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Twisted two-dimensional transition metal dichalcogenide (TMD) moiré superlattices provide an additional degree of freedom to engineer electronic and optical properties. Nevertheless, controllable synthesis of marginally twisted homo TMD moiré superlattices is still a challenge. Here, physical vapor deposition grown spiral WS2nanosheets are demonstrated to be a marginally twisted moiré superlattice using scanning tunneling microscopy and spectroscopy. Periodic moiré superlattices are found on the third layer (3L) and 4L of the spiral WS2nanosheet owing to the marginally twisted alignment between two neighboring layers, resulting in a highly localized flat band near the valence band maximum. Their bandgap depends on atomic stacking configurations, which gives a good interpretation for split moiré excitons using photoluminescence at 77 K. This work can benefit the development of twisted homo TMD moiré superlattices and could promote the profound research of twisted TMDs in the prospective field, such as strongly correlated physics and twistronics.

A modified impregnation technique was used to prepare carbon nanotube-confined InPt-based catalysts with varying In content. The findings of physicochemical characterizations, such as X-ray diffraction, N2adsorption/desorption isotherms, H2-temperature programmed reduction, high-resolution transmission electron microscopy, thermogravimetric/differential thermal analysis, Raman, X-ray photoelectron spectroscopy, and CO probed in situ diffuse reflectance Fourier transform infrared, revealed that the addition of the second metal In restricted the agglomeration of active sites during the reaction and successfully lowered the reduction temperature of active metals. The structure and electronic characteristics of the platinum species were altered as a result of the creation of an alloy between platinum and indium. The presence of In species diluted the surface Pt species and transferred electrons to the Pt species, resulting in improving the catalytic activity and suppressing the C–C bond breakage simultaneously, which was beneficial to improve the selectivity of propylene. The apparent activation energy of 0.5InPt/CNTs-catalyzed propane dehydrogenation decreased from 120.0 to 57.2 kJ/mol when compared to that of Pt/CNTs, and the propane conversion rose by 4.3 times from 3.8 to 20.1%, while also demonstrating superior catalytic stability.

Advanced synthesis of highly-dispersed Au nanoparticles is vital to catalysis and green chemistry. In this work, a facile one-pot coordination–calcination method was developed to prepare uniform Au nanoparticles loaded on ZnO using metal ions and the 2-methylimidazole ligand. This Au/ZnO–MZ catalyst was efficient and stable towards sustainable synthesis of vanillin viathe base-free aerobic oxidation of vanillyl alcohol. A turnover number of 335 and 100% yield of vanillin were obtained at 120 °C and 5 bar of O2, the best result to date among all the supported noble-metal catalysts. Meanwhile other Au/ZnO catalysts were prepared for comparison by a one-pot precipitation method using ammonia, triethylamine and sodium hydroxide, respectively. The Au/ZnO–MZ catalyst demonstrated unique properties as shown by PXRD, N2physisorption, SEM, TEM, H2-TPR, O2-TPD, XPS, PL spectroscopy and CO adsorbed DRIFT-IR. Small and metallic-state Au nanoparticles (about 2.2 nm) as active sites were highly dispersed on ZnO hexagonal nanosheets. Sufficient surface oxygen species bearing enhanced oxygen mobility were observed for ZnO carriers. The strong metal–support interaction due to the interfacial electron transfer from Au to ZnO was elucidated. These catalytic features allowed excellent base-free oxidation catalysis by lowering the activation energy. Moreover, the Au/ZnO–MZ catalyst displayed a wide substrate scope of alcohols to produce the corresponding aldehydes. The present findings may probably inspire new preparation methods and applications for Au heterogeneous catalysts.

MnOx-based catalysts possess excellent low-temperature NH3selective catalytic reduction (NH3-SCR) activity, but the poor SO2/sulfate poisoning resistance and the narrow active-temperature window limit their application for NOxremoval. Herein, TiO2nanoparticles and sulfate were successively introduced into MnOx-based catalysts to modulate the NH3-SCR activity, and the active-temperature window (NO conversion above 80%, T80) was significantly broadened to 100–350 °C (SO42––TiO2@MnOx) compared to that of the pristine MnOxcatalyst (ca. T80: 100–268 °C). Combined with advanced characterizations and control experiments, it was clearly shown that the poisonous effects of sulfate on the MnOxcatalyst could be efficiently inhibited in the presence of TiO2species due to the interaction between sulfate and TiO2to form a solid superacid (SO42––TiO2) species as NH3adsorption sites for the low-temperature process. Furthermore, such solid superacid (SO42––TiO2) species could weaken the redox ability to inhibit the excessive oxidation of NH3and thus enhance the high-temperature activity significantly. This work not only puts forward the TiO2predecoration strategy that converts sulfate to a promoter to broaden the active temperature window but also experimentally proves that the requirement of redox ability and acidity in the MnOx-based NH3-SCR catalyst was dependent on the reaction temperature range.

