Ethanol Reforming Research Articles

Application of BICOVOX catalyst for hydrogen production from ethanol

Catalytic activity of cobalt-doped bismuth vanadate [Bi4(V0.90Co0.10)2O11−δ ; BICOVOX] powder, prepared by a solution combustion synthesis and calcined at 800 °C (BICOVOX-800), for hydrogen production using low-temperature steam reforming of ethanol, has been reported in this paper. The effects of reaction temperature (250–400 °C) and feed concentration (H2O/EtOH = 2.5:1 and 23:1 mol ratio) on the steady-state ethanol conversion and selectivity of H2, CO2, CO, and CH4 have been investigated (up to 30 h). It is observed that with an increase in reaction temperature and H2O/EtOH mole ratio, H2 and CO2 selectivity increases and CO and CH4 selectivity decreases. The maximum H2 selectivity and ethanol conversion are observed to be 63 and 88%, respectively, for H2O/EtOH = 23:1 mol ratio at 400 °C. The XRD results show that the fresh BICOVOX-800 has pure γ-phase and is highly crystalline. The used catalyst (more than 150 h total) is detected to have less crystallinity and to partially decompose into Bi2O3 and BiVO4 phases.

Syngas production from ethanol dry reforming over Rh/CeO2 catalyst

Carbon dioxide reforming of ethanol over Rh/CeO2 catalyst was deeply investigated at different reaction temperatures of 450–700°C and reactant ratios (CO2/ethanol from 1 to 3) under atmospheric pressure. The obtained results indicated that Rh/CeO2 catalyst presented a promising activity and stability for syngas production from renewable bio-ethanol instead of conventional methane. Typically, CO2-rich conditions (CO2/ethanol=3) were favorable for reaction process and dynamic coke cleaning, which led to remarkably stable performance over 65h on stream. The strong redox capacity of CeO2 support might also accelerate CO2 activation and prevent the carbon accumulation over the catalyst surface. Additionally, tunable H2/CO ratios were available by changing the CO2/ethanol ratios. The results from characterization of samples before and after catalytic tests allowed to establish the relationship between textural properties and catalytic performance.

Influence of Catalytic Formulation and Operative Conditions on Coke Deposition over CeO2-SiO2 Based Catalysts for Ethanol Reforming

In this work, a series of CeO2-SiO2 (30 wt % of ceria)-based catalysts was prepared by the wetness impregnation method and tested for ESR (ethanol steam reforming) at 450–500 °C, atmospheric pressure and a water/ethanol ratio increasing from 4 to 6 (the ethanol concentration being fixed to 10 vol %); after every test, coke gasification measurements were performed at the same water partial pressure, and the temperature of the test and the gasified carbon was measured from the areas under the CO and CO2 profiles. Finally, oxidation measurements under a 5% O2/N2 stream made it possible to calculate the total carbon deposited. In an attempt to improve the coke resistance of a Pt-Ni/CeO2-SiO2 catalyst, the effect of support basification by alkali addition (K and Cs), as well as Pt substitution by Rh was investigated. The novel catalysts, especially those containing Rh, displayed a lowering in the carbon formation rate; however, a faster reduction of ethanol conversion with time-on-stream and lessened hydrogen selectivities were recorded. In addition, no significant gain in terms of coke gasification rates was observed. The most active catalyst (Pt-Ni/CeO2-SiO2) was also tested under different operative conditions, in order to study the effect of temperature and water/ethanol ratio on carbon formation and gasification. The increase in the water content resulted in an enhanced reactor-plugging time due to reduced carbonaceous deposits formation; however, no effect of steam concentration on the carbon gasification rate were recorded. On the other hand, the increase in temperature from 450–500 °C lowered the coke selectivity by almost one order of magnitude improving, at the same time, the contribution of the gasification reactions.

Cobalt Carbide Identified as Catalytic Site for the Dehydrogenation of Ethanol to Acetaldehyde

Two cobalt catalysts, Co/SBA-15 and Co/SiO2, have been studied in steam reforming of ethanol (SRE). Besides the steam reforming products, ethoxide dehydrogenation to acetaldehyde is observed as one of the main reactions. Although by hydrogen treatment cobalt is reduced to the metallic state, under SRE conditions, a phase appears that has been identified as cobalt carbide and correlates with acetaldehyde production. These findings provide insights about the catalytic sites, for SRE, in cobalt catalysts. Comparison with previous results shows that these conclusions are not translatable to other cobalt catalysts, stressing the importance of the support on the catalytic behavior of cobalt.

