Spherical γ-Al2O3 Research Articles

An egg-shell type Ni/Al2O3 catalyst derived from layered double hydroxides precursor for selective hydrogenation of pyrolysis gasoline

Egg-shell type catalysts, in which a thin layer of catalytically active component is distributed on the outer surface of the support particle, have been theoretically and experimentally proved to be useful in processes where the reaction has a very high rate and the intraparticle diffusion becomes the limiting step. Herein we report the preparation of an egg-shell Al2O3-supported nickel (Ni/Al2O3) catalyst derived from layered double hydroxides (LDHs) precursor, and its catalytic performance for selective hydrogenation of pyrolysis gasoline (PyGas), an important by-product of ethylene industry from thermal decomposition of heavier oil fractions, which was carried out in the liquid phase. Firstly, a Ni2+Al3+-containing LDHs (NiAl-LDHs) precursor was in situ grown on the surface of γ-Al2O3 spheres by using a diluted ammonia solution as precipitator. Then, egg-shell Al2O3-supported nickel oxide (NiO/Al2O3) sample with NiO crystallites highly dispersed on the external edge of the Al2O3 support was obtained after calcination at 450°C. The experimental study of selective hydrogenation of styrene (PyGas model 1) for revealing the intrinsic hydrogenation kinetics was carried out in a batch reactor at 60°C using the egg-shell Ni/Al2O3 catalyst (denoted LP-Ni/Al2O3; LP is expressed as layered precursor) fabricated by subsequent ex situ presufidation and final H2 reduction at 500°C of the NiO/Al2O3 sample. In addition, an Ni/Al2O3 catalyst with uniform distribution of Ni in the catalyst was prepared by a conventional wet impregnation method (denoted IM-Ni/Al2O3; IM is expressed as impregnation method) with the consistent Ni loading amounts and given into the consideration for comparison. The estimated effectiveness factor (η) of the LP-Ni/Al2O3 catalyst was higher than that of the IM-Ni/Al2O3 one, demonstrating the catalyst with egg-shell structure has a lower intraparticule mass transfer resistance. The catalytic hydrogenation activities of both Ni-based catalysts were further evaluated by selective hydrogenation of diolefins (PyGas model 2), along with selective hydrogenation of PyGas model 1, in a micro-flow reactor. The egg-shell Ni/Al2O3 catalyst derived from LDHs precursor exhibited a superior catalytic hydrogenation performance, which mainly be due to Ni metal being deposited on the Al2O3 support in a much thinner outer layer, as well as a smaller average size of nickel particles with stronger interaction between the nickel species and support. Several characterization techniques including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), low temperature N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction of hydrogen (TPR)/temperature programmed desorption of hydrogen (H2-TPD) were adopted to investigate the physical–chemical properties of the two supported Ni catalysts in detail.

Effect of Polyethylene Glycol on the Properties of γ-Al2O3 Formation by Polyaluminum Chloride

A polyaluminium chloride solution with high Al13 content self-prepared was used as material for preparing the spherical γ-Al2O3 by the sol-gel and oil-drop method. Polyethylene glycol with different molecular mass was used as surfactant to investigate the effect on property of γ-Al2O3. The physical property was characterized by 27Al NMR (nuclear magnetic resonance) spectra, X-ray diffraction, FT-IR (Fourier transform infrared spectroscopy) and TG-DTA (thermogravimetric-differential thermal analysis). The results showed that surface area, pore volume and pore size of γ-Al2O3 all increased with the increase of polyethylene glycol molecular mass in the experimental research range, and polyethylene glycol 10000 was the most suitable pore forming additive. γ-Al2O3 with surface area of 339 m2·g−1, pore volume of 0.59 cm3·g−1 and pore diameter of 6.9 nm were obtained at 450 °C.

