Search

Highlights: [•] Pd/Ni–Co catalyst and CaO based sorbent have been studied for sorption enhanced water gas shift reaction. [•] Fuel cell grade hydrogen was achieved in one-step water gas shift reaction with in-situ CO2 capture. [•] Improved resistance to methanation reaction was found by using 30%Ni–10%Co catalyst. [•] CaCeZr mix oxide sorbent was evaluated for enhanced capture capacity and better stability than dolomite. [ABSTRACT FROM AUTHOR]

Graphical abstract The P-O-Fe bond and the redox cycle between N-P-O-Fe-O and N-P-O-Fe-O 2 on atomically dispersed Fe-N-P-C complex catalyst prepared directly form woody biomass efficiently reduced adsorption strength of OH*, which leads to outstanding ORR activity. Highlights • Atomically dispersed Fe-N-P-C catalysts produced from woody biomass. • Outstanding ORR performance achieved. • Fe charge in the active site identified as descriptor. • P-O-Fe bond and the redox cycle of active sites resulted in the high activity. Abstract Development of cost-effective electrocatalysts as an alternative to platinum for oxygen reduction reaction (ORR) is of great significance for boosting the applications of green energy devices such as fuel cells and metal-air batteries. Here we report a nitrogen and phosphorus tri-doped hierarchically porous carbon supported highly cost-effective, efficient and durable Fe single-site electrocatalyst derived from biomass. Combined aberration-corrected HAADF-STEM, XPS and XAFS measurements and theoretical calculations reveal the atomically dispersed Fe-N-P-C-O complex as the dominant active sites for ORR. This work also shows the design principle for enhancing the ORR activity of single Fe site catalysts with higher Fe charge, which can be manipulated by the coordinated structure in the active centre. Theoretical calculations reveal that the main effective sites are singleN-P-O-Fe-O centers, where the associated P-O-Fe bond can significantly lower the stability of strongly adsorbed O* and OH* on the catalytically active sites and thus give rise to enhanced ORR performance. The insights reported here open a new avenue for constructing highly efficient molecule-like heterogeneous catalysts in electrochemical energy technologies. [ABSTRACT FROM AUTHOR]

This work gives an insight into combined experimental and DFT study of water gas shift reaction on Ni catalysts at moderately elevated temperatures. The relative reactivity of surface adsorbed species O*, OH* and H* with CO* and their catalytic consequence in reaction mechanism and kinetics was studied. DFT investigation and microkinetic analysis pointed out that the favorable reaction pathway depends on the relative reactivity of O*, OH* and H* with CO* on the surface. It rationalizes the experimental observed changes in kinetics with hydrogen pressure. • Experimental and DFT study leads to WGS reaction mechanism insight on Ni catalyst. • It reveals dependency of the reaction mechanism and kinetics on hydrogen pressure. • Reaction pathway is dependent on relative reactivity of O*, OH* and H* with CO*. • DFT studies rationalize the experimental changes in kinetics with H 2 pressure. This paper presents a combined experimental and density functional theory study of the relative reactivity of surface species O*, OH*, and H* with CO* on nickel catalysts and their catalytic consequence in reaction mechanism and kinetics of water gas shift reaction. The kinetic study illustrates the hydrogen reaction order changes from 0.5 at relatively low hydrogen pressures to -1 at high hydrogen pressures. Detailed kinetic analysis indicated a hydrogen-induced change of the corresponding reaction pathway from hydrogen assisted CO activation to the redox mechanism with CO*+O* as a rate-determining step. The DFT investigation revealed that the surrounding surface H* atoms destabilize more significantly O* adsorption than H* adsorption, thus enhance more the reactivity of O* than H* towards reaction with CO* at high H* coverage. This kinetic study provides an insightful depiction for the future study of CO activation on other transition metals and the catalyst development for WGS reaction. [ABSTRACT FROM AUTHOR]