Parallel plates reactor simulation: Ethanol steam reforming thermally coupled with ethanol combustion

This work presents a theoretical study on the thermal coupling of ethanol steam reforming with ethanol combustion in a parallel plates reactor. A one-dimensional, heterogeneous, mathematical model is used and the effects of the main operative and constructive variables on the performance of the system are analyzed. Thermal coupling between combustion and reforming of ethanol is plausible and an adequate behavior of the reactor in terms of hydrogen yield and conversion of ethanol is predicted. The importance of distributing the source of heat is evidenced since high molar fractions of ethanol in the combustion stream can lead to excessive hot spots.

Anodic Layers Based on Doped-Ceria/Ni Cermet for Direct Ethanol Fuel Cells

Latest generation of solid oxide fuel cells (SOFCs) is a multilayer device in which several functional layers were incorporated to the anode/electrolyte/cathode configuration. Therefore, using an active layer that enables the fuel cell to run using a renewable fuel such as bioethanol is a reasonable strategy. Separating the catalytic and electrochemical reactions in different anodic layers has two main advantages: keeping the high-performance YSZ/Ni cermet and allowing an active and stable catalyst for ethanol reforming. Doped-cerium oxide is an attractive ceramic material for solid oxide fuel cells (SOFCs) because of the excellent electrochemical and catalytic properties and good compatibility with remaining cell components. In the present study, we have investigated the effect of different dopants on the properties of doped-ceria in Ni cermets aiming at using such cermets as the catalyst for ethanol internal reforming in SOFCs. High surface area ceria doped (10 mol%) with Gd, Y, Zr, and Nb were prepared by an hydrothermal method. The ceria-based solid solutions were mixed with Ni by a wet impregnation method to obtain 18 wt.% Ni relative fraction. Such relatively low Ni volume fraction (~15 vol.%) aims at minimizing coke formation while promoting electronic conductivity. The catalyst materials were deposited onto the anode of standard electrolyte-supported cells [(La,Sr)xMnO3 / YSZ / YSZ/Ni] and tested on dry ethanol. The fuel cell tests results were analysed along with data of both steam reforming and decomposition catalytic reactions for ethanol. Post-test analyses evidenced that water electrochemically generatedpromotes ethanol reforming, in agreement with catalytic tests in which doped-ceria/Ni showed no evidence of carbon deposits in the steam reforming reaction. On the other hand, analyses on spent catalysts of ethanol decomposition revealed carbon deposits. Nevertheless, no significant differences were observed for the studied dopants with the notable exception of niobium, which has a limited solubility in the ceria matrix. The experimental results confirm that upon fuel cell operation, ceria-Ni based catalysts promote alcohol steam reforming resulting in stable direct ethanol SOFCs.

An intelligent oxygen carrier of La2−xSrxNiO4−λ for hydrogen production by chemical looping reforming of ethanol

This work studied an intelligent perovskite of La2−xSrxNiO4−λ as oxygen carrier (OC) to produce hydrogen in chemical looping reforming (CLR) process. It was prepared by co-precipitation method and investigated by XRD, TEM, ICP-OES, H2-TPR, TGA technologies and fixed-bed experiment. The ‘intelligence’ refers to the self-regeneration ability and structural flexibility of perovskite. The former was verified by the movement that Ni ions repeatedly immerse into and out of perovskite bulk during CLR process. The movement suppressed the growth of Ni particles and maintained its high dispersion. The latter was confirmed by the addition of promoters. The insertion of Sr increased lattice oxygen mobility and greatly strengthened the reversible evolution of metallic Ni, which boosted the carbon-resistance and hold favorable stability of OC. The La1.4Sr0.6NiO4−λ was the optimized composition owing to the superior activity, higher hydrogen selectivity (87%) and admirable stability. Moreover, shortened ‘dead time’ and more ideal self-regeneration property of perovskite were attained due to easier reducibility of Ni ions.

Efficient heat allocation in the two-step ethanol steam reforming and solid oxide fuel cell integrated process

To avoid a carbon formation in the ethanol steam reforming process from the polymerization of ethylene, a two-step reforming of ethanol via a dehydrogenation reaction and a steam reforming reaction for hydrogen production is proposed in this work. The study of using a CaO sorbent for CO2 capture to enhance the hydrogen production for solid oxide fuel cells is also carried out. Modeling of the two-step ethanol steam reforming and solid oxide fuel cell integrated process based on a thermodynamic approach is performed using a flowsheet simulator. The results show that the presence of CaO in the two-step ethanol steam reforming process has several advantages, such as having higher hydrogen yield, gaining additional heat, and providing a higher power output at a relative low reforming temperature. However, the exergy analysis indicates that this process has a higher total exergy destruction compared to the process without CaO because of the high amount of heat needed in the regenerator. Therefore, a heat allocation technique based on the first and second laws of thermodynamics is used to identify the optimal operating condition. The results show that when the reformer is operated at a temperature of 800 K and a steam-to-ethanol ratio of one, the minimum total exergy destruction to power ratio can be achieved and heat is also sufficient.

