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Sorption-enhanced chemical looping reforming of ethanol for hydrogen production was investigated using Fe2O3 as oxygen carrier and modified CaO-based Al2O3 as CO2 sorbent. Combined Fe2O3/CaO-Al2O3 multifunctional catalysts were demonstrated and prepared by different methods including sol-gel, mechanical mixing, and impregnation at different Fe contents (5, 10, and 15 wt%). The results showed that the multifunctional catalyst prepared by impregnation method with 5 wt% Fe loading provided the highest H2 purity of 70% in the pre-breakthrough period which lasted for 60 min at 600 °C. This was attributed to the preserving of Ca12Al14O33 inert support in the structure during the preparation as shown by XRD results, leading to higher surface area as determined by N2 physisorption and to prevention of particle agglomeration as evidenced by SEM-EDX. Although the H2 production was inhibited by the presence of Ca2Fe2O5 phase, a stable performance was found for at least 5 repeated cycles both for sorption capacity and oxygen carrier. The ease of decarbonation was also observed with this material as confirmed by DSC-TGA analysis. This highlighted the mutual advantages of Fe in CaO sorption stability and Ca in Fe oxygen carrier stability which could offset their intrinsic weak robustness. [ABSTRACT FROM AUTHOR]

Silicon is a promising photocathode material in photoelectrochemical water splitting for hydrogen production, but it is primarily limited by photocorrosion in aqueous electrolytes. As an extensively used protective material, crystalline TiO2 could protect Si photoelectrode against corrosion. However, a large number of grain boundaries (GBs) in polycrystalline TiO2 would induce excessive recombination centers, impeding the carrier transport. This paper describes the introduction of oxygen vacancies (Ovac) with controllable spatial distribution for GBs to promote carrier transport. Two kinds of Ovac distribution, Ovac along GBs and Ovac inside grains, are compared, where the latter one is demonstrated to facilitate carrier transport owing to the formation of tunneling paths across GBs. Consequently, a simple p‐Si/TiO2/Pt heterojunction photocathode with controllable Ovac distribution in TiO2 shows a +400 mV onset potential shift and yields an applied bias photon‐to‐current efficiency of 5.9 %, which is the best efficiency reported among silicon photocathodes except for silicon homojunction. [ABSTRACT FROM AUTHOR]

A graphene‐wrapped polyaniline nanoparticles film embedded in carbon cloth (CC/PANI/G) was fabricated and used as a 3D anodic electrocatalyst for oxidation of toluene methyl C−H groups. The methyl C−H bonds can be oxidized effectively at the CC/PANI/G anode with 99.9 % toluene conversion at a low applied voltage of only 1.0 V, which implies low energy input. Importantly, 86.6 % of toluene methyl C−H groups were converted to benzoyl groups (C=O), and hydrogen was produced efficiently at the cathode. The electrocatalytic efficiency at the CC/PANI/G anode was higher at lower voltage (1.0 V) than at higher voltage (1.5 V), and more hydrogen was produced at the corresponding cathode. The synergistic effect between the dynamic redox chemistry of nanoPANI and the excellent conductivity and anticorrosive action of graphene determined the high electrocatalytic efficiency of the oxidation of toluene methyl C−H groups at the CC/PANI/G anode. Owing to the chemical bonding between graphene and PANI, the anticorrosive CC/PANI/G anodic electrocatalyst was durable and effective for oxidation of toluene methyl C−H groups in acidic environment. This approach provides advanced electrode materials for transforming stable chemical bonds (C−H) into useful functional groups (C=O), which will be beneficial for the synthesis of organic intermediates with coupled hydrogen production. [ABSTRACT FROM AUTHOR]

Water splitting for hydrogen production by harvesting sunlight is widely accepted as one of the most promising routes to relieve the energy crisis and environmental issues caused by excessive use of fossil fuels. Earth-abundant silicon (Si) is emerging as a suitable candidate for a photoelectrode material for efficient solar water splitting. This review describes the current status and prospects of single-crystal Si-based photoelectrodes in photoelectrochemical (PEC) water splitting for hydrogen production. We start with highlighting the recent achievements in single-crystal Si-based photocathodes and photoanodes for PEC water reduction and oxidation. We then discuss the recent progress in the design and fabrication of unbiased solar water splitting cells with single-crystal Si-based photoelectrodes. Finally, we provide an overview from the optimization of a single-crystal Si-based electrode (both a photocathode and a photoanode) to the integration of a full cell for unassisted overall solar water splitting. [ABSTRACT FROM AUTHOR]

