Strong Electrostatic Adsorption Method Research Articles

Reaction pathways control of long-chain alkanes hydroisomerization and hydrocracking via tailoring the metal-acid sites intimacy

Designing a bifunctional catalyst to achieve efficient hydroisomerization of long-chain alkanes is very essential for producing high-performance fuel and lubricant base oils. Herein, a bifunctional catalyst composed of an intimate mixture of ZSM-48 zeolite and alumina binder and with platinum (Pt) metal controllably deposited on zeolite or alumina was fabricated by a strong electrostatic adsorption method. The dependence of reaction pathways of hydroisomerization and hydrocracking of n-hexadecane on the metal-acid sites intimacy was investigated. High Brønsted acid density and suitable metal-acid sites intimacy favored to promote the catalytic activity. The selectivity, hydroisomerization mechanism and hydrocracking mechanism were significantly altered by tailoring the metal-acid sites intimacy. Too large or too small metal-acid sites intimacy was conducive to inhibit the occurrence of pore-mouth mode. A linear decease of the hydroisomerization selectivity with the increase of acid steps (nas) was observed. The catalyst with nanoscale intimacy of metal-acid sites (Pt/A-48) showed the highest catalytic activity and isomer selectivity (87%) and the least acid steps (nas = 1.4). This work provides a promising approach to fabricating highly efficient and shape-selective bifunctional catalysts for selective hydroisomerization of long-chain alkanes. A reaction network was proposed over the catalysts with different metal-acid intimacy.

Sandwich-type Co core@shell nanocomposite (SiO2 @Co@CeO2): Coke resistant catalyst toward CO2 reforming with ethanol

The design of highly efficient catalysts for CO2 reforming with ethanol is of great interest due to the serious coke deposition and the sintering of active metal. In this work, sandwich-type Co core@shell catalyst (SiO2 @Co@CeO2) with Co nanoparticles between SiO2 core and CeO2 shell was synthesized by strong electrostatic adsorption method. Interestingly, SiO2 @Co@CeO2 catalyst exhibited the outstanding activity/stability toward CO2 reforming of ethanol in comparison with Co-SiO2 catalyst. A bi-functional mechanism involving active sites on CeO2 shell was proposed. Indeed, cobalt nanoparticles between SiO2 core and CeO2 shell maintained the high dispersion because of the confinement effect, which supplied a stable Co-ceria interface area where the reaction occurred. In addition, CO2 could readily react with the O vacancies in CeO2 shell to form surface oxygen species and CO, which allowed a continuous cleaning of coke. These positive factors could make it as an attractive candidate for dry reforming process.

Tailoring the selectivity of Cu-based catalysts in the furfural hydrogenation reaction: Influence of the morphology of the silica support

Cu nanoparticles were incorporated on different porous silica supports (commercial silica, SBA-15 synthesized both at room temperature and under hydrothermal conditions, and mesocellular foam) by the strong electrostatic adsorption method and tested in the gas-phase furfural hydrogenation for the production of furfuryl alcohol and 2-methylfuran, being the latter a promising biofuel. The incorporated copper species provided metal particle sizes lower than 5 nm in all cases. However, different catalytic behaviors, both in terms of conversion and selectivity, were detected due to the morphology and textural properties of each support. Cu over commercial silica was more prone to suffer from deactivation, and it provided higher furfuryl alcohol yields, probably due to its higher acidity and lower metallic surface area. On the other hand, the agglomeration of Cu nanoparticles together with larger pore sizes complicated the access of furfural to the active sites using the hydrothermal SBA-15 support, thus decreasing the activity. In contrast, the addition of fluoride in the synthesis of mesoporous silica, which shortened the length of the silica channels (mesocellular foam), facilitated the furfural access and provided both higher metallic surface area and lower acidity. This fact led to a more gradual deactivation, still attaining high values of furfural conversion and 2-methylfuran yield (95 and 76%, respectively) after 5 h at 190 °C. However, Cu over mesocellular foam changed its selectivity pattern along 48 h and after regeneration, increasing the furfuryl alcohol selectivity due to the decreased number of available active sites.

