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• Customised H 2 -rich syngas production from CO 2 /CH 4 mixtures. • Ni stabilised on complex inorganic mixed oxides as versatile catalysts for reforming reactions. • Effect of water, temperature and space velocity on H 2 /CO ratio. • Overcoming coke deposition and sintering by introducing Ni in a pyrochlore-perovskite structure. The bi-reforming of methane (BRM) has the advantage of utilising greenhouse gases and producing H 2 rich syngas. In this work Ni stabilised in a pyrochlore-double perovskite structure is reported as a viable catalyst for both Dry Reforming of Methane (DRM) and BRM. A 10 wt.% Ni-doped La 2 Zr 2 O 7 pyrochlore catalyst was synthesised, characterised and tested under both reaction conditions and its performance was compared to a supported Ni/La 2 Zr 2 O 7. In particular the effect of steam addition is investigated revealing that steam increases the H 2 content in the syngas but limits reactants conversions. The effect of temperature, space velocity and time on stream was studied under BRM conditions and brought out the performance of the material in terms of activity and stability. No deactivation was observed, in fact the addition of steam helped to mitigate carbon deposition. Small and well dispersed Ni clusters, possibly resulting from the progressive exsolution of Ni from the mixed oxide structure could explain the enhanced performance of the catalyst. [ABSTRACT FROM AUTHOR]

The work in this paper evidences the viability of producing synthetic natural gas (SNG) via the methanation reaction tackling two fundamental challenges on methanation catalysis (i) the development of advanced catalysts able to achieve high CO 2 conversion and high methane yields and (ii) the unexplored effect of residual methane on the methanation stream. Both challenges have been successfully addressed using Ni/CeO 2 -ZrO 2 catalysts promoted with Mn and Co. Mn does not seem to be a good promoter while Co prevents carbon deposition and secondary reactions. In fact, our Co-doped sample reached high levels of CO 2 conversion and CH 4 selectivity, especially at low reaction temperatures. In addition, this catalyst exhibits excellent catalytic behaviour when methane is introduced into the gas mixture, indicating its feasibility for further study to be conducted in realistic flue gases environments and methanation units with recycling loops. Furthermore, when methane is introduced in the reactant mixture, the Ni-Co/CeO 2 -ZrO 2 sample is very stable maintaining high levels of conversion and selectivity. Overall our Co-doped catalyst can deliver high purity synthetic natural gas for long-term runs, promising results for gas-phase CO 2 conversion units. • Synthetic natural gas production over highly effective bimetallic Ni-Co catalysts. • First report on CO 2 methanation in the presence of methane. • Chemical CO 2 recycling via CO 2 methanation. • Design of methanation units with recycling loops. [ABSTRACT FROM AUTHOR]

A comparative study of three different ceria synthesis procedures (template- and MW- assisted hydrothermal synthesis and urea homogeneous precipitation) is reported in this paper. The obtained materials were employed as supports for Pt nanoparticles, and the Pt/CeO 2 catalysts were evaluated in the WGS reaction under model and realistic conditions. The influence of the support, e.g., its morphology and electronic properties, has been studied in detail by means of XRD, H 2 -TPR, XPS, UV–Vis spectroscopy and toluene hydrogenation (for metal dispersion assessment). The catalytic performance of the samples is directly correlated with the modification of the electronic properties, as a result of the preparation method used. The conventional homogeneous precipitation method with urea resulted to be the best option, leading to enhanced ceria reducibility and adequate Pt dispersion, which in turns resulted in a very efficient WGS catalyst. Image 1 • Three different ceria synthesis routes have been compared. • The synthesis procedure modulates the redox and electronic properties of CeO 2. • Pt dispersion and metal-support interaction are depend on the morphology of CeO 2. • The highest activity with realistic conditions was shown by the Pt/CeO 2 urea catalyst. [ABSTRACT FROM AUTHOR]

This paper evidences the viability of chemical recycling of CO 2 via reverse water-gas shift reaction using advanced heterogeneous catalysts. In particular, we have developed a multicomponent Fe-Cu-Cs/Al 2 O 3 catalyst able to reach high levels of CO 2 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/Al 2 O 3 , Fe-Cu/Al 2 O 3 and Fe-Cs/Al 2 O 3 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/Al 2 O 3 catalyst. [ABSTRACT FROM AUTHOR]

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 CeO 2 -Al 2 O 3 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. [ABSTRACT FROM AUTHOR]

