Bimetallic Precursors Research Articles

Enhanced response and selectivity of H2S sensing through controlled Ni doping into ZnO nanorods by using single metal organic precursors

We report on enhancing the selectivity and response of room (23 °C) and high temperature H2S gas sensing through controlled Ni doping (0–10 at%) into ZnO nanorods (NRs) grown with a facile solution growth method using a single hybrid bimetallic metal-organic precursor (nickel/zinc acetylacetonate). The morphology, microstructure, surface chemistry and photoluminescence properties of the as-grown NRs are extensively examined. The gas sensing results are discussed in terms of doping concentration, operating temperature, gas type, gas concentrations and relative humidity. The optimal response toward 100 ppm of H2S reaches 3.1 at 23 °C and increases to 45.3 at 200 °C for 8 at% Ni-doped ZnO NR sensors, where the corresponding response/recovery time at 23 °C and 200 °C also reaches 76/160 and 48/60 s, respectively. The same sensor exhibits high H2S selectivity over other gases, including CH4, CH3OH and C2H5OH. The enhancement of gas sensing is attributed to increasing the number of active sites for adsorption of oxygen and target gases on the surface through incorporation of Ni3+ over Ni2+ ions. At 23 °C, the sensing mechanism is related to the formation of a 7 nm-thick ZnS layer over the NRs through reactions between H2S and adsorbed oxygen.

Magnetoelectrical Transport Improvements of Postgrowth Annealed Iron–Cobalt Nanocomposites: A Possible Route for Future Room-Temperature Spintronics

Focused-electron-beam-induced deposition (FEBID) constitutes a direct-writing maskless technique, which has been employed to prepare nanodots, nanolines, as well as laminar and even three-dimensional nanostructures with potential in many technological fields. Here, we report direct-writing of functional nanostructures with the HFeCo3(CO)12 bimetallic carbonyl precursor. The metal content as well as the magnetotransport properties of Fe–Co–C–O deposits were reproducibly tuned upon ex situ postgrowth annealing at 100, 200, and 300 °C in a high-vacuum system. The atomic composition obtained by energy-dispersive X-ray spectroscopy (EDX) analysis revealed that carbonyl groups release during annealing, although principally sole oxygen is released from the deposits, yielding an atomic ratio of Co:Fe:C:O = 52:17:22:9 with respect to the atomic composition of as-grown Co:Fe:C:O = 41:13:26:20. Interestingly, the amorphous carbon contained in the as-grown material turns into graphite nanocrystals with an average size of around 11 nm with annealing at moderate temperatures, as suggested by Raman analysis. These compositional and microstructural changes permit tuning the deposits’ electrical resistivity over 2 orders of magnitude from 4200 down to 65 μΩ cm. The anisotropic magnetoresistance (AMR) of the annealed deposits is about 1.2%, which represents the highest value so far reported for FEBID-grown materials. In addition, as a key feature for technological applications of the postgrowth treatment presented herein, the magnetotransport properties of the nanosized FEBID material degrade minimally after being stored at ambient conditions for more than one year. It turns out that both the iron and cobalt are protected from being oxidized under ambient atmosphere by the graphitic matrix. Furthermore, the incorporation of carbon atoms in ferromagnetic films allows for consistent improvements in their magnetic coercivity and reversing fields. This makes our material especially interesting and advantageous for applications in high-density magnetic recording devices, nanoelectronics, nanoelectromechanical system-based (NEMS-based) sensors, and logic devices.

