxide (CO) formation, and slow electrooxidation kinetics. This work introduces carbon nanocages (CNCs) that were obtained through the pyrolysis of polypyrrole (Ppy) as the carbon source. The CNCs were characterized using BET, XRD, HRTEM, TEM, SEM, and FTIR techniques. The CNCs derived from the Ppy source, pyrolyzed at 750 °C, exhibited the best morphologies with a high specific surface area of 416 m2g-1, allowing for good metal dispersion. Subsequently, PtRu catalyst was doped onto the CNC-Ppy750 support using chemical reduction and microwave-assisted methods. In electrochemical tests, the PtRu/CNC-Ppy750 electrocatalyst demonstrated improved CO tolerance and higher performance in MOR compared to PtRu-supported commercial carbon black (CB), with values of 427 mA mg-1 and 248 mA mg-1, respectively. The superior MOR performance of PtRu/CNC-Ppy750 was attributed to its high surface area of CNC support, uniform dispersion of PtRu catalyst, and small PtRu nanoparticles on the CNC. In DMFC single-cell tests, the PtRu/CNC-Ppy750 exhibited higher performance, approximately 1.7 times higher than PtRu/CB. In conclusion, the PtRu/CNC-PPy750 represents a promising electrocatalyst candidate for MOR and anodic DMFC applications.

Calcium decorated Copper@Nitrogen-Doped carbon towards highly selective hydrogenation of biomass derived furfural

In the present research, calcium decorated copper@nitrogen-doped carbon (marked as Cu1Cax@CN) derived from biomass was constructed for highly selective hydrogenation of bio-based furfural (FFR), which remarkably favored furan ring hydrogenation for tetrahydrofurfuryl alcohol (THFA) formation via regulating the hydrogenation path. Remarkably, the in-situ generated basic sites from N- and Ca-containing species were beneficial to the good metal dispersion as well as the chemical activation of aldehyde and C=C groups, thus favoring the FFR-to-THFA transformation. The optimal basic density-to-copper mass ratio in a range of 3.0 ∼ 4.0 was attained, in consideration of THFA generation. The as-prepared Cu1Ca0.87@CN catalyst could afford full FFR conversion as well as 75.6 % THFA yield under 3 MPa H2 atmosphere, which also exhibited excellent stability and could be recycled four times without any deactivation. In addition, the basic sites in the as-prepared Cu1Cax@CN samples were capable of activating both the C=O and C=C bonds, and the activation of C=O bond took precedence over that of C=C bond, especially in the case of relative low temperatures. Plausible reaction mechanism for FFR-to-THFA transformation under the synergistic effect of active Cu0 center and basic sites was proposed in detail.

On the scope of mechanochemical activation: The case of Cu/ZnO catalytic systems

ZnO was submitted to different conditions of high-energy ball milling to thoroughly study the outcome of mechanochemical activation. Structural modifications led to a decrease in crystallite size and an increase in micro-strain and specific surface area (SBET) with milling time. Different copper amounts were added on pristine (reference) and activated support by incipient wetness impregnation. Cu deposited over activated support showed an enhanced metal-support interaction since part of Cu2+ could be introduced into milled ZnO lattice, replacing Zn2+ ions and/or locating in lattice interstitials. Moreover, further analyses suggested an electron transfer from activated support to metal, generating a mixture of Cu2O–CuO species, particularly at the interface between metal and support. N2O chemisorption studies gave Cu particle sizes of 1.3, 1.9 and 3.5 nm (for 0.2, 0.5 and 1 wt% Cu, respectively) and thus a good metal dispersion over ZnO was achieved. Hence, support's activation by milling process showed to be an excellent approach to improve both metal-support interaction and metal dispersion of supported catalysts.

