High Metal Dispersion Research Articles

Synthesis of PtCo3 polyhedral nanoparticles and evolution to Pt3Co nanoframes

Bimetallic nanoframes have great potential for achieving new levels of catalytic activity in various heterogeneous reactions due to their high surface area dispersion of expensive noble metals on the exterior and interior surfaces of the structure. PtCo3 nanoparticles with polyhedral shapes were synthesized by a hot-injection method. Scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy (EDS) showed that these nanoparticles demonstrated elemental segregation of platinum to the edges of the polyhedron, forming the basis for a framework nanostructure. The process of preferential oxidative leaching which removed cobalt from the interior of the framework was tracked by EDS and inductively coupled plasma optical emission spectroscopy. This evolution procedure left the platinum-rich edges intact to form a Pt3Co nanoframe. This is the first reported synthesis of a platinum–cobalt nanoframe and could have potential applications in catalytic reactions such as oxygen reduction.

Catalytic Biomass Gasification to Syngas Over Highly Dispersed Lanthanum‐Doped Nickel on SBA‐15

AbstractCatalytic biomass gasification is an environmentally benign solution to energy problems. A series of Ni catalysts on mesoporous SBA‐15 are synthesized with various La2O3 loadings. The catalytic activity of unpromoted Ni/SBA‐15 catalyst indicates that it has a high carbon formation rate, resulting in fast deactivation. In contrast, addition of La2O3 to Ni/SBA‐15 catalyst helps to remove deposited carbon by formation of oxycarbonate, resulting in higher CO production. A 1 % La doping in the Ni/SBA‐15 catalyst is sufficient to achieve high activity and stability in biomass gasification with various raw materials and in the steam reforming of toluene as a tar model compound. The combination of small metal particle size, high metal dispersion, high surface area of SBA‐15, the crucial role of La in carbon removal, and the novel synthesis method result in a highly active, stable, and effective 1 % La‐Ni/SBA‐15 catalyst for biomass gasification.

PtZn‐ETS‐2: A novel catalyst for ethane dehydrogenation

Catalysts having unprecedented selectivity toward ethane dehydrogentation were prepared by combining platinum and zinc on the surface of the titanate ETS‐2. This high surface area, sodium titanate ion exchanger affords high metal dispersion, presents many active sites to the gas stream, and is free of any pore structure that can influence mass transfer to and away from the active sites. It was determined that the addition of zinc to platinum‐loaded ETS‐2 changes the electronic properties of the metals and significantly improves the specificity of the catalyst. By changing the zinc‐to‐platinum ratio, and by manipulating the space velocity of the gas, the production of side products and coke can be suppressed or eliminated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4367–4376, 2015

Palladium-nanoparticles on end-functionalized poly(lactic acid)-based stereocomplexes for the chemoselective cinnamaldehyde hydrogenation: Effect of the end-group

Differently carboxylic acid end-functionalized poly(lactic acid) (PLA)-based stereocomplexes were used as polymer support to stabilize Pd-nanoparticles (NPs) generated by the metal vapor synthesis technique. The dispersion of Pd was strongly dependent on the end-group present in the polymer structure, as shown by HRTEM measurements. 2,2′-Bipyridine- and pyridine-based stereocomplexes showed high metal dispersion (i.e. well-separated Pd-NP size of 2.0±0.6nm), whereas stereocomplexes bearing benzyl and carboxylic acid end groups exhibited strong Pd-NPs aggregation. The heterogenous catalysts were employed to chemoselectively hydrogenate the CC double bond in cinnamaldehyde, showing for Pd-NPs, stabilized by the 2,2′-bipyridine-modified polymer support, the best performance in terms of chemoselectivity (99%) and recyclability in THF solution. Even under bulk cinnamaldehyde hydrogenation conditions, chemoselectivity for 3-phenylpropanal of 90% at 88% conversion was obtained.

