Bimetallic Pt–Ni composites on ceria-doped alumina supports as catalysts in the aqueous-phase reforming of glycerol (original) (raw)
Related papers
2014
A detailed and in-depth study of the deactivation of Pt and/or Ni-based ␥-Al 2 O 3 catalysts prepared by impregnation and acid and basic sol-gel methods, previously tested in glycerol aqueous phase reforming (APR) for H 2 production, has been made. The aim has been to get a further and advanced understanding of the factors behind this deactivation. Accordingly, all the used catalysts were systematically characterized by appropriate techniques, such as ICP-AES, XRD, XPS and TG/DGT-O 2 . Some used samples were also examined by BET, TPD-NH 3 , TPR-H 2 and TEM. The characterization results corroborate the following: (i) a significant part of ␥-Al 2 O 3 in sol-gel catalysts was structurally transformed into ␥-AlOOH, changing their textural properties, such as surface area and porosity, surface acidity and metal dispersion, and (ii) the Ni metallic particles in the impregnated catalysts underwent major agglomeration, while the Ni particles in the sol-gel counterparts were more affected by re-oxidation phenomena. Data obtained by ICP-AES and thermal analysis indicate, respectively, that Pt and Ni phase leaching and the formation of highly graphitized coke were negligible. However, some adsorption of carbonaceous molecular species has been detected on some catalysts. All these observations clearly confirm that the metallic and acid active sites of Pt and/or Ni-based ␥-Al 2 O 3 catalysts experimented quantitative and qualitative modifications during the glycerol APR process that compromised their catalytic performances.
Renewable Energy, 2011
Aqueous-phase reforming of oxygenated hydrocarbons for hydrogen production presents several advantages as feed molecules can be easily found in a wide range of biomass, there is no need for its vaporization and the process allows thorough exploitation of the environmental benefits of using hydrogen as an energy carrier. The use of glycerol in particular is motivated due to its availability as a consequence of increasing biodiesel production worldwide. In this contribution, the performance of Ptbased catalysts supported on different oxides (Al 2 O 3 , ZrO 2 , MgO and CeO 2 ) is studied on glycerol reforming. All catalysts led to a hydrogen-rich gas phase. However, a good potential activity with high production of hydrogen and low concentration of undesired hydrocarbons was accomplished over the catalysts supported on MgO and ZrO 2 . The high electron donating character of such oxides indicates the influence of the nature of the support in catalytic performance for glycerol reforming.
International Journal of Hydrogen Energy, 2012
The catalytic activity of Pt and PtNi catalysts supported on g-Al 2 O 3 modified by La and Ce oxides was investigated in the steam reforming of ethanol/glycerol mixtures. In general, all the catalysts fully converted the glycerol at the temperatures tested. However, the conversion of ethanol depended on the reaction temperature and catalyst type. The conversion into gaseous products operating at 500 C and 450 C was 100% using the most active catalysts (PtNiAl6La and PtNiAl10Ce). These two bimetallic catalysts gave H 2 yields close to those predicted by thermodynamic equilibrium at these temperatures. However, when the reaction temperature was lowered to 400 C, these catalytic systems and the PtNiAl one recorded a significant decrease in ethanol conversion and H 2 yield, which moved away from the thermodynamic equilibrium value. This deviation was due to intermediate liquid products (acetaldehyde, acrolein, etc.) not being further reformed and the formation of other gaseous ones (light alkanes and ethylene). PtNiAl10Ce catalyst presented the highest conversion into gas at 400 C, resulting in the largest H 2 yield, followed by PtNiAl6La and PtNiAl catalysts. This order is in agreement with the Ni/Al surface atomic ratio measured by XPS technique in reduced samples. However, filamentous carbon nanotubes were detected but this carbon type maintained the active sites accessible for reactants, since TEM and TGA results showed that the density of this carbon was lower for PtNiAl 10 Ce catalyst. Pt catalysts presented lower activity than PtNi catalysts possibly due to the formation of carbon nanotubes, which covered some metallic active sites.
