Metal telluride nanosheets by scalable solid lithiation and exfoliation.

Transition metal tellurides (TMTs) have been ideal materials for exploring exotic properties in condensed-matter physics, chemistry and materials science1-3. Although TMT nanosheets have been produced by top-down exfoliation, their scale is below the gram level and requires a long processing time, restricting their effective application from laboratory to market4-8. We report the fast and scalable synthesis of a wide variety of MTe2 (M = Nb, Mo, W, Ta, Ti) nanosheets by the solid lithiation of bulk MTe2 within 10 min and their subsequent hydrolysis within seconds. Using NbTe2 as a representative, we produced more than a hundred grams (108 g) of NbTe2 nanosheets with 3.2 nm mean thickness, 6.2 µm mean lateral size and a high yield (>80%). Several interesting quantum phenomena, such as quantum oscillations and giant magnetoresistance, were observed that are generally restricted to highly crystalline MTe2 nanosheets. The TMT nanosheets also perform well as electrocatalysts for lithium-oxygen batteries and electrodes for microsupercapacitors (MSCs). Moreover, this synthesis method is efficient for preparing alloyed telluride, selenide and sulfide nanosheets. Our work opens new opportunities for the universal and scalable synthesis of TMT nanosheets for exploring new quantum phenomena, potential applications and commercialization.

Synergistic oxidation of toluene through bimetal/cordierite monolithic catalysts with ozone.

Toluene treatment has received extensive attention, and ozone synergistic catalytic oxidation was thought to be a potential method to degrade VOCs (violate organic compounds) due to its low reaction temperature and high catalytic efficiency. A series of bimetal/Cord monolithic catalysts were prepared by impregnation with cordierite, including MnxCu5-x/Cord, MnxCo5-x/Cord and CuxCo5-x/Cord (x = 1, 2, 3, 4). Analysis of textural properties, structures and morphology characteristics on the prepared catalysts were conducted to evaluate their performance on toluene conversion. Effects of active component ratio, ozone addition and space velocity on the catalytic oxidation of toluene were investigated. Results showed that MnxCo5-x/Cord was the best among the three bimetal catalysts, and toluene conversion and mineralization rates reached 100 and 96% under the condition of Mn2Co3/Cord with 3.0 g/m3 O3 at the space velocity of 12,000 h-1. Ozone addition in the catalytic oxidation of toluene by MnxCo5-x/Cord could efficiently avoid the 40% reduction of the specific surface area of catalysts, because it could lower the optimal temperature from 300 to 100 °C. (Co/Mn)(Co/Mn)2O4 diffraction peaks in XRD spectra indicated all the four MnxCo1-x/Cord catalysts had a spinel structure, and diffraction peak intensity of spinel reached the largest at the ratio of Mn:Co = 2:3. Toluene conversion rate increased with rising ozone concentration because intermediate products generated by toluene degradation might react with excess ozone to generate free radicals like ·OH, which would improve the toluene mineralization rate of Mn2Co3/Cord catalyst. This study would provide a theoretical support for its industrial application.

Potential Risk of Significant N2O Emission without Changing NOx Conversion on Commercial V2O5/TiO2 Catalyst under Working Conditions.

Vanadium-based catalysts play a pivotal role in the emission control of industrial NOx via selective catalytic reduction (SCR) technology. However, little attention has been paid to the potential emission of greenhouse gas N2O under complex working conditions. This work reports that a commercial V2O5/TiO2 catalyst may lead to significant N2O emission without greatly changing the outlet NOx concentration after chromium (Cr) deposition. With a Cr loading of 2 wt %, N2O concentration increased from 27.8 to 199.2 ppm at 350 °C with the value of outlet N2O/(N2O+N2) from 2.5% to 19.4%. Experimental results combined with DFT+U calculations suggest that nonselective catalytic reduction (NSCR) is the main route for N2O formation in a wide temperature range of 250 ∼ 400 °C. It is stemmed from the fact that the covalent interaction between Cr and V species on the V2O5/TiO2 surface accelerates the conversion of V4+ + Cr6+ → V5+ + Cr3+, leading to a larger proportion of surface V5+. More importantly, surface V5+ is highly related to the redox property of the V2O5/TiO2 catalyst, which is beneficial to NSCR reaction rather than the standard SCR process. The work suggests that to better inhibit the emission of greenhouse gases during the NH3-SCR process, monitoring N2O emission should be included along with the NOx concentrations, especially in complex flue gases.

Reverse oxygen spillover triggered by CO adsorption on Sn-doped Pt/TiO2 for low-temperature CO oxidation.