In this work, the low-temperature hydrogen production via glycerol steam reforming over activated carbon-supported Ni and Ni-Sn catalysts promoted by ceria was studied. A combination of N 2 adsorption, powder X-ray diffraction, temperature-programmed reduction with H 2 , X-ray photoelectron spectroscopy and TEM analysis were used to characterise the Ni-Sn-CeO 2 interactions and the CeO 2 dispersion over the activated carbon support. The catalytic activity results show that the presence of ceria enhances the water-gas shift reaction, thus promoting the selectivity towards hydrogen. The inclusion of Sn stresses the influence of ceria in the displayed performance. Moreover, the formation of a Ni-Sn alloy seems to be an efficient way to mitigate Ni sintering and therefore to improve the overall catalyst’s stability. [ABSTRACT FROM AUTHOR]

Ni nanoparticles have been selectively loaded inside or outside commercial carbon nanotubes by the wet impregnation method, and their catalytic performance on the conversion of guaiacol in batch reactor at 5 MPa and 573 K has been studied. Different characterization techniques were used to investigate the effect of confinement in nanotubes. The catalysts showed different selectivity to cyclohexene compared to cyclohexane was enhanced when the nanoparticles were loaded inside. This result was attributed to the different adsorption mode of the molecule inside the nanotubes. [ABSTRACT FROM AUTHOR]

The low temperature water-gas shift (WGS) reaction has been studied over two commercial multiwall carbon nanotubes-supported nickel catalysts promoted by ceria. For comparison purposes, activated carbon-supported catalysts have also been studied. The catalytic performance and the characterization by N 2 adsorption analysis, powder X-ray diffraction (XRD), temperature-programmed reduction with H 2 (TPR-H 2 ), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis showed that the surface chemistry has an important effect on the dispersion of ceria. As a result, ceria was successfully dispersed over the carbon nanotubes (CNTs) with less graphitic character, and the catalyst afforded better activity in WGS than the catalyst prepared over massive ceria. Moreover, a 20 wt.% CeO 2 loading over this support was more active than the analogous catalyst with a 40 wt.% loading. The ceria nanoparticles were smaller when the support was previously oxidized, however this resulted in a decrease of the activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni 12 P 5 -CeAl, Ni 12 P 5 -Al 2 O 3 and Ni 2 P/SiO 2 were developed and tested active for CO 2 hydrogenation. • Ni 2 P/SiO 2 catalyst is a highly selective catalyst for reverse water–gas shift (RWGS) reaction, producing over 80% CO in the full temperature range. • Ni 12 P 5 -CeAl and Ni 12 P 5 -Al 2 O 3 catalysts show activity for methanation at low temperatures with a switchover to RWGS at higher temperatures (reaching or approaching thermodynamic equilibrium behaviour). We report for the first time the support dependent activity and selectivity of Ni-rich nickel phosphide catalysts for CO 2 hydrogenation. New catalysts for CO 2 hydrogenation are needed to commercialise the reverse water–gas shift reaction (RWGS) which can feed captured carbon as feedstock for traditionally fossil fuel-based processes, as well as to develop flexible power-to-gas schemes that can synthesise chemicals on demand using surplus renewable energy and captured CO 2. Here we show that Ni 2 P/SiO 2 is a highly selective catalyst for RWGS, producing over 80% CO in the full temperature range of 350–750 °C. This indicates a high degree of suppression of the methanation reaction by phosphide formation, as Ni catalysts are known for their high methanation activity. This is shown to not simply be a site blocking effect, but to arise from the formation of a new more active site for RWGS. When supported on Al 2 O 3 or CeAl, the dominant phase of as synthesized catalysts is Ni 12 P 5. These Ni 12 P 5 catalysts behave very differently compared to Ni 2 P/SiO 2 , and show activity for methanation at low temperatures with a switchover to RWGS at higher temperatures (reaching or approaching thermodynamic equilibrium behaviour). This switchable activity is interesting for applications where flexibility in distributed chemicals production from captured CO 2 can be desirable. Both Ni 12 P 5 /Al 2 O 3 and Ni 12 P 5 /CeAl show excellent stability over 100 h on stream, where they switch between methanation and RWGS reactions at 50–70% conversion. Catalysts are characterized before and after reactions via X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), temperature-programmed reduction and oxidation (TPR, TPO), Transmission Electron Microscopy (TEM), and BET surface area measurement. After reaction, Ni 2 P/SiO 2 shows the emergence of a crystalline Ni 12 P 5 phase while Ni 12 P 5 /Al 2 O 3 and Ni 12 P 5 /CeAl both show the crystalline Ni 3 P phase. While stable activity of the latter catalysts is demonstrated via extended testing, this Ni enrichment in all phosphide catalysts shows the dynamic nature of the catalysts during operation. Moreover, it demonstrates that both the support and the phosphide phase play a key role in determining selectivity towards CO or CH 4. [ABSTRACT FROM AUTHOR]

