Aqueous-phase Reforming Of Ethanol Research Articles

H2 production through aqueous phase reforming of ethanol over molybdenum carbide catalysts supported on zirconium oxide.

Molybdenum carbide catalysts supported on monoclinic and tetragonal zirconium oxide were studied for hydrogen production through aqueous phase reforming of ethanol. Catalysts were characterized by N2 physisorption, XRD, TPR and XPS. Results showed that 10%Mo2C/m-ZrO2 was less carburized and had a lower surface area than 10%Mo2C/t-ZrO2 and 10%MoC/t-ZrO2. Mo oxide was identified on the surface as well as two types of Mo oxycarbide and Mo oxynitride. The α crystalline phase of the carbide was more active than β phase and was ascribed to its higher relative superficial distribution. However, the α phase generated less H2 probably because there was less oxycarbide presence. 10%Mo2C/m-ZrO2 produced significantly more H2 and was stable for five consecutive reactions. This catalyst showed higher carburization degree after the reaction, which greatly enhanced the generation of H2, suggesting that carbides species improved H2 production compared to oxycarbides.

Surface processes occurring during aqueous phase ethanol reforming on Ru/TiO2 tracked by ATR-IR spectroscopy

Surface processes occurring at the solid-liquid interface of Ru/TiO2 catalysts during aqueous phase reforming of ethanol at reaction conditions (200 °C and 20 bar) have been examined using attenuated total reflection infrared spectroscopy (ATR-IR). Depending on the loading and particle size of Ru significant differences in the population dynamics of adsorbed species were observed. On the catalyst with high loading (5 wt%) and large particle size (∾ca. 4 nm) formation of intermediate acetylide was detected, which is attributed to enhanced C–O bond cleavage promoting methanation and thus leading to lower efficiency of H2 generation. In contrast, on the catalyst with low loading (0.5 wt%) and smaller particle size (∾ca. 1 nm) no acetylide was detectable, indicating that C–O bond cleavage was suppressed.

Synergistic bimetallic Ru–Pt catalysts for the low‐temperature aqueous phase reforming of ethanol

Aqueous phase reforming (APR) of ethanol has been studied over a series of Ru and Pt catalysts supported on carbon and titania, with different metal loadings and particle sizes. This study proposed that, on both metals, ethanol is first dehydrogenated to acetaldehyde, which subsequently undergoes CC cleavage followed by different paths, depending on the catalyst used. For instance, although monometallic Pt has high selectivity toward H2 via dehydrogenation, it has a low efficiency for CC cleavage, lowering the overall H2 yield. Large Ru particles produce CH4 through methanation, which is undesirable because it consumes H2. Small Ru particles have lower activity but higher selectivity toward H2 rather than CH4. On these small particles, CO blocks low‐coordination sites, inhibiting methanation. The combination of the two metals in bimetallic Ru–Pt catalysts results in improved performance, benefiting from the desirable properties of each Ru and Pt, without the negative effects of either. © 2018 American Institute of Chemical Engineers AIChE J, 65: 151–160, 2019

Mechanistic Study of Hydrogen Production By Aqueous Phase Reforming of Ethanol and Acetic Acid over Various Supported Ru Catalysts

