查看更多>>摘要：Methanol is a suitable raw material for in situ hydrogen generation by steam reforming that enables the safe storage and transportation of hydrogen. Pt-based catalysts have been considered promising and effective for methanol steam reforming but suffer from deactivation by metal sintering. In this study, we developed an efficient K-modified Pt catalyst confined within silicate-1 zeolite with a high activity and unprecedented stability for methanol steam reforming. Owing to the confinement effect, the K-promoted Pt@S-1 catalyst remained stable for more than 50 h. The combination of TPSR-MS and DFT calculations revealed that the Pt-K@S-1 catalyst exhibited a synergistic effect between the Pt~0 and Pt~(δ+) species. The cleavage of the O-H bond in CH3OH was activated over Pt~0 sites to produce HCOOCH3, whereas Pt~(δ+) sites promoted the hydrolysis of HCOOCH3 to HCOOH and ultimately CO2 and H2, thus suppressing the formation of CO and boosting H2 production.
查看更多>>摘要：An alternative reduction route of Pd-promoted Co3O4 supported on SBA-15 under ethanol dehydrogenation and decomposition (ED) was studied by an operando time-resolved X-ray absorption spectroscopy (TR-XAS) to understand the insight nature of materials. The catalysts, xPd-10Co/SBA-15, were prepared by co-impregnation method where the Pd content, x = 0.2, 0.5 or 1.0 wt% and Co content = 10.0 wt%. The precursors were transformed to PdO and Co3O4 after calcination and to metallic form after reduction. The reducibility of Co3O4 to metallic Co in 1Pd-10Co/SBA-15 was 98.0%, whereas the metallic form was not produced in the absence of Pd. This catalyst also provided the highest H2 yield of 80% from ED at 500 °C. The ED-reduced 1Pd-10Co/SBA-15 was tested in reverse water gas shift reaction (RWGS) and characterized by the operando TR-XAS. The CO selectivity from CO2 was 97.8%, slightly higher than conventional H2-reduced 1Pd-10Co/SBA-15.
查看更多>>摘要：The preparation of transition metal oxides based on traditional hydrothermal and calcination processes for heterogeneous PMS activation in contaminants' abatement has been widely reported. A satisfactory PMS activation efficiency often demands the transition metal oxides with crystallographic structure; however, the preparation processes of crystalline metal oxides require more energy input. Besides, achieving the targeted electron transfer between pollutants and reactive oxygen species (ROS) to overcome the disturbance of the actual water matrix is still challenging. Herein, we immobilized manganese oxides onto polymeric substrates under room temperature by a novel redox method with lower energy consumption. The obtained composite was applied for PMS activation to degrade multiple phenolic pollutants mainly through non-radical pathways. Combining the results of multiple characterizations and 180 isotope-tracer experiments, we proposed that the interfacial high-spin ≡Mn~III-peroxy complex was the primary reactive oxidant. Besides, a small portion of ≡Mn~III-peroxy complex could further undergo interspecies oxygen-transfer to form ≡Mn~V-oxo species as the secondary reactive oxidant, resulting in the different manganese reduction products (≡Mn~III/Mn~IV). The proposed mechanism could explain the average oxidation state of Mn changed after PMS activation. Comparing with the radical-based systems, interfacial reactive manganese intermediates exhibited satisfactory resistance against complex water matrices, such as chloride, bicarbonate, natural organic matter (NOM), and effluent organic matter (EfOM). We believe that this study could inspire novel methods with lower energy consumption to prepare active manganese oxides and provide intriguing mechanistic insights into PMS activation mediated by amorphous manganese oxides.
查看更多>>摘要：Utilizing mechanochemical interactions to fabricate hybrid catalysts composed of two or more materials is an important emerging area in heterogeneous catalysis. Here, we report unusual deactivation of vanadia catalyst derived from mechanical grinding with Al-rich zeolite, initially designed to overcome the ammonium bisulfate poisoning in low-temperature selective catalytic reduction (SCR) of NO_x. Various characterizations reveal that mechanical force applied to zeolite imparts mobility to extra-framework AlO_x moieties. Some of the diffused AlO_x species bound to VO_x sites lower reducibility of catalyst, degrading its initial performance. These phenomena are effectively resolved by novel strategy of covering the surface of zeolite with a thin carbon layer, suppressing the diffusion of AlO_x moieties during grinding. The hybrid catalyst prepared by tailoring mechanochemical interaction demonstrates superior sulfur resistance in low-temperature (180 °C) SCR operation. Our study critically describes effects of mechanical forces on catalytic properties and efficient modulation of these interactions through surface functionalization.
查看更多>>摘要：Electrocatalytic N2 fixation represents an energy-efficient and long-term sustainable approach, which can convert N2 to NO_3~- or NH3 via the electrochemical N2 oxidation reaction (NOR) or N2 reduction reaction (NRR). However, the inert N2 molecule, low activity of electrocatalysts, and predisposed competitive reactions result in the poor yields and Faradaic efficiencies of N2 fixation reactions, which greatly restrict the application of such green synthesis technology. In this work, a molecular-level post-modification strategy has been explored to integrate diverse alkyl chains on a ferriporphyrin-based metal-organic framework (MOF) PCN-222(Fe), which provides adjustable hydrophobicity and highly dispersed active sites. The increased lengths of alkyl groups can gradually improve the hydrophobicity of decorated MOFs, which effectively suppress the competitive reactions and boost the electrocatalytic NOR and NRR performances. Significantly, the highest Faradaic efficiency of 70.7% so far and a state-of-the-art NO_3~- yield of 110.9 μg h~(-1) mg_(cat.)~(-1) can be achieved for NOR, which are attributed to the synergistic effect of FeN4 active sites, high porosity, and strong hydrophobicity for n-octade-cylphosphonic acid (OPA) decorated PCN-222(Fe).