An investigation on reaction scheme and kinetics for ethanol steam reforming on skeletal nickel catalysts is described. Catalytic activity of skeletal nickel catalyst for low-temperature steam reforming has been studied in detail, and the reasons for its high reactivity for H2 production are attained by probe reactions. Higher activity of water gas shift reaction and methanation contributes to the low CO selectivity. Cu and Pt addition can promote WGSR and suppress methanation, and, thus, improve H2 production. A reaction scheme on skeletal nickel catalyst has been proposed through temperature programmed reaction spectroscopy experiments. An Eley-Rideal model is put forward for kinetic studies, which contains three surface reactions: ethanol decomposition, water gas shift reaction, and methane steam reforming reaction. The kinetics was studied at 300-400°C using a randomized algorithms method and a least-squares method to solve the differential equations and fit the experimental data; the goodness of fit obtained with this model is above 0.95. The activation energies for the ethanol decomposition, methane steam reforming, and water gas shift reaction are 187.7 kJ/mol, 138.5 kJ/mol and 52.8 kJ/mol, respectively. Thus, ethanol decomposition was determined to be the rate determining reaction of ethanol steam reforming on skeletal nickel catalysts. © 2013 American Institute of Chemical Engineers AIChE J 60: 635-644, 2014 [ABSTRACT FROM AUTHOR]

This article describes a strategy for increasing oxygen storage capacity (OSC) of ethanol steam reforming (ESR) catalysts. Sintering and carbon deposition are major defects of nickel-based catalysts for ESR; tuning oxygen mobility (OM) of CeO2-based supports can overcome these drawbacks and promote H2 production. We have successfully increased OSC and OM by adding Mg into the lattice of Ni/CeO2 to promote H2 production in ESR. The insertion of Mg into the CeO2 lattice efficiently promotes the reduction of Ce4+ according to X-ray powder diffraction (XRD) and temperature-programmed reduction (TPR) analysis. Mg-modified Ni/CeO2 catalysts have larger OSC and smaller nickel crystallite size compared with bare Ni/CeO2. The optimal Mg addition is 7 mol % (Ni/7MgCe) with the best OM. We also present evidence indicating that Mg addition significantly promotes ethanol conversion and H2 production in ESR, and that Ni/7MgCe yields the best performance due to the high OM of the support. These Mg-modified catalysts also produce less carbon deposition compared with Ni/CeO2, and the amount of deposited carbon decreases with increasing Mg addition. Ni/7MgCe has the best resistance to carbon deposition owing to the excellent OM. © 2011 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

This communication describes the design and synthesis of anti-sintering and -coke nickel phyllosilicate (PS) nanotubes (Ni/PSn) for hydrogen production via reforming reactions. The introduction of nickel particles in PS nanotubes could effectively maintain the Ni size and increase the resistance of metal particles for carbon deposition. [ABSTRACT FROM AUTHOR]

This communication describes the synthesis of a nanocomposite Ni@ZrO2 catalyst with enhanced metal–support interaction by introducing metal nanoparticles into the framework of the oxide support. The catalyst shows high catalytic activity and stability for hydrogen production via steam reforming of ethanol. [ABSTRACT FROM AUTHOR]

The modulation of oxygen species is an effective strategy for selective H 2 production with relevant chemical looping processes. This paper describes the promoted oxygen release from CuO-CeO 2 redox catalysts for selective H 2 production in chemical looping oxidative steam reforming of methanol (CL-OSRM). Despite the complete oxidation of methanol from CuO, the excess H 2 production of CL-OSRM with respect to methanol steam reforming (MSR) increases linearly with the amount of active oxygen in CeO 2 induced by the copper-ceria interaction. In situ spectroscopic characterizations and mechanistic study demonstrate that copper-ceria interfacial sites induce oxygen release from CeO 2 to facilitate the partial oxidation of methoxy to formate species, which promotes the H 2 production rate. This study provides an instructive strategy for the construction of redox catalysts for selective H 2 production with chemical looping processes. [Display omitted] • An interfacial engineering strategy for selective hydrogen production is proposed. • The copper-ceria interaction activates the ceria oxygen species. • Interfacial oxygen species facilitate the partial oxidation of methoxy to formate species. • Stable performance and reversible structure can be maintained in redox cycles. [ABSTRACT FROM AUTHOR]

