We gratefully acknowledge funding and support from King Abdullah University of Science and Technology (KAUST). Thanks are also due to the KAUST communication department for designing several images for this Review.

Magnetically recoverable nanocatalysts.

Green chemistry by nano-catalysis

Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenom...

Prospects of Nanoscience with Nanocrystals

C2 to C4 olefins are traditionally produced from steam cracking of naphtha. The necessity for alternative production routes for these major commodity chemicals via non-oil-based processes has driven research in past times during the oil crises. Currently, there is a renewed interest in producing lower olefins from alternative feedstocks such as coal, natural gas, or biomass, in view of high oil prices, environmental regulations, and strategies to gain independence from oil imports. This review describes the major routes for the production of lower olefins from synthesis gas with an emphasis on a direct or single step process, the so-called FTO or Fischer–Tropsch to olefins process. The different catalysts for FTO are outlined and compared, and the key issues and requirements for future developments are highlighted. Iron-based catalysts are prevailing for FTO, and reproducible lower olefin selectivities of 50 wt % of hydrocarbons produced have been realized at CO conversions higher than 70% for 60 to 1000 ...

Catalysts for Production of Lower Olefins from Synthesis Gas: A Review

This critical review deals with the applications of nanocatalysts in Suzuki coupling reactions, a field that has attracted immense interest in the chemical, materials and industrial communities. We intend to present a broad overview of nanocatalysts for Suzuki coupling reactions with an emphasis on their performance, stability and reusability. We begin the review with a discussion on the importance of Suzuki cross-coupling reactions, and we then discuss fundamental aspects of nanocatalysis, such as the effects of catalyst size and shape. Next, we turn to the core focus of this review: the synthesis, advantages and disadvantages of nanocatalysts for Suzuki coupling reactions. We begin with various nanocatalysts that are based on conventional supports, such as high surface silica, carbon nanotubes, polymers, metal oxides and double hydroxides. Thereafter, we reviewed nanocatalysts based on non-conventional supports, such as dendrimers, cyclodextrin and magnetic nanomaterials. Finally, we discuss nanocatalyst systems that are based on non-conventional media, i.e., fluorous media and ionic liquids, for use in Suzuki reactions. At the end of this review, we summarise the significance of nanocatalysts, their impacts on conventional catalysis and perspectives for further developments of Suzuki cross-coupling reactions (131 references).

Nanocatalysts for Suzuki cross-coupling reactions

The modern chemical industry uses heterogeneous catalysts in almost every production process. They commonly consist of nanometre-size active components (typically metals or metal oxides) dispersed on a high-surface-area solid support, with performance depending on the catalysts' nanometre-size features and on interactions involving the active components, the support and the reactant and product molecules. To gain insight into the mechanisms of heterogeneous catalysts, which could guide the design of improved or novel catalysts, it is thus necessary to have a detailed characterization of the physicochemical composition of heterogeneous catalysts in their working state at the nanometre scale. Scanning probe microscopy methods have been used to study inorganic catalyst phases at subnanometre resolution, but detailed chemical information of the materials in their working state is often difficult to obtain. By contrast, optical microspectroscopic approaches offer much flexibility for in situ chemical characterization; however, this comes at the expense of limited spatial resolution. A recent development promising high spatial resolution and chemical characterization capabilities is scanning transmission X-ray microscopy, which has been used in a proof-of-principle study to characterize a solid catalyst. Here we show that when adapting a nanoreactor specially designed for high-resolution electron microscopy, scanning transmission X-ray microscopy can be used at atmospheric pressure and up to 350 degrees C to monitor in situ phase changes in a complex iron-based Fisher-Tropsch catalyst and the nature and location of carbon species produced. We expect that our system, which is capable of operating up to 500 degrees C, will open new opportunities for nanometre-resolution imaging of a range of important chemical processes taking place on solids in gaseous or liquid environments.

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Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy

A newly developed SiN microhotplate allows specimens to be studied at temperatures up to 1000 K at a resolution of 100 picometer (see image). Aberration-corrected transmission electron microscopy has become a commonplace tool to investigate stable crystals; however, imaging transient nanocrystals is much more demanding. Morphological transformations in gold nanoparticles and layer-by-layer sublimation of PbSe nanocrystals is imaged with atomic resolution.

Atomic imaging of phase transitions and morphology transformations in nanocrystals.

A closer look: Investigation of the reduction properties of a single Fischer-Tropsch catalyst particle, using in situ scanning transmission X-ray microscopy with spatial resolution of 35 nm, reveals a heterogeneous distribution of Fe(0), Fe(2+), and Fe(3+) species. Regions of different reduction properties are defined and explained on the basis of local chemical interactions and catalyst morphology.

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Nanoscale Chemical Imaging of the Reduction Behavior of a Single Catalyst Particle

In-situ Scanning X-ray Transmission Microscopy (STXM) allows the measurement of the soft X-ray absorption spectra with 10 to 30 nm spatial resolution under realistic reaction conditions. We show that STXM-XAS in combination with a micromachined nanoreactor can image a catalytic system under relevant reaction conditions, and provide detailed information on the morphology and composition of the catalyst material. The nanometer resolution combined with powerful chemical speciation by XAS and the ability to image materials under realistic conditions opens up new opportunities to study many chemical processes.

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In-situ scanning transmission X-ray microscopy of catalytic materials under reaction conditions

The accuracy of piezoresistive based silicon sensors is partially determined by the uncertainty in the piezoresistive coefficients. In the production of sensors it is therefore desirable to measure the coefficients for the used technological process to avoid costly calibration of the sensors after production. A practical measurement method consists of bending a three-element rosette. The resulting resistance changes are used to calculate the independent piezoresistive coefficients (pi) 11, (pi) 12, and (pi) 44. A recognized problem of this method are the large uncertainties in the smallest calculated coefficients. These uncertainties arise partially from errors in the resistance measurements. This paper shows that the calculation of the coefficients is very sensitive to the measurement errors. This sensitivity is especially pronounced if there are large differences in magnitude between (pi) 11, (pi) 12, and (pi) 44, such as in p-type silicon. It appears, however, that the error sensitivity can be greatly reduced by optimizing the rosette orientation in the (001) crystal plane. For a p-type silicon rosette the optimum orientation is k*(pi) /2 (k equals 0, 1, 2,...) with respect to the [100] axis. Orientation along these angles may result in a reduction of the uncertainties up to a factor 48.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

J. Fredrik Creemer

Papers

Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy

Atomic imaging of phase transitions and morphology transformations in nanocrystals.

Nanoscale Chemical Imaging of the Reduction Behavior of a Single Catalyst Particle

In-situ scanning transmission X-ray microscopy of catalytic materials under reaction conditions

Reduction of uncertainty in the measurement of the piezoresistive coefficients of silicon with a three-element rosette