Catalytic structure and reaction performance of PtSnK/ZSM-5 catalyst for propane dehydrogenation: influence of impregnation strategy

In this study, a series of PtSnK/ZSM-5 catalysts for propane dehydrogenation were prepared by changing the impregnation sequence of platinum and tin precursors (co-impregnation and successive impregnation). To investigate the influence of impregnation strategy on the catalyst structure and the reaction performance, the prepared samples were studied by several techniques, including XRD, nitrogen adsorption, ICP, TEM, NH3-TPD, FT-IR, hydrogen chemisorption, H2-TPR, and TPO. It was found that the prepared sample with co-impregnation method showed the highest reaction stability and selectivity when comparing with the ones prepared by the sequential impregnation. As for the co-impregnated catalyst, high metal dispersion, strong interaction of Pt with Sn oxide together with the decreased catalyst acidity were all responsible for the improved reaction properties and better catalytic capacity to resist the coke. Nevertheless, over the sequentially impregnated catalysts, the increased catalyst acidity and the relatively easy reduction of tin species were found when the Pt components were deposited first. Furthermore, the successive impregnation with inverse sequence led to the wide metallic distribution and the restricted transformation of the active sites. All of these factors were disadvantageous to the reaction to be carried out. Finally, a model for the influences of impregnation sequence was proposed based on the obtained results.

Effect of Strontium on the Catalytic Activity and Physicochemical Properties of Ru/Mn Catalysts for CO<sub>2</sub> Methanation Reaction

The recycling technology by the catalytic conversion offers a very promising technique for reducing greenhouse CO2 gas from flue gases of coal burning power plant by converting the carbon dioxide gas to methane. The methane produced from the reaction can be used as other fuel to run turbine for electricity generation. Therefore, the strontia based catalysts was prepared by impregnated with RuMn/Al2O3 catalyst and then calcined at 1000°C for 5 hour. Strontia catalyst is an effective material because of its highly basic properties which could enhance carbon dioxide adsorption and chemisorption on the catalyst surface but not been widely explored. The result obtained revealed that the addition of Sr to RuMn/Al2O3 as based catalyst had increased the catalytic activity and found to be more active for promoting the CO2 methanation reaction. Under reducing pretreatment at 300°C, the activity of CO2 conversion increased about 30.98% which is from 50.45% over RuMn-65/Al2O3 catalyst to 73.10% over RuMnSr-65/Al2O3 catalyst with 40% of methane yielded at reaction temperature of 210°C. The Sr addition did not modify the crystalline structure of the catalyst but gave higher surface area, smaller particle size and high metal dispersion as well as increased the degree of reduction and CO chemisorption.

Catalytic steam reforming of volatiles released via pyrolysis of wood sawdust for hydrogen-rich gas production on Fe–Zn/Al2O3 nanocatalysts

Thermo-chemical processing of biomass is a promising alternative to produce renewable hydrogen as a clean fuel or renewable syngas for a sustainable chemical industry. However, the fast deactivation of catalysts due to coke formation and sintering limits the application of catalytic thermo-chemical processing in the emerging bio-refining industry. In this research, Fe–Zn/Al2O3 nanocatalysts have been prepared for the production of hydrogen through pyrolysis catalytic reforming of wood sawdust. Through characterization, it was found that Fe and Zn were well distributed on the surface with a narrow particle size. During the reactions, the yield of hydrogen increased with the increase of Zn content, as Zn is an efficient metal promoter for enhancing the performance of the Fe active site in the reaction. The 20% Fe/Al2O3 catalyst with Zn/Al ratio of 1:1 showed the best performance in the process in relation to the hydrogen production and resistance to coke formation on the surface of the reacted catalyst. All the catalysts showed ultra-high stability during the process and nearly no sintering were observed on the used catalysts. Therefore, the nanocatalysts prepared in this work from natural-abundant and low-cost metals have promising catalytic properties (high metal dispersion and stability) to produce H2-rich syngas with optimal H2/CO ratio from the thermo-chemical processing of biomass.

Preparation of highly active and stable NiO–CeO2 nanocatalysts for CO selective methanation

In the present work, a group of nickel-ceria nanocatalysts was synthesized by co-precipitation method and their catalytic performances were considered in CO methanation reaction. The catalysts were characterized by XRD, BET, SEM, TEM, H2-TPR, CO chemisorption and CO-TPD techniques. The results showed that addition of nickel content up to 50 wt.% increased both the CO conversion and CH4 selectivity at low temperatures while further increase in nickel content adversely affected them. The 50%Ni/CeO2 catalyst revealed an excellent activity in CO methanation due to high surface area (258 m2/g), small nickel particle size (below 5 nm) and high metal dispersion (7.31%). In CO selective methanation, CO2 conversion was completely suppressed until CO conversion reached to a maximum value, which is an important factor from commercial view point where is needed to extend operating temperature window between maximum of CO conversion and suppressing of CO2 methanation.