查看更多>>摘要：Realizing large-scale production of low-cost bifunctional catalysts is pivotal to promoting the practical application of Zn-air batteries. Herein, we successfully constructed unique bifunctional CoN3 catalytic sites atomically dispersed on N-doped graphitic carbon nanosheets (CoSA/NCs), which enable Zn-air batteries with ultrahigh durability for over 6000 cycles (～ 2000 h). The 2D carbon construction and single-atom Co formation were achieved simultaneously in salt-assisted process employing CoCl2. CoCl2 serves as a recyclable template, a pore-making agent, and a catalyst for graphitization, which effectively enables the catalyst with abundant active sites catalyze ORR and OER. Our experimental and theoretical modeling results confirm that of CoN3 surpasses CoN4 in term of the ORR and OER catalytic activity. The Zn-air battery based on CoSA/NCs catalyst exhibits a high peak power density of 255 mW cm~(-2). With unparalleled catalytic performance and low production cost, this catalyst paves the way for the potential large-scale application of Zn-air batteries.
查看更多>>摘要：Photocatalytic H2O2 production from H2O and O2 is a sustainable alternative to the present anthraquinone process, but most available systems need sacrificial reagents to maintain continuous activity. In this work, BiPO4 photocatalyst is reported to produce H2O2 efficiently from non-sacrificial systems. The photocatalyst exhibits H2O2 production activity as high as 12.0 mM/h/g and negligible decay for 40 cycles (ca. 200 h) with only H2O and O2. The photocatalyst is demonstrated to show a core-shell structure. The monoctinic BiPO4 core exhibits a wide bandgap of 3.85 eV, supplying sufficient driven force for photogenerated e~- and h~+ to produce H2O2. More importantly, instinct hydrate voids in coated hexagonal BiPO4 cause strong adsorption with H2O and O2 rather than H2O2 via the steric hindrance effect, which facilitates the diffusion of H2O2 away from the active photocatalyst surface, avoiding its overreaction. The findings may help to design more efficient and stable photo-catalysts for H2O2 production in the future.
查看更多>>摘要：Much work has focused on metal chalcogenides as photocatalysts for water splitting. Herein ZnIn2S4 (ZIS) has been deposited with 10 wt% CoWO4, followed by mixing with 3 wt% Co3O4. Reaction was conducted under a 420 nm LED lamp in the presence of triethanolamine (TEOA). In terms of the amounts of H2 evolved at 2 h (n_(H2h)), Co3O4/CoWO4/ZIS, Co3O4/ZIS, and CoWO4/ZIS were more active than ZIS, respectively, by factors of approximately 9.2, 7.0, and 2.5. In addition, Co3O4/CoWO4/ZIS was more photostable than ZIS. The trend for the n_(H2h) not only coincided widi those for proton reduction and water (TEOA) oxidation on a dark electrode, respectively, but also matched the reduced emission intensity of the solid in ambient air. However, for water oxidation on a photoanode, Co3O4/ZIS was less active than CoWO4/ZIS. Then the larger n_(H2h) of Co3O4/ZIS than CoWO4/ZIS is due to Co3O4 being more active than CoWO4 for catalyzing proton reduction. Based on the solid band edge potentials, a possible mechanism is discussed. The photoholes of ZIS recombine with the photoelectrons of Co3O4 (CoWO4), improving the efficiency of charge separation, and hence increasing the rates of proton reduction on ZIS and TEOA oxidation on Co3O4 (CoWO4), respectively. Because of the combined Z-scheme pathways, Co3O4/CoWO4/ZIS is more photoactive than others.
查看更多>>摘要：Polyacrylonitrile (PAN) has slow surface dynamics due to its low electron transport capacity, which greatly limits its application in the extraction of uranium (U(VI)) from seawater. Here, we propose a local conjugation domain (LCD) structure between adjacent microdomains of cyclized polyacrylonitrile (CPAN) with different conjugation structures. This structure uses the potential difference between different degrees of conjugate domains to form a built-in field that promotes charge separation. Cyclized polyacrylonitrile amideoxime (CPAO) formed by hydrolyzing the cyano groups that are not involved in conjugation in CPAN can better capture the U(VI) in seawater. After floating in marine for 30 days, the U(VI) extraction capacity of CPAO can reach 5.2 mg g~(-1), which is 3 times that of PAO. This LCD strategy can be extended to other conjugated high-molecular polymers, thereby it is proposed as a general method for rational design of efficient seawater U(VI) extraction materials.
查看更多>>摘要：Herein, a hybrid nanowire-nanosheet structure made of the cerium oxide and nickel-cobalt phosphide (CeO2-NiCoP_x) compound is in situ engineered on the Ni-Co foam (CeO2-NiCoP_x/NCF) for the robust water splitting (HER and OER), and the overpotentials of synthesized CeO2-NiCoP_x/NCF are about 39 mV for HER and 260 mV for OER at a current density of 10 mA cm~(-2) (j_(10)). Meanwhile, the nanostructure of Ceo2-NiCoP_x is well preserved after a long-term electrocatalytic process (100 h) at a large current density of 100 mA cm~(-2) (j_(100)). When the CeO2-NiCoP_x/NCF simultaneously acts as the HER and OER electrodes, the potential of 1.49 V is obtained for transferring j_(10) with an excellent durability. Theoretical simulations and in operando Raman spectroscopy reveal that the Co and Ni atoms for CeO2-NiCoP_x/NCF catalyst are likely to act as the pivotal reaction centers for HER and OER processes, respectively.
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