Hydrogen from glycerol steam reforming with a platinum catalyst supported on a SiO2-C composite

This work studies 2 wt% Pt catalysts. The support is a SiO₂-C composite whose main features are a high specific surface due to its mesoporosity, a higher thermal stability than the C support, and the absence of surface acid sites which could promote the dehydration reactions that produce coke precursors. The Pt/SiO₂-C catalyst has very small metallic particles (d_va = 1.37 nm) that favor the CC bond cleavage reactions which allow obtaining total gas conversion at 450 °C. With this catalyst, it is possible to obtain high yields to H₂, between 4 and 5, which indicates that the active sites promote the WGS reaction, even with glycerol concentrations of 30 and 50%. Pt/SiO₂-C is a very stable catalyst since it loses only 10% of its initial activity after 66 h on stream and is resistant to sintering and coke deposition.     

Hydrogen production from acetic acid steam reforming over nickel-based catalyst synthesized via MOF process

In our earlier work, we have reported that Ni supported on γ-Al₂O₃–La₂O₃–CeO₂ (ALC) catalyst prepared via metal organic framework (MOF) was more active for acetic acid steam reforming (AASR) [1]. Here we report detailed study on the performance of this catalyst for AASR. Effects of operating conditions such as temperatures (400–650 °C), steam to carbon molar ratio (S/C) and feed flow rate (1.5–5.5 mL/h) were evaluated and optimized. Results showed an excellent activity for AASR at the molar ratio S/C = 6.5, feed flow rate = 2.5 mL/h and, at 600 °C with almost total conversion and more than 90% of H₂ yield. The ordered porous structure of embedded nickel supported catalyst promotes excellent steam reforming activity and water gas shift reaction even at low temperatures, which leads to the good stable behaviour up to 36 h of TOS. The coke formation was also significantly suppressed by ALC support. Catalyst regenerated by passing oxygen at 500 °C and followed by reduction in hydrogen also show a good activity. Catalysts were characterized by DT-TGA, XRD, TEM, H₂-TPR and N₂-adsorption-desorption to understand the micro structure and coke deposition behaviour.     

Hydrogen production from glycerol steam reforming over Co-based catalysts supported on La2O3, AlZnOx and AlLaOx

A comparative study of 10 wt% Co-based catalysts supported on La₂O₃, AlZnO_x and AlLaO_x was performed for glycerol steam reforming (GSR). The catalysts physicochemical characterization was done through several techniques. All catalysts were screened in terms of catalytic activity and time-on-stream stability for GSR. The catalytic activity experiments aimed to assess the effect of temperature (400–700 °C) on the glycerol conversion and yield of gaseous products (H₂, CO₂, CO and CH₄). Additionally, catalytic stability experiments were conducted at 625 °C to investigate deactivation of the catalysts, in which a drop in the activity was observed, especially for Co/La₂O₃. The glycerol conversion into gaseous products as a function of the time-on-stream was more affected for all catalysts in comparison to total glycerol conversion, being this effect assigned to the increase in the formation of liquid products and to the formation of coke. CoAlLaO_x was observed to be more carbon-resistant, followed by CoAlZnO_x, through the measurement of the quantity of carbonaceous species formed during the GSR experiments. A NiAlLaO_x catalyst was also prepared and assessed in terms of catalytic stability for GSR; a stable behavior was observed throughout all experiment in relation to glycerol conversion into gaseous products and H₂ yield.     

Application of aspen plus to renewable hydrogen production from glycerol by steam reforming

Steam reforming is the most favored method for the production of hydrogen. Hydrogen is mostly manufactured by using steam reforming of natural gas. Due to the negative environmental impact and energy politics, alternative hydrogen production methods are being explored. Glycerol is one of the bio-based alternative feedstock for hydrogen production. This study is aimed to simulate hydrogen production from glycerol by using Aspen Plus. First of all, the convenient reactor type was determined. RPlug reactor exhibited the highest performance for the hydrogen production. A thermodynamic model was determined according to the formation of byproduct. The reaction temperature, water/glycerol molar feed ratio as reaction parameters and reactor pressure were investigated on the conversion of glycerol and yield of hydrogen. Optimum reaction parameters are determined as 500 °C of reaction temperature, 9:1 of water to glycerol ratio and 1 atm of pressure. Reactor design was also examined. Optimum reactor diameter and reactor length values were determined as 5 m and 50 m, respectively. Hydrogen purification was studied and 99.9% purity of H₂was obtained at 25 bar and 40 °C. The obtained results were shown that Aspen Plus has been successfully applied to investigate the effects of reaction parameters and reactor sizing for hydrogen production from glycerol steam reforming.     

