Simultaneous Ni Doping at Atom Scale in Ceria and Assembling into Well-Defined Lotuslike Structure for Enhanced Catalytic Performance

POM-promoted synergistic catalysis of NO and chlorobenzene over amorphous MnCeOx catalysts: Activation of lattice oxygen, role of acid site, catalytic mechanism

The release rate of lattice oxygen and surface acidic sites are key factors for the multi-pollutant synergistic catalysis such as nitrogen oxides (NOx) and chlorine-containing volatile organic compounds (Cl-VOCs). In this study, a polyoxometalate (POM)-assisted strategy was employed to optimize the synergistic catalytic performance of MnCeOx for NO and chlorobenzene. The strong proton conductivity of the surface POM structure effectively suppresses the deposition of chlorinated species, preventing the poisoning of active sites. Specifically, POM-SiW structure can act as a dechlorination site in place of Mn3O4 and exhibits the highest density of acidic sites and oxygen vacancies, leading to a reduction of the T90 for chlorobenzene to 167 ℃ and an expansion. The assistance of POM-SiW structure facilitates the electron transfer from POM-SiW to lattice oxygen (Olat), resulting in reduced orbital overlap between Mn and O atoms, thereby weakening the Mn-O bond and activating Olat. Furthermore, in-situ DRIFTs, TOF-SIMS and DFT results confirmed that POM-SiW structure can inhibit the competitive adsorption of NO, NH3 and chlorobenzene, NO2 and NH4+ act as additional oxidants and dechlorinating agents, effectively promoting the catalytic decomposition of chlorobenzene and its intermediate products. This work provides a novel strategy for catalyst design in low-temperature multi-pollutant synergistic catalysis.

Efficient Solar-Driven CO2 Methanation and Hydrogen Storage Over Nickel Catalyst Derived from Metal-Organic Frameworks with Rich Oxygen Vacancies

Solar-driven photothermal conversion of carbon dioxide (CO2 ) to methane (CH4 ) is a promising approach to remedy energy shortage and climate changes, where highly efficient photothermal catalysts for CO2 methanation urgently need to be designed. Herein, nickel-based catalysts (Ni/ZrO2 ) derived from metal-organic frameworks (MOFs) are fabricated and studied for photothermal CO2 methanation. The optimized catalyst 50Ni/ZrO2 achieves a stable CH4 production rate of 583.3 mmol g-1  h-1 in a continuous stability test, which is almost tenfold higher than that of 50Ni/C-ZrO2 synthesized via commercial ZrO2 . Physicochemical properties indicate that 50Ni/ZrO2 generates more tetragonal ZrO2 and possesses more oxygen vacancies (OVs) as well as enhanced nickel-ZrO2 interaction. As a result, 50Ni/ZrO2 exhibits the strong abilities of light absorption and light-to-heat conversion, superior adsorption capacities of reactants (H2 , CO2 ), and an intermediate product (CO), which finally boosts CH4 formation. This work provides an efficient strategy to design a photothermocatalyst of CO2 methanation through utilizing MOFs-derived support.

Synergistic Activation of Inert Iron Oxide Basal Planes through Heterostructure Formation and Doping for Efficient Hydrogen Evolution

Iron oxides have emerged as a very promising and cost-effective alternative to precious metal catalysts for hydrogen production. However, the inert basal plane of iron oxides needs to be activated to enhance their catalytic efficiency. In this study, we employed heterostructure engineering and doped nickel to cooperatively activate the basal planes of iron oxide (Ni-Fe2 O3 /CeO2 HSs) to achieve high hydrogen evolution reaction (HER) activity. The Ni-Fe2 O3 /CeO2 HSs electrocatalyst demonstrates excellent basic HER activity and stability, such as an extremely low overpotential of 43 mV at 10 mA cm-2 current density and corresponding Tafel slope of 58.6 mV dec-1 . The increase in electrocatalyst activity and acceleration of hydrogen precipitation kinetics arises from the dual modulation of Ni doping and heterostructure, which not only modulates the electrocatalyst's electronic structure, but also increases the number and exposure of active sites. Remarkably, the generation of heterogeneous structure makes the catalyst se. The Ni-doped catalyst has not only increased HER activity but also low-temperature resistance. These results suggest that the synergistic activation of inert iron oxide basal planes through heterostructure formation and doping is a feasible strategy. Furthermore, for efficient electrocatalytic water splitting, this technique can be extended to other non-noble metal oxides.

