Effect of noble metal on oxidative steam reforming of methanol over CuO/ZnO/Al2O3 catalysts

Noble metals of Pd, Pt, Ru and Rh were introduced into the CuO/ZnO/Al₂O₃(30/60/10) catalyst via incipient impregnation and co-precipitation methods to examine their effects on the oxidative steam reforming of methanol (OSRM). No obvious effect of Pd and even a negative effect of Pt were observed by incipient impregnation method. With co-precipitation, noble metals were homogeneously dispersed in CuO/ZnO/Al₂O₃(30/60/10) and interacted with CuO and ZnO. They improved the reducibility of the catalysts and enhanced the dissociative adsorption of methanol. Introducing Pd, Rh or Ru promoted the conversion of methanol, but enhanced the formation of CO. Depositing platinum exhibited a high conversion of methanol and a low selectivity of CO in the OSRM reaction. The promoting effect of noble metals involved facilitating the split and adsorption of H atoms during the dehydrogenation of the intermediates in OSRM.     

Oxidative steam reforming of methanol over CuO/ZnO/CeO2/ZrO2/Al2O3 catalysts

The composition (CuO/ZnO/Al₂O₃ = 30/60/10) of a commercial catalyst G66B was used as a reference for designing CuO/ZnO/CeO₂/ZrO₂/Al₂O₃ catalysts for the oxidative (or combined) steam reforming of methanol (OSRM). The effects of Al₂O₃, CeO₂ and ZrO₂ on the OSRM reaction were clearly identified. CeO₂, ZrO₂ and Al₂O₃ all promoted the dispersions of CuO and ZnO in CuO/ZnO/CeO₂/ZrO₂/Al₂O₃ catalysts. Aluminum oxide lowered the reducibility of the catalyst, and weakened the OSRM reaction. Cerium oxide increased the reducibility of the catalyst, but weakened the reaction. Zirconium oxide improved the reducibility of the catalyst, and promoted the reaction. A lower CuO/ZnO ratio of the catalyst was associated with greater promotion of ZrO₂. The critical CuO/ZnO ratio for the promotion of ZrO₂ was approximately 0.75–0.8. Introducing of ZrO₂ into CuO/ZnO/Al₂O₃ also improved the stability of the catalyst. Although Al₂O₃ inhibited the OSRM reaction, a certain amount of it was required to ensure the stability and the mechanical strength of the catalysts.     

Methanol steam reforming in an Al2O3 supported thin Pd-layer membrane reactor over Cu/ZnO/Al2O3 catalyst

In this experimental study, a membrane reactor housing a composite membrane constituted by a thin Pd-layer supported onto Al₂O₃ is utilized to perform methanol steam reforming reaction to produce high-grade hydrogen for PEM fuel cell applications. The influence of various parameters such as temperature, from 280 to 330 °C, and pressure, from 1.5 to 2.5 bar, is analyzed. A commercial Cu/Zn-based catalyst is packed in the annulus of the membrane reactor and the experimental tests are performed at space velocity equal to 18,500 h⁻¹ and H₂O:CH₃OH feed molar ratio equal to 2.5:1. Results in terms of methanol conversion, hydrogen recovery, hydrogen yield and products selectivities are given. As a best result of this work, 85% of methanol conversion and a highly pure hydrogen stream permeated through the membrane with a CO content lower than 10 ppm were reached at 330 °C and 2.5 bar. Furthermore, a comparison between the experimental results obtained in this work and literature data is proposed and discussed.     

