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This work analyses the catalytic activity displayed by Cu/SiO2, Cu-Fe/SiO2 and Cu/FSN (Fe-SiO2 nanocomposite) catalysts for the Reverse Water Gas Shift reaction. Compared to Cu/SiO2 catalyst, the presence of Fe resulted on higher CO’s selectivity and boosted resistances against the constitution of the deactivation carbonaceous species.
Regarding the catalytic performance however, the extent of improvement attained through incorporation Fe species strongly relied on the catalysts’ configuration. At 30 L/gh and H2:CO2 ratios = 3, the performance of the catalysts’ series increased according to the sequence: Cu/SiO2 < Cu-Fe/SiO2 << Cu/FSN. The remarkable catalytic
enhancements provided by Fe-SiO2 nanocomposites under different RWGS reaction atmospheres were associated to enhanced catalyst surface basicity’s and stronger Cu-support interactions. The catalytic promotion achieved by Fe-SiO2 nanocomposites argue an optimistic prospective for nanocomposite catalysts within future
CO2-valorising technologies.
By evaluating the functional modifications induced by Zr and Fe as dopants in Pt/CeO2‐MOx/Al2O3 catalysts (M = Fe and Zr), the key features for improving water gas shift (WGS) performance for these systems have been addressed. Pt/ceria intrinsic WGS activity is often related to improved H2 surface dynamics, H2O absorption, retentions and dissociation capacities which are influenced greatly by the support nature. Two metals, iron and zirconia, were chosen as ceria dopants in this work, either in separate manner or combined. Iron incorporation resulted in CO‐redox properties and oxygen storage capacities (OSC) improvement but the formation of Ce‐Fe solid solutions did not offer any catalytic benefit, while the Zr incorporation influenced in a great manner surface electron densities and shows higher catalytic activity. When combined both metals showed an important synergy evidenced by 30% higher CO conversions and attributed to greater surface electron densities population and therefore absorption and activity. This work demonstrates that for Pt/ceria catalysts OSC enhancement does not necessarily imply a catalytic promotion.
The circular economy is calling for the rapid use of already-developed renewable energies. However, the successful implementation of those new fuels is limited by economic and political issues. For instance, in the Brandenburg region, Germany, biogas production from anaerobic digestion of biomass and wastes is a current alternative. However, the upgrading biogas to biomethane is still challenging and the economic viability is unknown. Therefore, we performed an economic analysis for biogas upgrading to biomethane in the Brandenburg region. Five biogas plant sizes were analyzed by the method of discounted cash flow. This method yields the net present value of the projects, thus revealing the profitability or non-profitability of the plants. Results indicate profitable outputs for medium and large plants, with net present values between 415 and 7009 k€. However, the smallest plants have net present values from -4250 to -3389 k€, thus needing further economic efforts or subsidies to reach profitability. Indeed, biomethane prices should range between 52.1 and 95.6 €/MWh to make these projects profitable. Combinations of 50% of investment subsidized and 11.5 €/MWh feed-in tariffs subsidies could make the projects reach profitability. These findings reveal that political actions such as green policies and subsidies are needed to implement green energy. This case study should serve as a potential tool for policy-makers toward a sustainable bioeconomy.
Herein a novel path is analysed for its economic viability to synergize the production of biomethane and dimethyl ether from biogas. We conduct a profitability analysis based on the discounted cash flow method. The results revealed an unprofitable process with high cost/revenues ratios. Profitable scenarios would be reached by setting prohibitive DME prices (1983–5566 €/t) or very high feed-in tariffs subsidies (95.22 €/MWh in the best case scenario). From the cost reduction side, the analysis revealed the need of reducing investment costs. For this purpose, we propose a percentage of investment as incentive scheme. Although the size increase benefits cost/revenues ratio, only the 1000 m3/h biogas plant size will reach profitability if 90% of the investment is subsidized. A sensitivity analysis to check the influence of some important economical parameters is also included. Overall this study evidences the big challenge that our society faces in the way towards a circular economy.
