Aqueous Phase Reforming Research Articles

A highly active and hydrothermal-resistant Cu/ZnO@NC catalyst for aqueous phase reforming of methanol to hydrogen

Aqueous-phase reforming (APR) of methanol provides a safe way to store and transport hydrogen by in situ production of H2. It remains, however, a challenge to develop an efficient and hydrothermal-stable non-noble-metal catalyst. Herein, a robust Cu/ZnO@NC catalyst is successfully constructed by encapsulating Cu/ZnO species in nitrogen-doped carbon (NC), using ZIF-8 as precursor. It is demonstrated that the activity for APR of methanol increases exponentially with rise of catalyst wettability. With good wettability, a high hydrogen releasing rate of 146.9 μmol·gcat−1·s−1 is achieved on the 27%Cu/ZnO@NC catalyst at 230 °C, about four times higher than that of a traditional 29%Cu/ZnO catalyst, and surprisingly comparable to a commercial Pt/C catalyst. Notably, Cu/ZnO@NC also shows excellent stability, as the NC coating protects ZnO from hydrolyzing and prevents aggregation of Cu nanoparticle largely in the severe aqueous-phase-reaction conditions. This work develops a convenient method to prepare efficient and hydrothermal-stable catalyst with commercial potential.

Synthesis Gas Production via Aqueous Phase Reforming over Hydrotalcite-supported Catalysts

Depletion of fossil fuel has gained attention to find an alternative of energy resources. The consumption of fossil fuel is increased gradually, raising many unfavourable challenges such as exploiting the unrenewable resources and causing environmental damages. This study aimed to produce clean energy derived from renewable resources. Glycerol as a by-product from biodiesel production from palm oil through esterification process. Conversion of glycerol to synthetis gas (syngas) which produced hydrogen as the main product is considered as a renewable-clean fuel. Glycerol has been successfully converted to syngas by Aqueous Phase Reforming (APR) process over solid base catalysts. Hydrotalcite which is a layered double hydroxide used as catalyst support was impregnated with various metal promoters such as Ni, Cu, Co, Zn, and Sn. Those catalysts were characterized by Brunauer-Emmett-Teller surface area analysis, Thermal Gravimetry Analysis, Fourier Transform Infrared Spectrometry and X-Ray Diffraction to investigate the properties and structure of the catalysts. Catalytic activity was evaluated in a continuous fixed- bed reactor to produce syngas through APR reaction. The gas products were analyzed by GC-TCD, resulting Cu/hydrotalcite catalyst produced hydrogen, 55.2% v/v.

Elucidating the Strain-Vacancy-Activity Relationship on Structurally Deformed Co@CoO Nanosheets for Aqueous Phase Reforming of Formaldehyde.

Lattice strain modulation and vacancy engineering are both effective approaches to control the catalytic properties of heterogeneous catalysts. Here, Co@CoO heterointerface catalysts are prepared via the controlled reduction of CoO nanosheets. The experimental quantifications of lattice strain and oxygen vacancy concentration on CoO, as well as the charge transfer across the Co-CoO interface are all linearly correlated to the catalytic activity toward the aqueous phase reforming of formaldehyde to produce hydrogen. Mechanistic investigations by spectroscopic measurements and density functional theory calculations elucidate the bifunctional nature of the oxygen-vacancy-rich Co-CoO interfaces, where the Co and the CoO sites are responsible for CH bond cleavage and OH activation, respectively. Optimal catalytic activity is achieved by the sample reduced at 350°C, Co@CoO-350 which exhibits the maximum concentration of Co-CoO interfaces, the maximum concentration of oxygen vacancies, a lattice strain of 5.2% in CoO, and the highest aqueous phase formaldehyde reforming turnover frequency of 50.4 h-1 at room temperature. This work provides not only new insights into the strain-vacancy-activity relationship at bifunctional catalytic interfaces, but also a facile synthetic approach to prepare heterostructures with highly tunable catalytic activities.

Efficient Base-Free Aqueous Reforming of Methanol Homogeneously Catalyzed by Ruthenium Exhibiting a Remarkable Acceleration by Added Catalytic Thiol.

