Enhancing the Catalytic Activity of Mo(110) Surface via Its Alloying with Submonolayer to Multilayer Boron Films and Oxidation of the Alloy: A Case of (CO + O2) to CO2 Conversion.

In-situ formation of boron thin films on the Mo(110) surface, as well as the formation of the molybdenum boride and its oxide and the trends of carbon monoxide catalytic oxidation on the substrates formed, have been studied in an ultra-high vacuum (UHV) by a set of surface-sensitive characterization techniques: Auger and X-ray photoelectron spectroscopy (AES, XPS), low-energy ion scattering (LEIS), reflection-absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD), electron energy loss spectroscopy (EELS) and work function measurements using the Anderson method. The boron deposited at Mo(110) via electron-beam deposition at a substrate temperature of 300 K grows as a 2D layer, at least in submonolayer coverage. Such a film is bound to the Mo(110) via polarized chemisorption bonds, dramatically changing the charge density at the substrate surface manifested by the Mo(110) surface plasmon damping. Upon annealing of the B-Mo(110) system, the boron diffuses into the Mo(110) bulk following a two-mode regime: (1) quite easy dissolution, starting at a temperature of about 450 K with an activation energy of 0.4 eV; and (2) formation of molybdenum boride at a temperature higher than 700 K with M-B interatomic bonding energy of 3.8 eV. The feature of the formed molybdenum boride is that there is quite notable carbon monoxide oxidation activity on its surface. A further dramatic increase of such an activity is achieved when the molybdenum boride is oxidized. The latter is attributed to more activated states of molecular orbitals of coadsorbed carbon monoxide and oxygen due to their enhanced interaction with both boron and oxygen species for MoxByOz ternary compound, compared to only boron for the Mox'By' double alloy.

Identification of a pyrone-type species as the active site for the oxygen reduction reaction.

A bicyclic pyrone-type species on oxygen-doped carbon catalysts was identified as the active site for the oxygen reduction reaction in acidic solution. It has much higher activity than that of typical nitrogen-doped carbon catalysts (0.219 e s-1 site-1vs. 0.021-0.088 e s-1 site-1 at 0.6 VRHE). The ortho-carbon atom in the carbonyl ring of the pyrone-type species was revealed as the reactive site by theoretical calculations.

Hybrid Metal-Boron Diatomic Site Embedded in C2 N Monolayer Promotes C-C Coupling in CO2 Electroreduction.

Double-atom catalyst (DAC) has gained much interest for its versatile tuning and synergistic effect of dual-atom active sites. Metal (M)-metal (M) diatomic sites, either homo- or heteronuclear, are typically researched. Hybrid metal-non-metal combined sites have rarely been studied and even the viability of such active sites are unknown. Herein, CO2 electroreduction (CO2 RR) is explored on M@X-C2 N (M = Fe, Co, Ni, and Cu; X = S, P, and B) which renders naturally generated M-X diatomic site. Using spin-polarized density functional theory coupled with computational hydrogen electrode model, it is demonstrated that the functionality of hybrid M-B dual-atom center is superior over that of a single- or double-M center in driving CO2 RR especially C-C coupling. Among metal-boron DACs studies, Fe@B-C2 N (µ = 2µB ) exhibits the lowest free energy barrier of 0.17 eV in C-C coupling whereas Ni@B-C2 N (µ = 0µB ) mainly produces CH4 with the lowest barrier of 0.42 eV. Hence, the electronic spin state of M can be particularly important in modulating selectivity and C-C coupling barrier in CO2 RR. Fe@B-C2 N is predicted as the promising catalyst for CO2 RR towards C2+ products owing partially to its enhanced spin state. The findings can enrich the design strategy of electrocatalysts normally running at ambient conditions.

Hexagonal and Monoclinic Phases of La2O2CO3 Nanoparticles and Their Phase-Related CO2 Behavior.

In this study, we prepared hexagonal and monoclinic phases of La2O2CO3 nanoparticles by different wet preparation methods and investigated their phase-related CO2 behavior through field-emission scanning microscopy, high-resolution transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, CO2-temperature programmed desorption, and linear sweeping voltammetry of CO2 electrochemical reduction. The monoclinic La2O2CO3 phase was synthesized by a conventional precipitation method via La(OH)CO3 when the precipitation time was longer than 12 h. In contrast, the hydrothermal method produced only the hexagonal La2O2CO3 phase, irrespective of the hydrothermal reaction time. The La(OH)3 phase was determined to be the initial phase in both preparation methods. During the precipitation, the La(OH)3 phase was transformed into La(OH)CO3 owing to the continuous supply of CO2 from air whereas the hydrothermal method of a closed system crystallized only the La(OH)3 phase. Based on the CO2-temperature programmed desorption and thermogravimetric analysis, the hexagonal La2O2CO3 nanoparticles (HL-12h) showed a higher surface CO2 adsorption and thermal stability than those of the monoclinic La2O2CO3 (PL-12h). The crystalline structures of both La2O2CO3 phases predicted by the density functional theory calculation explained the difference in the CO2 behavior on each phase. Consequently, HL-12h showed a higher current density and a more positive onset potential than PL-12h in CO2 electrochemical reduction.

