Torstein Fjermestad

• Gutterød, Emil Sebastian; Lazzarini, Andrea; Fjermestad, Torstein; Kaur, Gurpreet; Manzoli, Maela & Bordiga, Silvia [Vis alle 12 forfattere av denne artikkelen] (2019). Hydrogenation of CO2 to Methanol by Pt Nanoparticles Encapsulated in UiO-67: Deciphering the Role of the Metal−Organic Framework. Journal of the American Chemical Society. ISSN 0002-7863. 142. doi: 10.1021/jacs.9b10873. Fulltekst i vitenarkiv Vis sammendrag

  Metal-organic frameworks (MOFs) show great prospect as catalysts and catalyst support materials. Yet, studies that address their dynamic, kinetic and mechanistic role in target reactions are scarce. In this study, an exceptionally stable MOF catalyst consisting of Pt nanoparticles (NPs) embedded in a Zr-based UiO-67 MOF was subject to steady-state and transient kinetic studies involving H/D and 13C /12C exchange, coupled with operando infrared spectroscopy and density functional theory (DFT) modeling, targeting methanol formation from CO2/H2 feeds at 170 C and 1-8 bar pressure. The study revealed that methanol is formed at the interface between the Pt NPs and defect Zr nodes, via formate species attached to the Zr nodes. Methanol formation is mechanistically separated from the formation of co-products CO and methane, except for hydrogen activation on the Pt NPs. Careful analysis of transient data revealed that the number of intermediates was higher than the number of open Zr sites in the MOF lattice around each Pt NP. Hence, additional Zr sites must be available to formate formation. DFT modelling revealed that Pt NP growth is sufficiently energetically favored to enable displacement of linkers and creation of open Zr sites during pretreatment. However, linker displacement during formate formation is energetically disfavored, in line with the excellent catalyst stability observed experimentally. Overall, the study provides firm evidence that methanol is formed at the interface of Pt NPs and linker-deficient Zr6O8 nodes resting on the Pt NP surface.

• Fjermestad, Torstein; Svelle, Stian & Swang, Ole (2015). Mechanism of Si island formation in SAPO-34. Journal of Physical Chemistry C. ISSN 1932-7447. 119(4), s. 2086–2095. doi: 10.1021/jp510845z. Vis sammendrag

  With the aim of understanding the Si island formation in SAPO-34, we have carried out a computational mechanistic study. Briefly, the Si island formation in SAPO-34 is explained by three successive reactions. First, the framework Si atom is removed from the framework through the action of four water molecules. Second, the hydrogarnet defect generated by the desilication is healed by an available H3PO4 molecule. Third, the extra framework Si(OH)4 species inserts in the framework position of a phosphorus atom while, in a concerted fashion, “kicking out” the phosphorus atom as a H3PO4 extra-framework species. When these exchanges of framework and extra-framework species are repeated, the isolated Si atoms may eventually cluster into Si islands.

• Fjermestad, Torstein; Svelle, Stian & Swang, Ole (2015). Desilication of SAPO-34: Reaction mechanisms from periodic DFT calculations. Journal of Physical Chemistry C. ISSN 1932-7447. 119(4), s. 2073–2085. doi: 10.1021/jp510844v. Vis sammendrag

  With the aim of understanding the desilication of SAPO-34, we compared three different reaction mechanisms for the hydrolysis of framework silicon by use of density functional theory (DFT) calculations. All three mechanisms are characterized by stepwise hydrolyses of Si–O–Al bonds. In the most favorable mechanism water molecules adsorb strongly to the Lewis acidic Al atoms neighboring the Si atom. Furthermore, evaluation of free energies reveals that an additional water molecule may catalyze the hydrolysis of the first Si–O–Al bond.

