Surface Properties Of Support Research Articles

Ordered mesoporous alumina-supported vanadium oxides as an efficient catalyst for ethylbenzene dehydrogenation to styrene with CO2

Ordered mesoporous alumina (OMA)-supported vanadia catalysts with different vanadium loading (denoted as nV/OMA) were employed for ethylbenzene dehydrogenation to styrene with CO2 as soft oxidant, and a commercial γ-Al2O3-supported vanadia catalyst for comparison. The catalytic behavior depends strongly on the vanadium loading and the support properties. With an optimal V loading of 0.8 mmol/g-support, 0.8 V/OMA catalyst exhibits superior catalytic performance than that of 0.8 V/γ-Al2O3, which can be attributed to the excellent structural, textual, and surface properties of OMA support. The important roles played by OMA lies in stabilizing highly dispersed V5+ active species and preventing the coke formation.

Carefully designed oxygen-containing functional groups and defects of porous carbon spheres with UV-O3 treatment and their enhanced catalytic performance

In this paper, the support surface properties (surface oxygen-containing functional groups and structure defects) of porous carbon spheres (PCSs) were carefully designed by as UV assisted O3 technology. CO catalytic oxidation reactions performed over the supported Pd-Ce catalysts on modified porous carbon spheres. Results illustrated that the Pd-Ce/PCSs catalysts exhibited high CO catalytic activity, which were increased at first, and then decreased with UV assistant-O3 treatment time. The Pd-Ce/PCSs-30 catalyst exhibited superior activity and T100 was only 15 °C. Moreover, the Pd-Ce/PCSs-30 catalyst obtained an excellent stability, and 100% CO conversion could be maintained as the time on stream evolutes up to 16h in the presence of H2O in the feed. Based on characterization results, there were two main factors: (a) the surface area and pore volume were decreased with UV-O3 treatment, leading to the enhancement of Pd-Ce particle size, and the decrease of Pd-Ce nanoparticle dispersion and mass transfer efficiency, as well as the decrease of catalytic activity of Pd-Ce/PCSs, (b) the surface oxygen content and defect sites of PCSs were raised by UV-O3 treatment, which could improve surface loading of Pd, Ce and enhance PdOCe bonding interactions, thereby increasing the activity of Pd-Ce/PCSs.

A study of the synergy between support surface properties and catalyst deactivation for CO2 reforming over supported Ni nanoparticles

The correlation between surface acidity-basicity and catalyst deactivation have been investigated in the CO2 reforming of methane by adjusting the surface properties of the catalyst. Silica and alumina based support with different acidity-basicity have been prepared by two methods, (i) a solvothermal method and (ii) a sequential impregnation method. Then each of the supports has been decorated with Ni nanoparticles followed by variation of their activity towards CO2 reforming of methane (DRM). The catalytic materials have been analyzed before and after reaction by a variety of analytical techniques including BET, XRD, H2-TPR, XPS, CO2-TPD, NH3-TPD, O2-TPD, TG, O2-TPO, H2-TPH, SEM, and TEM. Catalysts with higher acidity were found to promote methane-cracking reactions, while the Boudouard and deactivation owing to metal oxidation were dominant at high basicity. Catalysts with more acidic or basic surfaces were found to be more prone to deactivation and metal sintering. The turnover frequency (TOF) and activation energy (Ea) of both the reactants showed a Gaussian curve with acidity-basicity of the catalyst surfaces. Among the tested catalysts, the best performing was those with homogeneous dispersion of surface acidic and basic sites, prepared by a single step synthesis. In contrast, under the same conditions, two-step synthesized supports with the significantly imbalanced distribution of acidic and basic sites favoured the Reverse water gas shift (RWGS) reaction, active metal oxidation by surface adsorbed oxygen and hence deactivated rapidly.

