Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared NieCu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al2O3, commercial Cu/ZnO/Al2O3 and prepared NieCu/Al2O3 catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in NieCu/Al2O3 catalyst with respect to the commercial Ni/ Al2O3 (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al2O3 (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H2 selectivity, CO2 and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H2, with H2 selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275-325 o C). However, methane steam reforming can be carried out at a relatively low temperature on NieCu catalyst (600-650 o C) and at higher temperature in commercial methane reforming catalyst (700-800 o C). Commercial Ni/Al2O3 catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared NieCu/Al2O3 (8.9%) and commercial Cu/ZnO/Al2O3 catalysts (3.5%).Web of Scienc

Reverse Water Gas Shift versus Carbon Dioxide Electro-Reduction: The Reaction Pathway Responsible for Carbon Monoxide Production in Solid Oxide Co-Electrolysis Cells

Solid oxide co-electrolysis cells can utilize renewable energy sources for the conversion of steam and carbon dioxide into valuable chemicals and feedstocks. An important challenge in the analysis of these devices is understanding the reaction pathway(s) that govern carbon monoxide generation. Studies in which co-electrolysis polarization lies between those of pure steam and pure carbon dioxide electrolysis suggest that carbon dioxide electro-reduction (CO2ER) and the reverse water gas shift (RWGS) reaction are both contributors to CO generation. However, experiments in which co-electrolysis polarization overlaps that of pure steam electrolysis propose that the RWGS reaction dominates CO production and CO2ER is negligible. Supported by dimensional analysis, thermodynamics, and reaction kinetics, this work elucidates the reasons for which the latter conclusion is infeasible, and provides evidence for why the observed overlap between co-electrolysis and pure steam electrolysis is a result of the slow kinetics of CO2ER in comparison to that of steam, with the RWGS reaction being inconsequential. For sufficiently thin cathode current collectors, we reveal that CO2ER is dominant over the RWGS reaction, while the rate of steam electro-reduction is much higher than that of carbon dioxide, which causes the co-electrolysis and pure steam electrolysis polarization curves to overlap. This is contrary to what has been proposed in previous experimental analyses. Ultimately, this work provides insight into how to design solid oxide co-electrolysis cells such that they can exploit a desired reaction pathway in order to improve their efficiency and product selectivity.publishedVersio

Laminar flame characteristics of natural gas and dissociated methanol mixtures diluted by nitrogen

The effect of dissociated methanol (H2:CO=2:1 by volume) on laminar burning velocity of natural gas (methane as the main component) was studied by using a constant volume bomb (CVB). Nitrogen, as diluent gas, was added into the natural gas (CH4) - dissociated methanol (DM) mixtures to investigate the dilution effect. Experiments were conducted at initial temperature of 343 K and initial pressure of 0.3 MPa with equivalence ratios from 0.8 to 1.4. Laminar burning velocities were calculated through Schlieren photographs, correlation of in-cylinder pressure data and Chemkin-Pro. Results show an increase in laminar burning velocity with initial temperature and proportion of dissociated methanol but a decrease with initial pressure and proportion of nitrogen. The laminar burning velocities were 25.1 cm/s, 38.7 cm/s and 83.2 cm/s respectively at stoichiometric ratio when the proportions of the dissociated methanol were 0%, 40% and 80%. Adding more dissociated methanol tends to shift the peak burning velocity towards the richer side while adding nitrogen has the opposite effect. More dissociated methanol will lead to earlier cellularity

Tantalum Carbide Supported Iridium Based Oxygen Evolution Reaction Electrocatalysts for Polymer Electrolyte Membrane Water Electrolysis

In this study, the effect of ball milled tantalum carbide (TaC) as a support on performance of an Iridium (Ir) based catalyst for polymer membrane water electrolyzers (PEMWE)s is assessed. Supported and un-supported Ir-based catalysts were synthesized via a surfactant-mediated method at room temperature. The synthesized catalysts were analyzed using physical and chemical characterization methods including nitrogen physisorption analysis, scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), SEM/wavelength dispersive spectroscopy (WDS), transmission electron microscopy (TEM)/ scanning transmission electron microscopy (STEM) and X-Ray photoelectron spectroscopy (XPS). It was observed that due to less agglomeration and better dispersion of supported catalyst on TaC, BET surface area of the supported catalyst was 25 times larger than the unsupported one. XPS results also indicated the oxidation state of Ir in synthesized catalysts is a mixture of Ir0, Ir+3 and Ir+4. Based on EDS and XPS results, it was concluded that the synthesized catalyst is a mixture of metallic iridium and iridium oxide (Ir-IrOx). Electrochemical properties of the synthesized catalysts were also studied using linear sweep voltammetry (LSV) and cyclic voltammetry (CV) in a 3-electrode system. The supported catalyst shows three times the voltammetric charge compared to the unsupported catalyst. Based on the LSV measurements, the mass activity of the supported catalyst had a 10-fold increase in comparison with that of the unsupported one. Ir-based catalyst synthesized via the surfactant-mediated method and supported on ball milled TaC showed the best performance. </jats:p