The production of hydrogen as a clean energy carrier from bio-renewable sources is considered to be one of the most promising ways to minimize the global environmental problems that are associated with fossil fuel combustion. Among bio-renewable liquid feedstock for producing hydrogen, ethanol (EtOH) and acetic acid (AcOH) are the most promising candidates because of their non-toxicity, facile storage, safe handling and possibility as model compounds of bio-oil or bio-ethanol. Liquid phase reforming of oxygenates have been reported fewer than steam reforming, although they have advantages as compared to steam reforming. It is possible to reduce the cost of the process since it can be operated at lower temperatures, generating H2 and CO2 with lower level of CO. In the present work, we have investigated the loading amount dependency of Ru upon H2 production by aqueous phase reforming (APR) of EtOH and AcOH over Ru/TiO2 and Ru/Na-Y-zeolite catalysts. In the case of EtOH-APR (473K) over 5wt% Ru/TiO2, the formation of H2 and CO2 showed a plateau at the later stage of the reaction, accompanied with a large increase of CH4 formation. On the other hand, over 0.5wt% Ru/TiO2 main product was H2 with a smaller amount of CH4 and CO2 (1:1 ratio), indicating the possibility of the prevention of undesirable methanation by employing the catalysts with smaller particle sizes. Similar loading amount dependency was observed in the cases of AcOH-APR (473K) over 5 and 0.5wt% Ru/TiO2 catalysts. In both cases, H2, CH4 and CO2 are the major products in the gas phase with small amount of liquid phase products. Over 5wt% catalyst, H2 was rapidly formed only at the beginning of the reaction and its formation rate became very slow at the later stage. On the other hand, 1:1 ratio of CH4 and CO2 were formed continuously, suggesting the occurrence of simple decomposition of acetic acid. Over 0.5wt% catalyst, the formation of H2 continued for longer period and the amount of formed CH4 was much less than CO2, clearly indicating the occurrence of the complete reforming process to form H2 and CO2. It is generally accepted that dehydrogenation of ethanol gives acetaldehyde (AcH), which goes to three different reaction pathways as follows, (1) decomposition to form CH4 and CO followed by the water gas shift to form H2 and CO2, (2) hydration to form acetic acid (AcOH) or (3) complete reforming to only H2 and CO2. Once CH4 is formed, it is rather difficult to reform it into H2 and CO2 at lower temperatures. In the case of 0.5wt% Ru/TiO2, EtOH-APR reaction proceeded through the decomposition of AcH forming 1:1 ratio of CO2 and CH4. Successive methanation reaction of CO2 with H2 was not observed at all, which was the predominant undesirable reaction in the case of 5wt% catalyst. However, no reforming of AcH seems to be operating on both catalysts, suggesting that particle size may not be the selectivity controlling factor for EtOH-APR reaction. On the contrary, in the case of AcOH-APR reaction over 0.5wt% catalyst, Ru metals with smaller particle sizes can participate in the reforming process of AcH, probably because of their stronger ability for H2O activation. The existence of such positively charged small Ru clusters was confirmed by in-situ XPS and FT-IR spectra of CO adsorption. We have also studied Ru/NaY-zeolite catalysts for APR reaction of AcOH (473K). NaY-zeolite has a unique three-dimensional ordered porous structure as well as cation-exchangeable ability. Such characteristics would be efficient for controlling the structural and electronic properties of supported Ru species. As we have expected, Ru/NaY-zeolite catalysts exhibited high selectivity for complete reforming. In this work, we have tried to characterize the efficient active site formed on NaY-zeolite. Catalytic activities of the supported ruthenium species on NaY-zeolite depended on immobilization conditions of [Ru(NH3)6]3+ and oxidation state controlled by treatment procedures. The catalysts NaY(exc), of which the ruthenium precursor was supported through cation-exchanging process, produced H2 continuously until 10 hrs. Reducing the loading amounts of ruthenium led to improve the selectivity toward complete reforming of AcOH giving H2 and CO2. Also, contents of sodium in the catalysts affected the reaction selectivity. The NaY(exc) catalysts, of which the part of sodium was exchanged to proton, exhibited relatively higher CH4 forming activity and that led to decrease the selectivity toward complete reforming.

Study of preparation method and oxidization/reduction effect on the performance of nickel-cerium oxide catalysts for aqueous-phase reforming of ethanol

The effect of preparation method and oxidation state of the active metal on the catalytic activity of Ni–Ce–O catalysts was studied for aqueous phase reforming of ethanol. A sol-gel (SG) route and a solution combustion synthesis (SCS) method were used for the preparation of 10 wt% Ni loaded catalysts. The catalytic activity of three groups of catalysts; reduced at 425 °C (HR, metallic Ni), reduced at 1000 °C (FR, metallic Ni), and not reduced (NR, as NiO) were tested at different operating conditions. The difference in the metal particle sizes, governed by the preparation method, affects the catalytic efficiency most, not the reduced or oxidized state of Ni. The SG samples were superior for ethanol conversion and selectivity for H2 and CO2 compared to the SCS samples. The X-ray photoelectron spectroscopy (XPS) analysis of the samples demonstrated that the relative ratio of Ce2O3 to CeO2 increased inside the reactor. While Ni doping increases oxygen mobility in the Ce–O lattice, Ce3+ converts Ni2+ to metallic Ni inside the reactor. This can explain why the reduction stage for Ni–Ce–O system in APR is irrelevant. Higher oxygen mobility through the support helps oxidation of CO to CO2 leading to improved catalytic performance.

Effects of Re addition upon aqueous phase reforming of ethanol over TiO2 supported Rh and Ir catalysts

Effect of addition of rhenium was investigated during catalysis of TiO2-supported Rh and Ir metals for aqueous phase reforming of ethanol. By adding Re to Rh/TiO2 and Ir/TiO2 catalysts, the initial rates of H2, CH4, and CO2 formation increased 3–4 times, together with the extraordinary increase of acetic acid formation. Detailed mechanisms of the reforming reaction were investigated using various physicochemical techniques. The role of added Re was the acceleration of the hydration of acetaldehyde to form acetic acid rather than the decomposition of acetaldehyde to form CH4 and CO on both Rh/TiO2 and Ir/TiO2 catalysts. Well dispersed bimetallic nano-composites would work as the active sites for ethanol dehydrogenation and acetaldehyde decomposition, whereas partially oxidized ReOx sites may work for the hydration of acetaldehyde to form acetic acid.

