Within the scope of CO2 activation, the programme group is carrying out several European projects Horizon 2020, among them also FReSMe and MefCO2. The group members participate in the multiscale modelling of the chemical process of CO2 valorisation. Heterogeneous catalytic hydrogenation of gaseous carbon dioxide into methanol is an important reductive transformation in chemical engineering, in the field of renewable energy and the nascent green chemistry as it offers means to utilize surplus electric energy and convert a pollutant and greenhouse gas into a useful building block and bio-fuel. On industrial scale, multifunctional copper/zinc catalysts on various supports (e.g. CZA with alumina) are most commonly used due to their high selectivity and conversion. In this work, we performed post-Hartree-Fock DFT-based calculations to evaluate the thermodynamics and elucidate the pathway, which lead to the formation of methanol from CO2 on actual spinel tri-metallic materials. First, a commercial Cu/ZnO/Al2O3 was prepared using co-precipitation and evaluated to obtain information on the structure of active sites for description. We performed X-ray powder diffraction (XRD), Brunauer–Emmett–Teller surface/mass measurements, scanning and transmission electron microscopy (SEM and TEM) and energy dispersion spectroscopy (EDS). Using quantum chemical ab initio CCSD(T)/aug-cc-pVQZ approach, we evaluated the Gibbs free energy, enthalpy, entropy and chemical equilibrium constants for direct production of methanol and the competing reverse water-gas shift (RWGS) reaction at 25, 150, 200, 250 and 300 °C and at pressures 1, 20, 40, 60 and 100 bar. To study kinetics, a mechanistic pathway with all known intermediates was postulated, while the energy of physical and chemical adsorption and desorption, structure, activation barriers and reaction rates for the individual steps of adsorbed intermediates were calculated using DFT with plane waves. The results show that the formate intermediate pathways predominates, as the corresponding activation barriers are lower. Thus, we postulate that CH3OH forms through HCOO, H2COO, H2COOH, CH2O and CH3O. The results of this work will enable the development of better catalyst for the conversion of CO2 into methanol and their optimisation as they reveal the mechanistic background of the reaction. This will increase yields in the process and decrease the energy consumption, making the conversion of CO2 into methanol commercially economically viable.
COBISS.SI-ID: 6096410
The research programme members synthesise new catalysts and research their action within several European projects. The catalysts are then used by the project partners in a pilot reactor. The results of the MefCO2 project is a working facility for the conversion of carbon dioxide into methanol in Germany, while the FReSMe project will results in a Stenaline ferry, which will use methanol from carbon dioxide as fuel. It is known experimentally that pure Cu is a poor catalyst for CO2 hydrogenation to methanol. Useful catalysts include secondary metals in oxide forms, dopants and supports. In this study, we revealed the synergistic effect of different perovskite materials (CaTiO3, SrTiO3, BaTiO3, PbTiO3) when used together with copper. Extensive DFT simulations were performed to elucidate the most stable form of the catalyst and describe all possible elementary reactions. These results were used in kinetic modelling to obtain the performance of the catalysts. The results, which showed that Sr and Pb perovskite materials should perform best, were nicely correlated with electronic structure of the catalysts. This is the first multiscale study of the action of complex multi-metallic catalysts for the conversion of carbon dioxide into methanol, where the results of quantum chemical calculations combine with the structure of catalysts and kinetical studies. The research programme members showed why these catalysts perform notably better than mono-metallic, as the synergistic effect of two phases increases the activity and selectivity. The knowledge of multiscale modelling is usefully applied on various systems, for instance the epoxidation on silver catalysts (A'' publication: HUŠ, Matej, HELLMAN, Anders. Ethylene epoxidation on Ag(100), Ag(110), Ag(111) : a joint ab initio and kinetic Monte Carlo study and comparison with experiments. ACS catalysis, ISSN 2155-5435). The most recent result is the first wholly multiscale description of any reaction on all scales (quantum chemistry, mesoscale, differential equations, computational fluid dynamics in a reactor), which was published as an invited paper in a special issue of Catalysis Today (HUŠ, Matej, GRILC, Miha, PAVLIŠIČ, Andraž, LIKOZAR, Blaž, HELLMAN, Anders. Multiscale Modelling from Quantum Level to Reactor Scale: An Example of Ethylene Epoxidation on Silver Catalysts. Catalysis Today).