Steam reforming of methanol over Cu/ZnO/ZrO2/Al2O3 catalyst

Steam reforming of methanol was investigated over Cu–ZnO–ZrO₂–Al₂O₃ catalysts at 473 and 573 K. The Cu:Zn:(Al + Zr) molar ratio was 3:3:4; however, the Zr:Al molar ratio was varied and the catalysts were pretreated at different calcination and reduction temperatures. The synthesized catalysts were characterized by N₂ physisorption, temperature-programmed reduction with H₂ (H₂-TPR), X-ray diffraction, oxidized surface TPR, and infrared spectroscopy after carbon monoxide chemisorption. The crystalline size of Cu decreased on increasing the calcination temperatures from 573 to 623 K and increased on increasing the reduction temperatures from 523 to 573 K. Among the tested catalysts, the Cu–ZnO–ZrO₂ catalyst exhibited the highest and lowest hydrogen-formation rates at 473 and 573 K, respectively. After the reaction at 573 K, all the tested catalysts exhibited an increase in the Cu crystalline size, causing the catalyst deactivation. Among the tested catalysts, the Cu–ZnO–ZrO₂–Al₂O₃ catalyst, where the Cu:Zn:Al:Zr molar ratio was 3:3:2:2, showed the highest and most stable catalytic activity at 573 K. Cu dispersion and catalyst composition affected the catalytic performance for steam reforming of methanol.     

Effect of higher alcohols on the performances of a 1%Rh/MgAl2O4/Al2O3 catalyst for hydrogen production by crude bioethanol steam reforming

The object of the present study was to study the role of alcohols, which are the major impurities found in a crude bioethanol feed, on the catalytic performances of a 1%Rh/MgAl₂O₄/Al₂O₃ catalyst during ethanol steam reforming. The alcohols studied were methanol, propan-1-ol, butan-1-ol, pentan-1-ol, isopropanol, 2-methyl propan-1-ol, 3-methyl butan-1-ol. Whereas the presence of 1% of methanol in the ethanol and water feed only slightly increased the hydrogen yield, the addition of the same amount of higher alcohols strongly decreased the stability of the catalyst during ethanol steam reforming, with a direct impact on the ethanol conversion and the hydrogen yield. It was shown that the deactivation is increased when the amount of carbon atoms in the molecule is increased. This effect is more pronounced in the presence of branched alcohols compared to the linear ones. It was demonstrated by studying the steam reforming of these higher alcohols that they are dehydrated to the corresponding olefin. The strong deactivation of the catalyst observed in the presence of higher alcohols was explained in terms of coke deposition.     

Oxidative steam reforming of ethanol for hydrogen production on M/Al2O3

In this work, we investigate oxidative steam reforming (OSR) of ethanol on a series of metals under various catalytic conditions (H₂O/ethanol and O₂/ethanol ratios) to understand the reaction mechanism and to optimize the catalytic conditions for optimal hydrogen production. There are three reaction pathways for OSR using these metals. Ethanol can be oxidized to acetaldehyde on Cu, Ag and Au, and it can be dehydrated to form ethylene on Co, Ni, Pd and Pt. Ethylene can form coke and degrade catalysts after the long-term OSR. In the third pathway, ethanol preferentially breaks its C–C bond and is further oxidized to CO or CO₂ on Ru, Rh and Ir, providing optimal hydrogen production. In addition, increasing H₂O/ethanol and O₂/ethanol ratios can improve catalytic activity, attributable to atomic oxygen from H₂O and O₂ efficiently rupturing the C–C bond of ethanol. This concept explains the improved performance of OSR on the CeO₂-modified catalyst, which shows better oxygen storage capability.     

One-step growth of CuO/ZnO/CeO2/ZrO2 nanoflowers catalyst by hydrothermal method on Al2O3 support for methanol steam reforming in a microreactor

CuO/ZnO/CeO₂/ZrO₂ nanoflowers catalyst was grown on an Al₂O₃ foam ceramic by a one-step hydrothermal process, while a naked Al₂O₃ foam ceramic and an Al₂O₃ foam ceramic grown with ZnO nanorods that directly impregnated into the catalyst precursor solution were also fabricated simultaneously. The morphology, composition, redox property and specific surface area of catalysts on the three ceramics were investigated in detail. The catalyst-loaded ceramics were used as catalyst supports in a microreactor to study the catalytic performance for methanol steam reforming. Results showed that the microreactor with Al₂O₃ support grown with nanoflowers catalyst achieved 99.8% methanol conversion rate, 0.16 mol/h H₂ flow rate at 310 °C, and an inlet methanol flow rate of 0.048 mol/h. Moreover, the microreactor exhibited 92% methanol conversion rate after 30 h continuous reaction.     