Copper promoted Co/MgO: A stable and efficient catalyst for glycerol steam reforming

Different types of cobalt-based mixed oxide catalysts (20 wt%Co/MgO, 5 wt%Cu-20 wt% Co/MgO, 20 wt%Co/50%MgO–50%Al₂O₃) were synthesized by the co-precipitation method and applied for hydrogen production from glycerol steam reforming. The catalysts were characterized using X-ray diffraction (XRD), H₂-Temperature-programmed reduction (H₂-TPR), CO₂-Temperature Programmed desorption, CO-Chemisorption, and CHN techniques. The H₂-TPR analysis showed the reducibility of cobalt-oxide (5Cu20CM; 5 wt%Cu-20 wt% Co/MgO) was enhanced by the copper, and reduction profiles of cobalt oxide shifted to a lower temperature (<450 °C). Among the catalysts, 5Cu20CM showed a maximum yield of hydrogen (74.6%) with 100% conversion of glycerol to the gaseous phase. The superior catalytic performance of 5Cu20CM for glycerol conversion was attributed to the smaller particle size (7 nm), higher dispersion of cobalt (35.0%), and the higher surface area (56 m²/g) of cobalt metal. Furthermore, Raman spectroscopy of the spent catalysts confirmed that the copper promoted cobalt-magnesium catalyst suppressed the carbon formation, consequently, 5Cu20CM catalyst showed a stable performance up to 30 h.     

Hydrogen production via the glycerol steam reforming reaction over nickel supported on alumina and lanthana-alumina catalysts

In the present work, a comparative study of Ni catalysts supported on commercially available alumina and lanthana-alumina carriers was undertaken for the glycerol steam reforming reaction (GSR). The supports and/or catalysts were characterized by PZC, BET, ICP, XRD, NH₃-TPD, CO₂-TPD, TPR and SEM. Carbon deposited on the catalytic surface was characterized by SEM, TPO and Raman. Concerning the Ni/LaAl sample it can be concluded that the presence of lanthana by: (a) facilitating the active species dispersion, (b) strengthening the interactions between nickel species and support, (c) increasing of the basic sites' population and redistributing the acid ones in terms of strength and density, provides a catalyst with improved performance for the GSR reaction, in terms of activity, H₂ production and long term stability. TPO and Raman indicate that the carbon on the Ni/LaAl catalyst was mostly amorphous and was deposited mainly on the support surface. For the Ni/Al catalyst, graphitic carbon was prevalent and likely covered its active sites.     

Hydrogen production from catalytic steam reforming of glycerol over various supported nickel catalysts

Supported Ni catalysts have been investigated for hydrogen production from steam reforming of glycerol. Ni loaded on Al₂O₃, La₂O₃, ZrO₂, SiO₂ and MgO were prepared by the wet-impregnation method. The catalysts were characterized by nitrogen adsorption–desorption, X-ray diffraction and scanning electron microscopy. The characterization results revealed that large surface area, high dispersion of active phase on support, and small crystalline sizes are attributes of active catalyst in steam reforming of glycerol to hydrogen. Also, higher basicity of catalyst can limit the carbon deposition and enhance the catalyst stability. Consequently, Ni/Al₂O₃ exhibited the highest H₂ selectivity (71.8%) due to small Al₂O₃ crystallites and large surface area. Response Surface Methodology (RSM) could accurately predict the experimental results with R-square = 0.868 with only 4.5% error. The highest H₂ selectivity of 86.0% was achieved at optimum conditions: temperature = 692 °C, feed flow rate = 1 ml/min, and water glycerol molar ratio (WGMR) 9.5:1. Also, the optimization results revealed WGMR imparted the greatest effect on H₂ selectivity among the reaction parameters.     

