Core–Shell NiO@PdO Nanoparticles Supported on Alumina as an Advanced Catalyst for Methane Oxidation

An alumina-supported core–shell-structured NiO@PdO catalyst was prepared for lean CH₄ combustion. NiO@PdO plays two roles in promoting the reaction. First, the enhanced NiO-PdO interfacial action accelerates the regular tetragonal PdO lattice construction, stabilizes the PdO particles, and suppresses the hydroxyl/water adsorption during the reaction. Second, the dispersion of shell PdO particles over core NiO improves PdO exposure and utilization efficiency. NiO@PdO/Al₂O₃ with a molar Ni/Pd ratio of 2/1 exhibits a (>)­99% CH₄ conversion and a good stability at 400 °C with a low 0.2 wt % Pd loading amount, which is among the best of the state-of-the-art Pd-based catalysts with respect to turnover frequency, Pd utilization efficiency, and Ni addition amount. Such interface-promoted core–shell-structured catalyst design strategy is inspiring for improving noble metal utilization efficiency in CH₄ oxidation and other related reaction systems

Enhanced Photocatalytic Mineralization of Gaseous Toluene over SrTiO₃ by Surface Hydroxylation

Perovskite structured SrTiO₃ (STO) was synthesized by a hydrothermal method followed by a second hydrothermal treatment with H₂O or NaOH (STO-H₂O or STO-NaOH) for the photocatalytic mineralization of gaseous toluene. The second hydrothermal treatment enhances the light absorption and enriches the surface hydroxyl groups of STO. The surface hydroxyls’ enrichment of STO promotes the generation of hydroxyl radicals and the separation of photocarriers by the combination of hydroxyl with holes, induces a negative shift of its band edge, and benefits the reduction of adsorbed oxygen. The facile generation of reactive radical species, enhanced light absorption, and improved photocarrier separation together lead to greatly enhanced photocatalytic efficiency of STO-NaOH. Toluene was completely oxidized into CO₂ under ultraviolet light illumination for 6 h at room temperature, demonstrating better performance than STO and commercial P25 catalysts. Such a surface hydroxylation promotion strategy may lead to new perceptions of designing an efficient photocatalyst

Strong Metal-Support Interaction in Pt/TiO₂ Induced by Mild HCHO and NaBH₄ Solution Reduction and Its Effect on Catalytic Toluene Combustion

Strong metal-support interaction (SMSI) in titania supported noble metals has been a subject of many studies due to its importance to many fields of science, in particular to material science and catalysis system. H₂ reduction at a high temperature has been commonly considered as the inducement to SMSI in TiO₂ supported noble metals. This work, however, demonstrates that SMSI in Pt/TiO₂ can occur through mild NaBH₄ and HCHO solution reduction processes based on CO chemisorption, transmission electron microscopy, and X-ray photoelectron spectroscopy characterizations. Moreover, the effect of TiO₂ crystalline forms on the degree of SMSI in NaBH₄ reduced Pt/TiO₂ and the performance of the as-reduced catalysts for trace toluene combustion reaction were studied. It was found that the degree of SMSI in Pt/TiO₂ drew a significant effect on the catalytic performance. Our discovery provides a new way to control the interaction between noble metals and the TiO₂ support as well as their catalytic activities

MnO₂ Promoted TiO₂ Nanotube Array Supported Pt Catalyst for Formaldehyde Oxidation with Enhanced Efficiency

Highly ordered pore-through TiO₂ nanotube arrays (TiNT) prepared by an electrochemical anodization method were modified with MnO₂ and used as the support for a Pt/MnO₂/TiNT catalyst. The monolith-like Pt/MnO₂/TiNT was then applied to low-concentration HCHO oxidation with enhanced efficiency. The effect of the MnO₂ promotion on its performance for HCHO oxidation was studied with respect to the behavior of adsorbed species on the catalyst surface using in situ diffuse reflectance Fourier transform spectroscopy. In comparison with Pt/TiNT, Pt/MnO₂/TiNT shows higher activity under parallel preparation and test conditions. A HCHO conversion of 95% with a more than 100 h stable performance is achieved over Pt/MnO₂/TiNT at 30 °C with a low 0.20 wt % Pt loading amount. The superior performance is related to the specific monolith-like structure and its confinement effect, metal–support interaction, and superior HCHO adsorption and storage properties of Pt/MnO₂/TiNT

Identification of the Nearby Hydroxyls’ Role in Promoting HCHO Oxidation over a Pt Catalyst

Insight into the relationship between catalytic trends and physicochemical properties of composite nanoparticles is essential for their rational design. Herein, a series of 3d-M (M = Mn, Fe, Co, Ni) metal hydroxide-promoted PtM­(OH)_<i>x</i>/Al₂O₃ catalysts are developed and well characterized for establishing the catalytic HCHO oxidation reactivity trend as a function of more fundamental properties, such as hydroxyl concentration and adsorption strength. The reactivity of PtM­(OH)_<i>x</i>/Al₂O₃ exhibits an increasing trend of Mn < Fe < Co < Ni, which is governed by their OH–M^2+δ bond strength (Ni < Co < Fe < Mn) and surface hydroxyl concentration (Mn < Fe < Co < Ni). Both PtCo­(OH)_<i>x</i>/Al₂O₃ and PtNi­(OH)_<i>x</i>/Al₂O₃ exhibit a (>)­95% HCHO conversion and (>)­100 h performance stability at 30 °C with a low 0.2 wt % Pt loading amount. The identification of these catalytic trends provides foundations for composite active sites design for HCHO oxidation and other hydroxyl-involved reactions

Carbon Dots Sensitized BiOI with Dominant {001} Facets for Superior Photocatalytic Performance

Degrading and removing harmful compounds by the use of semiconductor photocatalysts has been testified to be and effective and attractive green technique in wastewater treatment. Herein, carbon dots sensitized BiOI with highly exposed {001} facets has been prepared and used to study the photocatalytic degradation of methyl orange (MO). Due to the improved charge separation, transfer, and optical absorption, the photocatalytic performance for methyl orange degradation of the carbon dots/{001} BiOI nanosheets is 4 times higher than that of the {001} BiOI nanosheets under visible light irradiation. Additionally, the carbon dots/{001} BiOI nanosheets also have superior stability after 5 cyclings

Boosting Interfacial Interaction in Hierarchical Core–Shell Nanostructure for Highly Effective Visible Photocatalytic Performance

The major challenges faced by photocatalyst include poor visible-light response, low-efficient charge separation, and serious photoexcited electrons recombination. The nature of hybrid photocatalysts interfacial interaction plays a major role in improving these challenges. Here, highly active and stable visible photocatalytic performance of toxic organics mineralization is realized by a TiO₂-based hierarchical core–shell nanostructure, TiO₂@SrTiO₃@Pt@Bi₂O₃@Pt (denoted as TSPBP). TSPBP simultaneously exhibits the following advantages: (1) the multilayered core–shell structure extends the visible-light response and enhances light harvesting; (2) bridging with Pt at the intermediate enhances the electron interaction between the different semiconductor layers and lowers charge transfer resistance; (3) deposition of Pt nanoparticles at the outmost layer could stabilize photoexcited electrons for suppressing charge recombination and activate the adsorbed oxygen. These beneficial factors lead to the remarkably higher visible-light photocatalytic activity of TSPBP in comparison with commercial P25 that is 90 times for formaldehyde degradation and 15 times for toluene decomposition. The strategy here would provide some new insight into designing of highly effective visible photocatalyst