Microwave-assisted synthesis of high performance copper-based catalysts for hydrogen production from methanol decomposition

High performance copper-based catalysts (CuNiZnO/γ-Al₂O₃) for hydrogen production from methanol decomposition were successfully synthesized by the method of microwave-assisted thermal hydrolysis of urea. The ICP-OES, N₂ adsorption–desorption, SEM, TEM, XRD and H₂-TPR were applied to characterize the physicochemical properties of the prepared materials. These experiment results reveal that the higher thermal treatment temperature can improve the catalytic performance by enlarging the content of promoters (Zn and Ni) and promoting the dispersion of deposited particles. Moreover, the addition of Ni can significantly improve the catalytic performance of the copper-based catalysts, which is ascribed to the regulation of reaction process and inhibition of CuZn alloy. Among the obtained catalysts, the MW-Cu/Ni-95 developed at 95 °C exhibits a higher catalytic activity, which reaches 91.7% conversion at 250 °C. Most significantly, it shows the excellent catalytic performance as compared with the commercial catalyst under the same test conditions.     

Effects of synthesis methods on performance of CuZn/MCM-41 catalysts in methanol steam reforming

CuZn-based catalysts are active in production of hydrogen by methanol steam reforming. However, there is a need to have further insight on their physico-chemical properties to improve selectivity to hydrogen. Therefore, a series of CuZn/MCM-41 catalysts was synthesized by four different routes; one pot hydrothermal synthesis (OPMCM), co-impregnation (COMCM), serial impregnation (SRMCM) and copper impregnated on Zn-MCM-41 (ZNMCM). Samples of catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP) emission spectrometry, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). XRD revealed disruption in the ordered pore network typical in MCM-41 for all catalysts synthesized and also showed that the one pot synthesis catalyst had wide spread dispersion of Cu and Zn. SEM micrographs captured irregularly shaped particles of different sizes. While XPS showed that different Cu and Zn species were formed within the catalyst matrix. XPS also confirmed that there was wide spread dispersion and interaction of Cu and Zn with MCM-41 matrix in the OPMCM catalyst. COMCM and OPMCM demonstrated the highest activity with 88 and 65% methanol conversion with corresponding H₂ selectivity of 91 and 86% respectively. They are better than SRMCM and ZNMCM which had average H₂ selectivity of 19% and 31% respectively. CO selectivity was less than 1.8% for the COMCM and OPMCM catalysts. While SRMCM and ZNMCM had CO selectivity's as high as 8.9% and 7.2% respectively. The data generated shows that catalytic activity is largely affected by the nature of Cu species within the catalyst matrix.     

Comparison of hydrogen consumption behavior of chromium and manganese promoted copper-based catalysts

CuO/ZnO/Al₂O₃/MgO–Cr and -Mn catalysts are synthesized using nitrate route via co-precipitation method. The precursors are characterized by XRD. The decomposition behavior of the precursors is analyzed by Air-TGA. The catalysts calcined at 250, 300, 350 and 450 °C are characterized by XRD and BET. CuO particle size reduction and surface area of the catalysts are investigated. Increasing the calcination temperature from 350 °C to 450 °C crystallite size increases about 3 nm, and BET surface area decreases about 30 m²/g. The reduction characteristics of the catalysts are analyzed via TPR and H₂-TGA, and H₂ consumption values of Cr and Mn containing catalysts is found as 40% and 60%, respectively. Peak temperatures of Mn containing catalysts (290–325 °C) are lower than peak temperatures of Cr containing catalysts (300–360 °C) as confirmed by H₂-TGA and H₂-DTG. The optimum H₂ consumption value of 52% is obtained with CuO/ZnO/Al₂O₃/MgO–Mn catalyst calcined at 350 °C.     

