Selective Production Of Hydrogen Research Articles

Conversion of methane to synthesis-gas on conventional and membrane Pt/TiO2 catalysts

The use of a membrane catalyst makes it possible to attain a higher methane conversion, enhanced Н2/СО ratio in products of steam methane reforming, and improved selectivity to CO in the partial oxidation of methane compared to conventional supported catalysts. These advantages determine prospects of using membrane catalysts in the selective production of hydrogen or synthesis-gas in methane reforming. The influence of the TiO2 membrane support on the electron state of platinum was found using IR spectroscopy of adsorbed CO. It was shown by X-ray absorption that in the Pt/TiO2 membrane catalyst Ti4+ ions exist in the oxygen environment similarly to titanium ions in rutile.

Importance of Ligand Effect in Selective Hydrogen Formation via Formic Acid Decomposition on the Bimetallic Pd/Ag Catalyst from First-Principles

The critical role of the Ag–Pd ligand effect (which is tuned by changing the number of Pd atomic layers) in determining the dehydrogenation and dehydration of HCOOH on the bimetallic Pd/Ag catalysts was elucidated by using the spin-polarized density functional theory (DFT) calculations. Our calculations suggest that the selectivity to H2 production from HCOOH on the bimetallic Pd/Ag catalysts strongly depends on the Pd atomic layer thickness at near surface. In particular, the thinnest Pd monolayer in the Pd/Ag system is responsible for enhancing the selectivity of HCOOH decomposition toward H2 production by reducing the surface binding strength of specific intermediates such as HCOO and HCO. The dominant Ag–Pd ligand effect by the substantial charge donation to the Pd surface from the subsurface Ag [which significantly reduce the density of state (particularly, dz2–r2 orbital) near the Fermi level] proves to be a key factor for the selective hydrogen production from HCOOH decomposition, whereas the expansive (tensile) strain imposed by the underlying Ag substrate plays a minor role. This work hints on the importance of properly engineering the surface activity of the Ag–Pd core–shell catalysts by the interplay between ligand and strain effects.

Selective hydrogen production from formic acid decomposition on Pd-Au bimetallic surfaces.

Pd-Au catalysts have shown exceptional performance for selective hydrogen production via HCOOH decomposition, a promising alternative to solve issues associated with hydrogen storage and distribution. In this study, we utilized temperature-programmed desorption (TPD) and reactive molecular beam scattering (RMBS) in an attempt to unravel the factors governing the catalytic properties of Pd-Au bimetallic surfaces for HCOOH decomposition. Our results show that Pd atoms at the Pd-Au surface are responsible for activating HCOOH molecules; however, the selectivity of the reaction is dictated by the identity of the surface metal atoms adjacent to the Pd atoms. Pd atoms that reside at Pd-Au interface sites tend to favor dehydrogenation of HCOOH, whereas Pd atoms in Pd(111)-like sites, which lack neighboring Au atoms, favor dehydration of HCOOH. These observations suggest that the reactivity and selectivity of HCOOH decomposition on Pd-Au catalysts can be tailored by controlling the arrangement of surface Pd and Au atoms. The findings in this study may prove informative for rational design of Pd-Au catalysts for associated reactions including selective HCOOH decomposition for hydrogen production and electro-oxidation of HCOOH in the direct formic acid fuel cell.

Selective and mild hydrogen production using water and formaldehyde

With the increased efforts in finding new energy storage systems for mobile and stationary applications, an intensively studied fuel molecule is dihydrogen owing to its energy content, and the possibility to store it in the form of hydridic and protic hydrogen, for example, in liquid organic hydrogen carriers. Here we show that water in the presence of paraformaldehyde or formaldehyde is suitable for molecular hydrogen storage, as these molecules form stable methanediol, which can be easily and selectively dehydrogenated forming hydrogen and carbon dioxide. In this system, both molecules are hydrogen sources, yielding a theoretical weight efficiency of 8.4% assuming one equivalent of water and one equivalent of formaldehyde. Thus it is potentially higher than formic acid (4.4 wt%), as even when technical aqueous formaldehyde (37 wt%) is used, the diluted methanediol solution has an efficiency of 5.0 wt%. The hydrogen can be efficiently generated in the presence of air using a ruthenium catalyst at low temperature.

Hollow nickel-coated silica microspheres containing rhodium nanoparticles for highly selective production of hydrogen from hydrous hydrazine

Hollow nickel-coated microspheres containing Rh nanoparticles (Rh/Ni@SiO2) generate hydrogen (H2) from hydrazine (H2NNH2) with over 99% selectivity within 1.5 h at 25 °C.

