Guoyong Fang

Sulfur-Doped Graphene as an Efficient Metal-free Cathode Catalyst for Oxygen Reduction

Tailoring the electronic arrangement of graphene by doping is a practical strategy for producing significantly improved materials for the oxygen-reduction reaction (ORR) in fuel cells (FCs). Recent studies have proven that the carbon materials doped with the elements, which have the larger (N) or smaller (P, B) electronegative atoms than carbon such as N-doped carbon nanotubes (CNTs), P-doped graphite layers and B-doped CNTs, have also shown pronounced catalytic activity. Herein, we find that the graphenes doped with the elements, which have the similar electronegativity with carbon such as sulfur and selenium, can also exhibit better catalytic activity than the commercial Pt/C in alkaline media, indicating that these doped graphenes hold great potential for a substitute for Pt-based catalysts in FCs. The experimental results are believed to be significant because they not only give further insight into the ORR mechanism of these metal-free doped carbon materials, but also open a way to fabricate other new low-cost NPMCs with high electrocatalytic activity by a simple, economical, and scalable approach for real FC applications.

Extraordinarily High Activity in the Hydrodesulfurization of 4,6-Dimethyldibenzothiophene over Pd Supported on Mesoporous Zeolite Y

Design and preparation of highly active hydrodesulfurization (HDS) catalysts is very important for the removal of air pollution. Herein, we report an extraordinarily active HDS catalyst, which is synthesized by loading of Pd on mesoporous zeolite Y (Pd/HY-M). The mesoporous zeolite Y is successfully synthesized using a water glass containing N,N-dimethyl-N-octadecyl-N-(3-triethoxysilylpropyl) ammonium [(C(2)H(5)O)(3)SiC(3)H(6)N(CH(3))(2)C(18)H(37)](+) cation as a mesoscale template. Compared with mesoporous Beta and ZSM-5 supported Pd catalysts (80.0% and 73.4% for Pd/HBeta-M and Pd/HZSM-5-M, respectively) as well as commercial catalyst of γ-Al(2)O(3) supported Pd catalyst (31.4%), Pd/HY-M catalyst exhibited very high activity in HDS of 4,6-dimethyldibenzothiophene (4,6-DM-DBT, 97.3%). The higher activity of Pd/HY-M than that of Pd/HBeta-M and Pd/HZSM-5-M is assigned to the larger micropore size of zeolite Y compared to that of Beta and ZSM-5. Theoretical simulation and adsorption experimental data show that 4,6-DM-DBT has difficulty entering the micropores of ZSM-5 and Beta zeolites, but the micropores of Y zeolite are accessible.

Design and Synthesis of Metal Sulfide Catalysts Supported on Zeolite Nanofiber Bundles with Unprecedented Hydrodesulfurization Activities

Developing highly active hydrodesulfurization (HDS) catalysts is of great importance for producing ultraclean fuel. Herein we report on crystalline mordenite nanofibers (NB-MOR) with a bundle structure containing parallel mesopore channels. After the introduction of cobalt and molybdenum (CoMo) species into the mesopores and micropores of NB-MOR, the NB-MOR-supported CoMo catalyst (CoMo/NB-MOR) exhibited an unprecedented high activity (99.1%) as well as very good catalyst life in the HDS of 4,6-dimethyldibenzothiophene compared with a conventional γ-alumina-supported CoMo catalyst (61.5%). The spillover hydrogen formed in the micropores migrates onto nearby active CoMo sites in the mesopores, which could be responsible for the great enhancement of the HDS activity.

Superior Catalytic Performance of Mesoporous Zeolite TS‐1 for the Oxidation of Bulky Organic Sulfides

Oxidation is a fundamentally important reaction in organic synthesis. Over the past few decades, transition-metal complexes, including those of titanium, molybdenum, and vanadium, have been found to be highly effective catalysts for the selective oxidation of organic compounds and have played important roles in organic synthesis. However, these homogeneous catalysts suffer from several drawbacks, such as high cost, low stability, and limited reusability, which curtail their use in industrial applications. A solution to these problems is to replace the homogeneous catalysts with highly active porous solid catalysts. It is well-known that titanosilicate zeolite TS-1, as well as other titanium-containing zeolites, such as Ti-b, Ti-ZSM-12, and Ti-ZSM-48, are highly efficient catalysts for the oxidation of organic compounds. 4] However, one disadvantage of these zeolite catalysts is that the pores in their frameworks are too small to be accessed by bulky reactants. To overcome this limitation, Ti-containing mesoporous molecular sieves, such as Ti-MCM-41 and Ti-SBA15, have been synthesized. Unfortunately, those catalysts have shown relatively low catalytic activities, owing to the presence of hexa-coordinated titanium species. In recent years, tremendous efforts have been made to synthesize mesoporous zeolite TS-1 with a crystalline framework by using nanosized carbon and amphiphilic organosilanes as templates. However, the industrial application of these mesoporous zeolites is still limited by the complexity of the synthetic procedures that are involved in the use of nanosized carbon templates and by the expense of amphiphilic organosilane templates. Herein, we report a facile and universal route to mesoporous zeolite TS-1 (MTS-1) by using a mesoscale random copolymer that contains quaternary ammonium groups (RCQA-1) as a template (see section S1.2 in the Supporting Information). Compared with mesoporous-free TS-1, the MTS-1 zeolite shows extraordinarily catalytic activity and highly controllable chemose-