Graphical abstract: The introduction of surface K species suppressed the dry reforming but promoted the selective oxidation to produce ethylene.

SBA-15 with varied pore size from 4 to 8 nm were synthesized by tuning the temperature of hydrothermal treatment, the supports were then used to load the active phase CrOxthrough a conventional impregnation method. The resulting catalysts were characterized by small/wide angle XRD, N2adsorption/desorption, FT-IR, TEM-EDX, XPS, TPR and CO2-TPD to study the feature of structure, surface chemical state, redox and basicity. It was found from these results that the metal species could be well dispersed on catalysts with larger pore size. Cr6+species could enter into the framework by substituting the Si atoms of SBA-15, and Cr3+mainly exist on extra framework. Pore size had profound effects on reducibility, surface composition and basicity. Cr6+species were necessary to activate the C-H bonds of alkanes, while the basicity played an important role in activating C-O bonds of CO2. The best performances were achieved over the sample Cr supported on SBA-15 with a pore diameter of 7 nm in oxidative dehydrogenation of ethane in the presence of CO2.

Three kinds of mesoporous silica materials including SYSG (commercial silica gel), SBA-15, and KIT-6 are used as the carrier for supporting silver nitrate via incipient-wetness impregnation method. The resultant materials Ag/SYSG, Ag/SBA-15, Ag/KIT-6 are characterized by low-temperature nitrogen adsorption/desorption, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy and also are used as adsorbents for ethylene and ethane separation. It is found that both the surface area and the dispersion of Ag cations have significant influences on the separation performances. The surface modification by AgNO3has the adsorption mechanism changed through π-complexation, which is in contrast to the physical adsorption through van der Waals force that is usually dominated by the surface area. The loss of surface area weakens the physical adsorption of ethane, whereas the well-dispersed Ag cations could promote the adsorption of ethylene; therefore, the selectivity is improved. As a result, Ag/SBA-15 shows the best separation performances among the tested materials.

The synergistic effect between bimetallic nanoparticles, as well as the support effect, is particularly important for supported catalysts in heterogeneous catalysis. In this work, an AgPd/ZrO2bimetallic catalyst was reported for the base-free aerobic oxidation of vanillyl alcohol to vanillin, a challenging transformation of an aromatic bio-alcohol into a valuable fine chemical. The crystalline structure and textural properties of ZrO2were modulated by using different zirconium precursors and precipitants during the precipitation process. The ZrO2obtained from zirconium nitrate and trimethylamine was found to be the most suitable support. It displayed abundant reactive oxygen species and the largest specific surface area. Then, an Ag promoter was added to the Pd/ZrO2catalyst and the synergy between Ag and Pd was tuned by varying their ratios. The Ag0.5Pd1/ZrO2catalyst showed an enhanced performance, i.e., 100% conversion of vanillyl alcohol and 95% selectivity to vanillin at 120 °C and 3 bar O2within 4 h, in comparison with the Pd/ZrO2catalyst (69% and 87%, respectively). Moreover, the vanillin productivity reached 133.0 mol mol−1h−1, the best result reported in the literature to date. Various characterization methods demonstrated that the addition of Ag can reduce the mean size of Pd nanoparticles (4.9 nm vs.3.8 nm), and Ag+species were beneficial to stabilizing Pd0species in a high fraction due to electron transfer. The reactive Pd0sites closely interacting with the Ag promoter allowed lowering of the apparent activation energy of the reaction (27.3 vs.37.5 kJ mol−1). In addition, the Ag0.5Pd1/ZrO2catalyst exhibited superior stability during consecutive recycling uses owing to the strong metal–support interactions.

