Catalytically active surface of small nickel (min 99 wt%) plates for steam methane reforming was enhanced by successive temperature programmed oxidation−reduction (TPO−TPR) pretreatment and combined physical vapor deposition of Pt and Al2O3. The effect of annealing time, temperature, order and number of coatings on the catalytic activity was investigated by means of a pulse technique at the reaction temperature of 760 °C. The most active and stable surface phases resulted after the successively deposited layers of Pt, Al2O3, and Pt had been annealed for 12 h onto 2-cycle TPO−TPR pretreated nickel plate at the temperature of 700 °C in a circulating atmosphere of N2. The durability performance of the so-prepared surface phases on a specifically structured plate catalyst element (diameter 43 mm and length 42 mm) was tested in a tubular reactor for some 70 h in temperature range 500−650 °C. Deactivation was mainly caused by carbon surface deposition.
COBISS.SI-ID: 5158170
Intrinsic kinetics study of steam methane reforming (SMR) was performed on two different systemscommercial Ni-based pellet catalyst and Pt/Ni/Al2O3 structured plate catalyst. Experiments were carried out in the absence of external mass transfer resistance, and temperature 500−575 °C, pressure 2.5−7.5 bar, and H2O/CH4 reactant ratio range of 3−5 mol/mol. Reactors operated in the integral mode, and it was shown that both systems could be described by the same kinetics, based on Langmuir−Hinshelwood mechanism. In the case of plate catalyst, the regeneration treatment after deactivation led to platinum particle redispersion, which further influenced the values of the pre-exponential factors, whereas the activation energy values remained unchanged. Comparison of the two catalyst systems was made based on the active metal content, and it was shown that the catalytic activity of the Pt/Ni/Al2O3 plate catalyst after the second regeneration treatment was 8 times of that observed for the Ni-based pellet catalyst.
COBISS.SI-ID: 5299482
A model acknowledging reaction kinetics and thermal conduction during waste end-of-life (ELT) tyre pyrolysis was developed based on the individual consideration of elastomers, namely natural (NR), butadiene (BR) and styrene-butadiene (SBR) rubber; fabric, that is rayon, nylon and aramid; and wire. External diffusional and thermal film resistances proved to be negligible during the thermal cracking. An algorithm was developed to extract pre-exponential factors, activation energies, the orders of reactions, the enthalpies of reactions, and transport parameters. The pyrolysis of various formulations at different volumetric flow rates and heating rates was monitored by thermogravimetry (TG) and differential scanning calorimetry (DSC), whereas the pertinent thermodynamic properties (density, specific heat capacity, and thermal conductivity and diffusivity) were determined separately. The un-decomposable weight fraction containing carbon black, char and ash was 39% for the investigated rubber and 13% for the fabric formulation. The sensitivity analysis of the pyrolysis on compound and process(operating) conditions was performed. The obtained results (taking intoaccount their drawbacks) with the additional measurements and modelling may be used for the thermo-chemical treatment reactor scale-up and optimization, and consequently, a suitable design of energy and products recovery instead of disposal or landfilling, thus minimizing hazardous waste and contamination to soil and water resources.
COBISS.SI-ID: 5111834
The degradation of a commercial platinum polymer electrolyte membrane (PEM) fuel cell catalyst has been studied under severe simulated start–stop conditions (50,000 cycles from 0.2 V to 1.4 V vs. the reversible hydrogen electrode, RHE), employing a newly developed identical location scanning electron microscopy technique (IL-SEM). We show that significant platinum particle growth occurs on top of the catalyst film while platinum depletion takes place in the layers beneath. There is a possibility of misleading interpretation of thin film severe degradation experiments, when the catalyst loading and volume of electrolyte are neglected and when the non-identical location electron microscopy pictures are statistically analyzed.
COBISS.SI-ID: 26576935
Oxygen imaging using an epifluorescent microscope was performed inside a microfluidic chip by utilizing nanosensor particles stained with oxygen-sensitive luminescent dye. The oxidation reaction of β-d-glucose to hydrogen peroxide and δ-d-gluconolactone by molecular oxygen in the presence of glucose oxidase from Aspergillus niger inside microreactors with Y-shaped microchannels was followed with this measuring technique. This reaction is widely used in diagnostics and biotechnology. Dissolved oxygen concentrations were measured at various flow rates and microchannel dimensions. Additional batch experiments and microreactor experiments with a reaction-free set-up were conducted. Mathematical models, ranging from a full 3D description of transport phenomena, incorporating convection, diffusion and enzymatic reaction terms along with the parabolic velocity profile, to simplified less precise models were developed to simulate the concentration of dissolved oxygen inside the microchannels, to assess the required model complexity for achieving precise results and to depict the governing transport characteristics at the microscale.
COBISS.SI-ID: 36271621