Methanol Steam Reforming Reaction Research Articles

Construction of porous Cu/CeO2 catalyst with abundant interfacial sites for effective methanol steam reforming

Methanol is a promising hydrogen carrier for fuel cell vehicles (FCVs) via methanol steam reforming (MSR) reaction. Ceria supported copper catalyst has attracted extensive attentions due to the extraordinary oxygen storage capacity and abundant oxygen vacancies. Herein, we developed a colloidal solution combustion (CSC) method to synthesize a porous Cu/CeO2(CSC) catalyst. Compared with Cu/CeO2 catalysts prepared by other methods, the Cu/CeO2(CSC) catalyst possesses highly dispersed copper species and abundant Cu+-Ov-Ce3+ sites at the copper-ceria interface, contributing to methanol conversion of 66.3 %, CO2 selectivity of 99.2 %, and outstanding hydrogen production rate of 490 mmol gcat−1 h−1 under 250 °C. The linear correlation between TOF values and Cu+-Ov-Ce3+ sites amount indicates the vital role of Cu+-Ov-Ce3+ sites in MSR reaction, presenting efficient ability in activation of water. Subsequently, a deep understanding of CSC method is further presented. In addition to serving as a hard template, the colloidal silica also acts as disperser between nanoparticles, enhancing the copper-ceria interactions and facilitating the generation of Cu+-Ov-Ce3+ sites. This study offers an alternative approach to synthesize highly dispersed supported copper catalysts.

Numerical modeling of triply period minimal surface structures with catalyst coating for hydrogen production of methanol steam reforming

The catalyst support structure has a significant influence on the performance of the methanol steam reforming (MSR) microreactor for in-situ hydrogen production. Triply period minimal surface (TPMS) structures are emerging as an attractive option as porous MSR catalyst supports owing to their excellent specific surface area, smooth surface and highly interconnected pores. This paper develops a numerical model of the sheet TPMS unit structures with catalyst coating to investigate the flow and reaction characteristics for hydrogen production of MSR reaction. The P, G, and D curved surface structural models were constructed with different porosities. The numerical results indicated that the P curved surface structure with the porosity of 90% had the lowest pressure drop of 0.15 Pa and the highest permeability of 6.31 × 10−9 m2, while the G curved surface structure always demonstrated excellent flow performance within the porosity range of 50–90%. The D curved surface structure exhibited the best reaction performance with hydrogen production exceeding P and G curved surface structures by about 23% and 78% respectively. Furthermore, the performance differences between the two flow phases of the sheet TPMS structures were investigated for the bicontinuous characteristic. The flow phases of the G curved surface structure demonstrated the best consistency in flow and reaction performances. Finally, the optimal design of the sheet, network, and multi-unit heterogeneous TPMS structural catalyst supports was discussed.

Structured nanoporous Cu/ZnO catalysts for on-board methanol steam reforming prepared by laser powder bed fusion and dealloying

The development of efficient structural catalysts and reactors (SCRs) for on-board methanol steam reforming (MSR) has long been a focal point. Traditional MSR SCRs exhibit problems such as poor heat transfer, low catalyst loading, and coating delamination. In this study, novel three-dimensional graded nanoporous Cu/ZnO (3DNP-Cu/ZnO) SCRs were prepared via metal 3D printing technology and dealloying. For 3DNP-Cu/ZnO SCRs activated with MeOH/H2O steam, both the interfacial area of Cu-ZnO and the Cu+/(Cu0 + Cu+) molar ratio were greater than those of catalysts activated with H2/N2 mixtures. The experimental results showed that a 3DNP-Cu/ZnO SCR activated with MeOH/H2O for 20 min exhibited a high methanol conversion rate of 98.3 % with a CO selectivity of 0.86 % (with a reaction temperature of 280 °C, a water-to-alcohol molar ratio of 1.3 and a weight hourly space velocity of 30 h−1). The superior catalytic activity was attributed to the high Cu+/(Cu++Cu0) ratio, which enabled the generation of *CHOO during the MSR reaction. Additionally, the 3DNP-Cu/ZnO SCRs demonstrated low pressure drops and high mechanical strengths. Computational fluid dynamics simulations showed that the gyroid lattice-structured catalyst achieved a high H2 concentration due to its high mass and heat transfer. 3DNP-Cu/ZnO SCRs provide a new strategy for the preparation of MSR SCRs with broad application prospects.

