Davood Hosseini

Cooperativity and Dynamics Increase the Performance of NiFe Dry Reforming Catalysts

The dry reforming of methane (DRM), i.e., the reaction of methane and CO2 to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a MgxAlyOz matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m2/gcat), pore volume (0.51-0.66 cm3/gcat), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, Ni4Fe1 with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

CuO promoted Mn2O3-based materials for solid fuel combustion with inherent CO2 capture

We experimentally demonstrate the promising redox and oxygen release characteristics of a novel bimetallic Cu–Mn oxygen carrier for chemical-looping with oxygen uncoupling (CLOU) based CO2 capture. The new material was prepared via a co-precipitation technique and showed a higher oxygen partial pressure than pure CuO and a higher oxygen carrying capacity than Mn2O3, thus, synergistically combining the advantages of the individual metal oxides. The promising CLOU characteristics of the new material were demonstrated further by combusting charcoal fully in a fluidized bed and producing a pure stream of CO2.

Ethanol electro-oxidation on nanoworm-shaped Pd particles supported by nanographitic layers fabricated by electrophoretic deposition

Different morphologies of nanographitic flake coatings used as catalyst supports for nanoworm-shaped palladium (Pd) were fabricated via the electrophoretic deposition (EPD) of dispersed nanographitic flakes in isopropyl alcohol. Various concentrations of magnesium nitrate hexahydrate (MNH) were used as an additive binder in the EPD process. After that palladium nanoworms were deposited by a direct sputtering on the fabricated nanographitic flake coatings. It was observed that the variation of the MNH concentration has a remarkable influence on the flake packing density of the deposited coatings and the adhesion between the nanographitic flakes and indium tin oxide (ITO) coated glass plates, thus offering a control of the aggregation of the nanographitic flakes. The morphology change of the coatings caused by MNH, which can either improve or weaken the conductivity of the fabricated coatings, has an important role in determining the performance of the Pd-sputtered samples for ethanol electro-oxidation. The sample obtained with 1 mg mL−1 of MNH exhibited a high electrocatalytic activity and stability due to a high flake packing density and strong adhesion between the nanographitic flakes and ITO, and retained planar morphology of the nanographitic flakes during the EPD.

Development of a Steel‐Slag‐Based, Iron‐Functionalized Sorbent for an Autothermal Carbon Dioxide Capture Process

We propose a new class of autothermal CO2 -capture process that relies on the integration of chemical looping combustion (CLC) into calcium looping (CaL). In the new process, the heat released during the oxidation of a reduced metallic oxide is utilized to drive the endothermic calcination of CaCO3 (the regeneration step in CaL). Such a process is potentially very attractive (both economically and technically) as it can be applied to a variety of oxygen carriers and CaO is not in direct contact with coal (and the impurities associated with it) in the calciner (regeneration step). To demonstrate the practical feasibility of the process, we developed a low-cost, steel-slag-based, Fe-functionalized CO2 sorbent. Using this material, we confirm experimentally the feasibility to heat-integrate CaCO3 calcination with a Fe(II)/Fe(III) redox cycle (with regards to the heat of reaction and kinetics). The autothermal calcination of CaCO3 could be achieved for a material that contained a Ca/Fe ratio of 5:4. The uniform distribution of Ca and Fe in a solid matrix provides excellent heat transfer characteristics. The cyclic CO2 uptake and redox stability of the material is good, but there is room for further improvement.

Mechanochemically Activated, Calcium Oxide-Based, Magnesium Oxide-Stabilized Carbon Dioxide Sorbents

Carbon dioxide capture and storage (CCS) is a promising approach to reduce anthropogenic CO2 emissions and mitigate climate change. However, the costs associated with the capture of CO2 using the currently available technology, that is, amine scrubbing, are considered prohibitive. In this context, the so-called calcium looping process, which relies on the reversible carbonation of CaO, is an attractive alternative. The main disadvantage of naturally occurring CaO-based CO2 sorbents, such as limestone, is their rapid deactivation caused by thermal sintering. Here, we report a scalable route based on wet mechanochemical activation to prepare MgO-stabilized, CaO-based CO2 sorbents. We optimized the synthesis conditions through a fundamental understanding of the underlying stabilization mechanism, and the quantity of MgO required to stabilize CaO could be reduced to as little as 15 wt %. This allowed the preparation of CO2 sorbents that exceed the CO2 uptake of the reference limestone by 200 %.

Single-Step Electrophoretic Deposition of Non-noble Metal Catalyst Layer with Low Onset Voltage for Ethanol Electro-oxidation.

A single-step electrophoretic deposition (EPD) process is used to fabricate catalyst layers which consist of nickel oxide nanoparticles attached on the surface of nanographitic flakes. Magnesium ions present in the colloid charge positively the flakes surface as they attach on it and are also used to bind nanographitic flakes together. The fabricated catalyst layers showed a very low onset voltage (-0.2 V vs Ag/AgCl) in the electro-oxidation of ethanol. To clarify the occurring catalytic mechanism, we performed annealing treatment to produce samples having a different electrochemical behavior with a large onset voltage. Temperature dependence measurements of the layer conductivity pointed toward a charge transport mechanism based on hopping for the nonannealed layers, while the drift transport is observed in the annealed layers. The hopping charge transport is responsible for the appearance of the low onset voltage in ethanol electro-oxidation.

The influence of the thickness of nanographitic coatings fabricated by electrophoretic deposition on ethanol electro-oxidation

The catalyst support layer is fabricated by applying a DC electrophoretic deposition on a colloid consisting of dispersed nanographitic flakes along with magnesium ions in isopropyl alcohol. The thickness and conductivity of the deposited layers are controlled by varying the time of the voltage application in the electrophoretic deposition EPD technique. The catalyst supports are decorated by sputtering palladium nanostructures serving as the catalyst. The fabricated support layer with the optimum thickness exhibits an improved conductivity and electro-oxidation performance attaining 800 mA/cm2 per mg of palladium.