Steam reforming and oxidative steam reforming of methanol over CuO–CeO2 catalysts

Steam reforming (SRM) and oxidative steam reforming of methanol (OSRM) were carried out over a series of coprecipitated CuO–CeO₂ catalysts with varying copper content in the range of 30–80 at.% Cu (= 100 × Cu/(Cu + Ce)). The effects of copper content, reaction temperature and O₂ concentration on catalytic activity were investigated. The activity of CuO–CeO₂ catalysts for SRM and OSRM increased with the copper content and 70 at.% CuO–CeO₂ catalyst showed the highest activity in the temperature range of 160–300 °C for both SRM and OSRM. After SRM or OSRM, the copper species in the catalysts observed by XRD were mainly metallic copper with small amount of CuO and Cu₂O, an indication that metallic copper is an active species in the catalysis of both SRM and OSRM. It was observed that the methanol conversion increased considerably with the addition of O₂ into the feed stream, indicating that the partial oxidation of methanol (POM) is much faster than SRM. The optimum 70 at.% CuO–CeO₂ catalyst showed stable activities for both SRM and OSRM reactions at 300 °C.     

Hydrogen production by steam reforming of model bio-oil using structured Ni/Al2O3 catalysts

This study focuses on hydrogen production from the steam reforming of model bio-oil over Ni/Al₂O₃ catalysts prepared in two different geometries (monolith and pellet) using the dip-coating and wet impregnation methods and characterized using Powder X-Ray diffraction, Temperature Programmed Reduction, Scanning Electron Microscopy (SEM) and BET Surface area analysis. The effects of the catalyst geometry and reforming temperatures were studied by carrying out experiments at the optimal conditions of T = (823, 923, 1023) K and S/C ratio = 13 determined from the thermodynamic analysis of the process prior to the experiments using the process simulator PRO-II. The experimental results showed high steady state H₂ yield corresponding to 2.58 and 1.73 mol (out of 5.13 mol) using monolithic and the pelletized catalysts respectively. The product distribution achieved with the monolithic catalyst was closer to the thermodynamic results suggesting a higher selectivity to hydrogen production.     

Numerical simulation of configuration and catalyst-layer effects on micro-channel steam reforming of methanol

A micro-reactor with eight non-parallel channels is proposed to improve the performance of micro-channel steam reforming of methanol. The widths of some channels in the micro-reactor vary gradually along the reactor length direction. The Zn-Cr/CeO₂-ZrO₂ catalyst is coated in the reformer with a certain porosity and permeability. The effects of micro-reactor structures and catalyst-coated manners on several factors are studied, including temperature distributions, velocity distributions, reactant concentrations and the methanol conversion rate. The results indicate that such a structure with a certain entrance inclination angle and channel inclination angle guarantees flow distribution uniformity in each reforming channel. Flow distribution uniformity is conducive to the increase of the methanol conversion rate. Besides, in order to measure strengths and weaknesses of different catalyst-coated manners, a wall-coated reformer and a packed-bed reformer are studied respectively. It is found that compared to the packed-bed reformer, the temperature and the methanol conversion rate in wall-coated reformer are far higher. It is necessary to find an optimal catalyst thickness that is able to reduce the CO concentration because the catalyst thickness can affect CO concentration in the product gases indirectly. The optimal inclination angles and the catalyst thickness are proposed based on the simulating results.     