Well-dispersed ZIF-derived N-doped carbon nanoframes with anchored Ru nanoclusters as HER electrocatalysts

Nano-structuring and metal-support interactions are effective methods to improve the electrocatalytic activity of heterogeneous catalysis. In this study, we synthesized nitrogen-doped porous carbon substrates by using a SiO2-protected calcination strategy with ZIF-8 as a precursor. The experimental results revealed the prepared porous nitrogen-doped carbon (PNC) to have high dispersion, large specific surface area, and rich pore structure, allowing high exposure of active sites. The carbon support showed optimum characteristics to deposit precious metals with small particle sizes. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) showed that the N groups on the PNC substrates served as coordination sites for Ru, allowing the formation of ultrafine nanoclusters. The Ru clusters showed good metal dispersion, exposing more active sites and improving the utilization of the precious metal. At a current density of 10 mA/cm2, Ru/PNC showed a minimum overpotential of 40 mV. This work provided a simple and effective method for the preparation of excellent carbon substrates and the synthesis of metal clusters with small particle sizes.

An overview on Metal doped / Supported Ceria Catalysts: Synthesis, Characterization and Applications

Design of viable catalysts that exhibits high catalytic activity and stability, as well as resistance against deactivation could be achieved by selecting the right active metal and support, understanding their structure, synergy or the metal support interaction and by employing the right preparation technique. Numerous studies and reviews have dealt with various aspects of CeO2 based catalysts, with the sole target of understanding its activity in various reactions such as dry and steam reforming of methane. Good metal dispersion on CeO2 surface is explained to be the reason for the promising activity of this systems. This review focuses on the synthesis, characterization and application of some CeO2 doped/supported catalysts in hydrogen production by dry and steam reforming of methane, and other reactions. Various synthetic methods for the preparation of the metal doped/supported CeO2 catalysts were introduced with a focus on how to effectively produce stable and efficient catalysts. Subsequently, some advanced characterization techniques were presented to precisely probe the metal and CeO2 at the atomic level, which is critical in investigating the structure of the catalysts.

Hierarchical pore construction of alumina microrod supports for Pt catalysts toward the enhanced performance of n-heptane reforming

Regulation of pore hierarchy has been an important subject in the design of industrial catalysts. Synthesis of alumina without template/additive often results in poor control of morphologies, porosities, and metal dispersion thereafter. Herein, alumina microrods with a tailored pore hierarchy (Rod2) were fabricated without template/additive by tuning the pore structure of the synthetic precursors, which were used as supports of Pt for n-heptane reforming. Improved toluene selectivity was observed at low space velocities as a result of promoted dehydroisomerization of pentacyclic hydrocarbons, presumably due to a combined effect of the desired pore hierarchy and rod morphology. The Pt/Rod2 also showed better resistance to carbon deposition while maintaining good metal dispersion, as compared to alumina supports with spherical morphology or uncontrolled pore hierarchy. The simulation results revealed that the improved toluene selectivity of Pt/Rod2 is attributed to the proper pore combination of meso-pore1 (6–40 nm) and meso-pore 2 (40–300 nm).

Preparation of anisole in phenol by Zn/HZSM-5 catalyst from walnut shell catalyzed liquefaction

The promotional effect of Zn was investigated relative to the calcining activation of HZSM-5. It was found that the lignin separated from walnut shell could be liquefied into small molecular ethers such as anisole by the promotional effect of the modified catalyst. Experimental results showed that, after the loading of Zn, the HZSM-5 catalyst retained its original crystal structure, which exhibited good metal dispersion. Besides, due to the existence of two interactions respectively of Zn with Al and Zn with a Brønsted-Lowry acid on the Zn/HZSM-5 catalyst surface, the remaining catalyst intergranular distance increased, particularly for the 2% Zn/HZSM-5 catalyst. The inside of the catalyst was in a state of spherical particle aggregation with a narrow pore size distribution and uniform particle size. The peak intensity of the Si-O stretching vibration was affected by the content of Zn, which was least affected for the 2% Zn/HZSM-5 catalyst. The signal peak of this small molecule ether was not found in the absence of the metal ions, and the catalytic effect of 2% Zn/HZSM-5 was more distinct. Calculated by the mass difference method, the yield of the liquid via the 2% Zn/HZSM-5 catalyst was 59.8%, including phenol and small molecule ethers represented by anisole.

