Construction of versatile multijunctions with visible light response, effective charges transport and separation, suitable band positions, and good stability is highly expected for the photocatalytic VOCs degradation. Herein, one-dimensional titania nanotube supported SrTiO3 heterostructure (STO/TN) was developed by a hydrothermal process and then simultaneously sensitized with carbon nitride polymer (CN) and doped with nitrogen (CN-STO/TN) for photocatalytic mineralization of toluene. CN-STO/TN simultaneously exhibits the following advantages: (1) the nanotube structure enhances light-harvesting, enables effective charges transport and separation, retains sufficient energy of the charges, facilitates the pollutant species transport and reactants enrichment by the confinement effect; (2) synergistic effect of CN sensitization and N-doping extends the light response to the visible light region; (3) multichannel charges separation and transport among the multijunctions promote the photogenerated carriers separation. These beneficial factors lead to the remarkably higher visible light photocatalytic performance of CN-STO/TN in comparison with the component photocatalysts, 27 times that of TN, 13.5 times that of STO, and 4.9 times that of CN, respectively. These results demonstrate that the combination of morphology tailoring and energy band alignment manipulation is important in designing effective heterojunctions for photocatalytic applications.

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.Keywords: catalytic combustion; core−shell; methane; NiO; PdO;

Reversible conversion of Cu2+ and Cu+ under illumination and with oxidation is demonstrated over CuxO/SrTiO3. Such Cu2+/Cu+ homeostasis together with its photosensitizer function and p–n heterojunction formation has lead to highly active and stable visible photocatalytic performance. This strategy will provide some new insights into the design of highly efficient photocatalysts.

•Nickel hydroxide promoted Pt nanoparticles were prepared.•Hydroxyl groups confined interface promoted HCHO oxidation.•PtNi(OH)x/γ-Al2O3 demonstrated excellent HCHO oxidation performance.Rational design of efficient noble metal catalysts and its application process by the interface promoted strategy is an emerging research field. Herein, highly efficient nickel hydroxide promoted PtNi(OH)x/γ-Al2O3 catalysts for room temperature HCHO oxidation was developed. PtNi(OH)x/γ-Al2O3 demonstrates remarkably better performance than the state of the art non-reductive oxide supported Pt catalysts, and ranges among the best performance of the reductive metal oxide supported Pt catalysts. A (>)99% HCHO conversion and a (>)100 h stable performance at 30 °C were obtained over PtNi(OH)x/γ-Al2O3 with a 0.3 wt% Pt loading amount. Various characterizations, including in situ DRIFTS study, were performed to understand the reason for the enhanced performance of PtNi(OH)x/γ-Al2O3. The superior performance is attributed to the formation of enormous Pt/Ni(OH)x interface, and the preferred hydroxyl facilitated HCHO oxidation pathway through formate oxidation by the abundant associated hydroxyl groups nearby the Pt active sites. Such hydroxyl groups confined interface promotion strategy may bring new insight into the designing of highly efficient bimetallic catalysts and its potential technological applications for HCHO removal.Download high-res image (124KB)Download full-size image

•Pt/TiNT demonstrates superior performance for toluene oxidation.•Pt/TiNT holds rich active sites.•Decomposition of benzoate species is the key step for toluene oxidation.Featuring an assembly of identical pores, TiO2 nanotube array (TiNT) makes an ideal monolith-like support of noble metal catalysts for volatile organic compounds combustion. Herein, the deep oxidation of gaseous toluene over Pt/TiNT and anatase TiO2 (ATiO2) particles supported Pt catalysts are studied and compared. Pt/TiNT demonstrates remarkably enhanced performance over Pt/ATiO2 powder catalyst, and ranges among the best performances of the state of the art Pt based catalysts. A toluene conversion of (>)95% at 185 °C and a multiple heating-cooling cyclic stable performance with a time of (>)300 h are achieved over 0.4 wt% Pt/TiNT. In situ DRIFTS study indicates that toluene is sequentially oxidized to benzaldehyde, benzoate, aliphatic carboxylates species, CO and finally to CO2, and the decomposition of benzoate species is the key step. The unique performance of Pt/TiNT is attributed to its ordered monolith-like structure, well-dispersion and surface enrichment of Pt, and enhanced benzoate species decomposition rate.Download high-res image (85KB)Download full-size image

•Both oxygen vacancy and Pd site can promote the HCHO adsorption over anatase TiO2(101) surface.•The presence of Pd site is beneficial for the formation of oxygen vacancy.•Synergetic effect of oxygen vacancy and Pd site on the interaction between Pd/TiO2(101) and HCHO is demonstrated.Insights into the functions and the synergetic effects of oxygen vacancy and noble metal sites on the performance of the reducible oxide supported noble metal catalysts are very important in designing formaldehyde catalysts. Herein, the roles of oxygen vacancies and Pd sites, and their synergistic effect on the interaction between HCHO and Pd/Anatase TiO2(101) surface were systematically studied by a density functional theory (DFT) study. It is found that both the presence of oxygen vacancy and Pd site can promote the HCHO adsorption over TiO2(101) surface. The presence of Pd site is beneficial for the oxygen vacancy formation by reducing its formation energy. Furthermore, synergetic effect of oxygen vacancy and Pd site on the interaction between Pd/TiO2(101) and HCHO is demonstrated for the case with the co-presence of oxygen vacancy and Pd site. In this situation, the oxygen atom of HCHO molecular occupies the oxygen vacancy and the carbon atom of HCHO connects with the Pd site, and a larger adsorption energy is obtained in comparison with the cases with only oxygen vacancy or Pd site present. These results indicate that both oxygen vacancy manufacturing and Pd doping can strength the HCHO adsorption over TiO2(101) surface, and their synergistic effects further promote the interaction between HCHO and Pd/TiO2 catalyst, which is beneficial for the HCHO oxidation.Download high-res image (276KB)Download full-size image

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.

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.