The role of effectiveness factor on the modeling of methanol steam reforming over CuO/ZnO/Al2O3 catalyst in a multi-tubular reactor

A pseudo-homogeneous model for the methanol steam reforming process was developed based on reaction kinetics over a CuO/ZnO/Al₂O₃ catalyst and non-adiabatic heat and mass transfer performances in a co-current packed-bed reactor. A Thiele modulus method and an intraparticle distribution method were applied for predicting the effectiveness factors for main reactions and providing insights into the diffusion-reaction process in a cylindrical catalyst pellet. The results of both methods are validated and show good agreements with the experimental data, but the intraparticle distribution method provides better predictions. Results indicate that increases in catalyst size and bulk fluid temperature amplify the impact of intraparticle diffusion limitations, showing a decrease in effectiveness factors. To satisfy the requirements of a high temperature polymer electrolyte membrane fuel cell stack, the optimized operating conditions, which bring the methanol and CO concentrations to less than 1% vol in the reformate stream, are determined based on the simulation results.     

Morphology effect of ceria on the performance of CuO/CeO2 catalysts for hydrogen production by methanol steam reforming

Nano-rod(R), nano-particle(P) and sponginess(S) of ceria samples were used to study catalytic performance of hydrogen production by methanol steam reforming. The samples were prepared by hydrothermal method, precipitation method, and sol-gel method, respectively, and the CuO was supported on the different morpholopy of CeO₂ samples by wet impregnation. SEM, TEM, XRD, XRF, BET, H₂-TPR, XPS and N₂O titration methods were used to study correlation between the structure and the catalytic performance for methanol steam reforming. The results showed that the morphology of the prepared CeO₂ support dramatically influenced the performance of catalysts. Due to the stronger interaction between copper oxide and ceria support, the CuO/CeO₂-R catalyst had exhibited the better catalytic activity than those of the CuO/CeO₂P and CuO/CeO₂S catalysts. Moreover, higher Cu dispersion, lower reduction temperature of CuO, and higher content of active species Cu⁺ were also advantageous to raising catalytic effects. Besides, with the highest content of surface Ce³⁺, the CuO/CeO₂-R had estimated the content of oxygen vacancy on the surface of the catalyst. The existence of surface oxygen vacancy had a positive effect on the methanol steam reforming.     

Oxidative steam reforming of ethanol over a Pt/Al2O3 catalyst in a Pd-based membrane reactor

In this study, the ability of a Pd-Ag membrane reactor of producing ultrapure hydrogen via oxidative steam reforming of ethanol has been evaluated. A self supported Pd-Ag tube of wall thickness 60 μm has been filled with a commercial Pt-based catalyst and assembled into a membrane module in a finger-like configuration. In order to evaluate the hydrogen yield behavior under different operating conditions, experimental tests have been performed at temperatures of 400 and 450 °C and pressures of 150 and 200 kPa. The oxidative steam reforming of ethanol has been carried out by feeding the membrane reactor with a gas stream containing a dilute water-ethanol mixture and air. Different water/ethanol feed flow rates (5, 10, 15 g h⁻¹), several water/ethanol (4, 10, 13) and oxygen/ethanol (0.3, 0.5, 0.7) feed molar ratios have been tested. The results pointed out that the highest hydrogen yield (moles of permeated hydrogen per mole of ethanol fed) corresponding to almost 4.1 has been attained at 450 °C and 200 kPa of lumen pressure by using a water/ethanol/oxygen feed molar ratio of 10/1/0.5.The results of these tests have been compared with those reported for the ethanol steam reforming in a Pd-Ag membrane reactor filled with the same Pt-based catalyst. This comparison has shown a positive effect on the hydrogen yield of small oxygen addition in the feed stream.     