A novel RuxCoOy(OH) composite catalyst was prepared by the simple one-pot hydrolysis of Ru and Co salts at room temperature in the presence of NaBH4. This catalyst showed promise for aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) under environmentally benign conditions, i.e., using water as the solvent, O2as the oxidant, and no soluble base additives. Various physicochemical techniques, including ICP-MS, PXRD, DRIFT, TEM, H2-TPR, O2-TPD, XPS, and CO2-TPD, were used to study the catalytic properties that depend on the Ru load. The influence of reaction parameters (i.e., HMF/Ru ratio, O2pressure, reaction temperature, and time) and the reaction pathway was investigated. HMF oxidation was initiated mainly from the OH group on metallic Ru0active sites, and the cooperation of the Co(II)/Co(III) redox pair allowed the effective transformation of O2to reactive lattice oxygen and the regeneration of Ru0sites. It was shown that the Ru4CoOy(OH) catalyst with an enhanced Ru–Co metal interaction was the most active in giving a 99.9% yield of FDCA at 140 °C and 10 bar of O2after 18 h, corresponding to a high productivity (3.3 molFDCAmolRu–1h–1) compared to those of Ru-based benchmark catalysts in the literature. Moreover, this catalyst was considerably stable during seven reuses.

Bimetallic catalysts NiCo/CNTs with distribution-controlled Ni and Co species were prepared by modified impregnation method with the assistance of dimethylbenzene and characterized by XRD, N2adsorption/desorption, HAADF, TEM, XPS, TPR, and TG. The metal species could be well dispersed in calcined catalyst, and the distribution had profound influences on reducibility, surface property, and particle size. Sintering of active sites and coke deposition were mainly responsible for catalytic deactivation, and the former one played a negative role in promoting a water gas shift reaction. The sample where both Ni and Co were located in CNT caves performed the best in catalytic activity as well as in stability thanks to the confinement effect.

In this work, niobia supported cobalt catalysts with both high cobalt dispersion and high cobalt loading (15 wt %) were prepared through the assistance of glow discharge plasma treatment, and their catalytic performance was tested in Fischer–Tropsch synthesis (FTS). Plasma treatment on support and especially on the decomposition of the catalyst precursor leads to a noticeable enhancement of cobalt dispersion. However, in addition to the cobalt dispersion improvement, plasma assisted decomposition of the cobalt precursor also led to the formation of CoNb2O5, which was inactive in FTS; moreover, the small cobalt particles underwent severe sintering during the reaction and caused significant and contineous deactivation. Plasma treatment on nobia could modify its porosity and hydrophilicity and generate surface functional groups; these features enabled an improved cobalt-niobia interaction and better cobalt dispersion on CoN(P)-C than on CoN-C. The enhanced FTS activity and best reaction stability on the CoN(P)-C catalyst were due to the possession of a suitable cobalt particle size and moderate cobalt-niobia interaction.

Van der Waals (vdW) heterostructures are the fundamental blocks for two-dimensional (2D) electronic and optoelectronic devices. In this work, a high-quality 2D metal–semiconductor NiTe2/MoS2heterostructure is prepared by a two-step chemical vapor deposition (CVD) growth. The back-gated field-effect transistors (FETs) and photodetectors based on the heterostructure show enhanced electronic and optoelectronic performance than that of a pristine MoS2monolayer, owing to the better heterointerface in the former device. Especially, this photodetector based on the metal–semiconductor heterostructure shows 3 orders faster rise time and decay time than that of the pristine MoS2under the same fabrication procedure. The enhancement of electronic behavior and optoelectronic response by the epitaxial growth of metallic vdW layered materials can provide a new method to improve the performance of optoelectronic devices.

The various metals promoted Pt/Sn-SBA-15 catalysts (MPt/SSF, M = Ce, In, La, and Fe) were prepared by a conventional coimpregnation method and then were characterized by N2adsorption/desorption, XRD, XPS, H2-TPR, H2-TPD, CO2-TPD, Raman, and TG techniques. The track of Sn species was not detected by XRD and XPS analysis due to its rather low content and location in the framework of silica. The redox property and the surface composition together with the lattice oxygen capacity of catalysts were significantly affected by the nature of promotors. The results further implied that the lattice oxygen played an important role in determining the initial activity in propane dehydrogenation as a linear relationship was achieved, while the integrated impacts of redox property, antisintering ability, and resistance to coke deposition were responsible for catalytic stability. The sample FePt/SSF showed maximum initial propane conversion of 56.8%, while the InPt/SSF exhibited the best performance during the catalytic stability test.

A new self-propagated flaming (SPF) technique was applied to the synthesis of highly active layered CuO-δ-MnO2hybrid composites, for the de-polluting catalytic total oxidation of gaseous toluene vapor. Other transition metal oxide-doped MnO2hybrid composites were also successfully prepared and investigated, ensuring a feasible strategy for the fabrication of various layered MOx-δ-MnO2(MCo, Ni, or Zn) hybrids. By changing the molar ratio of the precursors (KMnO4and acetate salt) and the type of transition metal oxide introduced, it is possible to control the crystal structure and reducibility of the sheetlike hybrid composites as well as the catalytic activity for the total oxidation of toluene. The catalyst sample (CuO-δ-MnO2) with a Mn/Cu molar ratio of 10:1 exhibited the highest catalytic performance, with a lower reaction temperature of 300 °C for complete toluene removal, which was comparable to the reaction temperature for total toluene conversion by the Pt-based catalyst. The SPF technique provides an approach for developing highly efficient catalysts for the complete removal of volatile organic compounds, by allowing the facile and energy-saving fabrication of large quantities of layered CuO-δ-MnO2hybrids.

