Aqueous-phase Reforming Of Ethylene Glycol Research Articles

Aqueous Phase Reforming over Platinum Catalysts on Doped Carbon Supports: Exploring Platinum-Heteroatom Interactions.

A series of platinum catalysts supported on carbon nanofibers with various heteroatom dopings were synthesized to investigate the effect of the local platinum environment on the catalytic activity and selectivity in aqueous phase reforming (APR) of ethylene glycol (EG). Typical carbon dopants such as oxygen, nitrogen, sulfur, phosphorus, and boron were chosen based on their ability to bring acidic or basic functional groups to the carbon surface. In situ X-ray absorption spectroscopy (XAS) was used to identify the platinum oxidation state and platinum species formed during APR of EG through multivariate curve resolution alternating least-squares analysis, observing differences in activity, selectivity, and platinum local environment among the catalysts. The platinum-based catalyst on the nitrogen-doped carbon support demonstrated the most favorable properties for H2 production due to high Pt dispersion and basicity (H2 site time yield 22.7 h-1). Direct Pt-N-O coordination was identified by XAS in this catalyst. The sulfur-doped catalyst presented Pt-S contributions with the lowest EG conversion rate and minimal production of the gas phase components. Boron and phosphorus-doped catalysts showed moderate activity, which was affected by low platinum dispersion on the carbon support. The phosphorus-doped catalyst showed preferential selectivity to alcohols in the liquid phase, associated with the presence of acid sites and Pt-P contributions observed under APR conditions.

Tuning Pt characteristics on Pt/C catalyst for aqueous-phase reforming of biomass-derived oxygenates to bio-H2

Pt/C catalysts with varied Pt sizes and distributions were investigated for aqueous-phase reforming (APR) of ethylene glycol (EG) to H2. APR experiments were performed on a continuous-flow fixed bed reactor with a catalyst loading of 1 g and EG feeding of 120 mL h−1 at 225 °C and 35 bar for 7 h. The fresh and used Pt/C catalysts were characterized by XRF, BET, CO chemisorption, TEM, XTEM, and XPS. Catalyst preparation protocols changed Pt characteristics on Pt/C catalysts, leading to a distinguishable H2 production. The rates for EG conversion and H2 production increased linearly with mean Pt size (3–11 nm), while having a volcano relationship with the mean size of agglomerated Pt particles (17–30 nm). Pt with concentrated Pt particles on surface of Pt/C catalysts was more preferable for APR of EG than the homogeneously distributed in catalysts. Optimal performance was obtained over a Pt/C-PR catalyst, which was prepared by precipitation method, showing a superb turnover frequency of 248 molH2 molPt−1 min−1 for H2 production from EG in APR. Besides, Pt/C catalysts also showed excellent stability. These results have shown the promise of Pt/C catalyst for APR of EG, which can be extended for bio-H2 production via APR of biomass-derived oxygenates in waste streams.

Low temperature light-assisted hydrogen production from aqueous reforming ethylene glycol over Pt/Al2O3 and Pd/Al2O3 catalysts

Al2O3 supported Pt and Pd nanoparticle catalysts were prepared by impregnation-reduction method, and employed in the photocatalytic aqueous-phase reforming of ethylene glycol. Light illumination can decrease the reaction activation energy remarkably. Pt/Al2O3 exhibits much higher H2 turnover frequency (TOF) and lower CO selectivity than Pd/Al2O3 catalyst. Their morphology and structure were characterized by XRD, TEM, UV-vis techniques. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicates light can promote the cleavage of O–H bonds of ethylene glycol molecule. DFT calculation suggests the lower CO selectivity over Pt/Al2O3 catalyst can be attributed to the low energy barriers of reaction in the step of CO+O→CO2.

Hydrogen Production via Aqueous-Phase Reforming of Ethylene Glycol over a Nickel–Iron Alloy Catalyst: Effect of Cobalt Addition

Aqueous-phase reforming of ethylene glycol for hydrogen generation was investigated over Ni, Fe, NiFe, and NiFeCo catalysts. The effect of the reduction temperature of the NiFeCo alloy catalyst was...