Liquid phase conversion of Glycerol to Propanediol over highly active Copper/Magnesia catalysts

In this work, a series of Cu/MgO catalysts with different copper metal loading were prepared by the precipitation-deposition method. Their catalytic behaviour was investigated for glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO). The physico-chemical properties of the catalysts were characterized by various techniques such as BET surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), NH3-temperature programmed desorption (NH3-TPD) and scanning electron microscopy (SEM) methods. The characterization results showed that the copper metal was well-dispersed over MgO support and a new phase Cu-MgO was also identified from XRD results after calcination. The 25Cu/MgO (Cu:25 wt%) catalyst exhibited the highest glycerol conversion of 88.7% and 1,2-PDO selectivity of 91.7% at 210∘C, 4.5 MPa of hydrogen pressure after 12 h. The high glycerol conversion was mainly due to the Cu dispersion on MgO support and high acidic strength. Further, the effects of temperature, hydrogen pressure, catalyst loading and glycerol concentration were studied over 25Cu/MgO catalyst for optimization of reaction parameters. Kinetic study over highly active 25Cu/MgO catalyst showed that the reaction followed the pseudo second order rate with respect to glycerol and the apparent activation energy was found to be 28.7 ± 0.8 kcal/mol. Highly active Cu/MgO catalysts were prepared by precipitation-deposition method and investigated for glycerol hydrogenolysis to 1,2-propanediol. The 25Cu/MgO catalyst was exhibited the highest glycerol conversion of 88.7% with 91.7% selectivity to 1,2-propanediol. The higher activity is due to the high dispersion of copper metal and synergetic effect of Cu-MgO phase.

Investigation of the Pt/MOR–Al2O3 Catalysts by IR Spectroscopy

Pt/MOR–Al2O3 catalysts, with platinum supported from H2PtCl6 and [Pt(NH3)4]Cl2 solutions are investigated in the work with the methods of IR spectroscopy. The received results testify about platinum fixing mainly in channels of a mordenite in case of supporting from an ammine, and its localization on Al2O3 surface when supporting from chloroplatinic acid. Small concentration of the absorption bands referred to bridging CO species on platinum testify about high dispersion of metal on samples. Data explain higher activity of the catalysts prepared with [Pt(NH3)4]Cl2 in reactions of a hydroisomerization of benzene and an isomerization of cyclohexane.

A generalized method toward high dispersion of transition metals in large pore mesoporous metal oxide/silica hybrids

A series of transition metal acetylacetonates and acetates were used as precursors to generate high loadings of metal sites finely dispersed on SBA-15 silica. To achieve this, grafting of chelated transition metal precursors was performed directly to the surface of the as-synthesized SBA-15/P123 composite material. The thus-obtained metal/SBA-15 materials were studied by a variety of methods, e.g., elemental analysis, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance UV–visible spectroscopy (DR-UV–vis), X-ray photoelectron spectroscopy (XPS) and N2 physisorption measurements at −196°C. From the results, the proposed functionalization method was found to be a highly tunable and reproducible strategy to disperse transition metal oxides in mesoporous silica materials. The results from elemental analysis of the modified materials confirmed that the amount of grafted species is a function of the initial concentration of precursor in the solution used for grafting. The chelated complexes were found to strongly interact with the silanol groups of the silica material, resulting in a ligand-exchange process, as corroborated by FTIR. However, different metal precursors showed distinct reactivity towards the surface of mesoporous silica, owing to differences in the stability of the complexes under the conditions used for grafting. DR-UV–vis and XPS analyses suggest that when the stability of a given precursor decreases, the grafting procedure can lead to the formation of small clusters of the metal oxide on the silica surface. XRD and SEM also show that grafting of lower stability complexes, such as Mn(acac)3, Cu(acetate)2 and VO(acac)2, on the silica surface can result in the formation of large crystals on the external surface of the SBA-15 particles. Nevertheless, it was established by XPS analysis that only a small percentage of the grafted species leads to the formation of bulk crystals while the remaining species are substituted into the silica framework. Obviously, a well-controlled and increased dispersion of the metal cations/oxides on the surface of highly porous silica materials is of great interest since these MxOy–SiO2 mixed oxides could demonstrate high catalytic activity in a large variety of reactions.