Determination of redox pathways of supported bimetallic oxygen carriers in a methane fuelled chemical looping combustion system

The incipient wetness impregnation technique was used to synthesize supported bimetallic precursors (Ni and Co, Cu or Fe) by Al2O3, CeO2, TiO2 and ZrO2 in order to understand both oxidation and reduction reactions (redox) pathways during the methane chemical looping combustion (CH4-CLC). Understanding the reaction pathways helps to enable proper modifications of oxygen carriers, which later assists in choosing chemically stable precursors that could enhance the overall redox reaction rates. A higher solid conversion rate and fewer interactions with supports will produce highly reactive and thermally stable oxygen carriers. The BET surface area results showed highest increase in Ni-Fe/ZrO2 sample by 17.73% and highest decrease in Ni-Fe/CeO2 sample by 78.80%. The internal mass transfer results revealed that the reaction and internal diffusion for Ni-Fe/TiO2 and Ni-Fe/ZrO2 samples were similar; however, the effectiveness factor of the Ni-Cu/TiO2 sample showed isothermal surface reaction was the controlling step. Under the operating condition presented in this study (oxidation with air at 20 ml/min, and reduction with CH4 balanced with N2 at 20 ml/min), most stable samples for CLC practical deployment were Ni-Co/ZrO2, Ni-Cu/ZrO2, and Ni-Fe/ZrO2 due to their exhibition of stable oxygen transport capabilities, and nonexistence of interaction between precursors and supports.

Construction of Ni-Co-Mn layered double hydroxide nanoflakes assembled hollow nanocages from bimetallic imidazolate frameworks for supercapacitors

Layered double hydroxides (LDHs) with 3-dimentional (3D) hollow nanoarchitetures are highly desirable for energy related applications. In this study, Ni-Co-Mn LDH nanoflakes assembled hollow nanocages are constructed from bimetallic imidazolate framworks precursors. Benefiting from the 3D hierarchical porous strcuture and composition, the as-synthesized ternary Ni-Co-Mn LDH hollow nanocage, as a electrode for supercapacitor, demonstrates a remarkable electrochemical performance with a high specific capacitance of 2012.5 F g−1 at 1 A g−1 and a good rate capacity of 75.0% retention at 10 A g−1, significantly outperforming binary Ni-Co LDH (1266.2 F g−1 at 1 A g−1, 41.8% retention at 10 A g−1). This work demonstrates the construction of 3D hollow nanostructured LDH with multicomponent compositions for the first time, and can be simply extended to construct other hollow structured electrode materials for energy storage devices.

Solution state fluxionality and thermolysis reactions of bimetallic single source precursors for I-III-VI chalcopyrite materials

Complexes of the type (PPh3)2M(μ-SEt)2E(SEt)2 (M = Cu, Ag; E = Al, Ga, In) are effective and versatile molecular precursors for bimetallic and mixed MES2 chalcopyrite nanomaterials. In solution at room temperature, these compounds exhibit spectroscopic characteristics inconsistent with their cyclic solid state structures, and variable temperature NMR investigations in this report show that this discrepancy is a result of rapid exchange of thiolate groups between bridging and terminal positions. These experiments show that the exchange is unimolecular and does not involve phosphine dissociation or free thiol. Exchange rates are not strongly affected by thiolate electronic properties or the identity of E, but are significantly slower for more sterically demanding phosphine and thiolate ligands. Data are consistent with a simple turnstyle exchange mechanism involving dissociation of one bridging thiolate ligand from M, although crossover studies suggest that full ionic dissociation (into [(PPh3)2M][E(SEt)4]) is also facile, and that dissociation into neutral fragments (PPh3)2MSEt + E(SEt)3 may proceed at higher temperatures. Additional investigation of the solution state thermolyses of the same complexes demonstrates that the processes above do not correlate to their decomposition behavior, as thermal sensitivity is most strongly effected by thiolate electronic properties, and likely depends most strongly on cleavage of CS bonds.