Enhancing Pt-Ni/CeO2 performances for ethanol reforming by catalyst supporting on high surface silica

In this paper, bimetallic Pt-Ni/CeO2 catalysts supported over mesoporous silica were employed for ethanol reforming in the low-temperature range. In particular, catalyst behaviour was investigated under a H2O/C2H5OH/N2 as well as H2O/C2H5OH/AIR mixture between 300 and 600°C at different space velocities (10000–30000h−1). Ethanol conversion, for both steam (ESR) and oxidative steam reforming (OSR) reactions, was not affected by contact time decrease at T>480°C while at lower temperatures, the space velocity growth led to reduced C2H5OH conversion, more pronounced when tests were performed without O2 co-feeding. Moreover, the catalysts showed high resistance to deactivation during reforming tests at 500°C and 20000h−1: the improvement of active species dispersion, as a consequence of catalyst formulation enrichment by SiO2 addition, resulted in lower carbon selectivity with respect to the SiO2-free sample. However, the higher extent of coke gasification reaction for OSR further increased catalyst stability and total ethanol conversion was recorded for almost 3500min, 1000min more than ESR case.

Water neutrality and waste heat management in ethanol reformer - HTPEMFC integrated system for on-board hydrogen generation

On-board power generation for vehicular applications requires a compact, simplified and well-integrated fuel processor-fuel cell system. In the present paper, the integration of an ethanol reformer unit with a 50 kWe high temperature polymer electrolyte membrane (PEM) fuel cell is studied for potential automotive applications. A high-efficiency dual reformer system is used for on-board production of hydrogen from ethanol. Heat transfer equipment for recovery of water and effective utilization of waste heat has been incorporated into the integrated system. Detailed analysis using ASPEN simulations shows that gross system efficiencies of up to 39% can be achieved. Estimates of size, weight of the integrated system have been made to assess its suitability for application as auxiliary power units in automotive systems.

Hydrogen production by steam reforming of ethanol over Ni/Al2O3-La2O3 xerogel catalysts

A series of nickel catalysts supported on binary Al2O3-La2O3 xerogel supports with different La/Al molar ratio were prepared via a sol-gel method and a subsequent wetness impregnation method for use in the ethanol steam reforming reaction. The effect of La/Al molar ratio on the characteristics and catalytic activities of Ni/Al2O3-La2O3 catalysts in the hydrogen production by steam reforming of ethanol was investigated. The prepared Ni/Al2O3-La2O3 catalysts were characterized by nitrogen adsorption-desorption, ICP-AES (inductively coupled plasma atomic emission spectroscopy), XRD (X-ray diffraction), 27Al MAS NMR (magicangle spinning nuclear magnetic resonance), TPR (temperature-programmed reduction), TPO (temperature-programmed oxidation), TEM (transmission electron microscopy), and TPD (temperature-programmed desorption) analyses. Physicochemical properties of the catalysts were suppressed with increasing La/Al molar ratio because of the formation of defective structure within the alumina lattice. Acidity of Ni/Al2O3-La2O3 catalysts was weakened with increasing La/Al molar ratio, while basicity of the catalysts was strengthened. Nickel dispersion and nickel surface area increased with increasing La/Al molar ratio. On the contrary, ethanol adsorption capacity of the catalysts decreased with increasing La/Al molar ratio due to their unfavorable physicochemical properties. Hydrogen yield showed a volcano-shaped curve with respect to La/Al molar ratio, where an optimal amount of La content was required to achieve the most promising catalytic performance. The enhanced catalytic activity at an intermediate La/Al molar ratio is believed to be due to the offset of two opposite trends between nickel surface area and ethanol adsorption capacity of Ni/Al2O3-La2O3 catalysts.

Structural and catalytic stability assessment of Ni-La-Sn ternary mixed oxides for hydrogen production by steam reforming of ethanol.