Ferromagnetic-Like Behavior of Pt Nanoparticles

The magnetic properties of small 4d, 5d metal nanoparticles of Pd, Pt (clusters) are attracting a great attention because these materials in bulk are paramagnetic. In this work we report the ferromagnetic-like behavior of the small Pt nanoparticles prepared by chemical method. Highly dispersed Pt clusters have been synthesized on the surfaces of a porous spherical γ-Al2O3 particles. The process of the chemical deposition of metalorganic fluid with employment of the supercritical fluid was used. The samples of the Pt/γ-Al2O3 nanoparticles have been prepared in INEOS RAS. The nanoparticles size distribution was determined by small-angle X-rays scattering (SAXS). It was found that the Pt clusters have a bimodal particle size distribution with two peaks: R1max=20 Å and R2max=40 Å. The magnetic properties of the clusters have been investigated, using VSM magnetometer, in magnetic field up to ±3 kOe and at a temperature range from 80 to 400 K. It was observed that Pt/γ-Al2O3 nanoparticles show the ferromagnetic-like behavior in whole specified temperature range, the value of coercivity decreases gradually from 130 Oe to 80 Oe. The origin of ferromagnetic-like behavior of the Pt/γ-Al2O3 nanoparticles is discussed.

Catalytic removal of nitrates from waters in a continuous flow process: The remarkable effect of liquid flow rate and gas feed composition

The selective catalytic reduction of nitrates (NO3−) in water mediums towards N2 formation by the use of H2 and in the presence of O2 (air) in the gas feed has been investigated under a continuous flow process over Pd–Cu supported on various mixed metal oxides, xwt.% MxOy/γ-Al2O3 (MxOy=CeO2, MgO, Mn2O3, Cr2O3, Y2O3, MoO2, Fe2O3 and TiO2). It is demonstrated for the first time that a remarkable improvement of both catalysts activity and N2 reaction selectivity can be achieved when increasing the liquid flow rate in the continuous flow process. In particular, it was found that NO3− reduction rates up to more than two times higher and NH4+ selectivity values up to twenty times lower can be obtained when increasing the liquid flow rate from 2 to 6mL/min. Moreover, it was proven for the first time, in a continuous flow process, that the presence of oxygen (or air) has a remarkable positive effect on the reaction's selectivity towards nitrogen. The reaction's selectivity towards NH4+ can be decreased by up to three times when 20vol.% air is added in the gas feed of the NO3−/H2 continuous flow reaction. The Pd–Cu clusters supported on TiO2-, CeO2- and MgO-coated γ-Al2O3 spheres showed the best catalytic behaviour compared with the rest of supports examined, both in the presence and in the absence of oxygen in the reducing feed gas stream. In addition, it was found that the initial concentration of nitrates in the liquid feed can significantly affect catalysts activity and reaction's selectivity. A positive apparent reaction order towards nitrates of 0.9 was calculated on Pd–Cu/TiO2/Al2O3.

Kinetic Studies on the Cuo/γ-Al2O3 Sorbent Regeneration by Methane – Topochemical Approach

CuO impregnated γ-Al2O3 support provides convenient adsorption and regeneration characteristics. These features give the potential to regard this chemisorption process as more effective, feasible and widely accepted than lime and limestone scrubbing in the removal of SO2 from the outlet gases. Thermogravimetric tests on the regeneration of the CuO/γ-Al2O3 exhausted sorbent (first stage of the regeneration, CuSO4 → Cu0) with methane were conducted. Commercially available 1/8″ γ-Al2O3 spheres, loaded with 5.8 wt % of Cu were investigated. The tests concerning the isothermal regeneration kinetics were performed at temperatures: T = 700, 727 and 750 K, while a 20 cm3 min−1 flow of pure methane was used. To select the mechanism of the regeneration reaction, as well as to evaluate their kinetic parameters of the rate equations, the TGA data were compared with the series of theoretical topochemical kinetic models as advocated by Gardner, Hancock and Sharp's approach. The kinetic mechanism of the regeneration reaction in the initial stage of the process may be originally interpreted as the combination of both boundary–surface–controlled reaction (contracting sphere) and the first–order kinetics models. Various diffusion limited kinetic equations have proved useful for the description of the final stage of the process. Both proposed models (two kinetic and four diffusion ones) fit fairly well to the experimental data (in their limited validity ranges) obtained in all three temperature values studied.

