In this work biogas valorization – a renewable resource – for synthesis gas and hydrogen generation through dry reforming or tri-reforming (TR) is studied. Several Ni-based catalysts and a bimetallic ...Rh–Ni catalyst supported on magnesia or alumina modified with oxides like CeO2 and ZrO2 were used. For all the experiments, a synthetic biogas (molar composition: 60% CH4 and 40% CO2) was fed and the catalytic activities were measured in two different experimental facilities: a bench-scale fixed bed reactor system and a microreactor reaction system, at 1073 K and atmospheric pressure. Those catalysts which achieved high activity and stability in the fixed-bed reactor were impregnated in a microreactor to explore possible process intensification. For TR processes, different steam to carbon ratios, S/C, from 1.0 to 3.0, and O2/CH4 ratios of 0.25 and 0.50 were used. The high methane and carbon dioxide conversions reached in the fixed bed reactor were also achieved in the microreactor operating at much higher WHSV. In addition, process intensification improved catalysts stability. Physicochemical characterization of catalyst samples by ICP-OES, N2 physisorption, H2 chemisorption, TPR, SEM and XPS showed differences in chemical state, metal–support interactions, average crystallite sizes and redox properties of nickel and rhodium metal particles, indicating the importance of the morphological and surface properties of metal phases in driving the reforming activity.
► High methane and carbon dioxide conversions were reached in biogas DR process. ► For TR process at O2/CH4 = 0.25 and S/C = 1.0 the highest hydrogen yields were reached. ► The Rh–Ni/Ce–Al2O3 catalyst achieved the highest hydrogen production yield. ► Similar conversions were achieved at much higher WHSV in microreactors. ► Higher TOF and PROD values were obtained operating with microreactors.
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•Phenol HDO was compared on Pd catalysts supported on alumina, zeolite HY and mixtures.•The 20%HY–80%Al2O3 support is beneficial for phenol HDO reaction over Pd catalyst.•The density ...of active phases on the support surface influenced on the HDO activity.•Catalyst acidity influence on both activity and coke formation.
This contribution describes the effect of the support (zeolite ultrastable HY, alumina (Al) and mixed HY–Al carriers) on the catalytic activity of Pd catalysts in the phenol hydrodeoxygenation (HDO) reaction carried out in a flow fixed-bed reactor at T=523–573–623K, P=15bar and WHSV=0.5h−1. Phenol dissolved in n-octane was used as model compound of bio-oil species derived from fast pyrolysis of lignocellulosic biomass. The catalysts were characterized by N2 physisorption, XRD, TPR, TPD-NH3, DRIFT spectroscopy of adsorbed CO, HRTEM, X-ray photoelectron spectroscopy (XPS) and TPO/TGA techniques. The largest phenol conversion (63%) achieved at 523K over the reduced Pd/20%HY–Al catalyst was similar to that obtained on a commercial NiMo/Al2O3–zeolite hydrocracking sample (HCK) activated by sulfidation. Regardless of the reaction temperature, the only products detected in the HDO of phenol over all catalysts studied were four O-free compounds: benzene, cyclohexene, cyclohexane, and methylcylopentene. Both reduced Pd/20%HY–Al and sulfided commercial HCK catalysts produced similar yields of O-free products. From the catalyst activity-structure correlation, it can be concluded that the HDO of phenol is favoured on the bifunctional Pd/20%HY–Al catalyst which possesses moderate acidity and improved Pd dispersion on the support surface. The contributions of the acid sites to the catalyst activity and deactivation by coke are discussed.
The acetalization reaction between glycerol and formaldehyde using Amberlyst 47 acidic ion exchange resin was studied. These acetals can be obtained from renewable sources (bioalcohols and bioalcohol ...derived aldehydes) and seem to be good candidates for different applications such as oxygenated diesel additives. A preliminary kinetic study was performed in a batch stirred tank reactor studying the influence of different process parameters like temperature, feed composition and the stirring speed. A pseudo homogenous kinetic model able to explain the reaction mechanism was adjusted. Thus, the corresponding order of reaction was determined. Amberlyst 47 acidic ion exchange resin showed a fairly good behavior allowing 100% of selectivity towards acetals formation. However, the studied acetalization reaction showed high thermodynamic limitations achieving glycerol conversions around 50% using a stoichiometric feed ratio at 353 K. The product is a mixture of two isomers (1,3-Dioxan-5-ol and 1,3-dioxolane-4-methanol) and the conversion of 1,3-dioxolane-4-methanol into 1,3-Dioxan-5-ol was also observed.