Quench-induced Cu-ZnO catalyst for hydrogen production from methanol steam reforming

Methanol steam reforming (MSR) is considered as a promising approach to provide hydrogen for proton-exchange membrane fuel cells. However, it is challenging to develop effective and durable Cu-based catalysts. Herein, Cu-ZnO catalysts are prepared by facile quenching of ZnO in copper nitrate solution followed by reduction to obtain the desired metal loading and induce the doping of surface metal heteroatoms for producing more vacancies. Catalysts enriched with oxygen vacancies can efficiently activate H2O and rapidly transform C-containing intermediates, resulting in higher methanol conversion and lower CO selectivity. As a result, the quenched optimal catalyst achieves 100 % methanol conversion and 0.05 % CO selectivity at 280 ℃, exhibiting the excellent catalytic performance in MSR reaction. In practical applications, structured catalysts are more attractive for large-scale catalytic reactions owing to the low pressure drop and high utilization efficiency. Therefore, ZnO-Cu3 catalyst is coated on cordierite honeycomb ceramics with 100 % methanol conversion and 0.04 % CO selectivity at 280 ℃. After 100 h of the reaction, the structured catalyst remains ∼ 92.3 % with CO selectivity varying from 0.02 to 0.06 %, demonstrating the good catalytic stability in the long-term experiment. In addition, the evolution of reactants and intermediates on the catalyst surface are briefly described by FTIR spectra. This study offers a novel and efficient approach to obtain highly active and durable catalysts with great potential for industrial-scale preparation and application.

Efficient Low‐temperature Hydrogen Production by Electrochemical‐assisted Methanol Steam Reforming

AbstractMethanol steam reforming (MSR) provides an alternative way for efficient production and safe transportation of hydrogen but requires harsh conditions and complicated purification processes. In this work, an efficient electrochemical‐assisted MSR reaction for pure H2 production at lower temperature (~140 °C) is developed by coupling the electrocatalysis reaction into the MSR in a polymer electrolyte membrane electrolysis reactor. By electrochemically assisted, the two critical steps including the methanol dehydrogenation and water‐gas shift reaction are accelerated, which is attributed to decreasing the methanol dehydrogenation energy and promoting the dissociation of H2O to OH* by the applied potential. Furthermore, the reduced H2 partial pressure by the hydrogen oxidation and reduction process further promotes MSR. The combination of these advantages not only efficiently decreases the MSR temperature but also achieves the high rate of hydrogen production of 505 mmol H2 g Pt−1 h−1 with exceptionally high H2 selectivity (99 %) at 180 °C and a low voltage (0.4 V), and the productivity is about 30‐fold than that of traditional MSR. This study opens up a new avenue to design novel electrolysis cells for hydrogen production.

Numerical study on a novel solar-thermal-reaction system for clean hydrogen production of methanol-steam reforming

Renewable energy-driven hydrogen production methods offer a promising solution for mitigating energy crises. The present study introduces a new solar-driven hydrogen production system that within methanol steam reforming (MSR) process. The numerical analysis is carried out using a cylindrical Fresnel linear concentrator coupled with a solar thermal reactor (STR). A comprehensive kinetic model of the MSR reaction was constructed and combined with analytical methods based on Monte Carlo ray tracing methods and finite volume methods to analyze the multi-physical properties involved in the reaction process. The results indicate that a novel solar-driven MSR-STR system can generate a sufficient driving force after adjusting the concentrator structure and relative position to match the energy demand of the MSR reaction. The accuracy of the model is compared with the experimental values, and the average error is 7.8 %. Tracking error of the component should be maintained below 1.5° to ensure the optical efficiency. The annual hydrogen production was analyzed and the levelized cost of hydrogen is $1.77/kg. Finally, a comparison is presented between the proposed MSR-STR system and parabolic trough concentrator based MSR hydrogen production system to evaluate the feasibility of the former in terms of the economics of implementation.

