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 of industrial catalysts, including but not limited to platinum-based systems, more sustainable.
COBISS.SI-ID: 6027290
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 and 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%.
COBISS.SI-ID: 5537562
In this work, post-Hartree–Fock and density functional theory (DFT) calculations were carried out to assess the thermodynamics and to elucidate the pathway leading to the formation of methanol from CO2 on realistic spinel-type tri-metallic materials. Firstly, a commercial-like Cu/ZnO/Al2O3 was synthesised via co-precipitation and characterised to obtain the active sites’ structure for modelling. Powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area measurement, scanning/transmission electron microscopy (SEM and TEM) and energy-dispersive X-ray spectroscopy (EDS) were performed. Subsequently, the Gibbs free energy, enthalpy, entropy and chemical equilibrium constants of the direct methanol synthesis and the competing reverse water–gas shift (RWGS) reaction at the temperatures of 25, 150, 200, 250 and 300 °C, and the pressures of 1, 20, 40, 60 and 100 bar were evaluated using ab initio quantum chemistry method CCSD(T)/aug-cc-pVQZ. To investigate kinetics, a mechanistic pathway scheme with all established intermediates was constructed, whereas physical/chemical adsorption/desorption energies, geometries, barriers and rates for adsorbate elementary steps were calculated using plane-wave DFT. Results demonstrate that the formate precursor route predominates as the respective transition state activation energies are lower and, thus CH3OH is proposed to form through HCOO, H2COO, H2COOH, CH2O and CH3O species.
COBISS.SI-ID: 6096410
Solvolysis of wood, cellulose, hemicellulose and lignin in glycerol was investigated in the presence of homogeneous imidazolium-based ionic liquid (IL) catalysts, where the influence of the IL type, reaction time, temperature and mass transfer limitations on decomposition rate was investigated. The selection of anions (acetate, hydrogen sulphate or chloride/metal halide complex to form a Lewis acid) and cations (butyl-, methyl- or allyl-functionalised imidazolium) importantly influenced conversion, which was as high as 64.4 and 91.5 wt% for the beech wood liquefaction at 150 and 200 °C within 60 min. By following the mass of solid particles and their specific surface area (BET method) as a function of time and temperature, a novel kinetic model for the solvolysis of biomass and its components was developed, where reactive surface area is a key parameter that dictates the rate of solid–liquid reaction; kinetic model also considered different depolymerisation reactivity of main three wood components. Liquefied biomass was consequently hydrodeoxygenated at 225–275 °C in the presence of commercially available sulphide-form NiMo/γ-Al2O3 catalyst. Rates and selectivity of hydrogenolysis, decarbonylation, decarboxylation, hydrogenation and (hydro)cracking were followed and modelled by using previously developed lumped kinetic model, based on the Fourier transformed infrared spectroscopy (FTIR) analysis. The oxygen content of the oil phase of was less than 1.7 wt%.
COBISS.SI-ID: 37882629
Hydrogen, an important energy carrier of the future, produces no pollution and has a high content of energy. It is formed as a direct product of the water–gas shift (WGS) reaction, which occurs in various processes for the production of hydrogen, ammonia, methanol and different hydrocarbons, and is also a side reaction during the steam reforming of hydrocarbons and Fisher–Tropsch synthesis. Since it is an equilibrium reaction, it may be intensified by the selective removal of the products, which can lead to higher yields and energy savings. In this study, carbon dioxide was removed through chemisorption on CaO particles. In the first part, the WGS reaction kinetics were obtained on an industrial iron-chromium catalyst in a packed-bed reactor. In the second part, the CO2 chemisorption kinetics on CaO sorbent particles were examined, simultaneously with the WGS reaction. A modified dynamic shrinking-core model was used to describe the carbonation reaction, which accounted for the non-ideal core shrinkage. With the introduction of a sorbent conversion-dependent effective diffusion coefficient, the model perfectly reproduced the obtained experimental results. Valuable insight into the sorption-enhanced process was obtained with the full concentration profiles of the species involved (CO, H2O, CO2, H2) in time and space, as well as the conversion of the sorbent particles, also in the radial dimension. The developed model was used to simulate a cyclic sorption-enhanced water–gas shift operation in a revolver-type manner which allows for continuous sorbent regeneration and a much higher-than-equilibrium hydrogen production for various operational parameters. The significance of the model lies in the precise replication of the experimental results and its applicability to the vast area of the newly-emerged industrial sorption-enhanced technologies.
COBISS.SI-ID: 5942298