The effect of ZnO addition on Co/C catalyst for vapor and aqueous phase reforming of ethanol

The effect of ZnO addition on the oxidation behavior of Co along with catalytic performance in vapor and aqueous phase reforming of ethanol were investigated on Co supported on carbon black (XC-72R). Carbon was selected to minimize the support interactions. Effect of ZnO addition during both vapor and aqueous phase reforming were compared at 250°C. ZnO addition inhibited the reduction of cobalt oxides by H2 and created surface sites for H2O activation. During vapor phase reforming at 450°C the redox of cobalt, driven by steam oxidation and H2 reduction, trended to an equilibrium of Co0/Co2+. ZnO showed no significant effect on cobalt oxidation, inferred from the minor changes of C1 product yield. Surface sites created by ZnO addition enhanced water activation and oxidation of surface carbon species, increasing CO2 selectivity. At 250°C cobalt reduction was minimal, in situ XANES demonstrated that ZnO addition significantly facilitated oxidation of Co0 under vapor phase reforming conditions, demonstrated by lower C1 product yield. Sites introduced by ZnO addition improved the COx selectivity at 250°C. Both Co/C and Co-ZnO/C rapidly oxidized under aqueous phase reaction conditions at 250°C, showing negligible activity in aqueous phase reforming. This work suggests that ZnO affects the activation of H2O for Co catalysts in ethanol reforming.

Aqueous phase reforming of ethanol and acetic acid over TiO2 supported Ru catalysts

This study examined the dependence of Ru particle sizes upon the activity and selectivity for aqueous phase reforming reactions of ethanol and acetic acid over Ru/TiO2 at 473K. For ethanol, irrespective of the Ru particle size, the 1:1 ratio of CH4 and CO2 was formed at the initial stage, indicating the absence of complete reforming with water. At the later stage, unfavorable methanation of CO2 by H2 was observed over larger Ru particle catalysts. That methanation was suppressed completely over smaller Ru particle catalysts. In the case of acetic acid reforming over smaller Ru particle catalysts, a 2:1 ratio of H2 and CO2 was formed constantly, indicating the operation of complete reforming reaction with water. Positively charged small Ru particles were responsible for the efficient activation of acetic acid and water to form H2 and CO2 selectively.

Reaction Performance of Hydrogen from Aqueous-Phase Reforming of Methanol or Ethanol in Hydrogenation of Phenol

Reaction performances of hydrogen generated from aqueous-phase reforming (APR) of methanol or ethanol were investigated in hydrogenation of phenol, o-cresol and p-tert-butylphenol, over a Raney Ni or Pd/Al2O3 catalyst, respectively. The properties of the adsorbed hydrogen from aqueous-methanol/-ethanol, and H2-gas were studied by means of temperature-programmed surface reaction in liquid phase and temperature-programmed desorption. The results shown that the selectivities of cyclohexanone are 20.5% and 96.1%, 27.4% and 92.4%, and 12.6% and 71.1% in the hydrogenation of phenol with hydrogen from APR of methanol, APR of ethanol, and H2-gas over the Raney Ni and Pd/Al2O3 catalyst, respectively. The limited amount of adsorbed hydrogen from the APR of methanol or ethanol favors the formation of cyclohexanone, but excessive amounts of adsorbed hydrogen from H2-gas favors the formation of cyclohexanol in hydrogenation of phenol.

Hydrogen production by aqueous-phase reforming of ethanol over nickel catalysts prepared from hydrotalcite precursors

Abstract Derived hydrotalcite catalysts, with different Ni loadings, were prepared and tested in aqueous-phase reforming of ethanol. Upon calcination of the hydrotalcite-like compounds, there was formation of MgO periclase-type phase, where both nickel and aluminum oxides are well dispersed. The mixed oxides showed only one reduction peak in temperature range of 900–1000 °C. The catalytic tests were carried out in a batch reactor with an aqueous solution of 1 wt.% ethanol at different temperatures (200, 230 and 250 °C). The derived hydrotalcite catalysts showed high activity, with 65% of ethanol conversion at 230 °C, high hydrogen selectivity and lower methane production than alumina supported nickel catalyst.

Production of Hydrogen from Glucose as a Biomass Simulant: Integrated Biological and Thermochemical Approach

Hydrogen production from biomass was investigated using an integrated biological and thermochemical process. Glucose was used as a biomass surrogate and was first converted to ethanol in a fermentation process. The fermentation experiments were carried out using Saccharomyces cerevisiae. The fermentation broth was then used in aqueous phase reforming (APR) over a platinum-based catalyst. An economic analysis of the proposed process demonstrates the economic viability of producing hydrogen from biomass using fermentation combined with APR. The average production yield of hydrogen was ∼25%. The hydrogen obtained from APR of the fermentation broth was compared against the yield from a feed containing 5% ethanol in water. While the catalyst was stable for an extended time on stream during APR of ethanol, very rapid deactivation was observed during APR of fermentation broth. Different catalyst characterization techniques, including XRD, BET surface area, and ICP-AES, were employed to investigate the causes of catalyst deactivation. Although the analysis suggested similar catalyst changes in both cases, and the exact deactivation mechanism could not be concluded, these techniques helped to eliminate some mechanisms while suggesting other possible deactivation routes. Nanofiltration of the fermentation broth was shown to remove the impurities leading to deactivation.