Selective Hydrogen Production from Methanol with a Defined Iron Pincer Catalyst under Mild Conditions

Molecularly well-defined iron pincer complexes promote the aqueous-phase reforming of methanol to carbon dioxide and hydrogen, which is of interest in the context of a methanol and hydrogen economy. For the first time, the use of earth-abundant iron complexes under mild conditions for efficient hydrogen generation from alcohols is demonstrated.

Selective Hydrogen Production from Methanol with a Defined Iron Pincer Catalyst under Mild Conditions

AbstractMolecularly well‐defined iron pincer complexes promote the aqueous‐phase reforming of methanol to carbon dioxide and hydrogen, which is of interest in the context of a methanol and hydrogen economy. For the first time, the use of earth‐abundant iron complexes under mild conditions for efficient hydrogen generation from alcohols is demonstrated.

Electrolysis of Alcohols in High Temperature-High Pressure Water

ABSTRACTThe design of clean, efficient and environmentally friendly routes that reduce the waste production and fuel emissions of pollutants into the atmosphere, produce clean, affordable, and renewable energy sources to lessen energy consumption and toxicity on the environment, has become a central issue of chemical research both in industry and academia. One of the approaches being used in green chemistry practices is to use water as a solvent and reaction medium where possible. Much of this work deals with liquid water at temperatures exceeding the normal boiling point which is denoted as sub-critical water.Electrochemical reaction, usually operated at atmospheric condition in water, is generally slow, although it has advantages over chemical reaction such as suppression of side reaction by tuning operating conditions. Since sub-critical water (7 MPa and 250 °C) has remarkable properties such as high ion product and low dielectric constant, it could be a suitable reaction media.We have been studying electrolysis of organic compounds in sub-critical water as waste treatment and molecular degradation technologies. Electrolysis in sub-critical water could degrade harmful and thermally stable organic compounds into innocuous compounds such as hydrogen and water. In this research, we focused on the investigation of the electrochemical reactions of alcohols in sub-critical water to evaluate possibility for the selective production of hydrogen and value-added chemicals.Electrochemical reactions were carried out in sub-critical water using a specially designed autoclave made of SS 316 with a volume of 500 mL. For comparison, thermal degradation experiments of alcohols were also conducted without any direct current loading at identical conditions. Here we employed glycerol and 1-butanol as model compounds of alcohols.As a result of 1-butanol experiments, butanal and butyric acid were produced via partial oxidation at 250 °C and by applying 1-3 A of direct current while no oxidation products were observed at the hydrothermal degradation run. As a gaseous product, hydrogen gas was generated according to the electrochemical reaction mechanism. In the case of glycerol experiments, the main gaseous product was hydrogen gas, whereas glycolaldehyde, lactic acid, and formic acid were generated as the main liquid products at 280 °C. Results indicated that greater than 92% of the glycerol could be decomposed under optimum conditions by hydrothermal electrolysis technique.This presented research will help to degrade stable organic materials in an environmentally friendly way and without need for secondary treatment processes. It will also address the need for novel more efficient techniques for the degradation of stable organic compounds in aqueous conditions and it will advance the use of water as a reaction medium in an efficient way without any organic solvent.

Methanol oxidation over silica-supported Pt and Ag nanoparticles: Toward selective production of hydrogen and carbon dioxide

Pt, Ag, and Pt–Ag nanoparticles smaller than 5 nm were synthesized by a simple, alcohol reduction. These and similar materials may have many applications including photocatalysis because of the ability to tune the plasmonic and catalytic properties. After immobilization onto silica, the particles were tested for methanol decomposition and partial methanol oxidation. For methanol decomposition, Ag/silica was the more active than Pt/silica. This result was in agreement with product poisoning (CO) limiting turnover and CO generally binding more weakly to Ag than Pt surfaces. The properties of the bimetallic Pt–Ag were between the parent catalysts, but different than their physical mixture, which indicated Pt–Ag bimetallic formation. The catalytic activity for partial methanol oxidation was greater than methanol decomposition for all catalysts. The Pt/silica catalyst demonstrated the best hydrogen and carbon dioxide yields when oxygen was added. The results are discussed in the discussion of a two-step process in which methanol is decomposed to carbon monoxide and hydrogen and then these species are oxidized to water and carbon dioxide. Further work is needed to refine the process and the catalyst to achieve CO-free hydrogen from methanol and oxygen.