Experimental Control of a Methanol Catalytic Membrane Reformer

A simple proportional integral (PI) controller with scheduled gain has been developed and implemented in a catalytic membrane reactor (CMR) to obtain pure hydrogen from a methanol steam reforming process. The controller is designed to track the setpoint of the pure hydrogen flow rate in the permeate side of the CMR via the manipulation of the fuel inlet flow rate. Therefore, the controller actuator is the liquid pump that provides the mixture of methanol and water to the reactor. Within the CMR, the catalytic pellets of PdZn/ZnAl2O4/Al2O3 have been used to facilitate the methanol steam-reforming reaction under stoichiometric conditions (S/C = 1), and Pd–Ag metallic membranes have been employed to simultaneously separate the generated hydrogen. The PI controller design is based on a mathematical model constructed using transfer functions acquired from dynamic experiments conducted with the CMR. The controller has been successfully implemented, and experimental validation tests have been carried out at 450 °C and relative pressures of 6, 8, 10, and 12 bar.

ZnFexAl2-xO4 spinel supported PdZnβ bifunctional catalyst for methanol steam reforming

PdZnβ alloy catalysts, long regarded as a very promising copper replacement, not only possess copper-like reactivity, but also have superior thermal and chemical stability as well as non-pyrophoric nature that copper catalysts lack. In this contribution, we successfully synthesized the ZnFexAl2-xO4 (x = 0.05–0.2) spinel support, i.e., by replacing Al with a small amount of Fe in ZnAl2O4 spinel. The synthesized support, featuring a high surface area and superior stability, enabled the PdZnβ alloy formation at extremely low Pd loadings (e.g., 1000 ppm Pd), which shows high reactivity and CO2 selectivity toward methanol steam reforming (MSR) reaction. Moreover, it has the unique advantage of constructing bi-functional sites with a specific interfacial structure like PdZn/Fe2O3, the latter of which can effectively enhance water dissociation. Thanks to the synergetic effect, the 0.1 wt% Pd/ZnFe0.1Al1.9O4 catalyst exhibits a much higher ATOF value during the MSR reaction than the 0.1 wt% Pd/ZnAl2O4 counterpart, demonstrating excellent atomic utilization efficiency of noble metal and great potential in the practical application.

Comprehensive study on parabolic trough solar receiver-reactors via a novel efficient optical-thermal-chemical model of catalyst packed bed characteristics

The catalyst packed bed structure plays an important role in the promising solar-driven catalyst packed bed based thermochemical hydrogen production systems. However, corresponding accurate yet efficient numerical methods for characterizing and optimizing the catalyst packed bed structure as well as the whole complex solar-driven thermochemical process is still urgently needed. In this paper, a novel three-dimensional comprehensive model is proposed for the hydrogen production of methanol steam reforming reaction (MSRR) in parabolic trough solar receiver-reactors (PTSRR). A relatively realistic porosity distribution obtained by the discrete element method was combined with the optical-thermal-chemical coupling model. The proposed model was validated, proved to improve the accuracy of numerical predictions in a more efficient way. Moreover, it was effectively applied to tune the overall energy flow of the complex optical-thermal-chemical process of PTSRR-MSRRs for better performance, by optimizing the catalyst packed bed structure in aspects of catalyst sizes and packing methods. The results revealed that single packed beds of larger catalyst particles show better performance within the selected catalyst size range. The radial layered packing method of larger particle-to-particle diameter ratios can bring higher energy conversion efficiency and lower flow resistance, as compared to the single packing method and fully mixed packing method. This study could provide an efficient numerical modelling method and significant guidance for other similar solar-driven thermochemical applications of catalyst packed beds.

Assembly of hydrolysis, activation and reforming sites boosting steam reforming of DME over ZnO/TiO2 catalysts

Steam reforming of dimethyl ether (DME SR) through the tandem reactions of DME hydrolysis to methanol and methanol steam reforming (MSR) is a promising process for feeding hydrogen to fuel cells. Herein, we synthesize a series of ZnO/TiO2 catalysts with different Zn contents for DME SR. We discover that TiO2 exhibits excellent methanol activation ability by forming a large amount of methoxy species, and adjacent ZnO sites can directly utilize them for the substantial steam reforming. Compared with TiO2 and ZnO alone, the MSR reaction rate over the 2ZnO/TiO2 catalyst (with a Zn content of 2 wt%) at 340 °C increases by 56 and 38 times, respectively. For DME SR, DME hydrolysis could occur on strong acidic sites of the TiO2 support to generate methanol molecules to subsequently involve in MSR. The synergy as described above significantly enhances the DME SR activity. Additionally, the adsorption strength of the oxygenated intermediates formed on the ZnO/TiO2 catalysts is weaker than that on TiO2, which then inhibits the reactions of methanation and methanol/DME decomposition. The 2ZnO/TiO2 catalyst exhibits low CO (2.8%) and CH4 (0.3%) selectivity with DME conversion of 92% in DME SR at 400 °C.

