Going Beyond Silver in Ethylene Epoxidation with First-Principles Catalyst Screening

Ethylene epoxidation is industrially and commercially one of the most important selective oxidations. Silver catalysts have been state-of-the-art for decades, their efficiency steadily improving with empirical discoveries of dopants and co-catalysts. Herein, we perform a computational screening of the metals in the periodic table, identify prospective superior catalysts and experimentally demonstrate that Ag/CuPb, Ag/CuCd and Ag/CuTl outperform the pure-Ag catalysts, while they still confer an easily scalable synthesis protocol. Furthermore, we show that to harness the potential of computationally-led discovery of catalysts fully, it is essential to include the relevant in situ conditions e.g., surface oxidation, parasitic side reactions and ethylene epoxide decomposition, as neglecting such effects leads to erroneous predictions. We combine ab initio calculations, scaling relations, and rigorous reactor microkinetic modelling, which goes beyond conventional simplified steady-state or rate-determining modelling on immutable catalyst surfaces. The modelling insights have enabled us to both synthesise novel catalysts and theoretically understand experimental findings, thus, bridging the gap between first-principles simulations and industrial applications. We show that the computational catalyst design can be easily extended to include larger reaction networks and other effects, such as surface oxidations. The feasibility was confirmed by experimental agreement

Novel Ba-hexaferrite structural variations stabilized on the nanoscale as building blocks for epitaxial bi-magnetic hard/soft sandwiched maghemite/hexaferrite/maghemite nanoplatelets with out-of-plane easy axis and enhanced magnetization

Atomic-resolution scanning-transmission electron microscopy showed that barium hexaferrite (BHF) nanoplatelets display a distinct structure, which represents a novel structural variation of hexaferrites stabilized on the nanoscale. The structure can be presented in terms of two alternating structural blocks stacked across the nanoplatelet: a hexagonal (BaFeO) R block and a cubic (FeO) spinel S block. The structure of the BHF nanoplatelets comprises only two, or rarely three, R blocks and always terminates at the basal surfaces with the full S blocks. The structure of a vast majority of the nanoplatelets can be described with a SR∗S∗RS stacking order, corresponding to a BaFeO composition. The nanoplatelets display a large, uniaxial magnetic anisotropy with the easy axis perpendicular to the platelet, which is a crucial property enabling different novel applications based on aligning the nanoplatelets with applied magnetic fields. However, the BHF nanoplatelets exhibit a modest saturation magnetization, M, of just over 30 emu g. Given the cubic S block termination of the platelets, layers of maghemite, γ-FeO, (M), with a cubic spinel structure, can be easily grown epitaxially on the surfaces of the platelets, forming a sandwiched M/BHF/M platelet structure. The exchange-coupled composite nanoplatelets exhibit a remarkably uniform structure, with an enhanced M of more than 50 emu g while essentially maintaining the out-of-plane easy axis. The enhanced M could pave the way for their use in diverse platelet-based magnetic applications

Synthesis of Poly-Sodium-Acrylate (PSA)-Coated Magnetic Nanoparticles for Use in Forward Osmosis Draw Solutions

The synthesis of magnetic nanoparticles (MNPs) coated with hydrophilic poly-sodium-acrylate (PSA) ligands was studied to assess PSA-MNP complexes as draw solution (DS) solutes in forward osmosis (FO). For MNP-based DS, the surface modification and the size of the MNPs are two crucial factors to achieve a high osmolality. Superparamagnetic nanoparticles (NP) with functional groups attached may represent the ideal DS where chemical modifications of the NPs can be used in optimizing the DS osmolality and the magnetic properties allows for efficient recovery (DS re-concentration) using an external magnetic field. In this study MNPs with diameters of 4 nm have been prepared by controlled chemical co-precipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+ under inert atmosphere and a pure magnetite phase could be verified by X-ray diffraction. Magnetic colloid suspensions containing PSA-coated MNPs with three different molar ratios of PSA:MNP = 1:1, 1:2 and 1:3 were prepared and assessed in terms of osmotic pressure, aggregation propensity and magnetization. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of PSA on coated MNPs and pristine PSA-MNPs with a molar ratio PSA:MNP = 1:1 exhibited an osmotic pressure of 30 bar. Molar ratios of PSA:MNP = 1:2 and 1:3 lead to the formation of less stabile magnetic colloid solutions, which led to the formation of aggregates with larger average hydrodynamic sizes and modest osmotic pressures (5.5 bar and 0.2 bar, respectively). After purification with ultrafiltration, the 1:1 nanoparticles exhibited an osmotic pressure of 9 bar with no aggregation and a sufficient magnetization of 25 emu/g to allow for DS regeneration using an external magnetic field. However, it was observed that the amount of PSA molecules attached to the MNPs decreased during DS recycling steps, leaving only strong chelate-bonded core-shell PSA as coating on the MNPs. This demonstrates the crucial role of MNP coating robustness in designing an efficient MNP-based DS for FO