Nickel Phosphide Catalysts as Efficient Systems for CO2 Upgrading via Dry Reforming of Methane
(2021)
This work establishes the primordial role played by the support’s nature when aimed at the constitution of Ni2P active phases for supported catalysts. Thus, carbon dioxide reforming of methane was studied over three novel Ni2P catalysts supported on Al2O3, CeO2 and SiO2-Al2O3 oxides. The catalytic performance, shown by the catalysts’ series, decreased according to the sequence: Ni2P/Al2O3 > Ni2P/CeO2 > Ni2P/SiO2-Al2O3. The depleted CO2 conversion rates discerned for the Ni2P/SiO2-Al2O3 sample were associated to the high sintering rates, large amounts of coke deposits and lower fractions of Ni2P constituted in the catalyst surface. The strong deactivation issues found for the Ni2P/CeO2 catalyst, which also exhibited small amounts of Ni2P species, were majorly associated to Ni oxidation issues. Along with lower surface areas, oxidation reactions might also affect the catalytic behaviour exhibited by the Ni2P/CeO2 sample. With the highest conversion rate and optimal stabilities, the excellent performance depicted by the Ni2P/Al2O3 catalyst was mostly related to the noticeable larger fractions of Ni2P species established
For a bio-economy establishment, understanding the energy consumption needs to produce solid biofuels is a key point. Herein, olive tree pruning was treated by both dry (pyrolysis and torrefaction) and wet (hydrothermal carbonization) thermal treatments. Product yield, solid quality and energy consumption were assessed. The solids were characterized by means of chemical and thermogravimetric analysis. For all treatments, coal-like solid products were obtained, with higher heating values (HHV) of almost 30 MJ kg−1 in most of the conditions evaluated. Chars from pyrolysis presented the greater carbon content (between 76 and 85 wt%) but also the higher ash content (ranging from 6 to 9 wt%). From an energy consumption perspective, torrefaction registered the lowest energy consumption (between 5.85 and 20.76 MJ kg−1 char). The highest energy contents per kilogram of char produced were also reflected in torrefaction samples, with values around 11 MJ kg−1 char. Although the obtained HHVs were greater for pyrolysis chars the higher mass yields obtained in torrefaction makes it more profitable. The least severe conditions allowed to obtain a positive energy balance only with the solid phase considered. Nonetheless, further room for improvement is possible since the gas and liquid phases may also be valorised.
Profitability studies are needed to establish the potential pathways required for viable biomethane production in the Brandenburg region of Germany. This work study the profitability of a potential biomethane production plant in the eastern German region of Brandenburg, through a specific practical scenario with data collected from a regional biogas plant located in Alteno (Schradenbiogas GmbH & Co. KG). Several parameters with potential economic influence such as distance of the production point to the grid, waste utilization percentage, and investment, were analyzed. The results illustrate a negative overall net present value with the scenario of no governmental investment, even when considering trading the CO2 obtained throughout the process. Subsidies needed to reach profitability varied with distance from 13.5 €/MWh to 19.3 €/MWh. For a fixed distance of 15 kms, the importance of percentage of waste utilization was examined. Only 100% of waste utilization and 75% of waste utilization would reach profitability under a reasonable subsidies scheme (16.3 and 18.8 €/MWh respectively). Concerning the importance of investment, a subsidized investment of at least 70% is demanded for positive net present values. Besides, the sensitivity analysis remarks the energy consumption of the biogas upgrading stage, the electricity price, and the energy consumption of biogas production as major parameters to be tackled for the successful implementation of biogas upgrading plants. The results here obtained invite to ponder about potential strategies to further improve the economic viability of this kind of renewable projects. In this line, using the CO2 separated to produce added-value chemicals can be an interesting alternative.
This study delivers useful understanding towards the design of effective catalytic systems for upgrading real CO2erich residual streams derived from biomass valorization. Within this perspective, a catalysts' series based on (5 wt%) Cu - (X wt%) Mn/Al2O3with X¼0, 3, 8, and 10 is employed. The improved catalyst performance achieved through Mn incorporation is ascribed to enhanced Cu dispersions and promoted surface basic concentrations. Under standard RWGS conditions, the highest reaction rates achieved by(5 wt%) Cu - (8 wt%) Mn/Al2O3catalyst were associated to improved Cu dispersions along with the constitution of highly active Cu-MnOxdomains. Remarkably, variations on the optimal Cu to Mn ratios were detected as a function of the RWGS reaction conditions. Thus, under simulated CO2-rich residual feedstock's, i.e., in presence of CO and CH4, the further promotion on the Cu dispersion attained by the larger amounts of MnOxrendered the (5 wt%) Cu - (10 wt%) Mn/Al2O3catalyst as the best performing sample. Overall, the presented outcomes underline operative strategies for developing catalytic systems with advanced implementation potentialities.