Separation of Metal-N4 Units in Metal-Organic Framework for Preparation of M-Nx/C Catalyst with Dense Metal Sites.

Metal and nitrogen codoped carbon (M-Nx/C) materials with good metal dispersion in a carbon matrix have attracted great attention because they can efficiently catalyze various kinds of chemical/electrochemical reactions. However, the existing strategies for preparing M-Nx/C materials still face the challenge of metal site aggregation when the carbon skeleton in the precursor is substantially lost during pyrolysis. Herein, we propose a general strategy that the increase of metal site density and inhibition of metal aggregation could be realized by separating M-N4 units in metal-organic frameworks (MOFs). The metal sites can be well separated and distributed in carbon materials during the pyrolysis of a metal-coordinated block copolymer, one of the specific MOFs. The strategy can be widely applicable for the synthesis of M-Nx/C materials with dense metal sites, such as Fe-, Mn-, Ni-, and Co-Nx/C materials, which are potentially used as the efficient catalysts for various kinds of reactions. Taking Fe-Nx/C as a model oxygen reduction reaction (ORR) electrocatalyst, it shows the ORR half-wave potentials of 0.90 and 0.81 V vs RHE in alkaline and acidic electrolytes, respectively.

A silica-supported Ni-based catalyst prepared using TEPA for the plasma synthesis of ammonia

Ammonia is a potential hydrogen carrier and can be used as an alternative fuel. In this study, plasma cooperative catalytic synthesis ammonia was used. The catalyst consisted of Ni impregnated into silica, using one of three complexing agents (TEPA, EDTA and GLY) and compared with conventional impregnation methods. The unsaturated coordinated Ni(tepa)2+ will coordinate with the hydroxyl groups on the silica surface. When using the catalyst prepared by TEPA, the ammonia synthesis rate was 3.8 times higher than with no catalyst, and 1.4 times higher than the catalyst made by conventional impregnation method. XRD and TEM show that the catalyst prepared using TEPA exhibited the smaller metal particle size, the higher dispersion and the stronger interaction between metal and support than other catalysts. XPS indicate that the good metal dispersion of the catalyst facilitate form more Ni3N during the reaction, which will greatly improve the activity of the catalyst.

Pd/HZSM-5 catalyst for n-hexane isomerization: Properties, activities, and deactivation

The activity of n-hexane isomerization with 0,8 %kl Pd/HZSM-5 was studied in a micro reactor in the temperature range of 225-325 oC at 0,1 Mpa with the molar ratio H2/ hydrocarbon of 5.92, n-hexane concentration of 9.2 %mol, GHSV 2698 h-1 at atmospheric pressure. The catalyst owned suitable acidity, reasonable reductivity, good metal dispersion, and appropiate balance between metallic and acidic functions. The catalyst had high activity but low stability. The cause of deactivation was examined via a comparison of physico-chemical properties between a fresh catalyst and a used one. There was no metal sintering. The mono-metallic catalyst performed high activity for n-hexane hydro-isomerization but less stable. Deactivation is mainly attributed to coke formation. Catalyst activity and stability were significantly improved with activity of 0,7 MPa compared to that of 0,1 MPa at elevated pressure. The catalyst Pd-Co/HZSM-5 is capable of resisting against coke, thereby exhibiting high stability at 0,1 MPa. The highly stable and active catalyst helped to form high quality products to result in environment-friendly gasoline.