Four ethanol-derived hydrogen production processes including conventional ethanol steam reforming (ESR), sorption enhanced steam reforming (SESR), chemical looping reforming (CLR) and sorption enhanced chemical looping reforming (SECLR) were simulated on the basis of energy self-sufficiency, i.e. process energy requirement supplied by burning some of the produced hydrogen. The process performances in terms of hydrogen productivity, hydrogen purity, ethanol conversion, CO 2 capture ability and thermal efficiency were compared at their maximized net hydrogen. The simulation results showed that the sorption enhanced processes yield better performances than the conventional ESR and CLR because their in situ CO 2 sorption increases hydrogen production and provides heat from the sorption reaction. SECLR is the most promising process as it offers the highest net hydrogen with high-purity hydrogen at low energy requirement. Only 12.5% of the produced hydrogen was diverted into combustion to fulfill the process's energy requirement. The thermal efficiency of SECLR was evaluated at 86% at its optimal condition. Image 1 • Sustainable hydrogen production from ethanol. • Different processes include ESR, SESR, CLR and SECLR. • Performance was compared under their energy self-sufficiency condition. • A portion of hydrogen is burned to fulfill energy requirement in each process. • SECLR is the most promising process with highest net hydrogen and high purity. [ABSTRACT FROM AUTHOR]

This work studies the effects of Ce4+ and/or La3+ on NiO/Al 2 O 3 oxygen carrier (OC) on chemical looping steam reforming of ethanol for hydrogen production - alternating between fuel feed step (FFS) and air feed step (AFS). Suitable amount of Ce- and La-doping increases OC carbon tolerance. The solubility limit is found at 50 mol% La in solid solution. At higher La-doping, La 2 O 3 disperses on the surface and adsorbs CO 2 forming La 2 O 2 CO 3 during FFS. From the 1st cycle, 12.5 wt%Ni/7 wt%La 2 O 3 -3wt%CeO 2 –Al 2 O 3 (N/7LCA) displays the highest averaged H 2 yield (3.2 mol/mol ethanol) with 87% ethanol conversion. However, after the 5th cycle, 12.5 wt%Ni/3 wt%La 2 O 3 -7wt%CeO 2 –Al 2 O 3 (N/3LCA) exhibits more stability and presents the highest ethanol conversion (88%) and H 2 yield (2.7 mol/mol ethanol). Amorphous coke on the OCs decreases with increasing La3+ content and can be removed at 500 °C during AFS; nevertheless, fibrous coke and La 2 O 2 CO 3 cannot be eliminated. Therefore, after multiple redox cycles, highly La-doped OCs exhibits rather low stability. • Suitable Ce and La doping within solubility limit increases carbon tolerance of oxygen carriers. • Highly La-doped OCs exhibits rather low stability due to fibrous coke and La 2 O 2 CO 3 formation. • N/3LCA exhibits high stability, ethanol conversion (88%) and H 2 yield (2.7 mol/mol ethanol). [ABSTRACT FROM AUTHOR]

Process simulation of sorption enhanced chemical-looping reforming for hydrogen production from biomass was investigated. Corn stover was converted to bio-oil via pyrolysis prior to sorption enhanced chemical-looping reforming (SE-CLR). NiO was used as a catalyst and oxidizing agent and CaO was used as a CO 2 sorbent which are cycled between the reduction and oxidation reactors. Modification of the process to incorporate a step for catalyst and sorbent regeneration was examined and compared with conventional sorption enhanced chemical-looping reforming process. By modifying the SE-CLR process with the recirculating of solids from the air reactor directly to the reformer, a maximum bio-oil conversion rate of 92%, a maximum hydrogen production yield of 153.4 g H 2 /kg corn stover, and a maximum hydrogen purity of 77% v/v can be obtained with a circulated NiO to bio-oil molar ratio ( CNB ) of 12.3; a circulated CaO to bio-oil molar ratio ( CCB ) of 125.2; and where the ratio of solids recovered by the air reactor from the calcination reactor ( α ) was set as 1, and the ratio of solids flowing directly from the air reactor to the reformer ( β ) was set as 0.02. The split of a fraction of solids streams to feed directly back to the reformer offers a great impact process control as operating conditions can be broadened. [ABSTRACT FROM AUTHOR]