Study on catalytic performance of oil-soluble iron-nickel bimetallic catalyst in coal/oil co-processing

The oil-soluble iron-nickel bimetallic catalyst precursor was synthesized for the application of coal/oil co-processing. The catalyst precursor and its sulfurized product were characterized by FTIR, TG, XRD, and TEM. And the catalytic performance of this catalyst precursor in the coal/oil co-processing system was investigated and compared with the molybdenum naphthenate. The results showed that the average particle size of the synthesized catalyst precursor after sulfurization was about 40 nm, containing (Fe, Ni)9S8 mixed crystal, and the crystallinity was low with rough edge and large specific surface area. The synthesized catalyst precursor showed better hydrogenation activity compared with the relatively expensive molybdenum naphthenate catalyst. Under the experimental conditions, the yield of coke was only 2.9 wt%, the I value was 6.47, and the conversion yield of dry ash-free coal reached to 90.7 wt%. Characterization and analysis of the coke after reaction further confirmed that the synthesized catalyst precursor could promote the conversion of coal and showed potential application value in coal/oil co-processing.

Electron interactions with the heteronuclear carbonyl precursor H2FeRu3(CO)13 and comparison with HFeCo3(CO)12: from fundamental gas phase and surface science studies to focused electron beam induced deposition.

In the current contribution we present a comprehensive study on the heteronuclear carbonyl complex H2FeRu3(CO)13 covering its low energy electron induced fragmentation in the gas phase through dissociative electron attachment (DEA) and dissociative ionization (DI), its decomposition when adsorbed on a surface under controlled ultrahigh vacuum (UHV) conditions and exposed to irradiation with 500 eV electrons, and its performance in focused electron beam induced deposition (FEBID) at room temperature under HV conditions. The performance of this precursor in FEBID is poor, resulting in maximum metal content of 26 atom % under optimized conditions. Furthermore, the Ru/Fe ratio in the FEBID deposit (≈3.5) is higher than the 3:1 ratio predicted. This is somewhat surprising as in recent FEBID studies on a structurally similar bimetallic precursor, HFeCo3(CO)12, metal contents of about 80 atom % is achievable on a routine basis and the deposits are found to maintain the initial Co/Fe ratio. Low temperature (≈213 K) surface science studies on thin films of H2FeRu3(CO)13 demonstrate that electron stimulated decomposition leads to significant CO desorption (average of 8–9 CO groups per molecule) to form partially decarbonylated intermediates. However, once formed these intermediates are largely unaffected by either further electron irradiation or annealing to room temperature, with a predicted metal content similar to what is observed in FEBID. Furthermore, gas phase experiments indicate formation of Fe(CO)4 from H2FeRu3(CO)13 upon low energy electron interaction. This fragment could desorb at room temperature under high vacuum conditions, which may explain the slight increase in the Ru/Fe ratio of deposits in FEBID. With the combination of gas phase experiments, surface science studies and actual FEBID experiments, we can offer new insights into the low energy electron induced decomposition of this precursor and how this is reflected in the relatively poor performance of H2FeRu3(CO)13 as compared to the structurally similar HFeCo3(CO)12.

Electron Induced Surface Reactions of HFeCo3(CO)12, a Bimetallic Precursor for Focused Electron Beam Induced Deposition (FEBID)

The use of bimetallic precursors in focused electron beam induced deposition (FEBID) allows mixed metal nanostructures with well-defined metal ratios to be generated in a single step process. HFeCo3(CO)12 is an example of one such bimetallic precursor that has previously been shown to form deposits with unusually high metal content (>80%) as compared to that of typical FEBID deposits (<30% metal content). To better understand the elementary bond breaking steps involved in FEBID of HFeCo3(CO)12, we have employed a UHV surface science approach to study the effect of electron irradiation on nanometer thick films of HFeCo3(CO)12 molecules. Using a combination of in situ X-ray photoelectron spectroscopy and mass spectrometry, we observed that the initial step of electron induced HFeCo3(CO)12 dissociation is accompanied by desorption of ∼75% of the CO ligands from the precursor. A comparison with recent gas phase studies of HFeCo3(CO)12 indicates that this process is consistent with a dissociative ionization pr...

