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To improve the stability of molybdenum carbide catalysts in dimethyl ether steam reforming (DSR), the inactivation mechanism and the performance of Pt modified catalyst has been investigated. The Mo2C oxidation induced by H2O is verified to be the main reason of catalytic deactivation. After modified with Pt, the H2 production rate and selectivity are greatly enhanced, reaches 1605 μmol min−1·gcat−1 at 350 °C, in comparison to that of the Mo2C/Al2O3 catalyst. Moreover, the 2%Pt–Mo2C/Al2O3 catalyst is more stable with only 20% activity loss after 50 h on stream compares to the 73% activity loss in 12 h with Mo2C/Al2O3 catalyst. By means of in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the enhancement brought by Pt is ascribed to the consumption acceleration of intermediate oxygen species on catalyst surface and the decline of onset temperature of DSR reaction. It is expected that these findings can lead us to more practical molybdenum carbide catalysts in DSR.

Designing Pt-based nanoparticle (NP) catalysts is of great interest for the lowering of Pt usage and the enhancement of catalytic activity on the proton-exchange membrane fuel cells (PEMFCs). However, it is still challenging to develop well-arrayed catalyst NPs on supports over multiple-length scales. Herein, we presented a facile strategy of producing well-ordered Pt-based NPs toward oxygen reduction reaction (ORR) catalysts assisted by the self-assembly of block copolymers. In contrast to the conventional Pt/C ORR catalysts with a random dispersion on carbon, the as-prepared Pt, PtCo, and PtCo@Pt NPs in our work were hexagonally arranged with a uniform quasi-spherical shape and ordered distribution. The systematic study related to their ORR activities revealed that the PtCo@Pt core-shell NP arrays were more active and more durable than PtCo, Pt, and the commercial Pt/C catalyst. In the rotating-disk electrode test, a half-wave potential (E1/2) of 0.86 V versus RHE and a 4-e ORR mechanism were found for PtCo@Pt. Single-cell performance showed that the current density and the peak power density of PtCo@Pt achieved 0.86 A/cm2@0.7 V and 1.05 W/cm2, respectively, with a Pt loading of ∼0.15 mg/cm2 on the cathode. Also, they held 81.4 and 82.9% retention, respectively, after the durability test in the single-cell test. Density functional theory calculation results revealed that PtCo@Pt NPs had a lower d-band center and a weaker oxygen binding energy compared to Pt and PtCo, which contributed to the enhancement of the ORR activity.

Self-assembly of di-blcok copolymers (di-BCs) with precise control on morphologies and structures of nanomaterials makes it a promising technology for catalyst preparation. However, applications of the BC-synthesized Pt nanoparticles (NPs) on fuel cell have less been discussed. The major challenge may be the difficulty in achieving high-density nanopatterns which require a low degree of polymerization but a high effective segment-segment interaction parameter of the BC templates. As a resolution, sequentially double- or triple-layered BC route provides a new density-increased idea of harnessing these materials. In present work, monolayer of ordered and high-dispersed Pt-NP arrays with a density 27-folded has been achieved by the multiple di-BC routes consisted of identical self-assembly and plasma-cleaning processes. The multiplication has been proved to be equivalent to the duplication and oriented translation of the initial Pt-NP arrays, which provides not only a well-defined approach to control the spacing precisely, but also a bottom-up process to synthesize hexagonal-arranged arrays with predicable densities. Electrochemistry shows that the density multiplication has no negative effects on the Pt utilization of the monolayer arrays, and a remarkable ECSA value of ∼114.5 m2 g−1 is found. Further characterization of the monolayer arrays as cathodic catalysts for PEMFC reveals that, neither the ohmic losses nor the mass-transport losses are enhanced after the density multiplication, and the power density of the PEMFC assembled here is significantly higher than that using commercial Pt/C catalysts. All the results demonstrate that the multiple di-BC approach has great potential in preparation of BC-synthesized Pt-NP arrays for fuel cell applications.