Kinetic investigation on butanol steam reforming over Ru/Al2O3 catalyst

Steam reforming of biomass-derived oxygenates is an attractive technique for the renewable production of hydrogen (H₂). In this work, steam reforming of n-butanol – a representative of bio-oxygenates – was studied over commercial 5% Ru/Al₂O₃ catalyst in a fixed-bed reactor. Kinetics of butanol reforming was investigated between temperatures 623 and 773 K at steam/carbon (S/C) ratio equal to 33.3 mol/mol. The W/F_A0 ratio (W: mass of catalyst, F_A0: molar flow rate of butanol in feed) was varied between 3.3 and 16.7 g h/mol. At T = 773 K, butanol conversion and H₂ yield were 93.4% and 0.61 mol/mol. Evaluation of the kinetic data showed that reaction order with respect to butanol was unity. The activation energy for the investigated reaction was 78 kJ/mol. Finally, a Langmuir-Hinshelwood model that assumed the surface reaction between the adsorbed reactants as rate-determining was used to describe the kinetic data.     

Sequence of Ni/SiO2 and Cu/SiO2 in dual catalyst bed significantly impacts coke properties in glycerol steam reforming

Coke formation is a major challenge in steam reforming reactions. In addition to development of robust catalyst for tackling coking, in this study we explored the approach of using dual catalyst bed with the catalyst on top as the guard or sacrifice catalyst while with the bottom catalyst to catalyze the steam reforming. The rationale is that some oxygen-containing reactants are prone to polymerize on heating, and the polymeric coke could directly fall on surface of catalyst and leads to the rapid deactivation. Hence, glycerol was selected as the reactant for steam reforming in the catalyst bed with the Cu/SiO₂ placed on the top of Ni/SiO₂ catalyst. Our results demonstrate that first contact of glycerol to Cu/SiO₂ on top changed abundance/type of small intermediates and the π-conjugated oligomers reached the Ni/SiO₂ catalyst, rendering the Ni catalyst with a higher resistivity towards coking and deactivation. In addition, the carbon nanotube form of coke over Ni/SiO₂ was thinner in wall thickness and larger in inner diameter of the cavity due to the impact of D-Cu/SiO₂. Substantial polymeric coke with amorphous structure and low thermal stability formed over Cu/SiO₂ via polymerisation of reaction intermediates. The characterization (in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)) for the glycerol steam reforming indicated that the Cu/SiO₂ and Ni/SiO₂ catalyst induced the formation of the very different functionalities of the reaction intermediates.     

Influence of operating variables on the aqueous-phase reforming of glycerol over a Ni/Al coprecipitated catalyst

A systematic study focused on the aqueous-phase reforming of glycerol has been carried out in order to analyze the influence of several operating variables (system pressure, reaction temperature, glycerol content in feed, liquid feeding rate and catalyst weight/glycerol flow rate ratio) on the gas and liquid products. A continuous flow bench scale installation and a Ni/Al coprecipitated catalyst were employed. The system pressure was varied from 28 to 40 absolute bar, the reaction temperature was analyzed from 495 to 510 K, the glycerol content in the feed was studied from 2 to 10 wt%, the liquid feeding rate was changed from 0.5 to 3.0 mL/min and the catalyst weight/glycerol flow rate ratio varied from 10 to 40 g catalyst min/g glycerol. The main gas products obtained were H₂, CO₂ and CH₄, while the main liquid products were 1,2-propanediol, ethylene glycol, acetol and ethanol. A W/m_glycerol ratio of 40 g catalyst min/g glycerol, 34 bar, 500 K, 5 wt% glycerol and 1 mL/min, resulted in a high yield to H₂ (6.8%), the highest yield to alkanes (10.7%), the highest 1,2-propanediol yield (0.20 g/g glycerol) and the highest ethylene glycol yield (0.11 g/g glycerol). The highest acetol yield (0.06 g/g glycerol) was obtained at 34 bar, 500 K, 5 wt% glycerol, 20 g catalyst min/g glycerol and 3 mL/min.     