Pruning of the surface species on Ni/Al2O3 catalyst to selective production of hydrogen via acetone and acetic acid steam reforming

Catalytic behaviors of the different metallic Ni species on Ni/Al2O3 catalyst surface were investigated in steam reforming of acetone and acetic acid to hydrogen. The different Ni species showed distinct activities for activation of acetic acid and acetone, gasification of coke precursors, and other secondary reactions such as methanation, water–gas shift reaction, CO disproportion and methane decomposition. The Ni species weakly interacted with alumina solely showed negligible reforming activity, while the Ni species mildly interacted with alumina was very active and efficient for steam reforming reaction. In comparison, the Ni species strongly interacted with alumina existed in bigger particle sizes, which resulted in the side reactions for by-product generation and consequently led to serious coking. Suppression of its presence on catalyst is the key point to obtain a highly selective and stable Ni/Al2O3 catalyst.

Screening of nickel catalysts for selective hydrogen production using supercritical water gasification of glucose

We report the activity and the selectivity of several heterogeneous nickel catalysts for the supercritical water gasification (SCWG) of biomass. The effects of catalyst support on the carbon conversion and hydrogen selectivity were demonstrated using 44 different materials, covering a wide range of chemical and physical properties. At 5% nickel loading, α-Al2O3, carbon nanotubes (CNTs), and MgO supports resulted in high carbon conversions, while SiO2, Y2O3, hydrotalcite, yttria-stabilized zirconia (YSZ), and TiO2 showed modest activities. Utilization of different γ-Al2O3 supports resulted in a wide range of catalytic activities from almost inactive to highly active. Other catalyst carriers such as zeolites, molecular sieves, CeO2, and ZrO2 had insignificant activity under the conditions tested (i.e., 380 °C, 2 wt% feed). Aside from the catalytic activity, the stable metal oxide supports under the experimental conditions of this work, as identified by XRD, were α-Al2O3, boehmite, YSZ, and TiO2. Given the high hydrogen yield and carbon conversion as well as its superior stability in supercritical water, α-Al2O3 was chosen for a more elaborate investigation. It was found that when using the same amount of nickel, the methane yield significantly decreased by increasing the nickel to support ratio whereas the carbon conversion was only slightly affected. At a given nickel to support ratio, a threefold increase in methane yield was observed by increasing the temperature from 350 to 410 °C. The catalyst activation conditions (e.g., calcination and reduction) had a small impact on its catalytic performance. The catalyst activity increased with the addition of alkali promoters (i.e., K, Na, Cs) and decreased with the addition of tin. The highest catalytic activity was obtained with the addition of 0.5% potassium. In summary, nickel loading and alkali promoters improved the hydrogen selectivity and the carbon conversion of the Ni/α-Al2O3 catalyst.

Selective production of hydrogen by steam reforming of bio-ethanol

Experimental results of catalytic activity, selectivity and coking phenomenon on co-precipitated cobalt catalysts with the ZnO–Al 2O 3 support in the steam reforming of ethanol (SRE) are reported. The influence of the cobalt active phase content (9–41 wt.%) and the reaction temperature (350–600 °C) was the point at issue. From the point of view of activity and selectivity, temperatures 420 °C and higher favoured steam reforming of ethanol on supported cobalt catalysts. At these temperatures the conversion of ethanol reached 100%, simultaneously the hydrogen yield achieved the level of above 5 mol of H 2 formed from 1 mol of EtOH introduced to the reaction, as well as the selectivity of carbon monoxide formation was depressed to 2–3%. However, taking into account possibility of coking of catalysts, the optimum temperature of the SRE is 420 °C. The catalyst containing 24 wt.% of cobalt was the most effective one. The obtained results are very important in the aspect of electricity generation in fuel cells feed with a reformate gas.

Hydrogen production by glycerol steam reforming over CeZrCo fluorite type oxides

The glycerol steam reforming reaction was studied for selective hydrogen production. The effect of the reaction temperature and of the active phase was evaluated using two catalysts Ce 2Zr 1.5Co 0.5O 8− δ (CZCo) and Ce 2Zr 1.5Co 0.47Rh 0.07O 8− δ (CZCoRh) mixed oxides. For both catalysts the increment of temperature favoured the glycerol conversion into gaseous products. At 650 °C, 95% of the thermodynamic H 2 production was obtained (6.1 molH 2 mol Gly.in −1) using CZCoRh. For the CZCoRh diluted with SiC, the H 2 production increased to 6.7 molH 2 mol Gly.in −1 and remained during 16 h. The blank results showed that 0.5 molH 2 mol Gly.in −1 is formed using the SiC bed alone.

