Strategies for designing metal oxide nanostructures

Section: Introductionmentioning

confidence: 99%

Narrow-bandgap Nb2O5 nanowires with enclosed pores as high-performance photocatalyst

Zhang

Zhao

et al. 2018

“…Through a facile "hydrothermally-enhanced competitive adsorption and controlled calcination" method [40], Al was homogeneously introduced into the CeO2 lattice to create numerous active oxygen species. Upon supporting Au NPs, the Au/ACHS catalysts showed much higher activity than the non-doped Au/CHS catalyst.…”

Section: Discussionmentioning

confidence: 99%

Highly active CeO2 hollow-shell spheres with Al doping

Wang

Jiang

et al. 2017

Metal oxide hollow structures are of great interest in many current and emerging areas of technology. This paper presents a facile and controlled protocol for the synthesis of Al-doped CeO2 hollow-shell spheres (CHS), where the dopant confers enhanced stability and activity to the material. These Al-doped CeO2 hollow-shell spheres (ACHS) possess a controllable shell number of up to three, where the sizes of the exterior, middle, and interior spheres were about 250-100 nm,150-50 nm, and 40-10 nm, respectively, and the average shell thickness was~15 nm. The thermal stability of the ACHS structure was enhanced by the homogeneous incorporation of Al atoms, and more active oxygen species were present compared with those in the non-doped congener. Au NPs supported on ACHS (Au/ACHS) showed superior catalytic performance for the reduction of p-nitrophenol. For the same Au NP content, the reaction rate constant (k) of the Au/ACHS was nearly twice that of the non-doped Au/CHS, indicating that Al doping is promising for improving the performance of inert or unstable oxides as catalyst supports.

“…Reverse micro-emulsions (homogenous-like combinations of water, oils, and/or surfactants) is interesting and has been confirmed as an environment-friendly alternative to the preparation of metal or metal oxide NPs [96][97][98]. Typically, a reverse micro-emulsion is prepared by mixing an organic solution of the surfactant with a solution of metal salt precursor to produce a solid support that is then impregnated with a micro-emulsion in a similar way to traditional chemical impregnation [99][100][101].…”

Section: Reverse Micro-emulsionsmentioning

confidence: 99%

Graphitized nanocarbon-supported metal catalysts: synthesis, properties, and applications in heterogeneous catalysis

Huang

2017

Graphitized nanocarbon materials can be an ideal catalyst support for heterogeneous catalytic systems. Their unique physical and chemical properties, such as large surface area, high adsorption capacity, excellent thermal and mechanical stability, outstanding electronic properties, and tunable porosity, allow the anchoring and dispersion of the active metals. Therefore, currently they are used as the key support material in many catalytic processes. This review summarizes recent relevant applications in supported catalysts that use graphitized nanocarbon as supports for catalytic oxidation, hydrogenation, dehydrogenation, and C-C coupling reactions in liquid-phase and gas-solid phase-reaction systems. The latest developments in specific features derived from the morphology and characteristics of graphitized nanocarbon-supported metal catalysts are highlighted, as well as the differences in the catalytic behavior of graphitized nanocarbon-supported metal catalysts versus other related catalysts. The scientific challenges and opportunities in this field are also discussed. Keywords: nanocarbon materials; graphitized carbon supports; metal catalysts; hetergeneous catalysis INTRODUCTIONCarbon combines its atoms in diverse hybridization states (sp, sp 2 , sp 3 ) to form a variety of polymorphs. These are composed entirely of carbon but have different physical structures and different names, including diamond, graphite, fullerenes, and carbines, among others [1][2][3][4][5]. Because these various and versatile allotropes produce materials with a large range of properties, carbon materials can be used in a number of technological processes, including high-tech catalytic ones [6][7][8][9][10].In heterogeneous catalysis, carbon material plays wellestablished and important roles in a wide range of applications, both as catalyst in its own right and as a unique support material [11][12][13][14][15]. The chemical stability of carbon supports in some specifically aqueous phase biomass conversion surpasses that of metal oxide materials; in addition, carbon materials present other common and key advantages as support materials for catalysis [1,5]. From the point of physical structure, porous carbon can be prepared in different forms (granules, cloth, fibers, pallets, etc.). Due to its chemical properties, carbon structure is resistant to both acidic and basic media. The structure of carbon is stable at high temperature (even above 1023 K under inert atmosphere). The hydrophilic/ hydrophobic nature of carbon can be easily modified. Active metals on the support can be easily reduced. For the purposes of industrial economy and environment, the active phase can be easily recovered. Conventional carbon supports are lower-cost and more easily available than other conventional supports. Although several kinds of carbon materials have been studied, active carbon (AC) [12,[16][17][18][19] and, to a lesser extend, carbon black [20][21][22][23] have long been the most commonly used carbon supports. AC is an amorphous solid prepa...