Influenced of Ni loading on SBA-15 synthesized from oil Palm ash silica for syngas production

The nickel loading (1-3wt.%) effect on SBA-15 prepared via sol-gel method for dry reforming of methane (DRM) was investigated. Silica source of sodium silicate-oil palm ash (Na2SiO3-OPA) was obtained from extraction of OPA using mass ratio Na2SiO3/P123~2.9. The SBA-15 was synthesized via hydrothermal treatment reflux route at treatment temperature of 80 °C. A vertical stainless steel fixed-bed reactor was applied for catalytic DRM process at 800 °C, atmosphere pressure and ratio CH4:CO2 is 1:1 for 30 h. Characteristic of structure SBA-15 was successfully analyzed by TEM, indicates to the positive role of Na2SiO3-OPA as silica sources. XRD, BET and FTIR results revealed that 2Ni/SBA-15 exhibited high surface area (460.89 m2/g) and pore diameter (6.53 nm), small NiO particle (14.71 nm) which assist good metal dispersion and led to better metal-support interaction. The increase of Ni loading from 1 to 3wt.% results in lowering the surface area and pore volume of catalyst as more Ni particles tend to agglomerate and positioning on the SBA-15 pores. The performance of Ni/SBA-15 catalyst in DRM decrease with the trend of 2Ni/SBA-15>3Ni/SBA-15>1Ni/SBA-15 whereby the H2/CO followed the order of 2Ni/SBA-15≈3Ni/SBA-15>1Ni/SBA-15.These studies revealed the Ni loading influences the metal-support interaction and significantly affect the H2/CO production.

Catalytic Steam Gasification of Glucose for Hydrogen Production Using Stable Based Ni on a γ–Alumina Fluidizable Catalyst

Abstract Six different Ni-based fluidizable catalysts were synthesized using both incipient impregnation and co-impregnation. Ni-based catalysts were also promoted with 2.0 wt% La or alternatively with 2 wt% Ce. The preparation procedure included catalysts treated at high temperatures and under free of oxygen conditions. Catalysts were characterized using BET, XRD, AA, PSD, TPR, TPD, H2-chemisorption. TPR and H2 chemisorption showed good metal dispersion with 10 nm- 40 nm metal crystallites. Glucose catalytic gasification runs were performed in a CREC Riser Simulator to evaluate the following catalysts: (a) 5 %Ni/γ-Al2O3, (b) 5 %Ni-2 %La/γ-Al2O3 and (c) 5 %Ni-2 %Ce/γ-Al2O3. In all cases, the preparation steps involved acid solutions with pHs of 1 and 4. In between consecutive runs, different approaches were considered: (a) A catalyst was regenerated by air, (b) A catalyst was regenerated by air followed by hydrogen pretreatment, (c) A catalyst was reused directly without any regeneration or hydrogen pretreatment. It was observed that Ni-based catalysts, which were subjected after every run, to both, air regeneration and hydrogen pretreatment, displayed the best yields in close agreement with thermodynamic equilibrium. On the other hand, Ni-based catalysts regenerated with air only, showed the worst hydrogen yields. In between these two-hydrogen yield limits, where catalysts not contacted with air nor hydrogen, with these yields being moderately below chemical equilibrium. This shows that Ni-based fluidizable catalysts can perform on stream for extended periods, requiring limited reactivation with air and H2. This makes of gasification using the catalysts of the present study, a viable process alternative that could be implemented at industrial scale.

Enhanced Metal–Support Interaction in Ni/Co3O4/TiO2 Nanorods toward Stable and Dynamic Hydrogen Production from Phenol Steam Reforming

The fabrication of highly stable Ni and Co3O4 nanocube-supported TiO2 nanorods (NRs) catalysts with improved metal–support interaction for steam reforming of phenol (SRP) has been investigated. An enhanced catalytic performance of Ni/Co3O4/TiO2 NRs with H2-rich gas and hardly formed coke was achieved and rationalized with spectroscopic results and structural assessments. Over 10% Ni/5% Co3O4/TiO2 NRs, SRP and water gas shift reactions dominate, producing mostly H2 and CO2, yet Ni/TiO2 microparticles promoted CO. With catalyst loading, steam-to-carbon ratio, and gas hourly space velocity, the H2 yield was improved with higher CO2/CO ratio and low CO yield. A Ni/Co3O4/TiO2 NRs catalyst possesses excellent stability, which prevailed for more than 100 h without obvious deactivation. The high performance was due to a 1D TiO2 NRs/Co3O4 nanocubes heterojunction, good metal dispersion, and higher reducibility, thereby providing a strong interaction of bimetallic active sites. This study reveals that Co3O4 promote...