Highly improved soot combustion performance over synergetic MnxCe1-xO2 solid solutions within mesoporous nanosheets.

Constructing synergetic bimetal oxide solid solutions with exceptional catalytic performances for efficient soot elimination is becoming a research frontier in environmental catalysis. Herein, synergetic MnxCe1-xO2 solid solutions within mesoporous nanosheets, synthesized by a facile hydrothermal method for the first time, have been performed to catalyze the NOx-assisted soot combustion. Research results validate that MnxCe1-xO2 solid solutions displayed highly improved soot combustion performance with respect to activity and selectivity, mainly due to the synergetic effect by combining factors of the unique mesoporous nanosheet-shaped feature, the enhanced chemical nature stemmed from high-valence Mn species, abundant active oxygen species originated from the enriched oxygen vacancies and the escalated redox properties. Furthermore, the enhanced NOx storage and oxidation abilities, mainly derived from integrating reciprocal merits of high-valence Mn species and CeO2, were also responsible for the highly improved soot combustion performance via NOx-assisted mechanism. Moreover, MnxCe1-xO2 solid solutions also exhibited excellent reusability due to the unique morphological structure and stable crystal phase, showing good potential in practical applications.

Boosting total oxidation of acetone over spinel MCo2O4 (M = Co, Ni, Cu) hollow mesoporous spheres by cation-substituting effect.

Boosting total oxidation of volatile organic compounds (VOCs) over spinel Co3O4 by cation-substituting effect is an effective solution, but the underlying mechanism has not yet been clearly elucidated. Herein, a series of spinel MCo2O4 (M = Co, Ni, Cu) hollow mesoporous spheres (HMS) have been synthesized by solvothermal alcoholysis with goals to elaborate the cation-substituting effect on spinel Co3O4 for total oxidation of VOCs. The physicochemical properties of spinel MCo2O4 (M = Co, Ni, Cu) HMS have been well characterized and correlated with their catalytic activities. Results reveal that CuCo2O4 HMS exhibited superior catalytic activity than those of NiCo2O4 and CoCo2O4 HMS for total oxidation of acetone and their catalytic activities followed the sequence of CuCo2O4 > NiCo2O4 > CoCo2O4. This phenomenon can be attributed to the cation-substituting effect, which resulted in the synthesized catalysts with different amounts of surface Co3+ cations, active oxygen species, defective sites and reducible capabilities. Meanwhile, kinetics studies offer direct evidence to support that the cation-substituting effect played the decisive role in determining the catalytic activity, and the underlying mechanism has been proposed by correlating the structure-activity relationship. Moreover, CuCo2O4 HMS also showed excellent long-term stability and good water tolerance due to its highly stable crystal phase and robust morphological structure, demonstrating its potential applications in the field of VOCs elimination.

Highly enhanced soot oxidation activity over 3DOM Co3O4-CeO2 catalysts by synergistic promoting effect.

Three-dimensionally ordered macroporous (3DOM) Co3O4-CeO2 catalysts with controllable Co/Ce molar ratios synthesized by colloidal crystal template method were developed to catalyze the NOx-assisted soot oxidation for the first time, and the obtained 3DOM Co3O4-CeO2 catalysts exhibited highly enhanced soot oxidation activity. Detailed characterizations of 3DOM Co3O4-CeO2 catalysts revealed that the highly enhanced soot oxidation activity was originated from the synergistic promoting effect by combining the macroporous effect resulted from the unique 3DOM framework, the chemical nature associated with more Co3+ reactive sites, the surface enrichment of Ce species and the improved redox properties. Meanwhile, the high NOx storage and oxidation capacity resulted from the integrated respective merits of Co3O4 and CeO2 also accounted for the enhanced soot oxidation activity via NOx-assisted mechanism. Furthermore, the 3DOM Co3O4-CeO2 catalysts demonstrated strong stability because of the surface enrichment of Ce species improving the thermal stability and the robust 3DOM framework inhibiting the structural collapse, showing their potential applications under practical conditions.

C2N-graphene supported single-atom catalysts for CO2 electrochemical reduction reaction: mechanistic insight and catalyst screening.

Single-atom catalysts (SACs) have emerged as an excellent platform for enhancing catalytic performance. Inspired by the recent experimental synthesis of nitrogenated holey 2D graphene (C2N-h2D) (Mahmood et al., Nat. Commun., 2015, 6, 6486-6493), we report density functional theory calculations combined with computational hydrogen electrode model to show that C2N-h2D supported metal single atoms (M@C2N) are promising electrocatalysts for CO2 reduction reaction (CO2 RR). M confined at pyridinic N6 cavity promotes activation of inert O[double bond, length as m-dash]C[double bond, length as m-dash]O bonds and subsequent protonation steps, with *COOH → *CO → CHO predicted to be the primary pathway for producing methanol and methane. It is found that *CO + H+ + e- → *CHO is most likely to be the potential determining step; breaking the scaling relation of *CO and *CHO binding on M@C2N SACs may simply be a rare event that is sensitively controlled by the detailed geometry of the adsorbate. Among twelve metals screened, M@C2N SACs where M = Ti, Mn, Fe, Co, Ni, Ru were identified to be effective in catalyzing CO2 RR with lowered overpotentials (0.58 V-0.80 V).

