Synthesis and Applications of Colloidal Zeolites and Transition Metal Functionalized Ordered Mesoporous Carbons
In this thesis, colloidal zeolite particles were prepared, studied and further utilized in two applications. One of the first goals was to understand the formation of colloidal zeolites and more specifically the premature termination of their growth during synthesis. A pH-dependent equilibrium between the condensation and dissolution reactions is presented in this thesis to explain this behavior. By a controlled decrease in pH of the synthesis mixtures, it was possible to shift the equilibrium towards condensation and to favor the increase in particle size and reach full conversion. We showed that it is possible to cycle between zeolite growth and dissolution by cyclic acid and base adjustments of the pH. In addition, we gained new insights about the duration of the nucleation stage. Likewise, the chemical solution equilibria growth mechanism was studied in the synthesis of colloidal ZSM-5 particles, and besides observing an increase in the particle size and conversion yield, shifting the dynamic pH-dependent equilibrium led to an improved incorporation of aluminum into the zeolite framework.
As the second goal in this thesis, we used the colloidal zeolite particles for the preparation of two new materials: a hybrid zeolite-cellulose foam for CO2 capture and hierarchical micro-/mesoporous zeolite microspheres. The hybrid foams were produced by mixing colloidal silicalite-1 particles and cellulose nanofibrils/gelatin and applying a freeze-casting. The foams exhibited ultra-high loading of silicalite-1 particles and a linear relationship between the silicalite-1 and the CO2 adsorption capacity with a selectivity towards CO2-over-N2. In addition, a novel mesoporogen-free evaporation-driven colloidal assembly was developed to prepare mesoporous silicalite-1 microspheres. The synthesized materials exhibited interconnected porosity, high pore volume, and the method can be used with other colloidal particles to tailor the pore size, pore volume and surface area. Moreover, the method does not require long preparation times or high temperature which has a positive effect on production at industrial scale.
Porous carbon materials have received growing interest due to their unique properties, including porosity, high surface areas, low density and electrical conductivity. Here, special attention has been casted on the development of N-doped mesoporous carbon for energy conversion in fuel cell technologies. Numerous efforts have been devoted to developing inexpensive platinum-free catalysts, active towards oxygen reduction reaction (ORR). In this thesis, we synthesized Fe-N-doped ordered mesoporous carbon (OMC) materials using different types of iron salt and studied the effect of the counter anion on their structural and catalytic properties. Although the change of the anion led to a significant increase in the Fe content in the resultant Fe-N-OMC, it was found by rotating disc electrode (RDE) and fuel cell measurements, that such increase does not provide an noticeable improvement in the rate of ORR, suggesting that the additional fraction of iron consists of less active Fe species.
Fe-N-doped ordered mesoporous carbon
Walter Rosas Arbelaez
Chalmers, Kemi och kemiteknik, Tillämpad kemi, Teknisk ytkemi
Walter Rosas-Arbelaez and Anders E.C. Palmqvist, Establishing the Role of Solution Equilibria in Zeolite Growth
Walter Rosas-Arbelaez and Anders E.C. Palmqvist, Solution Equilibria-Controlled Growth of Colloidal Zeolite ZSM-5
Hierarchical micro-/mesoporous zeolite microspheres prepared by colloidal assembly of zeolite nanoparticles
RSC Advances,; Vol. 10(2020)p. 36459-36466
Artikel i vetenskaplig tidskrift
Influence of Iron Salt Anions on Formation and Oxygen Reduction Activity of Fe/N-Doped Mesoporous Carbon Fuel Cell Catalysts
ACS Omega,; Vol. 4(2019)p. 17662-17671
Artikel i vetenskaplig tidskrift
Bio-based Micro-/Meso-/Macroporous Hybrid Foams with Ultrahigh Zeolite Loadings for Selective Capture of Carbon Dioxide
ACS Applied Materials & Interfaces,; Vol. 11(2019)p. 40424-40431
Artikel i vetenskaplig tidskrift
Zeolites are porous materials with pore diameter of less than 1 nm that consist of a silica and alumina tetrahedra. These materials were discovered for the first time in 1756 by the Swedish mineralogist Axel Cronsted, but it was not until the 1930s that the first synthetic methods to prepare zeolites emerged. Since then, zeolites, both natural and synthetic, have been extensively investigated and used in catalytic applications like oil refining and petrochemistry. However, to this day their formation is still unclear and have generated a lot of debate.
Porous carbon materials have been used since the prehistoric era for water filtration and as medicine. Today, we know much more about these materials and their characteristics, including, good electrical, thermal, mechanical properties and low cost. These properties allow porous carbon materials to play a fundamental role in the new technologies like carbon capture, batteries and fuel cells. Fuel cell technology has long been considered as one of the renewable energies of the future, and recently their massive implementation is still finally taking off. However, the technology is still expensive and one of the reasons for this is the high cost of the platinum-based catalysts. Transition-metal modified mesoporous carbon catalysts have recently emerged as an alternative to replace platinum as for fuel cell catalysts due to the low cost and good performance. However, these materials still need to be optimized both from synthesis- and performance perspective before their commercialization.
This thesis includes the studies of the synthesis and characterization of zeolites and mesoporous carbons. One of the first goals in the synthesis of zeolites was to shed light on the recurrent questions regarding their formation and by understanding the formation, we can influence crucial properties that are needed for specific high-demanded applications. Also, zeolites were investigated in the preparation of functional materials that could offer solutions of processability and diffusion restrictions for some classical applications (e.g. catalyst) and emerging application (e.g. carbon capture). Besides zeolites, iron-nitrogen-doped mesoporous carbon materials were synthesized by using different iron salts and their catalytic performance as fuel cell catalysts was evaluated by a series of electrochemical experiments.
A multiscale approach towards mesostructured porous material design (MULTIMAT)
Europeiska kommissionen (EU), 2016-03-01 -- 2020-02-22.
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4870
Chalmers tekniska högskola
Opponent: Professor Dr. Ferdi Schüth, Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Germany