COBISS.SI-ID: 6532122
A great deal of previous research and in particular the development of advanced electrochemical characterization methods has led to this scientific achievement. In particular, the electrochemical method of an identical location electron microscopy and an electrochemical flow cell coupled with inductively coupled plasma mass spectrometry. At the same time, an article was published in the prestigious Nano Energy journal [COBISS.SI-ID 6224154] (with an impact factor of over 10) on the stability of the new IrRu catalyst. The two methods were developed at the department of catalysis and reaction engineering in cooperation with the department of analytical chemistry and department of materials chemistry, which enabled access to the instruments (SEM, TEM and ICP-MS). Prior to that, the platinum, as an electrocatalyst for low-temperature fuel cells, was studied and published in prestigious international journals such as 4x ACS Catalysis [COBISS.SI-ID 5864218, 5951258, 6032154, 5744666], ChemCatChem [COBISS.SI-ID 5403418], Journal of Power Sources [COBISS.SI-ID 5965082], Electrochimica Acta [COBISS.SI-ID 5942810], Journal of Physical Chemistry C [COBISS.SI-ID 5687322], Physical Chemistry Chemical Physics [COBISS.SI-ID 5459994], etc. The trend in the use of these advanced methods extends to other electrocatalytic reactions such as electrosynthesis (three articles in journals: Applied Catalysis B: Environmental [COBISS.SI-ID 6306074], Electrochimica Acta [COBISS.SI-ID 6443034] and Chemical Communications [COBISS.SI-ID 30681383]) and electrochemical dissolution of precious metals for recycling purposes. In the future, the popularity of these methods is expected to spread through the world as well, which is evident from a number of invited lectures that we receive in this field. In this scientific achievement, iridium-based particles, as the most promising electrocatalysts to be used in future electrolyzers, are studied. In the paper, the electrocatalytic performance (oxygen evolution reaction) of three promising types of iridium-based electrocatalysts: thermally prepared rutile type IrO2, pure metallic iridium nanoparticles and electrochemically pre-oxidized metallic nanoparticles, are investigated. The comprehensive study in which six different experimental techniques were used enabled important new insights into Ir corrosion mechanisms taking place in investigated materials. The findings offer new guidelines for preparation of the next generation of Ir-based electrocatalyst with significantly improved activity and stability. More specifically, iridium-based particles, regarded as the most promising low-temperature electrolyzer electrocatalysts, were investigated by transmission electron microscopy and by coupling of an electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometry. Additionally, studies using a thin-film rotating disc electrode, identical location transmission and scanning electron microscopy, as well as X-ray absorption spectroscopy have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that Ir particles dissolve well below oxygen evolution reaction (OER) potentials, presumably induced by Ir surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile-type IrO2 particles are substantially more stable and less active in comparison to as-prepared metallic and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER-relevant conditions, E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism, where the formation of unstable Ir()IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low-temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyzer.