Sorption-enhanced steam reforming of ethanol shows potential of supplying high-quality hydrogen with in situ CO 2 capture, but suffers from sorbent deactivation. This paper describers the design of functionalized x NiO/Ca 9 Co 12 O 28 materials, whose phases can be segregated once triggered by the lattice oxygen consumption via NiO/Ca 9 Co 12 O 28 -O2-→Ni-Co+CaO, thus acting as the catalytic sorbent. Their superiorities are demonstrated in: (i) low-temperature activation via lattice oxygen induction; (ii) recyclability via lattice oxygen replenishment; iii) high-quality hydrogen actuation via in situ CO 2 adsorption. Hydrogen concentration of 95.56 vol% and near-complete ethanol conversion can be achieved. Moreover, stability across 50 repeated cycles without obvious reduction in catalytic reforming and CO 2 adsorption is demonstrated. In situ XRD studies demonstrate the formation of the Ni-Co alloy and the reorganization of the catalytic sorbent. The adsorption energies of ethanol on the surface of Ni(111), Co(111), and Ni-Co(111) were studied by DFT calculations, reaffirming the higher catalytic activity of Ni-Co alloys. [Display omitted] • A series of lattice oxygen triggered NiO/Ca 9 Co 12 O 28 catalysts were fabricated. • Phase segregation and reformation of the catalyst can be proceeded via switch-on-off looping. • Hydrogen concentration of 95.56 vol% and near 100% ethanol conversion can be achieved. • The promotional role of Ni doping on catalytic activity and CO 2 uptake capacity was identified. • DFT results revealed the enhancement of Ni-Co alloy on ethanol activation and CO 2 adsorption. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of a group of meso- x LaNiAl catalysts with ordered mesostructure and La promoters, and their catalytic performance for hydrogen production from ethanol steam reforming. For comparison, the conventional 0LaNiAl catalyst was prepared by impregnation with γ-Al 2 O 3 . The characterization results exhibited that meso- x LaNiAl materials possessed excellent textural properties, such as high specific surface areas, large pore volumes and uniform pore sizes. The ordered mesostructure was beneficial to obtain and maintain the 4–6 nm Ni nanoparticles, which were smaller than that of the conventional 0LaNiAl catalyst (∼10 nm). Consequently, meso- x LaNiAl catalysts exhibited superior initial activity with respect to the reference 0LaNiAl catalyst, especially at higher temperatures (873 and 973 K). Particularly, the meso-3LaNiAl catalyst gained the highest amount of easily reduced Ni species and then the highest active surface areas. In addition, the highest initial activity at 873 K is exhibited over meso-3LaNiAl catalyst, which is mainly attributed to the highly dispersed nickel nanoparticles and abundant active surface areas. The meso-3LaNiAl catalyst also exhibited excellent long-term stability. Besides the excellent textural properties, the presence of La-modifiers enhanced the basicity of the catalyst, strengthened the metal-support interaction and cleaned the deposited carbon, resulting in the suppression of carbon deposition and the improvement of stability. [ABSTRACT FROM AUTHOR]

Abstract: Ni catalysts supported on ZrO2 with different crystalline phases and particle sizes were prepared to study the role of zirconia support in ethanol steam reforming for hydrogen production. Catalytic behavior of the catalysts was examined at relatively low temperature of 673 K with different contact times. The decrease in particle size of zirconia results in enhanced metal-support interaction, which accounts for the high activity of the catalyst. Regarding the impact of crystalline phase of zirconia on catalytic performance, tetragonal zirconia yields a higher activity in water gas shift reaction but a lower activity in methane steam reforming than that of monoclinic zirconia. Nevertheless, zirconia plays a secondary role in product distribution, especially at long contact times. Catalytic activity tests performed at elevated temperature demonstrated a high activity and stability of Ni/ZrO2 catalyst for hydrogen production from steam reforming of ethanol. [Copyright &y& Elsevier]

Abstract: This paper describes a study regarding the effect of Ni addition to NixMg1−xO solid solutions on the catalytic performances of ethanol steam reforming for hydrogen production. Nickel nanoparticles supported on NixMg1−xO demonstrated higher conversion of ethanol and yields of hydrogen than the bare support. We correlated the improved performances of Ni-based catalysts with the reducibility of nickel species. The addition of Ni to the solid solution support produced more easily reducible surface nickel species. Higher content of bulk nickel species in the support could inhibit the surface nickel species from diffusing into the bulk, leading to more surface nickel species that is easily reducible to its active form. [Copyright &y& Elsevier]