NixLaSn trimetallic catalysts (x=5 and 15% by weight) were prepared by a coprecipitation technique by pH change and then calcined at 700°C, 850°C, 900°C and 950°C. XRD analysis of the fresh and unreduced catalysts showed the formation of crystalline phases corresponding to the pyrochlore structure La2Sn2O7 and NiO following calcination at 850°C, 900°C and 950°C. Ni3Sn and Ni3Sn2 compounds were formed under a pure hydrogen atmosphere and 650°C in the well crystallized catalyst containing the pyrochlore. This catalyst was highly active in the ethanol steam reforming reaction at 650°C, giving yield to gaseous mixtures containing hydrogen, carbon monoxide, carbon dioxide and methane. XRD analysis of the spent catalyst showed the presence of Ni3Sn2, Ni3Sn and the pyrochlore as unique phases after 80 hours of reaction time. After an initial decay, H2 yield kept stable until the end of the test. Carbon formation was observed by TEM, TG and elemental analysis. Lanthanum carbonates were also revealed by Raman spectroscopy. The highly stable biphasic structure containing Ni-Sn intermetallic compounds and the La2Sn2O7 could be the basis of catalysts for the production of H2-rich gaseous mixtures starting from bioethanol.

Oxidative steam reforming of ethanol (OSRE) over stable NiCo–MgAl catalysts by microwave or sonication assisted coprecipitation

The present paper reports the physicochemical and catalytic characterization of NiCo–MgAl mixed oxides prepared from hydrotalcite (HT) precursors using ultrasound (US) or microwave radiation (MW)-assisted coprecipitation. The US or MW use reduces the preparation time and enhance both basicity and redox properties of the material compared to the solid obtained by the conventional method (coprecipitation).The oxidative steam reforming of ethanol (OSRE) was performed during 100 h (stability test) with or without solid pre-reduction in order to understand some aspects of the OSRE mechanism when transition metal catalysts are used without activation. The results demonstrate the potential of using 1Ni1Co mixed oxides obtained by MW or US assistance which exhibited better properties and catalytic stability employing shorter synthesis times. Furthermore, experiments conducted without material pre-reduction indicate the sensitivity of OSRE to the basic strength of the surface. A marked increase in basicity decrease H2 yield because of the formation of C3 byproducts.

Cu promoted Ni-Co/hydrotalcite catalyst for improved hydrogen production in comparison with several modified Ni-based catalysts via steam reforming of ethanol

Enhanced hydrogen production via catalytic steam reforming of ethanol has a huge potential. In the present investigation, several combinations of mixed metal oxide supported catalysts were evaluated for efficient and economical hydrogen generation from ethanol. The comparison was carried out in terms of ethanol conversion, hydrogen yield and cyclic stability over various catalyst-support systems. Several nickel based supported catalysts namely, Ni/MgO, Ni/Al2O3, Ni/CeO2 and Ni/ZrO2 were studied in this work among which Ni/MgO and Ni/Al2O3 showed satisfactory activity and stability for hydrogen production. Thereafter Ni/hydrotalcite (HTc)-type material was employed to combine features of the above catalysts which showed more than 90% ethanol conversion and yielded 82 mol% of hydrogen at optimized conditions. Finally, a novel combination of Cu promoted Ni-Co/HTc was synthesized and tested for improved hydrogen production. It showed almost complete conversion of ethanol (98.3%) with hydrogen yield of 83% at much lower temperature (673 K). The process conditions were optimized by studying effects of temperature, S/C ratio and GHSV on hydrogen production. Cu-Ni-Co/HTc also remained stable for up to 4 cycles justifying its multi-cycle activity, selectivity and durability. Such novel combination of catalyst-support system assists in improved hydrogen production in a sustainable manner.

Oxidative steam reforming of ethanol on rhodium catalyst – I: Spatially resolved steady-state experiments and microkinetic modeling

Oxidative steam reforming of ethanol is an important process for on board production of hydrogen in fuel cell based auxiliary power systems. Although the process has been extensively studied from a catalyst perspective, accurate models that capture species and temperature information required by model-based control algorithms during operation have not yet been developed adequately. In this work, we develop a reduced micro-kinetic model for ethanol oxidative steam reforming, which can be used in computational fluid dynamics (CFD) studies and subsequently to develop model-based control strategies. We experimentally study cordierite monolith based reactors in which Rh/CeO2 catalysts are prepared by the solution-combustion method. The catalyst system is characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), temperature programmed reduction and temperature programmed desorption analyses. The experimental reformer design enables measurement of species concentrations at various points along the reactor length, along with radial temperature profiles. A micro-kinetic model is adapted from the literature and validated against these experiments, with good agreement. The model results suggest a linear activation pathway for ethanol over rhodium catalysts by forming ethoxide, acetyl and acetate intermediates. After formation of single carbon species, the methane reforming pathway is followed. We expect that these studies, when coupled with transient studies will help in formulating model-based control strategies for ethanol reformers in complex fuel cell systems.