Fuel cell grade hydrogen production via methanol steam reforming over CuO/ZnO/Al2O3 nanocatalyst with various oxide ratios synthesized via urea-nitrates combustion method

Hydrogen production via steam reforming of methanol has been studied over a series of CuO/ZnO/Al₂O₃ catalysts synthesized by the combustion method using urea as fuel. Furthermore, the effect of alumina loading on the properties of the catalyst has been investigated. XRD analysis illustrated the crystallinity of the Cu and Zn oxides decreases by enhancing alumina loading. BET showed the surface area improvement and FESEM images revealed lower size distribution by increasing the amount of alumina. EDX results gave approximately the same metal oxide compositions of primary gel for the surface of the nanocatalysts. Catalytic performance tests showed the well practicability of catalysts synthesized by the combustion method for steam reforming of methanol process. Alumina addition to the CuO/ZnO catalyst caused the higher methanol conversion and the lower CO generation. Among different compositions the sample with molar component of CuO/ZnO/Al₂O₃ = 4/4/2.5 showed the best performance which without CO generation at 240 °C its methanol conversion decreased from 90 to 60% after 90 h.     

Catalytic properties of Ag promoted ZnO/Al2O3 catalysts for hydrogen production by steam reforming of ethanol

Ag promoted ZnO/Al₂O₃ catalysts were prepared by using the incipient wetness impregnation method. The catalytic properties of steam reforming reaction for hydrogen production on the prepared catalysts were evaluated with H₂O:C₂H₅OH molar ratios of 3:1 at 450 °C and atmospheric pressure. Ag promoted ZnO/Al₂O₃ catalysts show higher SRE catalytic activity than ZnO/Al₂O₃ catalysts. H₂ and CH₃CHO are the major products on Ag promoted catalysts, and C₂H₄ is also produced probably due to acid sites on Al₂O₃. SRE mechanism on Ag promoted ZnO/Al₂O₃ catalysts, which contains C-C scission, is different from that on ZnO/Al₂O₃ catalysts. A method based on thermogravimetry (TG), differential scanning calorimetry (DSC) and mass spectrometry (MS) was used to analysis the coking behavior on catalyst surface. The surfaces of Ag promoted ZnO/Al₂O₃ catalysts show two different types of coking, and suffer higher coke deposition during the steam reforming reaction.     

H2 production in silica membrane reactor via methanol steam reforming: Modeling and HAZOP analysis

The main aim of this work is the presentation of both qualitative safety and quantitative operating analyses of silica membrane reactor (MR) for carrying out methanol steam reforming (MSR) reaction to produce hydrogen. To perform the safety analysis, HAZOP method is used. Before the HAZOP analysis, a comprehensive investigation of most important operating parameters effects on silica MR performance is required. Therefore, for a quantitative analysis, a 1-dimensional and isothermal model is developed for evaluating the reaction temperature, reaction pressure, feed molar ratio (steam/methanol) and feed flow rate effects on silica MR performance in terms of methanol conversion and hydrogen recovery. The model validation results show good agreement with experimental data from literature. As a consequence, simulation results indicate that the reaction pressure and feed molar ratio have dual effect on silica MR performance. In particular, it is found that methanol conversion is decreased by increasing the reaction pressure from 1.5 to 4.0 bar, whereas over 4.0 bar, it is improved. Moreover, the hydrogen recovery is decreased by increasing the feed molar ratio from 1 to 5, while over 5, it was approximately constant. After the evaluation of modeling results, the HAZOP analysis for silica MR is carried out during MSR reaction. The analysed operating parameters in the modeling study have been considered as key parameters in the HAZOP analysis. The safety assessment results are presented in tables as check list. By considering the HAZOP results, safety pretreatment works are recommended before or during the experimental tests of MSR reaction in silica MR. According to different parameters consequences, reaction temperature is the most critical parameter in MSR reaction for the silica MR studied in this work. In particular, to avoid the consequences of temperature deviation, it is recommended to use a PID temperature controller in the silica MR for MSR reaction.     

