TY - BOOK
T1 - Part 1: Controlled Design of New Molecular Magnets by Rational Building-Block Approach Part 2: Tailoring High-Temperature Catalysts for Effective Induction-Heated Steam Reforming
AU - Vinum, Morten Gotthold
PY - 2018
Y1 - 2018
N2 - This thesis is build-up of two parts, the first involving molecular magnetism, and the latter dealing with induction-heated catalysis. Because of the diverse nature of the thesis, each chapter is briefly described to aid and guide the reader of this thesis. In chapters 1.1 through 1.3, the synthesis and characterization of new one-dimensional chain complexes encompassing rhenium(iv) is presented with fluoride as bridging ligand. Starting from (pph4)2[ref6]2h2o, it is possible to, in a controlled manner, produce magnetic chains involving transition metal ions and n-donor ligands such as pyridine, 3,5-dimethylpyridine and 4-tertbutylpyridine. Changing the steric bulk of the n-donor ligand has a direct impact on the bridging angle, increasing from slightly bent for n-donor being pyridine, strictly linear in the bulkier 3,5- dimethylpyridine and 4-tert-butylpyridine. The choice of ligand is also associated with a visible change in the separation of adjacent chains within the molecular crystal packing, increasing by 35% as the bulk of the ligand is increased. Investigating the magnetic properties of m(me2py)4ref6 (m = mn, fe, co, ni, zn; me2py = 3,5-dimethylpyridine) reveals a predominantly ferromagnetic interaction along the chain with a small antiferromagnetic contribution between adjacent chains, which largely manifests itself upon lowering the temperature below 4 k where a magnetic transition to an ordered antiferromagnetic state is observed (this is not the case for m = mn, zn). Single-chain magnetic behavior is confirmed in the compound fe(me2py)4ref6 with an ordering temperature of 3.2 k and barriers for the slow relaxing magnetization of 28 and 36 k respectively for the two regimes traditionally found in single-chain magnets (vide infra). In chapters 1.4 and 1.5 a transition is made from pure d-block chemistry into the chemistry of the lanthanides. Especially lanthanide complexes of high symmetry are desirable as high symmetry often makes parametrization easier by limiting the number of parameters to be determined by spectroscopic techniques. A series of binuclear complexes are prepared by reacting [ln(hfac)3]2h2o with 12 homoleptic d-block complexes employing bidentate ligands such as acetylacetonate, 2- mercaptophenolate and 2-mercaptopyridine n-oxide, to produce complexes of the type [ln(hfac)3m(l)3]. The intention was to produce trigonal single-molecule magnets, unfortunately this was never realized. In an attempt to produce molecular structures without solvent we also synthesize trinuclear compounds of the type [{ln(hfac)3}2m(acac)2(oh2)2] (ln = y, gd, tb, dy, er, yb; m = mn, co, ni, zn). The magnetic properties of a selection of these (ln = y, dy; m = co, ni, zn) is studied but the data is still inconclusive at this point. The ac susceptibility measurements shows a slow magnetic relaxation in all studied cases, indicative of single-molecule magnetic behavior, yet the relaxation is very fast, presumably quenched by the 3d-4f interaction leading to quantum tunneling of the magnetization. In the compound featuring diamagnetic zn (and hence no 3d-4f interaction) between two dy, the relaxation is slow enough to be studied in the frequency window available and has successfully been modelled to a raman-type relaxation process, suggesting that the magnetic relaxation is dissipated via lattice vibrations. Finally, chapter 1.6 concludes on the work presented in part 1. In chapters 2.1 through 2.3, a general introduction to heterogeneous catalysis with emphasis on steam methane reforming (smr) is made, followed by an introduction to magnetic induction heating of nanoparticles and uses thereof. Problems pertaining to the current design of a smr reformer are highlighted, and justifications for pursuing induction-heated steam reforming are presented. In chapter 2.4, prior work related to the current project is presented, as well as considerations given in designing and planning part 2 of this phd project. Synthesis and characterization of the produced magnetic nanoparticles are presented, and it is shown that by alloying co and ni together, it is possibly to obtain a nanoparticle product with a well-defined metal distribution, placed homogeneously within an inert alumina carrier, which synergistically utilizes the magnetic properties of co and the catalytic properties of ni in steam methane reforming at elevated temperatures. The synthesized nanoparticles can compete with industrially relevant catalysts in terms of turnover frequency numbers, and the heat transfer from the magnetic field to the process gas via the catalyst is found to not be the limiting factor in a dedicated induction heated smr experiment. Finally, chapter 2.5 concludes on the work presented in part 2, and highlights future projects within this area which could be undertaken to further investigate the possibility of industrially implementing induction-heated catalysis.
