Showing papers by "Hilde Poelman published in 2019"
TL;DR: A review of chemical looping-based process concepts for converting CO2 into carbon monoxide can be found in this article, where the focus lies on the direct conversion of carbon dioxide into CO2, a process deemed to have economic potential.
Abstract: Driven by the need to develop technologies for converting CO2, an extraordinary array of chemical looping based process concepts has been proposed and researched over the past 15 years. This review aims at providing first a historical context of the molecule CO2, which sits at the center of these developments. Then, different types of chemical looping related to CO2 are addressed, with attention to process concepts, looping materials, and reactor configurations. Herein, focus lies on the direct conversion of carbon dioxide into carbon monoxide, a process deemed to have economic potential.
37 citations
TL;DR: It is discussed how in situ and operando X‐ray spectroscopy, scattering, and diffraction can be used as a complementary toolbox to interrogate the working principles of today's and tomorrow's bimetallic nanocatalysts.
Abstract: Bimetallic nanocatalysts are key enablers of current chemical technologies, including car exhaust converters and fuel cells, and play a crucial role in industry to promote a wide range of chemical reactions. However, owing to significant characterization challenges, insights in the dynamic phenomena that shape and change the working state of the catalyst await further refinement. Herein, we discuss the atomic-scale processes leading to mono- and bimetallic nanoparticle formation and highlight the dynamics and kinetics of lifetime changes in bimetallic catalysts with showcase examples for Pt-based systems. We discuss how in situ and operando X-ray spectroscopy, scattering, and diffraction can be used as a complementary toolbox to interrogate the working principles of today's and tomorrow's bimetallic nanocatalysts.
29 citations
TL;DR: In this article, the stability of Fe2O3-MgAl2O4 oxygen storage materials (OSMs) was investigated over 1000 redox cycles using H2 as reductant and CO2 as oxidant.
Abstract: The stability of Fe2O3-MgAl2O4 oxygen storage materials (OSMs) was investigated over 1000 redox cycles using H2 as reductant and CO2 as oxidant. Three different materials, with a nominal Fe2O3 amount of 10 wt%, 30 wt% and 50 wt%, were evaluated. Characterization techniques such as N2 adsorption, XRD and STEM-EDX were applied to study the evolution of morphological and crystallographic properties. XRD results show that Fe is incorporated in the MgAl2O4 lattice of the as prepared materials, yielding a Mg-Fe-Al-O spinel structure. After redox cycling, part of Fe still remains within the spinel. The results of redox cycling reveal superior properties for 10Fe2O3-MgAl2O4, exhibiting stability in terms of morphology and, with an average space-time yield of 700 mmolCO s−1 kgFe−1, the highest activity among the OSMs studied. However, 50Fe2O3-MgAl2O4 performs best in terms of overall CO yield, i.e. 0.6 mol CO kgOSM−1, more than twofold higher compared to 10Fe2O3-MgAl2O4 and 30Fe2O3-MgAl2O4 even after 1000 cycles. Deactivation through sintering occurs in all three materials, though to a lesser extent for 10Fe2O3-MgAl2O4. Phase transformation to a MgxFe1-xO phase predominantly causes a loss of oxygen storage capacity in 30Fe2O3-MgAl2O4 and 50Fe2O3-MgAl2O4.
23 citations
TL;DR: In this paper, the authors investigated the origin of reaction-related deactivation of a double-zone core-shell nanomaterials in an auto-thermally catalyst-assisted chemical looping dry reforming process.
Abstract: Catalyst-assisted chemical looping dry reforming is a promising technology for CO-rich syngas production with maximized CO2 utilization, especially when performed auto-thermally, over core-shell nanomaterials in a double-zone reactor bed with first a Fe/Zr@Zr-Ni@Zr bifunctional catalyst and next a Fe/Zr@Zr oxygen storage material. Understanding the origin of the material deactivation under high-pressure conditions is essential to advance this technology towards industrial application. Therefore, pressure-induced material deactivation was studied through a series of on-site assessments (steady-state CH4 reforming and prolonged redox cycling at 750 °C and 1–10 bar) and ex-situ characterization (STEM-EDX, XRD and N2 adsorption-desorption). At high pressure, both Fe/Zr@Zr-Ni@Zr and Fe/Zr@Zr show reaction-related deactivation, the origin of which can be ascribed to carbon deposition and particle sintering, respectively. During regular catalyst-assisted dry reforming over Fe/Zr@Zr-Ni@Zr, the rise of pressure decreases CH4 conversion and increases carbon deposition on the Ni surface. Rapidly growing carbon filaments destroy the core-shell structure, resulting in segregation of the Ni-based particles from the catalyst bulk with concomitant severe sintering. During H2/CO2 redox cycling of Fe/Zr@Zr, an increased pressure decreases the time-averaged space-time yield of CO. In the reduction half-cycle, high pressure prolongs the existence of the FeO intermediate phase in the transformation of Fe/Zr@Zr, which decreases the material’s melting point, leading to fast sintering. Adding a small amount of O2 makes the chemical looping dry reforming process auto-thermal, which is advantageous in eliminating carbon. Nevertheless, deactivation of the double-zone reactor bed still occurs and is mainly ascribed to particle sintering, following similar principles as mentioned above. For both regular and auto-thermal catalyst-assisted chemical looping dry reforming, the decreasing ability for CO2 utilization is naturally due to the deactivation of the oxygen storage material, but also controlled by the stability of the bifunctional catalyst. The latter determines the reduction capacity of the gas product mixture in the reduction half-cycle, thereby affecting the achievable reduction degree of the oxygen storage material.