Preparation of supported catalyst by adsorption of polyoxometalate on graphene oxide/reduced graphene oxide

Adsorption of tungstophosphoric acid (H3PW12O40) as a polyoxometalate (POM) on graphene oxide (GO) and two reduced graphene oxide supports (RGO-a/RGO-b) for producing supported catalysts was studied using an equilibrium adsorption technique by ultraviolet–visible spectroscopy analysis. The surface properties of supports were analyzed by XPS to interpret their different adsorption properties. The samples were characterized by XRD, RAMAN, FTIR, SEM-EDX, and TEM analyses. The three most determinant parameters in adsorption phenomena are presence of oxygen functional groups on the support, the polarization of surface functional groups in accordance to the suspension pH, and the solvent type. The supported polyoxometalate on GO (GO/POM) prepared by adsorption in a suspension of 1:1 water/methanol mixture with pH = 3.5 yielded the highest adsorption capacity of 427 mg/g while the adsorption capacities of supported polyoxometalate on reduced samples were 74 mg/g and 54 mg/g, respectively. The pH-dependent behavior of ionizable surface oxygen functional groups was investigated and results revealed that also played a key role in the adsorption capacity. The highest POM adsorption was obtained in the pHs below isoelectric point of GO where POM anions can establish chemical bonds with the positive net surface charge. The highest adsorption capacity was obtained in the water-methanol mixture. The kinetics of adsorption mechanism was best described by a pseudo-second-order model.

Fabrication of Thin Metal-Organic Framework MOF Films on Metal-Ion-crosslinked GO-modified Supports

ABSTRACTThin films of metal-organic frameworks (MOFs) have shown promising for applications such as gas separation, gas storage, optoelectronics or sensing. However, synthesis of polycrystalline MOF films and membranes depends largely on the surface properties of supports, limiting the availability of common supports. It is, therefore, highly desirable to develop ways to modify the surface properties of common supports for the preferred heterogeneous nucleation of the MOFs. Here, we demonstrated that graphene-oxide (GO) can be exploited to readily modify the surface properties of common supports, thereby leading to well inter-grown polycrystalline MOF films. A prototypical zeolitic-imidazolate framework ZIF-8 was chosen as a model MOF system. The stabilization of GO layers with divalent metal ions was found a key step to synthesize well inter-grown ZIF-8 films. The effect of divalent metal ions on the stability of GO layers and the quality of the resulting ZIF-8 films were systematically investigated. Finally, the single gas permeation behaviors of the ZIF-8 films grown on GO-modified supports were tested.

CO Oxidation on Metal Oxide Supported Single Pt atoms: The Role of the Support

Supported metal single atoms have demonstrated excellent catalytic performance for many chemical transformations. The effects of support on the catalytic performance of supported single metal atoms, however, have not been clearly elucidated. We carried out a systematic investigation of the effects of supports on CO oxidation by single Pt (Pt1) atoms dispersed on different metal oxides: highly reducible Fe2O3, reducible ZnO, and irreducible γ-Al2O3. It was found that Pt1 atoms on three metal oxides are active for CO oxidation, and the chemical properties of supports determine the catalytic performance of Pt1 single-atom catalysts (SACs). Both the presence of −OH groups on support surfaces and the addition of H2O significantly modify CO oxidation on three SACs and reduce the effects of supports on their catalytic performances. We conclude that the interaction between single metal atoms and support as well as surface properties of supports control the catalytic behavior of SACs.