Preparation of a Durable CuO/ZnO/CeO2/ZrO2 Catalyst on an SiC Support by an Inverse Microemulsion/Precipitation Method for Methanol Steam Reforming

AbstractDurable CuO/ZnO/CeO2/ZrO2 catalyst on SiC support for methanol steam reforming (MSR) was prepared by the combination of inverse microemulsion method and precipitation method which is termed as inverse microemulsion/precipitation method. The presence of Ce−O−Zr solid solution facilitated the production of oxygen vacancies and Ce3+ species in the prepared CuO/ZnO/CeO2/ZrO2 catalyst. Owing to the unique tiny reaction pool and the addition of precipitant for inverse microemulsion/precipitation method, the particle size of the prepared catalyst was principally between 2 and 6 nm, with an average size of 3.66 nm. Besides, the small particle size and the highly dispersed of Cu species boosted the reduction performance of the catalyst, enabling the reduction temperature to be only 201 °C. The methanol conversion of the reduced catalyst was still reached 98.8 % after 150 h, considerably higher than that of solution combustion method (70 %), without carbon deposition and pronounced sintering after MSR reaction.

A Joule-heated carbon nanofiber aerogel-supported catalyst for hydrogen production via methanol steam reforming

Copper (Cu)-containing catalysts are preferable in the methanol steam reforming (MSR) process because of their abundant sources, low cost, and high low-temperature activities. During operation, Cu-containing catalysts are typically heated by an external heat source and are most commonly used in their macroscopic powdered form, leading to uneven temperature distributions, nonuniform mass/heat transfer, slow heating rates, and difficult replacement. These issues must therefore be addressed in the design of specific catalysts for the MSR reaction. Herein, a three-dimensional Joule-heated carbon nanofiber aerogel (CNFA)-supported catalyst (Cu/CNFA-op10) was prepared by a facile one-pot method and followed by the catalytic evaluation. It was found that the even temperature distribution, effective heat/mass/electron transfer, and uniform distribution of the Cu nanoparticles, were responsible for the excellent catalytic activities. In addition, the deactivation of the CNFA-supported catalyst was also found and caused by the aggregation and sintering of Cu0/+ nanoparticles, the deposition of amorphous carbon on the surface of active sites, and the chemical state transition of the active particles. In this proof-of-concept demonstration, the high catalytic activity of the Joule-heating-driven catalyst provides a novel strategy for further designing and fabricating 3D monolithic catalysts related to the MSR reaction.

Catalytic behaviour of transition metal carbides of group 5 in the methanol steam reforming

Transition metal carbides of group 5 (G5TMC=VC, NbC and TaC) with similar crystallite sizes were prepared by a sol-gel route. The catalysts were characterized and studied in the methanol steam reforming (MSR) reaction in the temperature range of 573–723 K at atmospheric pressure and using a stoichiometric CH3OH/H2O = 1/1 mole ratio mixture. Under the MSR reaction conditions used, the route of methanol transformation depends on the G5TMC used as catalyst. The catalytic behaviour of VC differs from that of NbC and TaC, which in turn show a similar behaviour. Over VC, methanol is mainly converted to a mixture of H2+CH4, whereas over NbC and TaC the major product obtained is HCHO, formed from the dehydrogenation of methanol.