Aqueous phase reforming of polyols from glucose degradation by reaction over Pt/alumina catalysts modified by Ni or Co

A comparison of Pt-M/Al2O3 catalysts (M = Ni, Co, none) for the aqueous phase reforming (APR) of different polyols that can be obtained from glucose degradation was made. A standard monometallic Pt/Al2O3 catalyst was prepared by incipient wetness impregnation (IWI) of platinum on an alumina support. The bimetallic catalysts had Ni or Co promoters incorporated by the urea matrix combustion method (UCM) and Pt by IWI technique (PtNi and PtCo catalysts).The catalysts were characterized by ICP/MS analysis, CO/chemisorption, TPR, XPS, SEM-EPMA and XRD. The catalytic activity was assessed with the tests of APR of an aqueous solution of 10 %wt of ethylene glycol (EG), glycerol (Gly) or sorbitol (Sorb), in a tubular fixed bed reactor at 498 K, 2.2 MPa, WHSV = 2.3–2.5 h−1, 3 cm3min-1 He carrier. Monitored variables were: conversion to carbon product in the gas phase, hydrogen and methane yield, selectivities, TOF and coke content on the spent catalysts.PtNi and PtCo catalysts had better hydrogen yield and stability during the experiments than the un-promoted Pt catalyst, (H2 yield = 24.4, 21.2 and 15% for PtNi, 17.9 and 15.1 for PtCo and 13.7, 10.8 and 7.5% for Pt after 8 h on stream in APR of EG, Gly or Sorb solution, respectively). Especially PtNi showed excellent yield and selectivity to hydrogen and a good stability, steadily generating hydrogen for long times. Co addition mainly helped in keeping low levels of coke and a low selectivity to methane.

Bio-hydrogen production by APR of C2-C6 polyols on Pt/Al2O3: Dependence of H2 productivity on metal content

The effect of the platinum loading on the production of hydrogen by aqueous-phase reforming of ethylene glycol, glycerol, xylitol and sorbitol was studied on Pt/Al2O3 catalysts containing 0.30, 0.57, 1.50 and 2.77 Pt%. Catalytic runs were performed at a space velocity of 1.2h−1, 498K, 29.3bar and using a polyol(1.0%)/water feed. The total polyol conversion and the polyol conversion to gaseous products increased with surface Pt concentration (Pts, μmol Pt/gcat). Similarly, the yield and the productivity to hydrogen (Pr, molH2/gh) increased continuously with Pts in all the cases, but the Pr values diminished with the polyol chain length. Coke formation depended on Pts and the polyol size; the amount of carbon formed on the catalyst increased indeed with Pts and diminished with the polyol chain length. The metal fraction was severely sintered during the APR reaction, irrespective of the reactant size. Nevertheless, the magnitude of the Pt dispersion drop was not dependent on the amount of platinum on Pt/Al2O3 catalysts.

Oriented Pt Nanoparticles Supported on Few-Layers Graphene as Highly Active Catalyst for Aqueous-Phase Reforming of Ethylene Glycol.

Pt nanoparticles (NPs) strongly grafted on few-layers graphene (G) have been prepared by pyrolysis under inert atmosphere at 900 °C of chitosan films (70-120 nm thickness) containing adsorbed H2PtCl6. Preferential orientation of exposed Pt facets was assessed by X-ray diffraction of films having high Pt loading where the 111 and 222 diffraction lines were observed and also by SEM imaging comparing elemental Pt mapping with the image of the 111 oriented particles. Characterization techniques allow determination of the Pt content (from 45 ng to 1 μg cm-2, depending on the preparation conditions), particle size distribution (9 ± 2 nm), and thickness of the films (12-20 nm). Oriented Pt NPs on G exhibit at least 2 orders of magnitude higher catalytic activity for aqueous-phase reforming of ethylene glycol to H2 and CO2 compared to analogous samples of randomly oriented Pt NPs supported on preformed graphene. Oriented [Formula: see text]/fl-G undergoes deactivation upon reuse, the most probable cause being Pt particle growth, probably due to the presence of high concentrations of carboxylic acids acting as mobilizing agents during the course of the reaction.

Hydrogen production from ethylene glycol reforming catalyzed by Ni and Ni–Pt hydrotalcite-derived catalysts

In this work, we report a study of the steam reforming (SR) and the aqueous phase reforming (APR) of ethylene glycol (EG) with catalysts based on Ni, prepared from hydrotalcite-like compounds. The Pt–Ni bimetallic catalyst was synthesized using controlled techniques derived from Surface Organometallic Chemistry on Metals (SOMC/M). This methodology allows obtaining very well-defined active phases, with low atomic Pt/Ni bulk values (∼0.004) and a specific interaction between both metals.We demonstrate that in the APR of EG, in which the CO bond cleavage reactions are more favored than in SR, the Ni catalyst is more efficient than the bimetallic Pt–Ni. However, this Pt–Ni bimetallic catalyst is more active and selective to hydrogen in the SR at 450 °C.The interaction of ethylene glycol with the catalyst surface was studied combining diffuse reflectance infrared spectroscopy with mass spectrometry. Through these studies carried out on the Pt–Ni catalyst, we observed low stability of the formate and carboxylate intermediate species, which would explain its higher activity to produce H2 and CO2 through the water gas shift reaction.