Production of H2 by methanol reforming is of particular interest due the low cost, ready availability, and high hydrogen content of methanol. However, most current methods either require very high temperatures and pressures or strongly rely on the utilization of large amounts of base. Here we report an efficient, base-free aqueous-phase reforming of methanol homogeneously catalyzed by an acridine-based ruthenium pincer complex, the activity of which was unexpectedly improved by a catalytic amount of a thiol additive. The reactivity of this system is enhanced by nearly 2 orders of magnitude upon addition of the thiol, and it can maintain activity for over 3 weeks, achieving a total H2 turnover number of over 130 000. On the basis of both experimental and computational studies, a mechanism is proposed which involves outer-sphere dehydrogenations promoted by a unique ruthenium complex with thiolate as an assisting ligand. The current system overcomes the need for added base in homogeneous methanol reforming and also highlights the unprecedented acceleration of catalytic activity of metal complexes achieved by the addition of a catalytic amount of thiol.

Biohydrogen production by glycerol Aqueous-Phase Reforming: Effect of promoters (Ce or Mg) in the NiAl2O4 spinel-derived catalysts

Biohydrogen production by Aqueous-Phase Reforming (APR) of glycerol was studied over nickel aluminate spinel-derived catalysts modified by Ce or Mg. As reference, an alumina supported nickel catalyst was also investigated. Catalysts were characterised by a sort of techniques in order to elucidate any structure-activity relationship, and tested for the WGS and CO hydrogenation reactions. It was concluded that the spinel catalyst allowed a better dispersion of the metallic Ni, and led to a more APR active and more hydrogen-selective catalyst. Mg and Ce doping further increased the nickel dispersion and increased basicity what could be related to their higher WGS relative reaction rate. Also, Mg doping hindered nickel reduction due to Ni-Mg interactions. Both promoters improved the stability of the textural properties under APR conditions, minimizing the formation of boehmite. Leaching of Ni was found, at lesser extent after Mg doping.

Aqueous phase reforming of distiller's grain derived biogas Plant wastewater over α-MoO3 nanosheets

A novel method which combines aqueous phase reforming (APR) and activated carbon adsorption (ACA) was proposed to treat the distiller's grain derived biogas plant wastewater (DGBW). APR was performed over α-MoO3 nanosheets with oxygen vacancies (α-MNOV), Pt/C and Ni/α-MNOV catalysts under temperature of 225 °C and residence time of 30 min. An optimal yield of 4.91 mLhydrogen/mLDGBW was obtained over α-MNOV, which also exhibited the highest organic pollutants removal efficiency. After APR over α-MNOV and following ACA, the removal efficiencies of non-purgeable organic carbon (NPOC), chemical oxygen demand (COD) and total nitrogen (TN) reached 79.45%, 87.82% and 44.78%, respectively. The significant performance of α-MNOV could be attributed to two aspects: shorter van der Waals (vdW) heterostructures presented α-MNOV which enhanced the hydrogen generation process, and the abundant oxygen vacancies (OVs) in α-MNOV which increased its stability and lattice oxygen generation capability, facilitating the decomposition of the organics during APR.

Effect of impurities of CH3OH, CH3COOH, and KOH on aqueous phase reforming of glycerol over mesoporous Ni–Cu/CeO2 catalyst

Impurities are inevitable in crude glycerol, a by-product of biodiesel, which has a great influence on aqueous phase reforming (APR). This work investigates three impurities (CH3OH, CH3COOH, and KOH) in the aqueous phase reforming of glycerol (GAPR) using a mesoporous Ni–Cu/CeO2 catalyst at three temperatures. The experiment results indicate that the increase of temperature is beneficial to the conversion of glycerol into gas products, but not favor to the proportion of H2 in the gas phase. The presence of CH3OH almost has not affected the total gas volume, while CH3COOH and KOH decreased and increased the gas volume, respectively. The deactivation of the catalyst occurs under acidic conditions because the active phase Ni on the catalyst surface is lost in the hydrogen evolution reaction. KOH has the greatest influence on the gas phase composition, which greatly increases the H2 production and the proportion of H2. The results of liquid-phase solution analysis show that the addition of CH3COOH promoted the dehydration of glycerol, which is contrary to the results obtained by adding KOH. CH3OH, as the final product of glycerol dehydrogenation and decarbonization, is added to the initial solution, which will be conducive to the dehydration reaction. The addition of CaO can increase the H2 production in the APR of glycerol solution containing impurities.