The spillover of oxygen species is fundamentally important in redox reactions, but the spillover mechanism has been less understood compared to that of hydrogen spillover. Herein Sn is doped into TiO2 to activate low-temperature (<100 °C) reverse oxygen spillover in Pt/TiO2 catalyst, leading to CO oxidation activity much higher than that of most oxide-supported Pt catalysts. A combination of near-ambient-pressure X-ray photoelectron spectroscopy, in situ Raman/Infrared spectroscopies, and ab initio molecular dynamics simulations reveal that the reverse oxygen spillover is triggered by CO adsorption at Pt2+ sites, followed by bond cleavage of Ti-O-Sn moieties nearby and the appearance of Pt4+ species. The O in the catalytically indispensable Pt-O species is energetically more favourable to be originated from Ti-O-Sn. This work clearly depicts the interfacial chemistry of reverse oxygen spillover that is triggered by CO adsorption, and the understanding is helpful for the design of platinum/titania catalysts suitable for reactions of various reactants.

To be support or promoter: the mode of introducing ceria into commercial V2O5/TiO2 catalyst for enhanced Hg0 oxidation.

Ce-modified commercial vanadium-based catalysts are still in a rapid development stage in terms of optimizing Hg0 oxidation performance. Due to the universal property of ceria, it can act as either support or promoter to supported vanadium-based catalysts. However, the introduction mode of Ce on the Hg0 oxidation is still unclarified. Herein, introducing Ce to vanadium-based catalysts as a promoter (VCe/Ti) plays a more effective role in the Hg0 oxidation than only doping Ce into TiO2 support (V/CeTi). It is revealed that the strong interaction between V and Ce increases the orbital hybridization, and reduces the lowest unoccupied molecular orbital (LUMO) of V, which is conducive to adsorbing and activating HCl. The excellent performance of the VCe/Ti catalyst can be ascribed to its superior redox ability, stronger HCl adsorption capacity, abundant surface oxygen vacancies, and the redox equilibrium (Ce3+ + V5+ ↔ Ce4+ + V4+), which improves electron transfer, and thus the catalytic activity. This work provides the potential application of Ce-modified V-based catalysts for the simultaneous control of NOx and Hg0 in stationary sources.

Recent Status and Developments of Vacancies Modulation in the ABO3 Perovskites for Catalytic Applications.

Perovskite oxides (ABO3 ) have attracted comprehensive interest for wide range of functional applications (especially for chemical catalysis) due to their high design flexibility, controllable vacancies sites creation, abundant chemical properties, and stable crystal structure. Herein, the previous research and potential development of ABO3 through adjusting the vacancy at different sites (A-site, B-site, and O-site) to enhance catalytic performance are systematically analyzed and generalized. Briefly, the ABO3 with different vacancies sites prepared by multifarious direct and indirect methods, accompanied with the improved physical-chemical properties, endow them with distinct and intensified development of catalysis application. In addition, the impressive optimization proved by the vacancies sites adjustment over the ABO3 is studied to continuously facilitate the advance in some common catalysis reactions, further expanding to other optimized functional applications. At last, the constructive suggestions for fine regulation and analysis of vacancies sites over ABO3 are also put forward.

Gas-template directed in situ synthesis of highly nitrogen-doped carbon nanotubes with superior sulfur compatibility and enhanced functionalities.

Herein, we develop a low temperature gas template route for in situ growth of highly nitrogen-doped (5.68 wt%), multi-walled carbon nanotubes (N-MWCNTs). The N-MWCNTs exhibit superior sulfur compatibility in hydrogen sulfide (H2S) resource utilization, thus resulting in their enhanced functionality as Li-S cathodes with high sulfur-specific capacity and retention rate.

Structure-Directing Role of Support on Hg0 Oxidation over V2O5/TiO2 Catalyst Revealed for NOx and Hg0 Simultaneous Control in an SCR Reactor.

The crystal structure of TiO2 strongly influences the physiochemical properties of supported active sites and thus the catalytic performance of the as-synthesized catalyst. Herein, we synthesized TiO2 with different crystal forms (R = rutile, A = anatase, and B = brookite), which were used as supports to prepare vanadium-based catalysts for Hg0 oxidation. The Hg0 oxidation efficiency over V2O5/TiO2-B was the best, followed by V2O5/TiO2-A and V2O5/TiO2-R. Further experimental and theoretical results indicate that gaseous Hg0 reacts with surface-active chlorine species produced by the adsorbed HCl and the reaction orders of Hg0 oxidation over V2O5/TiO2 catalyst with respect to HCl and Hg0 concentration were approximately 0 and 1, respectively. The excellent Hg0 oxidation efficiency over V2O5/TiO2-B can be attributed to lower redox temperature, larger HCl adsorption capacity, and more oxygen vacancies. This work suggests that to achieve the best simultaneous removal of NOx and Hg0 on state-of-the-art V2O5/TiO2 catalyst, a combination of anatase and brookite TiO2-supported vanadyl tandem catalysts is supposed to be employed in the SCR reactor, and the brookite-type catalyst should be on the downstream of the anatase-based catalyst due to the inhibition of NH3 on Hg0 oxidation.