Ethylene glycol reforming on Pt(111): first-principles microkinetic modeling in vapor and aqueous phases

Reaction chemistry for vapor- and aqueous-phase reforming of ethylene glycol over Pt(111) is similar with early dehydrogenation steps being rate-controlling.

Hydrogen production by aqueous-phase reforming of ethylene glycol over a Ni/Zn/Al derived hydrotalcite catalyst

The article presented the aqueous-phase reforming of ethylene glycol over Ni/Zn/Al hydrotalcite. The results showed that the H2 yield and selectivity were 73% and 96%, respectively. The conversion of ethylene glycol was >99%.

Aqueous phase reforming of ethylene glycol on Pt/CeO2–ZrO2: effects of cerium to zirconium molar ratio

The superior activity of aqueous-phase reforming of ethylene glycol on optimal Pt/CeO2–ZrO2was attributed to the strongly interacting platinum species on the oxygen vacancy defect sites of the support, forming thermally-stable platinum crystallites.

Towards Stable Catalysts for Aqueous Phase Conversion of Ethylene Glycol for Renewable Hydrogen

Aqueous-phase reforming of ethylene glycol over alumina-supported Pt-based catalysts is reported. Performance of the catalysts is investigated by conducting kinetics and in situ attenuated total reflectance (ATR)-IR spectroscopic analysis. Pt/γ-Al2 O3 is unstable under APR conditions (270 °C, 90 bar) and undergoes phase transformation to boehmite [AlO(OH)]. This conversion of alumina is studied in situ by using ATR-IR spectroscopy; transition into boehmite proceeds even at milder conditions (210 °C, 40 bar). Pt/γ-Al2 O3 deactivates irreversibly because the Pt surface area decreases owing to an increasing metal particle size and coverage with boehmite. However, Pt supported on boehmite itself shows stable activity. Surprisingly, the rate of formation of hydrogen per Pt surface atom is significantly higher on boehmite compared to an alumina-supported catalyst. This observation seems correlated to both increased concentration of surface OH groups as well as to enhanced oxidation of Pt when comparing Pt/γ-Al2 O3 with Pt/AlO(OH).

Hydrogen Production through Aqueous‐Phase Reforming of Ethylene Glycol in a Washcoated Microchannel

Aqueous-phase reforming (APR) of biocarbohydrates is conducted in a catalytically stable washcoated microreactor where multiphase hydrogen removal enhances hydrogen efficiency. Single microchannel experiments are conducted following a simplified model based on the microreactor concept. A coating method to deposit a Pt-based catalyst on the microchannel walls is selected and optimized. APR reactivity tests are performed by using ethylene glycol as the model compound. Optimum results are achieved with a static washcoating technique; a highly uniform and well adhered 5 μm layer is deposited on the walls of a 320 μm internal diameter (ID) microchannel in one single step. During APR of ethylene glycol, the catalyst layer exhibits high stability over 10 days after limited initial deactivation. The microchannel presents higher conversion and selectivity to hydrogen than a fixed-bed reactor. The benefits of using a microreactor for APR can be further enhanced by utilizing increased Pt loadings, higher reaction temperatures, and larger carbohydrates (e.g., glucose). The use of microtechnology for aqueous-phase reforming will allow for a great reduction in the reformer size, thus rendering it promising for distributed hydrogen production.

Hydrogen production from aqueous-phase reforming of ethylene glycol over Ni/Sn/Al hydrotalcite derived catalysts

Ni/Sn/Al hydrotalcites (Ni/Sn/Al-HT) are synthesized by a coprecipitation method. The microstructure and properties of Ni/Sn/Al-HT precursors and derived catalysts are characterized by means of X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), thermo-gravimetric/differential thermal analyzer (TG–DTA), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The result shows that Sn2+ is not introduced in the layers because of its large ionic radii. As-prepared samples consist of a hydrotalcite phase and a SnO phase. As a noval catalyst for H2 production from aqueous-phase reforming of biomass-derived ethylene glycol (EG), Ni/Sn/Al-HT shows a high H2 production rate, and a good H2 selectivity of ca. 100%, as well as a good catalytic stability over 120h. The superior catalytic performance is likely to be related with the Ni3Sn alloy formed via the reduction of Ni/Sn/Al-HT.

Catalytic properties of Pt/Al2O3 catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al2O3 catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H2PtCl6. The highest rate of hydrogen production (452 μmol min−1 g−1) obtained with the Pt/α-Al2O3 catalyst can be related to the highest extent of dispersion of Pt on α-Al2O3. XPS, TEM-EDX and TPR-H2 measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al2O3 catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al2O3 and Pr/δ-Al2O3 catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.

