M. González-Castaño, E. Le Saché, S. Ivanova, F. Romero-Sarria, M.A. Centeno, J.A. Odriozola (2018) Tailoring structured WGS catalysts: Impact of multilayered concept on the water surface interactions
A novel multilayer approach for designing structured WGS catalyst is employed in this study as a response to the lack of new strategies in the literature. The approach proposes the use of two successive layers with different functionalities on metallic micromonolith substrate. The WGS catalyst behavior is modulated by the nature of the inner layer which determines the active species surface population by acting on the water activation step.
The catalytic promotion attained by introducing inner ceria containing solids with increasing number of oxygen defects is intensely analyzed through FT-IR and H2O-TPD. Several evidences about the participation of the oxygen vacancies, as key sites, for water absorption processes are established. Besides, remarkable relationships between the water absorption strengths and the water splitting processes within their influence on the catalyst performance are also discussed.
C. Price, L. Pastor-Pérez, E. le Saché, A. Sepúlveda-Escribano, T. R. Reina (2017) Highly active Cu-ZnO catalysts for the WGS reaction at mediumehigh space velocities: Effect of the support composition
Cu-ZnO based catalysts are the benchmark materials for the low-temperature WGS reaction. However, they present a crucial drawback which limits their application in portable devices: they only work under very low space velocities. In this study, we have developed a series of multicomponent Cu-ZnO catalysts able to work at relatively high space velocities with outstanding activity and stability. Different reference supports have been utilised with CeO2-Al2O3 being the most promising system. Overall, this work describes a strategy to design advanced Cu-based catalysts that can overcome the residence time restrictions in the WGS reaction.
L. Pastor-Pérez, F. Baibars, E. le Saché, H. Arellano-García, S. Gu, T.R. Reina (2017) CO2 valorisation via Reverse Water-Gas Shift reaction using advanced Cs doped Fe-Cu/Al2O3 catalysts
This paper evidences the viability of chemical recycling of CO2 via reverse water-gas shift reaction using advanced heterogeneous catalysts. In particular, we have developed a multicomponent Fe-Cu-Cs/Al2O3 catalyst able to reach high levels of CO2 conversions and complete selectivity to CO at various reaction conditions (temperature and space velocities). In addition, to the excellent activity, the novel-Cs doped catalyst is fairly stable for continuous operation which suggests its viability for deeper studies in the reverse water-gas shift
reaction. The catalytic activity and selectivity of this new material have been carefully compared to that of Fe/Al2O3, Fe-Cu/Al2O3 and Fe-Cs/Al2O3 in order to understand each active component’s contribution to the catalyst’s performance. This comparison provides some clues to explain the superiority of the multicomponent Fe-Cu-Cs/Al2O3 catalyst.
L. Pastor-Pérez, E. le Saché, C. Jones, S. Gu, H. Arellano-Garcia, T.R. Reina (2017) Synthetic natural gas production from CO2 over Ni-x/CeO2-ZrO2 (x = Fe, Co) catalysts: Influence of promoters and space velocity
Herein, the production of synthetic natural gas is proposed as an effective route for CO2 conversion. Typical catalysts for this reaction are based on Ni. In this study, we demonstrated that the addition of promoters such as iron and cobalt can greatly benefit the activity of standard Ni methanation catalysts. In particular cobalt seems to be a very efficient promoter. Our Co doped material is an outstanding catalysts for the CO2 methanation leading to high levels of CO2 conversion with selectivities close to 100%. Additionally, this catalyst is able to preserve
excellent performance at relatively high space velocity which allows flexibility in the reactor design making easier the development of compact CO2 utilisation units. As an additional advantage, the Co-promoted catalysts is exceptionally stable conserving high levels of CO2 conversion under continuous operations in long terms runs.
T. Stroud, T.J. Smith, E. le Saché, J.L. Santos, M.A. Centeno, H. Arellano-Garcia, J.A. Odriozola, T.R. Reina (2018) Chemical CO2 recycling via dry and bi reforming of methane using Ni-Sn/Al2O3 and Ni-Sn/CeO2-Al2O3 catalysts
Carbon formation and sintering remain the main culprits regarding catalyst deactivation in the dry and bireforming of methane reactions (DRM and BRM, respectively). Nickel based catalysts (10 wt.%) supported on alumina (Al2O3) have shown no exception in this study, but can be improved by the addition of tin and ceria. The effect of two different Sn loadings on this base have been examined for the DRM reaction over 20 h, before selecting the most appropriate Sn/Ni ratio and promoting the alumina base with 20 wt.% of CeO2. This catalyst then underwent activity measurements over a range of temperatures and space velocities, before undergoing experimentation in BRM. It not only showed good levels of conversions for DRM, but exhibited stable conversions towards BRM, reaching an equilibrium H2/CO product ratio in the process. In fact, this work reveals how multicomponent Ni catalysts can be effectively utilised to produce flexible syngas streams from CO2/CH4 mixtures as an efficient route for CO2 utilisation.