The low temperature water–gas shift (WGS) reaction has been studied over carbon-supported nickel catalysts promoted by ceria. To this end, cerium oxide has been dispersed (at different loadings: 10, 20, 30 and 40 wt.%) on the activated carbon surface with the aim of obtaining small ceria particles and a highly available surface area. Furthermore, carbon- and ceria-supported nickel catalysts have also been studied as references. A combination of N 2 adsorption analysis, powder X-ray diffraction, temperature-programmed reduction with H 2 , X-ray photoelectron spectroscopy and TEM analysis were used to characterize the Ni–CeO 2 interactions and the CeO 2 dispersion over the activated carbon support. Catalysts were tested in the low temperature WGS reaction with two different feed gas mixtures: the idealized one (with only CO and H 2 O) and a slightly harder one (with CO, CO 2 , H 2 , and H 2 O). The obtained results show that there is a clear effect of the ceria loading on the catalytic activity. In both cases, catalysts with 20 and 10 wt.% CeO 2 were the most active materials at low temperature. On the other hand, Ni/C shows a lower activity, this assessing the determinant role of ceria in this reaction. Methane, a product of side reactions, was observed in very low amounts, when CO 2 and H 2 were included in the WGS feed. Nevertheless, our data indicate that the methanation process is mainly due to CO 2 , and no CO consumption via methanation takes place at the relevant WGS temperatures. Finally, a stability test was carried out, obtaining CO conversions greater than 40% after 150 h of reaction. [ABSTRACT FROM AUTHOR]

• Advanced catalysts for Chemical CO 2 recycling. • Opening the possibility to couple a RWGS unit with a syngas upgrading reactor. • Cu as an excellent promoter to improve the activity/selectivity of FeOx-based catalysts. • Remarkable RWGS activity at low medium-low temperatures with very high selectivity. The RWGS reaction represents a direct approach for gas-phase CO 2 upgrading. This work showcases the efficiency of Fe/CeO 2 -Al 2 O 3 catalysts for this process, and the effect of selected transition metal promoters such as Cu, Ni and Mo. Our results demonstrated that both Ni and Cu remarkably improved the performance of the monometallic Fe-catalyst. The competition Reverse Water-Gas Shift (RWGS) reaction/CO 2 methanation reaction was evident particularly for the Ni-catalyst, which displayed high selectivity to methane in the low-temperature range. Among the studied catalysts the Cu promoted sample represented the best choice, exhibiting the best activity/selectivity balance. In addition, the Cu-doped catalyst was very stable for long-term runs – an essential requisite for its implementation in flue gas upgrading units. This material can effectively catalyse the RWGS reaction at medium-low temperatures, providing the possibility to couple the RWGS reactor with a syngas conversion reaction. Such an integrated unit opens the horizons for a direct CO 2 to fuels/chemicals approach. [ABSTRACT FROM AUTHOR]

Dry reforming of methane is a very appealing catalytic route biogas (mainly composed by greenhouse gases: carbon dioxide and methane) conversion into added value syngas, which could be further upgraded to produce liquid fuels and added value chemicals. However, the major culprits of this reaction are coking and active phase sintering that result in catalysts deactivation. Herein we have developed a highly stable bimetallic Ni–Rh catalyst supported on mixed CeO 2 –Al 2 O 3 oxide using low-noble metal loadings. The addition of small amounts of rhodium to nickel catalysts prevents coke formation and improves sintering resistance, achieving high conversions over extended reaction times hence resulting in promising catalysts for biogas upgrading. [Display omitted] • H 2 -rich syngas can be obtained efficiently from biogas reforming. • Ni-based catalysts are deactivated by metal sintering and coke deposition. • Doping with low Rh loadings deactivation can be successfully prevented. [ABSTRACT FROM AUTHOR]

• Novel in-situ HDO strategy with H 2 O as hydrogen source. • N-doped reduced graphene oxide (RGO) advanced supports. • Comparison among Pt-based and Ni N-doped RGO supported catalysts for 'H 2 -free' HDO of guaiacol. • Innovate route for economically viable biomass upgrading. Herein we present an innovative route for model biomass compounds upgrading via "H 2 -free" hydrodeoxygenation (HDO) reactions. The underlaying idea is to implement a multifunctional catalyst able to activate water and subsequently use in-situ generated hydrogen for the HDO process. In this sense we have developed a series of effective Ni and Pt based catalysts supported on N-promoted graphene decorated with ceria. The catalyst reached commendable conversion levels and selectivity to mono-oxygenated compounds considering the very challenging reaction conditions. Pt outperforms Ni when the samples are tested as-prepared. However, Ni performance is remarkably boosted upon applying a pre-conditioning reductive treatment. Indeed, our NiCeO 2 /GOr-N present the best activity/selectivity balance and it is deemed as a promising catalyst to conduct the H 2 -free HDO reaction. Overall, this "proof-concept" showcases an economically appealing route for bio-compounds upgrading evidencing the key role of advanced catalysts for a low carbon future. [ABSTRACT FROM AUTHOR]