In this work the economic performance of valorizing the gaseous stream coming from hydrothermal carbonization (HTC) of olive tree pruning is presented as a novel strategy to improve the competitiveness of HTC. The valorization of the commonly disregarded gaseous stream produced in this thermochemical treatment was proposed via the Reverse Water–Gas Shift reaction. This allows to obtain syngas for selling and therefore improving the overall economic performance of the process. To this end, three plant sizes were selected (312.5, 625 and 1250 kg/h of biomass processing). The parameters with a higher share in the total cost distribution along with the revenues from the hydrochar and the syngas selling were further evaluated. The results evidenced that with the assumptions taken, the overall process is still not profitable. To reach profitability, syngas selling prices between 2.2 and 3.4 €/m3 are needed, revealing that this proposal is not economically attractive. Alternatively, a lack of competitiveness in the current market is revealed with hydrochar selling prices between 0.41 and 0.64 €/kg to make the project profitable. The catalyst cost, sharing approximately 20% of the total cost, is the parameter with the highest impact in the total economics of the process. The second one is the hydrogen price production, representing almost 16% of the total. Investment subsidies are also examined as a potential tool to cover part of the initial investment. These results evidenced that further efforts and measures are needed to push forward in the path towards circular economy societies.
Seeking for advanced catalytic systems for the CO2 methanation reaction, the use of Ni supported catalysts over redox materials is often proposed. Profiting the superior redox properties described for layered perovskite systems, this work has investigated a series Ni supported YMn1-xAlxO3 (x = 0, 0.2, 0.5, 0.8, 1) perovskite catalysts.
The obtained results evidenced the impact of the support nature on the systems redox properties and Ni-support interactions. Within the catalysts series, the greater methanation rates displayed by Ni/YMn0.5Al0.5O3 catalyst (0.748 mmolCO2,conv.s–1 gNi –1 at 400 ◦C and 60 L/gh) were associated to the interplay between the support redox
properties and superior Ni dispersion. The improved redox behavior attained through the Al-incorporation (up to x = 0.5) was associated to the layered perovskite structures which, being distorted and constituted by smaller crystal sizes, facilitated the behavior of Mn redox couples as surface species readily interconverted. Exhibiting
catalytic performances comparable to precious metals based catalysts, this work proposes the Ni/YMn0.5Al0.5O3 catalyst as an effective system for the CO2 methanation reaction.
CO2 methanation: on the modeling of reacting laminar flows in structured Ni/MgAl2O4 catalysts
(2022)
CO2 methanation: on the modeling of reacting laminar flows in structured Ni/MgAl2O4 catalysts
(2022)
Promoting the performance of catalytic systems by incorporating small amount of alkali has been proved effective for several reactions whilst controversial outcomes are reported for the synthetic natural gas production. This work studies a series of Ni catalysts for CO2 and CO methanation reactions. In-situ DRIFTS spectroscopy evidenced similar reaction intermediates for all evaluated systems and it is proposed a reaction mechanism based on: i) formate decomposition and ii) hydrogenation of lineal carbonyl species to methane. Compared to bare Ni, the enhanced CO2 methanation rates attained by NiFe/Al and NiFeK/Al systems are associated to promoted formates decomposition into lineal carbonyl species. Also for CO methanation, the differences in the catalysts’ performances were associated to the relative concentration of lineal carbonyl species. Under CO methanation conditions and opposing the CO2 methanation results where the incorporation of K delivered promoted catalytic behaviours, worsened CO methanation rates were discerned for the NiFeK/Al system.