Self‐Sustainable Production of Hydrogen, Chemicals, and Energy from Renewable Alcohols by Electrocatalysis

The selective and simultaneous production of hydrogen and chemicals from renewable alcohols, such as ethanol, glycerol, and ethylene glycol, can be accomplished by means of electrolyzers in which the anode electrocatalyst is appropriately designed to promote the partial and selective oxidation of the alcohol. In the electrolyzers described herein, the production of 1 kg of hydrogen from aqueous ethanol occurs with one-third the amount of energy required by a traditional H(2)/O(2) electrolyzer, by virtue of the much lower oxidation potential of ethanol to acetate vs. water to oxygen in alkaline media (E(0)=0.10 V vs. 1.23 V). The self-sustainability of H(2) production is ensured by the simultaneous production of 25 kg of potassium acetate for every kg of H(2), if the promoting co-electrolyte is KOH.

A comparative study between Co and Rh for steam reforming of ethanol

Rh and Co-based catalyst performance was compared for steam reforming of ethanol under conditions suitable for industrial hydrogen production. The reaction conditions were varied to elucidate the differences in reaction pathways on both catalysts. On Co/ZnO, CH4 is a secondary product formed through the methanation reaction, while it is produced directly by ethanol decomposition on Rh. The difference in the reaction pathway is shown to favor Co-based catalysts for selective hydrogen production under elevated system pressures (up to 15bar) of industrial importance. The carbon deposition rate was also studied, and we show that Co is more prone to coking and catalyst failure. However, the Co/ZnO catalyst can be regenerated, by mild oxidation, despite the high carbon deposition rate. We conclude that Co/ZnO is a more suitable catalyst system for steam reforming of ethanol due to the low methane selectivity, low cost and the possibility of regeneration with mild oxidation.

Unusually Large Tunneling Effect on Highly Efficient Generation of Hydrogen and Hydrogen Isotopes in pH-Selective Decomposition of Formic Acid Catalyzed by a Heterodinuclear Iridium−Ruthenium Complex in Water

A heterodinuclear iridium-ruthenium complex [Ir(III)(Cp*)(H(2)O)(bpm)Ru(II)(bpy)(2)](SO(4))(2) {1(SO(4))(2), Cp* = eta(5)-pentamethylcyclopentadienyl, bpm = 2,2'-bipyrimidine, bpy = 2,2'-bipyridine} acts as the most effective catalyst for selective production of hydrogen from formic acid in an aqueous solution at ambient temperature among catalysts reported so far. An unusually large tunneling effect was observed for the first time for the catalytic hydrogen production in H(2)O vs D(2)O.

Selective production of hydrogen from partial oxidation of methanol over supported silver catalysts prepared by method of redox coprecipitation

Supported silver catalysts showed good activity for hydrogen production from partial oxidation of methanol (POM) at a low temperature of 160 °C. Ag/CeO 2–ZnO catalysts, prepared by the method of redox coprecipitation, displayed distinguished hydrogen selectivity ( S H 2 ) and methanol conversion. In preparation of the catalysts, Ag + ions were found reduced into metal clusters by Ce 3+ ions. X-ray diffraction study revealed that the active silver crystallites were dispersed amorphously on the catalysts. Thermal characterization of temperature programmed hydrogen reduction and temperature programmed hydrogen desorption further suggested that CeO 2 and ZnO played different roles in the high S H 2 over Ag/CeO 2–ZnO. Promoter CeO 2 served as a spillover sink to collect hydrogen dissociated on silver crystallites while ZnO acted as a porthole for a fast desorption of hydrogen from the catalyst. These two oxides corporately raised the high S H 2 over Ag/CeO 2–ZnO catalysts.

Selective hydrogen generation from real biomass through hydrothermal reaction at relatively low temperatures

The effect of additives, such as an inorganic alkali and a nickel catalyst, on the hydrothermal process was examined to generate hydrogen from biomass with high selectivity at relatively low temperatures around 400 °C. At first, a cellulose sample as model biomass was subjected to the hydrothermal process at 400 °C under 25 MPa in the presence of an alkali (Na 2 CO 3 ) and a nickel catalyst (Ni/SiO 2 ). The combination of these two additives led not only to highly efficient generation of hydrogen but also to effective dissolution of CO 2 into an alkaline liquid layer. Here the molar yields of gas products from the cellulose sample were compared with the equilibrium quantities obtained using a thermodynamics calculation software. Furthermore, the hydrothermal process of real biomass, such as wood chips, organic fertilizer and food waste, in the presence of both the two additives resulted in highly selective production of hydrogen even at 400 °C.

Catalytic Abatement of Nitrous Oxide Coupled with Selective Production of Hydrogen and Ethylene

Catalytic Abatement of Nitrous Oxide Coupled with Selective Production of Hydrogen and Ethylene

Catalytic Abatement of Nitrous Oxide Coupled with Selective Production of Hydrogen and Ethylene

Catalytic Abatement of Nitrous Oxide Coupled with Selective Production of Hydrogen and Ethylene