Dynamic optimization of a novel radial-flow,spherical-bed methanol synthesis reactor in the presence of catalyst deactivation using Differential Evolution (DE) algorithm

In this work, a novel radial-flow spherical-bed methanol synthesis reactor has been optimized using Differential Evolution (DE) algorithm. This reactor's configuration visualizes the concentration and temperature distribution inside a radial-flow packed bed with a novel design for improving reactor performance with lower pressure drop. The dynamic simulation of spherical multi-stage reactors has been studied in the presence of long-term catalyst deactivation. A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methanol production in radial-flow spherical-bed methanol synthesis reactor. The simulation results have been shown that there are optimum values of the reactor inlet temperatures, profiles of temperatures along the reactors and reactor radius ratio to maximize the overall methanol production. The optimization methods have enhanced additional yield throughout 4 years of catalyst lifetime, respectively.     

Effect of methanol, ethylene glycol and their oxidation by-products on the activity of Pt-based oxygen-reduction catalysts

Direct-oxidation fuel cells (DOFC) are promising electrochemical devices for various applications. In addition to methanol (MeOH), alternative fuels are being tested in a search for lower toxicity, safer handling, and higher energy density. Ethylene glycol (EG) was employed as one of such fuels. However, DOFCs face several problems, such as fuel crossover through the membrane during its operation. This not only lowers the cell potential but also poisons the catalyst for the oxygen-reduction reaction (ORR). Experiments were performed on the poisoning of Pt and Pt-alloy ORR catalysts (both commercial and homemade, by electroless deposition), by fuels and their oxidation by-products. At 25 °C, methanol poisoning was found to be reversible and the catalytic activity measured afterwards in a fuel-free solution and the electrochemical surface area (ECSA) were enhanced. The effect of poisoning by methanol and ethylene glycol and their oxidation intermediates is reported here for the first time. The severity of poisoning was found to be MeOH ? formaldehyde < formic acid. In solutions of EG and its oxidation by-products, the poisoning order was EG ≤ glycolic acid < oxalic acid, the poisoning of all three being more severe than that of methanol. The catalysts most resistant both to MeOH and EG poisoning were commercial acid-treated PtCo and homemade PtCoSn. The reasons for the enhanced tolerance were investigated and PtCoSn was found to be the less active both in the methanol and ethylene glycol oxidation processes.     

A numerical performance study of a fixed-bed reactor for methanol synthesis by CO2 hydrogenation

Synthetic fuels are needed to replace their fossil counterparts for clean transport. Presently, their production is still inefficient and costly. To enhance the process of methanol production from CO₂ and H₂ and reduce its cost, a particle-resolved numerical simulation tool is presented. A global surface reaction model based on the Langmuir-Hinshelwood-Hougen-Watson kinetics is utilized. The approach is first validated against standard benchmark problems for non-reacting and reacting cases. Next, the method is applied to study the performance of methanol production in a 2D fixed-bed reactor under a range of parameters. It is found that methanol yield enhances with pressure, catalyst loading, reactant ratio, and packing density. The yield diminishes with temperature at adiabatic conditions, while it shows non-monotonic change for the studied isothermal cases. Overall, the staggered and the random catalyst configurations are found to outperform the in-line system.     

The performance evaluation of an industrial membrane reformer with catalyst-deactivation for a domestic methanol production plant

Methane reforming is the most important and economical process for hydrogen and syngas generation. In this work, the dynamic simulation of methane steam reforming in an industrial membrane reformer for synthesis gas production is developed. A novel deactivation model for commercial Ni-based catalysts is proposed and the monthly collected data from an existing reformer in a domestic methanol plant is used to optimize the model parameters. The plant data is also employed to check the model accuracy. It was observed that the membrane reformer could compensate for the catalyst deactivating effect.In order to assure the long membrane lifetime and decrease the unit price, the membrane reformer with 5 μm thick Pd on stainless steel supports is modeled at the temperature below the maximum operating temperature of Pd based membranes (around 600 °C). The dynamic modeling showed that the methane conversion of 76% could be achieved at a moderate temperature of 600 °C for an industrial membrane reformer. The cost-effective generation of syngas with an appropriate H₂/CO ratio of 2.6 could be obtained by membrane reformer. This is while the conventional reformer exhibits a maximum conversation of 64 at 1200 °C challenging due to its high syngas ratio (3.7). On the other hand, the pure hydrogen from membrane reformer can supply part of the ammonia reactor feed in an adjacent ammonia plant.     