► The reaction between glycerol and acetaldehyde shows thermodynamic limitations. ► Amberlyst 47 ion exchange resins show 100% of selectivity. ► A pseudo-homogeneous kinetic model is able to predict the reaction progress. ► Isomerization reactions were observed from dioxalanes to dioxanes.
In this paper glycerol steam reforming over Ni catalysts supported on bare CeO
2 and Al
2O
3, and CeO
2-promoted Al
2O
3 to produce H
2 was studied. The catalytic activity results for the NiAl5Ce and ...NiAl10Ce catalysts showed that the incorporation of low ceria loadings enhances the activity of the NiAl catalyst prepared using a similar composition to the commercial Ni/Al
2O
3 catalysts. The catalyst surface characterization revealed that the good behaviour of the NiAl5Ce and the NiAl10Ce catalysts depends on the stabilization of Ni° particles which is promoted by the formation of nickel–ceria interactions. The increase of ceria content reduced the capacity of the NiAl20Ce catalyst to convert intermediate oxygenated hydrocarbons into H
2.
In this work, a renewable source, biogas, was used for synthesis gas and hydrogen generation by steam reforming (SR) or oxidative reforming (OR) processes. Several Ni-based catalysts and a bimetallic ...Rh–Ni catalyst supported on magnesia or alumina modified with oxides like CeO2 and ZrO2 were used. For all the experiments, a synthetic biogas which consisted of 60% CH4 and 40% CO2 (vol.) was fed and tested in a fixed bed reactor system and in a microreactor reaction system at 1073 K and atmospheric pressure. The catalysts which achieved high activity and stability were impregnated in a microreactor to explore the viability of process intensification. For the SR process different steam to carbon ratios, S/C, varied from 1.0 to 3.0 were used. In the case of OR process the O2/CH4 ratio was varied from 0.125 to 0.50. Comparing conventional and microreactor reaction systems, one order of magnitude higher TOF and productivity values were obtained in the microreactors, while for all the tested catalysts a similar activity results were achieved. Physicochemical characterization of catalysts samples by ICP-AES, N2 physisorption, H2 chemisorption, TPR, SEM, XPS and XRD showed differences in chemical state, metal–support interactions, average crystallite sizes and redox properties of nickel and rhodium metal particles, indicating the importance of the morphological and surface properties of metal phases in driving the reforming activity.
► In biogas SR process lower CO2 conversions were measured increasing the S/C ratio. ► In biogas OR process at O2/CH4 = 0.25 the best operation conditions were measured. ► Rh–Ni/Ce–Al2O3 and Ni/Ce–Zr–Al2O3 catalysts were the most active catalysts. ► In microreactors, at higher WHSV similar conversions were achieved.
•Zinc recycling from Waelz oxide (treating EAFD) to increase sustainability of steelmaking industry.•Evaluation of sustainable technologies to recover zinc from unpurified secondary sources.•These ...techniques proven to solve limitations of Waelz oxide to be industrially processed as sole source.•Revision of most promising hydrometallurgical processes to produce high-purity ZnO and zinc metal.
The steelmaking industry that uses electric arc furnaces to recycle steel scrap generates dust (EAFD) as its main residue. This waste must be treated to recycle some heavy metals for economic reasons and to prevent negative environmental impacts. It is formed basically by different metallic oxides with heterogeneous composition and size. The Waelz Kiln Technology is the most commonly used technology for this purpose, generating concentrates of Zn and Pb oxides (called Waelz oxides). The main component of Waelz oxides is zinc and nowadays the production of metallic zinc and high purity zinc oxide covers approximately 97 % of the zinc market. The impurities content in the Waelz oxides (different heavy metals, halogens, …) makes impossible to use it as raw material to produce industrial high purity zinc oxide or in the electrolytic production of metallic zinc. At present, the Waelz oxides are blended with other purer raw materials. That supposes the unfeasibility of obtaining these products only through direct recycling EAFD. Therefore, the goal of this work is an in-depth study of the newest hydrometallurgical processes in order to achieve the production of these zinc products from Waelz oxides, showing their possibilities and limitations.