COBISS.SI-ID: 6203674
A new recycling process for precious metals, for which we also applied the international patent [COBISS.SI-ID 5899034], was proposed as a result of an in-depth studies of the degradation of electrocatalysts of low temperature cells. The finding that platinum nanoparticles are degradating that is dissolving via transient dissolution mechanism (published in ChemCatChem COBISS.SI-ID 5403418 in 2014) gave us the idea to use this for recycling purposes (a circular economy). At the same time, a postdoctoral project no. Z2-8161: Study of novel environmentally friendly noble metals recycling process based on reactive gas or liquid induced surface electrochemical potentials. This department field has an extremely high potential because there is more and more electrical and electronic equipment waste containing precious metals in the world. As these waste streams are now not recycled or the current recycling processes are environmentally unfriendly, this scientific achievement is even more important. This is confirmed by the high visibility of this achievement in the media where several television and radio and other types of interviews were made [COBISS.SI-ID 6040858, 6041114, 6032410, 6041626, 6042138, 6041882, 6088218, 6041370, 6050074, 6104090]. The recycling of precious metals, for example platinum, is an essential aspect of sustainability for the modern industry and energy sectors. However, due to its resistance to corrosion, platinum-leaching techniques rely on high reagent consumption and hazardous processes, for example, boiling aqua regia; a mixture of concentrated nitric and hydrochloric acid. Here we demonstrate that complete dissolution of metallic platinum can be achieved by induced surface potential alteration, an ‘electrode-less’ process utilizing alternatively oxidative and reductive gases. This concept for platinum recycling exploits the so-called transient dissolution mechanism, triggered by a repetitive change in platinum surface oxidation state, without using any external electric current or electrodes. The effective performance in non-toxic low-concentrated acid and at room temperature is a strong benefit of this approach, potentially rendering recycling feasible for other systems beyond platinum (for instance recycling industrial catalysts).
COBISS.SI-ID: 6027290
Selective carbon monoxide (CO) oxidation reaction was studied over mono- and bimetallic Co, Cu and Fe, as well as Cu–Co and Cu–Fe heterogeneous catalysts, using multi-walled carbon nanotubes (MWCNT) as substrates. Materials were synthesized by wet (co-)impregnation technique and characterised. It was found that hydrophilic hydroxyl and carboxyl nanotubes’ (CNT) functional groups were favourable for a strong metal–support interaction. The catalytic conversion performance for preferential CO oxidation (PROX) process was carried out in hydrogen, water, and carbon dioxide-containing feedstock gasses. The addition of iron or cobalt to Cu/CNT improved the activity with comparison to Cu/CNT. The optimized Cu–Fe/CNT could preferentially oxidize dilute CO in H2-rich simulated WGS streams within a wide temperature range of 120–220?°C. The temperatures, where 50% CO conversion was achieved, were as follows: Cu–Fe/CNT (120?°C) ) Cu–Co/CNT (140?°C) ? Cu/CNT (140?°C). A high determined selectivity towards CO2 for Cu–Fe/CNT could be attributed to the presence of CuFe2O4 and the synergy between Co and Cu for Cu-Co/CNT. At 220?°C and in a 1% CO/1% O2/10% H2O/10% CO2/60% H2/18% He stream, Cu–Fe/CNT could achieve a 100% CO conversion, granting a low H2 conversions, not differing from those in the absence of CO2, while its turnover performance remained stable for a longer continuous time-on-stream with basically no deactivation. By comparison, Cu–Fe/CNT exhibited a higher apparent rate and lower activation energy of CO conversion (with and without H2O and CO2).