Study on solar-driven methanol steam reforming process in parabolic trough solar receiver-reactors by developing an optical-thermal-chemical model of realistic porosity distributions

The catalyst particle packing characteristics have a significant impact on improving the comprehensive energy conversion performance and economic benefits of sustainable solar-driven thermochemical hydrogen production systems. However, corresponding accurate and efficient numerical research tools or methods still need to be developed. In this paper, a three-dimensional comprehensive optical-thermal-chemical coupling model with catalyst particle packing characteristics is proposed for the parabolic trough solar receiver-reactor (PTSRR) of methanol steam reforming reaction (MSRR) for hydrogen production. This model is developed by combining a Monte Carlo ray tracing optical model, a computational fluid dynamics model, a MSRR comprehensive kinetic model with a Blender rigid body packing model. After validation, it was found from comparisons with previous studies that this model can represent relatively realistic catalyst porosity distributions of packed-bed reactors at a very low computational cost. Then, this model was applied to obtain the porosity of different PTSRR-MSRRs and optimize the catalyst size and shape, to achieve better comprehensive performance as well as economic benefits of higher overall efficiency and catalyst utilization efficiency. The results reveal that the PTSRR-MSRRs filled with cylinders and Raschig rings (R-PTSRR) can achieve similar high methanol conversion rate, while the R-PTSRR has more advantages with its lower average resistance coefficient and CO selectivity. After weighing the methanol conversion rate, the overall efficiency and the catalyst utilization efficiency, the optimum R-PTSRR is highly recommended. This study provides a useful option for rapid comprehensive analysis and optimization of similar solar-driven thermochemical conversion processes on catalyst particle packed beds.

Mechanism of methanol steam reforming on dual-atom catalysts of PtZn/TiO2 and PdZn/TiO2: Density functional theory studies

Methanol steam reforming (MSR) is a potential method for producing hydrogen in situ. Finding excellent catalysts to improve reaction activity and CO2 selectivity is crucial. In this study, we used density functional theory (DFT) methods and the CP2K software package to investigate the mechanism of the MSR reaction on dual-atom catalysts of PtZn/TiO2 and PdZn/TiO2. The results showed that the most favorable reaction paths on these two catalysts are the same, namely CH3OH→CH3O→CH2O→CH2OOH→CHOOH→CHOO→CO2, in which the rate-determining step is CH2O+OH→CH2OOH with reaction barriers of 1.17 eV on PtZn/TiO2 and 1.29 eV on PdZn/TiO2, respectively. The reported PtZn/TiO2 and PdZn/TiO2 catalysts show improved activity compared to pure metal or corresponding alloy catalysts. The synergistic effect between metal atoms and the surface of TiO2 supports as well as the role of Zn atom doping were discussed. This work provides a new perspective for the design of atomic-level catalysts for the MSR reaction.

Baffled-type thermochemical reactor for high-efficient hydrogen production by methanol steam reforming

A baffled-type thermochemical reactor (BTR) for high-efficient hydrogen production by methanol steam reforming (MSR) based on the novel concept of methanol-based solar-driven hydrogen station is proposed and numerically investigated in terms of geometric and operating conditions with a multi-physics coupled model. It is found that the radius of heat-exchanging tube shows a significant impact on hydrogen yield (YH2) whereas the radius of heat-exchanging tube array shows little effect. Both the inlet velocity (Vin,HTF) and temperature (Tin,HTF) of heat transfer fluid (HTF) affect the reactor performance by influencing the heat transfer inside BTR. Excessively higher Vin,HTF and higher Tin,HTF would promote the side reaction of methanol decomposition (MD) against the main reaction of MSR, which finally decreases YH2. Moreover, it is also found that for each gas hourly space velocity (GHSV) there is a corresponding optimal value of Vin, HTF to maximize YH2. Based on this, an optimal operating curve has been obtained via data-fitting, where YH2 decreases while the hydrogen production rate (RH2) increases nonlinearly against GHSV, and the corresponding maximal values of 97.84% and 1.66 mol h−1 have been achieved separately. The results suggest that the practical operating conditions should follow the optimal operating curve with the compromise between YH2 and RH2. Finally, based on the performance evaluation against the traditional tubular reactor, the hydrogen yield of BTR is up to 1.79% higher than that of the tubular reactor due to (30.44%) more uniform temperature distribution, (15.30%) longer contact time and (7.46%) higher thermal-to-hydrogen energy conversion efficiency.