Metal-Organic Framework (MOF) Derivatives as Promising Chemiresistive Gas Sensing Materials: A Review

The emission of harmful gases has seriously exceeded relative standards with the rapid development of modern industry, which has shown various negative impacts on human health and the natural environment. Recently, metal-organic frameworks (MOFs)-based materials have been widely used as chemiresistive gas sensing materials for the sensitive detection and monitoring of harmful gases such as NO_x, H₂S, and many volatile organic compounds (VOCs). In particular, the derivatives of MOFs, which are usually semiconducting metal oxides and oxide-carbon composites, hold great potential to prompt the surface reactions with analytes and thus output amplified resistance changing signals of the chemiresistors, due to their high specific surface areas, versatile structural tunability, diversified surface architectures, as well as their superior selectivity. In this review, we introduce the recent progress in applying sophisticated MOFs-derived materials for chemiresistive gas sensors, with specific emphasis placed on the synthesis and structural regulation of the MOF derivatives, and the promoted surface reaction mechanisms between MOF derivatives and gas analytes. Furthermore, the practical application of MOF derivatives for chemiresistive sensing of NO₂, H₂S, and typical VOCs (e.g., acetone and ethanol) has been discussed in detail.

Application of two morphologies of Mn2O3 for efficient catalytic ortho-methylation of 4-chlorophenol

Vapor phase ortho-methylation of 4-chlorophenol with methanol was studied over Mn₂O₃ catalyst with two kinds of morphologies. Here, Mn₂O₃ was prepared by a precipitation and hydrothermal method, and showed the morphology of nanoparticles and nanowires, respectively. XRD characterization and BET results showed that, with the increase of calcination temperature, Mn₂O₃ had a higher crystallinity and a smaller specific surface area. N₂ adsorption/desorption and TPD measurements indicated that Mn₂O₃ nanowires possessed larger external surface areas and more abundant acid and base sites. Simultaneously, in the fixed bed reactor, methanol was used as the methylation reagent for the ortho-methylation reaction of 4-chlorophenol. XRD, XPS, TG-MS and other characterizations made it clear that methanol reduced 4-chlorophenol and its methide, which were the main side-reactions. And Mn³⁺ was reduced to Mn²⁺ under the reaction conditions. Changing the carrier gas N₂ to a H₂/Ar mixture further verified that the hydrogen generated by the decomposition of methanol was not the reason for dechlorination of 4-chlorophenol compounds. Here we summarized the progress of 4-chlorophenol methylation based on the methylation of phenol. Also, we proposed a mechanism of the 4-chlorophenol dechlorination effect which was similar to the Meerwein-Ponndorf-Verley-type (MPV) reaction. The crystal phase and carbon deposition were investigated in different reaction periods by XRD and TG-DTA. The reaction conditions for the two kinds of morphologies of the Mn₂O₃ catalyst such as calcination temperature, reaction temperature, phenol-methanol ratio and reaction space velocity were optimized.