• Fjermestad, Torstein; Svelle, Stian & Swang, Ole (2013). Mechanistic Comparison of the Dealumination in SSZ-13 and the Desilication in SAPO-34. Journal of Physical Chemistry C. ISSN 1932-7447. 117(26), s. 13442–13451. doi: 10.1021/jp4028468. Vis sammendrag

  With the purpose of understanding the behavior of aluminosilicate zeolites and silicoaluminophosphates (SAPOs) in the presence of steam, we carried out a computational density functional theory (DFT) study on the desilication of SAPO-34. The mechanism studied was a stepwise hydrolysis of the four bonds to the Si heteroatom. An analogous process to the desilication of SAPO-34 is the dealumination of SSZ-13. To investigate possible mechanistic differences between the two processes, we compared the results of this study with the results of a previous study on dealumination in SSZ-13. We found that the intermediates along the dealumination path of SSZ-13 have one of the protons bonded to a bridging oxygen atom. In the corresponding intermediates of the desilication path in SAPO-34, the same proton prefers to be part of an aqua ligand coordinated to an Al atom. The principal factor determining the different proton locations is the electronic requirement of the atoms surrounding the proton. The different proton locations in SSZ-13 and SAPO-34 put clear conditions on possible mechanisms, thus causing them to be different for the two materials. We expect the principles determining the proton location also to be valid for other mechanisms of dealumination in SSZ-13 and desilication in SAPO-34.

Se alle arbeider i Cristin

• Fjermestad, Torstein; Uglietti, Riccardo; Micale, Daniele; Bracconi, Mauro; Phan, Anh & Striolo, Alberto [Vis alle 9 forfattere av denne artikkelen] (2023). Modelling the methanol to dimethyl ether reaction – coupling kinetic with transport from Å to cm scale.
• Fjermestad, Torstein; Uglietti, Riccardo; Micale, Daniele; Bracconi, Mauro; Phan, Anh & Striolo, Alberto [Vis alle 9 forfattere av denne artikkelen] (2023). Modelling the Methanol to Dimethyl Ether Reaction – Coupling Kinetics with Transport from CM to Å Scale.
• Fjermestad, Torstein; Uglietti, Riccardo; Micale, Daniele; Bracconi, Mauro; Phan, Anh & Striolo, Alberto [Vis alle 9 forfattere av denne artikkelen] (2023). Modelling the Methanol to Dimethyl ether reaction – coupling kinetics with transport from CM to Å scale.
• Fjermestad, Torstein; Uglietti, Riccardo; Micale, Daniele; Bracconi, Mauro; Phan, Anh & Striolo, Alberto [Vis alle 9 forfattere av denne artikkelen] (2022). Modelling the Methanol to Dimethyl ether reaction – coupling kinetics with transport from Å to CM scale.
• Fjermestad, Torstein; Micale, Daniele; Ahn, Phan; Striolo, Alberto; Stamatakis, Michail & Iacoviello, Francesco [Vis alle 8 forfattere av denne artikkelen] (2021). The effective diffusivity bridges the kinetics at the active sites and the fluid flow in the reactor.
• Olsbye, Unni; Gutterød, Emil Sebastian; Lazzarini, Andrea; Fjermestad, Torstein; Pulumati, S.H. & Nova, Ainara [Vis alle 7 forfattere av denne artikkelen] (2021). Mechanistic studies of CO2 hydrogenation to methanol, methane and CO over Pt-containing Zr-MOFs .
• Fjermestad, Torstein; Malola, Sami; Svelle, Stian; Bleken, Francesca Lønstad & Swang, Ole (2013). Mechanisms of dealumination in zeolite SSZ-13 and of desilication in SAPO-34.
• Fjermestad, Torstein; Zokaie, Mahsa; Svelle, Stian & Swang, Ole (2013). Towards atomistic understanding of silicon island formation in SAPO-34.
• Svelle, Stian; Fjermestad, Torstein; Malola, Sami; Zokaie, Mahsa; Lillerud, Karl Petter & Swang, Ole (2013). Theoretical studies of T-atom distribution and mobility in zeolites and zeotypes.
• Svelle, Stian; Fjermestad, Torstein; Zokaie, Mahsa; Lillerud, Karl Petter & Swang, Ole (2013). DFT studies of T-atom distribution and mobility in zeolites and zeotypes.
• Fjermestad, Torstein; Svelle, Stian & Swang, Ole (2012). Mechanisms of dealumination in zeolite SSZ-13 and of desilication in SAPO-34.

Se alle arbeider i Cristin