COBISS.SI-ID: 6424346
The development of efficient and greener routes for the removal of protein from crustacean shell waste remains a challenge. This work was published in the prestigious journal Green Chemistry with an impact factor over 8 (COBISS.SI-ID 6344474). This was the first report of using plasma for marine biomass pre-treatment greatly intensifying the chitin isolation process. Chitin, a polysaccharide consisting of acetyl-glucosamine and N-acetyl-glucosamine monomer units, is a bio-renewable, biocompatible, environmentally friendly, biodegradable and bio-functional polysaccharide. It is easily functionalized and as such has been used for various applications in the biomedical, pharmaceutical, tissue engineering sectors. This renewable electricity-based separation operation can serve as a scalable green alternative to the conventional chemical purification in the production of the chitin biopolymer, which applies unrecyclable mineral bases. The development of a sustainable fractionation method to separate proteins, calcium carbonate and chitin, one that avoids corrosive or hazardous reagents and minimizes waste, is being envisioned as a solution. The DBD plasma treatment process showed an efficient and fast protein removal capability without a significant influence on the chitin biopolymer. Furthermore, the plasma based process does not require any solvents and therefore no (solid and liquid) waste is formed. Using relatively cheap gaseous O2/N2 mixture and working under atmospheric pressure without using any expensive vacuum components enables a straightforward scale-up of this technology. Examples can be found in the cited reference for the industrial-scale plasma processing for various commercial applications. With this in mind, after an initial investment to build a new plasma system, the day-to-day expenses for the operation are mostly limited to the cost for electricity, which makes it even more appealing to be embraced for the chitin isolation process in the future. For complete chitin isolation, the demineralization and complete deproteinization should be performed. However, any protocol for further isolation of the chitin from the plasma pre-treated shrimp shell should be able to isolate chitin in an intensified way saving costs on the chemicals and waste removal.
COBISS.SI-ID: 6344474
Mammalian cells have become the dominant environment for the production of recombinant proteins. From the very beginning in 1986 when the human tissue plasminogen activator (tPA) obtained the market approval, nowadays more than 60% of all recombinant proteins are generated from mammalian cell cultures with the total global market approaching $100 billion per year. Transition from CHO cells as a biological platform to relevant pharmaceutical compounds is accompanied by numerous optimization challenges. Many of these are tackled by trial and error methods, where high-throughput experiments are performed to understand system under investigation. Such approach may yield decent results, but requires a lot of chemicals, equipment and manual labor, making a drug development expensive and time-consuming. Though successful, many biological principles remain poorly understood. To bridge this gap, in silico approaches can be very useful tools. In our modelling work [COBISS.SI-ID 6545690], a novel approach is presented which transits from a broad mechanistic description of the individual metabolic pathways to a simplified macro-kinetic model. The latter is characterized within the concept of metabolic flux analysis and associated elementary modes, which obey the constraints of phenotype. Unlike the piecewise-defined kinetic expressions with a discrete separate treatment of different cell phases, the Monod equation rate law is extended herein, allowing for a dynamic reversal of macro-reactions, and thus, a uniform continuous functionality from growth to death cultivation periods. The enzymatic biochemical reactions of complete metabolic network are defined to satisfy the composition of mammalian culture structure which reflects on stoichiometry. This affords us an opportunity to handle the density of the viable cells (biomass) along with central metabolisms’ transformations, rather than as a decoupled constituent function, as habitually assumed in the literature. The methodology of the extracellular metabolite measurements for the Chinese hamster ovary (CHO) cells is confronted, confirming the applicability in multi-scale biologically-relevant systems. Temporal species’ behaviour reveals inflection points that switch among stages. In further extensions metabolic models have a potential to forecast the outcomes of growth medium perturbations, feeding protocols, and process parameters in order to facilitate the productivity and quality of biosimilars in biotechnology. Besides this the review article entitled Metabolic network modelling of Chinese hamster ovary (CHO) culture bioreactors operated as microbial cell factories, was published [COBISS.SI-ID 39867141], where recent the review literature survey in this field shown the high potential of our work in this field. Our reached beyond the purely theoretical approach, enabling the real industry people work and improve their processes in biologics production. Further fruitful collaboration was established between our research and leading biopharmaceutical industry, where this work is continuing on the basis of their process data.