Thermodynamic analysis of hydrogen production via glycerol steam reforming with CO2 adsorption

Thermodynamic equilibrium for glycerol steam reforming to hydrogen with carbon dioxide capture was investigated using Gibbs free energy minimization method. Potential advantage of using CaO as CO₂ adsorbent is to generate hydrogen-rich gas without a water gas shift (WGS) reactor for proton exchange membrane fuel cell (PEMFC) application. The optimal operation conditions are at 900 K, the water-to-glycerol molar ratio of 4, the CaO-to-glycerol molar ratio of 10 and atmospheric pressure. Under the optimal conditions, complete glycerol conversion and 96.80% H₂ and 0.73% CO concentration could be achieved with no coke. In addition, reaction conditions for coke-free and coke-formed regions are also discussed in glycerol steam reforming with or without CO₂ separation. Glycerol steam reforming with CO₂ adsorption has the higher energy efficiency than that without adsorption under the same reaction conditions.     

Glycerol steam reforming over Ni catalysts supported on ceria and ceria-promoted alumina

In this paper glycerol steam reforming over Ni catalysts supported on bare CeO₂ and Al₂O₃, and CeO₂-promoted Al₂O₃ to produce H₂ 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/Al₂O₃ 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 H₂.     

Improvement of steam methane reforming via in-situ CO2 sorption over a nickel-calcium composite catalyst

Optimization of steam methane reforming (SMR) reaction by CO₂ sorption enhancement was investigated. In this study, the sorption-enhanced steam methane reforming reaction (SESMR) was conducted to maximize hydrogen production via suitable adjustments in the operating conditions of the reaction, which include the molar ratio of steam to CH₄, space velocity, and temperature. The reforming catalysts were prepared by a physical mixture of 20 wt% Ni/Al₂O₃ and CaO. The results reveal that there are significant differences in CH₄ conversion between the SMR and the SESMR from 18% to 108%; this conversion strongly depended on the reaction conditions. High-purity H₂ products (98.9%) with <0.1 ppmv CO were obtained by SESMR under the suitable conditions of 2600 cm³/g/h, steam/CH₄ molar ratio of 4 and 823 K. This implies that the high-quality H₂ produced through the SESMR process could be directly used for the proton-exchange membrane fuel cell.     

Steam reforming of ethanol over nickel-tungsten catalyst

Ni-W/Al₂O₃ catalysts were synthesized, characterized and tested for the steam reforming of ethanol from 300 to 600 °C. Addition of Ni and W on the alumina, decreased the surface area and increased the pore volume of the mesoporous materials synthesized. The reaction products obtained were: H₂, CO₂, C₂H₄, CH₄, CO₂, CO and CH₃CHO. A promoting effect of Ni-W was observed in the conversion of ethanol to H₂ from 15 to 30 wt.% Ni and 1 wt.% W. The selectivity to H₂ on the alumina with Ni-W, was between 66.53 and 68.53% at 550 °C, appearing some undesirable products, with low ratio of CO/CO₂. Reaction was studied on a fixed bed reactor at atmospheric pressure with an ethanol/water molar ratio of 1:4, from 300 to 600 °C. The catalysts were characterized by the thermal gravimetric analysis (TGA)-Differential thermal analysis (DTA), N₂ physisorption (BET and BJH methods), X-ray diffraction (XRD) and scanning electron microscopy (SEM), these techniques were used for characterization, before and after of the steam reforming.     

Kinetics of ethanol steam reforming over Ni/Olivine catalyst

Olivine, a natural mineral consisting of different metal oxides (mainly Mg, Si and Fe oxides) was used as a support for nickel catalyst used in steam reforming of ethanol. Catalyst containing different wt% of Ni on olivine were prepared by conventional wet-impregnation method and characterized by BET, XRD, SEM (coupled with EDS) and H₂-TPR. The reaction was carried out in a tubular fixed bed reactor. Among all the catalysts, 5% Ni on olivine catalyst gave highest hydrogen yield as well as ethanol conversion through ethanol steam reforming reaction. The catalyst activity was analyzed by varying three important process parameters (temperature, ethanol to water molar ratio and space-time). The reaction was performed in the temperature range of 450 °C to 550 °C with 1:6 to 1:12 M feed ratio of ethanol to water at a space-time range 7.21–15.87 kg cat h/kmol ethanol. A maximum yield of 4.62 mol of hydrogen per mole of ethanol reacted was obtained at 550 °C with ethanol to steam molar ratio of 1:10 and space-time of 7.94 kg cat h/kmol ethanol with the ethanol conversion level of 97%. CHNS analysis of the spent catalyst was performed to find the coke deposited over the catalyst surface during the reaction. The power law and LHHW type kinetic models were developed. The power law model predicts the activation energy as 29.07 kJ/mol, whereas the LHHW type model gives the activation energy as 27.4 kJ/mol.     