A series of Sn-incorporated SBA-15 materials with high specific surface areas and highly ordered mesoporous structures were synthesized by a facile one-pot method and used as catalyst supports. A reference sample was also prepared using a conventional impregnation method. The catalysts were characterized using various methods, and their activities in propane dehydrogenation were investigated. The incorporation of Sn into the SBA-15 matrix led to strong interactions between Sn species and the support, and these helped to maintain the oxidation states of Sn species during the reaction. Substitution with Sn changed the interfacial properties of the Pt species and improved the function and effect of the Sn promoter. The catalytic activities and stabilities of the Pt catalysts supported on Sn-incorporated SBA-15 were better than those of the impregnated sample. However, the catalytic performance deteriorated when an excessive amount of Sn was introduced and the interactions among Pt, Sn species, and the support became weaker. The Pt/0.5Sn-SBA-15 catalyst gave the best propene selectivity, i.e., 98.5%, with a corresponding propane conversion of about 43.8%.

Two type zirconia (monoclinic and tetragonal phase ZrO2) carriers were synthesized via hydrothermal route, and nano-sized zirconia supported nickel catalysts were prepared by incipient impregnation then followed thermal treatment at 300°C to 500°C, for the CO2selective hydrogenation to synthetic natural gas (SNG). The catalysts were characterized by XRD, CO2-TPD-MS, XPS, TPSR (CH4, CO2) techniques. For comparison, the catalyst NZ-W-400 (monoclinic) synthesized in water solvent exhibited a better catalytic activity than the catalyst NZ-M-400 (tetragonal) prepared in methanol solvent. The catalyst NZ-W-400 displayed more H2absorbed sites, more basic sites and a lower temperature of initial CO2activation. Then, the thermal treatment of monoclinic ZrO2supported nickel precursor was manufactured at three temperature of 350, 400, 500°C. The TPSR experiments displayed that there were the lower temperature for CO2activation and initial conversion (185°C) as well as the lower peak temperature of CH4generation (318°C), for the catalyst calcined at 500°C. This sample contained the more basic sites and the higher catalytic activity, evidenced byCO2-TPD-MS and performance measurement. As for the NZ-W-350 sample, which exhibited the less basic sites and the lower catalytic activity, its initial temperature for CO2activation and conversion was higher (214°C) as well as the higher peak temperature of CH4formation (382°C).

Copper-promoted nickel-based metal nanoparticles (NPs) with high dispersion and good thermal stability were derived from layered-double hydroxides (LDHs) precursors that were facilely developed by a co-precipitation strategy. The copper-promoted Ni-based metal NPs catalysts were investigated for methane reforming with carbon dioxide to hydrogen and syngas. A series of characterization techniques including XRD, N2adsorption and desorption, H2-TPR, XPS, CO2-TPD, TEM, TGA and in situ CH4-TPSR were utilized to determine the structure-function relationship for the obtained catalysts. The copper addition accelerated the catalyst reducibility as well as the methane activation, and made the Ni species form smaller NPs during both preparation and reaction by restricting the aggregation. However, with higher copper loading, the derived catalysts were less active during methane reforming with CO2to syngas. It was confirmed that the catalyst with 1wt% Cu additive gave the higher catalytic activity and remained stable during long time reaction with excellent resistance to coking and to sintering. Furthermore, the mean size of metal NPs changed minimally from 6.6 to 7.9nm even after 80h of time on stream at temperature as high as 700°C for this optimized catalyst. Therefore, this high dispersed anti-coking copper-promoted nickel catalyst derived from LDHs precursor could be prospective catalyst candidate for the efficient heterogeneous catalysis of sustainable CO2conversion.