Fuel-cell grade H 2 has been produced by the sorption enhanced steam reforming (SESR) of acetic acid, a model compound of the bio-oil obtained from the fast pyrolysis of biomass. A Pd/Ni–Co catalyst derived from a hydrotalcite-like material (HT) with dolomite as CO 2 sorbent was used in the process. A fixed-bed reactor with three temperature zones was employed to favor the catalytic steam reforming reaction in the high-temperature segment, the SESR reaction in the intermediate-temperature part, as well as the water-gas shift (WGS) and CO 2 capture reactions in the low-temperature segment. Different conditions of pressure, temperature, steam/C molar ratio and weight hourly space velocity (WHSV) in the feed were evaluated. Higher steam/C molar ratios and lower WHSV values facilitated the production of H 2 and reduced the concentrations of CH 4 , CO and CO 2 in the produced gas. A fuel-cell grade H 2 stream with a H 2 purity of 99.8 vol.% and H 2 yield of 86.7% was produced at atmospheric pressure, with a steam/C ratio of 3, a WHSV of 0.893 h −1 and a temperature of 575 °C in the intermediate part of the reactor (675 °C in the upper segment and 425 °C in the bottom part). At high pressure conditions (15 atm) a maximum H 2 concentration of 98.31 vol.% with a H 2 yield of 79.81% was obtained at 725 °C in the intermediate segment of the reactor (825 °C in the upper segment and 575 °C in the bottom part). Under these conditions an effluent stream with a CO concentration below 10 ppm (detection limit) was obtained at both low and high pressure, making it suitable for direct use in fuel cell applications. [ABSTRACT FROM AUTHOR]

The dynamic nature of active sites on La-Fe-based perovskites in chemical looping methane oxidation has been studied. According to experimental observations, the reduction of the oxygen carrier is divided into three stages occurring at different active ensembles where the Fe cations are in different coordination environments. The Mars van Krevelen mechanism formulated by microkinetic analysis describes well the effect of oxygen vacancy on the catalytic performance of LaFeO 3. CO 2 is not produced by CO oxidation but rather is a primary product of methane oxidation, and the presence of surface oxygen vacancies would dramatically increase the overall energy barrier for total combustion, thus decreasing the selectivity toward CO 2. Hence, the Fe coordination environment (and hence the oxygen vacancy concentration) is the key parameter governing the catalyst selectivity, in the sense that methane oxidation can vary from total combustion on the O-rich surface to fully selective partial oxidation on the O-deficient surface. [Display omitted] • The dynamic nature of active sites for chemical looping methane oxidation. • The different active ensembles at different reaction stages are identified. • The Fe coordination environment is the key parameter governing the selectivity. • CO 2 is a primary product rather than produced by CO oxidation. • Controlling oxidation time is proposed to achieve methane partial oxidation. [ABSTRACT FROM AUTHOR]

Highlights: [•] First direct evidence of pore blocking for the deactivation of Au/TS-1 catalysts. [•] Uncalcined TS-1 with blocked micropores has higher gold loading efficiency. [•] Au/TS-1-B catalyst exhibits enhanced stability for over 30h. [•] Au/TS-1-B catalyst prepared by DP method shows high PO formation rate. [ABSTRACT FROM AUTHOR]

Fischer–Tropsch synthesis of light olefins plays a vital role in the production of major chemical building blocks from non-petroleum resources, having great academic and commercial importance. Herein, Na and S modulated FeMnO x catalysts were employed to systematically investigate the influence of additives, which not only enhanced the CO conversion but also facilitated the olefin formation and suppressed the undesired methane formation. Multiple characterizations confirmed that the existence of promoters would enhance the formation of active species of Fe 5 C 2 at FTO conditions because of the promoted carbon insertion into the iron species from the intermediates dissociation. Combined the steady-state isotopic transient kinetic analysis with dynamic calculation, it confirmed that the promoters indeed had the ability to lower CO activation energy, as well as increase the carbon chain growth activity and the energy barrier to hydrogenation. This study provides a practical strategy for exploring the highly active and stable FTO catalysts. [Display omitted] • Na and S additives over FeMnO x catalyst promoted both the CO conversion and the olefin formation. • Pomotes facilitated the Fe5C2 formation by suppressing the oxidation cycle of iron and enhancing the insertion of carbon. • The presence of promoters reduced the charge of iron and caused more compact bonds of Fe-C, lowing the CO activation energy. • Promoters indeed increased the carbon chain growth activity and the energy barrier to hydrogenation. [ABSTRACT FROM AUTHOR]

