Monday, January 15, 2018

Pt/Cu single-atom alloys as coke-resistant catalysts for efficient C – H activation

Pt/Cu single-atom alloys as coke-resistant catalysts for efficient C–H activation


M. D. Marcinkowski, M. T. Darby, J. Liu, J. M. Wimble, F. R. Lucci, S. Lee, A. Michaelides, M. Flytzani-Stephanopolous, M. Stamatakis, E. C. H. Sykes

Nature Chem. 2018, ASAP
DOI: 10.1038/nchem.2915

Abstract:


The recent availability of shale gas has led to a renewed interest in CH bond activation as the first step towards the synthesis of fuels and fine chemicals. Heterogeneous catalysts based on Ni and Pt can perform this chemistry, but deactivate easily due to coke formation. Cu-based catalysts are not practical due to high CH activation barriers, but their weaker binding to adsorbates offers resilience to coking. Using Pt/Cu single-atom alloys (SAAs), we examine CH activation in a number of systems including methyl groups, methane and butane using a combination of simulations, surface science and catalysis studies. We find that Pt/Cu SAAs activate CH bonds more efficiently than Cu, are stable for days under realistic operating conditions, and avoid the problem of coking typically encountered with Pt. Pt/Cu SAAs therefore offer a new approach to coke-resistant CH activation chemistry, with the added economic benefit that the precious metal is diluted at the atomic limit.


Monday, January 1, 2018

Preparation and Characterization of Bimetallic Pd-Cu Colloids by Thermal Decomposition of Their Acetate Compounds in Organic Solvents

Preparation and Characterization of Bimetallic Pd-Cu Colloids by Thermal Decomposition of Their Acetate Compounds in Organic Solvents

Kunio Esumi, Takafumi Tano, Kanjiro Torigoe, and Kenjiro Meguro
University of Tokyo

Chem. Mater. 1990, 2, 564-567  (http://pubs.acs.org/doi/pdf/10.1021/cm00011a019)

Abstract:

Bimetallic Pd-Cu/Cu2O colloids are prepared by the thermal decomposition of their acetates dissolved in methyl isobutyl ketone and bromobenzene. In methyl isobutyl ketone, the average diameter of Pd-Cu2O colloids decreases from about 130 to 50 nm with an increase of molar fraction of palladium acetate, while in bromobenzene the size of Pd-Cu colloids increases from about 8 to 15 nm. The composition of Pd-Cu or Pd-Cu2O colloids is almost hte same as that of the feed ratio of their acetates. The dispersion stability of these colloids is further addressed by measuring their ζ potentials.
  

Sunday, November 26, 2017

Selective Activation of Methane on Single-Atom Catalyst of Rhodium Dispersed on Zirconia for Direct Conversion


Selective Activation of Methane on Single-Atom Catalyst of Rhodium
Dispersed on Zirconia for Direct Conversion 

Y. Kwon, T. Y. Kim, G. Kwon, J. Yi, and H. Lee

J. Am. Chem. Soc. ASAP
(http://pubs.acs.org/doi/pdf/10.1021/jacs.7b11010)

Abstract:


Direct methane conversion into value-added products has become increasingly important. Because of inertness of methane, cleaving the first CH bond has been very difficult, requiring high reaction temperature on the heterogeneous catalysts. Once the first CH bond becomes activated, the remaining CH bonds are successively dissociated on the metal surface, hindering the direct methane conversion into chemicals. Here, a single-atom Rh catalyst dispersed on ZrO2 surface has been synthesized and used for selective activation of methane. The Rh single atomic nature was confirmed by extended X-ray fine structure analysis, electron microscopy images, and diffuse reflectance infrared Fourier transform spectroscopy. A model of the single- atom Rh/ZrO2 catalyst was constructed by density functional theory calculations, and it was shown that CH3 intermediates can be energetically stabilized on the single-atom catalyst. The direct conversion of methane was performed using H2O2 in the aqueous solution or using O2 in gas phase as oxidants. Whereas Rh nanoparticles produced CO2 only, the single-atom Rh catalyst produced methanol in aqueous phase or ethane in gas phase.

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