Optimised hydrogen production by aqueous phase reforming of glycerol on Pt/Al2O3
International Journal of Hydrogen Energy, 2016
Aqueous phase reforming of glycerol was studied over a series of γ-Al2O3 supported metal nanoparticle catalysts for hydrogen production in a batch reactor. Of the metals studied, Pt/Al2O3 was found to be the most active catalyst under the conditions tested. A further systematic study on the impact of reaction parameters, including stirring speed, pressure, temperature, and substrate/metal molar ratio, was conducted and the optimum conditions for hydrogen production (and kinetic regime) were determined as 240 °C, 42 bar, 1000 rpm, and substrate/metal molar ratio ≥ 4100 for a 10 wt% glycerol feed. The glycerol conversion and hydrogen yield achieved at these conditions were 18% and 17%, respectively, with negligible CO and CH4 formation. Analysis of the spent catalyst using FTIR provides an indication that the reaction pathway includes glycerol dehydrogenation and dehydration steps in the liquid phase in addition to typical reforming and water gas shift reactions in the gas phase.
Journal of Molecular Catalysis A: Chemical, 2013
A series of platinum catalysts supported over various supports (Al 2 O 3 , Al 2 O 3-SiO 2 and TiO 2) were prepared and characterized by X-ray diffraction, N 2 sorption, H 2 chemisorption, temperature programmed reduction, FTIR of adsorbed pyridine, 3,3-dimethyl-1-butene isomerization and cyclohexane dehydrogenation. These catalysts were evaluated for aqueous-phase process (APP) of glycerol at 210 • C, under N 2 or H 2 atmosphere (60 bar as total pressure). Among the tested catalysts, Pt/TiO 2 was the most active and the most selective toward C 3 products (propanediols, propanol) which can be further valorized into chemicals. TiO 2 was identified as the support leading to the most stable Pt metallic phase, catalytic phase on which the hydrogenation/dehydrogenation reactions take place. The presence of acidic sites brought by the oxide support is necessary for the dehydration reactions (i.e. for C O cleavages), but a too high quantity of these sites can promote the C C bond cleavages via an acidic cracking mechanism. Among the various supported Pt-based catalysts studied in this work, Pt/TiO 2 sample appears to be the most promising system for the transformation of polyol in aqueous phase.
2010
The glycerol catalytic steam reforming over Ni and PtNi catalysts to produce H 2 was studied. The activity results indicate that the catalyst with the lower content of MgO, the NiA1M, provides higher H 2 molar ratios than the Ni catalyst. The behaviour of the NiA1M catalysts seems to be related to the Niº species stabilization by nickel-magnesia interactions, which are favoured by the presence of well dispersed MgAl 2 O 4 spinels. The bimetallic catalyst, PtNiA3M named, reforms the intermediate products improving the activity of the Ni monometallic catalyst toward H 2 production. The characterization results suggest that the Pt in the Ni monometallic catalyst enhances the Niº particles dispersion and the nickel species reducibility by H 2 spillover.
Catalysts
A promising route for the energetic valorisation of the main by-product of the biodiesel industry is the steam reforming of glycerol, as it can theoretically produce seven moles of H2 for every mole of C3H8O3. In the work presented herein, CeO2–Al2O3 was used as supporting material for Ir, Pd and Pt catalysts, which were prepared using the incipient wetness impregnation technique and characterized by employing N2 adsorption–desorption, X-Ray Diffraction (XRD), Temperature Programmed Reduction (TPR), Temperature Programmed Desorption (TPD), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The catalytic experiments aimed at identifying the effect of temperature on the total conversion of glycerol, on the conversion of glycerol to gaseous products, the selectivity towards the gaseous products (H2, CO2, CO, CH4) and the determination of the H2/CO and CO/CO2 molar ratios. The main liquid effluents produced during the reaction were quantified. The results...