Spontaneously Healable Thermoplastic Elastomers Achieved through One-Pot Living Ring-Opening Metathesis Copolymerization of Well-Designed Bulky Monomers.

We report here a series of novel spontaneously healable thermoplastic elastomers (TPEs) with a combination of improved mechanical and good autonomic self-healing performances. Hard-soft diblock and hard-soft-hard triblock copolymers with poly[exo-1,4,4a,9,9a,10-hexahydro-9,10(1',2')-benzeno-l,4-methanoanthracene] (PHBM) as the hard block and secondary amide group containing norbornene derivative polymer as the soft block were synthesized via living ring-opening metathesis copolymerization by use of Grubbs third-generation catalyst through sequential monomer addition. The microstructure, mechanical, self-healing, and surface morphologies of the block copolymers were thoroughly studied. Both excellent mechanical performance and self-healing capability were achieved for the block copolymers because of the interplayed physical cross-link of hard block and dynamic interaction formed by soft block in the self-assembled network. Under an optimized hard block (PHBM) weight ratio of 5%, a significant recovery of tensile strength (up to 100%) and strain at break (ca. 85%) was achieved at ambient temperature without any treatment even after complete rupture. Moreover, the simple reaction operations and well-designed monomers offer versatility in tuning the architectures and properties of the resulting block copolymers.

"Brill Transition" Shown by Green Material Poly(octamethylene carbonate).

Poly(octamethylene carbonate) (POMC), as the eighth member of the newly developed biodegradable aliphatic polycarbonate family, demonstrates a reversible crystal-crystal transition, which is highly similar to Brill transition extensively studied in the nylon family. With the dipole-dipole interaction in POMC much weaker than the hydrogen bonding, POMC exhibits its "Brill transition" temperature at around 42 °C, much lower than nylons. The two crystalline structures of POMC at below and above the transition temperature can be identified. The transition of POMC is largely associated with the reversible conformation change of methylene sequences from trans-dominated at low temperatures to trans/gauche coexistence at high temperatures.

Design and construction of an organic crystal with a novel interpenetrated n-Borromean linked topology.

An organic crystal has been designed and constructed by the hydrogen-bond-directed self-assembly of TCA and dpyb, which possesses the large honeycomb net with 5.1 x 5.1 nm cavities and a novel interpenetrated n-Borromean linked topology.

Rational construction of 2D and 3D borromean arrayed organic crystals by hydrogen-bond-directed self-assembly.

Borromean organic networks: The rigid and trigonal pyramidal molecule, 1,3,5-tris(4-carboxyphenyl)adamantane (TCA), self-assembles into a 2D Borromean linked network by hydrogen bonds. Different linkers (methanol, phenazine, 4,4'-bipyridine, and 4,4'-azopyridine) result in more complex Borromean networks or a 3D polycatenation network.

Low temperature catalytic combustion of propane over Pt-based catalyst with inverse opal microstructure in a microchannel reactor.

A novel Pt-based catalyst with highly regular, periodic inverse opal microstructure was fabricated in a microchannel reactor, and catalytic testing revealed excellent conversion and stable activity for propane combustion at low temperatures.

Adsorption/desorption studies on nanocrystalline alumina surfaces.

Two kinds of nanocrystalline alumina powders, boehmite (gamma-AlOOH, particle size d approximately 10 nm, BET surface area A(BET) = 180-200 m(2) g(-1)) and corundum (alpha-Al(2)O(3), d approximately 400 nm, A(BET) = 7 m(2) g(-1)) were used for comparative investigation by thermogravimetry (TG). The remarkable difference in the dehydration profiles between the two samples gives evidence for a distinct difference in their structures. In the following pyridine adsorption/desorption experiment, gamma-alumina was found to possess much more (20 times) and much stronger acidic sites than corundum. The activation energy of pyridine desorption was obtained from the respective minima in the first derivative of the TG-curves (DTG) at various heating rates (1-20 K min(-1)); the activation energy for pyridine desorption is smaller for gamma-alumina (61.5 kJ mol(-1)) than for corundum (78.8 kJ mol(-1)). Furthermore, the adsorption of water, carbon tetrachloride, and hexane on those alumina specimens provides evidence for the highly hydrophilic nature of their surfaces. The shift of T(max) to higher temperatures upon desorption of water was ascribed to the different adsorption coverage and the different energy required for removal of adsorbed water molecules.