Hydrogen production via aqueous-phase reforming for high-temperature proton exchange membrane fuel cells - a review

Aqueous-phase reforming (APR) can convert methanol and other oxygenated hydrocarbons to hydrogen and carbon dioxide at lower temperatures when compared with the corresponding gas phase process. APR favours the water-gas shift (WGS) reaction and inhibits alkane formation; moreover, it is a simpler and more energy efficient process compared to gas-phase steam reforming. For example, Pt-based catalysts supported on alumina are typically selected for methanol APR, due to their high activity at temperatures of circa 200°C. However, non-noble catalysts such as nickel (Ni) supported on metal-oxides or zeolites are being investigated with promising results in terms of catalytic activity and stability. The development of APR kinetic models and reactor designs is also being addressed to make APR a more attractive process for producing in situ hydrogen.

Enhancement of catalytic performance of graphene supported Pt catalysts by Ni and W for hydrogen gas production by hydrothermal gasification of biomass-derived compounds

A more practical approach to reduce the cost of the precious metal catalysts is to replace some of the precious metal particles with non-expensive metals that do not cause considerable loss of catalytic performance. In the present study, Ni and W metal particles deposited on graphene support along with and without Pt particles by ultrasound-assisted wet impregnation that followed chemical and thermal reduction process. The catalytic activities of the resulted catalysts were evaluated by aqueous-phase reforming (APR), an hydrothermal gasification process using glucose solution as feed. Although metal particles on Ni-based catalysts were well dispersed on the support, they had larger particle sizes with a broader size distribution compared to W-based catalysts. The combination of Ni and W metals with Pt showed positive synergy and the catalytic performance of bimetallic catalysts significantly enhanced for conversion of glucose to hydrogen.

Aqueous phase reforming of biodiesel byproduct glycerol over mesoporous Ni-Cu/CeO2 for renewable hydrogen production

Aqueous phase reforming (APR), regarded as one method for inexpensive H2 production, was widely studied due to lower temperature and unnecessary to vaporize water and fuels. In this study, the mesoporous CeO2, regarded as a metal oxide carrier, was first prepared by colloidal solution combustion, and then the Ni-Cu bimetallic supported on mesoporous CeO2 was successfully synthesized to investigate the catalytic performance in APR of biodiesel byproduct glycerol. The results show that the Cu element in the catalysts can effectively improve water–gas shift (WGS) reaction and inhibit the formation of methane, which increases the H2 production rate from 125.08 to 195.57 µmol⋅min−1⋅g cat−1. The higher reaction temperature is beneficial to the H2 production rate, but not to H2 selectivity. Kinetics analysis indicates that catalyst of 1Ni2Cu/CeO2 + 0.2gCaO has the lowest apparent activation energy (29.86 kJ⋅mol−1). CaO is introduced as an absorbent to improve WGS reaction and reduce methanation reactions through in-situ CO2 removal and capture. The reaction path and mechanism of APR of glycerol are also discussed in this paper.

Monitoring Aqueous Phase Reactions by Operando ATR‐IR Spectroscopy at High Temperature and Pressure: A Biomass Conversion Showcase

AbstractSpectroscopic insight into aqueous phase catalytic reactions under realistic conditions aids detailed understanding and fosters further improvements. However, this is also very challenging, particularly in the liquid phase, given the typically elevated temperatures and pressures employed. Here, we report an operando Attenuated Total Reflectance‐Infrared (ATR‐IR) spectroscopic method to monitor the Aqueous Phase Reforming (APR) of Kraft lignin at 225 °C and 30 bar over a Pt/Al2O3 catalyst. This is a showcase reaction, while the presented method developed is more generic. In addition to the high temperature and pressures conditions, spectral interference from bulk water is a major challenge. Other challenges include self‐absorption of IR light, molecular interactions, high substrate loadings and the noise resulting from water vapor and CO2. We present a protocol utilizing the temperature‐dependent single‐beam method to obtain high‐quality ATR‐IR spectra virtually free from temperature, background and matrix effects. The protocol allowed for effective correction for the aqueous solvent as a function of reaction temperature. A comparison with conventional spectral acquisition and correction shows the advantages of this approach.