Nano sheets, needles and grains-like CuO/γ-Al2O3 catalysts’ performance in carbon monoxide oxidation

This research deals with preparation, characterization and shape dependent performance of copper oxide nanomaterials (CuO NMs) in simple carbon monoxide (CO) oxidation catalysis. Uniform and high purity rice grains-like, needle-like and sheet-like CuO NMs were achieved by adopting different experimental conditions. The shape selective CuO NMs were physically mixed and re-pelletized with γ-Al2O3 thus 1 wt% CuO/γ-Al2O3 catalyst was prepared. The catalysts exhibited good surface area (186–190 m2 g−1), crystallinity, thermal stability and metal dispersion. The performance of various shape CuO/γ-Al2O3 catalysts in CO oxidation catalysis showed that needle-like CuO NMs performed superior against grains-like or sheet like CuO NMs in the temperature region between 200 and 225 °C. The 100% CO2 formation was achieved at 325 and 400 °C in the dry and wet conditions. Also, in every process temperature, differences in the catalytic activity due to catalyst's shape could be noted significantly. It was observed that the catalyst morphology played main role in achieving efficient catalytic process.

Understanding the performance and mechanism of Mg-containing oxides as support catalysts in the thermal dry reforming of methane.

Dry reforming of methane (DRM) is one of the more promising methods for syngas (synthetic gas) production and co-utilization of methane and carbon dioxide, which are the main greenhouse gases. Magnesium is commonly applied in a Ni-based catalyst in DRM to improve catalyst performance and inhibit carbon deposition. The aim of this review is to gain better insight into recent developments on the use of Mg as a support or promoter for DRM catalysts. Its high basicity and high thermal stability make Mg suitable for introduction into the highly endothermic reaction of DRM. The introduction of Mg as a support or promoter for Ni-based catalysts allows for good metal dispersion on the catalyst surface, which consequently facilitates high catalytic activity and low catalyst deactivation. The mechanism of DRM and carbon formation and reduction are reviewed. This work further explores how different constraints, such as the synthesis method, metal loading, pretreatment, and operating conditions, influence the dry reforming reactions and product yields. In this review, different strategies for enhancing catalytic activity and the effect of metal dispersion on Mg-containing oxide catalysts are highlighted.

Catalytic wet oxidation of aniline over Ru catalysts supported on a modified TiO2

The catalytic wet air oxidation of aniline over Ru catalysts supported on modified TiO2 (TiO2, Ti0.9Ce0.1O2, Ti0.9Zr0.1O2) is investigated. A series of characterization techniques are conducted to determine the relationship between the physico-chemical properties and the catalytic performance. As a result of the good metal dispersion and large number of surface oxygen species, the Ru/Ti0.9Zr0.1O2 catalyst presents the best catalytic activity among the tested samples. The effects of the operating conditions on the reaction are investigated and the optimal reaction conditions are determined. Based on the relationship between the by-products concentration and the reaction time, the reaction path for the catalytic oxidation of aniline is established. Carbonaceous deposits on the surface of the support are known to be the main reason for catalyst deactivation. The catalysts maintain a constant activity even after three consecutive cycles.