Probing crystalline phase effect of rare earth metal oxides (REO) on Cu/REO (RE=Gd, Eu, Sm) catalysts for methanol steam reforming (MSR) to produce H2

In this work, to study the phase structure effect, three groups of Cu/REO catalysts were prepared with cubic and monoclinic Gd2O3, Eu2O3 and Sm2O3 supports for MSR reaction to produce H2. Based on CH3OH conversion and H2 yield, the reaction performance of the catalysts ranks as Cu/Sm2O3-M > Cu/Sm2O3–C > Cu/Gd2O3-M > Cu/Gd2O3–C > Cu/Eu2O3-M > Cu/Eu2O3–C. For the same kind of REO, Cu supported on the monoclinic support shows better performance than on the cubic one. Despite the phase structure difference, Sm2O3 is the best support among all the three kinds of REOs. Compared with Cu/REO catalysts prepared with cubic supports, the corresponding catalysts prepared with monoclinic supports generally possess more surface oxygen vacancies, which can generate more surface active oxygen (O2–) and moderate basic sites. Moreover, the contents of Cu + on the catalysts follow the same sequence. The reaction performance is positively related to the amount of these three types of surface sites. But metallic Cu0 species is necessary to maintain the Cu+ ↔ Cu0 redox cycle. Furthermore, on a catalyst with good performance, those vital surface reaction intermediates can be stabilized during the reaction. Cu/Sm2O3-M possesses the largest quantities of these surface sites, and has the appropriate amount of Cu+ and Cu0 after reduction, thereby displaying the optimal performance in all the catalysts. In conclusion, evident support crystal structure effect is observed for Cu/REO catalysts, and a monoclinic phase REO is a better support than the respective cubic phase one.

Hydrogen generation by coupling methanol steam reforming with metal hydride hydrolysis.

Methanol steam reforming (MSR) and hydrolysis of metal hydrides are two important hydrogen generation reactions with complementary characteristics. Coupling of the above two reactions leads to better hydrogen generation performance. The CO2 generated from MSR can be absorbed by the hydroxide generated from hydrolysis, leading to higher H2 purity. The hydrolysis heat can be utilized to drive the endothermic MSR reaction. By carrying out MSR on a CaH2-CuO composite, a hydrogen density of 6.56 wt% based on all the reactants with H2 purity higher than 99% can be obtained at 250 °C.

Theoretical insight into hydrogen production from methanol steam reforming on Pt(111)

Pt-based catalysts are widely used for hydrogen production from methanol steam reforming (MSR), but they show high CO selectivity. The reaction pathways of MSR on Pt(111) surface are systemically studied using density functional theory and kinetic Monte Carlo to reduce the selectivity of CO. The results show that CH3OH (g) → CH3OH* → CH2OH *→ CHOH * → CHO * → CO * → CO (g) is the main reaction pathway at 423–623 K and 0.1–10 atm with CH3OH: H2O of 3:1–1:1, and water is very difficult to dissociate. The difference between H2O* + * → OH* + H* and CH3OH* +*→ CH2OH * + H* is the key factor for MSR reaction on Pt(111) surface. The actual ratio of H2/(CO+CO2) is close to the theoretical ratio for MSR (2.91 vs. 3.00) when the energy barrier of H2O* + * → OH* + H* is smaller than that of CH3OH* +*→ CH2OH * + H* by 0.30 eV. The elimination of CO* is mainly from CO * + OH * → COOH*, and the ratio of CO/(CO+CO2) is 6.71%. These results may be useful for the design and optimization of Pt-based catalysts at low temperature for MSR reaction.

Mechanistic insights into methanol steam reforming over a ZnZr oxide catalyst with improved activity

Methanol steam reforming (MSR) holds great potential for mobile hydrogen production, but it still requires an active and stable catalyst. In this work, we report a high-performance ZnZr-0.5 composite oxide catalyst for this reaction, with a hydrogen production rate of 2.80 mol·gcat−1·h−1 and CO2 selectivity of 99.6% at a methanol space velocity of 22,762 mL·gcat−1·h−1. It also exhibits superior long-term durability in the TOS test for more than 100 h. Such good activity results from a synergistic effect of ZnO–ZrO2 dual sites. ZrO2 is capable of stabilizing and storing more CH3O∗ and HCOO∗ intermediates while ZnO is in charge of the dehydrogenation of these key intermediates. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemisorption results reveal that the MSR reaction experiences successively the hydrolysis of methyl formate and dehydrogenation of formate. More importantly, it is found that H2O significantly promotes the dehydrogenation of HCOO∗ intermediate by directly participating in this reaction from pulse chemisorption experiments.