Effect of Carbon Support and Synthesis Method on Pt NP Utilization and Activity

A key requirement for the large-scale commercialization of proton exchange membrane (PEM) fuel cells is to produce highly active, durable catalysts, while minimizing the use of precious noble metals, especially platinum (Pt). Higher utilization of Pt catalyst can be realized by understanding the effect of the carbon support microstructure on the distribution and formation of Pt nanoparticles (NPs) and by optimizing the synthesis method. In this work, Pt NPs were fabricated using a simple alcohol reduction method and then varying the carbon support pore structure and surface properties. The catalysts were then tested for their activity in 1 M C2H5OH + 0.5 M H2SO4 solutions. For Pt NP preparation, either ethanol or butanol were used as the solvent and reductant. The ethanolic or butanolic solution containing H2PtCl6 was then added to the carbon support dispersed in the same solvent at room temperature, and the mixture was heated at the boiling point for 2 hrs. In the case of the ethanol solvent, an aqueous alkaline solution was added to ensure the completion of Pt reduction [1]. However, this step was not used during synthesis when using butanol, due to its higher reducing power. Three types of carbon supports were investigated, Vulcan carbon (VC), Ketjenblack (KB), and colloid-imprinted carbon powders (CICs). The structure and distribution of the Pt NPs were confirmed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Figure 1 shows the cyclic voltammograms of JM Pt/VC and Pt/CIC85 (i.e., 85 nm pore size), prepared by both the ethanol and butanol synthesis methods, in 0.5 M H2SO4. Even though the theoretical specific surface areas were 70-80 m2/gPt (particle size of 3-3.5 nm), the electrochemical active surface area (ECSA) was found to depend on the synthesis method and the carbon support. The ethanol oxidation activity of catalysts per Pt area for the three carbon supports is shown in Figure 2. A strong dependence on the carbon microstructure was observed, with Pt/CIC and Pt/KB, showing a higher activity than Pt/VC, likely due to their higher content of mesopores in the catalyst layer [2]. The correlation between catalyst activity and the carbon microstructure for each synthesis method will be discussed in detail.

Ni nanoparticles supported on carbon as efficient catalysts for steam reforming of toluene (model tar)

Abstract This paper investigated the influences of surface properties of carbon support and nickel precursors (nickel nitrate, nickel chloride and nickel acetate) on Ni nanoparticle sizes and catalytic performances for steam reforming of toluene. Treatment with nitric acid helped to increase the amount of functional groups on the surface and hydrophilic nature of carbon support, leading to a homogeneous distribution of Ni nanoparticles. The thermal decomposition products of nickel precursor also played an important role, Ni nanoparticles supported on carbon treated with acid using nickel nitrate as the precursor exhibited the smallest mean diameter of 4.5 nm. With the loading amount increased from 6 wt% to 18 wt%, the mean particle size of Ni nanoparticles varied from 4.5 nm to 9.1 nm. The as-prepared catalyst showed a high catalytic activity and a good stability for toluene steam reforming: 98.1% conversion of toluene was obtained with the Ni content of 12 wt% and the S/C ratio of 3, and the conversion only decreased to 92.0% after 700 min. Because of the high activity, good stability, and low cost, the as-prepared catalyst opens up new opportunities for tar removing.

Superiority of Activated Carbon versus MCM‐41 for the Immobilization of Molybdenum Dithiocarbamate Complex as Heterogeneous Epoxidation Catalyst

AbstractTwo heterogeneous catalysts were developed by covalent anchoring of molybdenum‐dithiocarbamate complex onto the mesoporous silica (MCM‐41) and activated carbon (AC). Characterization of the functionalized materials by various physicochemical techniques indicated that the molybdenum complex is grafted successfully on the surface of supports. Textural properties of the prepared catalysts proved that the surface properties of supports have been changed after grafting of molybdenum‐dithiocarbamate complex. These heterogeneous catalysts were utilized for the epoxidation of olefins with tert‐butyl hydroperoxide (TBHP) as oxidant, presenting high efficiency and facile recovery. These catalysts can be reused five times without apparent loss of their catalytic performance. Also, the effect of the nature of MCM‐41 and AC supports on the catalytic activity has been discussed based on their hydrophobic and hydrophilic character.

Permeability and selectivity of acid gases in supported conventional and novel imidazolium-based ionic liquid membranes

The novel imidazolium salts based on bis(2-ethylhexyl) sulfosuccinate anion have been developed as ionic liquids (ILs) which can potentially be used as absorbents of acid gases. The transport of CO2, H2S, CH4 and N2 in a series of supported ionic liquid membranes (SILMs) with immobilized conventional (bmim[PF6], bmim[BF4], bmim[Tf2N]) and novel ILs was investigated. The supported ionic liquid membrane containing 1-butyl-3-methylimidazolium bis(2-ethylhexyl) sulfosuccinate (bmim[doc]) yielded a very high H2S solubility and, hence, H2S/N2 selectivity equal to 65. However, the permeability of acid gases through such a membrane had relatively low values varying in a range of 100–200 Barrer, whereas permeability for SILMs impregnated by conventional ILs achieved 565 Barrer. The most effective separation of CO2 was observed for SILMs impregnated by bmim[BF4] predominantly owing to solubility component of permeability. In order to estimate the stability of SILMs, the polymeric support surface properties such as free surface energy, surface topology and roughness parameters were evaluated. Analysis of experimental data revealed that among the tested ILs, bmim[BF4] immobilized in porous polymeric support was more resistant to losses and determined the higher stability of membranes.