Synthesis and characterization of mesoporous aluminas with different pore sizes: Application in NiMo supported catalyst for hydrotreating of heavy gas oil

The mesoporous alumina materials having different textural properties were synthesized by modifying the procedures mentioned in literature. Pluronic P-123 was used as structure directing agent (SDA) and aluminum isopropoxide was used as precursor for aluminum. The materials were characterized using N2 adsorption–desorption isotherms (BET), X-ray diffraction, FTIR and high resolution-TEM (HRTEM). BET, XRD and HRTEM analyses had confirmed the synthesis of mesoporous aluminas with different textural characteristics. The synthesized mesoporous aluminas were utilized as a support material for NiMo catalyst for hydrotreating of oil sands bitumen derived heavy gas oil, in a fixed bed reactor at industrial conditions. The catalytic activity was measured in terms of hydrodesulfurization (HDS) and hydrodenitrogenation (HDN). The catalysts were characterized by BET, XRD, FTIR, Raman, CO-chemisorption, HRTEM, TPD and TPR. The activity study for conventional NiMo/γ-Al2O3 was also performed for comparison. Six types of mesoporous aluminas and corresponding catalysts were synthesized based on HNO3/H2O ratio varying from 0 to 2. It was observed that with increase in water content the surface area, pore volume and pore diameter of mesoporous aluminas increase. Moreover, the structure changes form ordered hexagonal to wormlike/sponge-like and fibular and then to corrugated platelets/rod like structures with increase in water content. However, the morphology of structure was changed after loading of active metals and the catalytic active follows the order NiMo/Meso-Al-0.6>NiMo/Meso-Al-0.4>NiMo/Meso-Al-2≈NiMo/Meso-Al-0.2>NiMo/Meso-Al-0>NiMo/γ-Al2O3>NiMo/Meso-Al-1.25. The highest activity shown by catalyst NiMo/Meso-Al-0.6 could be assigned to (i) its higher pore volume and surface area, (ii) highest metal dispersion, (iii) more number of weak acidic sites and (iv) lower Mo reduction temperatures.

Diesel pre-reforming over highly dispersed nano-sized Ni catalysts supported on MgO–Al2O3 mixed oxides

Abstract A highly dispersed 50 wt% Ni/MgO–Al 2 O 3 catalyst was prepared by deposition–precipitation (DP) method for the diesel pre-reforming reaction. The pH of the precursor solution was controlled from pH 9.5 to 12.0 to examine the effects on NiO crystallite size and metal dispersion. The increase of pH of the precursor solution causes an increase of specific surface area and metal dispersion, and reduces NiO crystallite size. The pre-reforming reaction was carried out using n -tetradecane as surrogate compound of diesel. The coke formation of used catalysts was examined by TGA, TEM, SEM, and Raman analysis. The 50 wt% Ni/MgO–Al 2 O 3 catalyst prepared at pH 11.5 showed a high catalytic activity and excellent coke resistance due to high metal dispersion (8.71%), small NiO crystallite size (3.5 nm), and strong interaction between Ni and support. Furthermore, this catalyst showed a good stability in the pre-reforming reaction at S/C ratio of 3.5 and 450 °C for 88 h.

Hydrogen production from steam reforming of glycerol over Ni/CeZrO catalysts

Ni catalysts supported on the CeZrO solid solution with different compositions were prepared and characterized by powder X-ray diffraction, N2 physical adsorption, H2 chemisorption, temperature programmed reduction, and temperature programmed oxidation. Hydrogen production from the steam reforming of glycerol over these catalysts was investigated. Among the catalysts, Ni/CeZrO-3 with 77.3% Ce content shows the highest conversion of glycerol and selectivity of H2 as well as the best stability during the reaction. This could be due to the fact that Ni/CeZrO-3 has the highest metal dispersion which can prevent or minimize the carbon formation on the surface of the catalyst. On the other hand, the catalyst could generate the most mobile oxygen species during reaction, thus, decoking activity will likely be enhanced through the participation of the lattice oxygen. The effects of reaction temperature, H2O/glycerol molar ratio, and the feed flow rate on the steam reforming of glycerol over Ni/CeZrO-3 were also examined.