Cycle analysis of solid oxide fuel cell-gas turbine hybrid systems integrated ethanol steam reformer: Energy management

A solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system that uses such liquid fuels as ethanol is attractive for distributed power generation for applications in remote rural areas or as an auxiliary power unit. The SOFC system includes units that require and generate heat; thus, its energy management is important to improve its efficiency. In this study, a SOFC-GT integrated system with the external steam reforming of ethanol to produce hydrogen for the SOFC is proposed. Two SOFC-GT hybrid systems using a high-temperature heat exchanger and cathode exhaust gas recirculation are considered under isothermal conditions. The effects of key operating parameters, such as pressure, fuel use and turbomachinery efficiency, on the SOFC-GT hybrid system performance are discussed. The simulation results indicate that recycling the cathode exhaust gas from the SOFC-GT system requires less fresh air from the compressor, to maintain the SOFC stack temperature, and the heat recovered from the SOFC system is sufficient to supply both the fuel processor and air pre-heater. In contrast, an external heat is needed for the SOFC-GT system coupled to a recuperative heat exchanger.

Coke-resistant Pt-ni/ceo2/sio2 Catalysts for Ethanol Reforming

Coke-resistant Pt-ni/ceo2/sio2 Catalysts for Ethanol Reforming

Hydrogen production from oxidative steam reforming of ethanol over Ir catalysts supported on Ce–La solid solution

The Ce1−xLaxO2−δ solid solution (CL) supported Ir (nIr/CL, n = 2, 5 and 10 wt.%) catalysts are studied for H2 production from ethanol oxidative steam reforming (OSR). The Ir dispersion, surface area, oxygen vacancy density and carbon deposition resistance of nIr/CL catalysts are greatly enhanced compared with Ir/CeO2. Among the tested catalysts, 5%Ir/CL shows the best catalytic performance, exhibiting >99.9% ethanol conversion at 400 °C with H2 yield rate of 323 μmol·gcata−1·s−1 and no obvious carbon deposition after used. The 5%Ir/CL catalyst contains the highest amount of reducible interface Ce4+, leading to a strong interaction with surface Ir species at the metal-support interface during the OSR reaction. The strong interaction induces Ir to be well dispersed on the CL support, and is associated with more redox-active sites (interface Ce4+/Ce3+), to guarantee high activity.

YSZ monoliths promoted with Co as catalysts for the production of H2 by steam reforming of ethanol

Steam reforming of ethanol was investigated between 400°C and 600°C over 3mol% Y2O3 doped ZrO2 monolith infiltrated with Co, known as an effective catalyst for this reaction. Monoliths were fabricated by implementing the freeze-casting technique in order to obtain hierarchical, vertical and highly ordered porous microstructure resulting in very low pressure drop, high surface area and accessibility to active sites. Catalytic monoliths were firstly loaded with 3wt% of Co. Catalytic activity of Co-containing monolith was compared with the catalytic activity of a powdered material with the same chemical composition than the catalytic monolith. The results show a clear improvement all over the temperature range of the ethanol conversion and H2 yield and a decrease of the by-products contents when using a freeze-cast monolith support. The incorporation of La enabled a strong decrease in coke deposition over the activated monolith. The effect of the addition of 0.25wt.% of Pt was also studied. Pt makes possible to inhibit carbon deposition but has a detrimental effect on ethanol conversion at temperatures above 500°C and on H2 selectivity at low temperature. A higher Pt loading of 0.8wt% did not bring any beneficial effect and was even detrimental at low temperature. Finally, the beneficial effect of the implementation of freeze-cast monolith in comparison with the not structured fixed-bed configuration is explained by the difference of packing since and improved fluid dynamics at similar GHSV, the former one promotes in a higher proportion the Water Gas Shift Reaction (WGSR) further in the monolith length.

Highly active and stable Ni supported on CNTs-SiO2 fiber catalysts for steam reforming of ethanol

In this research, a new kind of carbon nanotubes-silica fibrous composite (CNTs-SF) was successfully synthesized by the steam reforming of ethanol over a Ni/silica fiber catalyst prepared by electrospinning technique. The fibrous composite was then used as a support for the ethanol steam reforming by loading nickel at 5 and 10wt%. The prepared catalysts were characterized by BET, SEM, TEM, XRD, TPR, and TG/DTG. The reaction performance of the NiCNTs-SF catalysts was investigated and compared with the Ni/silica fiber (NiSF) and Ni/silica porous (NiSP) catalysts. The effect of temperatures on the ethanol conversion and product distribution was studied in the range of 300 and 500°C. The NiCNTs-SF catalyst exhibited the best performance in term of stability and high activity at lower reaction temperature. The outstanding performance of the NiCNTs-SF catalyst could be associated with highly metallic dispersion and easily accessible to the reactants.