Effect of surface properties of polysulfone support on the performance of thin film composite polyamide reverse osmosis membranes

ABSTRACTIn this work, influence of initial conditions and surface characteristics of porous support layer on structure and performance of a thin film composite (TFC) polyamide reverse osmosis (RO) membrane was investigated. The phase inversion method was used for casting of polysulfone (PSf) supports and interfacial polymerization was used for coating of polyamide layer over the substrates. The effect of PSf concentrations that varied between 16 wt % and 21 wt %, and kind of the solvent (DMF and NMP) used for preparation of initial casting solution were investigated on the properties of the final RO membranes. SEM imaging, surface porosity, mean pore radius, and pure water flux analysis were applied for characterization of the supports. The substrate of the membrane, which synthesized with 18 wt % of PSf showed the most porosity and the synthesized RO membrane had the lowest salt rejection. In case of the solvents, the membranes synthesized with DMF presented better separation performance that can be attributed to their lower thickness and sponge‐like structure. The best composition of support for TFC RO membranes reached 16 wt % PSf in DMF solvent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44444.

CoMoNi Catalyst Texture and Surface Properties in Heavy Oil Processing. Part II: Macroporous Sepiolite-Like Mineral

A set of novel CoMoNi hydrotreating catalysts supported on sepiolite-like mineral and modified by H3PO4 have been prepared and studied in hydrodesulfurization (HDS) and hydrodemetallization (HDM) of heavy Tatar oil with extremely high viscosity and sulfur content. Catalysts had a multiphase composition, represented by calcium/magnesium oxides, silicates, or phosphates, and were found to be of great interest for studying the role of support surface properties in heavy oil hydrotreating. For monitoring the catalyst properties, all the samples have been investigated by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XFS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), CO- and CDCl3-Fourier transform infrared (FTIR), mercury porosimetry, and N2 adsorption methods. The catalyst with a small phosphate content showed higher initial HDS conversion due to the more developed specific surface area, increased Lewis acidity, and better active component distribution; however, ...

Mesoporous Zeolite ZSM-5 Supported Ni2P Catalysts with High Activity in the Hydrogenation of Phenanthrene and 4,6-Dimethyldibenzothiophene

Mesoporous zeolite ZSM-5 (ZSM-5-M) was synthesized and used as support for the preparation of highly efficient nickel phosphide catalyst (Ni2P/ZSM-5-M) in the deep hydrogenation of phenanthrene and in the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DM-DBT). Compared with Ni2P catalysts supported silica and high surface area hexagonal mesoporous silica (HMS) (Ni2P/SiO2 and Ni2P/HMS), Ni2P/ZSM-5-M exhibits higher hydrogenation and HDS activity. The phenanthrene conversion and deep hydrogenation products selectivity over Ni2P/ZSM-5-M (95% and 83%) are much higher than those over Ni2P/SiO2 (61% and 73%) and Ni2P/HMS (69% and 45%) under mild conditions. The 4,6-DM-DBT conversion over Ni2P/ZSM-5-M (93%) was higher than that over Ni2P/SiO2 (62%). This feature is attributed to the difference in surface properties of support. A large amount of acidic hydroxyl groups on the zeolites can interact strongly with catalyst precursor, resulting in the formation of highly dispersed Ni2P particles with ...

