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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.


Light-off curves for catalysts with 1.2% Au-RANR and commercial Au–TiO2 after multiple 700 and 800 °C heating cycles (10 cycles in total).
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fig4: Light-off curves for catalysts with 1.2% Au-RANR and commercial Au–TiO2 after multiple 700 and 800 °C heating cycles (10 cycles in total).

Mentions: Catalytic testing was undertaken with the use of the CO oxidation reaction. The reaction served two purposes. Firstly, CO oxidation is an industrially important reaction in various applications and secondly, CO oxidation is highly structure sensitive with respect to the Au nanoparticle size.3,4 Thus, the reaction acts as an ideal probe to aid in characterizing the catalyst via catalytic data. Thermal cycling under harsh conditions, long duration, high temperature, oxidizing atmosphere, and multiple cycles is important to determine a catalysts durability. Catalysts were therefore thermally cycled to 700 °C, 5 times using a heating rate of 8 °C min–1 and then held isothermally for 3 h before being cooled to 20 °C. Light-off curves were then measured and the catalyst was cycled again. After 4 cycles the catalysts were again heated to 700 °C but held isothermally for 12 h, cooled and then light-off curves attained. Thermal cycling was then conducted using the same catalyst to 800 °C in the same manner as before comprising 4 cycles to 800 °C and finally a 12 h isothermal treatment at 800 °C. Samples comprised 1.2 and 5% Au loadings by mass. Heating cycles were conducted under oxygen-rich atmosphere as this has been shown to enhance sintering of Au nanoparticles.32 The results of catalytic tests are shown in Fig. 4 and 5.


Achieving nano-gold stability through rational design † † Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc01597b Click here for additional data file.
Light-off curves for catalysts with 1.2% Au-RANR and commercial Au–TiO2 after multiple 700 and 800 °C heating cycles (10 cycles in total).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig4: Light-off curves for catalysts with 1.2% Au-RANR and commercial Au–TiO2 after multiple 700 and 800 °C heating cycles (10 cycles in total).
Mentions: Catalytic testing was undertaken with the use of the CO oxidation reaction. The reaction served two purposes. Firstly, CO oxidation is an industrially important reaction in various applications and secondly, CO oxidation is highly structure sensitive with respect to the Au nanoparticle size.3,4 Thus, the reaction acts as an ideal probe to aid in characterizing the catalyst via catalytic data. Thermal cycling under harsh conditions, long duration, high temperature, oxidizing atmosphere, and multiple cycles is important to determine a catalysts durability. Catalysts were therefore thermally cycled to 700 °C, 5 times using a heating rate of 8 °C min–1 and then held isothermally for 3 h before being cooled to 20 °C. Light-off curves were then measured and the catalyst was cycled again. After 4 cycles the catalysts were again heated to 700 °C but held isothermally for 12 h, cooled and then light-off curves attained. Thermal cycling was then conducted using the same catalyst to 800 °C in the same manner as before comprising 4 cycles to 800 °C and finally a 12 h isothermal treatment at 800 °C. Samples comprised 1.2 and 5% Au loadings by mass. Heating cycles were conducted under oxygen-rich atmosphere as this has been shown to enhance sintering of Au nanoparticles.32 The results of catalytic tests are shown in Fig. 4 and 5.

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.