Nowadays, global climate change is likely the most compelling problem mankind is facing. In this scenario, decarbonisation of the chemical industry is one of the global challenges that the scientific community needs to address in the immediate future. Catalysis and catalytic processes are called to play a decisive role in the transition to a more sustainable and low-carbon future. This critical review analyses the unique advantages of structured reactors (isothermicity, a wide range of residence times availability, complex geometries) with the multifunctional design of efficient catalysts to synthesise chemicals using CO2 and renewable H2 in a Power-to-X (PTX) strategy. Fine-chemistry synthetic methods and advanced in situ/operando techniques are essential to elucidate the changes of the catalysts during the studied reaction, thus gathering fundamental information about the
active species and reaction mechanisms. Such information becomes crucial to refine the catalyst’s formulation and boost the reaction’s performance. On the other hand, reactors architecture allows
flow pattern and temperature control, the management of strong thermal effects and the incorporation of specifically designed materials as catalytically active phases are expected to significantly contribute
to the advance in the valorisation of CO2 in the form of high added-value products. From a general perspective, this paper aims to update the state of the art in Carbon Capture and Utilisation (CCU)
and PTX concepts with emphasis on processes involving the transformation of CO2 into targeted fuels and platform chemicals, combining innovation from the point of view of both structured reactor
design and multifunctional catalysts development.
Compared to a Reverse Water Gas Shift (RWGS) process carried out under ideal conditions, the valorization of CO2-rich residues involve additional challenges. Indeed, for an ideal RWGS reaction unit, the CO2 methanation reaction and the constitution of carbon deposits via Boudouard reaction are the main side reactions to take into consideration. For CO2-rich residues derived from biomass treatment and heavy metal industries, the presence of CH4 and CO species (among others) constitute an, although often disregarded, much complex panorama where side reactions like CO methanation, dry reforming of methane, the forward Water Gas Shift reaction and the decomposition of CO and CH4 resulting in carbon deposits, are occurring to some extent within the catalytic reactor. This work aimed at designing advanced catalytic systems capable of converting the CO2/CO/CH4 feedstocks into syngas mixtures. Thus, with the RWGS reaction considered as the major process, this work focusses on the side reactions involving CO/CH4 species. In this context, a series Cu-MnOx/Al2O3 spinel derived catalysts were optimized for syngas production in presence of CO and CH4 fractions. Once the optimal active phase was determined, the optimal Cu contents and the impact of the support nature (Al2O3, SiO2-Al2O3 and CeO2-Al2O3) was evaluated for the valorization of realistic CO2-rich feedstocks. Remarkably, the obtained outcomes underline operative strategies for developing catalytic systems with advanced implementation potential. For that aim, the catalyst design should present, along with an active and selective phase for RWGS reaction, superior cooking resistances, activities towards methane reforming and low tendencies towards the forward WGS reaction. Further developments should tackle difficult tasks like improving the RWGS reaction rate while inhibiting the forwards WGS reaction as well as improving the CH4 conversion to CO without affecting the process selectivity. Strategies towards advancing catalytic systems capable of operating under variable conditions also arise as appealing routes.
Nowadays, the majority of the Reverse Water Gas Shift (RWGS) studies assume somehow model feedstock (diluted CO2/H2) for syngas production. Nonetheless, biogas streams contain certain amounts of CO/H2O which will decrease the obtained CO2 conversion values by promoting the forward WGS reaction. Since the rate limiting step for the WGS reaction concerns the water splitting, this work proposes the use of hydrophobic RWGS catalysts as an effective strategy for the valorization of CO2-rich feedstock in presence of H2O and CO. Over Fe-Mg catalysts, the different hydrophilicities attained over pristine, N- and B-doped carbonaceous supports accounted for the impact on the activity of the catalyst in presence of CO/H2O. Overall, the higher CO productivity (4.12 μmol/(min·m2)) attained by Fe-Mg/CDC in presence of 20% of H2O relates to hindered water adsorption and unveil the use of hydrophobic surfaces as a suitable approach for avoiding costly pre-conditioning units for the valorization of CO2-rich streams based on RWGS processes in presence of CO/H2O.