Ni/Hydrochar Nanostructures Derived from Biomass as Catalysts for H2 Production through Aqueous-Phase Reforming of Methanol

Aqueous-phase reforming of organic molecules to hydrogen is a promising strategy to address the production and storage of sustainable hydrogen with lower costs; however, the synthesis of inexpensive transition metal (TM) catalysts with desirable activity and stability for the reaction is still challenging. In this work, a green and efficient approach for modulating the geometric/electronic structure of metal/hydrochar nanocomposites from sustainable biomass was proposed for enhancing H2 production via aqueous-phase reforming of methanol (APRM). A Ni/HC nanocomposite with a special thistle (a perennial species of flowering plant)-like three-dimensional (3D) architecture was first constructed as a model catalyst to expatiate the critical role of modulating an ordered mesoporous structure and interface electron transfer for enhancing APRM. Deliberately balancing heteroatom doping and soft templates contribute to the successful fabrication of the thistle-like superstructure, and such hierarchically porous architectures demonstrated efficient catalysis for APRM, owing to their unique properties, including a highly uniform morphology, narrow particle size distribution, and mesoporous texture with excellent accessibility. In addition, the experimental investigation and density functional theory calculations both substantiated that the combination of heteroatom doping and soft templates was beneficial for the strong electronic metal–support interaction (EMSI) of the metal/hydrochar nanocomposite, which leads to enhanced methanol adsorption, activation, and subsequently improved APRM performance. The electronic structure of the metal/hydrochar nanocomposite played a more significant effect on the intrinsic APRM activity than the geometric structure like the formation of the thistle-like superstructure. Benefiting from the tailored electronic and geometric structure, the resulting Ni0.1/HC-N1.5-S1 catalyst exhibited an unprecedented average turnover frequency (TOF) of 89.5 molH2/molNi/min, higher than any other known platinum group metal-free catalysts, approaching the reactivity of the state-of-the-art noble metal-based APRM catalysts, while showing excellent stability over 10 consecutive reaction cycles.

In-situ hydrogenolysis of glycerol using hydrogen produced via aqueous phase reforming of glycerol over sonochemically synthesized nickel-based nano-catalyst

1,3-Propanediol (1,3-PDO) is a commercially valuable chemical for the production of polytrimethylene terephthalate polymers and polyurethane. In this study, the production of 1,3-PDO was investigated via aqueous phase reforming (APR) and selective hydrogenolysis of glycerol over Ni-Ca/CeO2 catalysts synthesized by sonochemical (Us) and wet impregnation (WI) methods. The experiments were performed in a batch reactor at 20 bar, 230 ℃, and 450 rpm for 1 h. The synthesized catalysts were characterized using XRD, TEM, FESEM, BET, H2-TPR, XPS, CO-chemisorption, and NH3-TPD to better understand the physio-chemical and surface characteristics. The results revealed that sonochemical catalysts showed a larger surface area, smaller crystallite size, low reduction temperature and more homogenous particle distribution than wet impregnation catalysts. For both preparation methods, monometallic Ni/CeO2 catalysts showed the highest activity, whereas Ca modification of Ni/CeO2 catalysts significantly decreased the activity of the catalysts. The highest yield and selectivity of 1,3-PDO were 19.54% and 52.73%, respectively, using Ni/CeO2_Us catalyst. The best catalyst was further utilized for parameters optimization study to observe the effect of varying glycerol concentration (10 to 25 vol.%), temperature (210 to 250 ℃) and pressure (10 to 30 bar) on the yield and selectivity of 1,3-PDO and glycerol conversion. The results demonstrated that the highest yield (19.54%) and selectivity (52.73%) of 1,3-PDO were obtained over 10 vol.%, 230 ℃ and 20 bar with glycerol conversion of 54.26%. This present study provides a promising and economical process of converting glycerol to 1,3-PDO, which has wide applications in the industry.