E. le Saché, J.L Santos, T.J. Smith, M.A. Centeno, H. Arellano-Garcia, J.A. Odriozola, T.R. Reina (2018) Multicomponent Ni-CeO2 Nanocatalysts for Syngas production from CO2/CH4 mixtures
The dry reforming of methane with CO2 is a common route to transform CO2/CH4 mixtures
into added value syngas. Ni based catalysts are highly active for this goal but suffer from
deactivation, as such promoters need to be introduced to counteract this, and improve
performance. In this study, mono- and bi-metallic formulations based on 10 wt.% Ni/CeO2-
Al2O3 are explored and compared to a reference 10 wt.% Ni/γ-Al2O3. The effect of Sn and Pt
as promoters of Ni/CeO2-Al2O3 was also investigated. The formulation promoted with Sn
looked especially promising, showing CO2 conversions stabilising at 65% after highs of 95%.
Its increased performance is attributed to the additional dispersion Sn promotion causes.
Changes in the reaction conditions (space velocity and temperature) cement this idea, with the
Ni-Sn/CeAl material performing superiorly to the mono-metallic material, showing less
deactivation. However, in the long run it is noted that the mono-metallic Ni/CeAl performs
better. As such the application is key when deciding which catalyst to employ in the dry
reforming process.
E. le Saché, L. Pastor-Pérez, D. Watson, A. Sepúlveda-Escribano, T. R. Reina (2018) Ni stabilised on inorganic complex structures: superior catalysts for chemical CO2 recycling via dry reforming of methane
CO2utilisation is becoming an appealing topic incatalysisscience due to the urgent need to deal with greenhouse gases (GHG) emissions. Herein, the dry reforming ofmethane(DRM) represents a viable route to convert CO2and CH4(two of the major GHG) into syngas, a highly valuable intermediate in chemical synthesis. Nickel-based catalysts are economically viable materials for this reaction, however they show inevitable signs of deactivation. In this work stabilisation of Ni in a pyrochlore-perovskite structure is reported as a viable method to prevent fast deactivation. Substitution ofZirconiumby Ni at various loadings in thelanthanumzirconate pyrochlore La2Zr2O7is investigated in terms of reactant conversions under various reaction conditions (temperature and space velocity). XRD analysis of the calcined and reduced catalysts showed the formation of crystalline phases corresponding to the pyrochlore structure La2Zr2-xNixO7-δ and an additional La2NiZrO6perovskitephase at high Ni loadings. Carbon formation is limited using this formulation strategy and, as a consequence, our best catalyst shows excellent activity for DRM at temperatures as low as 600 °C and displays great stability over 350 h of continuous operation. Exsolution of Ni from theoxidestructure, leading to small and well dispersed Ni clusters, could explain the enhanced performance.
U. Guharoy, E. le Saché, Q. Cai, T. R. Reina, S. Gu (2018) Understanding the role of Ni-Sn interaction to design highly effective CO2 conversion catalysts for dry reforming of methane
CO2reforming of methane is an effective route for carbon dioxide recycling to valuable syngas. However conventional catalysts based on Ni fail to overcome the stability requisites in terms of resistance to co*king and sintering. In this scenario, the use of Sn as promoter of Ni leads to more powerful bimetallic catalysts with enhanced stability which could result in a viable implementation of the reforming technology at commercial scale. This paper uses a combined computational (DFT) and experimental approach, to address the fundamental aspects of mitigation of co*ke formation on the catalyst’s surface during dry reforming of methane (DRM). The DFT calculation provides fundamental insights into the DRM mechanism over the mono and bimetallic periodic model surfaces. Such information is then used to guide the design of real powder catalysts. The behaviour of the real catalysts mirrors the trends predicted by DFT. Overall the bimetallic catalysts are superior to the monometallic one in terms of long-term stability and carbon tolerance. In particular, low Sn concentration on Ni surface effectively mitigate carbon formation without compromising the CO2conversion and the syngas production thus leading to excellent DRM catalysts. The bimetallic systems also presents higher selectivity towards syngas as reflected by both DFT and experimental data. However, Sn loading has to be carefully optimized since a relatively high amount of Sn can severely deter the catalytic performance.