In Situ Modulation of A-Site Vacancies in LaMnO3.15 Perovskite for Surface Lattice Oxygen Activation and Boosted Redox Reactions.

Modulation of A-site defects is crucial to the redox reactions on ABO3 perovskites for both clean air application and electrochemical energy storage. Herein we report a scalable one-pot strategy for in situ regulation of La vacancies (VLa ) in LaMnO3.15 by simply introducing urea in the traditional citrate process, and further reveal the fundamental relationship between VLa creation and surface lattice oxygen (Olatt ) activation. The underlying mechanism is shortened Mn-O bonds, decreased orbital ordering, promoted MnO6 bending vibration and weakened Jahn-Teller distortion, ultimately realizing enhanced Mn-3d and O-2p orbital hybridization. The LaMnO3.15 with optimized VLa exhibits order of magnitude increase in toluene oxidation and ca. 0.05 V versus RHE (reversible hydrogen electrode) increase of half-wave potential in oxygen reduction reaction (ORR). The reported strategy can benefit the development of novel defect-meditated perovskites in both heterocatalysis and electrocatalysis.

Efficiently Selective Oxidation of H2S to Elemental Sulfur over Covalent Triazine Framework Catalysts.

As a highly toxic and corrosive waste gas in the industry, hydrogen sulfide (H2S) usually originates from the utilization of coal, petroleum, and natural gas. The selective catalytic elimination of H2S shows great significance to ensure the safety of industrial processes and health of human beings. Herein, we report efficiently selective oxidation of H2S to elemental sulfur over covalent triazine framework (CTF-1-x, x = 400, 500, 600, 400-600 °C) catalysts. CTF-1-x samples were prepared from polymerization of 1,4-dicyanobenzene to form polyaryl triazine networks under ion solidothermal conditions in the presence of ZnCl2, which acts as both an initiator and a porogen. The resultant CTF-1-x samples possess abundant micro-mesoporosity, large Brunauer-Emmett-Teller (BET) surface areas, and tunable structural base sites with edge amine and graphitic nitrogen characteristics, which were homogeneously decorated onto their frameworks. As a result, CTF-1-x samples act as efficient and long-lived catalysts in selective oxidation of H2S to sulfur under ambient conditions (100% H2S conversion, 100% sulfur selectivity at 180 °C, 12 000 mL/(g·h)), and their activities were superior to those of commercial Fe2O3 and g-C3N4 desulfurization catalysts. Abundant nitrogen structural base sites of CTF-1-x effectively activate the reactants, and abundant micro-mesoporosity facilitates mass transfer in and out of CTF-1-x. The improved design of the nitrogen-doped carbon material for H2S activation and conversion could enhance the development of more active and robust nitrogen-doped carbon catalysts.

Mechanochemically synthesized MgAl layered double hydroxide nanosheets for efficient catalytic removal of carbonyl sulfide and H2S.

A solid-state mechanochemical route for rapid synthesis of MgAl layered double hydroxide (LDH) nanosheets large in surface area and decorated with abundant hydroxyl groups was developed for catalytic elimination of carbonyl sulfide and H2S, showing activity superior to those of commercial LDHs and porous metal oxides.

Design of Efficient, Hierarchical Porous Polymers Endowed with Tunable Structural Base Sites for Direct Catalytic Elimination of COS and H2S.

Hydrogen sulfide (H2S) is malodorous and highly toxic, and its selective removal from industrial feedstock is highly recommended for safety and environment protection. We report here a class of nitrogen-functionalized, hierarchical porous polymers (N-HPPs) synthesized from one-step alkylation-induced cross-linking without any involvement of templates. The as-engineered N-HPPs are large in BET surface area (792-1397 m2/g) and endowed with hierarchical porosity. The incorporated nitrogen species of N-HPPs act as structural base sites with properties that can be precisely controlled. By molecular simulation, the enhanced interactions between N-HPPs and H2S were verified. The synthesized N-HPPs show superb capacities for H2S adsorption (9.2 mmol/g at 0 °C, 1.0 bar) and display satisfactory IAST H2S/N2 and H2S/CH4 selectivity (88.3 and 119.6, respectively, at 0 °C). Catalyzed by the structural base sites located in the N-HPPs, the COS together with its derived H2S can be effectively eliminated under mild conditions.