Aqueous-Phase Reforming of Ethylene Glycol to Hydrogen on Supported Pt Catalysts

Aqueous-phase reforming of 5 wt% ethylene glycol was studied at temperature of 498 K over Pt supported on Al2O3, SiO2, TiO2, CeO2. High selectivity about 90% for generation of hydrogen was observed over the supported Pt catalysts, suggesting that the methanation or the Fischer-Tropsch reactions involving CO/CO2 and H2 does not appear to be important over these catalysts under the present conditions. Compared with Pt/SiO2 and Pt/CeO2, Pt supported on Al2O3 and TiO2 produced measurable amounts of gaseous alkane that may be due to the acidity of the supports. To verify this suppose, the water-gas shift reaction was carried out over the catalysts under the same reaction conditions, and no CH4 was observed over these Pt catalysts. Relatively higher generation rates of hydrogen and carbon dioxide were achieved over Pt/Al2O3 and Pt/SiO2 catalysts.

Aqueous-phase reforming of ethylene glycol on Co/ZnO catalysts prepared by the coprecipitation method

Co/ZnO catalysts with different Co/Zn ratios have been prepared by the coprecipitation method. It is revealed that below the nominal Co/Zn molar ratio of 2, the calcined Co/ZnO samples were constituted by ZnO and ZnCo 2O 4 spinel. At the nominal Co/Zn ratio of 2, a small amount of Co 3O 4 spinel emerged. After reduction, the catalysts were composed of fcc Co and ZnO. In aqueous-phase reforming (APR) of ethylene glycol, it is found that the intrinsic activity and selectivity to H 2 increase with the increment of the ZnO content. H 2 selectivities over the Co/ZnO catalysts ranged from 52% to 89%, which are substantially higher than that of the Raney Ni catalyst at similar conversion. Moreover, the Co/ZnO catalysts produced much less CO in the product gas. With the aid of literature works as well as additional experiments on APR of acetic acid, methanol, and ethanol, the reaction pathways of ethylene glycol in the presence of water on the Co/ZnO catalysts were discussed.

Aqueous-phase reforming of ethylene glycol to hydrogen on Pd/Fe 3O 4 catalyst prepared by co-precipitation: Metal–support interaction and excellent intrinsic activity

A high-performance Pd/Fe 3O 4 catalyst for aqueous-phase reforming (APR) of ethylene glycol (EG) to H 2 was prepared facilely by the co-precipitation method. After proper activation, the Pd was present as highly dispersed metallic nanoparticles with dimension of <3 nm, and the Fe was present as magnetite. When compared to Pd catalyst supported on Fe 2O 3, NiO, Cr 2O 3, Al 2O 3, or ZrO 2 prepared by incipient wetness impregnation, the Pd/Fe 3O 4 catalyst displayed superior catalytic performance in terms of activity, selectivity, and stability. The intrinsic activity of the Pd/Fe 3O 4 catalyst was about three times of that of the second most active Pd/Fe 2O 3 catalyst under the same reaction conditions. In addition, the Pd/Fe 3O 4 catalyst retained ∼80% of its initial activity after reaching the steady-state. Notably, the Pd/Fe 3O 4 catalyst possessed the highest turnover frequency of H 2 (109 min −1) reported so far, showing its promise as a new practical catalyst for APR of biomass-derived oxygenates to H 2. The excellent catalytic performance of the Pd/Fe 3O 4 catalyst was attributed to the enhanced synergistic effect between small Pd nanoparticles and magnetite in promoting the water–gas shift reaction, the rate-determining step in APR of EG over Pd-based catalysts.

Bioenergy II: Hydrogen Production by Aqueous-Phase Reforming

The present work is focused on the aqueous-phase reforming of ethylene glycol at 500 K. The influence of the system pressure (27 to 36 bar) and the catalyst weight/ethylene glycol flow rate ratio has been studied using a Pt/Al2O3 research catalyst. A comparison of the latter with a Ni/Al coprecipitated catalyst showed a significant influence on hydrogen and alkane selectivities.

Preparation and catalytic properties of Pt supported Fe-Cr mixed oxide catalysts in the aqueous-phase reforming of ethylene glycol

Abstract Fe-Cr mixed oxides were synthesized using citric acid as fuels by solid thermal decomposition reaction. The samples were characterized by BET, XRD and TPR. These analyses showed that the addition of chromium compounds not only increased the BET surface area of the mixed oxides, but also affected the phase composition of iron oxide in the product. Using Fe-Cr mixed oxides as supports, the platinum catalysts were prepared. The catalysts were tested in the aqueous-phase reforming of 10wt% ethylene glycol solutions and results showed that the rate of hydrogen production was promoted with the addition of chromium compounds at certain contents.