MgO-supported Ni-Sn Catalysts: Characterization and Catalytic Properties for Aqueous-phase Catalytic Reforming of Glycerol

The aqueous phase reforming (APR) of glycerol into value-added products, including H2 and alkanes, is environmentally green. In this work, the conversion of glycerol into syngas was demonstrated using MgO-supported Ni-Sn catalysts. Ni species is known for its capability of converting glycerol, but the activity towards water gas shift (WGS) reaction has not been satisfied. Loading Ni-Sn onto MgO has increased the catalyst basicity, which promotes a positive effect in WGS reaction. A series of bimetallic catalysts, impregnated Ni-Sn on MgO support, was prepared with various Ni-Sn loading amounts. To better understand the behavior of prepared catalysts, they were evaluated physio-chemically through XRD, BET, and FTIR. The catalytic activity test was performed for APR in a continuous flow reactor with aqueous glycerol 10 v-% as a feedstock at a reaction temperature of 250°C. As a result, the maximum hydrogen selectivity was obtained at about 73 v-%.

An Insight into the Separation of 1,2-Propanediol, Ethylene Glycol, Acetol and Glycerol from an Aqueous Solution by Adsorption on Activated Carbon

Glycerol conversion processes such as aqueous phase reforming and hydrogenolysis generate value-added compounds highly diluted in water. Because distillation is a high energy demand separation step, adsorption could be an attractive alternative to recover these chemicals. Adsorption isotherms of 1,2-propanediol, acetol, ethylene glycol and glycerol onto activated carbon were determined by batch adsorption experiments. These isotherms were fitted slightly better to the Freundlich equation than to the Langmuir equation. Acetol is the compound with the highest adsorption at concentrations smaller than 1 M. Properties of the adsorbate such as the −OH group number, chain length, molecular size and dipole moment, besides characteristics of the adsorbent such as the surface area, oxygen and ash content, are considered to explain the observed results. Moreover, adsorption experiments were performed with mixtures of compounds and it was determined that the molar amount adsorbed is less than predicted from the adsorption isotherms of the individual compounds treated separately. In addition, the influence of the activated carbon thermal pre-treatment temperature on the adsorption capacity has been studied, the optimum being 800 °C. An analysis of the influence of the activated carbon characteristics showed that the most important parameters are the total pore volume and the ash content.

Active sites and effects of co-adsorbed H2O on isolated methanol dehydrogenation over Pt/γ-Al2O3

Dehydrogenation is the first reaction of the aqueous phase reforming (APR) mechanism of polyols, and its rate is likely affected by the environment at the active site. This study focuses on reactions of methanol on benchmark Pt/γ-Al2O3 catalysts probed by infrared spectroscopy under high vacuum. CO in linear and bridging coordination are the dominant surface species on metal sites. Pt particle sizes and reaction temperatures are varied to identify the kinetically preferred active site for methanol dehydrogenation as either lowly coordinated (edges, corners, interface) or highly coordinated (terraces) metal atoms. Interpretation of temperature-dependent IR spectra up to 450 °C show that larger Pt particles produce more CO at lower temperatures from complete methanol dehydrogenation. Similarly, time-resolved isothermal experiments at 150 °C showed equilibrium conversion occurred much faster on larger Pt particles than smaller ones. Features of evolving ν(C≡O) bands (shape, vibrational frequencies, integrals) suggest that, even on small Pt particles, CO first forms on the scarcely available terraces, or possibly in the form of islands. We have thus experimentally identified highly coordinated Pt metal as the more active site in overall methanol dehydrogenation. The electronic and chemical effects of co-adsorbed water and hydrogen on dehydrogenation activity and the CO spectra are discussed. The co-adsorption of water, an abundant APR component needed for the water-gas shift reaction, does not appear to affect methanol dehydrogenation on large Pt particles but hinders the reaction on small Pt particles as evident by limited growth in the respective ν(C≡O) bands.

Effect of Calcium Doping Using Aqueous Phase Reforming of Glycerol over Sonochemically Synthesized Nickel-Based Supported ZrO2 Catalyst

The aqueous phase reforming (APR) of glycerol was studied using sonochemically synthesized 10%Ni-x%Ca/ZrO2 catalysts (where x = 0, 0.5, 3, and 5) for the production of value-added liquid products. The APR reaction was performed in a batch reactor under the following conditions: 20 bar, 230 °C 450 rpm, and 1 h of reaction time. The synthesized catalysts were characterized using XRD, FESEM, BET, and H2-TPR to observe the effect of Ca doping on the physio-chemical properties of the catalysts. The results revealed that, at higher Ca loading, the catalysts experienced serious particles’ agglomeration, which resulted in a larger particles’ size, smaller surface area, and smaller pore volume owing to uneven distribution of the particles. The characterization results of the catalysts confirmed that the Us catalysts have a slightly higher surface area, pore volume, and pore size, as well as highly reducible and fine crystalline structure, compared with WI catalysts. The catalytic performance of the catalysts shows that 1,3-propanediol (1,3-PDO) and 1,2-propanediol (1,2-PDO) were the two main liquid products produced from this reaction. The highest selectivity of 1,3-PDO (23.84%) was obtained over the 10%Ni/ZrO2 catalyst, while the highest selectivity of 1,2-PDO (25.87%) was obtained over the 10%Ni-5%Ca/ZrO2 catalyst.