Nonpremixed Catalytic Combustion of Methane in a Fluidized Bed Reactor

The catalytic combustion of methane has been investigated in a 0.10 m bubbling fluidized bed reactor with nonpremixed feedings of reactants. Copper dispersed on porous γ-Al2O3 spheres (1 mm diameter) characterized by high mechanical strength has been used as catalyst. The effect of design variables such as methane inlet concentration, bed temperature, and superficial gas velocity on methane conversion has been quantified in the ranges 4−10 vol %, 650−750 °C, and 0.40−1.30 m s-1, respectively. The propensity to attrition of the catalyst has been separately investigated under the experimental conditions tested. Results have been interpreted in the light of a simple reactor model which assumes a plug-flow pattern for the gas through the bed and mth-order catalytic kinetics with respect to fuel concentration.

Cycling effects on the methane regeneration kinetics of CuO/γ-Al2O3 sorbent

Due to the excellent adsorption capacity coupled with convenient regeneration characteristics demonstrated by copper oxide impregnated γ-Al2O3 spheres this process has the potential of being more effective, feasible and widely accepted over the lime and limestone scrubbing in the removal of SO2. Thermogravimetric tests concerning the copper oxide on γ-Al2O3 (both fresh and spent) sorbent regeneration kinetics by methane were performed. Commercially available (SELEXSORB™) 1/8 in. diameter γ-Al2O3 spheres loaded with 5.8 wt.% of Cu were used for these studies. The regeneration experiment temperatures were: 700, 727 and 750 K, while a 20 cm3/min flow of pure methane was applied. To determine the reaction mechanism and its kinetic parameters evaluation, the TGA data were subjected to a rigorous series of theoretically developed models of topochemical reaction kinetics. Hancock and Sharp's tabulations were used to establish the reaction mechanisms and their rate constants evaluation. The various diffusion kinetic equations found themselves useful for the description of the reaction time—courses in the final stage of each experiment.

Study of catalysts for catalytic burners for fuel cell power plant reformers

Catalytic burners for fuel cell power plant reformers are alternatives to conventional flame burners. Their application is expected to provide uniform temperatures in the reformer, efficient use of low-calorific gaseous by products and reduction of pollutant emissions. For testing in the burners, a series of spherical Pd/CeO2/Al2O3 catalysts were prepared. An optimum concentration of ceria providing the highest thermal stability of catalysts was determined. An effect of catalyst activation in the reaction mixture-1% methane in air was observed. A series of Mn containing oxide catalysts on spherical γ-Al2O3 or (γ+Χ)-Al2O3, both pure and doped with La, Ce and Mg oxides were prepared. The catalysts were characterized by chemical analysis, X-ray phase analysis, BET surface area and activity measurements in methane oxidation. A batch of Mn-Mg-La-Al-O catalyst was prepared for further long-term testing in a model reformer with a catalytic burner. A model reformer with a catalytic burner was designed and fabricated for testing in the composition of the bench-scale Fuel Cell Power Plant. Preliminary testing of this catalyst showed that it provided complete methane combustion at the specified operational temperatures over 900 °C.

Cu/γ-Al2O3 catalyst for the combustion of methane in a fluidized bed reactor

The applicability of a catalyst based on copper dispersed on γ-Al2O3 spheres (1mm diameter) for fluidized bed catalytic combustion of methane has been assessed. Catalyst properties have been determined by physico-chemical characterization techniques and fixed bed activity tests revealing the presence of a surface CuAl2O4 spinel phase, still active and stable in methane combustion after repeated thermal ageing treatments at 800°C. Methane catalytic combustion experiments have been performed in a 100mm premixed fluidized bed reactor under lean conditions (0.15–3% inlet methane concentration), showing that complete CH4 conversion can be attained below 700°C in a fluidized bed of 1mm solids with a gas superficial velocity about twice the incipient fluidization velocity.