This work offers a typical understanding of the factors that govern the nanostructures of poly(4-vinyl pyridine)-b-polystyrene-b-poly(4-vinyl pyridine) (P4VP-b-PS-b-P4VP) block copolymers (BCs) in dioxane/water, in which water is a selective solvent for the P4VP block. It is achieved through an investigation of the amphiphilic triblock copolymer micelles by variation of three different factors, including water content (above CWC but under the immobile concentration), temperature (ranging from 20 °C to 80 °C), and copolymer composition (low and high PS block length). Transition of bead-like micelles to vesicles is observed with the increase of water content due to the increase of interfacial energy between the copolymer and the solvent. Effect of temperature superposed on that of water content results in various morphologies, such as beads, fibers, rods, capsules, toroids, lamellae, and vesicles. The interfacial tension between the BC and the solvent increases with the increase of water content but decreases with the increase of temperature, indicating that the micellar morphologies are resulted from the competitive interplay between the temperature and the water content and always change in a direction that decreases the interfacial energy. Based on the micellar structures obtained in this work and the effects of temperature superposed on water concentration, a diagram of phase evolution of different micellar morphologies is illustrated here, covering the temperature range from 20 °C to 80 °C and the water content changing from 20 vol% to 35 vol%. For the investigation of BC composition, morphological transition of vesicle-to-fiber, for high PS length, is observed as compared with bead-to-capsule for low PS length, as the temperature changes from 20 °C to 80 °C. Our research complements the protocols to control over the morphologies and the phase diagram describing P4VP-b-PS-b-P4VP micellar nanostructures in aqueous solution.

A series of Cu-X/?-Al2O3 (X = Fe, Co, Ni) catalysts were synthesized by a rapid intermittent microwave irradiation method for hydrogen generation from dimethyl ether steam reforming. Different parameters, such as the promoters of X (X = Fe, Co, Ni), microwave irradiation procedure and the ratio of metal to ?-Al2O3, were investigated. The results show that 2Cu-Fe/72?-Al2O3 has the best performance, for which the agglomeration is prevented, CuO is well dispersed and the catalytic activity is improved. Promoter iron oxide in 2Cu-Fe/9?-Al2O3 facilitates the watergas shift reaction, which lead to an increase in the conversion of CO to CO2 and hydrogen yield. Particularly, the 2Cu-Fe/72?-Al2O3 catalyst, with the best molar ratio of metal to ?-Al2O3, shows a dimethyl ether conversion of >99% and a hydrogen yield of >98% and produces the lowest CO content of 1.4%, indicating that the synergism between dimethyl ether hydrolysis and methanol reforming requires an appropriate balance between the metallic Cu-Fe and the acid ?-Al2O3. The intermittent microwave irradiation technique provides a simple but effective method of the Cu-Fe/?-Al2O3 synthesis with a good catalyst performance for the dimethyl ether steam reforming.

Sorption enhanced steam reforming of acetic acid over sorbent assisted catalyst of Ni-CaO-La2O3 were investigated for high-purity H2 production. Ni-CaO-La2O3 with 8, 16 and 20 wt% Ni were developed by sol-gel combustion synthesis and were characterized by TG, TPR, BET, SEM, XRD and XPS. The catalytic activities and stability of the catalysts were tested in a fixed reactor. H2 yield and H2 concentration through Ni-CaO-La2O3 with 20 wt% Ni reaches 86.02% and 92.24% during pre-breakthrough period, respectively, which is attributed to sufficient Ni active sites on the surface and good Ni dispersion. Catalytic activities of Ni-CaO-La2O3 with 20 wt% Ni maintain stable during sorption-enhanced steam reforming reaction, but CO2 sorption capacity slightly decreases due to blockage of pores and size increase of CaO particles within nine sorption/desorption cycles.

This contribution focuses on the impact of shear flow on size and nanostructure of PS-based amphiphilic block copolymer (BC) micelles by varying the stirring rate and copolymer composition. The results show that the vesicles formed from diblock copolymer (di-BC) of PS-b-PAA remain with vesicular morphology, although the average size decreases, with the increase of stirring rate. However, the multi-compartment micelles (MCMs) formed from tri-block copolymer (tri-BC) of PS-b-P2VP-b-PEO are quite intricate, in which the copolymer first self-assembles into spheres, then to clusters, to large compound micelles (LCMs), and finally back to spheres, as stirring rate increases from 100 r/min to 2200 r/min. Formation mechanism studies manifest that vesicles form simultaneously as water is added to the di-BC solution, termed as directassembly, and remain with vesicular structure in the flowing process. While for the PS-b-P2VP-b-PEO copolymer, spherical micelles at initial stage can further assemble into clusters and LCMs, termed as second-assembly, due to the speeding-up-aggregation of the favorable stirring. As a result, an invert V-relationship between tri-BC micelle dimension and stirring rate is observed in contrast to the non-linear decreasing curve of di-BC vesicles. It is by investigating these various amphiphilic BCs that the understanding of shear dependence of size and morphology of micelles is improved from self-assembly to second-assembly process.