19 citations
TL;DR: In this paper, three different CO2 sorbents based on lithium orthosilicate (Li4SiO4) were prepared and characterized: (i) Li4 SiO4 as such; (ii) zirconia coated Li4 siO4, denoted as Li4Si O4@ZrO2; and (iii) Li 4SiO 4@Li 2 ZrO3.
Abstract: The application of a CO2 sorbent which releases CO2 at a lower temperature than calcium oxide is of interest in view of reducing the operating temperature or increasing the operating pressure of the super-dry reforming process. To this end, three different CO2 sorbents based on lithium orthosilicate (Li4SiO4) were prepared and characterized: (i) Li4SiO4 as such; (ii) zirconia coated Li4SiO4, denoted Li4SiO4@ZrO2; (iii) Li4SiO4, coated with lithium metazirconate and denoted as Li4SiO4@Li2ZrO3. While the carbonation properties of Li4SiO4 were found satisfactory, its decarbonation was incomplete. Li4SiO4@ZrO2 on the other hand, was found to contain Li2SiO3 and Li2ZrO3 rather than the anticipated Li4SiO4 and showed fast carbonation and decarbonation of Li2ZrO3. The best performing material in terms of CO2 sorption capacity, stability and rate of carbonation-decarbonation was Li4SiO4@Li2ZrO3. Its superior performance is ensured by the core-shell structure saturated with Li, allowing for easy restructuring during carbonation and fast regeneration upon decarbonation.
15 citations
TL;DR: In this paper, the cyclic stability of a 50Fe(2)O(3)/MgFeAlOx (containing 50 wt % Fe2O3 and 50 Wt % MgAl2O4) oxygen storage material is investigated.
Abstract: Fe2O3/MgFeAlOx materials are promising oxygen storage candidates for chemical looping CO2 conversion. In this work, the cyclic stability of a 50Fe(2)O(3)/MgFeAlOx (containing 50 wt % Fe2O3 and 50 wt % MgAl2O4) oxygen storage material is investigated. The evolution of its bulk properties over the course of 1000 H-2/CO2 redox cycles has been studied by means of( 57)Fe Mossbauer spectroscopy and in situ X-ray diffraction. As expected, all iron in the as-prepared oxygen storage material was present as Fe3+, 64% of which in iron-rich phases alpha-Fe2O3 and alpha-FeOOH and 36% in the form of a MgFeAlOx spinel. In contrast, after 1000 redox cycles, only 19% of iron was present in an iron-rich spinel such as Fe3O4, gamma-Fe2O3, and MgFe2O4. The remaining 81% was present in the form of Mg-Fe-Al-O, including Mg-x Fe1-xO. ILEEMS measurements showed surface enrichment of Fe3+ in 50Fe(2)O(3)/MgFeAlOx after 1000 redox cycles, with 36% of all surface Fe present as Fe3+ in iron-rich spinel phases such as gamma-Fe2O3 and/or MgFe2O4.
15 citations
01 Jan 2019
TL;DR: The increasing energy consumption creates the need to investigate new routes for the utilization of the available resources, like natural gas and biogas, to produce fuels and chemicals as discussed by the authors, which makes CH4 one of the most affordable carbon feedstocks in the world.
Abstract: The increasing energy consumption creates the need to investigate new routes for the utilization of the available resources, like natural gas and biogas, to produce fuels and chemicals. Natural gas, which primarily consists of methane (CH4), has an actual market price of 1.9 USD/GJ. This makes CH4 one of the most affordable carbon feedstocks in the world. Direct conversion of CH4 into chemicals results in low yields due to the high C―H bond dissociation energy (436 kJ/mol). As a result, CH4 is mainly converted indirectly, by reforming it to syngas, a mixture of H2 and CO, as an intermediate step. Syngas is a key building block with many downstream applications, as it is used in a number of synthesis processes of a wide range of chemicals and fuels. Most of the produced syngas is used for the synthesis of ammonia for fertilizers and for hydrogen production, which is exploited in refining processes, while the “gas-to-liquid” routes (i.e., Fischer-Tropsch) for fuel production account for ~ 8% consumption.
9 citations
TL;DR: Pt-doped semiconducting metal oxides and Pt metal clusters embedded in an oxide matrix are of interest for applications such as catalysis and gas sensing, energy storage, and memory devices as discussed by the authors.
Abstract: Pt-doped semiconducting metal oxides and Pt metal clusters embedded in an oxide matrix are of interest for applications such as catalysis and gas sensing, energy storage, and memory devices. Accura...
8 citations
01 Jan 2019
TL;DR: In this paper, high temperature O2-H2 redox cycling was applied to mimic the lifetime changes in model Pt13In9 nanocatalysts, while monitoring the induced changes by in-situ quick X-ray absorption spectroscopy with one second resolution.
Abstract: Abstract Alloyed metal nanocatalysts are of environmental and economic importance in a plethora of chemical technologies. During the catalyst lifetime, supported alloy nanoparticles undergo dynamic changes which are well‐recognized but still poorly understood. High‐temperature O2–H2 redox cycling was applied to mimic the lifetime changes in model Pt13In9 nanocatalysts, while monitoring the induced changes by in situ quick X‐ray absorption spectroscopy with one‐second resolution. The different reaction steps involved in repeated Pt13In9 segregation‐alloying are identified and kinetically characterized at the single‐cycle level. Over longer time scales, sintering phenomena are substantiated and the intraparticle structure is revealed throughout the catalyst lifetime. The in situ time‐resolved observation of the dynamic habits of alloyed nanoparticles and their kinetic description can impact catalysis and other fields involving (bi)metallic nanoalloys.