Hollow porous zinc cobaltate nanocubes photocatalyst derived from bimetallic zeolitic imidazolate frameworks towards enhanced gaseous toluene degradation

Aiming at promoting the photocatalytic performance of spinel oxides, an efficient method of constructing hollow porous zinc cobaltate (ZnxCo3−xO4) nanocubes was established in this work. Bimetallic zeolitic imidazolate frameworks (ZIFs) were prepared through a facile self-assembly strategy, then hollow ZnxCo3−xO4 nanocubes were obtained by calcining the bimetallic ZIFs precursor. The structural features and optical properties of the ZnxCo3−xO4 nanocubes were comprehensively investigated by a series of characterization techniques. With higher specific surface area (about 100 m2 g−1), enhanced light absorbance in the whole range of 350–800 nm and lowered recombination of photogenerated electron-hole pairs, these hollow nanocubes demonstrated attractive photocatalytic activity in degrading gaseous toluene, superior to traditional stoichiometric ZnCo2O4 nanoparticles. The photocatalytic process and related mechanism of toluene degradation were further investigated with in situ Fourier transform infrared (FTIR) spectroscopy and electron paramagnetic resonance (EPR) techniques. Photo-induced O2− and holes were assigned as main reactive species in the photocatalytic system with hollow ZnxCo3−xO4 nanocubes.

Low energy electron-induced decomposition of (η5-Cp)Fe(CO)2Mn(CO)5, a potential bimetallic precursor for focused electron beam induced deposition of alloy structures.

The production of alloyed nanostructures presents a unique problem in focused electron beam induced deposition (FEBID). Deposition of such structures has historically involved the mixing of two or more precursor gases in situ or via multiple channel gas injection systems, thereby making the production of precise, reproducible alloy compositions difficult. Promising recent efforts to address this problem have involved the use of multi-centred, heterometallic FEBID precursor species. In this vein, we present here a study of low-energy electron interactions with cyclopentadienyl iron dicarbonyl manganese pentacarbonyl ((η5-Cp)Fe(CO)2Mn(CO)5), a bimetallic species with a polyhapto ligand (Cp) and seven terminal carbonyl ligands. Gas phase studies and coupled cluster calculations of observed low-energy electron-induced reactions were conducted in order to predict the performance of this precursor in FEBID. In dissociative electron attachment, we find single CO loss and cleavage of the Fe-Mn bond, leading to the formation of [Mn(CO)5]-, to be the two dominant channels. Contributions through further CO loss from the intact core and the formation of [Mn(CO)4]- are minor channels. In dissociative ionization (DI), the fragmentation is significantly more extensive and the DI spectra are dominated by fragments formed through the loss of 5 and 6 CO ligands, and fragments formed through cleavage of the Fe-Mn bond accompanied by substantial CO loss. The gas phase fragmentation channels observed are discussed in relation to the underlying processes and their energetics, and in context to related surface studies and the likely performance of this precursor in FEBID.

Effective Oxygen Reduction and Evolution Catalysts Derived from Metal Organic Frameworks by Optimizing Active Sites

Electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are core materials in many renewable energy technologies including fuel cells, metal-air batteries, and water splitting devices. However, the high cost of the catalysts such as platinum and iridium oxide severely hinders the commercial development of these devices. Herein, we report a simple method for synthesizing effective bifunctional oxygen reduction and oxygen evolution catalysts through the rationally design of bimetallic metal organic framework precursor. The ratio of Zn and Co was optimized to search the critical factors affecting the catalysis of the ORR and OER. We found that for ORR catalysis, both Co/Co9S8 species and heteroatom-doped porous carbons played important roles. In contrast, the Co/Co9S8 species play more important role in OER catalysis. The optimized catalyst NSC-1-5 showed excellent ORR performance, with an onset potential of 0.879 V and a half wave potential of 0.81 V, as well as good OER catalytic activity. This was achieved simply by controlling the ratio of Co and Zn in the precursor, and NSC-1-5 could serve as a bifunctional catalyst for both ORR and OER. This work could shed some light on the design of bifunctional catalyst for both ORR and OER.