Inorganic Chemistry

Navodila za laboratorijske vaje pri predmetu Anorganska kemija za 1. letnik študijskega programa druge stopnje Kemija, ki se izvaja na Fakulteti za kemijo in kemijsko tehnologijo Univerze v Mariboru.Laboratory manual for Inorganic chemistry course for students attending Inorganic chemistry. The course is for students in 1st year of master level in Chemistry

Superparamagnetic nanocomposites based on superparamagnetic iron oxide nanoparticles and polymethyl methacrylate

V pričujočem delu sem se ukvarjal s sintezo superparamagnetnih nanokompozitov na osnovi nanodelcev γ-Fe2O3 in PMMA. Nanodelce sem sintetiziral s koprecipitacijo Fe2+/Fe3+ ionov v vodni raztopini. Nanodelce prevlečene z oleinsko ali ricinolejsko kislino sem sintetiziral s koprecipitacijo Fe2+/Fe3+ ionov v vodni raztopini v prisotnosti oleinske oz. ricinolejske kisline. Preliminarne raziskave so jasno pokazale, da je nemogoče pripraviti superparamagnetne nanokompozite γ-Fe2O3 v PMMA matrici brez ustrezne funkcionalizacije površine magnetnih nanodelcev. Iz slik s presevnega elektronskega mikroskopa (TEM) sem zaključil, da je vzorec pripravljen z mešanje nanodelcev γ-Fe2O3 s PMMA v acetonu in kasnejšim obarjanjem polimera v vodi, fazno separiran. Vzorec je sestavljen iz aglomeratov nanodelcev γ-Fe2O3, ki niso vgrajeni v polimerno matrico. Nanokompozite sem pripravil z obarjalno polimerizacijo PMMA v prisotnosti nanodelcev prevlečenih z oleinsko kislino. Koloidno stabilni suspenziji nanodelcev prevlečenih z oleinsko kislino v n-dekanu sem dodal monomer metil metakrilat. Polimerizacijo monomera sem izvedel pri povišani temperaturi. Delež nanodelcev v nanokompozitu sem kontroliral preko razmerja nanodelci/monomer. S pomočjo TEM analize sem ugotovil, da so nanodelci homogeno porazdeljeni v polimerni matrici. Z višanjem razmerja prehaja mehanizem nastanka polimernih zrn preko homogene v heterogeno nukleacijo. Nanokompozit ohrani superparamagnetno naravo tudi ob vgradnji relativno velikega deleža vgrajenih nanodelcev, do 48 ut. %. Vgradnja velikega deleža magnetnih nanodelcev je razlog za visoko nasičeno magnetizacijo nanokompozitov, do 31 emu/g. Nanokompozitne delce sem pripravil s polimerizacijo monomera metil metakrilata v prisotnosti nanodelcev v miniemulziji. Koloidno stabilno suspenzijo sestavljeno iz nanodelcev prevlečenih z ricinolejsko kislino, ultrahidrofoba in iniciatorja v monomeru, sem dodal k vodni raztopini surfaktanta. Miniemulzijo sem pripravil s pomočjo ultrazvoka. Polimerizacijo sem izvajala pri povišani temperaturi. S spreminjanjem deleža surfaktanta sem prilagajal povprečni premer nanokompozitnih delcev v razponu med ~25 nm in ~50 nm. Zaradi visokega ζ-potenciala je suspenzija nanokompozitnih delcev v vodi koloidno stabilna. S TEM slik nanokompozitnih delcev sem ugotovil, da so nanokompozitni delci sestavljeni iz nanodelcev, ki tvorijo jedro delca in tankega sloja polimera okrog jedra. V nanokompozitne delce sem uspel vgraditi do 39 ut. % magnetnih nanodelcev, ne glede na