Industrial catalysts | EPFL Graph Search

The first time a catalyst was used in the industry was in 1746 by J. Roebuck in the manufacture of lead chamber sulfuric acid. Since then catalysts have been in use in a large portion of the chemical industry. In the start only pure components were used as catalysts, but after the year 1900 multicomponent catalysts were studied and are now commonly used in the industry. In the chemical industry and industrial research, catalysis play an important role. Different catalysts are in constant development to fulfil economic, political and environmental demands. When using a catalyst, it is possible to replace a polluting chemical reaction with a more environmentally friendly alternative. Today, and in the future, this can be vital for the chemical industry. In addition, it's important for a company/researcher to pay attention to market development. If a company's catalyst is not continually improved, another company can make progress in research on that particular catalyst and gain market s

Active sites on copper-based catalysts for electrochemical CO2 reduction selectively to C2+ products

Jie Zhang

Electrochemical CO2 reduction (eCO2RR) towards value-added chemicals, powered by renewable electricity, is a promising technology for storing the intermittent renewable energy in the form of chemical bonds. Among the various products of eCO2RR, multi-carbon (C2+) molecules, such as ethylene and ethanol, are particularly interesting because they can be either important commodity chemicals or liquid fuels compatible with the current storage and transport facilities. Production of C2+ molecules from eCO2RR still suffers from low selectivity, reactivity, and stability, mainly due to the lack of proper catalysts and optimal reaction conditions. The main objective of this thesis is to develop advanced copper catalysts for and understand the eCO2RR process. First, to reveal the active sties on monometallic copper catalysts for eCO2RR to C2+ products, we used copper phthalocyanine as a precursor, which contains a single copper atom in each molecule, allowing us to observe the evolution of single copper atoms to nanoclusters to nanoparticles. We found that the average size of the copper nanoparticles was correlated to the selectivity of the C2+ products and identified the grain boundaries as the active sites for C2+ products. In addition, the reaction intermediates, such as CO, were found to accelerate the reconstruction of the copper nanoparticles.Next, we investigated the active sites of copper-based bimetallic catalysts. We designed and synthesized Ag@Cu and Ag@C@Cu core-shell nanoparticles to control the interface formation between silver and copper, making it possible to distinguish between the tandem and interface effects. By using this specially designed bimetallic catalysts, we found that the high local concentration of CO, generated by the eCO2RR on silver, suppressed the production of ethylene but improved the selectivity of ethanol compared with that on monometallic copper. These results indicate that the tandem effect in bimetallic catalysts for eCO2RR has the potential to switch the dominant C2+ product from ethylene to ethanol.Afterwards, we developed self-supported copper-based gas diffusion electrodes and achieved a current density up to 300 mA cm-2 with a high selectivity for C2+ products (> 40%). The self-supported gas diffusion electrodes also allowed us to compare the selectivity and activity of eCO2RR directly on the same catalysts in the batch and flow cells. This comparison revealed that the copper catalyst in the batch cell was limited by the mass transfer of CO2. However, the Cu catalyst in the flow cell produced a much higher selectivity of C2+ products at a higher current density due to the fast CO2 diffusion and high pH. The electrode design strategies and the experimental findings presented in this section are valuable for the development of other self-supported electrodes for practical applications.Finally, we found that more than 30% of the liquid products from eCO2RR passed through the gas diffusion electrode and anion exchange membrane (AEM) at commercial current densities from 50 mA cm-2 to 300 mA cm-2. Volatile products pass through the gas diffusion electrode mainly by evaporation, and the migration rate increases linearly with the applied current density and CO2 flow rate. Non-volatile products prefer to cross the AEM through electromigration, and the migration rate is affected by the current density and the flow rate of the catholyte.