Modulating Ni/Ce Ratio in NiyCe100-yOx Electrocatalysts for Enhanced Water Oxidation

Oxygen evolution reaction (OER) is the key reaction for water splitting, which is used for hydrogen production. Oxygen vacancy engineering is an effective method to tune the OER performance, but the direct relationship between the concentration of oxygen vacancy and OER activity is not well understood. Herein, a series of Ni_yCe_100−yO_x with different concentration of oxygen vacancies were successfully synthesized. The larger concentration of oxygen vacancies in Ni₇₅Ce₂₅O_x and Ni₅₀Ce₅₀O_x result in their lower Tafel slopes, small mass-transfer resistance, and larger electrochemical surface areas of the catalysts, which account for the higher OER activities for these two catalysts. Moreover, with a fixed current density of 10 mA/cm², the potential remains stable at 1.57 V for more than 100 h, indicating the long-term stability of the Ni₇₅Ce₂₅O_x catalyst.

Selective immobilization of single-atom Au on cerium dioxide for low-temperature removal of C1 gaseous contaminants

Selective immobilization of single-atom Au on the specific facets of CeO₂ has been successfully performed by redox etching precipitation (REP), which makes it possible to clearly refine the interfacial effect of multiple-facet support on single atom. With systemic characterizations, it is found that single-atom Au is apt to lie on nonpolar facets of CeO₂ (111) and (110) rather than polar facet of CeO₂ (100). The modification of morphology-dependent properties is attributed to the different interaction between Au atom and each CeO₂ interface. Because of synergy between Au and CeO₂, more oxygen vacancies and more active oxygen species are generated; meanwhile, the interfacial effect stabilizes the charged Au species which serves as active site. Therefore, the performance in catalytic oxidation of HCHO and CO on CeO₂ is facilitated by loading Au. Among them, CeO₂ rod-supported Au as an optimal catalyst exhibits a remarkable activity and stability. With in-situ characterization, the reaction mechanisms for HCHO and CO oxidation over Au/r-CeO₂ are studied. Meanwhile, it is proved that REP strategy is also valid to obviously promote catalytic performance whenever commercial CeO₂ is used or Au is replaced with Ag, so the improvement of recently applied catalyst with REP process is promising.

Ni-Doped CuS as an efficient electrocatalyst for the oxygen evolution reaction

Ni-Doped CuS synthesized by a facile solvothermal method is demonstrated as an efficient oxygen evolution catalyst in alkaline medium.

Ce-Doped NiFe-Layered Double Hydroxide Ultrathin Nanosheets/Nanocarbon Hierarchical Nanocomposite as an Efficient Oxygen Evolution Catalyst

Developing convenient doping to build highly active oxygen evolution reaction (OER) electrocatalysts is a practical process for solving the energy crisis. Herein, a facile and low-cost in situ self-assembly strategy for preparing a Ce-doped NiFe-LDH nanosheets/nanocarbon (denoted as NiFeCe-LDH/CNT, LDH = layered double hydroxide and CNT = carbon nanotube) hierarchical nanocomposite is established for enhanced OER, in which the novel material provides its overall advantageous structural features, including high intrinsic catalytic activity, rich redox properties, high, flexible coordination number of Ce³⁺, and strongly coupled interface. Further experimental results indicate that doped Ce into NiFe-LDH/CNT nanoarrays brings about the reinforced specific surface area, electrochemical surface area, lattice defects, and the electron transport between the LDH nanolayered structure and the framework of CNTs. The effective synergy prompts the NiFeCe-LDH/CNT nanocomposite to possess superior OER electrocatalytic activity with a low onset potential (227 mV) and Tafel slope (33 mV dec^-1), better than the most non-noble metal-based OER electrocatalysts reported. Therefore, the combination of the remarkable catalytic ability and the facile normal temperature synthesis conditions endows the Ce-doped LDH nanocomposite as a promising catalyst to expand the field of lanthanide-doped layered materials for efficient water-splitting electrocatalysis with scale-up potential.

Low-temperature CO oxidation over CeO2 and CeO2@Co3O4 core–shell microspheres

The excellent CO catalytic activity and stability of CeO₂@Co₃O₄ composite were ascribed to the synergistic interactions between Co₃O₄ and CeO₂.