This paper reviews and compares state-of-the-art cobalt-based catalysts and catalytic systems used to produce green and sustainable fuels using FTS. Being focused on comparing the effect of the catalyst formulation and synthesis method, the reactor type and operating parameters, as well as the quality of the obtained fuels, the aim is to identify the research gaps between these relevant research areas concerning production of green and sustainable fuels.
Das pulverbasierte 3D-Metalldrucken ermöglicht die Fertigung von hochkomplexen Integralbauteilen, die als Trägerstruktur für Mikroreaktoren benutzt werden. Nach einer Beschichtung der Struktur mit einem Katalysatormaterial, können diese Mikroreaktoren höchst effizient für die CO2-Methanisierung eingesetzt werden. Durch die additive Fertigung mit dem selektiven Laserstrahlschmelzen (SLM) wurden adaptierte dreidimensionale periodische Gitterstrukturen mit sehr geringen Wandstärken hergestellt. Diese weisen ein sehr günstiges Verhältnis von Oberfläche zu Volumen (TPMS - Triply periodic minimal surface) auf. Des Weiteren zeigen die TPMS-Strukturen vorteilhafte Strömungseigenschaften, die sowohl für die Beschichtung mit dem Katalysator-Material als auch die Durchströmung mit den Reaktionsmedien im Betrieb essentiell sind. So ist es beispielsweise möglich, durch die Variation der Dimension einer TPMS-Struktur die Oberfläche pro Volumeneinheit, den hydraulischen Durchmesser des Reaktors und somit auch den Transportprozess des Fluids deutlich zu verbessern. Diese Faktoren ermöglichen eine effektivere Gas-Katalysator-Reaktion. Im Vergleich zu Mikroreaktorstrukturen aus den traditionellen Herstellungsverfahren liefern die additiv gefertigten Strukturen sowohl eine höhere CO2-Umwandlungsrate als auch eine CH4-Selektivität innerhalb des diffusionskontrollierten Bereichs.
This work presents a comparative study towards the development of efficient micro-reactors based on 3D-printed structures. Thus, the study evaluates the influence of the metal substrate geometry on the performance of structured catalysts for the CO2 methanation reaction. For this purpose, 0.5%Ru–15%Ni/MgAl2O4 catalyst is wash coated over two different micro-monolithic metal substrates: a conventional parallel channel honeycomb structure and a novel 3D-printed structure with a complex gyroid geometry. The effect of the metal substrate geometry is analyzed for several CO2 sources including ideal flue gas atmospheres, the presence of residual CH4 and CO in the flue gas, as well as simulated biogas sources. The advantages of the gyroid-3D complex geometries over the honeycomb structures are shown for all evaluated conditions, providing at the best-case scenario a 14% improvement of CO2 conversion. Moreover, this contribution shows that systematically tailoring geometrical features of structured catalysts becomes an effective strategy to achieve improved catalysts performances independent of the flue gas composition. By enhancing the transport processes and the gas-catalyst interactions, the employed gyroid 3D metal substrates enable boosted CO2 conversions and greater CH4 selectivity within diffusional controlled regimes.
Assessing the impact of textural properties in Ni–Fe catalysts for CO2 methanation performance
(2021)
In heterogeneous catalysis, the benefits of employing adequate textural properties on the catalytic performances are usually stated. Nevertheless, the quantification of the extent of improvement is not an easy task since variations on the catalysts’ specific areas and pore structures might involve modifications on a number of other
surface catalytic features. This study establishes the impact of the catalyst textural properties on the CO2 methanation performance by investigating bimetallic Ni–Fe catalysts supported over carbon supports with different textural properties regarding surface area and pore structure. The comparable metal loading and dispersions
attained for all systems enabled establishing forthright relationships between the catalyst textural properties and CO2 methanation rate. Once the influence of the external mass diffusions on the catalysts’ performance was experimentally discarded, the estimated Thiele modulus and internal effectiveness (φ and ηEff) values showed that the catalyst performance was majorly governed by the surface reaction rate whilst the pore size affected in no significant manner within the examined range (Dpore = 10.2 to 5.8 nm). Therefore, the rapport
between the catalyst performance and surface area was quantified for the CO2 methanation reaction over Ni–Fe catalysts: increasing the surface area from 572 to 802 m2/g permit obtaining ca. 10% higher CO2 conversions.