COBISS.SI-ID: 6545690
Hydrotreatment of secondary hexanone and hexanol, and primary hexene species was investigated over the sulphide-form NiMo/?-Al2O3 heterogeneous catalyst within the process temperature range 200–275 °C. The mechanistic microkinetic model for a three-phase slurry reactor was developed, comprising the mass transfer flux from the dispersed gaseous H2 bubbles to liquid solvent bulk, the external convective resistance at catalytic surface interface, material lattice adsorption and desorption, and intrinsic conversion kinetics (homogeneous and catalysed). It reported the reaction rate constants and activation energies for ketones and alcohols. Intermediate alkene isomers were identified and quantified, demonstrating the same reactive selectivity regardless of the cascade reactant compound. Furthermore, the C6 olefin isomerisation studies under pressurised hydrogen and nitrogen (up to 9.5 times slower) atmospheres indicated a similar equilibrium distribution of the concentrations of 1-hexene, cis-2-hexene, trans-2-hexene, cis-3-hexene and trans-3-hexene. The position of the oxygen-containing (heteroatom) functional group on an aliphatic hydrocarbon chain exhibited only a minor kinetic effect on parallel and serial hydrogenation or de-hydroxylation steps. Quantum chemical (QC) calculations utilising density functional theory (DFT) computational framework were performed to elucidate the mechanism of hydrodeoxygenation (HDO). The competing main and side pathways were considered in calculating transition state barriers. Deoxygenation valorisation routes were examined as they are vital upon converting ligno-cellulosic biomass resources and for the production of the bio-based platform oxygenates in bio-refineries. Hexose(s), for example, are (poly)alcohols, the monomer building blocks of cellulose, which is besides lignin and hemicellulose the principal wood, grass and straw constituent. Work has been published in one of the best catalytic journals (impact factor 11.7). Work has continued with other functional groups (primary alcohol, aldehyde, carboxylic acid, ether, esters) and published separately in Chemical engineering journal [COBISS.SI-ID 6530842]. By using the same catalysts, hydrotreatment of levulinic acid (LA) at solvent-free conditions was also studied and results were published in Chemical engineering journal [COBISS.SI-ID 6199322]. Main catalytic hydrodeoxygenation (HDO) product ?-valerolactone (GVL) was formed on NiMoSx phase exclusively by LA hydrogenation to hydroxypentanoic acid, and its subsequent intramolecular esterification, while cyclisation of LA to angelica lactones and their saturation was negligible. Within the scope of cooperation between research groups from Bulgaria, Hungary and Germany, a scientific article related to levulinic acid valorisation has been published in Applied Catalysis A: General [COBISS.SI-ID 6383898]. Catalytic hydrodeoxygenation (HDO) and hydrogenation of eugenol, a lignin building block model component, was investigated in-silico and experimentally in a three-phase slurry reactor over the ruthenium supported on carbon (published in Chemical Engineering Journal [COBISS.SI-ID 6226458]) as well as Cu/C, Ni/C, Pd/C, Pt/C, Rh/C (published in Chemical Engineering Journal [COBISS.SI-ID 6531098]). Experimental results revealed that allyl group and benzene ring saturation was favoured over the competitive deoxygenation reactions, namely dehydroxylation and demethoxylation of oxygen moieties on aromatic ring. Precursors responsible for cyclohexane-ring contraction to substituted 5-member ring compounds were also identified and mechanism and kinetics of transformation was proposed. Detailed reaction mechanism with all the energy barriers was also proposed based on DFT studies (Journal of Catalysis, [COBISS.SI-ID 6294554])
COBISS.SI-ID: 6179354
Hydrotreatment of liquefied lignocellulosic biomass was investigated at 300 °C under the total pressure of 8 MPa in a slurry reactor over unsupported molybdenum (disulphide, dioxide and carbide) and tungsten (disulphide) catalysts. Novel nanostructured urchin-like MoS2 and inorganic-fullerene MoS2 interconnected with carbon materials were synthetized and tested, while the influence of metal variation and the sulphide replacement with carbide or oxide was also investigated by using commercially-available MoS2, Mo2C, MoO2 in WS2. Catalysts were structurally characterised by field-emission scanning (SEM) and high-resolution transmission (HRTEM) electron microscopies, energy-dispersive X-ray (EDX) and Raman