Spectroscopy and Microreactor Technology for Single Catalyst Particle Diagnostics

Abstract

This PhD thesis describes research on the use of microfluidics and spectroscopy for single catalyst particle diagnostics. In Chapter 2, a 3-D printed microfluidic chip has been used to magnetophoretically sort a set of fluid catalytic cracking (FCC) particles into five different fractions. Each of these fractions could be analyzed in great detail, which allowed to relate their chemical composition to their magnetic moment. The increase in magnetic moment originates from the presence of metal poisons, in particularly Fe. We believe that this technology could be used to sort other magnetic catalysts for analysis purposes, for example Fe-based Fischer-Tropsch synthesis catalysts. It can also serve as a tool to decrease the heterogeneity of the samples from an industrial reactor unit, thereby providing an alternative method for catalyst quality control measurements. Chapter 3 shows that correlating information from multiple characterization techniques per FCC catalyst particle, provides valuable insights in the heterogeneity of density-separated FCC particles. Furthermore, the possibility to measure multiple catalyst particles adds statistical value to the data obtained. Where bulk characterization measurements can give insight in the trends between the six density-separated ECAT fractions, the diagnostics of single catalyst particles can show acidity and accessibility trends even within each fraction, as provided by catalyst staining with dye molecules in combination with fluorescence microscopy. Furthermore, the large intrinsic interparticle heterogeneity of each density separated fraction was visualized by overlaying micro-X-ray fluorescence (μXRF) maps of Fe and Ni with the fluorescence microscopy maps, obtained after catalyst particle staining. In Chapters 4 and 5, two droplet-based microreactors were described that can be used for chemical analysis at elevated temperatures and pressure. Stable formation of monodisperse droplets, as well as heating of the droplets up to 120 °C and up to pressures of 7 bar, has been achieved with the droplet microreactor in Chapter 4. The temperature of the heater elements can be controlled at a standard deviation of approximately 2.6 °C from the setpoint. This microreactor was used for high-throughput screening of individual FCC catalyst particles, based on their activity. The screening was performed in-situ at elevated temperatures up to 95 °C using the oligomerization of 4-methoxystyrene as a marker for the catalysts’ activity. In total ~1000 FCC catalyst particles were detected at an average rate of 1 particle per 2.4 seconds. The microreactor set-up described in Chapter 5 also has an implemented sorting system using dielectrophoresis (DEP). FCC particles stained with 4-fluorostyrene were sorted based on their fluorescence intensity, and thus their Brønsted acidity. After sorting and retrieving the FCC particles, they were analyzed in the same manner as was described in Chapter 3. Chapters 6 and 7 are dedicated to other catalytic systems. In Chapter 6, we show the proof of concept of a polydimethylsiloxane (PDMS) microreactor for high-throughput, multiphase catalytic reactions, demonstrating the liquid-phase hydrogenation of methylene blue (MB). A liquid channel with Pd/SiO2 particles of 40 μm encapsulated in droplets containing MB in ethanol are flanked by two gas channels with H2, separated with 50 μm PDMS walls. Due to the high permeability of PDMS, H2 diffuses into the liquid channels and facilitates the Pd-catalyzed hydrogenation of MB at room temperature. Chapter 7 describes a simple fluorinated ethylene propylene (FEP)-based tube-in-tube microreactor for single catalyst particle diagnostics. The system was tested for the synthesis of a fluorescent benzocoumarin via a Knoevenagel condensation, catalyzed by several hydrotalcite derivatives. Due to the mechanical instability of the catalyst particles, no single particle diagnostics could be performed. However, fluorescence intensity measurements were carried out to screen the performance of four different hydrotalcite catalysts for the synthesis of the fluorescent coumarin.