Overcoming Limitations in the Strong Interaction between Pt and Irreducible SiO2 Enables Efficient and Selective Hydrogenation of Anthracene.

Interactions between metals and oxide supports are crucial in determining catalytic activity, selectivity, and stability. For reducible oxide supported noble metals, a strong metal-support interaction (SMSI) has been widely recognized. Herein we report the intermediate selectivity and stability over an irreducible SiO2 supported Pt catalyst in the hydrogenation of anthracene that are significantly boosted due to the SMSI-induced formation of intermetallic Pt silicide and Pt-SiO2 interface. The limitation in the strong interaction between Pt nanoparticles and irreducible SiO2 has been breached by combining the strong electrostatic adsorption method and following the high temperature reduction strategy. Due to the isolated Pt active sites by Si atoms, the activated H species produced over the Pt2Si/SiO2 catalyst with an initial catalytic activity of 2.49 μmol/(m2/g)/h as well as TOF of 0.95 s-1 preferentially transfer to the outer ring of anthracene to 87% yield of symmetric octahydroanthracene (sym-OHA) by subsequent hydrogenation. In addition, the Pt2Si/SiO2 catalyst presents an excellent stability after five cycles, which can be attributed to the fact that intermetallic Pt2Si nanoparticles are anchored firmly onto the surface of the SiO2 support. The discovery contributes to broaden the horizons on the SMSI effect in the irreducible oxide supported metal particle catalysts and provides guidance to design the metal-SiO2 interface and tune the surface chemical properties in diverse application conditions.

The synthesis of highly active Cu and N co-doped electrocatalysts via strong electrostatic adsorption method for oxygen reduction reaction

The development of non-precious metal catalysts to replace scarce and costly Pt-based catalysts is crucial for oxygen reduction reaction (ORR), which involves various electrochemical energy conversions, such as fuel cells and metal-air batteries. However, it is still a challenge to devise a simpler method to obtain high-performance non-noble metal catalyst, which can be used for large-scale production. Herein, Cu and N co-doped mesocellular carbon foam (n-Cu/NC) has been developed by strong electrostatic adsorption (SEA) method, which inherits the original morphology of carbon foam, exhibiting high ORR performance with a half-wave potential of 0.825 V vs. RHE and excellent long-term durability. The outstanding performance of n-Cu/NC is attributed to the high specific surface area, hierarchical porous carbon matrix doped by multiple N atoms and uniform Cu2O/CuO active sites induced by the SEA method. The strategy of SEA method is applied to the preparation of carbon-supported catalysts, which shows great potential in the design and large-scale production of M and N co-doped carbon materials.

The H2-Treated TiO2 Supported Pt Catalysts Prepared by Strong Electrostatic Adsorption for Liquid-Phase Selective Hydrogenation

The H2-treated TiO2 supported Pt catalysts were prepared by strong electrostatic adsorption method and tested in the liquid-phase selective hydrogenation of various organic compounds such as 3-nitrostyrene to vinylaniline (VA) and furfural to furfuryl alcohol (FA). A combination of high Pt dispersion, strong interaction of Pt-TiOx, and the presence of low coordination Pt sites was necessary for high hydrogenation activity. However, while the selectivity of VA in 3-nitrostyrene hydrogenation did not depend much on the catalyst preparation method used, the selectivity of FA in furfural hydrogenation was much higher when the catalysts were prepared by SEA, comparing to those obtained by impregnation in which the solvent product was formed, due probably to the non-acidic conditions used during Pt loading by SEA method.

Electrostatic adsorption-microwave synthesis of palladium nanoparticles on graphene for improved cross-coupling activity

Graphene materials as catalyst supports have shown tremendous promise for improving catalytic activity. Pd nanoparticles supported by graphene defects have been shown to improve catalytic activity in Suzuki reactions, but understanding their formation and factors that affect their formation is still elusive. In order to gain a better understanding of this phenomenon, a new synthetic method was developed combining strong electrostatic adsorption method for directed ionic Pd precursor uptake with a new solventless microwave irradiation method to simultaneously form Pd nanoparticles and graphene defect sites. Catalytic activities an order of magnitude higher than commercial Pd-carbon catalysts were obtained using this new method with low microwave powers, short reaction times, under atmospheric conditions, and without the use of reducing agents or solvents. The systematic comparison of catalysts synthesized from four different graphene materials and two different Pd precursors revealed Pd-graphene defects form through three routes that are affected by the initial oxygen content of graphene support and choice of ionic Pd precursor.