Effects of preparation conditions on performance of carbon-supported nanosize Pt-Co catalysts for methanol electro-oxidation under acidic conditions

Carbon-supported Pt-Co and Pt catalysts are prepared by NaBH₄ reduction of metal precursors. The particles size of Pt-Co varies with the pH used in the preparation, it is largest (12 nm) in alkaline solution and smallest (3.7 nm) in un-buffered solution. For the latter, X-ray photoelectron spectroscopy shows that Pt exists principally in the metallic state, whereas cobalt is mostly oxidized. The performance of the catalysts for methanol electro-oxidation in acidic media at room temperature is evaluated and compared with that of a Pt/C catalyst. Electrochemical measurements by cyclic voltammetry and chronoamperometry demonstrate consistently high catalytic activities and improved resistance to carbon monoxide for the Pt-Co catalysts, particularly for that prepared in un-buffered solution.     

Enhancement of methanol production in a novel fluidized-bed hydrogen-permselective membrane reactor in the presence of catalyst deactivation

In this study, a dynamic model for a novel bubbling fluidized-bed membrane dual-type methanol reactor has been developed in the presence of long-term catalyst deactivation. The proposed model has been used to compare the performance of a novel fluidized-bed membrane dual-type methanol reactor (FMDMR) with membrane dual-type methanol reactor (MDMR) and conventional dual-type methanol reactor (CDMR). In this new concept, the feed synthesis gas is preheated in the tubes of the gas-cooled reactor and flowing in a counter-current mode with reacting gas mixture in the shell side. Due to the hydrogen partial pressure driving force, hydrogen can penetrate from feed synthesis gas into the reaction side through the membrane. The outlet synthesis gas from this reactor is fed to tubes of the water-cooled packed-bed reactor and the chemical reaction is initiated by the catalyst. The methanol-containing gas leaving this reactor is directed into the shell of the gas-cooled reactor and the reactions are completed in this fluidized-bed side. This reactor configuration solves some observed drawbacks of new conventional dual-type methanol reactor such as pressure drop, internal mass transfer limitations, radial gradient of concentration and temperature in gas-cooled reactor. The proposed dynamic model has been validated against measured daily process data of a methanol plant recorded for a period of four years and a good agreement has been achieved. The simulation results show there is a favorable profile of temperature and activity along the fluidized-bed membrane dual-type reactor relative to membrane and conventional dual-type reactor systems. Therefore, the performance of methanol reactor system improves when membrane assisted fluidized-bed concept is used for conventional dual-type reactor system.     

Comparison of methanol and ethylene glycol oxidation by alloy and Core-Shell platinum based catalysts

Two Core-Shell, Ru_Core-Pt_Shell and IrNi_Core-PtRu_Shell, XC72-supported catalyst were synthesized in a two-step deposition process with NaBH₄ as reducing agent. The structure and composition of the Core-Shell catalysts were determined by EDS, XPS and XRD. Electrochemical characterization was performed with the use of cyclic voltammetry. Methanol and ethylene glycol oxidation activities of the Core-Shell catalysts (in terms of surface and mass activities) were studied at 80 °C and compared to those of a commercial Pt-Ru alloy catalyst. The surface activity of the alloy based catalyst, in the case of methanol oxidation, was found to be superior as a result of optimized surface Pt:Ru composition. However, the mass activity of the PtRu/IrNi/XC72 was higher than that of the alloy based catalyst by ∼50%. Regarding ethylene glycol oxidation, while the surface activity of the alloy based catalyst was slightly higher than that of the Pt/Ru/XC72 catalyst, the latter showed ∼66% higher activities in terms of A g⁻¹ of Pt. These results show the potential of Core-Shell catalysts for reducing the cost of catalysts for DMFC and DEGFC.     