velikost nanokompozitnih delcev. Nasičena magnetizacija nanokompozitnih delcev znaša 27 emu/g.Presented work describes synthesis of superparamagnetic nanocomposites, based on superparamagnetic γ-Fe2O3 nanoparticles and PMMA. Nanoparticles were synthesized by the coprecipitation of Fe2+/Fe3+ ions from an aqueous solution. Oleic or ricinoleic acid coated nanoparticles were synthesized by the coprecipitation of Fe2+/Fe3+ ions from an aqueous solution in the presence of oleic or ricinoleic acid. Preliminary study clearly demonstrated that it is impossible to prepare superparamagnetic nanocomposite of the γ-Fe2O3 in the PMMA matrix without nanoparticles functionalization. Sample prepared by the mixing of the γ-Fe2O3 and the PMMA in the acetone and subsequent precipitation of the polymer by water addition, was composed of two separated phases, as observed by transmission electron microscopy (TEM). The phases were identified as agglomerates of the γ-Fe2O3 which were not encapsulated by the PMMA matrix. Nanocomposites were prepared by the precipitation polymerization of the methyl methacrylate in the presence of oleic acid coated nanoparticles. Methyl methacrylate was added to the colloidal suspension of the oleic acid coated nanoparticles in n-decane and in-situ polymerization was carried out at elevated temperatures. The content of nanoparticles was controlled by varying the nanoparticles/monomer ratio. The TEM analysis showed that the nanoparticles were well dispersed in the polymer matrix. The mechanism of formation of the polymer grain changes from homogeneous to heterogeneous nucleation as the ratio is increased. Nanocomposites retained their superparamagnetic nature even when encapsulated by polymer with concentrations up to 48 wt. %. The high loading of magnetic nanoparticles resulted in relatively high saturation magnetizations of the nanocomposites, up to 31 emu/g. Nanocomposite particles were prepared using the mini-emulsion polymerization of a monomer in the presence of the nanoparticles. A colloidal suspension composed of ricinoleic acid coated iron-oxide nanoparticles, the initiator and the ultrahydrophobe in the monomer, methyl methacrylate, was added to an aqueous solution of surfactant and then ultrasonified to promote the formation of the mini-emulsion. The polymerization was initiated by raising the temperature. By changing the content of surfactant, nanocomposite particles with an average diameter ranging from 25 to 50 nm were obtained. Because of the high ζ-potential, the nanocomposite particles formed a stable suspension in water. TEM showed that the core of the prepared nanocomposite particles was composed of iron-oxide nanoparticles homogeneously distributed within a polymer matrix and a thin polymer shell. The content of magnetic nanoparticles dispersed in the polymer was as high as 39 wt. %, resulting in a high saturation magnetization of 27 emu/g

Preparation of Co-ferrite nanoparticles with a narrow size distribution by the thermal decomposition of oleates