Carbon Supported Metal Oxide Nanoparticles: Hierarchical Porous Structure and Electrochemical Properties

Energy storage devices made from nanostructured electrodes are reported to be lightweight and possess promising performance. Interest is growing in new energy storage devices that are low cost, lightweight, and deliver high energy and power densities. Supercapacitors are important energy storage devices that can deliver high power during short periods of time, making them attractive for electric vehicle applications.Porous carbon supported metal oxide materials have been successfully used as electrode in supercapacitors. The efficiency of the electrochemical properties can be improved by using novel electrode with controlled nanostructure, nanoparticle size and electrochemical performance. In this work, hierarchically porous carbon supported metal oxides, including cobalt oxide and molybdenum oxide nanoparticles are designed, aiming to improve metal loading and dispersion with uniform nanoparticles, which in-turn enhances eletrochemical performance.The hierarchically porous carbon matrix synthesized has bimodal porous structure with 300-400 nm macropores and ~ 20 nm mesopores with a BET surface area of ~370 m2/g. Cobalt oxides and molybdenium oxides were loaded by a wet impregnation method. The electrochemical properties of the synthesized hybrid materials will be demonstrated.Current results demonstrate that cobalt oxide particles in the synthesized composites can be tuned from < 5 nm to 10 nm and are dispersed uniformly across the carbon matrix with loading as high as 15 wt%. Molybdenum oxide particles also can be well dispersed in the carbon matrix with a high loading up to 40 wt% and the valence of molybdenum can be tuned. We also demonstrate the network of meso- and macro- pores and high surface area offered by this type of carbon materials is promising to achieve high metal loadings and dispersion for better activity and mass transport.

Effects of synthesis methods on the performance of Pt + Rh/Ce0.6Zr0.4O2 three-way catalysts

The 0.7 wt% Pt + 0.3 wt% Rh/Ce0.6Zr0.4O2 catalysts were fabricated via different methods, including ultrasonic-assisted membrane reduction (UAMR) co-precipitation, UAMR separation precipitation, co-impregnation, and sequential impregnation. The catalysts were physico-chemically characterized by N2 adsorption, XRD, TEM, and H2-TPR techniques, and evaluated for three-way catalytic activities with simulated automobile exhaust. UAMR co-precipitation- and UAMR separation precipitation-prepared catalysts exhibited a high surface area and metal dispersion, wide λ window and excellent conversion for NOx reduction under lean conditions. Both fresh and aged catalysts from UAMR-precipitation showed the high surface areas of ca. 60–67 m2/g and 18–22 m2/g, respectively, high metal dispersion of 41%–55%, and small active particle diameters of 2.1–2.7 nm. When these catalysts were aged, the catalysts prepared by the UAMR method exhibited a wider working window (Δλ = 0.284–0.287) than impregnated ones (Δλ = 0.065–0.115) as well as excellent three-way catalytic performance, and showed lower T50 (169°C) and T90 (195°C) for NO reduction than the aged catalysts from impregnation processes, which were at 265 and 309°C, respectively. This implied that the UAMR-separation precipitation has important potential for industrial applications to improve catalytic performance and thermal stability. The fresh and aged 0.7 wt% Pt + 0.3 wt% Rh/Ce0.6Zr0.4O2 catalysts prepared by the UAMR-separation precipitation method exhibited better catalytic performance than the corresponding catalysts prepared by conventional impregnation routes.

Photocatalytic degradation of DIPA using bimetallic Cu-Ni/TiO2 photocatalyst under visible light irradiation.

