Unravelling the Zn‐Cu Interaction during Activation of a Zn‐promoted Cu/MgO Model Methanol Catalyst

We report on an inverse model Cu/MgO methanol catalyst modified with 5 % zinc oxide at the Cu surface to element-specifically probe the interplay of metallic copper and zinc oxide during reductive activation. The structure of copper and zinc was unraveled by in situ X-ray diffraction (XRD) and in situ X-ray absorption spectroscopy (XAS) supported by theoretical modelling of the extended X-ray absorption fine structure and X-ray absorption near-edge structure spectra. Temperature-programmed reduction in H2 during in situ XAS showed that copper was reduced starting at 145 °C. With increasing reduction temperature, zinc underwent first a geometrical change in its structure, followed by reduction. The reduced zinc species were identified as surface alloy sites, which coexisted from 200 °C to 340 °C with ZnO species at the copper surface. At 400 °C Zn−Cu bulk-alloyed particles were formed. According to in situ XRD and in situ XAS, about half of the ZnO was not fully reduced, which can be explained by a lack of contact with copper. Our experimental results were further substantiated by density functional theory calculations, which verified that ZnO with neighboring Cu atoms reduced more easily. By combining these results, the distribution, phase and oxidation state of Zn species on Cu were estimated for the activated state of this model catalyst. This insight into the interplay of Cu and Zn forms the basis for deeper understanding the active sites during methanol synthesis

Exploring RE-MOFs with spn Topology and their Stimuli-Responsive Structural Properties

The work described herein explores an emerging class of metal–organic frameworks (MOFs) that are synthesized using rare-earth (RE) metals, known as RE-MOFs. In this work, these RE-MOFs are comprised of RE-hexanuclear clusters and tritopic organic linkers that give rise to a framework with spn topology. This thesis explores the (i) design, synthesis, and characterization of a yttrium (Y(III)) hexanuclear-cluster based RE-MOF, known as CU-45 (CU = Concordia University, experiment 45), (ii) the implementation of neodymium oxide (Nd2O3) precursors as templating agents, and (iii) the design, synthesis, and characterization of terbium and europium (Tb(III) and Eu(III)) MOFs with preliminary exploration of luminescence properties for potential sensing applications. Chapter 2 explores the synthesis, characterization, and stimuli-responsive structural transformation of CU-45. CU-45, an achiral MOF, is exposed to various external stimuli including pressure, pH, temperature, and solvent, and in each case undergoes a phase transformation to give a chiral, RE-chain based MOF, known as Y-MOF-76. The physical and chemical properties of CU-45 and Y-MOF-76, as well as the underlying mechanism of the stimuli-responsive structural transformation is discussed. Chapter 3 aims to address and improve the stability of CU-45, first by exploring a phenomenon known as lanthanide templating, which can facilitate the assembly and stabilization of lanthanide clusters. By adding a Nd2O3 precursor template to the CU-45 synthetic mixture, a phase pure MOF with improved crystallinity can be obtained. Furthermore, the effect of incorporating other rare-earth ions in CU-45, including Tb(III)- and mixed-metal Tb(III)/Eu(III)-CU-45, on stability is examined

Unravelling the synthesis of a rare-earth cluster-based metal–organic framework with spn topology

Y-CU-45, an analogue of Zr-MOF-808, is synthesized for the first time. Several reaction conditions are tested demonstrating that two fluorinated modulators are required for a reproducible synthesis yielding high quality material. Y-CU-45 shows high crystallinity and surface area, shining light on the potential for rare-earth cluster-based MOFs with open metal sites

Unravelling the synthesis of a rare-earth cluster-based metal–organic framework with spn topology

Y-CU-45, an analogue of Zr-MOF-808, is synthesized for the first time. Several reaction conditions are tested demonstrating that two fluorinated modulators are required for a reproducible synthesis yielding high quality material. Y-CU-45 shows high crystallinity and surface area, shining light on the potential for rare-earth cluster-based MOFs with open metal sites