Hydrogenation of Polymeric Petroleum Resins in the Presence of Unsupported Sulfide Nanocatalysts

Unsupported Ni–Mo and Ni–W sulfide catalysts for the hydrogenation of polymeric petroleum resins are ex situ in a hydrocarbon solvent by the decomposition of oil-soluble bimetallic precursors. It is shown that the activity of the nanocatalysts is higher than that of conventional supported catalysts. The Mo: Ni ratio (1.5: 1) provides the maximum conversion of aromatic and unsaturated moieties of the substrate molecule. It is found that an increase in the process temperature and pressure leads to intensification of polymer chain degradation reactions. The highest degree of hydrogenation is achieved in polymeric petroleum resin solutions with a concentration of 40 wt %; further increase in concentration contributes to the inhibition of thermal degradation reactions. It is shown that the catalyst can be reused without any loss of activity; in addition, the degree of sulfiding of the active phase remains unchanged and the particles do not undergo agglomeration.

Highly Stable and Recyclable Graphene Layers Protected Nickel–Cobalt Bimetallic Nanoparticles as Tunable Hydrotreating Catalysts for Phenylpropane Linkages in Lignin

Nickel–cobalt bimetallic nanoparticles coated with several layers of graphene were developed through direct heating treatment of bimetallic oxide precursor prepared by the modified Pechini-type sol–gel method. These nanomaterials were demonstrated to be versatile catalysts for lignin depolymerization. The catalysts showed unexpectedly tunable selectivity that directly depends on the composition of bimetallic nanoparticles. Dimeric lignin model compounds can be converted totally and the hydrogenolysis selectivities above 85% over Ni–Co@C (Ni:Co = 1:3). During the recycling test, the nanocatalyst showed excellent recyclability in the ten-batch investigation. The deposition of graphene layers over bimetal nanoparticles fosters a subtle balance between protecting effects and surface accessibility to catalytic reactions and significantly improves their stability to air and moisture. Ni–Co@C catalysts were readily separated from the liquid mixtures with high recycling ratio due to their magnetic properties. Ni–Co bimetallic nanoparticles are coated with graphene layers. Graphene layers over the nanoparticles protect them from deactivation. Ni–Co@C shows tunable selectivity in the hydrogenolysis of dimeric lignin linkage. The non-precious metal catalyst showed excellent recyclability and can be reused ten times without significant loss of activity.

Preparation of electrochemically reduced graphene oxide-based silver-cobalt alloy nanocatalysts for efficient oxygen reduction reaction

The synthesis and performance of electrochemically reduced graphene oxide-based silver-cobalt (AgCo/ERGO) alloy electrocatalysts for the oxygen reduction reaction (ORR) are discussed in this study. The surface morphology, alloying nature, and chemical changes of the bimetallic precursors within the AgCo/ERGO catalyst has examined in detail. The presence of poly(ethylene glycol) (PEG) and a cobalt precursor during the electroreduction step is a necessary condition for synthesizing a highly active and stable alloy electrocatalyst for the ORR. Morphological analysis demonstrated that the AgCo nanoparticles (NPs) are homogeneously dispersed on the ERGO support with the assistance of PEG, thus resulting in higher electrochemical surface area and mass activity. X-ray analysis also confirmed the successful formation of the AgCo alloy NPs and the electrochemical reduction of graphene. The direct four-electron transfer pathway for ORR with minimal H2O2 yield has committed at the AgCo/ERGO catalyst over other catalysts. The as-prepared AgCo/ERGO catalyst has shown better electrocatalytic activity, stability, and tolerance to crossover effects compared to the state-of-the-art Pt/C catalyst for ORR.

Direct observations of dynamic PtCo interactions in fuel cell catalyst precursors at the atomic level using E(S)TEM.

