Solid-State Ion-Exchange of Copper into Zeolites Facilitated by Ammonia at Low Temperature

The effect of the gas phase during solid-state ion-exchange of copper into zeolites was studied by exposing physical mixtures of copper oxides (CuI2O and CuIIO) and zeolites (MFI, *BEA and CHA) to various combinations of NO, NH3, O2 and H2O. It is shown that heating these mixtures to 250\ub0C results in active catalysts for the selective catalytic reduction of NO with NH3 (NH3-SCR), indicating that the Cu has become mobile at that temperature. Such treatment allows for a fast

From Colloidal Monodisperse Nickel Nanoparticles to Well-Defined Ni/Al2O3 Model Catalysts

In the past few decades, advances in colloidal nanoparticle synthesis have created new possibilities for the preparation of supported model catalysts. However, effective removal of surfactants is a prerequisite to evaluate the catalytic properties of these catalysts in any reaction of interest. Here we report on the colloidal preparation of surfactant-free Ni/Al2O3 model catalysts. Monodisperse Ni nanoparticles (NPs) with mean particle size ranging from 4 to 9 nm were synthesized via thermal decomposition of a zerovalent precursor in the presence of oleic acid. Five weight percent Ni/Al2O3 catalysts were produced by direct deposition of the presynthesized NPs on an alumina support, followed by thermal activation (oxidation–reduction cycle) for complete surfactant removal and surface cleaning. Structural and morphological characteristics of the nanoscale catalysts are described in detail following the propagation of the bulk and surface Ni species at the different treatment stages. Powder X-ray diffraction, electron microscopy, and temperature-programmed reduction experiments as well as infrared spectroscopy of CO adsorption and magnetic measurements were conducted. The applied thermal treatments are proven to be fully adequate for complete surfactant removal while preserving the metal particle size and the size distribution at the level attained by the colloidal synthesis. Compared with standard impregnated Ni/Al2O3 catalysts, the current model materials display narrowed Ni particle size distributions and increased reducibility with a higher fraction of the metallic nickel atoms exposed at the catalyst surface. © 2017 American Chemical Societ

Solid-State Ion-Exchange of Copper into Zeolites Facilitated by Ammonia at Low Temperature

The effect of the gas phase during solid-state ion-exchange of copper into zeolites was studied by exposing physical mixtures of copper oxides (CuI2O and CuIIO) and zeolites (MFI, *BEA and CHA) to various combinations of NO, NH3, O2 and H2O. It is shown that heating these mixtures to 250\ub0C results in active catalysts for the selective catalytic reduction of NO with NH3 (NH3-SCR), indicating that the Cu has become mobile at that temperature. Such treatment allows for a fast

Assessing and controlling the size, morphology and composition of supported bimetallic catalyst nanoparticles

Supported bimetallic nanoparticles are frequently used for applications in catalysis [1]. Ideally we would like to be able to synthesize stable alloy nanoparticles with (i) a well-defined and narrow size range, (ii) very specific morphologies (i.e. random alloy, ordered alloy, core-shell structures) and (iii) closely controlled compositions. In reality, our ability to simultaneously control all of these physical parameters by conventional catalyst preparation methods is still somewhat lacking. We have found that aberration corrected analytical electron microscopy is an excellent way of performing ‘quality control’ measurements on such bimetallic catalyst systems. In particular, the combination of HAADF imaging and XEDS compositional analysis in the STEM has given us considerable insight into the way in which elemental distributions evolve in these bimetallic catalyst systems during processing and use. Our studies have especially highlighted the need to create simple chemical synthesis protocols which afford a tighter control of composition from particle-to-particle. In this presentation some case studies will be given, using the Au-Pd, Pt-Pd and Au-Pt bimetallic systems as specific examples, to illustrate the complex relationships that can exist between preparation route, compositional homogeneity and catalytic performance