Halogenated MOF-5 variants show new configuration, tunable band gaps and enhanced optical response in the visible and near infrared

Inspired by recent experimental fabrication of mono-halogenated versions of Metal-Organic Framework MOF-5 (i.e., X-MOF-5, X = F to I) and some experimentally known fully halogenated MOF compounds, we systematically studied frameworks incorporating full halogenation of the BDC linkers of the prototypical Iso-Reticular Metal-Organic Framework (IRMOF) series, exemplified by MOF-5. Using quantum chemistry calculations, we find that halogenation leads to a 90° rotation of the aryl group, which is mainly ascribed to overcrowding between halogen atoms and the carboxyl and benzene ring and strong repulsion among in-plane atoms/groups. The 90° configuration decreases the repulsion, and maximizes the stabilization energy, and is therefore more stable than 0° configuration. We find that the band gap can be tuned from 4.1 to 1.5 eV as we go from F, Cl, Br, to I. This extends the optical response of these experimentally accessible materials through the visible and infrared region. We have also considered a broader range of new materials that substitute various metals for Zn. Totally, 70 materials were systematically examined computationally including (M4O)(BDC-Z4)3 (M = Zn, Cd, Be, Mg, Ca, Sr, Ba; Z = H, F, Cl, Br, I). For the full range of materials, we calculate band gaps of 4.2 to 1.0 eV, corresponding to a threshold of absorption of 290-1240 nm. Four selected materials were tested for stability using short 5 ps molecular dynamics simulations up to 600 K. The new materials with the smallest band gaps could potentially be used in near-infrared (NIR) light-emitting devices. Other properties, e.g., bulk moduli, formation energy, chemical bonding, and optical properties, were also investigated. The present results may provide new materials for use as novel photocatalysts, photoactive materials for photovoltaic cells, or functional devices in nanoelectronics and optoelectronics.

Stepwise mechanism and H2O-assisted hydrolysis in atomic layer deposition of SiO2 without a catalyst

Atomic layer deposition (ALD) is a powerful deposition technique for constructing uniform, conformal, and ultrathin films in microelectronics, photovoltaics, catalysis, energy storage, and conversion. The possible pathways for silicon dioxide (SiO2) ALD using silicon tetrachloride (SiCl4) and water (H2O) without a catalyst have been investigated by means of density functional theory calculations. The results show that the SiCl4 half-reaction is a rate-determining step of SiO2 ALD. It may proceed through a stepwise pathway, first forming a Si-O bond and then breaking Si-Cl/O-H bonds and forming a H-Cl bond. The H2O half-reaction may undergo hydrolysis and condensation processes, which are similar to conventional SiO2 chemical vapor deposition (CVD). In the H2O half-reaction, there are massive H2O molecules adsorbed on the surface, which can result in H2O-assisted hydrolysis of the Cl-terminated surface and accelerate the H2O half-reaction. These findings may be used to improve methods for the preparation of SiO2 ALD and H2O-based ALD of other oxides, such as Al2O3, TiO2, ZrO2, and HfO2.

Interfacial catalysis in and initial reaction mechanism of Al2O3 films fabricated by atomic layer deposition using non-hydrolytic sol–gel chemistry

Atomic layer deposition (ALD) is a powerful nanofabrication technique that can precisely control the composition, structure, and thickness of thin films at the atomic scale, and is widely used in the fields of electronic displays, microelectronics, catalysis, coatings, and energy storage and conversion. ALD of metal oxide thin films can be completed using metal alkoxides as the oxygen source, which is similar to the non-hydrolytic sol-gel (NHSG) technique. Density functional theory calculations show that metal alkoxides, such as Al(OiPr)3 and Al(OEt)3, can directly form M-O bonds through strong chemisorption on the surface. Meanwhile, alkyl groups can be eliminated through the formation of alkyl halides and alkenes, which can be catalyzed by interfacial interactions between alkyl groups and the surface. Such noncovalent catalysis resulting from interfacial interaction can be termed as interfacial catalysis. This can be characterized by the difference between the interfacial interaction energies of the transition state and the corresponding intermediate based on natural bond analysis. We expect that such interfacial catalysis can be used in precursor designs, improvement of ALD of oxides and as a new characterization method for other interfacial catalysis and noncovalent catalysis processes.