Gold-Iron Oxide Catalyst for CO Oxidation: Effect of Support Structure

Gold-iron oxide (Au/FeOx) is one of the highly active catalysts for CO oxidation, and is also a typical system for the study of the chemistry of gold catalysis. In this work, two different types of iron oxide supports, i.e., hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O), have been used for the deposition of gold via a deposition-precipitation (DP) method. The structure of iron oxide has been tuned by either selecting precipitated pH of 6.7–11.2 for Fe_OH or changing calcination temperature of from 200 to 600 °C for Fe_O. Then, 1 wt. % Au catalysts on these iron oxide supports were measured for low-temperature CO oxidation reaction. Both fresh and used samples have been characterized by multiple techniques including transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and temperature-programmed reduction by hydrogen (H2-TPR). It has been demonstrated that the surface properties of the iron oxide support, as well as the metal-support interaction, plays crucial roles on the performance of Au/FeOx catalysts in CO oxidation.

Evaluation of surface properties and pore structure of carbon on the activity of supported Ru catalysts in the aqueous-phase aerobic oxidation of HMF to FDCA

Different oxygen- and nitrogen-containing carbons were studied as supports of ruthenium catalysts for the alkaline aqueous-phase oxidation of 5-hydroxymethylfurfural (HMF) to the corresponding diacid 2,5-furandicarboxylic acid FDCA. The surface properties of catalyst support (active carbon or mesoporous carbon replicated from mesostructured silica) were suggested to be a key factor deeply influencing the oxidation rates of the different steps of this reaction of ruthenium nanoparticles. The results highlight that the HMF oxidation reaction in water does not well tolerate O-functional groups, which strongly adsorb water and then block access of the substrate to the active metal sites and decrease the reaction rates. N-containing carbons were anticipated to be beneficial for the acceleration of the first step of ruthenium-alcoholate species formation. The result was the opposite, with a detrimental effect on the reaction rate when the Ru precursor was reacted with the amine-functionalized surface.

Synergistic effects of amine and protein modified epoxy-support on immobilized lipase activity

We have developed an improved and effective method to immobilize Yarrowia lipolytica lipase Lip2 (YLIP2) on an epoxy poly-(glycidylmethacrylate-triallyisocyanurate-ethyleneglycoldimethacrylate) (PGMA-TAIC-EGDMA) support structure with or without amine or/and protein modifications. Our results show that there is an increase in the activity of the immobilized lipase on n-butylamine (BA) modified support (420U/g support) and the biocompatible gelatin modified support (600U/g support) when compared to the support without modification (240U/g support). To further study the influences of BA and gelatin modification on the activity of the immobilized lipase, gelatin and BA were concurrently used to decorate the support structure. Lipase immobilized on 2% BA/gelatin (1:1) modified support obtained the highest activity (1180U/g support), which was five-fold higher than that on a native support structure. These results suggest that the activity of a support-immobilized lipase depends on the support surface properties and a moderate support surface micro-environment was crucial for elevated activity. Collectively, these data show that a combined gelatin and BA modification regulates the support surface more suitable for immobilizing YLIP2.

Oxidative CO2 reforming of methane over stable and active nickel-based catalysts modified with organic agents

This study targeted the novel silica-supported nickel-based catalyst (Ni/SiO2) modified by organic agents. The synergic modification effect of ethylene glycol (EG) and citric acid (CA) on the nickel catalyst was investigated. EG was used to pretreat the silica support and CA was used in the impregnation solution to synthesize the nickel based catalysts with different CA loadings. NiCA-x/SiO2-EG (x: molar ratio of CA/Ni ranging from 0.25 to 1.5) catalysts achieved an excellent stability and higher catalytic activity than the catalysts without EG in oxidative CO2 reforming of methane (CH4/CO2/O2 = 40/20/10, total flow rate = 60 ml/min, reaction temperature = 750 °C, and reaction pressure = 1 atm). EG addition modified the surface properties of silica support. The use of CA in the impregnation solution had a clear effect on the dispersion of NiO and Ni in the silica matrix. For the catalysts with the same content of CA, the catalysts with EG modification showed the synergic effect of EG and CA by improving the chemical interaction between Ni and support, resulting in higher dispersion of nickel. The temperature programmed reduction revealed that the reduction peak shifted to higher temperature with increasing CA loading, which was attributed to the smaller metallic Ni size of the reduced catalysts. The transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed that the addition of organic additive modified the silica surface and retained the metallic Ni species, and thus preventing the metal aggregation at high reaction temperature. The NiCA-1.5/SiO2-EG catalyst exhibited the highest activity, which was due to the small metallic metal size (4 nm) and the strong interaction between silica support and metal species.

