Carbon dioxide capture and reduction (CCR) process emerges as an efficient catalytic strategy for CO2 capture and conversion to valuable chemicals. K-promoted Cu/Al2O3 catalysts exhibited promising CO2 capture efficiency and highly selective conversion to syngas (CO + H2). The dynamic nature of the Cu-K system at reaction conditions complicates the identification of the catalytically active phase and surface sites. The present work aims at more precise understanding of the roles of the potassium and copper and the contribution of the metal oxide support. While γ-Al2O3 guarantees high dispersion and destabilisation of the potassium phase, potassium and copper act synergistically to remove CO2 from diluted streams and promote fast regeneration of the active phase for CO2 capture releasing CO while passing H2. A temperature of 350℃ is found necessary to activate H2 dissociation and generate the active sites for CO2 capture. The effects of synthesis parameters on the CCR activity are also described by combination of ex-situ characterisation of the materials and catalytic testing.@en

Direct valorization of methane via oxidative coupling of methane (OCM) is an encouraging alternative to conventional oil-based processes for the production of light hydrocarbons (ethane and ethylene). Abundant, inexpensive simple oxides such as MgO and La2O3 possess the ability to selectively activate methane. However, during OCM, the selective conversion to ethane and the following dehydrogenation to ethylene are threatened by the thermodynamically favored partial and total oxidation reactions to form CO and CO2, respectively. With the aid of spatially resolved operando analysis of temperature and gas concentration along the catalytic bed, we demonstrate the relevance of highly exothermic reaction paths developed in the gas phase, i.e., the homogeneous reaction, during OCM conditions at the front of the catalytic bed, largely determining the total C2 yield obtained on those systems. With the new insights provided by the analysis of temperature and concentration gradients along the bed, we redefine the positive effect of promoters (Li, Sr), which enhance the influence of catalyst surfaces. The effect of promoters is recognized in the suppression of the exothermic oxidation paths leading to undesired COx, thus limiting the formation of hotspots and driving the reaction toward the desired C2 products.@en

Dynamic coke-mediated dry reforming of methane (DC-DRM) is an unsteady-state strategy to overcome the limitations of co-feed operation, including the fast deactivation of the catalysts and the loss of valuable H2 in the reverse water gas-shift reaction. This paper proves the feasibility of DC-DRM on Ni-based catalytic systems, identifying suitable metal oxides supports and evaluating the role of metallic promoters. A La-promoted Ni/ZrO2 catalyst exhibited excellent and stable catalytic performances at 800 °C approaching complete conversion of the CH4 and CO2 reactant pulses in the reaction loop, and separation of the H2 and CO product streams. Adding the redox functionality of reducible oxides (TiO2) in the catalyst support is demonstrated as a powerful tool to enable direct formation of syngas in the methane pulse with control on the H2/CO ratio.@en

Industrial-scale reforming of methane is typically carried out with an excess of oxidant to suppress coking of the catalyst. On the other hand, many academic studies on dry reforming employ a CO2/CH4 ratio of unity to quickly observe coking which can be reduced by adding a catalyst promoter. In this work, Ni/Al2O3 catalysts were tested for dry reforming of methane (CO2/CH4=1) with additional regeneration steps to test the resistance against an oxidation treatment. Thereby, we wanted to evaluate catalyst stability for industrial relevance. The effects of three promoters, Cr, Mn and Fe, that differ in their degree of CO2 interaction, are compared. A higher iron loading on Ni/Al2O3 leads to higher stability in dry reforming with lower coke formation. However, the higher the concentration of a promoter with high CO2 affinity, the quicker the catalyst is oxidized during regeneration with CO2. Subsequent reduction of a catalyst oxidized with CO2 leads to considerable sintering in all cases. This sintering induces formation of more coke during dry reforming. On such sintered samples only highly effective promoters in large concentrations still have a noticeable effect compared to unpromoted Ni/Al2O3.@en

The electrochemical CO2 reduction reaction (CO2RR) is an attractive method to produce renewable fuel and chemical feedstock using clean energy sources. Formate production represents one of the most economical target products from CO2RR but is primarily produced using post-transition metal catalysts that require comparatively high overpotentials. Here a composition of bimetallic Cu–Pd is formulated on 2D Ti3C2Tx (MXene) nanosheets that are lyophilized into a highly porous 3D aerogel, resulting in formate production much more efficient than post-transition metals. Using a membrane electrode assembly (MEA), formate selectivities >90% are achieved with a current density of 150 mA cm−2 resulting in the highest ever reported overall energy efficiency of 47% (cell potentials of −2.8 V), over 5 h of operation. A comparable Cu-Pd aerogel achieves near-unity CO production without the MXene templating. This simple strategy represents an important step toward the experimental demonstration of 3D-MXenes-based electrocatalysts for CO2RR application and opens a new platform for the fabrication of macroscale aerogel MXene-based electrocatalysts.@en