Bimetallic Cu-Ni/TiO2 photocatalysts were synthesized using wet impregnation (WI) method with TiO2 (Degussa-P25) as support and calcined at different temperatures (180, 200, and 300°C) for the photodegradation of DIPA under visible light. The photocatalysts were characterized using TGA, FESEM, UV-Vis diffuse reflectance spectroscopy, fourier transform infrared spectroscopy (FTIR) and temperature programmed reduction (TPR). The results from the photodegradation experiments revealed that the Cu-Ni/TiO2 photocatalysts exhibited much higher photocatalytic activities compared to bare TiO2. It was found that photocatalyst calcined at 200°C had the highest photocatalyst activities with highest chemical oxygen demand (COD) removal (86.82%). According to the structural and surface analysis, the enhanced photocatalytic activity could be attributed to its strong absorption into the visible region and high metal dispersion.

Facile synthesis and enhanced catalytic performance of graphene-supported Ni nanocatalyst from a layered double hydroxide-based composite precursor

In this paper, graphene-supported Ni nanocatalyst (Ni/G) was prepared via self-reduction of a hybrid Ni–Al layered double hydroxide/graphene (NiAl-LDH/G) composite precursor. NiAl-LDH/G nanocomposite was assembled via a facile one-step coprecipitation route, which involved the nucleation and growth of NiAl-LDH, simultaneously accompanied by the reduction of graphene oxide without the addition of any reducing agents. The characterization results demonstrated that NiAl-LDH nanoplatelets were homogeneously dispersed on both sides of an exfoliated, structurally flexible graphene The graphene component in the precursor, serving as reducing agent, could in situ reduce Ni2+ species to Ni0 on heating under an inert atmosphere, thus facilitating the formation of highly dispersed Ni nanoparticles with a uniform size. Compared with those prepared by conventional methods, as-formed graphene-supported Ni nanocatalyst exhibited superior catalytic performance in the liquid phase selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde owing to the much higher metal dispersion and smaller size of Ni nanoparticles in the catalyst. The present finding provides a simple approach to fabricate new types of graphene-supported, metal-based heterogeneous catalysts with advanced catalytic performance.

Wet Air Oxidation of phenol over Pt and Ru catalysts supported on cerium-based oxides: Resistance to fouling and kinetic modelling

Ceria and doped ceria supported Pt and Ru catalysts were tested at 160°C in the Catalytic Wet Air Oxidation (CWAO) of phenol. Catalysts were compared in terms of activity, selectivity and resistance towards fouling. The respective influences of metal phase and support were studied. Under the selected operating conditions, 100% phenol conversion could be reached. Contrary to what was expected, improved Oxygen Storage Capacities (OSC) accelerated the accumulation of adsorbed species on the catalyst surface, therefore limiting the catalytic performance. By contrast, high metal dispersions enhanced both the elimination of aqueous organic compounds and the degradation of heavy molecules involved in the catalyst fouling. The progressive decrease in activity induced by carbonaceous deposits could be kinetically modelled using a simple reaction scheme.

Evaluating the performance of non-precious metal based catalysts for sulfur-tolerance during the dry reforming of biogas

A portfolio of catalysts with a nominal composition 15wt.%Ni+(0/5wt.%)Co/MaOx–NaOx–Al2O3 (where M=Mg, Ca, La, Y, Gd; N=Al, Zr) were synthesized and evaluated for biogas reforming application. Structure activity relations (SARs) were designed to help explain the significant difference in activity observed among the catalysts containing monometallic (Ni) and bimetallic species (Ni–Co) and among the bimetallic catalysts impregnated by altering the sequence of impregnation. The order of activity observed among the various catalyst formulations was: bi-metallic (reverse stepwise Co→Ni)>bi-metallic (simultaneous Ni+Co)>mono-metallic>bi-metallic (stepwise Ni→Co). From SARs it is established that high pore volume to surface area ratio, high metal dispersion, high reducibility and high support basicity are the essential traits of an active and stable catalyst. Analysis of variability (ANOVA) was performed to identify the main and interaction effects of various factors on both catalyst activity and catalyst textural properties. Impregnation sequence and promoter composition are found to have significant effects on both catalysts activity and its textural properties. Also, an empirical model equation that establishes a statistical relationship between the factors and the response variable was developed. In addition, a sensitivity analysis was performed to study the effect of surfactant to metal ratio, CH4-to-CO2 ratio, operating temperature, H2S concentration, cobalt amount, and support basicity on catalyst performance.