Speaker
Description
Understanding the interaction of a metal catalyst with its support is essential for the development of metal-based catalysts. The formation of a functional interface influences the stability and electronic properties of the catalyst. The interplay between the catalyst and the substrate is expected to have a crucial effect on the population of active centers that are created under the reaction conditions. In our studies we focus on investigations of a new type of metal thin film catalyst with reduced geometry (AC 4.1) and standard powder catalyst with 3D geometry (AC 4.2). We are also interested in catalyst regeneration that leads to coke removal leaving the metal catalyst unaffected (AC 4.3).
In the CatLab project the new route of catalyst design and synthesis is realized by reducing conventional 3D catalyst materials to two dimensions. The thin films (< 10 nm) are deposited with our Helmholtz-Zentrum Berlin partner on a homogeneous support material by different deposition techniques. Due to reduced geometry the catalyst has to consist of a landscape of active centers that guarantee the required catalytical activity. This should be obtained by a functional interface where interaction of support on thin metal film creates a frustrated active phase. A first system containing a Si wafer support with or without buffer layer (SiO$_{2}$ or ZnO or SiN$_{x}$) and Pd (3, 11 nm) was developed. As a test reaction acetylene hydrogenation was used. The catalytical activity normalized to the amount of available Pd centers obtained from calorimetric / volumetric measurements was compared with standard powder catalysts showing good film conversion and selectivity. We studied the role of the buffer, its thickness and influence of applied pretreatments on electronic properties, morphology and catalytical performance. To use relatively flat thin-films as catalysts it requires an adaption of the catalytic reactors optimized for sample geometries and low total surface area of the catalyst. A recycle reactor, among others, has been adapted for thin films, enabling gradient-free catalytic measurements. (AC 4.1)
Our group has also explored the NiCu powder catalyst. The NiCuAl layered double hydroxides (LDH) have been synthesized as precursor to prepare a catalyst with Ni-Cu nanoparticles over alumina. We have varied synthesis parameters of the precursor and we have found that our synthetic pathway is quite robust showing little sensitivity to small changes in the preparation parameters. The strong influence of one metal on the other was observed by (i) TPO/TPR (Cu is lowering the Ni reduction temperature), (ii) photoelectron spectroscopy (changes in Cu L-edge in presence of Ni, change in the electron structure of Cu in presence of Ni) and (iii) catalysis (under rWGS Cu promotes Ni selectivity while maintaining high stability). (AC 4.2)
The regeneration process for industrial silicalite-supported Pt catalyst with low Pt loading (<1 wt% Pt) coked under propane dehydrogenation (PDH) was investigated. The need of catalyst regeneration after the coking under a catalytic reaction is a very well-known problem. We were able to demonstrate regeneration of coked catalyst at temperatures as low as 310 °C using strong oxidizing agents, mostly NO$_{x}$, present in HNO3 vapor without significant loss in its catalytic activity. The developed procedure can be successfully transferred to other systems that suffer from coking under the reaction conditions. (AC 4.3)
| Abstract Number (department-wise) | AC 4.0 |
|---|---|
| Department | AC (Schlögl) |