spectroscopies, as well as X-ray diffraction (XRD). The hydrodeoxygenation (HDO), decarbonylation, decarboxylation and hydrocracking kinetics of depolymerised cellulose, hemicellulose and lignin were determined according to the transformation of their functional groups in liquid phase, and the corresponding gaseous products by an innovative lumped kinetic model based on Fourier transform infrared spectroscopy. Unsupported MoS2 catalysts showed high hydrogenolysis selectivity, the morphology clearly affecting its rate. A high HDO activity reflected in the mass balance and phase distribution of the upgraded liquid product by reducing tar residue and increasing the yield of oil phase with the gross calorific value of 38 MJ kg–1 and oxygen content below 8.5 wt%. In addition to Mo and W-based catalysts, nickel nanoparticles, generated in-situ from metal-organic framework precursors, were also found to have very high hydrotreatment activity and managed to significantly reduce the oxygen content in liquefied biomass, results were published in ChemSusChem [COBISS.SI-ID 5667866]. Kinetics of lignocellulosic biomass solvolysis has been investigated separately and reported in Catalysis Today [COBISS.SI-ID 37882629]. Furthermore simultaneous solvolysis and hydrotreatment has also been investigated and published in ChemCatChem [COBISS.SI-ID 5821466]. Oak, fir and beech sawdust was upgraded in a slurry reactor by using tetralin, phenol and glycerol solvents and representative heterogeneous catalysts used in petrochemical industry for hydrogenolysis (sulphide form of NiMo/Al2O3), hydrogenation (Pd/Al2O3) or fluid catalytic cracking (zeolite Y). Deoxyliquefaction products of cellulose, hemicellulose and lignin were characterised in terms of solvent fractionation, Fourier transform infrared (FTIR) and DRIFT spectroscopy, elemental analysis and an innovative method for particle-size distribution and mean grain size determination by scanning electron microscopy (SEM) image processing. A novel lumped kinetic model was developed according to reaction mechanisms, containing wood depolymerisation, decarbonylation, decarboxylation and demethanation, tar phase hydrodeoxygenation by molecular and in-situ generated hydrogen, as well as charring inhibition by free radical stabilisation hydrogen transfer.
COBISS.SI-ID: 5537562
Multiscale modelling is becoming the key approach to catalysis, as it links experimental data from kinetic studies to theoretical predictions from materials sciences through microkinetic simulations. In collaboration with a research group from Chalmers University of Technology in Sweden, with whom we have established a close collaboration, we performed the first comprehensive multiscale modelling of the most important oxidation reaction in the chemical industry and engineering. We have studied the epoxidation of ethylene, which is industrially run in hundreds of thousands tonnes each year. For this reaction, silver is used as the catalyst of choice. This is due to experimental data, which show its unmatched activity and selectivity. However, there had been limited theoretical data in the reaction. Research had focused on individual aspects of the reaction such as potential energy surface or microkinetic description without ab initio considerations. We were the first to perform a detailed and systematic study of the reaction, using ab initio quantum chemical information and propagating it to a microkinetic model. Moreover, the results were compared to experimental data, where very good agreement was obtained. We have shown that, contrary to common expectations, different facets of silver not only influence the activity of the catalyst but also markedly change the selectivity. For instance, Ag(111) is the most stable surface but is least active and only moderately selective. Ag(110), on the other hand, is very active but produces only undesired side-products. Ag(100), however, is also quire active and produces mostly the desired product. The difference is in activity, surface coverage and selectivity. These data were compared with experiments for Ag(111), where excellent agreement was obtained. The collaboration with the Chemical Physics group of Chalmers University of Technology is continuing. We are working on studying the effect of different base metals, dopants and oxidation states. Moreover, we plan to study the effect of the catalytic particle size. The results will be compared with experimental work, which is being done at Langhammer Lab of the Chalmers University of Technology.
COBISS.SI-ID: 39873285