Review of methanol reforming-Cu-based catalysts,surface reaction mechanisms,and reaction schemes

Recent development in proton-exchange membrane fuel cell technology has stimulated research in fuel processing for hydrogen production. Hydrogen can be produced from four different types of methanol reforming processes, namely methanol decomposition, partial oxidation of methanol, steam reforming of methanol and oxidative steam reforming of methanol. This review paper discusses commonly used Cu-based catalysts including their kinetic, compositional, and morphological characteristics in methanol reforming reactions. Although research exploring surface reaction mechanism over various Cu-based catalysts was first attempted about three decades ago, the scheme remains controversial. This technical discussion will focus on the commonly reported surface intermediate species, which are methoxy, formaldehyde, dioxymethylene, formate and methyl formate. The surface reaction mechanism could be complicated by the introduction of reactants such as oxygen and steam, into the system as they would subsequently initiate secondary reactions. Different reaction schemes of methanol reforming are presented.     

Recent progress of anode catalysts and their support materials for methanol electrooxidation reaction

This review paper summarizes the recent progress of anode catalysts for methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). The electrocatalytic activities of the noble and noble-free catalysts in different electrolyte media are compared and discussed. Noble-free catalysts exhibit high activity in alkaline medium, whereas Pt-based catalysts are the most active MOR catalysts in acidic medium. The types of catalyst support materials for DMFC anodes are also discussed and further divided into carbonaceous and non-carbonaceous materials. The ion and electron transport through the support materials and their effects on the overall performance are elaborated. Lastly, this paper highlights the major challenges in achieving the optimum DMFC performance from the aspect of tailoring the properties of MOR electrocatalysts to pave its way for commercialisation.     

Enhancement of simultaneous hydrogen production and methanol synthesis in thermally coupled double-membrane reactor

Coupling the methanol synthesis with the dehydrogenation of cyclohexane to benzene in a co-current flow, catalytic fixed-bed double-membrane reactor configuration in order to simultaneous pure hydrogen and methanol production was considered theoretically. The thermally coupled double-membrane reactor (TCDMR) consists of two Pd/Ag membranes, one for separation of pure hydrogen from endothermic side and another one for permeation of hydrogen from feed synthesis gas side (inner tube) into exothermic side. A steady-state heterogeneous model is developed to analyze the operation of the coupled methanol synthesis. The proposed model has been used to compare the performance of a TCDMR with conventional reactor (CR) and thermally coupled membrane reactor (TCMR) at identical process conditions. This comparison shows that TCDMR in addition to possessing advantages of a TCMR has a more favorable profile of temperature and increased productivity compared with other reactors. The influence of some operating variables is investigated on hydrogen and methanol yields. The results suggest that utilizing of this reactor could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the recuperative reactor.     

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.     

Investigation of the effect of carbonaceous supports on the activity and stability of supported palladium catalysts for methanol electro-oxidation reaction

In this study, nitrogen doped graphene (NG) and multi-walled carbon nanotubes (MWCNT) were used as supporting materials for palladium active phase to investigate their performance in direct methanol fuel cells (DMFCs). The facile and low temperature solvothermal method was used for the synthesis of NG. Palladium nanoparticles were deposited on the surface of NG and MWCNT by a modified polyol reduction method. The morphologies and microstructures of the prepared catalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Also, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were carried out to evaluate the electrocatalytic activity and the durability of the obtained catalysts towards methanol oxidation reaction. Pd/NG catalyst had a better activity and durability of methanol electrocatalytic oxidation rather than Pd/MWCNT catalyst, which is related to good dispersion of Pd nanoparticles on the surface of nitrogen doped graphene and the physicochemical characteristics of NG.     

Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

Methanol synthesis from CO2 hydrogenation over CuO-ZnO-ZrO2-MxOy catalysts (M=Cr,Mo and W)

Three CuO-ZnO-ZrO₂-M_xO_y (CZZM, M = Cr, Mo and W) mixed oxides were prepared by a co-precipitation method and tested as catalysts for methanol synthesis from CO₂ hydrogenation. The catalysts were characterized by XRD, N₂ adsorption/desorption, XPS, reactive N₂O adsorption, H₂-TPR, and CO₂-TPD techniques. The results indicated that the methanol selectivity and yield of the CuO-ZnO-ZrO₂ catalyst noticeably increased by the additions of MoO₃ and WO₃, but slightly decreased by Cr₂O₃ doping. Combining with the characterization results, the difference in methanol yield over the three catalysts can be attributed to the differences in their BET specific surface areas (S_BET) and adsorption capacities for CO₂, while the methanol selectivity is closely correlated to the ratio of surface contents of Zn to Cu, as well as the fraction of strong basic sites in the total basic sites of the investigated catalysts.     