[Display omitted] • The ratio of Ni0 to Ni2+ in Ni-MgO is tuned by a non-equilibrium synthetic method. • 11.5 L∙h−1∙g cat −1 H 2 is generated at 400 °C with balanced Ni° to Ni2+ sites. • Ni0 particles facilitate the oxidation of α-C in ethanol to acetate intermediate. • Ni2+ stabilized by Ni x Mg 1− x O promotes the dehydrogenation of methyl group. Steam reforming of bio-ethanol is one of the most promising methods to produce renewable hydrogen and reduce carbon footprint. Nickel and magnesium are two main elements in commercial steam reforming catalysts for which Ni x Mg 1− x O solid solution contributes its unique property. This paper describes the interplay between Ni and Ni x Mg 1− x O to explore the roles of Ni0 and Ni2+ in hydrogen production from bio-ethanol steam reforming. With a non-equilibrium synthetic method, the ratio of metallic Ni0 to Ni2+ in Ni/Ni x Mg 1− x O system could be altered with same Ni loading. The catalytic performance of Ni/Ni x Mg 1− x O is dependent on the surface area of metallic Ni0 and the surface concentration of Ni2+ sites. Ni/Ni x Mg 1− x O with balanced Ni0 to Ni2+ sites could achieve H 2 production rate of 11.5 L∙h−1∙g cat −1 from renewable bio-ethanol at 400 °C. The results from in-situ diffuse reflectance infrared Fourier transform spectroscopy suggest that geometrically adjacent Ni0 nanoparticles facilitate the oxidation of α-C in ethanol and electron-deficient Ni2+ sites promote the dehydrogenation of methyl group, further increasing H 2 selectivity and suppressing the formation of CH 4. [ABSTRACT FROM AUTHOR]

• Cu-MgO/Al 2 O 3 bifunctional catalysts exhibit superior activity and stability in SESRM. • The incorporation of Cu2+ into MgO promotes CO 2 sorption and desorption capacity. • MgO facilitates the production of formate and consequent reduction of CO. • Cu sintering can be inhabited due to the strong interaction between Cu and MgO. Sorption enhanced steam reforming of methanol (SESRM) can significantly promote the hydrogen production process with simultaneous CO 2 sorption. The mechanical mixture of catalysts and sorbents as a conventional approach is complex and requires high temperatures for regeneration, which results in serious sintering of Cu-based catalysts. This paper describes a novel Cu-MgO/Al 2 O 3 bifunctional catalysts (x CMA, x is denoted as the mass fraction of Cu, 0%–10%) via a sol–gel method for the SESRM process. We find that Cu species, including metallic Cu and Cu ions, co-exist on the catalyst. The metallic Cu on the catalyst surface is an active site for methanol steam reforming while the Cu ion in MgO lattice promotes the CO 2 sorption capacity. Moreover, the incorporation of Cu ion into MgO also facilitates CO 2 desorption by forming more bidentate carbonates. Due to the strong interaction between Cu and MgO, the Cu sintering is inhabited in comparison with the mechanical mixture of catalysts and sorbents. Meanwhile, MgO is found to induce more formate species to inhibit the generation of carbon monoxide. As a result, the optimal bifunctional catalyst, 8 wt% Cu-MgO/Al 2 O 3 (8CMA) shows a superior performance in both catalytic reforming and CO 2 sorption with a highest H 2 selectivity of 99.3% and lowest CO selectivity (<0.15%) over 10 repeated cycles. This study suggests that the appropriate control of bifunctional catalysts can lead to powerful potential for high H 2 production performance in SESRM. [ABSTRACT FROM AUTHOR]

• La 1- x Ce x FeO 3 (x = 0, 0.5, 1) catalysts with orthorhombic structure were designed and prepared. • A site Ce3+ substitution improved the surface reactivity in H 2 O splitting step. • La 0.5 Ce 0.5 FeO 3 exhibited high oxygen restoration kinetics in re-oxidation step. • A redox mechanism for La 0.5 Ce 0.5 FeO 3 in chemical looping was proposed. Chemical looping steam reforming of methane (CL-SRM) has emerged as an attractive pathway on H 2 O splitting for H 2 production. However, this process still faces a major challenge in efficiently producing H 2 with high redox kinetics and yields. In this paper, the promoting effects of Ce3+ substitution into LaFeO 3 redox catalysts on thermochemical H 2 O splitting as well as partial oxidation of methane are presented. An appropriate amount of Ce3+ substitution in A site of LaFeO 3 (La 0.5 Ce 0.5 FeO 3) promotes the lattice oxygen conversion rate in methane partial oxidation step and boosts the reaction kinetics in H 2 O splitting step by enhancing the surface water activation and lattice oxygen mobility of the perovskite. In the CL-SRM process, the perovskite is reduced into Fe0/(La 0.5 Ce 0.5) 2 O 3 and Fe0/(La 0.5 Ce 0.5)O 2- x phases in methane partial oxidation step and recovered to the original perovskite structure in H 2 O splitting step with simultaneous production of hydrogen, which maintains a reversible phase transformation during 100 redox cycles. As a result, the La 0.5 Ce 0.5 FeO 3 achieves high stability with the superior performance for syngas and hydrogen production. These findings provide the fundamental understanding on the synergy between the catalytic sites and enhanced lattice oxygen mobility for the promotion of H 2 O activation and hydrogen productivity in chemical looping process. [ABSTRACT FROM AUTHOR]