V prispevku opisujemo sintezo nanodelcev kobaltovega ferita z ozko porazdelitvijo velikosti z metodo termičnega razpada organskega kompleksa. Sinteza nanodelcev je potekala v dveh stopnjah. V prvi smo sintetizirali železov in kobaltov oleat z reakcijo kobaltovega (II) in železovega (III) klorida z natrijevim oleatom v mešanici topil. V drugi stopnji smo raztopino oleatov, ki smo ji dodali različne količine oleinske kisline, segreli do vrelišča topila (heksadeken 282 °C ali oktadeken 316 °C). Na povišani temperaturi oleati razpadejo in tvorijo oksidne nanodelce. Na nanodelce je vezan monomolekulski sloj oleinske kisline, ki omogoča dispergiranje nanodelcev v nepolarnih topilih. Povprečna velikost nanodelcev kobaltovega ferita je odvisna od temperature, časa siteze in količine dodane oleinske kisline. Sintetizirani nanodelci v območju velikosti med 9 nm in 20 nm izkazujejo ferimagnetno vedenje ter magnetne lastnosti, ki se spreminjajo s povprečno velikostjo nanodelcev. Predpostavili smo mehanizem nastanka nanodelcev kobaltovega ferita, ki vključuje koalescenco manjših nanodelcev in njihovo rekristalizacijo.A synthesis method for the preparation of narrow-size-distribution Co-ferrite nanoparticles by thermal decomposition of oleates is presented. A two-step method was used to produce the nanoparticles. In the first step cobalt and iron oleates were synthesized by reacting iron (III) and cobalt (II) chlorides with sodium oleate in a mixture of solvents. In the second step the oleates solution, to which different amounts of oleic acid were added, was heated to the solvents’ boiling point (hexadecene 282 °C or oktadecene 316 °C). At elevated temperatures oleates decompose and oxide nanoparticles are formed. The nanoparticles are than coated with a mono-molecular layer of oleic acid, are hydrophobic and can be dispersed in non-polar organic solvents. The average size of the cobalt ferrite nanoparticles depends on the temperature, time of the synthesis and the concentration of oleic acid. In the size range between 9 nm and 20 nm the synthesized nanoparticles exhibited ferromagnetic behavior and size-dependent magnetic properties. A mechanism for the formation of cobalt ferrite nanoparticles with re-crystallization of nanoparticles composed of smaller nanoparticles is proposed

The magnetic and colloidal properties of CoFe2O4CoFe_2O_4 nanoparticles synthesized by co-precipitation

Magnetic $CoFe_2O_4$ nanoparticles were synthesized by co-precipitation at 80 °C. This co-precipitation was achieved by the rapid addition of a strong base to an aqueous solution of cations. The investigation of the samples that were quenched at different times after the addition of the base, using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) and X-ray powder diffractometry, revealed the formation of a Co-deficient amorphous phase and $Co(OH)_2$, which rapidly reacted to form small $CoFe_2O_4$ nanoparticles. The nanoparticles grew with the time of aging at elevated temperature. The colloidal suspensions of the nanoparticles were prepared in both an aqueous medium and in a non-polar organic medium, with the adsorption of citric acid and ricinoleic acid on the nanoparticles, respectively. The measurements of the room-temperature magnetization revealed the ferrimagnetic state of the $CoFe_2O_4$ nanoparticles, while their suspensions displayed superparamagnetic behaviour.Magnetne nanodelce $CoFe_2O_4$ smo sintetizirali s soobarjanjem na temperaturi 80 °C. Soobarjanje smo dosegli s hitrim dodatkom močne baze k vodni raztopini kationov. Mehanizem nastanka nanodelcev $CoFe_2O_4$ smo študirali tako, da smo odvzeli vzorce pri različnih časovnih intervalih po dodatku baze in ustavili kemijske reakcije. Analize vzorcev s presevno elektronsko mikroskopijo (TEM) v kombinaciji z EDXS spektroskopijo in rentgensko praškovno difrakcijo (XRD) so pokazale nastanek amorfne Co deficitne faze in $Co(OH)_2$, ki hitro reagirata in nastanejo majhni $CoFe_2O_4$ nanodelci. Med staranjem na povišani temperaturi nanodelci rastejo. Koloidne suspenzije nanodelcev v vodnem in organskem ne- polarnem mediju smo pripravili z adsorpcijo citronske ozirom ricinolejske kisline. Meritve magnetnih lastnosti na sobni temperaturi so pokazale ferimagnetne lastnosti nanodelcev $CoFe_2O_4$ medtem, ko so suspenzije kazale superparamagnetno obnašanje