The well-designed FeCo-MOF/Fe 2 O 3 compound photoanode displays favorable PEC performances, which can be attributed to the coating of multifunctional FeCo MOF nanolayer that passivate the surface states, construct the p-n heterojunction and improve the water oxidation kinetics, all of these enable the substantially promoted charge separation and transport. [Display omitted] • Ultrathin FeCo MOF nanolayers coated on Fe 2 O 3 photoanode are in-situ formed. • Multifunctional roles of FeCo MOF on Fe 2 O 3 is disclosed. • This design endows photoanode with boosted charge separation/injection efficiency. • The catalytic mechanism for PEC water oxidation is unravelled. Owing to the high theoretical photocurrent density, the hematite (α -Fe 2 O 3) based photoanode has been intensively concerned in photoelectrochemical (PEC) water splitting, but its serious charge recombination and sluggish water oxidation kinetics are still the stumbling blocks. This work reports a high-performance Fe 2 O 3 -based photoanode achieved by coating multifunctional FeCo-bimetal organic framework (MOF) nanolayers (NLs) on Fe 2 O 3 nanoarrays via an in-situ solvothermal process. The FeCo MOF NLs introduced not only effectively passivate the surface states of Fe 2 O 3 photoanode and boost the water oxidation kinetics serving as the cocatalyst, but also construct p-n heterojunctions with Fe 2 O 3 to accelerate the directional migration and separation of photogenerated charge carriers. Expectedly, the as-obtained FeCo-MOF/Fe 2 O 3 photoanode exhibits an apparent negative shift of onset potential, an excellent long-term PEC stability, and highly improved photocurrent density. This finding provides a novel and effective strategy to introduce advanced multifunctional surface coating for enhancing the PEC performance of photoelectrodes. [ABSTRACT FROM AUTHOR]

Abstract: Fe nanoparticles on the top of carbon nanofibers (CNFs) were synthesized by catalytic CVD on a purpose as catalysts for ammonia decomposition. The size and shape of Fe particles on the top of CNFs depended on the Fe particle reconstruction and CNF morphology. On a mica support Fe catalyst, platelet structure of CNFs was obtained with small, uniform, and unwrapped Fe particles on the top. HRTEM illustrated that the Fe particle surface is covered by a few graphene layers, which redissolves into the Fe particle and does not prevent the access of NH3 to active surface sites at reaction conditions. The catalyst is highly active and stable because the Fe particles are highly dispersed and physically isolated by CNFs, and the surfaces are largely exposed to the reactants. [ABSTRACT FROM AUTHOR]

Abstract: Co, Mo, NiMo and CoMo catalysts supported on alumina, fishbone and platelet carbon nanofibers (CNFs) have been prepared. The dispersion of the oxide phases was qualitatively studied and compared using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reducibility of the catalysts was studied by temperature programmed reduction (TPR). Hydrodesulfurization (HDS) of thiophene was used as a model reaction to compare the activity of different catalysts. The activity tests showed that the alumina supported catalysts exhibited higher activity compared to the corresponding CNF supported catalysts, and the NiMo catalysts were more active than the corresponding CoMo catalysts. The thiophene HDS activity was correlated with the dispersion of the molybdenum species and the reducibility of different catalysts. Interestingly, the CNF supported Co catalysts have higher thiophene HDS activity than the CNF supported Co(Ni)Mo catalysts. [Copyright &y& Elsevier]

Abstract: Nanocomposite catalysts containing carbon nanofiber (CNF) and Cu-Ce-Zr mixed metal oxide (MMO) have been prepared by homogeneous co-precipitation with urea. The water-gas shift (WGS) reaction has been used as test reaction. The CNF-containing nanocomposite catalysts exhibit similar overall catalytic activity and stability as the corresponding CNF-free catalyst. Thirteen weight percent of the MMO could be replaced by CNF without decreasing the overall activity and stability of the catalyst. The specific activity of the nanocomposites based on the total metal oxide content is similar or higher than the activity of the CNF-free material, depending on the CNF content. Similar activation energies are, however, obtained for the CNF-free and CNF-containing materials. We cannot exclude that the CNF material acts as reaction promoter under certain conditions, but suggest that the impact of CNF addition on the precipitation of the mixed oxide particles, and hence the catalytic activity relative to the CNF-free MMO, should also be considered. CNF may be regarded as inert dispersing agent material improving the precipitation of the MMO under conditions where the co-precipitation of the MMO precursors does not result in materials with high surface area. [Copyright &y& Elsevier]

• Pt/MgAl 2 O 4 shows robust dehydrogenation activity being twice that of Pt/CNF. • Edge Pt sites are discriminated to be the dominant active sites. • Partial positively charged Pt prevents the strong adsorption of products on catalyst. Platinum group metals hold pronounced potential for the dehydrogenation process of liquid organic hydrogen carriers (LOHCs) such as decalin, but the strong adsorption of dehydrogenation product has suppressed the moving forward of these catalysts. Herein, we described that the strong interactions between Pt and MgAl 2 O 4 trigger partial positively charged Pt, which mitigates the adsorption of naphthalene on highly active Pt sites, thus achieving an outstanding decalin dehydrogenation activity that is nearly twice that of state-of-the-art Pt/CNF catalysts. As revealed by various characterization outcomes and DFT calculations, the strong electronic interactions between Pt and spinel oxygen surface resulted in partial positively charged Pt on MgAl 2 O 4 , which inhibits the electron transfer from Pt to unsaturated carbon of naphthalene, thus weakening the bond strength between Pt and naphthalene. As a result, the combination of small-sized Pt nanoparticles and facile desorption of products endows tremendous dehydrogenation activity of Pt/MgAl 2 O 4. This study may shed new light on the rational construction of highly efficient metal catalysts for the application of LOHCs. [ABSTRACT FROM AUTHOR]