A Comparison of Pt(II) and Pt(IV) Chloride Precursors for Strong Electrostatic Adsorption Synthesis of Pt/Alumina and Pt/Carbon Catalysts

Platinum (II) tetrachloride (PTC) has been studied as an anionic metal precursor in strong electrostatic adsorption method of catalyst preparation. Compared to the conventionally used platinum (IV) hexachloride precursors, PTC exhibited greater pH stability in aqueous solution. As a result, PTC uptake on high PZC supports remained nearly unchanged irrespective of precursor aging. Upon reduction of these PTC catalysts small (~2.0 nm) and well-dispersed Pt nanoparticles were obtained on alumina, whereas on carbon, Pt sizes were significantly larger (4–10 nm).

Ni-doped carbon xerogels for H2 storage

Activated carbon xerogels, with selected characteristics, were doped with Ni, using different methods, and tested for hydrogen storage. The results obtained show that the amount of nickel incorporated, the Ni–carbon interaction and the nickel particle size distribution depend more on the doping method used than on the textural properties of the carbon support. The amount of nickel incorporated by strong electrostatic adsorption is lower than that incorporated by dry impregnation. However, the strong electrostatic adsorption method produces Ni-doped carbon xerogels with a high Ni–carbon interaction and a narrower Ni particle size distribution. The influence of Ni on H2 storage capacity depends on the operating conditions and the doping conditions used. Thus, at −196°C and 40bar, storage capacity seems to be mainly influenced by the textural properties of carbon support while, at 25°C and 200bar, the spillover effect plays a significant role, being the interaction between the support and Ni particles key factor in the storage process. The best Ni-doped carbon xerogels obtained in this work exhibit hydrogen storage capacities of 6wt.% and 31.8gl−1 at −196°C and 40bar.

Preparation of highly loaded Pt/carbon xerogel catalysts for Proton Exchange Membrane fuel cells by the Strong Electrostatic Adsorption method

Pt/carbon xerogel catalysts were prepared by the Strong Electrostatic Adsorption method: impregnation of the support was performed under optimal conditions, leading to maximum metal weight percentage while keeping the highest possible dispersion. After impregnation with H 2PtCl 6, the samples were filtered, dried and reduced. In order to increase the Pt weight percentage, up to three successive impregnation–drying–reduction cycles were performed. The final metal content of the catalysts was found to increase regularly: 7.5, 15.0 and 22.3 wt.%, after one, two and three cycles, respectively. This indicates that the adsorption sites were fully regenerated after the reduction treatment, and that they were available for the next impregnation step. In each case, the metal particles were found to be highly dispersed (particle size ∼2 nm); in addition, the average particle size did not change upon repeated impregnation. The 15.0 wt.% sample was tested as a cathodic catalyst in an H 2/air Proton Exchange Membrane fuel cell: the cathode activity, expressed as a function of the mass of Pt involved, increased up to twice that of previous catalysts prepared by impregnation with H 2PtCl 6 and reduction in aqueous phase by NaBH 4, provided the final reduction temperature of the catalyst was increased up to 450 °C.

Synthesis of very highly dispersed platinum catalysts supported on carbon xerogels by the strong electrostatic adsorption method

Highly dispersed Pt/carbon xerogel catalysts are obtained by applying the “strong electrostatic adsorption” (SEA) of hexachloroplatinic acid to carbon xerogels (PZC = 9.4) and platinum tetraammine chloride to oxidized carbon xerogels (PZC = 2.4). After the reduction step, all these Pt/carbon xerogel catalysts display a very high level of metal dispersion: very small platinum particles (1.1–1.3 nm) are observed by TEM. Pt particle sizes obtained by CO chemisorption are in good agreement with TEM micrographs, which shows that the metal is accessible to reactants. These Pt/carbon xerogel catalysts are very active for the hydrogenation of benzene into cyclohexane.