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Achieving nano-gold stability through rational design † † Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc01597b Click here for additional data file.

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ABSTRACT

When Au is subdivided to the nanoscale its reactivity changes from an inert nature to one of incredible reactivity which is not replicated by other catalysts. When dispersed onto metal oxides such as TiO2, nano-Au has shown high reactivities for a multitude of reduction and oxidation reactions of industrial importance with potential and current uses such as, CO oxidation, NOx reduction, purification of hydrogen for fuel cells, water gas shift reactions, abatement of volatile organic compounds (VOC's) as well as pollution and emission control systems such as autocatalysts. However, many industrially important reactions and applications operate under harsh conditions where the catalyst is exposed to high temperatures and further needs to operate for extended periods of time. These conditions cause Au nanoparticle sintering whereby small, highly active clusters form large clusters which are catalytically inactive. For this reason, research into stabilizing Au nanoparticles has abounded with a goal of producing durable, thermally stable catalysts for industrial applications. Here we show a durable, thermally stable Au–TiO2 catalyst which has been developed by rational design. The catalyst exhibits a 3-dimensional, radially aligned nanorod structure, already locked into the thermodynamically stable polymorph, via a scalable and facile synthesis, with Au nanoparticles isolated on the support structure. As the Au nanoparticles are highly stable the new catalyst is able to maintain light-off for CO oxidation below 115 °C even after multiple cycles at 800 °C. This ability of the catalyst to resist multiple thermal cycles to high temperature while remaining active at low temperatures shows promise for various industrial applications. The thermal stability of the catalyst is investigated and characterized through morphological and structural studies.

No MeSH data available.


A selection of images used for the TEM tilt series of the 5% Au-RANR catalyst after in situ PXRD measurements. Selected Au nanoparticles were tracked using fiducial tracking during the rotation to confirm their positions. The reconstruction video can be accessed in the ESI.†
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fig2: A selection of images used for the TEM tilt series of the 5% Au-RANR catalyst after in situ PXRD measurements. Selected Au nanoparticles were tracked using fiducial tracking during the rotation to confirm their positions. The reconstruction video can be accessed in the ESI.†

Mentions: Scanning electron microscopy (SEM), back scatter SEM (BSE), high angle annular dark field (HAADF), TEM, and TEM tomography confirmed the presence of the Au nanoparticles isolated on the nanorods both before and after thermal treatments (in situ PXRD) under synthetic air to 810 °C (Fig. 1A and B and 2). Prior to thermal treatment, the catalysts were activated under hydrogen flow at 300 °C for 1 hour. A TEM tilt series (Fig. 2) conducted after the in situ PXRD data collection (heating for over 200 h and holding at 810 °C for 5 h) confirmed the minimal growth of the Au and RANR structure. A TEM tilt series (Fig. 2) conducted after thermal treatment of the catalyst was used to track the location of the Au nanoparticles for confirmation that Au was not located within the structure but remained highly dispersed and isolated even after high-temperature exposure (Tomo video available in ESI†).


Achieving nano-gold stability through rational design † † Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc01597b Click here for additional data file.
A selection of images used for the TEM tilt series of the 5% Au-RANR catalyst after in situ PXRD measurements. Selected Au nanoparticles were tracked using fiducial tracking during the rotation to confirm their positions. The reconstruction video can be accessed in the ESI.†
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5134759&req=5

fig2: A selection of images used for the TEM tilt series of the 5% Au-RANR catalyst after in situ PXRD measurements. Selected Au nanoparticles were tracked using fiducial tracking during the rotation to confirm their positions. The reconstruction video can be accessed in the ESI.†
Mentions: Scanning electron microscopy (SEM), back scatter SEM (BSE), high angle annular dark field (HAADF), TEM, and TEM tomography confirmed the presence of the Au nanoparticles isolated on the nanorods both before and after thermal treatments (in situ PXRD) under synthetic air to 810 °C (Fig. 1A and B and 2). Prior to thermal treatment, the catalysts were activated under hydrogen flow at 300 °C for 1 hour. A TEM tilt series (Fig. 2) conducted after the in situ PXRD data collection (heating for over 200 h and holding at 810 °C for 5 h) confirmed the minimal growth of the Au and RANR structure. A TEM tilt series (Fig. 2) conducted after thermal treatment of the catalyst was used to track the location of the Au nanoparticles for confirmation that Au was not located within the structure but remained highly dispersed and isolated even after high-temperature exposure (Tomo video available in ESI†).

View Article: PubMed Central - PubMed

ABSTRACT

When Au is subdivided to the nanoscale its reactivity changes from an inert nature to one of incredible reactivity which is not replicated by other catalysts. When dispersed onto metal oxides such as TiO2, nano-Au has shown high reactivities for a multitude of reduction and oxidation reactions of industrial importance with potential and current uses such as, CO oxidation, NOx reduction, purification of hydrogen for fuel cells, water gas shift reactions, abatement of volatile organic compounds (VOC's) as well as pollution and emission control systems such as autocatalysts. However, many industrially important reactions and applications operate under harsh conditions where the catalyst is exposed to high temperatures and further needs to operate for extended periods of time. These conditions cause Au nanoparticle sintering whereby small, highly active clusters form large clusters which are catalytically inactive. For this reason, research into stabilizing Au nanoparticles has abounded with a goal of producing durable, thermally stable catalysts for industrial applications. Here we show a durable, thermally stable Au–TiO2 catalyst which has been developed by rational design. The catalyst exhibits a 3-dimensional, radially aligned nanorod structure, already locked into the thermodynamically stable polymorph, via a scalable and facile synthesis, with Au nanoparticles isolated on the support structure. As the Au nanoparticles are highly stable the new catalyst is able to maintain light-off for CO oxidation below 115 °C even after multiple cycles at 800 °C. This ability of the catalyst to resist multiple thermal cycles to high temperature while remaining active at low temperatures shows promise for various industrial applications. The thermal stability of the catalyst is investigated and characterized through morphological and structural studies.

No MeSH data available.