Insights into the effects of surface properties of oxides on the catalytic activity of Pd for C-C coupling reactions.

Understanding the interaction between Pd nanocatalysts and metal oxide supports for heterogeneous C-C coupling reactions is still ambiguous since many factors influence the catalytic behavior of Pd nanocatalysts. Herein, three porous nanorods of CeO2 with controllable surface properties were employed as supports for Pd nanocatalysts with similar dispersion, which avoided the impact of other factors including surface area, morphology and accessible active sites. It provides an ideal approach to probe synergetic catalytic behavior of metal nanoparticles on supports. The results obtained by studying three C-C coupling reactions (Ullman, Suzuki and Heck) indicate a strong correlation between the surface properties of supports and the catalytic activity of Pd nanocatalysts: supports with a strong basicity and a high concentration of oxygen vacancies result in a rich electron density of Pd and accelerate the first step of oxidative addition reaction for C-C coupling. The infrared spectroscopic study on ν[CO] of CO-treated catalysts and XPS analysis of the Pd(3d) core level provide strong evidence supporting the interaction of Pd/supports for C-C coupling reactions.

Aminosilanes grafted to basic alumina as CO2 adsorbents--role of grafting conditions on CO2 adsorption properties.

Solid oxide-supported amine sorbents for CO2 capture are amongst the most rapidly developing classes of sorbent materials for CO2 capture. Herein, basic γ supports are used as hosts for amine sites through the grafting of 3-aminopropyltrimethoxysilane to the alumina surface under a variety of conditions, yielding the expected surface-grafted alkylamine groups, as demonstrated by FTIR spectroscopy and (29)Si and (13)C cross-polarization magic-angle spinning (CPMAS NMR) spectroscopy. Grafting amine sites on the surface in the presence of water leads to a high density of amine sites on the surface whereas simultaneously creating a unique type of aluminum species on the surface, as demonstrated by both 1D and 2D (27)Al MAS NMR spectroscopy. The thus prepared sorbents result in higher CO2 adsorption capacities and amine efficiencies compared to sorbents prepared in the absence of water or similar amine loading sorbents prepared using silica supports. In situ FTIR spectra of the sorbents exposed to CO2 at various pressures show no distinct difference in the nature of the adsorbed CO2 species on alumina- versus silica-supported amines, whereas water adsorption isotherms show that the improved performance of the amine-grafted alumina support is not a consequence of retained water on the more hydrophobic aminoalumina materials. The findings demonstrate that amine-grafted, basic alumina materials can be tuned to be more efficient than the corresponding silica-supported materials at comparable amine loadings, further demonstrating that the properties of amine sites can be tuned by controlling or adjusting the support surface properties.

Enhancement of activity, selectivity and stability of CNTs-supported cobalt catalyst in Fischer–Tropsch via CNTs functionalization

Functionalization of carbon nanotubes (CNTs) was performed, during preparation of Fischer–Tropsch synthesis (FTS) cobalt nanocatalysts, to modify the surface properties of CNTs support. Common CNTs and functionalized CNTs supported cobalt nanocatalysts were prepared using microemulsion technique with cobalt loading of 15wt%. The catalysts were characterized by Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), temperature program reduction (TPR), H2 chemisorption, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques. Most of the cobalt particles were homogeneously distributed inside the tubes and the rest on the outer surface of the functionalized CNTs. Functionalization of CNTs shifted the TPR reduction peaks to lower temperatures, improved the reduction degree, and increased the dispersion of cobalt particles. The proposed cobalt catalyst supported on functionalized CNTs increased the FTS rate (g HC/gcat./h), and percentage CO conversion from 0.1476, and 32.4% to 0.24, and 54%, respectively. Catalysts supported on functionalized CNTs showed better stability.