Certain acetals can be produced from renewable resources (bioalcohols) and seem to be good candidates for different applications, such as oxygenated diesel additives. This paper addresses the ...production of acetals (5-hydroxy-2-methyl-1,3 dioxane and 4-hydroxymethyl-2-methyl-1,3 dioxolane) from glycerol and acetaldehyde using Amberlyst 47 acidic ion exchange resin. This ion exchange resin performed well, recording 100% selectivity toward acetal formation at a suitably high initial glycerol concentration. When the initial acetaldehyde concentration was significantly higher than the glycerol concentration, 2,4,6 trimethyl-1,3,5 trioxane was the main reaction product. Unlike other acetalization reactions, the one studied here does not have thermodynamic limitations, and 100% conversion is achieved under different reaction conditions. A kinetic study was performed in a batch stirred tank reactor to study the influence of different process parameters, such as temperature, feed composition and stirring speed. A pseudo-homogeneous kinetic model was developed to describe this reaction kinetics, proving that its rate is just first order on the acetaldehyde concentration under the conditions studied.
•The reaction between glycerol and acetaldehyde behaves as an irreversible reaction.•Amberlyst 47resin shows 100% of selectivity when excess of aldehyde is not used.•An excess of acetaldehyde leads to 2,4,6trimethyl-1,3,5trioxane formation.•Isomerization reactions were observed from dioxalanes to dioxanes.
Ni-based (over MgO and Al2O3) and noble metal-based (Pd and Pt over Al2O3) catalysts were prepared by wet impregnation method and thereafter impregnated in microreactors. The catalytic activity was ...measured at several temperatures, atmospheric pressure and different steam to carbon, S/C, ratios. These conditions were the same for conventional, fixed bed reactor system, and microreactors. Weight hourly space velocity, WHSV, was maintained equal in order to compare the activity results from both reaction systems. For microreactor systems, similar activities of Ni-based catalyst were measured in the steam methane reforming (SMR) activity tests, but not in the case of natural gas steam reforming tests. When noble metal-based catalysts were used in the conventional reaction system no significant activity was measured but all catalysts showed some activity when they were tested in the microreactor systems. The analysis by SEM and TEM revealed a carbon-free surface for Ni-based catalyst as well as carbon filaments growth in case of noble metal-based catalysts.
► Hydrogen production from methane and natural gas steam reforming process was studied. ► Two different reaction systems were used: fixed bed reactor and microreactor systems. ► Ni/MgO catalyst was more selective for WGS reaction than Ni/Al2O3 catalyst. ► Ni/Al2O3 catalyst suffered a quick deactivation in natural gas SR process. ► For Pd/Al2O3 and Pt/Al2O3catalysts a very low activity was measured.
Nickel and Nickel–Palladium-catalysts supported on Al2O3–ZrO2, Al2O3–ZrO2–La2O3 and on Olivine were synthesized using a combination of sol–gel and wet impregnation methods. The influence of the ...formulation on their textural properties was examined by XRF, XRD and XPS. The influence of supports, promoters and temperatures of reactions was studied on glycerol steam reforming to produce hydrogen. C3H8O3 and H2O mixture was fed into a fixed bed reactor in a molar ratio of S/C = 5.0 (Steam/Carbon) and tested under atmospheric pressure at 800,700, 600 °C for 4 h. The most suitable catalyst was determined as Ni–Pd/Al2O3–ZrO2specifically in the process carried out at 800 °C, since it reached the highest hydrogen yield around 74%.
•Ni/Al2O3–ZrO2, Ni–Pd/Al2O3–ZrO2, Ni–Pd/Al2O3–ZrO2–La3O4, Ni/Olivine were synthesized by sol–gel and impregnation methods.•Ni/Al2O3–ZrO2, Ni–Pd/Al2O3–ZrO2, Ni–Pd/Al2O3–ZrO2–La3O4, Ni/Olivine were characterized by XRD, XRF, BET and XPS.•Activity of catalyst tested on steam reforming of glycerol.
The catalytic activity of Pt and PtNi catalysts supported on γ-Al2O3 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 H2 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 H2 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 H2 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 PtNiAl10Ce catalyst. Pt catalysts presented lower activity than PtNi catalysts possibly due to the formation of carbon nanotubes, which covered some metallic active sites.
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► H2 production from ethanol/glycerol mixtures SR on Pt & PtNi systems was studied. ► Pt–Ni cooperative effect provides a better performance for the bimetallic catalysts. ► PtNiAl10Ce showed good performance due to higher Ni exposure and lower coke amount. ► CeO2 seems to removal carbon from the support. ► PtNi catalysts promote filamentous while Pt counterparts are partially covered by CNTs.