EPFL2022

Rational Design of Pd-Based Catalysts for Selective Alkyne Hydrogenations

Rocio Micaela Crespo Quesada

Traditionally, the search for active and selective catalysts involved a rather tedious "hit-and-miss" approach in which hundreds, if not thousands catalysts were tested until the optimal substance was identified. With the advancing theoretical understanding of catalysis and the development of computational power, a new era of rational catalyst design is dawning. This approach, grounded on first principles, is based on new advances in synthesis, characterization and modeling with the ultimate aim of predicting the expected behavior of a catalyst based on chemical composition, molecular structure and morphology. The rational design of a catalyst is a complex process which spans across several levels of scale. In this thesis, the pursuit of a rational design for Pd-based catalysts effective in alkyne hydrogenations is presented. A multi-level integrated approach was thus applied ranging from the nano-scale design of the active sites for a specific reaction, taking into account its structure sensitivity, to the micro-scale design of the supported Pd nanoparticles including metal-additive and metal-support interactions as well as mass and heat transfer phenomena. In order to rationally design a catalyst at a nano-scale, i.e. a catalyst's active site, several methodologies have been hitherto applied, such as the study on single crystals or model catalysts. Here we present the use of metal nanoparticles with tuned sizes (5-30 nm) and shapes (cubes, octahedra and cube-octahedra) prepared via colloidal techniques. These nanoparticles can be tested per se and represent a new generation of model catalysts, complementing single crystal studies, which inherently lack the complexity of industrial catalysis. However, metal nanoparticles, especially those prepared in a controlled manner in order to tailor their shape and size, require the use of stabilizing and/or capping agents capable of directing their growth. These substances can mask the true catalytic behavior of the nanoparticles. Thus, it is of great importance to study the interactions of the active phase with the substances that are in close contact with it, in the so-called meso-scaled level of rational catalyst design. Therefore, the effect of the nature of the stabilizing agent on the catalytic response was studied, as well as the promoting effect of some of these substances. Finally, a methodology was developed capable of eliminating organic stabilizing agents from the surface of nanoparticles without compromising their morphological stability. The knowledge gathered in the first two levels can be applied further to reach the microscale rational catalyst design. In this thesis, a final catalyst consisting on well-defined stabilizer-free supported Pd nanoparticles was used in the hydrogenation of acetylene. This deep study of the catalytic behavior of well-defined Pd catalysts throughout several levels of scale and complexity have given us the tools needed to perform a rational catalyst design for alkyne hydrogenations. Depending on the specific reaction, the active phase can be optimized in terms of the desired activity and selectivity and can be tuned even further with the use of specific additives. Finally, the appropriate support also exerts a promoting effect on the nanoparticles and ensures their anchoring in addition to avoiding heat and mass transfer artifacts.

EPFL2011

Metal-organic framework derived copper catalysts for CO2 to ethylene conversion

Jun Li, Ning Wang

The electrochemical reduction of CO2 to ethylene provides a carbon-neutral avenue for the conversion of CO2 to value-added fuels and feedstocks, so contributing to the storage of intermittent renewable electricity. The exploration of efficient electrocatalysts with high ethylene selectivity and productivity is highly desirable but remains challenging. Here, we present a Cu-based catalyst derived from a metal-organic framework (Cu-MOF) which shows enhanced performance due to its porous morphology, complex oxidation states and strong lattice strain. X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy are utilized to track the evolution of the crystal structure and oxidation states during the reaction, and the results reveal that Cu2+ ions are rapidly reduced to Cu+ and then slowly to Cu-0, resulting in a Cu@CuxO core@shell structure. The tensile strain caused by the distorted grain is beneficial for the activation of CO2. Cu+/Cu-0 interfaces formed through stabilized Cu+ facilitate *CO-CO dimerization, promoting conversion to C2+ products and suppressing conversion to C-1 products. The optimized catalyst exhibits a 51% Faraday efficiency (FE) for ethylene and a 70% FE for C2+ products, with 20 h operational stability in an H-cell configuration, and a partial ethylene current density of 150mA cm(-2) in a flow-cell configuration.

ROYAL SOC CHEMISTRY2020