Enhanced Production of Aromatic Hydrocarbons by Rapeseed Oil Conversion over Ga and Zn Modified ZSM-5 Catalysts

Rapeseed oil conversion has been investigated over catalysts based on Ga- and Zn-modified nanocrystalline HZSM-5 zeolite aimed to the production of hydrocarbons that could be used as both raw chemicals and/or fuels. The reactions have been carried out in a fixed bed reactor operating under nitrogen at 550 °C and atmospheric pressure. The incorporation of the metallic species to the parent zeolite was carried out by wetness-impregnation, resulting in a good metal dispersion, which is facilitated by the relatively high external surface area available in the nanocrystalline zeolitic support. This metal addition causes significant changes in the textural and acidic properties of the ZSM-5 zeolite. In all cases, a high deoxygenation degree of the raw oil was achieved through the formation of CO, CO2, and H2O, whereas the main products obtained were light olefins (mainly ethylene and propylene) and aromatic hydrocarbons (BTX). The incorporation of Ga and Zn in the parent zeolite increased the formation of gasol...

Synthesis and facile size control of well-dispersed cobalt nanoparticles supported on ordered mesoporous carbon

Ordered mesoporous carbons, as potential catalyst supports, have attracted great attention in the catalysis field in recent years. Researchers have attempted to introduce guest particles into these carbons by versatile methods. Great success has been achieved with noble metal particles because of their lower sintering tendency. However, challenges occurred with more active metals such as cobalt because of their much higher sintering tendency, the hydrophobic nature of the carbon surface and channel confinement effects, which were believed to have prevented the wetness of the surface. Most researchers found that the carbon surface had to be specially treated to achieve good metal dispersion. In our current work, cobalt@carbon composites were synthesized using CMK-3 as the carbon support and cobalt nitrate hexahydrate as the metal precursor. We demonstrated the facile control of the metal particle size and dispersion by carefully controlling the impregnation conditions according to the physical chemistry of the precursor. Our results suggested that not only the acid pre-treatment of the carbon surface and the ammonia post-treatment of the cobalt nitrate precursor improved the metal dispersion but also simple impregnation itself could achieve good metal dispersion if the preparation conditions were controlled as suggested. Highly thermal stable cobalt@carbon composites with very well-controlled cobalt dispersion (15 wt%) and particle size (∼4–20 nm) were produced.

Influence of alumina binder content on catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone.

The influence of the amount of alumina binders on the catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone was investigated in a fixed-bed reactor. N2 sorption, X-ray diffraction, H2-chemisorption and temperature-programmed desorption of ammonia were used to characterize the catalysts. It can be observed that the Ni/HZSM-5 catalyst bound with 30 wt.% alumina binder exhibited the best catalytic performance. The high catalytic performance may be due to relatively good Ni metal dispersion, moderate mesoporosity, and proper acidity of the catalyst.

Supported palladium–copper catalysts: Preparation and catalytic behavior in hydrogen-related reactions

Two series of highly dispersed supported Pd–Cu catalysts were prepared using different supports: highly acidic aluminum fluoride HS-AlF3, characterized by high surface area, and active carbon, both prepared by different preparation methods (fluorolytic sol–gel method and co-impregnation). A variety of techniques: chemisorption of hydrogen, XRD, TEM, and catalytic performance in two hydrogen-related probe reactions (in n-pentane hydroisomerization and CCl4 hydrodechlorination) were employed to probe metal dispersion and the extent of interaction between two metal components. A reasonable degree of bimetal intermixing in Pd–Cu/HS-AlF3 catalysts synthesized by fluorolytic co-gelation was recognized by the catalytic behavior in bifunctional hydroisomerization of n-pentane. A significantly decreased, compared to pure palladium, hydrogenation–dehydrogenation potential of Pd–Cu alloys led to a weaker performance of bimetallic catalysts. Similarly, it was found that incipient wetness co-impregnation of active carbon resulted in the formation of catalysts characterized by good metal dispersion and significant extent of Pd–Cu alloying. Although the monometallic 2wt% Cu/carbon catalyst is nearly inactive in CCl4 hydrodechlorination, copper addition to palladium in the co-impregnated catalysts had very pronounced effect, vastly increasing the selectivity toward longer than methane hydrocarbons.