Reduction reactions in practical bimetallic platinum-cobalt electrode catalyst precursors containing platinum, cobalt and cobalt oxides in hydrogen at 200, 450 and 700 °C for 6 h have been studied in situ using an aberration corrected environmental (scanning) transmission electron microscope (AC E(S)TEM). Little difference was observed in reduction at 200 °C but during and after reduction at 450 °C, small nanoparticles less than 3 nm in diameter with tetragonal PtCo structures were observed and limited Pt3 Co ordering could be seen on the surfaces of larger nanoparticles. During and after reduction at 700 °C, fully ordered Pt3 Co and PtCo nanoparticles larger than 4 nm were produced and the average nanoparticle size almost trebled relative to the fresh precursor. After reduction at 450 and 700 °C, most nanoparticles were disordered platinum/cobalt alloys with fcc structure. After reduction at 700 °C many of the smallest nanoparticles disappeared suggesting Ostwald ripening had occurred. Mechanisms concerning the thermal transformation of mixed cobalt and platinum species are discussed, offering new insights into the creation of bimetallic platinum-cobalt nanoparticles in fuel cell catalysts.

Nickel–molybdenum and cobalt–molybdenum sulfide hydrogenation and hydrodesulphurization catalysts synthesized in situ from bimetallic precursors

Unsupported nickel–molybdenum and cobalt–molybdenum sulfide catalysts are synthesized via the in situ decomposition of water-soluble bimetallic precursors in a hydrocarbon feedstock using nickel–molybdenum and cobalt–molybdenum complexes with citric, oxalic, succinic, glutaric, and tartaric acids as precursors. The sulfide catalysts are characterized by means of transmission electron microscopy and X-ray photoelectron spectroscopy. The catalyst activity in the hydrogenation of bicyclic aromatic hydrocarbons and the hydrodesulfurization of dibenzothiophene is studied. The effect the composition of the precursor solution in the hydrocarbon feedstock emulsion has on the activity of the resulting catalyst is determined. It is shown that the activity reaches high values even after 1 h of reaction. The hydrogenation of mono-, di-, and trimethylnaphthalenes and ethylnaphthalene is studied. The optimum promoter-to-molybdenum ratio (0.25: 1) is found. It is shown that the catalyst activity does not fall during recycling, due to the elimination of the negative effect of water contained in the emulsion, which results in oxidation of the catalyst surface. After the second reaction cycle, the catalyst particles are longer and have a greater number of MoS2 layers than the respective parameters of the catalyst particles after the first cycle. XPS shows that the content of oxygen on the catalyst’s surface falls during recycling, while the fraction of metals in the sulfide environment and the sulfur in the sulfide state grows.

Single-phase mixed molybdenum-niobium carbides: Synthesis, characterization and multifunctional catalytic behavior in toluene conversion

Single-phase mixed molybdenum-niobium carbides were synthesized to establish structure–activity relationships. Precursors for carburization were obtained by hydrothermal synthesis or, to achieve high molybdenum content (metal fraction xMo=0.86), by flash-freezing of salt solutions and subsequent freeze-drying. Thermogravimetric and evolved gas analysis during carburization showed that bimetallic precursors were more easily reduced than monometallic ones; and as the niobium content increased, the removal of oxygen shifted to higher temperatures and from H2O to CO formation (from H2 or CH4, respectively), and the final carburization temperature rose from 650 to 950°C. Carbides crystallized in cubic NbC/MoC(cF8) structure for xNb≥0.38 and hexagonal Mo2C(hP3) structure for xNb≤0.14. After passivation, mixed metal carbides could be reduced at lower temperatures than Mo2C. With increasing molybdenum content of the carbides, CO uptake per gram increased, and turnover frequencies for hydrogenation of toluene to methylcyclohexane increased from 0 to 3.1s−1 (at a temperature of 250°C, 21bar pressure, and H2/toluene=36). At 400°C, mixed carbides with xNb≥0.38 were more selective toward acid-catalyzed products and less selective toward hydrogenolysis products than carbides with lower niobium content.