The density functional theory was used to investigate the adsorption of CH4and H2O on different rank coal surfaces. The coal rank is the dominant factor in affecting the adsorption capacity of coal. In order to better understand gas and water interaction with coal of different maturity, we developed fourteen coal models to represent the different rank coal. The interactions of CH4and H2O with coal surfaces were studied and characterized by their adsorption energies, Mulliken charges and electrostatic potential surfaces. The results revealed that the interaction between coal and CH4was weak physical adsorption, and that the interaction between coal and H2O consisted of physical and chemical adsorption. Adsorption energy of coal–H2O system was larger than that of coal–CH4on all rank coals, suggesting that the adsorption priority in the coal models is H2O>CH4. Consequently, the injection of H2O into the different rank coal could effectively enhance the coal bed methane (CBM) recovery.

A series of mixed Keggin-type heteropolysalts Csx(NH4)3−xHPMo11VO40with various ammonia/caesium ratios was prepared by the precipitation method and characterized by TGA, N2adsorption/desorption, XRD, FT-IR, and NH3-TPD techniques. Correlations between the ammonia/caesium ratio and the specific surface area, as well as with the total number of acid sites, were established. Furthermore, the introduction of Cs to the catalytic formulation was beneficial to the stabilization of the Keggin structure and helped limiting the elimination of the V atoms from the primary structure. The as-prepared samples were applied in the catalytic selective oxidation of isobutane at 340 °C under atmospheric pressure. The best results were obtained over Cs1.7(NH4)1.3HPMo11VO40with an isobutane conversion of 9.6% and a total selectivity to valuable products (methacrylic acid and methacrolein) of 57.1%. This was explained by the well-balanced acidity and specific surface of this catalyst, promoting the C–H bond activation (adequate acid properties) over a large number of accessible active sites (high acid sites density).

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have great potential applications in the electronic and optoelectronic devices. Nevertheless, due to the difficulty in the efficient doping of atomic-thickness TMDCs or Fermi level pinning (FLP) effects at the metal/semiconductor interface, most TMDC devices exhibit the n-type conduction polarity, which significantly limits their functional applications based on the p–n junction. Here, 2D semi-metal NiTe2nanosheets were epitaxially grown on the WS2monolayer by a two-step chemical vapor deposition route. The microstructure and optical characterizations confirm that the vertically stacked NiTe2/WS2heterostructures are formed by van der Waals epitaxy. Interestingly, p-type WS2field-effect transistors can be obtained with the hole mobility of ∼4.22 cm2/V·s, when the epitaxial NiTe2sheets act as the source/drain electrodes. This is attributed to the decreased FLP effect and hence the low potential barrier for holes at the van der Waals contacts. Furthermore, the photodetectors based on the heterostructures show a 2 orders of magnitude increase in the switch ratio, responsivity, and detectivity and a 1 order of magnitude increase in the rise and decay speeds relative to those based on pristine WS2. This work paves the way to realize the p-type contact for monolayer WS2with significantly enhanced optoelectronic performance.

The bimetallic CeNi/SiO2catalysts were prepared by impregnation method and characterized by N2adsorption/desorption, XRD, HRTEM, XPS, H2-chemisorption, H2-TPR, NH3-TPD, in situpyridine FT-IR and TG etc.techniques. The results showed that the addition of ceria could help the Ni nanoparticles disperse better through keeping them from aggregating, and generate more abundant oxygen vacancy which further facilitated the reduction of nickel oxides to give more active sites through the interaction between Ce and Ni species. Meanwhile, the bimetallic catalysts involved newly the medium acidic site that was favorable for the formation of desired product γ-valerolactone (GVL) and for the improvement of coke resistance. The synergistic effect in CeNi species boosted the conversion of levulinic acid reach 82.5% with a GVL selectivity of 96.1% on 10Ce10Ni/SiO2sample.

A new, to our knowledge, neodymium-doped lanthanum calcium borate crystal (Nd3+:La2CaB10O19, Nd:LCB) has been grown by the flux method. The spectroscopic parameters for Nd:LCB crystal have also been calculated based on Judd-Ofelt theory. The intensity parameters Omega_t are Omega_2 = 4.96×10^−20 cm², Omega_4 = 3.94×10^−20 cm², and Omega_6 = 3.71×10^−20 cm². The radiative lifetime taur is 349 µs. The absorption band at 800 nm has a FWHM of 12 nm. The absorption cross section is sigmaa = 2.40×10^−20 cm², and the emission cross sections at 1070 nm are sigma_X = 3.02×10^−19 cm², sigma_Y = 2.33×10^−19 cm², and sigma_Z = 2.68×10^−19 cm². The measured fluorescence lifetime tauf is 64 µs, and the quantum efficiency epsilon is 18.3%. In comparison with other Nd-doped laser crystals, the calculated parameters show that Nd:LCB crystal satisfies the fundamental spectral condition for laser emission.