• An ion exchange based strategy was used to synthesize the hierarchy structured mutimetal MOFs derived electrocatalyst. • This strategy prevents the collapse of well-designed MOF nanostructures during the air calcination process. • The unique electronic modulation of Co-Ni-Fe in spinel oxides can optimize the binding strength of OER intermediates. • CoNiFeO x -NC catalyst delivers highly efficient OER performance (η 50 = 265 mV). Metal-organic frameworks (MOFs) have recently emerged as promising precursors to construct efficient non-noble metal electrocatalyst for oxygen evolution reaction (OER). Herein, a Co-Ni-Fe spinel oxide-carbonitrides hybrids (CoNiFeO x -NC) electrocatalyst with hierarchical structure was synthesized from Fe-MIL-101-NH 2 through a unique ion-exchange based strategy. The ion exchange of Fe-MIL-101-NH 2 with both Ni and Co ions induced a hierarchically structured 2-D ternary metal MOF shell layer encapsulated 3-D octahedral MOF crystals as a core. This prevents the collapse of MOF frameworks during the air calcination process and affords highly porous structure and large surface area. Additionally, the unique combination of Co-Ni-Fe in spinel oxides derived from calcination of the hierarchically structured core-shell MOF provides a favorable electronic environment for the adsorption of OER intermediates, which was further verified by the XPS characterizations and DFT calculations. DFT study revealed the Ni-Co coordinated O h sites in the MFe 2 O 4 reverse spinel structures as the main active sites, which tuned the binding strength of oxygen species with a catalyst through electron transfer of Fe→Co→Ni, thereby lowered the energy barriers for OER. As a result, the rationally designed CoNiFeO x -NC catalyst manifests superior OER performance with a low overpotential of 265 mV at 50 mA cm−2 and a decent Tafel slope of 64.1 mV dec-1. The ion-exchange based strategy may serve as a versatile platform for rational design and synthesis of multi-metallic MOF derived electrocatalysts. [ABSTRACT FROM AUTHOR]

We successfully realized the directional construction of Pt-Mn 2 O 3 interfacial sites (by the combination of in-situ doping and impregnation methods) to boost selective oxidation of ethylene glycol under mild conditions. It is found that the pre-distribution of Mn 2 O 3 inside support unexpectedly induced the formation of Pt-Mn 2 O 3 interfacial active sites with strong electron coupling effect, leading to an unprecedented glycolic acid oxidation activity (turnover frequency: 3196.9 h−1) and glycolic acid yield (86.4 %). • Enhanced catalytic performance of ethylene glycol oxidation was achieved. • Strong electron coupling effect was revealed in the Pt-Mn interface. • Quantitative analysis of the intrinsic active sites was performed. • The promotion role of Pt-Mn interfacial on reaction mechanism was correlated. Rational design of desirable active sites is still a grand challenge for the efficient conversion of polyols to value-added products. Herein, we successfully constructed the Pt-Mn 2 O 3 interfacial sites rather than Pt-MnO x solid solution to boost selective oxidation of ethylene glycol to glycolic acid under mild conditions. X-ray absorption spectroscopy and high-resolution transmission electron microscope revealed that the pre-distribution of Mn 2 O 3 inside support unexpectedly induced the formation of Pt-Mn 2 O 3 interfacial active sites with strong electron coupling effect, leading to an unprecedented catalytic activity (turnover frequency: 3196.9 h−1) and glycolic acid yield (86.4 %). In addition, quantitative analysis of the intrinsic active sites was performed, and a "volcano-shape" relationship was established between initial reaction rate and Pt/Mn ratio. Moreover, the structure-dependent reaction kinetics and density functional theory calculation revealed that the synergistic effect between the Mn 2 O 3 redox cycle and Pt promotes the adsorption of ethylene glycol and the activation of C H bond, resulting in the lower activation energy of ethylene glycol oxidation. The outcome of this work offers a promising avenue for the direct construction of efficient Pt-based catalysts with desired active sites. [ABSTRACT FROM AUTHOR]