Engineering Ultrathin Co(OH)2 Nanosheets on Dandelion–like CuCo2O4 Microspheres for Binder‐Free Supercapacitors

AbstractA stepwise synthetic approach is developed for large‐scale growth of three‐dimensional branched CuCo2O4@Co(OH)2 core−shell structures on nickel foam as a high‐performance supercapacitor electrode. The synthesis procedure involves the hydrothermal treatment of a bimetallic (Cu, Co) hydroxide precursor on a Ni foam substrate and subsequent thermal transformation to dandelion‐like CuCo2O4 microspheres. The Co(OH)2 shells are then coated onto the branches of as‐prepared CuCo2O4 microspheres by using an electrodeposition method. The loading of Co(OH)2 nanosheets is dependent on the electrodeposition time in Co(NO3)2 solution. The resulting unique core−shell structure promotes fast electron and ion transport, large electroactive surface area, and excellent structural stability. As a result, superior electrochemical performance is achieved with a specific capacitance of 424 F g−1 at a current density of 0.5 A g −1, and good cycling performance (85.8 % retention after 10000 cycles), suggesting its promising application in supercapacitors. These good electrochemical properties could be attributed to the synergic interaction of each component. In addition, the asymmetric supercapacitor exhibits an energy density of 19.2 Wh kg−1 at a power density of 350 W kg−1.

A sensitive bisphenol A voltammetric sensor relying on AuPd nanoparticles/graphene composites modified glassy carbon electrode

In this work, a sensitive bisphenol A (BPA) electrochemical sensor was assembled using a surfactant-free AuPd nanoparticles-loaded graphene nanosheets (AuPdNPs/GNs) modified electrode. The AuPdNPs monodispersed on GNs were successfully prepared by the spontaneous redox reaction between bimetallic precursors and GNs. Because no surfactant or halide ions were involved in the proposed synthesis, the prepared composite was enabled to directly modify a glassy carbon electrode without any pre-treatments. Moreover, due to the synergetic effect of Au and Pd, AuPdNPs/GNs displayed high electrochemical activity with well-defined voltammetric peaks of BPA oxidation and lower overpotential compared with monometallic PdNPs and AuNPs supported GNs. According to the results of differential pulse voltammetry (DPV), under optimized conditions, a good linear response was observed for the concentration of BPA in the range of 0.05–10μM with a detection limit of 8nM. The developed electrochemical sensor was successfully applied to determine BPA in food package. This study indicated that AuPdNPs/GNs based electrochemical sensor can be a promising and reliable tool for rapid analysis of emergency pollution affairs of BPA.

Towards Understanding Structure–Activity Relationships of Ni–Mo–W Sulfide Hydrotreating Catalysts

AbstractThe relation between activity and selectivity of a series of unsupported Ni–Mo, Ni–W, and Ni–Mo–W sulfides and the physicochemical properties of the sulfides and oxide precursors were explored. Bimetallic oxide precursors were a crystalline molybdate with layered structure ((NH4)HNi2(OH)2(MoO4)2) or a wolframite‐type nickel tungstate (NiWO4). Trimetallic precursors were mixed Mo–W–Ni phases appearing amorphous in XRD analysis, in which metal cations had environments similar to those in the bimetallic precursors. The XRD‐amorphous layered structure (obtained for a Ni–Mo–W precursor) led to the fastest sulfidation of Ni cations. The proximity of metal cations in precursors was retained after sulfidation, which lead to intralayer mixed Mo1−xWxS2 (in trimetallic materials) and varying concentrations of Ni at the perimeter of the Mo(W)S2 slabs. At MoS2 and WS2 edges, Ni has a square‐pyramidal coordination, which is significantly distorted at the Mo–W mixed edges. The catalyst with the lowest Mo/W–Ni coordination had the lowest rates for hydrodenitrogenation of o‐propylaniline and hydrodesulfurization of dibenzothiophene. Among the materials with significant Ni–Mo(W) coordinations, the most active sulfide catalyst at low temperatures was Ni–W with highly defective slabs, at high temperatures the Ni–Mo–W sulfide with the highest Ni concentration at the perimeter was the most active catalyst.