IrO2 was electro-deposited on hydrogenated TiO2 nanotube arrays (TNTA) to form IrO2/H-TNTA for oxygen evolution reaction (OER). Hydrogenation by calcining in H2 atmosphere was conducted to improve the electric conductivity, which was owing to partially reduce of Ti4+ in TNTA. It was found that hydrogenated TiO2 can facilitate the electro-deposition of IrO2, and elevate the OER activity compared to that of non-calcined and air-calcined TNTA, which would be due to the improved conductivity of H-TNTA. IrO2/H-TNTA shows a five-fold higher activity than IrO2/air-TNTA with the same loading amount. The coverage of IrO2 on the surface of hydrogenated TNTA is crucial to the stability of catalyst and with the increased loading amount of IrO2, IrO2/H-TNTA shows much higher stability.

A series of Ni-based catalysts supported on Ce–Zr–O were synthesized via impregnation and applied in the reverse water gas shift reaction (RWGS). BET, XRD, TPR, SEM, TEM and XPS were employed as the characterization of catalysts. Catalytic activities of Ni/Ce–Zr–O with different Ni contents were evaluated in RWGS under atmospheric pressure and at the temperature range of 550–750 °C in a fixed-bed quartz reactor. CO2 conversion reaches 49.66% and maintains stable after 80 h of reaction over 3 wt% Ni/Ce–Zr–O. CO selectivity can reach 99.65% for the catalyst with 10 wt% Ni at 750 °C. The Ni/Ce–Zr–O catalyst provides high activity, stability and selectivity in the conversion of CO2 to CO at high temperature. Ce–Zr–O solid solution is formed by co-precipitation and Ni is able to be incorporated into the Ce–Zr–O lattice via impregnation. The Ni species on catalyst surface can be considered as the active site for RWGS.

The effect of various strain rates on the tensile behavior of a single crystal nickel-base superalloy was studied. Single crystals with (001) crystal orientation were tested at 800 and 1000 degrees C under three kinds of strain rate of 10(-3), 10(-4) and 6x10(-5) s(-1). The yield strength increased with the increase of strain rate, while the configuration of the stress-strain curves was independent of strain rate. Additionally, fracture surface was related to strain rate at two temperatures. At 800 degrees C the amount of cleavage surface was different at three strain rates, which resulted from the difference of activated slip systems. The elongation increased with the decrease of strain rate, which was influenced by the heterogeneous ductile deformation. At 1000 degrees C the difference of fracture Surface was attributed to the microvoid at higher strain Fate, while the gamma/gamma' interfaces also played an important role at lower strain rate; elongation rate was independent of strain rate. (c) 2008 Elsevier B.V. All rights reserved.

A Ni-base single crystal superalloy was transient liquid phase (TLP) bonded using a Ni-Cr-B amorphous foil at 1230 degrees C for 8 h. Stress rupture tests of the TLP joint and a matrix sample were carried out at 982 degrees C/248 MPa and 1010 degrees C/248 MPa. The microstructures and fracture surfaces were studied using scanning electron microscopy (SEM). Transmission electron microscopy (TEM) investigations were performed after creep rupture testing to examine the deformation substructures. The results show that the stress rupture ductility of TLP joints is significantly decreased compared to the matrix sample. This reduction of the ductility of TLP joints can be attributed to solid solution strengthening by boron atoms, subgrain boundaries formed in the bonding zone and the concentration of creep cavities formed during the last stage of the stress rupture test. (c) 2006 Elsevier Inc. All rights reserved.

The microstructure of experimental nickel-base single crystal superalloys with different levels of carbon has been studied. With increasing carbon addition, the incipient melting point decreases obviously and the carbide morphology is changed from blocky to script-like shape. Minor carbon addition also affects the shrinkage porosity and eutectic in as-cast state. The segregation behavior of elements W and Ta is also influenced by the minor carbon addition.

Microstructural evolution of a nickel-base single crystal superalloy during thermal exposure at 900 and 1000 degreesC was investigated. In addition to growing and linking of gamma' particles, carbides M6C and M23C6 precipitated in this testing alloy. During exposure at 900 degreesC, M6C carbide precipitated in cubic shape, while at 1000 degreesC, M6C carbide was separated out in needle-like or cubic shape. M23C6 carbide was all precipitated in the gamma matrix channel. The TCP phase was not found in this alloy during thermal exposure both at 900 and 1000 degreesC before 1500 h. (C) 2003 Elsevier Science B.V. All rights reserved.