Thermodynamic performance analysis of the influence of multi-factor coupling on the methanol steam reforming reaction

This work presents the H₂ production from methanol steam reforming (MSR) process by thermodynamic equilibrium analysis using the Gibbs free energy minimization method and multi-factor coupling method. To determine desirable procedure parameters with maximum methanol conversion and H₂ content and minimum CO content, the impacts of the temperature: 100–400 °C, steam-to-methanol (S/C) molar ratio: 1.0–3.0, and pressure: 0.5–3.0 atm were investigated. The dominant factor under the action of multiple factors and the specific influence of each factor on the MSR process were verified, simultaneously. For proton exchange membrane fuel cell (PEMFC), to keep the CO content of the reformate within a desired range, and under the premise of complete methanol conversion, the MSR process can be operated at lower temperature, higher S/C ratio and atmospheric pressure. Combined with practice process, the optimum values of the temperature, S/C ratio and pressure to produce reformate were identified to be 200–300 °C,1.6–2.0 and 1.0 atm, respectively.     

Influence of preparation methods and Zr and Y promoters on Cu/ZnO catalysts used for methanol steam reforming

Binary Cu/ZnO catalysts were prepared using three different methods (coprecipitation, sequential precipitation and homogeneous precipitation) and tested in a methanol steam reforming reaction. Zirconium and yttrium were tested as promoters, and their effects were evaluated in the same reaction. The studied preparation methods influenced the surface area of the Cu-based catalysts and consequently their catalytic activity; however, we verified that surface area was not the only factor influencing activity. Different structural changes in the aurichalcite precursor resulted from the different preparation methods used, and these differences were also observed in the reduced catalysts. An expansion of the Cu lattice with an increase in microstrain were identified and attributed to the formation of a Cu–Zn alloy. Based on the correlation found between these structural changes and the catalytic activity, the Cu–Zn alloy was proposed as active site. We concluded that the preparation methods used influenced Cu dispersion and overall catalyst structure, and Cu–Zn alloy formation resulted from the incorporation of Zn atoms into the Cu lattice. This influence was more pronounced in the catalysts prepared by homogeneous precipitation and coprecipitation. The yttrium promoter did not provide textural or structural advantages. In contrast, the incorporation of Zr promoted both greater Cu dispersion and structural changes in the Cu lattice.     

Methanol steam reforming kinetics using a commercial CuO/ZnO/Al2O3 catalyst: Simulation of a reformer integrated with HT-PEMFC system

This study provides a kinetic examination of methanol steam reforming (MSR) over a Cu-based commercial catalyst (CuO/ZnO/Al₂O₃, Alfa Aesar) as a function of CH₃OH and H₂O partial pressures at 246 °C and 1 atm in a once-through flow reactor. A power rate law was used to best describe the experimental rate data by linear and non-linear regressions at the operating conditions where transport bottlenecks were eliminated. Comparison of the rate parameters indicated that a strong correlation was suggested by non-linear regression giving reaction orders of 0.29 for methanol and 0.09 for water along with a frequency factor of 53.48 (mol_CH3OH s⁻¹ g_catalyst⁻¹ kPa^−0.38) and an activation energy of 65.59 kJ mol⁻¹. A simulation study of the rate equation to analyze an integrated system of a reformer and an HT-PEMFC was also conducted. The results demonstrate that the system has the potential to produce 15 W power output.     

Stacked etched aluminum flow-through membranes for methanol steam reforming

Electrochemical etching has been used to obtain aluminum foil with high surface area for use as electrodes in electrolytic capacitors. In this approach, direct current etching first generates straight penetrating microchannels, and then a second etching step enlarges the microchannel diameter. In the present work, we developed catalyst supports using aluminum etched with microchannels as a microreactor. The metal aluminum foil catalyst support obtained by etching contained microchannels with a diameter of 1.0–3.0 μm (10,000–15,000 microchannels/mm²). We stacked membrane layers and evaluated their performance in methanol steam reforming. The performance of the reactors containing stacked membranes improved as the layer number increased. The microchannels in this catalytic membrane could be used as reaction channels, were easy to fabricate at low cost, and could be mass-produced continuously. This novel catalytic membrane support opens up new possibilities for practical fabrication of industrial materials.