The well-designed MoO 3- x /Fe 2 O 3- x photoanode exhibits superior PEC water oxidation performance due to the efficient charge separation and transport derived from the introduced MoO 3 surface passivation layer and oxygen vacancy. • Establishing passivation effect of MoO 3 on Fe 2 O 3 photoanode. • Collaboration of passivation layer and oxygen vacancy on Fe 2 O 3 was designed. • The boosted charge separation and transport are achieved on modified photoanode. • Exhibiting superior water oxidation performance on MoO 3- x /Fe 2 O 3- x photoanode. To seek effective strategies that improve the photoelectrochemical water oxidation performance of hematite (α -Fe 2 O 3) photoanodes is still challenging owning to their abundant surface states and low charge transfer efficiency. Herein, a facile impregnation method with an annealing process was developed to synthesize MoO 3 modified Fe 2 O 3 photoanodes using the MoO 3 layer as an effective passivation component to decrease surface states and thus to improve the charge separation and transfer process at the electrode/electrolyte interfaces. The oxygen vacancies were subsequently introduced to steer the electrical conductivity, and further to boost the charge separation and transfer. The optimized MoO 3- x /Fe 2 O 3- x photoanode displays a photocurrent density of 2.6 mA cm–2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G irradiation, 2.2 times that of the Fe 2 O 3 (1.2 mA cm–2). The synergetic integration of passivation layer and oxygen vacancies on photoelectrodes heralds an efficient paradigm for solar energy conversion. [ABSTRACT FROM AUTHOR]

The decoration of In 2 O 3 nanolayers on hematite nanoarray photoanode are successfully synthesized to reduce the surface recombination of charge carriers and prolong their lifetimes. The coupling effects of surface passivation and interface electric field enhancement for In 2 O 3 endows the Fe 2 O 3 photoanode with significantly enhanced PEC performance for water oxidation. • In 2 O 3 effectively passivated surface states and enhanced interface electric field of Fe 2 O 3 photoanode. • High charge separation and transportation are achieved both in bulk and surface. • The catalytic mechanism of In 2 O 3 /Fe 2 O 3 nanoarray photoanode is fully excavated. • The high IPCE of 80 % is recorded at 400 nm. Hematite (α -Fe 2 O 3) based nanomaterials are considered as the most promising photoelectrodes for solar water splitting. However, some inherent shortcomings like high density of surface states is still the critically challengeable issue. This paper reports the integration of In 2 O 3 nanolayers (NLs) on the surface of worm-like Fe 2 O 3 films to significantly improve the photoelectrochemical (PEC) water oxidation activity. The In 2 O 3 NLs on the modified α -Fe 2 O 3 photoelectrodes exhibit dual positive effects on PEC performance: i) acting as the passivation material to decrease surface electron-hole recombination losses; ii) constructing heterojunctions with Fe 2 O 3 to facilitate efficient separation of surface charges and spatial transfer with extended lifetimes. The resulting treated Fe 2 O 3 photoanode yields a current density of 3.4 mA cm―2 at 1.23 V vs. reversible hydrogen electrode and high incident photon-to-current efficiency of 80 % at 400 nm. These results may bring inspiration to introduce multifunctional modifiers on photoelectrodes that offer practically high-performance PEC applications. [ABSTRACT FROM AUTHOR]

In W 2 C@C/HTMs (hollow TiO 2 microspheres) heterojunction nanostructures, the decorating of W 2 C@C can enhance the light harvesting ability and effectively steer the charge kinetics of HTMs, maximizing the separation of photogenerated electron-hole pairs. As a result, compared with bare HTMs, the photocatalytic water reduction performance of W 2 C@C/HTMs sharply improved. • For the first time, W 2 C@C/TiO 2 is developed for photocatalytic H 2 generation. • The behaviors of charge carriers in TiO 2 is well steered by W 2 C@C. • High H 2 generation rate and apparent quantum efficiency are achieved on W 2 C@C/TiO 2. The constructing of functional materials with well-defined nanostructure, showing efficient charge separation and transportation properties, has been intensively and in depth investigated to fabricate catalysts for H 2 generation from solar-driven water reduction. Here we demonstrate that loading W 2 C@C structure in which each W 2 C nanoparticle (NP) is wrapped by carbon shell on surface of hollow TiO 2 microspheres (HTMs) can enhance the separation of photogenerated electron-hole pairs by building an internal electric field in W 2 C@C/HTMs composite structure and act as the reaction active sites for water reduction. As expected, the optimized W 2 C@C/HTMs construction exhibits the highest photocatalytic H 2 generation rate of 6.91 mmol h−1 g−1 under simulated solar light illumination, over 20 times larger than that of bare HTMs. The underlying mechanism has been investigated from the perspective of photochemistry and photophysics based on a series of characterization techniques, which suggests that W 2 C@C can effectively steer the charge kinetics, maximizing the charge carriers' separation. [ABSTRACT FROM AUTHOR]