Biogas steam and oxidative reforming processes for synthesis gas and hydrogen production in conventional and microreactor reaction systems

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.     

Hydrogen production by oxidative steam reforming of methanol over anodic aluminum oxide-supported Cu-Zn catalyst

Oxidative steam reforming of methanol (OSRM), which is a convenient reaction for producing hydrogen, suffers from the hot spot formation problem when conventional particle catalysts are used. Recently, an anodic aluminum oxide (AAO)-supported Cu-Zn catalyst was proposed as an OSRM catalyst for its high thermal conductivity through the aluminum metal body. In this study, OSRM was conducted in a prototype reactor packed with the AAO plate catalyst strips. It was verified that the high thermal conductivity of the catalyst effectively suppresses the hot spot formation and makes the temperature profile smooth along the reactor. The start-up time of the reactor depended on the preheating temperature and was very short (less than 2 min) for preheating over 503 K. The methanol conversion and reactor temperature increased with increasing O₂/CH₃OH mole ratio, indicating that the mole ratio can be used as a control variable to operate the reactor at desired conditions. Further, a reactor model was developed and verified, and the simulation showed that for a given total reactor volume, an optimal reactor configuration could be achieved by shortening the reactor length while widening the cross-sectional area.     

Production of hydrogen by ethanol steam reforming over catalysts from reverse microemulsion-derived nanocompounds

In the present work, hydrotalcite-like compound precursor for preparing mixed oxide catalyst was successfully synthesized by a novel method, which was a combination of the reverse microemulsion and coprecipitation methods. It was observed that the precursor obtained from the above method possessed superior characteristics for preparing mixed oxide catalyst used in ethanol steam reforming (ESR). Furthermore, for comparison, catalysts prepared from conventional coprecipitation and impregnation methods had been characterized together with the catalyst prepared from the new method. Besides ICP, BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), H₂-TPD, TG, and TEM analytic techniques, catalytic performance for ESR was also investigated. The results of XRD and TPR indicated that a solid solution phase existed in the catalysts obtained from reverse microemulsion and coprecipitation methods, while spinel phase together with solid solution were observed in the catalyst obtained from the impregnation method. The high BET surface area of the catalyst obtained from the reverse microemulsion method enhanced the dispersion and the surface area of nickel, which improved the catalyst performance. From TEM images, the aggregated Ni could be found in the catalyst obtained from the impregnation method, while the hydrotalcite-like compound precursors prepared from reverse microemulsion and coprecipitation methods produced homogeneously distributed active Ni metal species. The catalyst obtained from reverse microemulsion exhibited the best activity, stability, and least carbon deposition because of the formation of hydrotalcite-like compound precursor, uniform dispersion of active Ni metal species, and much more surface area supporting the active Ni metal sites.     

Developing a mathematical model for reforming of glycerol towards a comparative evaluation of the liquid vs. gas phase medium

Glycerol might be converted into hydrogen through a catalytic reforming process. In order to design an effective route, the choice of reaction conditions and in particular its medium considered yet a crucial issue still needing further investigations. In this research, a mathematical model of reforming processes in vapor (i.e., steam reforming (SR) and liquid phase (i.e.; aqueous phase reforming (APR)) were developed. This was performed in terms of understudying effects of parameters including the reactor diameter, catalyst morphology (i.e., particle size) and mass flow rate on the glycerol conversion. Then, a superior reaction medium in terms of these variables was determined. For data validation, experimental values were adopted from glycerol reforming over Pt/CeZrO₂ catalyst with BET surface area of 81–102 m² g⁻¹, mean particle size of 5.29–7.18 nm and crystallinity of 40–53%. It was revealed that, for the same WHSV and reactor length, conversion of the APR was considerably more than that of the SR process. Moreover, it was demonstrated that, if the SR had to have the same conversion as that of the APR, the utilized reactor length should have approximately increased by about 80 folds for the liquid phase. Overall, this study provided a simple pathway through the developed model to comparatively evaluate the medium (i.e.; gaseous as in the SR vs. liquid as in the APR) for the glycerol conversion aiming at reducing experimental costs a head of going to the laboratory.