A novel configuration for hydrogen production from coupling of methanol and benzene synthesis in a hydrogen-permselective membrane reactor

Coupling energy intensive endothermic reaction systems with suitable exothermic reactions improve the thermal efficiency of processes and reduce the size of the reactors. One type of reactor suitable for such a type of coupling is the heat-exchanger reactor. In this work, a distributed mathematical model for thermally coupled membrane reactor that is composed of three sides is developed for methanol and benzene synthesis. Methanol synthesis takes place in the exothermic side and supplies the necessary heat for the endothermic dehydrogenation of cyclohexane reaction. Selective permeation of hydrogen through the Pd/Ag membrane is achieved by co-current flow of sweep gas through the permeation side. A steady-state heterogeneous model of the two fixed beds predicts the performance of this novel configuration. The co-current mode is investigated and the simulation results are compared with corresponding predictions for an industrial methanol fixed-bed reactor operated at the same feed conditions. The results show that although methanol productivity is the same as conventional methanol reactor, but benzene is also produced as an additional valuable product in a favorable manner, and auto-thermal conditions are achieved within the both reactors and also pure hydrogen is produced in permeation side. This novel configuration can increase the rate of methanol synthesis reaction and shift the thermodynamics equilibrium. The performance of the reactor is numerically investigated for various key operating variables such as inlet temperatures, molar flow rates of exothermic and endothermic streams, membrane thickness and sweep gas flow rate. The reactor performance is analyzed based on methanol yield, cyclohexane conversion and hydrogen recovery yield. The results suggest that coupling of these reactions in the presence of membrane could be feasible and beneficial. Experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.     

The role of CO adsorption and CuO formation on the catalyst deactivation during the long-term performance evaluation of methanol steam reforming process for hydrogen production: Comparison of sono-coprecipitation and spray pyrolysis method

In this study, microreactors were coated with catalysts synthesized by two different methods and hydrogen was produced by methanol steam reforming. The structure of the catalysts was characterized by XRD, SEM and EDS analyses in the synthesis, activation and after long-term evaluation stages. The effect of CO adsorption and the structural changes of catalysts on the product stream and conversion were investigated and compared in detail. As a result, it was observed that the catalyst prepared by sono-coprecipitation (SCC) was more active although lost its performance much faster. Considering the performance graphs, SEM/EDS analyses and XRD results, it was revealed that the main reason for the performance decrease of the SPC-reactor (spray pyrolysis coating) was the increase of CO adsorption on the surface. Also, the formation of CuO structures and CO adsorption in the SCC-reactor were responsible for the faster performance decrease.     

Performance assessment and evaluation of catalytic membrane reactor for pure hydrogen production via steam reforming of methanol

The steam reforming of methanol was investigated in a catalytic Pd–Ag membrane reactor at different operating conditions on a commercial Cu/ZnO/Al₂O₃ catalyst. A comprehensive two-dimensional non-isothermal stationary mathematical model has been developed. The present model takes into account the main chemical reactions, heat and mass transfer phenomena in the membrane reactor with hydrogen permeation across the PdAg membrane in radial direction. Model validation revealed that the predicted results satisfy the experimental data reasonably well under the different operating conditions. Also the impact of different operating parameters including temperature, pressure, sweep ratio and steam ratio on the performance of reactor has been examined in terms of methanol conversion and hydrogen recovery. The modeling results have indicated the high performance of the membrane reactor which is related to continuous removal of hydrogen from retentate side through the membrane to shift the reaction equilibrium towards formation of hydrogen. The obtained results have confirmed that increasing the temperature improves the kinetic properties of the catalyst and increase in the membrane's H₂ permeance, which results in higher methanol conversion and hydrogen production. Also it is inferred that the hydrogen recovery is favored at higher temperature, pressure, sweep ratio and steam ratio. The model prediction revealed that at 573 K, 2 bar and sweep ratio of 1, the maximum hydrogen recovery improves from 64% to 100% with increasing the steam ratio from 1 to 4.