Integrated CO2 capture and conversion processes bring the promise of drastic abatement of CO2 emission together with its valorisation to chemical building blocks such as CH4 and CO. Isothermal CO2 capture and reduction (CCR) on a K-promoted Cu/Al2O3 was recognised as an effective catalytic strategy for removing CO2 from diluted stream and converting it to syngas (H2 + CO) employing green H2 as reducing agent. The dual functionality of the catalyst is the key of this dynamic process, in which the alkaline metal introduces the capture functionality and copper ensures the selective conversion of the captured CO2 to CO. However, the highly dynamic state of the catalyst at reaction conditions represents a barrier for the identification of the catalytic mechanism of CCR, which is vital for rational process improvement and design. In this work, we conducted a mechanistic investigation of CCR by means of spatiotemporal operando methodologies, gaining insights into dynamic variation of temperature, gas concentration and reactive surface species in the CCR reactor. The results show the unique potassium state exothermically captures CO2 as surface carbonates which can be reduced to CO rapidly under H2 atmosphere. When the surface carbonates are transformed to formates the reaction path is altered and the reduction to CO becomes slower. By designing controlled catalytic experiments, we further demonstrate the active involvement of CO in the capture mechanism and the effectiveness of CO2 capture in presence of an oxidised surface, extending the perspectives and suitability of CCR to treat actual complex effluent streams.@en

CH4 and CO2 are ideal candidates in the context of C1 chemistry as alternatives to oil-based feedstocks for chemicals and fuels production, due to their abundancy, low cost and potential to develop a closed carbon cycle. Large scale utilisation of CO2 in the chemical industry is currently limited to a few applications (e.g. synthesis of urea, carboxylic acids, food industry) and generally requires high purity feedstock. Integrated processes that combine CO2 capture from diluted sources (e.g. industrial flue gases, air) and its conversion to value-added chemicals represent a solution to enhance the utilisation of CO2 and mitigate its emissions. CH4 is an abundant hydrocarbon with diversified sources ranging from fossil-based (natural gas, shale gas) to renewable ones (biomass, biogas), which can potentially substitute oil for the synthesis of valuable chemicals and fuels, including higher hydrocarbons. At the moment, however, CH4 utilisation is circumscribed to combustion for heat and energy production or energy-intensive production of H2 and syngas (H2 + CO) via steam reforming, resulting in a high carbon footprint. In general, the thermodynamic stability of CO2 and CH4 molecules imposes severe limitations to their exploitation as chemical feedstocks, in terms of low conversion efficiencies and control on the selectivity of products. Their efficient conversion requires harsh reaction conditions (high temperatures and pressures, highly chemically reactive substances) at which the stability of the desired products is threatened, resulting in low selectivity. In this scenario, catalysis is essential to identify functional materials and develop new catalytic processes able to maximise the selective conversion of CO2 and CH4 feedstocks to value-added products. Unsteady-state operation in catalysis is an option to overcome the thermodynamic constraints imposed by the conventional steady-state operation. Integrated CO2 capture and conversion, sorption-enhanced reactions, chemical looping combustion are examples of intrinsically unsteady-state catalytic processes that demonstrated enhanced performances compared to their steady state analogues. Moreover, the analysis of the transient catalytic behaviour developed in unsteady-state conditions leads to a deeper understanding of the catalytic processes in terms of identification of specific reactant-catalyst interactions, the steps involved in products formation and the mechanism of catalyst deactivation. This dissertation deals with the catalytic activation of CO2 and CH4 molecules targeting at their valorisation to important chemical commodities as CO (syngas) and light hydrocarbons. Unsteady-state catalysis is explored as a means to overcome thermodynamic constraints associated to the conventional CO2 and CH4 conversion routes....@en

Oxidative coupling of methane (OCM) to produce ethane and ethylene is one of the dream reactions of researchers in catalysis. Despite the extensive efforts over the last three decades, our general understanding on OCM is rather poor due to the complexity arising from the reaction network, and also from the various gradients such as temperature and gaseous concentration present in OCM reactors. This chapter highlights reactions active under OCM conditions and how they are interlinked. Special emphasis is given on space-resolved analytical methodologies as promising key enabling tools towards rational development of catalytic materials and processes for OCM.@en

Oxidative coupling of methane (OCM) to produce ethane and ethylene is one of the dream reactions of researchers in catalysis. Despite the extensive efforts over the last three decades, our general understanding on OCM is rather poor due to the complexity arising from the reaction network, and also from the various gradients such as temperature and gaseous concentration present in OCM reactors. This chapter highlights reactions active under OCM conditions and how they are interlinked. Special emphasis is given on space-resolved analytical methodologies as promising key enabling tools towards rational development of catalytic materials and processes for OCM.@en