Continuous aqueous phase reforming of wastewater streams: A catalyst deactivation study

This paper reports on the catalytic performance and deactivation in aqueous phase reforming of wastewater streams for H2 production. Brewery wastewater was chosen as representative of this type of effluent. The effect of catalyst support textural characteristics was evaluated using an activated carbon and different modified supports obtained by infiltration and carbonization of a phenolic resol resin into activated carbon. The effect of active phase was evaluated using Pt and PtRe catalysts with different metal molar ratio. At short time on stream values, Pt catalysts supported on modified activated carbon showed higher H2 production than those supported on unmodified activated carbon, indicating that a lower microporosity facilitates the transport of reactants to catalytic active sites and release of reaction products. Bimetallic PtRe catalysts showed higher activity than Pt, particularly using a metal molar ratio of 1:1, which yielded the highest H2 production (117.2 μmol min−1). Despite the different catalysts tested, early and significant deactivation was observed. The characterization of used catalysts allows postulating the adsorption of organic species and/or coke-like matter deposition on the catalysts surface as main causes of deactivation.

Hydrogen production via aqueous-phase reforming for high-temperature proton exchange membrane fuel cells - a review

Aqueous-phase reforming (APR) can convert methanol and other oxygenated hydrocarbons to hydrogen and carbon dioxide at lower temperatures when compared with the corresponding gas phase process. APR favours the water-gas shift (WGS) reaction and inhibits alkane formation; moreover, it is a simpler and more energy efficient process compared to gas-phase steam reforming. For example, Pt-based catalysts supported on alumina are typically selected for methanol APR, due to their high activity at temperatures of circa 200°C. However, non-noble catalysts such as nickel (Ni) supported on metal-oxides or zeolites are being investigated with promising results in terms of catalytic activity and stability. The development of APR kinetic models and reactor designs is also being addressed to make APR a more attractive process for producing in situ hydrogen.

Simulation-based environmental-impact assessment of glycerol-to-hydrogen conversion technologies

Abstract This simulation-based comparative assessment aims to quantify the environmental and human-health impacts of greener hydrogen (H2) production via three glycerol-based technologies, including: supercritical water reforming (SCWR), aqueous-phase reforming (APR) and autothermal reforming (ATR). The GaBi (2018 edition) life-cycle assessment (LCA) platform is used to develop cradle-to-gate product system models for these technologies and the TRACI 2.1 methodology is used to quantify their midpoint impact categories. Aspen HYSYS (v11) process-simulation software is used to generate the life-cycle inventory (LCI) primary data required to produce 1 kg of H2 via each of the indicated glycerol-reforming technologies. Per ISO 14040:2006 reporting requirements for the LCA results interpretation step, three base case (BC) scenarios and four sensitivity scenarios (SS) are developed and quantified to compare the effects of different process electricity sources (US grid mix versus wind power) and thermal energy sources (natural gas versus biogas) on the LCA results. The high operating pressure (viz. 240 bar) of SCWR enabled assessment of the impact of in situ electricity generation to offset some of electricity required for this technology. The major insights from this research are as follows: (i) per 1 kg of produced H2, APR reduces CO2 emissions by ≈95% compared to ATR and by ≈92% compared to SCWR, (ii) for BC scenarios, the primary energy consumption (in MJ/kg of produced H2) is in the following order from highest to lowest: ATR > SCWR > APR and (iii) H2 production via glycerol APR is more environmentally sustainable than SCWR and ATR, and thus offers a promising path for greener H2 production. Future environmental sustainability studies should focus on expanding the scope of this study to include H2 production via water electrolysis using renewable electricity sources and via solar and nuclear-driven thermochemical water splitting.