AB - This thesis is build-up of two parts, the first involving molecular magnetism, and the latter dealing with induction-heated catalysis. Because of the diverse nature of the thesis, each chapter is briefly described to aid and guide the reader of this thesis. In chapters 1.1 through 1.3, the synthesis and characterization of new one-dimensional chain complexes encompassing rhenium(iv) is presented with fluoride as bridging ligand. Starting from (pph4)2[ref6]2h2o, it is possible to, in a controlled manner, produce magnetic chains involving transition metal ions and n-donor ligands such as pyridine, 3,5-dimethylpyridine and 4-tertbutylpyridine. Changing the steric bulk of the n-donor ligand has a direct impact on the bridging angle, increasing from slightly bent for n-donor being pyridine, strictly linear in the bulkier 3,5- dimethylpyridine and 4-tert-butylpyridine. The choice of ligand is also associated with a visible change in the separation of adjacent chains within the molecular crystal packing, increasing by 35% as the bulk of the ligand is increased. Investigating the magnetic properties of m(me2py)4ref6 (m = mn, fe, co, ni, zn; me2py = 3,5-dimethylpyridine) reveals a predominantly ferromagnetic interaction along the chain with a small antiferromagnetic contribution between adjacent chains, which largely manifests itself upon lowering the temperature below 4 k where a magnetic transition to an ordered antiferromagnetic state is observed (this is not the case for m = mn, zn). Single-chain magnetic behavior is confirmed in the compound fe(me2py)4ref6 with an ordering temperature of 3.2 k and barriers for the slow relaxing magnetization of 28 and 36 k respectively for the two regimes traditionally found in single-chain magnets (vide infra). In chapters 1.4 and 1.5 a transition is made from pure d-block chemistry into the chemistry of the lanthanides. Especially lanthanide complexes of high symmetry are desirable as high symmetry often makes parametrization easier by limiting the number of parameters to be determined by spectroscopic techniques. A series of binuclear complexes are prepared by reacting [ln(hfac)3]2h2o with 12 homoleptic d-block complexes employing bidentate ligands such as acetylacetonate, 2- mercaptophenolate and 2-mercaptopyridine n-oxide, to produce complexes of the type [ln(hfac)3m(l)3]. The intention was to produce trigonal single-molecule magnets, unfortunately this was never realized. In an attempt to produce molecular structures without solvent we also synthesize trinuclear compounds of the type [{ln(hfac)3}2m(acac)2(oh2)2] (ln = y, gd, tb, dy, er, yb; m = mn, co, ni, zn). The magnetic properties of a selection of these (ln = y, dy; m = co, ni, zn) is studied but the data is still inconclusive at this point. The ac susceptibility measurements shows a slow magnetic relaxation in all studied cases, indicative of single-molecule magnetic behavior, yet the relaxation is very fast, presumably quenched by the 3d-4f interaction leading to quantum tunneling of the magnetization. In the compound featuring diamagnetic zn (and hence no 3d-4f interaction) between two dy, the relaxation is slow enough to be studied in the frequency window available and has successfully been modelled to a raman-type relaxation process, suggesting that the magnetic relaxation is dissipated via lattice vibrations. Finally, chapter 1.6 concludes on the work presented in part 1. In chapters 2.1 through 2.3, a general introduction to heterogeneous catalysis with emphasis on steam methane reforming (smr) is made, followed by an introduction to magnetic induction heating of nanoparticles and uses thereof. Problems pertaining to the current design of a smr reformer are highlighted, and justifications for pursuing induction-heated steam reforming are presented. In chapter 2.4, prior work related to the current project is presented, as well as considerations given in designing and planning part 2 of this phd project. Synthesis and characterization of the produced magnetic nanoparticles are presented, and it is shown that by alloying co and ni together, it is possibly to obtain a nanoparticle product with a well-defined metal distribution, placed homogeneously within an inert alumina carrier, which synergistically utilizes the magnetic properties of co and the catalytic properties of ni in steam methane reforming at elevated temperatures. The synthesized nanoparticles can compete with industrially relevant catalysts in terms of turnover frequency numbers, and the heat transfer from the magnetic field to the process gas via the catalyst is found to not be the limiting factor in a dedicated induction heated smr experiment. Finally, chapter 2.5 concludes on the work presented in part 2, and highlights future projects within this area which could be undertaken to further investigate the possibility of industrially implementing induction-heated catalysis.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01011962970&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Part 1: Controlled Design of New Molecular Magnets by Rational Building-Block Approach Part 2: Tailoring High-Temperature Catalysts for Effective Induction-Heated Steam Reforming
PB - Department of Chemistry, Faculty of Science, University of Copenhagen
ER -